Quark Compositeness Search with γ +Jet Final State at the LHC

Satyaki Bhattacharya, Sushil S. Chauhan, Brajesh

Choudhary, Debajyoti Choudhury

Department of Physics & AstrophysicsUniversity of Delhi, India

India-CMS Meeting @ Delhi

28th September 2007

2

Outline

• Motivation for the Study

• Earlier studies within the same model

• Signal and Backgrounds

• Future Plans

3

Motivation

• Probes coupling of excited quark to its SM counterparts

• Physics at low luminosity (~100 pb-1 to 1 fb-1)

• Direct search for mass peak

• Limits can be set on parameter space much above the Tevatron reach

• Di-jet QCD background is reducible due to clean hard photon (with tight isolation cuts)

4

Earlier Work with Di-photon Final State

arXive:0705.3472v1[hep-ph]

CMS IN 2007/039

Submitted to PRD

(responding to referees comments)

5

Poster Presented at Lepton Photon 2007, Daegu, Korea

SELECTED AS BEST POSTER IN

EXPERIMENTAL PARTICLE PHYICS

CATEGORY

CERTIFICATE & PRIZE AWARDED

6

Signal and Backgrounds

Feynman diagrams for the γ+jet background (Type-I).

Z(jj)+γ and W(jj)+γ Background (Type-II).

Feynman diagrams for the signal.

Mass PeakNo Peak, Excess

over SM part

7

Matrix Element for qgγ+Jet via q*

SM Piece

By: Prof. Debajyoti Choudhury

8

Background and X-sections

Pt –hat

50-100

GeV

100-200

GeV

200-400

GeV

400-600

GeV

600-1000

GeV

1000-1500

GeV

>1500

GeV

qg 4458 425.3 33.2 1.517 2.22x10-1 1.19x10 -2 7.6x10-4

qqbar 375.4 47.44 5.01 3.15x10-1 5.66x10-2 3.77x10 -3 2.77x10 -4

gg 1.528 8.01x10-2 3.08x10 -3 7.02x10-5 6.33x10-6 1.75x10 -6 5.81x10 -9

Cross Section (pb) for backgrounds in different PT-hat bin

Type-1: SM γ+jet Background – Non-Reducible

Interested above 200 GeV onwards.

9

Background and X-Section

Pt –hat 50-100

GeV

100-200

GeV

200-400

GeV

400-600

GeV

600-1000

GeV

1000-1500

GeV

>1500

GeV

Z(jj)+γ 2.80 6.18x10-1 8.61x10-2 6.18x10-3 1.20x10-3 8.47x10-5 6.54X10-6

W(jj)+γ 2.54 4.81x10-1 6.06x10-2 4.09x10-3 7.39x10-4 4.68x10-5 2.9 x10-6

Type-2: From Z(jj)+ & W(jj)+ - small &

reducible but comparable to gg γ+jet)

Type-3: SM Jet-Jet background where one of the

Jet(s) fakes a Photon – Largest Background –

Reduce with isolation requirements

10

Photon and Jets

• Algorithm to “reconstruct” the photon at the generator level (Reference - Marco Pieri et al. CMS IN 2005/018, and CMS IN 2007/039 – our earlier study) Select a seed with P,e±

T> 5 GeV Search around the seed in 10x10 crystal geometry in φ

and η directions With Δφ=0.09 and Δη=0.09 Add 4-momentum vectors of found EM objects Vector additions provides Photon Candidate

For Jet used Iterative Cone Algorithm with R=0.5 and seed PT 1.0 GeV (Inclusive jet i.e. neutrinos and muons are included in the jet definition)

11

Preliminary Distributions (I)

Generation cuts:

PT-hat ≥ 190 GeV on partons with no cut on η

All plots are for Lint=10 pb-1Signal is qg γ+jet via q*

12

Preliminary Distributions (II)

Selection Cuts:

PTγ ≥ 200GeV, PT jet ≥200 GV

| ηγ | ≤ 2.5 , |ηjet | ≤ 2.5

13

Preliminary Distribution (III)

14

Preliminary Distribution (IV)

15

Preliminary Distribution (V)

Backgrounds and signal separately

Invariant Mass distribution without any isolation cuts

16

Preliminary Distribution (VI)

Isolation variables: To decide track minimum PT to count them as track (final state, pi±, e±, p± & K± are considered as tracks )

17

Preliminary Distribution (VII)

With Isolation cut:

Riso ≤ 0.35,

ET SUM < 5GeV

Study in progress to understand other isolation variables such as – number of tracks etc. and optimize various isolation cuts

18

Future Plans

• Complete the generator level study for q* to γ+jet final state with large statistics and set limits on Λ and Mq* for CMS setup (Submit as CMS IN)

• This study will be presented in the SUSY/BSM meeting on 28th September at CERN

• At present interfacing γγ and γ+Jet final states via q* within CMSSW framework as an external routine.

• Will soon provide .cfg file for both channels to the production team.

Thank you!

20

Backup Slides

21

Available Literature

For Quark & Lepton compositeness:• Dijet channel (Phys.Rev. D-03110, Robert Harris

hep-ph/9609319)• Drell -Yan (S. Jain et. al.hep-ex/0005025 )• Gamma+Jet final State: ATLAS collaboration

(ATL –PHYS-99-002). (No such study exists for CMS) • Two photon final state: Some

phenomenological studies have been done without complete SM background e.g., Thomas G.

Rizzo PRD v51,Num-3 (No such study exists for CMS) Existing Limit at the LHC’s center of mass energy, with two

photon final state is: ~Λ >2.8 TeV for contact interaction (depends on kinematical cuts and luminosity)

22

Compositeness scale

Compositeness scale:• Λ >> sqrt (s-hat) : Contact interaction• Λ << sqrt (s-hat) : Excited state• Λ ~ sqrt (s-hat) : Model Dependent

23

Present Limit on M*

– CDF: M* > 80 GeV (q*q )– CDF: M* > 150 GeV (q* q W )– CDF (All channels): M* >200 GeV – D0 : M*> 200 GeV

• Simulation study: Mass reach up to 0.94 TeV at Tevatron ( 2 TeV, 2 fb-1, q*q-qbar)

• ATLAS Study: upto 6.5 TeV at LHC ( f=fs=1, q*q )

Limits from Tevatron: