Contact Interactions Contact Interactions

SUSY07, Karlsruhe, 31/07/2007 SUSY07, Karlsruhe, 31/07/2007

15th International Conference on Supersymmetry 15th International Conference on Supersymmetry and the Unification of Fundamental Interactions and the Unification of Fundamental Interactions

Contact Interactions Contact Interactions

@ the LHC

@ the LHC

M M ó ó nica nica L. V L. V á á zquez zquez Acosta (CERN) Acosta (CERN)

on behalf of the ATLAS and CMS Collaborations

on behalf of the ATLAS and CMS Collaborations

Search for Contact Interactions at the LHC Search for Contact Interactions at the LHC Search 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

1 A

) q q

)(

q q

A (

2 ⁶

1 j , i

jL jL

iL 2 iL

±

=

γ Λ γ

= π ∑

=

µ

L µ

M ~ Λ M ~ Λ

q

q

q

q sˆ < Λ

q Λ

q q

q

Λ

f f

Contact Interaction

Contact Interactions in Mass Distributions Contact Interactions in Mass Distributions Contact Interactions in Mass Distributions

Contact interaction produces increase in rate relative to QCD at high mass Observation in mass distribution

alone requires precise understanding of 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 Q ²

q Λ

q q

q

CI

Contact Interactions in Angular Distributions Contact Interactions in Angular Distributions Contact Interactions in Angular Distributions

θ*

Center of Momentum

Frame

q q

Jet

Jet

cos θ*

0 1

d N / d co s θ*

Contact interaction is often more isotropic than QCD

Angular distribution has much smaller systematic uncertainties than cross section vs. dijet mass Effects emerge at high mass

QCD Background

Signal

ATLAS: Dijet Cross Section Contact Interaction Sensitivity

ATLAS: Dijet Cross Section ATLAS: Dijet Cross Section Contact Interaction Sensitivity Contact Interaction Sensitivity

GeV 1100

E ) ,

E E ( N

) E E ( / N )

E E ( N

) E E (

R N

QCD 0

T T

0 T T QCD

CI 0 T T

0 T

T

⎟⎟ =

⎠

⎜⎜ ⎞

⎝

⎛

<

⎟⎟ >

⎠

⎜⎜ ⎞

⎝

⎛

<

= >

+

20 fb ^-1

ATLAS ATLAS Preliminary Preliminary

10 TeV

40 TeV QCD 20 TeV

5 TeV 3 TeV Fast simulation

p _T (GeV)

N/45 GeV

20 fb ^-1

ATLAS ATLAS Preliminary Preliminary

10 TeV

40 TeV QCD 20 TeV

5 TeV 3 TeV Fast simulation

p _T (GeV)

N/45 GeV

10 TeV 3 TeV

40 TeV 20 TeV

5 TeV 20 fb ^-1

ATLAS ATLAS Preliminary Preliminary

p _T (GeV)

R dis t

10 TeV 3 TeV

40 TeV 20 TeV

5 TeV 20 fb ^-1

ATLAS ATLAS Preliminary Preliminary

p _T (GeV)

10 TeV 3 TeV

40 TeV 20 TeV

5 TeV 20 fb ^-1

ATLAS ATLAS Preliminary Preliminary

p _T (GeV)

R dis t

) ( R dist

) SM ( R ) ( R R

σ

−

= Λ

Luminosity to achieve sensitivity R _dist =3

Λ (TeV) 3 5 10 20 40

Lumi 4.3 pb ^-1 15 pb ^-1 1.4 fb ^-1 19 fb ^-1 234 fb ^-1 No systematics

(GeV)

1000 1500 2000 2500 3000

p

Lin Nonl in

dp σ d

0.5 0.6 0.7 0.8 0.9 1 1.1

. = 10 TeV, 100 fb

b = 0.045, 2% @ 2TeV

AT LA S AT LA S Pre lim

ina ry Pre lim

ina ry )

E ln b ) 1 h / e ( 1 ( c E 1 .) meas ( E

T T

T

= + −

L=100 fb ^-1

Calorimeter non linearity

p _T (GeV)

ATLAS: Dijet Cross Section Systematics ATLAS: Dijet Cross Section Systematics ATLAS: Dijet Cross Section Systematics

1% uncertainty in Energy Scale is enough to hide Λ = 20 TeV

PDF and calorimeter non linearity systematic uncertainties under study

QCD

QCD +1,2,3%

QCD -1,2,3%

15 TeV 3TeV 5 TeV

20 TeV 10 TeV

30 fb ^-1

N/45 GeV

p _T (GeV)

QCD

QCD +1,2,3%

QCD -1,2,3%

15 TeV 3TeV 5 TeV

20 TeV 10 TeV

30 fb ^-1

N/45 GeV

p _T (GeV)

central value

error PDFs Λ=10 TeV, L=30 fb ^-1

ATLAS ATLAS Preliminary Preliminary

p _T (GeV)

central value

error PDFs Λ=10 TeV, L=30 fb ^-1

ATLAS ATLAS Preliminary Preliminary

p _T (GeV)

ATLAS: Dijet Angular Distributions ATLAS: Dijet Angular Distributions ATLAS: Dijet Angular Distributions

| θ cos

| 1

| θ cos

|

e 1 _*

* 2

1

−

= + η

−

= η χ

θ*

CM Frame

q q

Jet

Jet

• to be much smaller than for dσ/dp

• 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

2 SM 1 2

cut

cut R ( ) R ( SM )

R ) , (

N

) (

R N

σ + σ

−

= Λ χ

>

χ χ

<

= χ

Λ χ χ

χ

Luminosity to achieve sensitivity R ₁ =3

χ _cut = 2.8 to maximize sensitivity

Λ(TeV) 3 5 10 20 40

Lumi < 1 pb ^-1 6 pb ^-1 0.7 fb ^-1 34 fb ^-1 426 fb ^-1

20 fb ^-1

p _T > 1 TeV Mjj > 4 TeV

ATLAS ATLAS Preliminary Preliminary

No systematics, Fast simulation

3 TeV 10 TeV

40 TeV QCD 20 TeV

5 TeV

20 fb ^-1

p _T > 1 TeV Mjj > 4 TeV

ATLAS ATLAS Preliminary Preliminary

No systematics, Fast simulation

3 TeV 10 TeV

40 TeV QCD 20 TeV

5 TeV 3 TeV 10 TeV

40 TeV QCD 20 TeV

5 TeV χ

Nd dN 1

χ

CMS: Dijet Cross Section Contact Interaction Sensitivity

CMS: Dijet Cross Section CMS: Dijet Cross Section Contact Interaction Sensitivity Contact Interaction Sensitivity

1 fb ^-1 Jet Energy

CMS estimates ±5 % is achievable

Changes dijet mass cross section 30-70%

Parton Distributions

CTEQ6 uncertainty

Resolution

Bounded by difference between

hadron level and detector level jets

Systematic uncertainties on the cross section versus

dijet mass are large

CMS: Dijet Angular Distributions CMS: Dijet Angular Distributions CMS: Dijet Angular Distributions

Dijet Ratio = N(|η|<0.5)/N(0.5<|η|<1)

Simple measure of the most sensitive part of the angular distribution Measure dijet ratio as a function of mass

Systematics on the dijet ratio are small

CMS: Dijet Ratio Systematic Uncertainties CMS: Dijet Ratio Systematic Uncertainties CMS: Dijet Ratio Systematic Uncertainties

Absolute Jet Energy Scale

No effect on QCD dijet ratio:

flat vs dijet mass

Causes 5% uncertainty in Λ

Relative Energy Scale

Energy scale in |η|<0.5 vs. 0.5 < |η| < 1 Estimate ±0.5 % is achievable in Barrel Changes ratio between ±0.01-0.03

Resolution

No change to the ratio when changing resolution Systematics bounded by MC statistics: 0.02

Parton Distributions

CTEQ6.1 uncertainties, Systematics on ratio <0.02

No testbeam data above 300 GeV. Discovery range is in the regime where the calorimetric response is extrapolated Corrected Dijet Mass (GeV)

Ratio N (|η|< 0.5)/N(0.5 <|η|< 1)

Corrected Dijet Mass (GeV)

Ratio N (|η|< 0.5)/N(0.5 <|η|< 1)

CMS: Dijet Ratio

Significance of Contact Interaction Signal CMS: Dijet Ratio

CMS: Dijet Ratio

Significance of Contact Interaction Signal Significance of Contact Interaction Signal

Significance in σ

1/Λ(TeV) 1/Λ(TeV)

Significance in σ Significance 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 15.1

95% CL

Exclusion All Syst 6.2 10.4 14.8

Stat Only 4.7 8.0 12.2

5σ

Discovery 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 sensitivity CMS: Dimuon Contact Interaction sensitivity CMS: Dimuon Contact Interaction sensitivity

Events

0.5-1TeV

100 fb ^-1

Events

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 fb CMS: Dimuon Double Ratio (100 fb ^{- - 1 1} ) )

R _i ^DATA = N _i ^D /N ₀ ^D = σ _i ^D .ε _i ^D / σ ₀ ^D .ε ₀ ^D

R _i ^MC = N _i ^MC /N ₀ ^MC = σ _i ^MC .ε _i ^MC / σ ₀ ^MC .ε ₀ ^MC

Absolute Efficiency, EW corrections, ...

cancel out in a ratio mass bin 250-500 GeV for normalization

• SM valid - Tevatron

• u quark PDF dominant which has the smallest uncertainty

Double Ratio

Double ratio: DR _i = R _i ^DATA / R _i ^MC

If theory understanding and detector modeling are both perfect DR = 1

CMS: Dimuon Contact Interactions Discovery Reach

CMS: Dimuon Contact Interactions CMS: Dimuon Contact Interactions

Discovery Reach Discovery Reach

Co ntact Interaction Scale TeV Co ntact Interaction Scale TeV

5σ Discovery 95% CL Exclusion

Luminosity fb ^-1 Luminosity fb ^-1

Up to 10 fb ^-1 (higher for Λ ₊ ) dominated by statistical errors

Even 30 % systematic errors have small impact

Summary Summary Summary

Contact interactions at a scale Λ are generally observed before any exchanged particle is directly seen

Many techniques have been developed and show good results with 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