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SUSY07, Karlsruhe, 31/07/2007SUSY07, Karlsruhe, 31/07/200715th International Conference on Supersymmetry15th International Conference on Supersymmetryand the Unification of Fundamental Interactionsand the Unification of Fundamental Interactions
Contact Interactions Contact Interactions @ the LHC@ the LHC
MMóónicanica L. VL. Váázquezzquez Acosta (CERN)Acosta (CERN)on behalf of the ATLAS and CMS Collaborationson behalf of the ATLAS and CMS Collaborations
Contact Interactions at the LHC, Mónica L. Vázquez Acosta (CERN) SUSY07, Karlsruhe, 31/07, 2007 - 2
Search for Contact Interactions at the LHCSearch for Contact Interactions at the LHCSearch for Contact Interactions at the LHC
New physics at a scale Λ above the observed dijet (dilepton) mass is effectively modelled as a contact interaction.• Quark compositeness• New interactions from massive particles exchanged
1A
)qq)(qq(A2 6
1j,ijLjLiLiL2
±=
γγΛπ
= ∑=
µµL
M ~ Λ
M ~ Λq
q
q
q Λ<s
Λq
q q
q
Λ
f
f
Con
tact
Inte
ract
ion
Contact Interactions at the LHC, Mónica L. Vázquez Acosta (CERN) SUSY07, Karlsruhe, 31/07, 2007 - 3
Contact Interactions in Mass DistributionsContact Interactions in Mass DistributionsContact Interactions in Mass Distributions
Contact interaction produces increase in rate relative to QCD at high mass
Observation in mass distributionalone requires precise understandingof QCD cross section
Hard to do:- Jet energy scale uncertainties give
large cross section uncertainties- Parton distribution uncertainties are significant at high mass = high x and Q2
Λq
q q
q
QCD CI
Contact Interactions at the LHC, Mónica L. Vázquez Acosta (CERN) SUSY07, Karlsruhe, 31/07, 2007 - 4
Contact Interactions in Angular DistributionsContact Interactions in Angular DistributionsContact Interactions in Angular Distributions
θ*
Center of Momentum
Frame
q q
Jet
Jet
cos θ*0 1
dN/ d
c osθ
*
Contact interaction is often more isotropic than QCD
Angular distribution has much smaller systematic uncertaintiesthan cross section vs. dijet mass
Effects emerge at high mass
QCD Background
Signal
Contact Interactions at the LHC, Mónica L. Vázquez Acosta (CERN) SUSY07, Karlsruhe, 31/07, 2007 - 5
ATLAS: Dijet Cross SectionContact Interaction SensitivityATLAS: Dijet Cross SectionATLAS: Dijet Cross Section
Contact Interaction SensitivityContact Interaction Sensitivity
GeV1100E,)EE(N)EE(N/
)EE(N)EE(NR 0
TQCD
0TT
0TT
QCDCI0TT
0TT =⎟⎟
⎠
⎞⎜⎜⎝
⎛<>
⎟⎟⎠
⎞⎜⎜⎝
⎛<>
=+
20 fb-1
ATLASATLASPreliminaryPreliminary
10 TeV
40 TeVQCD
20 TeV
5 TeV3 TeV
Fast simulation
pT (GeV)
N/4
5 G
eV 20 fb-1
ATLASATLASPreliminaryPreliminary
10 TeV
40 TeVQCD
20 TeV
5 TeV3 TeV
Fast simulation
pT (GeV)
N/4
5 G
eV
10 TeV
3 TeV
40 TeV
20 TeV
5 TeV 20 fb-1
ATLASATLASPreliminaryPreliminary
pT (GeV)
Rdi
st
10 TeV
3 TeV
40 TeV
20 TeV
5 TeV 20 fb-1
ATLASATLASPreliminaryPreliminary
pT (GeV)
10 TeV
3 TeV
40 TeV
20 TeV
5 TeV 20 fb-1
ATLASATLASPreliminaryPreliminary
pT (GeV)
Rdi
st)(R
dist)SM(R)(RR
Λσ−Λ
=Luminosity to achieve sensitivity Rdist=3
Λ (TeV) 3 5 10 20 40Lumi 4.3 pb-1 15 pb-1 1.4 fb-1 19 fb-1 234 fb-1 No systematics
Contact Interactions at the LHC, Mónica L. Vázquez Acosta (CERN) SUSY07, Karlsruhe, 31/07, 2007 - 6
(GeV)p1000 1500 2000 2500 3000 3500
Lin
No
nlin
Q
CD
Td
pσd
0.5
0.6
0.7
0.8
0.9
1
1.1
. = 10 TeV, 100 fb
b = 0.045, 2% @ 2TeV
ATLAS
ATLAS
Preliminary
Preliminary)Elnb)1h/e(1(c1E.)meas(E
TTT −+
=
L=100 fb-1
Calorimeter non linearity
pT (GeV)
ATLAS: Dijet Cross Section SystematicsATLAS: Dijet Cross Section SystematicsATLAS: Dijet Cross Section Systematics
1% uncertainty in Energy Scale is enough to hide Λ = 20 TeV
PDF and calorimeter non linearitysystematic uncertainties under study
QCD
QCD +1,2,3%
QCD -1,2,3%
15 TeV
3TeV5 TeV
20 TeV10 TeV
30 fb-1ATLASATLAS
PreliminaryPreliminary
N/4
5 G
eV
pT (GeV)
QCD
QCD +1,2,3%
QCD -1,2,3%
15 TeV
3TeV5 TeV
20 TeV10 TeV
30 fb-1ATLASATLAS
PreliminaryPreliminary
N/4
5 G
eV
pT (GeV)
central value
error PDFs
Λ=10 TeV, L=30 fb-1
ATLASATLASPreliminaryPreliminary
pT (GeV)
central value
error PDFs
Λ=10 TeV, L=30 fb-1
ATLASATLASPreliminaryPreliminary
pT (GeV)
Contact Interactions at the LHC, Mónica L. Vázquez Acosta (CERN) SUSY07, Karlsruhe, 31/07, 2007 - 7
ATLAS: Dijet Angular DistributionsATLAS: Dijet Angular DistributionsATLAS: Dijet Angular Distributions
|θcos|1|θcos|1e *
*21
−+
=η−η
=χ
θ*
CM Frameq q
Jet
Jet
• Systematics are expected to be much smaller than for dσ/dpT
• High-mass dijet angular distributions with first tens of pb-1 will allow the discovery of quark compositeness if the constituent interaction constant is Λ = 3-5 TeV
2SM
21cut
cut )SM(R)(RR,
)(N)(NR
σ+σ
−Λ=
χ>χχ<χ
=Λ
χχχ
Luminosity to achieve sensitivity R1=3
χcut = 2.8 to maximize sensitivity
Λ(TeV) 3 5 10 20 40Lumi < 1 pb-1 6 pb-1 0.7 fb-1 34 fb-1 426 fb-1
20 fb-1pT > 1 TeV
Mjj > 4 TeV
ATLASATLASPreliminaryPreliminary
No systematics, Fast simulation
3 TeV
10 TeV
40 TeVQCD
20 TeV
5 TeV20 fb-1pT > 1 TeV
Mjj > 4 TeV
ATLASATLASPreliminaryPreliminary
No systematics, Fast simulation
3 TeV
10 TeV
40 TeVQCD
20 TeV
5 TeV3 TeV
10 TeV
40 TeVQCD
20 TeV
5 TeVχNddN1
χ
Contact Interactions at the LHC, Mónica L. Vázquez Acosta (CERN) SUSY07, Karlsruhe, 31/07, 2007 - 8
CMS: Dijet Cross Section Contact Interaction Sensitivity
CMS: Dijet Cross Section CMS: Dijet Cross Section Contact Interaction SensitivityContact Interaction Sensitivity
1 fb-1Jet EnergyCMS estimates ±5 % is achievableChanges dijet mass cross section 30-70%
Parton DistributionsCTEQ6 uncertainty
ResolutionBounded by difference betweenhadron level and detector level jets
Systematic uncertainties onthe cross section versus
dijet mass are large
Contact Interactions at the LHC, Mónica L. Vázquez Acosta (CERN) SUSY07, Karlsruhe, 31/07, 2007 - 9
CMS: Dijet Angular DistributionsCMS: Dijet Angular DistributionsCMS: Dijet Angular Distributions
Dijet Ratio = N(|η|<0.5)/N(0.5<|η|<1)Simple measure of the most sensitive part of the angular distributionMeasure dijet ratio as a function of massSystematics on the dijet ratio are small
Contact Interactions at the LHC, Mónica L. Vázquez Acosta (CERN) SUSY07, Karlsruhe, 31/07, 2007 - 10
CMS: Dijet Ratio Systematic UncertaintiesCMS: Dijet Ratio Systematic UncertaintiesCMS: Dijet Ratio Systematic Uncertainties
Absolute Jet Energy ScaleNo effect on QCD dijet ratio:flat vs dijet massCauses 5% uncertainty in Λ
Relative Energy ScaleEnergy scale in |η|<0.5 vs. 0.5 < |η| < 1Estimate ±0.5 % is achievable in BarrelChanges ratio between ±0.01-0.03
ResolutionNo change to the ratio when changing resolutionSystematics bounded by MC statistics: 0.02
Parton DistributionsCTEQ6.1 uncertainties, Systematics on ratio <0.02
No testbeam data above 300 GeV. Discovery range is inthe regime where the calorimetric response is extrapolated
Corrected Dijet Mass (GeV)
Rat
io N
(|η|<
0.5)
/N(0
.5<|
η|<1
)
Corrected Dijet Mass (GeV)
Rat
io N
(|η|<
0.5)
/N(0
.5<|
η|<1
)
Contact Interactions at the LHC, Mónica L. Vázquez Acosta (CERN) SUSY07, Karlsruhe, 31/07, 2007 - 11
CMS: Dijet RatioSignificance of Contact Interaction Signal
CMS: Dijet RatioCMS: Dijet RatioSignificance of Contact Interaction SignalSignificance of Contact Interaction Signal
Sign
ifica
nce
in σ
1/Λ(TeV) 1/Λ(TeV)
Sign
ifica
nce
in σ
Sign
ifica
nce
in σ
1/Λ(TeV)
Left-Handed Quark Contact Interaction
Λ+ for 100 pb-1
(TeV)Λ+ for 1 fb-1
(TeV)Λ+ for 10 fb-1
(TeV)Stat Only 6.4 10.6 15.195% CL
Exclusion All Syst 6.2 10.4 14.8
Stat Only 4.7 8.0 12.25σDiscovery All Syst 4.7 7.8 12.0
D0 excludes at 95%CL scales of Λ+<2.7 TeV with 100 pb-1 (hep-ex/9807014)
Contact Interactions at the LHC, Mónica L. Vázquez Acosta (CERN) SUSY07, Karlsruhe, 31/07, 2007 - 12
CMS: Dimuon Contact Interaction sensitivityCMS: Dimuon Contact Interaction sensitivityCMS: Dimuon Contact Interaction sensitivityE
vent
s
0.5-1TeV
100 fb-1
Eve
nts
1-6 TeV
Dimuon Mass (GeV)
100 fb-1
Dimuon Mass (GeV)
Main sensitivity from cross section @ ~ 1 TeV and higher
Λ
f
f
Drell-Yan CI
Contact Interactions at the LHC, Mónica L. Vázquez Acosta (CERN) SUSY07, Karlsruhe, 31/07, 2007 - 13
CMS: Dimuon Double Ratio (100 fb-1)CMS: Dimuon Double Ratio (100 fbCMS: Dimuon Double Ratio (100 fb--11))
RiDATA = Ni
D/N0D = σi
D.εiD / σ0
D.ε0D
RiMC = Ni
MC/N0MC = σi
MC.εiMC / σ0
MC.ε0MC
Absolute Efficiency,EW corrections, ...cancel out in a ratio
mass bin 250-500 GeVfor normalization • SM valid - Tevatron• u quark PDF dominant
which has the smallest uncertainty
Dou
ble
Rat
io
Double ratio: DRi = RiDATA / Ri
MC
If theory understanding and detector modeling are both perfect DRi = 1
Contact Interactions at the LHC, Mónica L. Vázquez Acosta (CERN) SUSY07, Karlsruhe, 31/07, 2007 - 14
CMS: Dimuon Contact Interactions Discovery Reach
CMS: Dimuon Contact Interactions CMS: Dimuon Contact Interactions Discovery ReachDiscovery Reach
Con
tact
Inte
ract
ion
Scal
e T
eV
Con
tact
Inte
ract
ion
Scal
e T
eV5σ Discovery 95% CL Exclusion
Luminosity fb-1 Luminosity fb-1
Up to 10 fb-1 (higher for Λ+) dominated by statistical errorsEven 30 % systematic errors have small impact
Contact Interactions at the LHC, Mónica L. Vázquez Acosta (CERN) SUSY07, Karlsruhe, 31/07, 2007 - 15
SummarySummarySummaryContact interactions at a scale Λ are generally observed beforeany exchanged particle is directly seen
Many techniques have been developed and show good resultswith low systematic effects:- Angular distributions and simple angular ratios (jets)- Double ratio (dimuons)
Sensitivity of the LHC experiments to contact interactions has been investigated- The first hundred pb-1 of data will allow the discovery of
contact interactions with Λ up to ~5 TeV- 100fb-1 of data allows discovery of compositeness up to ~30TeV
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