sparticle reconstruction at benchmark points
DESCRIPTION
Sparticle reconstruction at benchmark points. Alessia Tricomi On behalf of ATLAS and CMS Collaboration Dipartimento di Fisica e Astronomia and INFN Catania. Outline. In the past years several inclusive studies done to understand the detector capabilities to discover SUSY - PowerPoint PPT PresentationTRANSCRIPT
Recontres de Moriond – QCD and Hadronic Interactions
La Thuile, 28 March – April 2004
Sparticle reconstruction at benchmark Sparticle reconstruction at benchmark points points
Alessia TricomiAlessia TricomiOn behalf of ATLAS and CMS Collaboration
Dipartimento di Fisica e Astronomia and INFN Catania
QCD and Hadronic Interactions, 28 March - 4 April 2004Alessia Tricomi
OutlineOutline
In the past years several inclusive studies done to understand the detector capabilities to discover SUSY
Counting excess of events over SM expectationsNo explicit sparticle reconstruction doneSeveral different final states analysed
Etmiss + jets
No lepton + Etmiss + jets
1 l + Etmiss + jets
2 l OS + Etmiss + jets
2 l SS + Etmiss + jets
3 l + Etmiss + jets
Scan in mSUGRA (m0,m1/2) plane (also studies in p-MSSM scenario performed )Fast MC simulation used: ATLFAST, CMSJET
Today I will focus on recent studies to reconstruct strongly interacting SUSY particles
S.Abdullin, F. Charles Nucl. Phys. B547 (1999) 60S. Abdullin et al., J. Phys. G28 (2002) 469M. Dzelalija et al., Mod. Phys. Lett. A15 (2000) 465
QCD and Hadronic Interactions, 28 March - 4 April 2004Alessia Tricomi
If Supersymmetry exists, If Supersymmetry exists, LHC will probably observe itLHC will probably observe it
Cosmologically interesting Cosmologically interesting region covered with 10 fbregion covered with 10 fb-1-1
Squark-gluino production Squark-gluino production dominates the total cross dominates the total cross section at low mass scalesection at low mass scale
Squarks and Gluinos Squarks and Gluinos detectable up to 2 TeV detectable up to 2 TeV mass with 100 fbmass with 100 fb-1-1
Inclusive SUSY reach vs integrated luminosityInclusive SUSY reach vs integrated luminosity
A0=0, tan=35, >0
S.Abdullin, F. Charles Nucl. Phys. B547 (1999) 60S. Abdullin et al., J. Phys. G28 (2002) 469M. Dzelalija et al., Mod. Phys. Lett. A15 (2000) 465
Expected squark-gluino mass reach
1.5 – 1.8 TeV with 10 fb-1
2.3 – 2.5 TeV with 100 fb-1
2.6 – 3.0 Tev with 300 fb-1
2.8 – 3.2 TeV with 1000 fb-1
QCD and Hadronic Interactions, 28 March - 4 April 2004Alessia Tricomi
It is not enough to observe the excess over the Standard Model…
Fix a set of points in the parameter space
Get information on the spectrum (i.e. end-points)
Reconstruct sparticles
DISCOVERYDISCOVERY SUSY SPECTROSCOPYSUSY SPECTROSCOPYThis requires a different approach…This requires a different approach…
But …But …
QCD and Hadronic Interactions, 28 March - 4 April 2004Alessia Tricomi
Decay chainsDecay chains
2 high pt isolated leptons OS
(leptons = e,)
2 high pt non-b jets
missing Et
2 high pt isolated leptons OS
(leptons = e,)
2 high pt b jets
missing Et
g~ pp
b~02
~
qq~ g~ pp
q~02
01
~~
SM bkg: tt, Z+jet, W+jet, ZZ, WW, ZW, QCD jets
Reconstruction of sbottoms, squarks and Reconstruction of sbottoms, squarks and gluinosgluinos
p
p
g~
b~
b
b
01
~02
~~
bb~
01
~
QCD and Hadronic Interactions, 28 March - 4 April 2004Alessia Tricomi
Benchmark pointsBenchmark points
Rather low mRather low m00 and m and m1/21/2 values in order to have values in order to have high SUSY cross sectionhigh SUSY cross section
Three differentThree different tantan values (tanvalues (tan = 10, 20, = 10, 20, 35) since BR35) since BR((22
00 ll++ll-- 1100) )
depends on tandepends on tan
Proposed Post-LEP Benchmarks for Supersymmetry, M. Battaglia Proposed Post-LEP Benchmarks for Supersymmetry, M. Battaglia et alet al. (hep-ph/0106204). (hep-ph/0106204)
QCD and Hadronic Interactions, 28 March - 4 April 2004Alessia Tricomi
Point B spectraPoint B spectra
95.610 = LSP
173.81±136.2lR
361.62±196.5lL
174.420520qR
339.930559qL
361.140524.0bR
575.9tR496.0bL
392.9tL595.1g
Point B
pb .TOTSUSY 7757
10
0100
250
00
21
tan
)(
A
sign
m
m
bb~
g~ pp
b~02
01~
(17% bL, 10% bR)
(37 % bL, 25% bR)
(0.04 %) 0
1~ ~(16.4 %)
01
~ ~ (83.2 %)
2 isolated leptons, pT>15 GeV, ||<2.4
2 b-jets, pT>20 GeV, ||<2.4
Sbottom reconstruction
QCD and Hadronic Interactions, 28 March - 4 April 2004Alessia Tricomi
p
p
g~
b~
b
b
01
~
02
~ ~
10 fb-1
First step: First step: 2200 l l++ll- - 11
00
02
~ 01
~
~
~
2
χ~2~
2~
2
χ~max
M
)M)(MM(MM
01
02
)μM(μ )eM(e - SUSY events
QCD and Hadronic Interactions, 28 March - 4 April 2004Alessia Tricomi
Bkg reductionBkg reduction
SUSY
ttbar
Z+jets
SM bkg can be strongly reduced cutting on ET
miss
(GeV) )μM(e -)μM(e - )μM(μ )eM(e --
Edge = 79 2 GeVGenerated = 78.2 GeV
Edge = 79 2 GeVGenerated = 78.2 GeV
QCD and Hadronic Interactions, 28 March - 4 April 2004Alessia Tricomi
Second step: sbottom (squark) Second step: sbottom (squark) reconstructionreconstruction
p
p
g~
b~
b
b
01
~
02
~ ~
• Assuming M(Assuming M(1100) known) known
• Selecting events “in edge”Selecting events “in edge”
• Combining theCombining the 2200 obtained obtained
from the two leptons with the from the two leptons with the most energetic b-jet in the most energetic b-jet in the eventevent
At the end-point:At the end-point:
GeV 80 )M( GeV 65
p
M
M1p
01
02
~
~
QCD and Hadronic Interactions, 28 March - 4 April 2004Alessia Tricomi
Squark mass peakSquark mass peak
GeV 906σ
GeV 10536q)χ~M( 02
Result of the fit:Result of the fit:
1 fb-1
GeV 0.537)~()u~M(
GeV 8.542)~()d~
M(
L
L
L
L
cM
sM
Generated valuesGenerated values
pb 4.1)chain decayq~pp(BR pb 5.0)chain decayq~g~pp(BR
fb 60chain)decay qBR(σ
pb 2chain)decay qBR(σ
R
L
~
~
QCD and Hadronic Interactions, 28 March - 4 April 2004Alessia Tricomi
Sbottom mass peakSbottom mass peak
The peak should be considered The peak should be considered as the superposition of two as the superposition of two
peakspeaks
10 fb-1
GeV 542σ
GeV7 500b)χ~M( 02
Result of the fit:
GeV 524.0)b~
M(
GeV 496.0)b~
M(
R
L
Generated masses:
pb 1.0)chain decayb~
pp(BR pb 6.0)chain decayb
~g~pp(BR
fb 212chain)decay bBR(σ
fb 535chain)decay bBR(σ
2
1
~
~
GeV 503.9)b
~BR(σ)b
~BR(σ
)b~
BR(σ)b~
M()b~
BR(σ)b~
M()b
~(M
21
2211
QCD and Hadronic Interactions, 28 March - 4 April 2004Alessia Tricomi
p
p
g~
b~
b
b
01
~
02
~ ~
Gluino reconstructionGluino reconstruction
10 fb-1
sbottom sbottom chainchain
10 fb-1
squark squark chainchain
GeV 1.955)g~M( GeV 742
GeV7 495bb)~M( 02
GeV 575
GeV7 295qq)~M( 02
Generated Generated
value:value:
Two separated gluino mass measurements, with Two separated gluino mass measurements, with two different samplestwo different samples
QCD and Hadronic Interactions, 28 March - 4 April 2004Alessia Tricomi
estimateestimate)b~
M(-)g~M(
GeV 471
GeV 392b)~M(-bb)~M( 02
02
The reconstruction is performed assuming M(The reconstruction is performed assuming M(1100) known but …) known but …
The difference between the two masses is independent of M(The difference between the two masses is independent of M(1100))
GeV 1.71)b~
M(-)g~M(
GeV 1.99)b~
M(-)g~M(
R
L
Result of the fit:Result of the fit:
Generated value:Generated value:
Worse resolution, but model independent resultWorse resolution, but model independent result
QCD and Hadronic Interactions, 28 March - 4 April 2004Alessia Tricomi
Results @ point BResults @ point B
GeV 441σ
GeV 4502b)χ~M( 02
60 fb-1
GeV 336σ
GeV 2497b)χ~M( 02
300 fb-1
GeV 80 )M( GeV 70 GeV 80 )M( GeV 75
60 fb-1
GeV 346
GeV 4295bb)~M( 02
GeV 339
GeV 1195bb)~M( 02
300 fb-1
GeV 80 )M( GeV 70 GeV 80 )M( GeV 75
GeV 136σ
GeV 2532q)χ~M( 02
GeV 131σ
GeV 1536q)χ~M( 02
60 fb-1300 fb-1
GeV 80 )M( GeV 77 GeV 80 )M( GeV 75
Sbottom Chain Squark Chain
10 fb-1 60 fb-1 300 fb-1 10 fb-1 60 fb-1 300 fb-1
M(sbottom)
500±7 502±4 497±2 M(squark) 536±10
532±2 536±1
(sbottom) 42±5 41±4 36±3 (squark) 60±9 36±1 31±1
M(gluino) 594±7 592±4 591±3 M(gluino) 592±7 595±2 590±2
(gluino) 42±7 46±3 39±3 (gluino) 75±5 59±2 59±2
M(gl)-M(sb)
92±3 88±2 90±2 M(gl)-M(sq)
57±3 47±2 44±2
gl-sb) 17±4 20±2 23±2 gl-sq) 9±3 16±5 11±2
Squark mass peak can be reconstructed in the first few weeks (resolution ~12%)Sbottom and gluino in the first year (resolution ~6÷8%)Two independent gluino mass measurementsThe resolutions can be improved with larger statistics (~5÷6% at 300 fb-1)
Errors are of the order of 1÷2 GeV (statistical) + 2÷3 GeV (energy scale of the calorimeters)The main source of error is from the lack of knowledge on M(1
0)
M(10) assumed known for these reconstructions
No systematic errors evaluated
QCD and Hadronic Interactions, 28 March - 4 April 2004Alessia Tricomi
Reconstruction @ point GReconstruction @ point G
10 fb-1
300 fb-1
sbottom chain
squark chain
With respect to the Point B:With respect to the Point B:
Lower total SUSY cross-sectionLower total SUSY cross-section
Lower BR of useful decaysLower BR of useful decays
Higher BR’s of competitive Higher BR’s of competitive decaysdecays
Lower BR of the last decayLower BR of the last decay
16.44%) Bpoint (
%26.2)~~(BR 0
2
%)48.27 Bintpo(
%58.26)bb~
g~(BR %)7.326 Bintpo(
%92.59)qq~g~(BR
%)19.2 Bintpo(
%52.21)Wt~b~
(BR 2
B)point at allowed(not
%83.7)W~~(BR 011
B) point @ pb57 ( pb 25.8TOTSUSY
QCD and Hadronic Interactions, 28 March - 4 April 2004Alessia Tricomi
Repeating the same procedure as Repeating the same procedure as Point B:Point B:
Results @ Point GResults @ Point G
sbottosbottomm
gluingluinoo
squarsquarkk
)~
()~( bMgM
gluingluinoo
)~()~( qMgM
Sbottom Chain
300 fb-1
M(sbottom) 720±26
(sbottom) 81±18
M(gluino) 851±40
(gluino) 130±43
M(sb)-M(gl) 127±10
sb-gl) 48±11
Squark Chain
300 fb-1
M(squark) 774±9
(squark) 84±9
M(gluino) 853±11
(gluino) 126±11
M(sq)-M(gl) 82±3
sq-gl) 35±3
QCD and Hadronic Interactions, 28 March - 4 April 2004Alessia Tricomi
Reconstruction @ point IReconstruction @ point I
%25.0)~~(BR 0
2
BBGG
300 fb-1
Neutralino BR’s
B G I
BR(20→ll) 16.4
42.26 0.25
BR(20→ 83.2
275.8
898.13
IITau channel becomes predominant at large tan Tau-pair edge is not as sharp as in the e and case, but could help to cover points in which the reconstruction is problematicIt could be exploited in regions with too low leptonic BR: work in progress both in ATLAS and in CMS
QCD and Hadronic Interactions, 28 March - 4 April 2004Alessia Tricomi
Di-tau lepton edgeDi-tau lepton edge
As l identification is not possible, must rely on hadronic decays – narrow, 1-prong jets (large QCD bkg though)
_
Can typically achieve /jet ~100 for ~50-60 %
Narrow isolated jets selection :
Rjet = 0.2, Risol = 0.4
Require 0.8 GeV < Mjet < 3.6 GeV (biased against 1-prong, but improves di-tau mass resolution - less neutrino momentum)Di-tau efficiency = 41 %
Mvis = 0.66 MAdditional cuts :
min. 4 jets : ET > 100
GeV,
ET > 50 GeV
missing ET > 100 GeV,
no e, with pT > 20 GeV
1
2- 4
30 fb-130 fb-1
SM bkgSM bkg
Real from SUSYReal from SUSY
Fake from SUSYFake from SUSY
expectedexpectedvisiblevisible
ATLAS Physics TDR study (full GEANT simulation) example (“Point 6”) :
Recent results – even more encouraging…
45tan
0
)(
200
200
6int
0
0
21
A
sign
m
m
Po
10tan
100
)(
100
250
1A-SPS Point
00
21
A
sign
m
m
QCD and Hadronic Interactions, 28 March - 4 April 2004Alessia Tricomi
2. Using mass of lightest neutralino and RH sleptons can discriminate between SUSY models differing only in slepton mass.
SUSY Dark Matter
3. Lightest Neutralino LSP excellent Dark Matter candidate.– Test of compatibility between LHC
observations and signal observed in Dark Matter experiments.
Why and how to measure the Why and how to measure the 1100 mass… mass…
1. Use as starting point for other sparticle mass measurements (sbottom, gluino, squark…)
1.E-06
1.E-05
1.E-04
1.E-03
1 10 100 1000 10000
Mass GeV
-N
ucl
eon
cro
ss s
ectio
n p
b
EDELWEISSZEPLIN I
CDMS
IGEX
DAMA
10-3
10-4
10-5
10-6
Allanach et al., 2001
QCD and Hadronic Interactions, 28 March - 4 April 2004Alessia Tricomi
ATLAS
PhysicsTDR
1% error(100 fb-1)
Point 5
e+e- + +-
30 fb-1
atlfast
Physics TDR
ATLASPoint 5
ATLAS PhysicsTDR
2% error(100 fb-1)
Point 5ATLAS
PhysicsTDR
1% error(100 fb-1)
Point 5
Why and how to measure the Why and how to measure the 1100 mass… mass…
Long decay chains allow multiple measurements
Use kinematics to measure end-points (in general both maximum and minimum value due to 2-body decays)
Starting point : di-lepton OS SF mass edge
Assume 2 hardest jets are from squarks,combine each of these with leptons to from :
Mllq
qL~
~
q
~
R
Also used endpoint from Mhq from h bb -
Turns out to have enough constraints to determine all masses involved (!)
Can measure mass relations to ~1% as a function of LSP mass, determined to ~10 %
Threshold : Tllq, requiring Mll > Mll / 2max
Use dilepton signature to tag presence of 02 in event, then work
back up decay chain constructing invariant mass distributions of combinations of leptons and jets
Endpoints:
> <Mlq, Mlq
~
~
hb
b-
QCD and Hadronic Interactions, 28 March - 4 April 2004Alessia Tricomi
Systematic uncertainties not evaluatedMain sources: Th: theoretical distributions of edges Ex: detector resolution (i.e. energy
resolution, b/-tagging efficiency, bias due to cuts applied…
Mass ReconstructionMass Reconstruction
Mllq High Mlq
Low Mlq
Mll
Mllq Mhq
Combine measurements from edges from different jet/lepton combinations
Numerical solution of simultaneous edge position equations
Gives sensitivity to masses
Sparticle Expected precision (100 fb-1)
qL 3%
02 6%
lR 9%
01 12%
~
~
~
~
ATLAS Physics TDRPoint 5
01 lR
02 qL
Mass (GeV)Mass (GeV)
Mass (GeV)Mass (GeV)
~
~
~
~
Allanach et al., 2001
ATLAS ATLAS
ATLAS ATLAS
Point 5Point 5
Point 5 Point 5
Same order precision also @ point SPS1A (similar to “CMS” point B)
2tan
300
)(
100
300
5 Point
00
21
A
sign
m
m
10tan
100
)(
100
250
1A-SPS Point
00
21
A
sign
m
m
Gjelsten et al., ATLAS-PHYS-2004-07
QCD and Hadronic Interactions, 28 March - 4 April 2004Alessia Tricomi
Conclusions Conclusions LHC experiments are expected to explore SUSY in a decisive way. The plausible part of mSUGRA-MSSM parameter space will be explored in a number of characteristic signaturesStrongly interacting SUSY particles can be accessed up to 2TeV for 100 fb -1
Information on the SUSY spectrum achievable , with favourable SUSY parameters, already after the first months of data taking
Low tan region (like point B, SPS1A, point 5):
first few weeks of LHC running period: reconstruction of squark
(resolution ~12%)first year: reconstruction of sbottom and
gluino (resolutions ~6÷8%) reconstruction of gluino in the
squark chain (independent channel)
high integrated luminosity: improvement on the resolutions double fit of the sbottom peak
Intermediate tan (i.e. point G):first year: dilepton edge hardly visible no reconstruction possible in e,
channelhigh integrated luminosity: reconstruction of squarks, sbottom
(~11%) and gluino (~15%)High tan (i.e point I):
no reconstruction possible in the e- channel even with high accumulated statisticsReconstruction in the tau channel exploited. Work is going on…
New analyses are going on: New benchmark points to be analyzed Full reconstruction studies in first priority Multi-edge technique to be fully exploited Deeper insight to the tau-tau channel Systematic uncertainties to be evaluated
Lot of work before LHC start-up!!!