precision simulations for lhc physics and beyond
TRANSCRIPT
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
Precision Simulations for LHC physics andbeyond
Frank Krauss
Institute for Particle Physics PhenomenologyDurham University
KEK, 10.3.2017
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
what the talk is about
matching & merging with parton showers
Electroweak corrections
Revisit Parton Showers
Revisit Soft Physics simulation
where we are and where we (should/could/would) go
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
motivation & introduction
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
motivation: the need for (more) accurate tools
- to date no survivors in searches for new physics & phenomena(a pity, but that’s what Nature hands to us)
- push into precision tests of the Standard Model(find it or constrain it!)
- statistical uncertainties approach zero(because of the fantastic work of accelerator, DAQ, etc.)
- systematic experimental uncertainties decrease(because of ingenious experimental work)
- theoretical uncertainties are or become dominant(it would be good to change this to fully exploit LHC’s potential)
=⇒ more accurate tools for more precise physics needed!
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
motivation: aim of the exercise
review the state of the art in precision simulations(celebrate success)
highlight missing or ambiguous theoretical ingredients(acknowledge failure)
suggest some further studies – experiment and theory(. . . )
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
matching @ (N)NLO
and
merging @ (N)LO
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
the aftermath of the NLO (QCD) revolution
establishing a wide variety of automated tools for NLO calculationsBLACKHAT, GOSAM, MADGRAPH, NJET, OPENLOOPS, RECOLA + automated IR subtraction methods (MADGRAPH, SHERPA)
first full NLO (EW) results with automated tools
technical improvements still mandatory(higher multis, higher speed, higher efficiency, easier handling, . . . )
start discussing scale setting prescriptions(simple central scales for complicated multi-scale processes? test smarter prescriptions?)
steep learning curve still ahead: “NLO phenomenology”(example: methods for uncertainty estimates beyond variation around central scale)
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
Fixed Order (higher-order QCD & EW)
automated Catani-Seymour subtraction, in two independent matrixelement generators within SHERPA
(that was a long time ago, though)
used in conjunction with many one-loop tools:BLACKHAT, GOSAM, NJET, OPENLOOPS, RECOLA
for practically all cutting-edge calculations(tt + 3 jets, V + 5 jets, 5 jets, . . . )
extending subtraction to EW corrections
added full UFO functionality for BSM models
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
example: tt + 3 jets at NLO(QCD) with OPENLOOPS
first computation of tt+3 jetsat NLO / MINLO accuracy
SHERPA NLO MC framework usingCOMIX combined with OPENLOOPS
public results in NTuple formata la BLACKHAT for easy analysis &recycling
scale dependence studied usingHT ,m =
∑m⊥ and MINLO
extended to massive partons
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
prequel: parton showers vs. resummation calculations
various schemes for various logs in analytic resummation
concentrate on parton shower instead ←→ compare with QT
resummation(transverse momentum of Higgs boson etc.)
parametric accuracy by comparing Sudakov form factors:
∆ = exp
−∫
dk2⊥
k2⊥
[A log
k2⊥
Q2+ B
],
where A and B can be expanded in αS(k2⊥)
showers usually include terms A1,2 and B1 (NLL)
A2 often realised by pre-factor multiplying scale µR ' k⊥
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
some parton shower fun with DY(example of accuracy in description of standard precision observable)
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Sher
paM
C
0 ≤ |yZ| ≤ 1
1 ≤ |yZ| ≤ 2 (×0.1)
2 < |yZ| ≤ 2.4 (×0.01)
b ATLAS dataJHEP 09 (2014) 145ME+PS (1-jet)5 ≤ Qcut ≤ 20 GeV
1 210−9
10−8
10−7
10−6
10−5
10−4
10−3
10−2
10−1pT spectrum, Z→ ee (dressed)
1σ
fidd
σfid
dp T
[GeV
−1 ]
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Sher
paM
C
|yZ| < 0.8
0.8 ≤ |yZ| ≤ 1.6 (×0.1)
1.6 < |yZ| (×0.01)
b ATLAS dataPhys.Lett. B720 (2013) 32ME+PS (1-jet)5 ≤ Qcut ≤ 20 GeV
3 2 1
10−4
10−3
10−2
10−1
1
10 1
φ∗η spectrum, Z→ ee (dressed)
1σ
fid.
dσ
fid.
dφ
∗ η
b b b b b b b b b b b b b b b b b b b b b b b b b b
0 ≤ |yZ| ≤ 1
1 2
0.80.91.01.11.2
| |
MC
/Dat
a
b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b
|yZ| < 0.8
3 2 1
0.80.91.01.11.2
→ | |
MC
/Dat
ab b b b b b b b b b b b b b b b b b b b b b b b b b
1 ≤ |yZ| ≤ 2
1 2
0.80.91.01.11.2
| |
MC
/Dat
a
b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b
0.8 ≤ |yZ| ≤ 1.6
3 2 1
0.80.91.01.11.2
→ ≤ | |
MC
/Dat
a
b b b b b b b b b b b b b b b b b b b b b b b b b b
2 < |yZ| ≤ 2.4
1 10 1 10 2
0.80.91.01.11.2
| |
pT,ll [GeV]
MC
/Dat
a
b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b
1.6 < |yZ|
10−3 10−2 10−1 1
0.80.91.01.11.2
→ | | ≥
φ∗η
MC
/Dat
a
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
matching at NLO and NNLO
avoid double-counting of emissions
two schemes at NLO: MC@NLO and POWHEG
mismatches of K factors in transition to hard jet regionMC@NLO: −→ visible structures, especially in gg → HPOWHEG: −→ high tails, cured by h dampening factorwell-established and well-known methods
(no need to discuss them any further)
two schemes at NNLO: MINLO & UN2LOPS (singlets S only)
different basic ideasMINLO: S + j at NLO with p
(S)T → 0 and capture divergences by
reweighting internal line with analytic Sudakov, NNLO accuracyensured by reweighting with full NNLO calculation for S productionUN2
LOPS identifies and subtracts and adds parton shower terms atFO from S + j contributions, maintaining unitarityavailable for two simple processes only: DY and gg → H
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
NNLOPS for H production: MINLO
K. Hamilton, P. Nason, E. Re & G. Zanderighi, JHEP 1310
also available for Z/W /VH production
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
NNLOPS for Z production: UN2LOPS
S. Hoche, Y. Li, & S. Prestel, Phys.Rev.D90 & D91
She
rpa+
Bla
ckH
at
NNLONLO'FEWZ
= 7 TeVs<120 GeV
ll60 GeV<m
NLO'll<2mR/F
µ/2< ll m NNLOll<2m
R/Fµ/2< ll m
[pb]
-e
+e
/dy
σd
20
40
60
80
100
120
140
160
180
200
Rat
io to
NLO
0.960.98
11.021.04
-e+ey
-4 -3 -2 -1 0 1 2 3 4
b
bb
b bb
bbb b
bbb b
b
b
b
b
b
ATLAS PLB705(2011)415b
UN2LOPSmll/2 < µR/F < 2 mllmll/2 < µQ < 2 mll
10−6
10−5
10−4
10−3
10−2
10−1Z pT reconstructed from dressed electrons
1/σ
dσ
/d
p T,Z
[1/G
eV]
b b b b b b b b b b b b b b b b b b b
1 10 1 10 2
0.6
0.8
1
1.2
1.4
pT,Z [GeV]
MC
/Dat
a
also available for H production
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
NNLOPS: shortcomings/limitations
MINLO relies on knowledge of B2 terms from analytic resummation−→ to date only known for colour singlet production
MINLO relies on reweighting with full NNLO result−→ one parameter for H (yH), more complicated for Z , . . .
UN2LOPS relies on integrating single- and double emission to lowscales and combination of unresolved with virtual emissions−→ potential efficiency issues, need NNLO subtraction
UN2LOPS puts unresolved & virtuals in “zero-emission” bin−→ no parton showering for virtuals (?)
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
merging example: p⊥,γγ in MEPS@LO vs. NNLO(arXiv:1211.1913 [hep-ex])
[p
b/G
eV
]γγ
T,
/dp
σd
510
410
310
210
110
1
10
1Ldt = 4.9 fb ∫ Data 2011,
1.3 (MRST2007)×PYTHIA MC11c
1.3 (CTEQ6L1)×SHERPA MC11c
ATLAS
= 7 TeVs
data
/SH
ER
PA
00.5
11.5
22.5
3
[GeV]γγT,
p
0 50 100 150 200 250 300 350 400 450 500
da
ta/P
YT
HIA
00.5
11.5
22.5
3 [
pb
/Ge
V]
γγT,
/dp
σd
510
410
310
210
110
1
10
1Ldt = 4.9 fb ∫ Data 2011,
DIPHOX+GAMMA2MC (CT10)
NNLO (MSTW2008)γ2
ATLAS
= 7 TeVs
da
ta/D
IPH
OX
00.5
11.5
22.5
3
[GeV]γγT,
p
0 50 100 150 200 250 300 350 400 450 500
NN
LO
γd
ata
/2
00.5
11.5
22.5
3
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
merging for loop-induced processesexample: merging for gg → ZH
(looking for H → inv. in `¯+ E/ final states at 13 TeV LHC)
10−8
10−7
10−6
10−5
10−4
10−3
10−2
dσ
/dE
mis
sT
[pb/
GeV
]
Sherpa+OpenLoops
H(inv)Z(ll)gg
H(inv)Z(ll)qq
ZZ, WWgg
ZZ, WWqq
100 200 300 400 500 600Emiss
T [GeV]
1
2
3
4 MEPS@Loop2/Loop2+PS
10−8
10−7
10−6
10−5
10−4
10−3
10−2
dσ
/d
pj lead⊥
[pb/
GeV
]
Sherpa+OpenLoops
H(inv)Z(ll)gg
H(inv)Z(ll)qq
ZZ, WWgg
ZZ, WWqq
100 200 300 400 500 600pjlead⊥ [GeV]
100
101
102 MEPS@Loop2/Loop2+PS
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
multijet-merging at NLO
sometimes “more legs” wins over more loops
basic idea like at LO: towers of MEs with increasing jet multi(but this time at NLO)
combine them into one sample, remove overlap/double-counting
maintain NLO and LL accuracy of ME and PS
this effectively translates into a merging of MC@NLO simulations andcan be further supplemented with LO simulations for even higherfinal state multiplicities
different implementations, parametric accuracy not always clear(MEPS@NLO, FxFx, UNLOPS)
starts being used, still lacks careful cross-validation
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
illustration: pH⊥ in MEPS@NLO
pp → h + jetsSherpa S-MC@NLO
0 50 100 150 200 250 30010−4
10−3
10−2
10−1
Transverse momentum of the Higgs boson
p⊥(h) [GeV]
dσ
/dp ⊥
[pb/
GeV
] first emission byMC@NLO
MC@NLO pp → h + jetfor Qn+1 > Qcut
restrict emission offpp → h + jet toQn+2 < Qcut
MC@NLO
pp → h + 2jets forQn+2 > Qcut
iterate
sum all contributions
eg. p⊥(h)>200 GeVhas contributions fr.multiple topologies
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
illustration: pH⊥ in MEPS@NLO
pp → h + jetspp → h + 0j @ NLO
0 50 100 150 200 250 30010−4
10−3
10−2
10−1
Transverse momentum of the Higgs boson
p⊥(h) [GeV]
dσ
/dp ⊥
[pb/
GeV
]
first emission byMC@NLO , restrict toQn+1 < Qcut
MC@NLO pp → h + jetfor Qn+1 > Qcut
restrict emission offpp → h + jet toQn+2 < Qcut
MC@NLO
pp → h + 2jets forQn+2 > Qcut
iterate
sum all contributions
eg. p⊥(h)>200 GeVhas contributions fr.multiple topologies
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
illustration: pH⊥ in MEPS@NLO
pp → h + jetspp → h + 0j @ NLOpp → h + 1j @ NLO
0 50 100 150 200 250 30010−4
10−3
10−2
10−1
Transverse momentum of the Higgs boson
p⊥(h) [GeV]
dσ
/dp ⊥
[pb/
GeV
]
first emission byMC@NLO , restrict toQn+1 < Qcut
MC@NLO pp → h + jetfor Qn+1 > Qcut
restrict emission offpp → h + jet toQn+2 < Qcut
MC@NLO
pp → h + 2jets forQn+2 > Qcut
iterate
sum all contributions
eg. p⊥(h)>200 GeVhas contributions fr.multiple topologies
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
illustration: pH⊥ in MEPS@NLO
pp → h + jetspp → h + 0j @ NLOpp → h + 1j @ NLO
0 50 100 150 200 250 30010−4
10−3
10−2
10−1
Transverse momentum of the Higgs boson
p⊥(h) [GeV]
dσ
/dp ⊥
[pb/
GeV
]
first emission byMC@NLO , restrict toQn+1 < Qcut
MC@NLO pp → h + jetfor Qn+1 > Qcut
restrict emission offpp → h + jet toQn+2 < Qcut
MC@NLO
pp → h + 2jets forQn+2 > Qcut
iterate
sum all contributions
eg. p⊥(h)>200 GeVhas contributions fr.multiple topologies
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
illustration: pH⊥ in MEPS@NLO
pp → h + jetspp → h + 0j @ NLOpp → h + 1j @ NLOpp → h + 2j @ NLO
0 50 100 150 200 250 30010−4
10−3
10−2
10−1
Transverse momentum of the Higgs boson
p⊥(h) [GeV]
dσ
/dp ⊥
[pb/
GeV
]
first emission byMC@NLO , restrict toQn+1 < Qcut
MC@NLO pp → h + jetfor Qn+1 > Qcut
restrict emission offpp → h + jet toQn+2 < Qcut
MC@NLO
pp → h + 2jets forQn+2 > Qcut
iterate
sum all contributions
eg. p⊥(h)>200 GeVhas contributions fr.multiple topologies
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
illustration: pH⊥ in MEPS@NLO
pp → h + jetspp → h + 0j @ NLOpp → h + 1j @ NLOpp → h + 2j @ NLO
0 50 100 150 200 250 30010−4
10−3
10−2
10−1
Transverse momentum of the Higgs boson
p⊥(h) [GeV]
dσ
/dp ⊥
[pb/
GeV
]
first emission byMC@NLO , restrict toQn+1 < Qcut
MC@NLO pp → h + jetfor Qn+1 > Qcut
restrict emission offpp → h + jet toQn+2 < Qcut
MC@NLO
pp → h + 2jets forQn+2 > Qcut
iterate
sum all contributions
eg. p⊥(h)>200 GeVhas contributions fr.multiple topologies
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
illustration: pH⊥ in MEPS@NLO
pp → h + jetspp → h + 0j @ NLOpp → h + 1j @ NLOpp → h + 2j @ NLOpp → h + 3j @ LO
0 50 100 150 200 250 30010−4
10−3
10−2
10−1
Transverse momentum of the Higgs boson
p⊥(h) [GeV]
dσ
/dp ⊥
[pb/
GeV
]
first emission byMC@NLO , restrict toQn+1 < Qcut
MC@NLO pp → h + jetfor Qn+1 > Qcut
restrict emission offpp → h + jet toQn+2 < Qcut
MC@NLO
pp → h + 2jets forQn+2 > Qcut
iterate
sum all contributions
eg. p⊥(h)>200 GeVhas contributions fr.multiple topologies
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
illustration: pH⊥ in MEPS@NLO
pp → h + jetspp → h + 0j @ NLOpp → h + 1j @ NLOpp → h + 2j @ NLOpp → h + 3j @ LO
0 50 100 150 200 250 30010−4
10−3
10−2
10−1
Transverse momentum of the Higgs boson
p⊥(h) [GeV]
dσ
/dp ⊥
[pb/
GeV
]
first emission byMC@NLO , restrict toQn+1 < Qcut
MC@NLO pp → h + jetfor Qn+1 > Qcut
restrict emission offpp → h + jet toQn+2 < Qcut
MC@NLO
pp → h + 2jets forQn+2 > Qcut
iterate
sum all contributions
eg. p⊥(h)>200 GeVhas contributions fr.multiple topologies
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
illustration: pH⊥ in MEPS@NLO
pp → h + jetspp → h + 0j @ NLOpp → h + 1j @ NLOpp → h + 2j @ NLOpp → h + 3j @ LO
0 50 100 150 200 250 30010−4
10−3
10−2
10−1
Transverse momentum of the Higgs boson
p⊥(h) [GeV]
dσ
/dp ⊥
[pb/
GeV
]
first emission byMC@NLO , restrict toQn+1 < Qcut
MC@NLO pp → h + jetfor Qn+1 > Qcut
restrict emission offpp → h + jet toQn+2 < Qcut
MC@NLO
pp → h + 2jets forQn+2 > Qcut
iterate
sum all contributions
eg. p⊥(h)>200 GeVhas contributions fr.multiple topologies
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
detailed comparison of approaches
in
H+jets
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
inclusive Higgs boson rapidity
LH
15pp
→h
+je
tsco
mpa
riso
n
ResBos 2Sherpa h Nnlo
0 1 2 3 4 50
5
10
15
20
25Higgs boson rapidity
y(h)
dσ
/dy
[pb]
0.6
0.8
1
1.2
1.4
Higgs boson rapidity
Rat
ioto
hN
nlo
0.6
0.8
1
1.2
1.4
Rat
ioto
hN
nlo
0 1 2 3 4 5
0.6
0.8
1
1.2
1.4
y(h)
Rat
ioto
hN
nlo
excellent agreement between NNLO and NNLOPS
multijet merged with NLO normalisation, PDF effects
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
inclusive Higgs boson rapidity
LH
15pp
→h
+je
tsco
mpa
riso
n
ResBos 2Sherpa h NnloPowheg NnloPsSherpa NnloPs
0 1 2 3 4 50
5
10
15
20
25Higgs boson rapidity
y(h)
dσ
/dy
[pb]
0.6
0.8
1
1.2
1.4
Higgs boson rapidity
Rat
ioto
hN
nlo
0.6
0.8
1
1.2
1.4
Rat
ioto
hN
nlo
0 1 2 3 4 5
0.6
0.8
1
1.2
1.4
y(h)
Rat
ioto
hN
nlo
excellent agreement between NNLO and NNLOPS
multijet merged with NLO normalisation, PDF effects
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
inclusive Higgs boson rapidity
LH
15pp
→h
+je
tsco
mpa
riso
n
ResBos 2Sherpa h NnloPowheg NnloPsSherpa NnloPsMG5_aMC FxFxSherpa MePs@NloHerwig 7.1
0 1 2 3 4 50
5
10
15
20
25Higgs boson rapidity
y(h)
dσ
/dy
[pb]
0.6
0.8
1
1.2
1.4
Higgs boson rapidity
Rat
ioto
hN
nlo
0.6
0.8
1
1.2
1.4
Rat
ioto
hN
nlo
0 1 2 3 4 5
0.6
0.8
1
1.2
1.4
y(h)
Rat
ioto
hN
nlo
excellent agreement between NNLO and NNLOPS
multijet merged with NLO normalisation, PDF effects
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
Higgs boson transverse momentum (nj ≥ 0)
LH
15pp
→h
+je
tsco
mpa
riso
n
HqTResBos 2
0 50 100 150 20010−2
10−1
1
Higgs boson transverse momentum (nj ≥ 0)
p⊥(h) [GeV]
dσ
/dp ⊥
[pb/
GeV
]
0.6
0.8
1
1.2
1.4
Higgs boson transverse momentum (nj ≥ 0)
Rat
ioto
Hq
T
0.6
0.8
1
1.2
1.4
Rat
ioto
Hq
T
0 50 100 150 200
0.6
0.8
1
1.2
1.4
p⊥(h) [GeV]
Rat
ioto
Hq
T
good agreement between HqT and NNLOPS, scale choice at high p⊥multijet merged with NLO normalisation, very different at low p⊥
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
Higgs boson transverse momentum (nj ≥ 0)
LH
15pp
→h
+je
tsco
mpa
riso
n
HqTResBos 2
Powheg NnloPsSherpa NnloPs
0 50 100 150 20010−2
10−1
1
Higgs boson transverse momentum (nj ≥ 0)
p⊥(h) [GeV]
dσ
/dp ⊥
[pb/
GeV
]
0.6
0.8
1
1.2
1.4
Higgs boson transverse momentum (nj ≥ 0)
Rat
ioto
Hq
T
0.6
0.8
1
1.2
1.4
Rat
ioto
Hq
T
0 50 100 150 200
0.6
0.8
1
1.2
1.4
p⊥(h) [GeV]
Rat
ioto
Hq
T
good agreement between HqT and NNLOPS, scale choice at high p⊥
multijet merged with NLO normalisation, very different at low p⊥
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
Higgs boson transverse momentum (nj ≥ 0)
LH
15pp
→h
+je
tsco
mpa
riso
n
HqTResBos 2
Powheg NnloPsSherpa NnloPsMG5_aMC FxFxSherpa MePs@NloHerwig 7.1
0 50 100 150 20010−2
10−1
1
Higgs boson transverse momentum (nj ≥ 0)
p⊥(h) [GeV]
dσ
/dp ⊥
[pb/
GeV
]
0.6
0.8
1
1.2
1.4
Higgs boson transverse momentum (nj ≥ 0)
Rat
ioto
Hq
T
0.6
0.8
1
1.2
1.4
Rat
ioto
Hq
T
0 50 100 150 200
0.6
0.8
1
1.2
1.4
p⊥(h) [GeV]
Rat
ioto
Hq
T
good agreement between HqT and NNLOPS, scale choice at high p⊥multijet merged with NLO normalisation, very different at low p⊥
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
Higgs boson transverse momentum (nj = 0)
LH
15pp
→h
+je
tsco
mpa
riso
n
Sherpa h Nnlo
0 20 40 60 80 10010−5
10−4
10−3
10−2
10−1
1
Higgs boson transverse momentum (nj = 0)
p⊥(h) [GeV]
dσ
/dp ⊥
[pb/
GeV
]
fixed-order has various unphysical features
good agreement between the NNLOPS
multijet merged with NLO normalisation,HERWIG7 has much less soft radiation
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
Higgs boson transverse momentum (nj = 0)
LH
15pp
→h
+je
tsco
mpa
riso
n
Powheg NnloPsSherpa NnloPs
0 20 40 60 80 10010−5
10−4
10−3
10−2
10−1
1
Higgs boson transverse momentum (nj = 0)
p⊥(h) [GeV]
dσ
/dp ⊥
[pb/
GeV
]
0.6
0.8
1
1.2
1.4
Higgs boson transverse momentum (nj = 0)
Rat
ioto
Powheg
0 20 40 60 80 100
0.6
0.8
1
1.2
1.4
p⊥(h) [GeV]
Rat
ioto
Powheg
fixed-order has various unphysical features
good agreement between the NNLOPS
multijet merged with NLO normalisation,HERWIG7 has much less soft radiation
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
Higgs boson transverse momentum (nj = 0)
LH
15pp
→h
+je
tsco
mpa
riso
n
Powheg NnloPsSherpa NnloPsMG5_aMC FxFxSherpa MePs@NloHerwig 7.1
0 20 40 60 80 10010−5
10−4
10−3
10−2
10−1
1
Higgs boson transverse momentum (nj = 0)
p⊥(h) [GeV]
dσ
/dp ⊥
[pb/
GeV
]
0.6
0.8
1
1.2
1.4
Higgs boson transverse momentum (nj = 0)
Rat
ioto
Powheg
0 20 40 60 80 100
0.6
0.8
1
1.2
1.4
p⊥(h) [GeV]
Rat
ioto
Powheg
fixed-order has various unphysical features
good agreement between the NNLOPS
multijet merged with NLO normalisation,HERWIG7 has much less soft radiation
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
exclusive over inclusive rate
LH
15pp
→h
+je
tsco
mpa
riso
n
inclusive
exclusive
Powheg NnloPsSherpa NnloPsMG5_aMC FxFxSherpa MePs@NloHerwig 7.1
0 20 40 60 80 10010−2
10−1
1
Ratio of exclusive over inclusive Higgs production
p⊥(h) [GeV]
dσ
/dp ⊥
[pb/
GeV
]
0.2
0.4
0.6
0.8
1
1.2
Ratio of exclusive over inclusive Higgs production
excl
/inc
l
0.2
0.4
0.6
0.8
1
1.2
excl
/inc
l
0 20 40 60 80 100
0.2
0.4
0.6
0.8
1
1.2
p⊥(h) [GeV]
excl
/inc
l
≈ 20% of Higgs with p⊥ = 60 GeV are not accompanied by a jet
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
Higgs boson transverse momentum (nj ≥ 1)
LH
15pp
→h
+je
tsco
mpa
riso
n
BFGLP hj Nnlo
0 50 100 150 20010−3
10−2
10−1
1Higgs boson transverse momentum (nj ≥ 1)
p⊥(h) [GeV]
dσ
/dp ⊥
[pb/
GeV
]
fixed-order has Sudakov shoulder at ph⊥ = 30 GeV due to jet cuthere: bins left and right set to average
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
Higgs boson transverse momentum (nj ≥ 1)
LH
15pp
→h
+je
tsco
mpa
riso
n
Powheg NnloPsSherpa NnloPs
0 50 100 150 20010−3
10−2
10−1
1Higgs boson transverse momentum (nj ≥ 1)
p⊥(h) [GeV]
dσ
/dp ⊥
[pb/
GeV
]
0.6
0.8
1
1.2
1.4
Higgs boson transverse momentum (nj ≥ 1)
Rat
ioto
Powheg
0.6
0.8
1
1.2
1.4
Rat
ioto
Powheg
0 50 100 150 200
0.6
0.8
1
1.2
1.4
p⊥(h) [GeV]
Rat
ioto
Powheg
good agreement between NNLOPS, different scales at large p⊥excess of POWHEG as p⊥ → 0 (Higgs strahlung off dijet)
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
Higgs boson transverse momentum (nj ≥ 1)
LH
15pp
→h
+je
tsco
mpa
riso
n
Powheg NnloPsSherpa NnloPsMG5_aMC FxFxSherpa MePs@NloHerwig 7.1
0 50 100 150 20010−3
10−2
10−1
1Higgs boson transverse momentum (nj ≥ 1)
p⊥(h) [GeV]
dσ
/dp ⊥
[pb/
GeV
]
0.6
0.8
1
1.2
1.4
Higgs boson transverse momentum (nj ≥ 1)
Rat
ioto
Powheg
0.6
0.8
1
1.2
1.4
Rat
ioto
Powheg
0 50 100 150 200
0.6
0.8
1
1.2
1.4
p⊥(h) [GeV]
Rat
ioto
Powheg
multijet merged different shape at p⊥ . 60 GeV
except aMC@NLO MADGRAPH5 (due to different scales?)
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
Higgs boson transverse momentum (nj ≥ 1)
LH
15pp
→h
+je
tsco
mpa
riso
n
Powheg NnloPsSherpa NnloPsMG5_aMC FxFxSherpa MePs@NloHerwig 7.1
GoSam+Sherpa hjNLO
0 50 100 150 20010−3
10−2
10−1
1Higgs boson transverse momentum (nj ≥ 1)
p⊥(h) [GeV]
dσ
/dp ⊥
[pb/
GeV
]
0.6
0.8
1
1.2
1.4
Higgs boson transverse momentum (nj ≥ 1)
Rat
ioto
Powheg
0.6
0.8
1
1.2
1.4
Rat
ioto
Powheg
0 50 100 150 200
0.6
0.8
1
1.2
1.4
p⊥(h) [GeV]
Rat
ioto
Powheg
multijet merged different shape at p⊥ . 60 GeV
same as at fixed-order NLO
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
Higgs boson transverse momentum (nj ≥ 1)
LH
15pp
→h
+je
tsco
mpa
riso
n
Powheg NnloPsSherpa NnloPsMG5_aMC FxFxSherpa MePs@NloHerwig 7.1
BFGLP hj Nnlo
GoSam+Sherpa hjNLOMiNLOnNLO
0 50 100 150 20010−3
10−2
10−1
1Higgs boson transverse momentum (nj ≥ 1)
p⊥(h) [GeV]
dσ
/dp ⊥
[pb/
GeV
]
0.6
0.8
1
1.2
1.4
Higgs boson transverse momentum (nj ≥ 1)
Rat
ioto
Powheg
0.6
0.8
1
1.2
1.4
Rat
ioto
Powheg
0 50 100 150 200
0.6
0.8
1
1.2
1.4
p⊥(h) [GeV]
Rat
ioto
Powheg
NNLO impacts on shape at p⊥ . 60 GeV
NLL+NLO resummation gets close to NNLO result
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
Higgs boson transverse momentum (nj ≥ 1)
LH
15pp
→h
+je
tsco
mpa
riso
n
Powheg NnloPsSherpa NnloPsMG5_aMC FxFxSherpa MePs@NloHerwig 7.1
ResBos 2BFGLP hj Nnlo
GoSam+Sherpa hjNLO
0 50 100 150 20010−3
10−2
10−1
1Higgs boson transverse momentum (nj ≥ 1)
p⊥(h) [GeV]
dσ
/dp ⊥
[pb/
GeV
]
0.6
0.8
1
1.2
1.4
Higgs boson transverse momentum (nj ≥ 1)
Rat
ioto
Powheg
0.6
0.8
1
1.2
1.4
Rat
ioto
Powheg
0 50 100 150 200
0.6
0.8
1
1.2
1.4
p⊥(h) [GeV]
Rat
ioto
Powheg
NNLO impacts on shape at p⊥ . 60 GeV
NLL+NLO resummation gets close to NNLO result
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
leading jet transverse momentum (nj ≥ 1)
LH
15pp
→h
+je
tsco
mpa
riso
n
BFGLP hj Nnlo
40 60 80 100 120 140 160 180 20010−3
10−2
10−1
1Leading jet transverse momentum (nj ≥ 1)
p⊥(j1) [GeV]
dσ
/dp ⊥
[pb/
GeV
]
NNLO and NLO show very good convergence for this scale choice
multijet merged ≈ 20% lower in high-p⊥ (due to showering)
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
leading jet transverse momentum (nj ≥ 1)
LH
15pp
→h
+je
tsco
mpa
riso
n
STWZResBos 2BFGLP hj Nnlo
40 60 80 100 120 140 160 180 20010−3
10−2
10−1
1Leading jet transverse momentum (nj ≥ 1)
p⊥(j1) [GeV]
dσ
/dp ⊥
[pb/
GeV
]
0.6
0.8
1
1.2
1.4
Leading jet transverse momentum (nj ≥ 1)
Rat
ioto
hjN
nlo
0.6
0.8
1
1.2
1.4
Rat
ioto
hjN
nlo
40 60 80 100 120 140 160 180 200
0.6
0.8
1
1.2
1.4
p⊥(j1) [GeV]
Rat
ioto
hjN
nlo
NNLO and NLO show very good convergence for this scale choice
multijet merged ≈ 20% lower in high-p⊥ (due to showering)
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
leading jet transverse momentum (nj ≥ 1)
LH
15pp
→h
+je
tsco
mpa
riso
n
STWZResBos 2BFGLP hj Nnlo
GoSam+Sherpa hjNLO
40 60 80 100 120 140 160 180 20010−3
10−2
10−1
1Leading jet transverse momentum (nj ≥ 1)
p⊥(j1) [GeV]
dσ
/dp ⊥
[pb/
GeV
]
0.6
0.8
1
1.2
1.4
Leading jet transverse momentum (nj ≥ 1)
Rat
ioto
hjN
nlo
0.6
0.8
1
1.2
1.4
Rat
ioto
hjN
nlo
40 60 80 100 120 140 160 180 200
0.6
0.8
1
1.2
1.4
p⊥(j1) [GeV]
Rat
ioto
hjN
nlo
NNLO and NLO show very good convergence for this scale choice
multijet merged ≈ 20% lower in high-p⊥ (due to showering)
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
leading jet transverse momentum (nj ≥ 1)
LH
15pp
→h
+je
tsco
mpa
riso
n
Powheg NnloPsSherpa NnloPs
STWZResBos 2BFGLP hj Nnlo
GoSam+Sherpa hjNLO
40 60 80 100 120 140 160 180 20010−3
10−2
10−1
1Leading jet transverse momentum (nj ≥ 1)
p⊥(j1) [GeV]
dσ
/dp ⊥
[pb/
GeV
]
0.6
0.8
1
1.2
1.4
Leading jet transverse momentum (nj ≥ 1)
Rat
ioto
hjN
nlo
0.6
0.8
1
1.2
1.4
Rat
ioto
hjN
nlo
40 60 80 100 120 140 160 180 200
0.6
0.8
1
1.2
1.4
p⊥(j1) [GeV]
Rat
ioto
hjN
nlo
NNLO and NLO show very good convergence for this scale choice
multijet merged ≈ 20% lower in high-p⊥ (due to showering)
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
leading jet transverse momentum (nj ≥ 1)
LH
15pp
→h
+je
tsco
mpa
riso
n
Powheg NnloPsSherpa NnloPsMG5_aMC FxFxSherpa MePs@NloHerwig 7.1
STWZResBos 2BFGLP hj Nnlo
GoSam+Sherpa hjNLO
40 60 80 100 120 140 160 180 20010−3
10−2
10−1
1Leading jet transverse momentum (nj ≥ 1)
p⊥(j1) [GeV]
dσ
/dp ⊥
[pb/
GeV
]
0.6
0.8
1
1.2
1.4
Leading jet transverse momentum (nj ≥ 1)
Rat
ioto
hjN
nlo
0.6
0.8
1
1.2
1.4
Rat
ioto
hjN
nlo
40 60 80 100 120 140 160 180 200
0.6
0.8
1
1.2
1.4
p⊥(j1) [GeV]
Rat
ioto
hjN
nlo
NNLO and NLO show very good convergence for this scale choice
multijet merged ≈ 20% lower in high-p⊥ (due to showering)
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
jet vetoed cross sections – inclusive
LH
15pp
→h
+je
tsco
mpa
riso
n
inclusive
STWZ
10 20 50 100 2000
10
20
30
40
50Jet veto cross section
pveto⊥ [GeV]
σ0(
pveto
⊥)
[pb]
0.6
0.8
1
1.2
1.4
Jet veto cross section
Rat
ioto
STW
Z
10 20 50 100 200
0.6
0.8
1
1.2
1.4
pveto⊥ [GeV]
Rat
ioto
STW
Z
very good agreement between NNLOPS and STWZ
multijet merged with larger spread in shape,but within uncertainties once NLO normalisation accounted for
PS resummation uncertainties nowhere fully assessed
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
jet vetoed cross sections – inclusive
LH
15pp
→h
+je
tsco
mpa
riso
n
inclusive
STWZPowheg NnloPsSherpa NnloPs
10 20 50 100 2000
10
20
30
40
50Jet veto cross section
pveto⊥ [GeV]
σ0(
pveto
⊥)
[pb]
0.6
0.8
1
1.2
1.4
Jet veto cross section
Rat
ioto
STW
Z
10 20 50 100 200
0.6
0.8
1
1.2
1.4
pveto⊥ [GeV]
Rat
ioto
STW
Zvery good agreement between NNLOPS and STWZ
multijet merged with larger spread in shape,but within uncertainties once NLO normalisation accounted for
PS resummation uncertainties nowhere fully assessed
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
jet vetoed cross sections – inclusive
LH
15pp
→h
+je
tsco
mpa
riso
n
inclusive
STWZPowheg NnloPsSherpa NnloPs
MG5_aMC FxFxSherpa MePs@NloHerwig 7.1
10 20 50 100 2000
10
20
30
40
50Jet veto cross section
pveto⊥ [GeV]
σ0(
pveto
⊥)
[pb]
0.6
0.8
1
1.2
1.4
Jet veto cross section
Rat
ioto
STW
Z
10 20 50 100 200
0.6
0.8
1
1.2
1.4
pveto⊥ [GeV]
Rat
ioto
STW
Zvery good agreement between NNLOPS and STWZ
multijet merged with larger spread in shape,but within uncertainties once NLO normalisation accounted for
PS resummation uncertainties nowhere fully assessed
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
aside: quark mass effects in GGF
include effects of quark masses
reweight NLO HEFT with LO ratio:(reweight virtual with Born ratio, real with real ratio)
dσ(NLO)mass ≈ dσ
(NLO)HEFT ×
dσ(LO)mass
dσ(LO)HEFT
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
example: mass effects in gg → H (LO merging for b contribution)
−0.2
−0.1
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
dσ
/d
pH ⊥[p
b/G
eV]
HEFTSM, mb = 0
SM, µbPS = mb
SM, µbPS = 9 GeV
SM, µbPS = 31 GeV
100 101 102
pH⊥ [GeV]
0.20.40.60.81.0
Rat
ioto
HEF
T
Sherpa+OpenLoopsy2
t -contributions: MC@NLOytyb-contributions: LO+PSpp→ H + X√
s = 13 TeV
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
dσ
/d
pH ⊥[p
b/G
eV]
HEFTSM, mb = 0
SM, Qbcut ∈ [1/
√2mb,
√2mb]
100 101 102 103
pH⊥ [GeV]
0.88
0.96
1.04
1.12
Rat
ioto
HEF
T
Sherpa+OpenLoopsy2
t -contributions: MC@NLOytyb-contributions: CKKW
pp→ H + X√s = 13 TeV
10−6
10−5
10−4
10−3
10−2
10−1
100
dσ
/dpH ⊥
[pb/
GeV
]
0 jet SM1 jet SM2 jet SM3 jet SM
0 jet HEFT1 jet HEFT2 jet HEFT3 jet HEFT
0 200 400 600 800 1000pH⊥ [GeV]
0.20.40.60.81.0
Rat
ioto
HEF
T
Sherpa+OpenLoopsMEPS@NLOpp→ H + X√
s = 13 TeV
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
Z+jets at 13 Tev: comparison with ATLAS datavarious merging codes at LO and NLO
jetsN
0≥ 1≥ 2≥ 3≥ 4≥ 5≥ 6≥ 7≥
) [p
b]je
ts*+
Nγ
(Z/
σ
-210
-110
1
10
210
310
410
510
610ATLAS Preliminary
1−13 TeV, 3.16 fb
jets, R = 0.4tanti-k
< 2.5jet
y > 30 GeV, jet
Tp
) + jets−l+ l→*(γZ/
Data
HERPAS + ATHLACK B
2.1HERPA S
6YP + LPGEN A
8 CKKWLYP + MG5_aMC
8 FxFxYP + MG5_aMC
jetsN
0≥ 1≥ 2≥ 3≥ 4≥ 5≥ 6≥ 7≥
Pre
d./D
ata
0.5
1
1.5
jetsN
0≥ 1≥ 2≥ 3≥ 4≥ 5≥ 6≥ 7≥
Pre
d./D
ata
0.5
1
1.5
jetsN
0≥ 1≥ 2≥ 3≥ 4≥ 5≥ 6≥ 7≥
Pre
d./D
ata
0.5
1
1.5
[GeV]TH
200 400 600 800 1000 1200 1400
[pb/
GeV
]T
/dH
σd
-410
-310
-210
-110
1
10
210
310ATLAS Preliminary
1−13 TeV, 3.16 fb
jets, R = 0.4tanti-k
< 2.5jet
y > 30 GeV, jet
Tp
1 jet≥) + −l+ l→*(γZ/ Data
NNLOjetti
1 jet N≥ Z + HERPAS + ATHLACK B
2.1HERPA S6YP + LPGEN A
8 CKKWLYP + MG5_aMC8 FxFxYP + MG5_aMC
[GeV]T
H
200 400 600 800 1000 1200 1400
Pre
d./D
ata
0.5
1
1.5
[GeV]T
H
200 400 600 800 1000 1200 1400P
red.
/Dat
a 0.5
1
1.5
[GeV]TH
200 400 600 800 1000 1200 1400
Pre
d./D
ata
0.5
1
1.5
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
including EW corrections
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
EW corrections
EW corrections sizeable O(10%) at large scales: must include them!
but: more painful to calculate
need EW showering & possibly corresponding PDFs(somewhat in its infancy: chiral couplings)
example: Zγ vs. pT (right plot)(handle on pZ⊥ in Z → νν)
(Kallweit, Lindert, Pozzorini, Schoenherr for LH’15)
difference due to EW charge of Z
no real correction (real V emission)
improved description of Z → ``
bb
b
bbb
b bb
bb b
bb
b
b
b
b
bb
b
b
bb
bb
bb
bb
bb
b b b b
bb
b
b
bb
bb
bb
bb
b b b b b b
Sher
pa+O
pen
Lo
ops
b NLO QCDb NLO QCD+EW
b CMS dataJHEP10(2015)128
0
0.01
0.02
0.03
0.04
0.05Z/γ ratio for events with njets ≥ 1
dσ
/dpZ T
/d
σ/d
pγ T
b
b
b b
b
b
b
b b
b bb
b
b
b
b
b
b
b
b
b b
b
b
b
b b
b bb
b
b
b
b
b
b
b b b b b b b b b b b b b b b b b b
100 200 300 400 500 600 700 800
0.8
0.9
1.0
1.1
1.2
pZ/γT [GeV]
MC
/Dat
a
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
inclusion of electroweak corrections in simulation
incorporate approximate electroweak corrections in MEPS@NLO
1 using electroweak Sudakov factors
Bn(Φn) ≈ Bn(Φn) ∆EW(Φn)
2 using virtual corrections and approx. integrated real corrections
Bn(Φn) ≈ Bn(Φn) + Vn,EW(Φn) + In,EW(Φn) + Bn,mix(Φn)
real QED radiation can be recovered through standard tools(parton shower, YFS resummation)
simple stand-in for proper QCD⊕EW matching and merging→ validated at fixed order, found to be reliable,→ difference . 5% for observables not driven by real radiation
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
results: pp → `−ν + jets(Kallweit, Lindert, Maierhofer, Pozzorini, Schoenherr JHEP04(2016)021)
Sher
pa+O
pen
Lo
ops
Qcut = 20 GeV
MEPS@LOMEPS@NLO QCDMEPS@NLO QCD+EWvirtMEPS@NLO QCD+EWvirt w.o. LO mix
100
10–3
10–6
10–9
pp → ℓ−ν + 0,1,2 j @ 13 TeV
dσ
/dp T
,V[p
b/G
eV]
50 100 200 500 1000 20000
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
pT,V [GeV]
dσ
/dσ
NL
OQ
CD
Sher
pa+O
pen
Lo
ops
Qcut = 20 GeV
MEPS@LOMEPS@NLO QCDMEPS@NLO QCD+EWvirtMEPS@NLO QCD+EWvirt w.o. LO mix
100
10–3
10–6
10–9
pp → ℓ−ν + 0,1,2 j @ 13 TeV
dσ
/dp T
,j 1[p
b/G
eV]
50 100 200 500 1000 20000
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
pT,j1 [GeV]
dσ
/dσ
NL
OQ
CD
⇒ particle level events including dominant EW corrections
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
NLO EW predictions for ∆R(µ, j1)
Sher
pa+O
pen
Lo
ops
LHC 8 TeVpp → µν + 1j inclusive
LO
0 1 2 3 4 50
0.05
0.1
0.15
0.2
0.25Angular separtion of leading jet and muon
∆R(µ, j)
dσ
/d∆
R[p
b] measure collinear W emission?LHC@8TeV, pj1⊥ > 500GeV, central µ and jet
LO pp →Wj with ∆φ(µ, j) ≈ π
NLO corrections neg. in peaklarge pp →Wjj component opening PS
sub-leading Born (γPDF) at large ∆R
restrict to exactly 1j , no pj2⊥ > 100 GeV
describe pp →Wjj @ NLO, pj2⊥ > 100 GeV
pos. NLO QCD,
neg. NLO EW,
∼ flat
sub-leading Born contribs positive
sub2leading Born (diboson etc) conts. pos.→ possible double counting with BG
merge using exclusive sums
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
NLO EW predictions for ∆R(µ, j1)
Sher
pa+O
pen
Lo
ops
LHC 8 TeVpp → µν + 1j inclusive
LONLO QCD
0
0.05
0.1
0.15
0.2
0.25Angular separtion of leading jet and muon
dσ
/d∆
R[p
b]
0 1 2 3 4 5
0.5
1
1.5
∆R(µ, j)
Rat
iow
rt.N
LO
QC
D
measure collinear W emission?LHC@8TeV, pj1⊥ > 500GeV, central µ and jet
LO pp →Wj with ∆φ(µ, j) ≈ πNLO corrections neg. in peaklarge pp →Wjj component opening PS
sub-leading Born (γPDF) at large ∆R
restrict to exactly 1j , no pj2⊥ > 100 GeV
describe pp →Wjj @ NLO, pj2⊥ > 100 GeV
pos. NLO QCD,
neg. NLO EW,
∼ flat
sub-leading Born contribs positive
sub2leading Born (diboson etc) conts. pos.→ possible double counting with BG
merge using exclusive sums
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
NLO EW predictions for ∆R(µ, j1)
Sher
pa+O
pen
Lo
ops
LHC 8 TeVpp → µν + 1j inclusive
LONLO QCDNLO QCD+EW
0
0.05
0.1
0.15
0.2
0.25Angular separtion of leading jet and muon
dσ
/d∆
R[p
b]
0 1 2 3 4 5
0.5
1
1.5
∆R(µ, j)
Rat
iow
rt.N
LO
QC
D
measure collinear W emission?LHC@8TeV, pj1⊥ > 500GeV, central µ and jet
LO pp →Wj with ∆φ(µ, j) ≈ πNLO corrections neg. in peaklarge pp →Wjj component opening PS
sub-leading Born (γPDF) at large ∆R
restrict to exactly 1j , no pj2⊥ > 100 GeV
describe pp →Wjj @ NLO, pj2⊥ > 100 GeV
pos. NLO QCD,
neg. NLO EW,
∼ flat
sub-leading Born contribs positive
sub2leading Born (diboson etc) conts. pos.→ possible double counting with BG
merge using exclusive sums
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
NLO EW predictions for ∆R(µ, j1)
Sher
pa+O
pen
Lo
ops
LHC 8 TeVpp → µν + 1j inclusive
LONLO QCDNLO QCD+EWNLO QCD+EW+subLO
0
0.05
0.1
0.15
0.2
0.25Angular separtion of leading jet and muon
dσ
/d∆
R[p
b]
0.5
1
1.5
Rat
iow
rt.N
LO
QC
D
0 1 2 3 4 5
0.5
1
1.5
∆R(µ, j)
Rat
iow
rt.N
LO
QC
D
measure collinear W emission?LHC@8TeV, pj1⊥ > 500GeV, central µ and jet
LO pp →Wj with ∆φ(µ, j) ≈ πNLO corrections neg. in peaklarge pp →Wjj component opening PS
sub-leading Born (γPDF) at large ∆R
restrict to exactly 1j , no pj2⊥ > 100 GeV
describe pp →Wjj @ NLO, pj2⊥ > 100 GeV
pos. NLO QCD,
neg. NLO EW,
∼ flat
sub-leading Born contribs positive
sub2leading Born (diboson etc) conts. pos.→ possible double counting with BG
merge using exclusive sums
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
NLO EW predictions for ∆R(µ, j1)
Sher
pa+O
pen
Lo
ops
LHC 8 TeVpp → µν + 1j exclusive
LONLO QCDNLO QCD+EWNLO QCD+EW+subLO
0
0.05
0.1
0.15
0.2
0.25Angular separtion of leading jet and muon
dσ
/d∆
R[p
b]
0.5
1
1.5
Rat
iow
rt.N
LO
QC
D
0 1 2 3 4 5
0.5
1
1.5
∆R(µ, j)
Rat
iow
rt.N
LO
QC
D
measure collinear W emission?LHC@8TeV, pj1⊥ > 500GeV, central µ and jet
LO pp →Wj with ∆φ(µ, j) ≈ πNLO corrections neg. in peaklarge pp →Wjj component opening PS
sub-leading Born (γPDF) at large ∆R
restrict to exactly 1j , no pj2⊥ > 100 GeV
describe pp →Wjj @ NLO, pj2⊥ > 100 GeV
pos. NLO QCD,
neg. NLO EW,
∼ flat
sub-leading Born contribs positive
sub2leading Born (diboson etc) conts. pos.→ possible double counting with BG
merge using exclusive sums
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
NLO EW predictions for ∆R(µ, j1)
Sher
pa+O
pen
Lo
ops
LHC 8 TeVpp → µν + 2j inclusive
LO
0 1 2 3 4 50
0.05
0.1
0.15
0.2
0.25Angular separtion of leading jet and muon
∆R(µ, j)
dσ
/d∆
R[p
b] measure collinear W emission?LHC@8TeV, pj1⊥ > 500GeV, central µ and jet
LO pp →Wj with ∆φ(µ, j) ≈ πNLO corrections neg. in peaklarge pp →Wjj component opening PS
sub-leading Born (γPDF) at large ∆R
restrict to exactly 1j , no pj2⊥ > 100 GeV
describe pp →Wjj @ NLO, pj2⊥ > 100 GeV
pos. NLO QCD,
neg. NLO EW,
∼ flat
sub-leading Born contribs positive
sub2leading Born (diboson etc) conts. pos.→ possible double counting with BG
merge using exclusive sums
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
NLO EW predictions for ∆R(µ, j1)
Sher
pa+O
pen
Lo
ops
LHC 8 TeVpp → µν + 2j inclusive
LONLO QCD
0
0.05
0.1
0.15
0.2
0.25Angular separtion of leading jet and muon
dσ
/d∆
R[p
b]
0 1 2 3 4 5
0.5
1
1.5
∆R(µ, j)
Rat
iow
rt.N
LO
QC
D
measure collinear W emission?LHC@8TeV, pj1⊥ > 500GeV, central µ and jet
LO pp →Wj with ∆φ(µ, j) ≈ πNLO corrections neg. in peaklarge pp →Wjj component opening PS
sub-leading Born (γPDF) at large ∆R
restrict to exactly 1j , no pj2⊥ > 100 GeV
describe pp →Wjj @ NLO, pj2⊥ > 100 GeV
pos. NLO QCD,
neg. NLO EW,
∼ flat
sub-leading Born contribs positive
sub2leading Born (diboson etc) conts. pos.→ possible double counting with BG
merge using exclusive sums
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
NLO EW predictions for ∆R(µ, j1)
Sher
pa+O
pen
Lo
ops
LHC 8 TeVpp → µν + 2j inclusive
LONLO QCDNLO QCD+EW
0
0.05
0.1
0.15
0.2
0.25Angular separtion of leading jet and muon
dσ
/d∆
R[p
b]
0 1 2 3 4 5
0.5
1
1.5
∆R(µ, j)
Rat
iow
rt.N
LO
QC
D
measure collinear W emission?LHC@8TeV, pj1⊥ > 500GeV, central µ and jet
LO pp →Wj with ∆φ(µ, j) ≈ πNLO corrections neg. in peaklarge pp →Wjj component opening PS
sub-leading Born (γPDF) at large ∆R
restrict to exactly 1j , no pj2⊥ > 100 GeV
describe pp →Wjj @ NLO, pj2⊥ > 100 GeV
pos. NLO QCD, neg. NLO EW, ∼ flat
sub-leading Born contribs positive
sub2leading Born (diboson etc) conts. pos.→ possible double counting with BG
merge using exclusive sums
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
NLO EW predictions for ∆R(µ, j1)
Sher
pa+O
pen
Lo
ops
LHC 8 TeVpp → µν + 2j inclusive
LONLO QCDNLO QCD+EWNLO QCD+EW+subLO
0
0.05
0.1
0.15
0.2
0.25Angular separtion of leading jet and muon
dσ
/d∆
R[p
b]
0.5
1
1.5
Rat
iow
rt.N
LO
QC
D
0 1 2 3 4 5
0.5
1
1.5
∆R(µ, j)
Rat
iow
rt.N
LO
QC
D
measure collinear W emission?LHC@8TeV, pj1⊥ > 500GeV, central µ and jet
LO pp →Wj with ∆φ(µ, j) ≈ πNLO corrections neg. in peaklarge pp →Wjj component opening PS
sub-leading Born (γPDF) at large ∆R
restrict to exactly 1j , no pj2⊥ > 100 GeV
describe pp →Wjj @ NLO, pj2⊥ > 100 GeV
pos. NLO QCD, neg. NLO EW, ∼ flat
sub-leading Born contribs positive
sub2leading Born (diboson etc) conts. pos.→ possible double counting with BG
merge using exclusive sums
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
NLO EW predictions for ∆R(µ, j1)
Sher
pa+O
pen
Lo
ops
LHC 8 TeVpp → µν + 2j inclusive
LONLO QCDNLO QCD+EWNLO QCD+EW+subLONLO QCD+EW+subLO+sub2LO
0
0.05
0.1
0.15
0.2
0.25Angular separtion of leading jet and muon
dσ
/d∆
R[p
b]
0.5
1
1.5
Rat
iow
rt.N
LO
QC
D
0.5
1
1.5
Rat
iow
rt.N
LO
QC
D
0 1 2 3 4 5
0.5
1
1.5
∆R(µ, j)
Rat
iow
rt.N
LO
QC
D
measure collinear W emission?LHC@8TeV, pj1⊥ > 500GeV, central µ and jet
LO pp →Wj with ∆φ(µ, j) ≈ πNLO corrections neg. in peaklarge pp →Wjj component opening PS
sub-leading Born (γPDF) at large ∆R
restrict to exactly 1j , no pj2⊥ > 100 GeV
describe pp →Wjj @ NLO, pj2⊥ > 100 GeV
pos. NLO QCD, neg. NLO EW, ∼ flat
sub-leading Born contribs positive
sub2leading Born (diboson etc) conts. pos.→ possible double counting with BG
merge using exclusive sums
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
NLO EW predictions for ∆R(µ, j1)
Sher
pa+O
pen
Lo
ops
LHC 8 TeVpp → µν + 1j exclusive+pp → µν + 2j inclusive
LONLO QCDNLO QCD+EWNLO QCD+EW+subLONLO QCD+EW+subLO+sub2LO
0
0.05
0.1
0.15
0.2
0.25Angular separtion of leading jet and muon
dσ
/d∆
R[p
b]
0.5
1
1.5
Rat
iow
rt.N
LO
QC
D
0.5
1
1.5
Rat
iow
rt.N
LO
QC
D
0 1 2 3 4 5
0.5
1
1.5
∆R(µ, j)
Rat
iow
rt.N
LO
QC
D
measure collinear W emission?LHC@8TeV, pj1⊥ > 500GeV, central µ and jet
LO pp →Wj with ∆φ(µ, j) ≈ πNLO corrections neg. in peaklarge pp →Wjj component opening PS
sub-leading Born (γPDF) at large ∆R
restrict to exactly 1j , no pj2⊥ > 100 GeV
describe pp →Wjj @ NLO, pj2⊥ > 100 GeV
pos. NLO QCD, neg. NLO EW, ∼ flat
sub-leading Born contribs positive
sub2leading Born (diboson etc) conts. pos.→ possible double counting with BG
merge using exclusive sums
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
NLO EW predictions for ∆R(µ, j1)R
) [fb]
∆/d
(σ
d
20
40
60
80
100
120
140
160
180 1 = 8 TeV, 20.3 fbs
Data
ALPGEN+PYTHIA6 W+jets
PYTHIA8 W+j & jj+weak shower
SHERPA+OpenLoops W+j & W+jj
NNLOjetti
1 jet N≥W +
> 500 GeVT
Leading Jet p
ATLAS
0 0.5 1 1.5 2 2.5 3 3.5 4
Pre
d./
Da
ta
0.5
1
1.5
2
, closest jet)µR(∆
0 0.5 1 1.5 2 2.5 3 3.5 4
Pre
d./
Da
ta
0.5
1
1.5
2
Data comparison(M. Wu ICHEP’16, ATLAS arXiv:1609.07045)
ALPGEN+PYTHIA
pp →W + jets MLM merged(Mangano et.al., JHEP07(2003)001)
PYTHIA 8pp →Wj + QCD showerpp → jj + QCD+EW shower
(Christiansen, Prestel, EPJC76(2016)39)
SHERPA+OPENLOOPS
NLO QCD+EW+subLOpp →Wj/Wjj excl. sum
(Kallweit, Lindert, Maierhofer,)
(Pozzorini, Schoenherr, JHEP04(2016)021)
NNLO QCD pp →Wj(Boughezal, Liu, Petriello, arXiv:1602.06965)
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
NLO EW predictions for ∆R(µ, j1)R
) [fb]
∆/d
(σ
d
20
40
60
80
100
1201 = 8 TeV, 20.3 fbs
Data
ALPGEN+PYTHIA6 W+jets
PYTHIA8 W+j & jj+weak shower
SHERPA+OpenLoops W+j & W+jj
< 600 GeVT
500 GeV < Leading Jet p
ATLAS
0 0.5 1 1.5 2 2.5 3 3.5 4
Pre
d./
Da
ta
0.5
1
1.5
2
, closest jet)µR(∆
0 0.5 1 1.5 2 2.5 3 3.5 4
Pre
d./
Da
ta
0.5
1
1.5
2
Data comparison(M. Wu ICHEP’16, ATLAS arXiv:1609.07045)
ALPGEN+PYTHIA
pp →W + jets MLM merged(Mangano et.al., JHEP07(2003)001)
PYTHIA 8pp →Wj + QCD showerpp → jj + QCD+EW shower
(Christiansen, Prestel, EPJC76(2016)39)
SHERPA+OPENLOOPS
NLO QCD+EW+subLOpp →Wj/Wjj excl. sum
(Kallweit, Lindert, Maierhofer,)
(Pozzorini, Schoenherr, JHEP04(2016)021)
NNLO QCD pp →Wj(Boughezal, Liu, Petriello, arXiv:1602.06965)
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
NLO EW predictions for ∆R(µ, j1)R
) [fb]
∆/d
(σ
d
5
10
15
20
25
30
35
40
45
501 = 8 TeV, 20.3 fbs
Data
ALPGEN+PYTHIA6 W+jets
PYTHIA8 W+j & jj+weak shower
SHERPA+OpenLoops W+j & W+jj
> 650 GeVT
Leading Jet p
ATLAS
0 0.5 1 1.5 2 2.5 3 3.5 4
Pre
d./
Da
ta
0.5
1
1.5
2
, closest jet)µR(∆
0 0.5 1 1.5 2 2.5 3 3.5 4
Pre
d./
Da
ta
0.5
1
1.5
2
Data comparison(M. Wu ICHEP’16, ATLAS arXiv:1609.07045)
ALPGEN+PYTHIA
pp →W + jets MLM merged(Mangano et.al., JHEP07(2003)001)
PYTHIA 8pp →Wj + QCD showerpp → jj + QCD+EW shower
(Christiansen, Prestel, EPJC76(2016)39)
SHERPA+OPENLOOPS
NLO QCD+EW+subLOpp →Wj/Wjj excl. sum
(Kallweit, Lindert, Maierhofer,)
(Pozzorini, Schoenherr, JHEP04(2016)021)
NNLO QCD pp →Wj(Boughezal, Liu, Petriello, arXiv:1602.06965)
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
improving parton showers
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
another systematic uncertainty
parton showers are approximations, based onleading colour, leading logarithmic accuracy, spin-averaged
parametric accuracy by comparing Sudakov form factors:
∆ = exp
−∫
dk2⊥
k2⊥
[A log
k2⊥
Q2+ B
],
where A and B can be expanded in αS(k2⊥)
showers usually include terms A1,2 and B1 (NLL)
A2 often realised by pre-factor multiplying scale µR ' k⊥(CMW rescaling: Catani, Marchesini, Webber, Nucl Phys B,349 635)
fixed-order precision necessitates to consistently assess uncertaintiesfrom parton showers (quite often just used as black box)
maybe improve by including higher orders?
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
event generation (on-the-fly scale variations)
basic idea: want to vary scales to assess uncertainties
simple reweighting in matrix elements straightforward
reweighting in parton shower more cumbersome
shower is probabilistic, concept of weight somewhat alienintroduce relative weightevaluate (trial-)emission by (trial-)emission
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
implementation in HERWIG7
Dipole (µR/√
2, µF /√
2)
Dipole (√
2µR,√
2µF )
Dipole (µR, µF )10−7
10−6
10−5
10−4
10−3
10−2
1/σ
×dσ/d
p⊥
(H)
[1/G
eV]
1 10 1 10 2
0.6
0.8
1
1.2
1.4
p⊥(H) [GeV]
Rew
eigh
t/D
irec
t
AO (µR/√
2, µF /√
2)
AO (√
2µR,√
2µF )
AO (µR, µF )10−7
10−6
10−5
10−4
10−3
10−2
1/σ
×dσ/d
p⊥
(H)
[1/G
eV]
1 10 1 10 2
0.6
0.8
1
1.2
1.4
p⊥(H) [GeV]
Rew
eigh
t/D
irec
t
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
weight variation for W+jets with MEPS@NLO
uncertainties in pW⊥
pW⊥ [GeV]
10−6
10−3
100
103
106
dσ/dpW T
[pb/GeV
]
NLOPS
W pT uncertainty bands
Sherpa MEPS@NLO
pp → W[eν], √s = 13 TeVnNLOPS = 1, nPS = 2
µF ,RαS
CT14
dedicated
100 101 102 103
pWT [GeV]
0.7
1.0
1.3
ratio
toCV
100 101 102 103
0.7
1.0
1.3
scale uncertainty
100 101 102 103
0.9
1.0
1.1
ratio
toCV
αS uncertainty
100 101 102 103
pWT [GeV]
0.9
1.0
1.1
CT14 uncertainty
CPU budget
0 1 2 3 4 6 8nPS
0.0
0.1
0.2
0.3
0.4
0.5
0.6
t rew/t ded
nPS =∞
Sherpa MEPS@LO
0/0 1/0 1/1 1/2 1/3 1/5 1/7nNLOPS / nPS
nNLOPS = 1, nPS =∞
Sherpa MEPS@NLO
0 1 2 3 4 6 8nPS
0.0
0.1
0.2
0.3
0.4
0.5
0.6
t rew/t ded
nPS =∞
Sherpa LOPS
pp → W[eν], √s = 13 TeV
0/0 1/0 1/1 1/2 1/3 1/5 1/7nNLOPS / nPS
nNLOPS = 1, nPS =∞
Sherpa NLOPS
parton-level only
+ non-perturbative eects
+ unweighting
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
going beyond leading colour
start including next-to leading colour(first attempts by Platzer & Sjodahl; Nagy & Soper)
0.001
0.01
0.1
1
average transverse momentum w.r.t. ~n3
DipoleShower + ColorFull
0.80.9
11.11.2
1 10
〈p⊥〉/GeV
fullshower
strict large-Nc
GeV
N−1
dN/d
〈p⊥
〉x/f
ull
also included in 1st emission in SHERPA’s MC@NLO
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
towards higher logarithmic accuracy(Catani, Hoeche, FK, Prestel, in prep.)
reproduce DGLAP evolution at NLOinclude all NLO splitting kernels
corrections to standard 1→ 2 trivial
2-loop cusp term subtracted &combined with LO soft contributionuse weighting algorithms
(Hoeche, Schumann, Siegert, 0912.3501)
new topology at NLO fromq → q and q → q′ splittings
generic 1→ 3 process in parton shower
first branching treated as soft gluonradiation, second as collinear splitting(to match diagrammatic structure)
implementation complete andcross-checked (PYTHIA vs. SHERPA)
y23 × 2
y34 × 10−1
y45 × 10−2
y56 × 10−3
Dir
ePS
e+e− → qq @ 91.2 GeV
1 → 2 only1 → 2 & 1 → 3
10−2
10−1
1
10 1
10 2
10 3
10 4
Differential jet resolution at parton level (Durham algorithm)
dσ
/d
log 10
y nn+
1[p
b]
y23
0.940.960.98
1.01.021.041.06
Rat
io
y34
0.940.960.98
1.01.021.041.06
Rat
io
y45
0.940.960.98
1.01.021.041.06
Rat
io
y56
-4 -3.5 -3 -2.5 -2 -1.5 -1 -0.5
0.940.960.98
1.01.021.041.06
log10 yn n+1
Rat
io
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
some first results:DY (pp → e+e−, left) ggF (pp → H → τ+τ−, right)
added scale uncertainties in parton shower by varying µR
Dir
ePS
pp → e+e− @ 8TeV
Γ1 ⊕ γ1Γ1 ⊕ γ1 ⊕ Γ21/2 t < µR < 2 tΓ1 ⊕ γ1 ⊕ Γ2 ⊕ γ2Γ1 ⊕ γ1 ⊕ Γ2 ⊕ γ2 ⊕ Γ31/2 t < µR < 2 t
1
10 1
10 2
10 3
Differential 0 → 1 jet resolution
dσ
/d
log 10
(d01
/G
eV)
[pb]
0.5 1 1.5 2 2.5
0.8
0.9
1.0
1.1
1.2
log10(d01/GeV)
Rat
io
Dir
ePS
pp → [h → τ+τ−] @ 8TeV
Γ1 ⊕ γ1Γ1 ⊕ γ1 ⊕ Γ21/2 t < µR < 2 tΓ1 ⊕ γ1 ⊕ Γ2 ⊕ γ2Γ1 ⊕ γ1 ⊕ Γ2 ⊕ γ2 ⊕ Γ31/2 t < µR < 2 t
10−3
10−2
10−1
Differential 0 → 1 jet resolution
dσ
/d
log 10
(d01
/G
eV)
[pb]
0.5 1 1.5 2 2.5
0.8
0.9
1.0
1.1
1.2
log10(d01/GeV)
Rat
io
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
some first results - comparison with data:y23 at LEP (left) and φ∗ distribution in Drell-Yan production (right)
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
hadronisation
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
colour reconnections and friends(Fischer, Sjostrand, 1610:09818)
(slide stolen from Torbjorn Sjostrand)
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
strange strangeness
(ALICE collaboration)
universality of hadronisation assumed
parameters tuned to LEP datain particular: strangeness suppression
for strangeness: flat ratiosbut data do not reproduce this
looks like SU(3) restorationnot observed for protons
needs to be investigated
|< 0.5η|⟩η/d
chNd⟨
10 210 310)+ π+− π
Rat
io o
f yie
lds
to (
3−10
2−10
1−10
16)× (+Ω+−Ω
6)× (+Ξ+−Ξ
2)× (Λ+Λ
S02K
ALICE = 7 TeVspp,
= 5.02 TeVNNsp-Pb, = 2.76 TeVNNsPb-Pb,
PYTHIA8DIPSYEPOS LHC
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
other “soft” aspects of event generation: QED FSR
QED FSR in Drell-Yan production
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
limitations
and
future challenges
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
limitation: computing short-distance cross sections – LO(Childers, Uram, LeCompte, Benjamin, Hoeche, CHEP 2016)
challenge of efficiency on tomorrow’s (& today’s) computers
2000’s paradigm: memory free, flops expensive(example: 16-core Xeon, 20MB L2 Cache, 64GB RAM)
2020’s paradigm: flops free, memory expensive & must be managed(example: 68-core Xeon KNL, 34MB L2 Cache, 16GB HBM, 96GB RAM)
may trigger rewrites of code to account for changing paradigm
CHEP San Francisco J. Taylor Childers October 2016
Code improvements enable scaling on KNL
31
9hr run-time
matrix element contributions
New results from two days ago… next test on Mira to see if we see similar improvements (figures stolen from Taylor Childers’ talk at CHEP)
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
theory limitations/questions
we have constructed lots of tools for precision physics at LHC−→ but we did not cross-validate them careful enough (yet)−→ but we did not compare their theoretical foundations (yet)
we also need unglamorous improvements on existing tools:
account for new computer architectures and HPC paradigmssystematically check advanced scale-setting schemes (MINLO)automatic (re-)weighting for PDFs & scalesscale compensation in PS is simple (implement and check)
4 vs. 5 flavour scheme −→ really?
how about αS : range from 0.113 to 0.118(yes, I know, but still - it bugs me)
−→ is there any way to settle this once and for all (measurements?)
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
achievable goals (I believe we know how to do this)
NLO for loop-induced processes:
fixed-order starting, MC@NLO tedious but straightforward
EW NLO corrections with tricky/time-consuming calculation setup
but important at large scales: effect often ∼ QCD, but opposite signneed maybe faster approximation for high-scales (EW Sudakovs)work out full matching/merging instead of approximations
improve parton shower:
beyond (next-to) leading log, leading colour, spin-averagedHO effects in shower and scale uncertaintiesstart including next-to leading colourinclude spin-correlations → important for EW emissions
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
more theory uncertainties/issues?
with NNLOPS approaching 5% accuracy or better:
non-perturbative uncertainties start to matter:−→ PDFs, MPIs, hadronization, etc.question (example): with hadronization tuned to quark jets (LEP)−→ how important is the “chemistry” of jets for JES?−→ can we fix this with measurements?example PDFs: to date based on FO vs. data−→will we have to move to resummed/parton showered?
(reminder: LO∗ was not a big hit, though)
g → qq at accuracy limit of current parton showers:−→ how bad are ∼ 25% uncertainty on g → bb?−→ can we fix this with measurements?
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
the looming revolution: going beyond NLO
H in ggF at N3LO (Anastasiou, Duhr and others)
explosive growth in NNLO (QCD) 2→ 2 results(apologies for any unintended omissions)
tt (1303.6254; 1508.03585;1511.00549)
single-t (1404.7116)
VV (1507.06257; 1605.02716;1604.08576; 1605.02716)
HH (1606.09519)
VH (1407.4747; 1601.00658;1605.08011)
Vγ (1504.01330)
γγ (1110.2375; 1603.02663)
Vj (1507.02850; 1512.01291; 1602.06965; 1605.04295; 1610.07922)
Hj (1408.5325; 1504.07922; 1505.03893; 1508.02684; 1607.08817)
jj (1310.3993; 1611.01460)
NLO corrections to gg → VV (1605.04610)
WBF at NNLO (1506.02660) and N3LO (1606.00840)
different IR subtraction schemes:N-jettiness slicing, antenna subtraction, sector decomposition,
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
living with the revolution
we will include them into full simulations(I am willing to place a bet: 5 years at most!)
practical limitations/questions to be overcome:
dealing with IR divergences at NNLO: slicing vs. subtracting(I’m not sure we have THE solution yet)
how far can we push NNLO? are NLO automated results stableenough for NNLO at higher multiplicity?matching for generic processes at NNLO?
(MINLO or UN2LOPS or something new?)
more scales (internal or external) complicated – need integrals
philosophical questions:
going to higher power of N often driven by need to include larger FSmultiplicity – maybe not the most efficient methodlimitations of perturbative expansion:−→ breakdown of factorisation at HO (Seymour et al.)−→ higher-twist: compare (αS/π)n with ΛQCD/MZ
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
outlookwill need precision for ballistics of smoking guns
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
extra: NLO EW subtraction in SHERPA
(M. Schoenherr in preparation)
adapt QCD subtraction (spl. fns. and colour-/spin-correlated MEs)(Catani, Dittmaier, Seymour, Trocsanyi Nucl.Phys.B627(2002)189-265)
replacements: αs → α, CF → Q2f , CA → 0,
replacements: αs → α, TR → Nc,f Q2f , nf TR →
∑f Nc,f Q
2f ,
replacements:Tij ·Tk
T2ij→ QijQk
Q2ij
bcbcbcbc
bc
bcbcbc
bc
νe νe → e+e− @√
s = 200 GeV
10−4 10−3 10−2 10−1 1
-0.33
-0.328
-0.326
-0.324
-0.322
-0.32
-0.318
-0.316
σIRS in dependence on α-parameter
αFF
σIR
S(α
)/σ
Bor
n[%
]
αFF
=α
FI=
αIF
=α
II=
1
αFF
=0.
001,
αFI
=α
IF=
αII
=1
αFI
=0.
001,
αFF
=α
IF=
αII
=1
αIF
=0.
001,
αFF
=α
FI=
αII
=1
αII
=0.
001,
αFF
=α
FI=
αIF
=1
αFF
=α
FI=
αIF
=α
II=
0.00
1
bc bc bc
bc
bc bc
pp → e+e− @√
s = 13 TeV, mee > 60 GeV, no γPDF
0.16
0.17
0.18
0.19
0.2
0.21
0.22
0.23
0.24
σIRS in dependence on α-parameter
σIR
S(α
)/σ
Bor
n[%
]
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
extra: NLO EW subtraction in SHERPA
(M. Schoenherr in preparation)
adapt QCD subtraction (spl. fns. and colour-/spin-correlated MEs)(Catani, Dittmaier, Seymour, Trocsanyi Nucl.Phys.B627(2002)189-265)
replacements: αs → α, CF → Q2f , CA → 0,
replacements: αs → α, TR → Nc,f Q2f , nf TR →
∑f Nc,f Q
2f ,
replacements:Tij ·Tk
T2ij→ QijQk
Q2ij
bcbcbcbc
bc
bcbc
bc
bc
νe νe → tt @√
s =2 TeV
10−4 10−3 10−2 10−1 1
-1.936
-1.934
-1.932
-1.93
-1.928
-1.926
-1.924
-1.922
σIRS in dependence on α-parameter
αFF
σIR
S(α
)/σ
Bor
n[%
]
αFF
=α
FI=
αIF
=α
II=
1
αFF
=0.
001,
αFI
=α
IF=
αII
=1
αFI
=0.
001,
αFF
=α
IF=
αII
=1
αIF
=0.
001,
αFF
=α
FI=
αII
=1
αII
=0.
001,
αFF
=α
FI=
αIF
=1
αFF
=α
FI=
αIF
=α
II=
0.00
1
bcbc
bc bc bc
bc
pp → tt @√
s = 13 TeV, no γPDF
3.52
3.54
3.56
3.58
3.6
3.62
3.64
σIRS in dependence on α-parameter
σIR
S(α
)/σ
Bor
n[%
]
F. Krauss IPPP
Precision Simulations for LHC physics and beyond
Introduction Matching & Merging EW corrections Parton Showers Soft Physics Future directions
extra: NLO EW subtraction in SHERPA
(M. Schoenherr in preparation)
adapt QCD subtraction (spl. fns. and colour-/spin-correlated MEs)(Catani, Dittmaier, Seymour, Trocsanyi Nucl.Phys.B627(2002)189-265)
replacements: αs → α, CF → Q2f , CA → 0,
replacements: αs → α, TR → Nc,f Q2f , nf TR →
∑f Nc,f Q
2f ,
replacements:Tij ·Tk
T2ij→ QijQk
Q2ij
bcbc
bcbc
bc bcbc bc bc
ldld
ldld
ld ld ld ld ld
νe νe → W+W− @√
s =2 TeVbc Subtraction as massive Quarkld Subtraction as massive Scalar
10−4 10−3 10−2 10−1 1
-8.245
-8.24
-8.235
-8.23
-8.225
-8.22
-8.215
σIRS in dependence on α-parameter
αFF
σIR
S(α
)/σ
Bor
n[%
]
αFF
=α
FI=
αIF
=α
II=
1
αFF
=0.
001,
αFI
=α
IF=
αII
=1
αFI
=0.
001,
αFF
=α
IF=
αII
=1
αIF
=0.
001,
αFF
=α
FI=
αII
=1
αII
=0.
001,
αFF
=α
FI=
αIF
=1
αFF
=α
FI=
αIF
=α
II=
0.00
1
bcbc
bcbc bc
bcld
ld
ldld ld
ld
pp → W+W− @√
s =13 TeV, no γPDFbc Subtraction as massive Quarkld Subtraction as massive Scalar
0.4
0.5
0.6
0.7
0.8
σIRS in dependence on α-parameter
σIR
S(α
)/σ
Bor
n[%
]
F. Krauss IPPP
Precision Simulations for LHC physics and beyond