mc tools and nlo monte carlos - institut national de
TRANSCRIPT
Introduction The Good: Fixed Order The Bad: Matching & Merging The Ugly
MC Tools and NLO Monte Carlosor
The Good, the Bad & the Ugly
Frank Krauss
Institute for Particle Physics PhenomenologyDurham University
“Higgs Hunting 2016”, Paris, 1.9.2016
F. Krauss IPPP
MC Tools and NLO Monte Carlos
Introduction The Good: Fixed Order The Bad: Matching & Merging The Ugly
what the talk is about
the cutting edge in theory inputs
matching & merging with parton showers
where we are and where we (should/could/would) go
F. Krauss IPPP
MC Tools and NLO Monte Carlos
Introduction The Good: Fixed Order The Bad: Matching & Merging The Ugly
motivation & introduction
F. Krauss IPPP
MC Tools and NLO Monte Carlos
Introduction The Good: Fixed Order The Bad: Matching & Merging The Ugly
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
MC Tools and NLO Monte Carlos
Introduction The Good: Fixed Order The Bad: Matching & Merging The Ugly
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
MC Tools and NLO Monte Carlos
Introduction The Good: Fixed Order The Bad: Matching & Merging The Ugly
reminder: fixed-order and its limits
F. Krauss IPPP
MC Tools and NLO Monte Carlos
Introduction The Good: Fixed Order The Bad: Matching & Merging The Ugly
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 such 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
MC Tools and NLO Monte Carlos
Introduction The Good: Fixed Order The Bad: Matching & Merging The Ugly
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)
tt̄ (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)
Vγ (1504.01330)
γγ (1110.2375; 1603.02663)
Vj (1507.02850; 1512.01291; 1602.06965)
Hj (1408.5325; 1504.07922; 1505.03893; 1508.02684)
jj (1310.3993)
WBF at NNLO and N3LO (1506.02660 and N3LO 1606.00840)
different IR subtraction schemes:N-jettiness slicing, antenna subtraction, sector decomposition,
F. Krauss IPPP
MC Tools and NLO Monte Carlos
Introduction The Good: Fixed Order The Bad: Matching & Merging The Ugly
challenging the revolution
some technical issues at NNLO (and beyond)(stability of automated NLO, robustness under integration, subtraction vs. slicing)
more scales (internal or external) complicated – need integrals
going to higher power of N often driven by need to include larger FSmultiplicity – maybe not the most efficient method
structural questions concerning convergence/importance
limitations of perturbative expansion:
breakdown of factorisation at HO (Seymour et al.)higher-twist: compare (αS/π)n with ΛQCD/MZ
(see Melnikov’s talk last week)
F. Krauss IPPP
MC Tools and NLO Monte Carlos
Introduction The Good: Fixed Order The Bad: Matching & Merging The Ugly
matching @ (N)NLO
merging @ (N)LO
F. Krauss IPPP
MC Tools and NLO Monte Carlos
Introduction The Good: Fixed Order The Bad: Matching & Merging The Ugly
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
MC Tools and NLO Monte Carlos
Introduction The Good: Fixed Order The Bad: Matching & Merging The Ugly
some parton shower fun with DY(example of accuracy in description of standard precision observable)
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b ATLAS dataPhys.Lett. B720 (2013) 32ME+PS (1-jet)5 ≤ Qcut ≤ 20 GeV
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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
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→ ≤ | |
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/Dat
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2 < |yZ| ≤ 2.4
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0.80.91.01.11.2
| |
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/Dat
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→ | | ≥
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/Dat
a
F. Krauss IPPP
MC Tools and NLO Monte Carlos
Introduction The Good: Fixed Order The Bad: Matching & Merging The Ugly
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
MC Tools and NLO Monte Carlos
Introduction The Good: Fixed Order The Bad: Matching & Merging The Ugly
NNLOPS for H production: MINLO
K. Hamilton, P. Nason, E. Re & G. Zanderighi, JHEP 1310
also available for Z production
F. Krauss IPPP
MC Tools and NLO Monte Carlos
Introduction The Good: Fixed Order The Bad: Matching & Merging The Ugly
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
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io to
NLO
0.960.98
11.021.04
-e+ey
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b bb
bbb b
bbb b
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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
MC Tools and NLO Monte Carlos
Introduction The Good: Fixed Order The Bad: Matching & Merging The Ugly
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
MC Tools and NLO Monte Carlos
Introduction The Good: Fixed Order The Bad: Matching & Merging The Ugly
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
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ta/P
YT
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3 [
pb
/Ge
V]
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/dp
σd
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10
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DIPHOX+GAMMA2MC (CT10)
NNLO (MSTW2008)γ2
ATLAS
= 7 TeVs
da
ta/D
IPH
OX
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[GeV]γγT,
p
0 50 100 150 200 250 300 350 400 450 500
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LO
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ata
/2
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F. Krauss IPPP
MC Tools and NLO Monte Carlos
Introduction The Good: Fixed Order The Bad: Matching & Merging The Ugly
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
MC Tools and NLO Monte Carlos
Introduction The Good: Fixed Order The Bad: Matching & Merging The Ugly
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
MC Tools and NLO Monte Carlos
Introduction The Good: Fixed Order The Bad: Matching & Merging The Ugly
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
MC Tools and NLO Monte Carlos
Introduction The Good: Fixed Order The Bad: Matching & Merging The Ugly
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
MC Tools and NLO Monte Carlos
Introduction The Good: Fixed Order The Bad: Matching & Merging The Ugly
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
MC Tools and NLO Monte Carlos
Introduction The Good: Fixed Order The Bad: Matching & Merging The Ugly
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
MC Tools and NLO Monte Carlos
Introduction The Good: Fixed Order The Bad: Matching & Merging The Ugly
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
MC Tools and NLO Monte Carlos
Introduction The Good: Fixed Order The Bad: Matching & Merging The Ugly
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
MC Tools and NLO Monte Carlos
Introduction The Good: Fixed Order The Bad: Matching & Merging The Ugly
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
MC Tools and NLO Monte Carlos
Introduction The Good: Fixed Order The Bad: Matching & Merging The Ugly
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
MC Tools and NLO Monte Carlos
Introduction The Good: Fixed Order The Bad: Matching & Merging The Ugly
results from various schemes in H+jets through ggF
F. Krauss IPPP
MC Tools and NLO Monte Carlos
Introduction The Good: Fixed Order The Bad: Matching & Merging The Ugly
F. Krauss IPPP
MC Tools and NLO Monte Carlos
Introduction The Good: Fixed Order The Bad: Matching & Merging The Ugly
F. Krauss IPPP
MC Tools and NLO Monte Carlos
Introduction The Good: Fixed Order The Bad: Matching & Merging The Ugly
aside: quark mass effects
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
MC Tools and NLO Monte Carlos
Introduction The Good: Fixed Order The Bad: Matching & Merging The Ugly
b–mass effects: playtime
use LO multijet merging for tb-interference
vary around µQ = mb vary around µQ = mh vary µF ,R
with Qcut = mb fixed
HEFTmt effects onlymt and mb effects, µb
s =√
2mbmt and mb effects, µb
s = mb
0
0.1
0.2
0.3
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0.5
0.6
Higgs boson transverse momentum
dσ
/dp ⊥
[pb/
GeV
]
0 10 20 30 40 50
00.20.40.60.8
1
p⊥(H) [GeV]
Rat
ioto
HE
FT
HEFTmt effects onlymt and mb effects, µb
s = mh/√
2mt and mb effects, µb
s = mh√
2
10−5
10−4
10−3
10−2
10−1
1Higgs boson transverse momentum
dσ
/dp ⊥
[pb/
GeV
]
1 10 1 10 2 10 30.9
0.95
1.0
1.05
p⊥(H) [GeV]
Rat
ioto
HE
FT
HEFTµ f ∈ [0.5, 2]mhµr ∈ [0.5, 2]mhmt and mb effects, Qcut = mb
10−5
10−4
10−3
10−2
10−1
1Higgs boson transverse momentum
dσ
/dp ⊥
[pb/
GeV
]
1 10 1 10 2 10 30.70.80.91.01.11.21.3
p⊥(H) [GeV]
Rat
ioto
HE
FT
F. Krauss IPPP
MC Tools and NLO Monte Carlos
Introduction The Good: Fixed Order The Bad: Matching & Merging The Ugly
limitations of full simulations
lots of routinely used tools for large FS multis (4 and more) at NLOaccuracy, but−→ not many detailled comparisons
(critical appraisals and learning curve in their phenomenological use still in infancy)
−→ no standard way of estimating uncertainties (yet?)
to improve: description of loop–induced processes−→ potentially important for new physics searches
users of codes: higher orders tricky → training needed(MC = black box attitude problematic - a new brand of pheno/experimenters needed?)
F. Krauss IPPP
MC Tools and NLO Monte Carlos
Introduction The Good: Fixed Order The Bad: Matching & Merging The Ugly
a systematic uncertainty
showering a source of uncertainty−→ (N)LL only, scale variations?
(quite often just used as black box)
maybe include higher orders?
example right:
µR uncertainty in p(emit)⊥ in ggF
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
MC Tools and NLO Monte Carlos
Introduction The Good: Fixed Order The Bad: Matching & Merging The Ugly
limitations
F. Krauss IPPP
MC Tools and NLO Monte Carlos
Introduction The Good: Fixed Order The Bad: Matching & Merging The Ugly
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)
will NNLO (or beyond) become as automated as NLO?−→ or more precisely: when and how?
we also need unglamorous improvements on existing tools:
systematically 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 still bugs me)
−→ is there any way to settle this once and for all (measurements?)
F. Krauss IPPP
MC Tools and NLO Monte Carlos
Introduction The Good: Fixed Order The Bad: Matching & Merging The Ugly
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 → qq̄ at accuracy limit of current parton showers:−→ how bad are ∼ 25% uncertainty on g → bb̄?−→ can we fix this with measurements?
F. Krauss IPPP
MC Tools and NLO Monte Carlos
Introduction The Good: Fixed Order The Bad: Matching & Merging The Ugly
plan
F. Krauss IPPP
MC Tools and NLO Monte Carlos
Introduction The Good: Fixed Order The Bad: Matching & Merging The Ugly
achievable goals in fixed order calculations: a roadmap (?)
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?)
NLO for loop-induced processes:
fixed-order starting, MC@NLO tedious but straightforward
EW NLO corrections with tricky/time-consuming calculational setup
but important at large scales: effect often ∼ QCD, but opposite signneed maybe faster approximation for high-scales (EW Sudakovs)
F. Krauss IPPP
MC Tools and NLO Monte Carlos
Introduction The Good: Fixed Order The Bad: Matching & Merging The Ugly
“curable” bottleneck: colours/spins in parton showers
parton shower usually is spin-averaged,leading colour, (next-to) leading log
start including next-to leading colour(first attempts by Platzer & Sjodahl; Nagy & Soper)
no big effects in e−e+ → hadrons seenmaybe more exclusive observables?
aside: can also include spin-correlationsimportant for EW emissions
(maybe relevant for ultra-high energies)
HO being implemented at nthemoment
0.001
0.01
0.1
1
average transverse momentum w.r.t. ~n3
DipoleShower + ColorFull
0.80.91
1.11.2
1 10
〈p⊥〉/GeV
fullshower
strict large-Nc
GeV
N−1dN/d
〈p⊥〉
x/full
F. Krauss IPPP
MC Tools and NLO Monte Carlos
Introduction The Good: Fixed Order The Bad: Matching & Merging The Ugly
outlookwill need precision for ballistics of smoking guns
F. Krauss IPPP
MC Tools and NLO Monte Carlos