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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. - PowerPoint PPT Presentation
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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 & 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
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Matrix Element for qgγ+Jet via q*
SM Piece
By: Prof. Debajyoti Choudhury
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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
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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)
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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
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Preliminary Distribution (III)
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Preliminary Distribution (IV)
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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
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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)
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Compositeness scale
Compositeness scale:• Λ >> sqrt (s-hat) : Contact interaction• Λ << sqrt (s-hat) : Excited state• Λ ~ sqrt (s-hat) : Model Dependent
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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: