Quark compositeness search with jet final state at the lhc
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Quark Compositeness Search with γ +Jet Final State at the LHC. Satyaki Bhattacharya, Sushil S. Chauhan , Brajesh Choudhary, Debajyoti Choudhury Department of Physics & Astrophysics University of Delhi, India. India-CMS Meeting @ Delhi 28 th September 2007. Outline.

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

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

Satyaki Bhattacharya, Sushil S. Chauhan, Brajesh Choudhary, Debajyoti Choudhury

Department of Physics & Astrophysics

University of Delhi, India

India-CMS Meeting @ Delhi

28th September 2007


  • Motivation for the Study

  • Earlier studies within the same model

  • Signal and Backgrounds

  • Future Plans


  • 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)

Earlier Work with Di-photon Final State


CMS IN 2007/039

Submitted to PRD

(responding to referees comments)

Poster Presented at Lepton Photon 2007, Daegu, Korea



Signal and Backgrounds

  • Feynman diagrams for the signal.

No Peak, Excess over SM part

Mass Peak

  • Feynman diagrams for the γ+jetbackground (Type-I).

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

Matrix Element for qgγ+Jetvia q*

SM Piece

By: Prof. Debajyoti Choudhury

Background and X-sections

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

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

Interested above 200 GeV onwards.

Background and X-Section

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

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)

Preliminary Distributions (I)

Generation cuts:

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

All plots are for Lint=10 pb-1

Signal is qg γ+jet via q*

Preliminary Distributions (II)

Selection Cuts:

PTγ ≥ 200GeV, PT jet ≥200 GV

| ηγ | ≤ 2.5 , |ηjet | ≤ 2.5

Preliminary Distribution (III)

Preliminary Distribution (IV)

Preliminary Distribution (V)

Invariant Mass distribution without any isolation cuts

Backgrounds and signal separately

Preliminary Distribution (VI)

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

Isolation variables:

Preliminary Distribution (VII)

With Isolation cut:

Riso≤ 0.35,


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

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!

Backup Slides

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)

Compositeness scale

Compositeness scale:

  • Λ >> sqrt (s-hat) : Contact interaction

  • Λ << sqrt (s-hat) : Excited state

  • Λ ~ sqrt (s-hat) : Model Dependent

Present Limit on M*

Limits from Tevatron:

  • 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  )

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