contact interactions at the lhc -...

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 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 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


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


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


pT (GeV)

Rdi

st

10 TeV

3 TeV

40 TeV

20 TeV

5 TeV 20 fb-1


pT (GeV)

10 TeV

3 TeV

40 TeV

20 TeV

5 TeV 20 fb-1


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


(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


pT (GeV)

central value

error PDFs

Λ=10 TeV, L=30 fb-1


pT (GeV)


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


No systematics, Fast simulation

3 TeV

10 TeV

40 TeVQCD

20 TeV

5 TeV20 fb-1pT > 1 TeV

Mjj > 4 TeV


No systematics, Fast simulation

3 TeV

10 TeV

40 TeVQCD

20 TeV

5 TeV3 TeV

10 TeV

40 TeVQCD

20 TeV

5 TeVχNddN1

χ


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


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


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

)


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)


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


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


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


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

contact interactions at the lhc -...

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