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Quark Compositeness With Di-Photon Final State at LHC:Update

Prof. Debajyoti Choudhury, Dr. Satyaki Bhattacharya & Prof. Brajesh C. Choudhary

Department of Physics & AstrophysicsUniversity of Delhi, India

Sushil S. Chauhan

India-CMS meeting 21st -22nd January 007

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Outline

• Brief Introduction• Last Presentation• Discriminating variables• Kinematical & Isolation cuts• Confidence Limit (CL) Calculation• Systematic Error• Future Plans

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Motivation

• At what scale quark substructure is possible?

• Compositeness scale Λ provides estimation of quark substructure scale (e.g., ΛQCD gives the distance scale for quarks inside the proton)

• Two photons final state gives a clean signal compared to other channels

• No excited quark study exist with two photon final state

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Feynman Diagrams: Signal

For signal one need to add SM q-qbar q γ γ contribution coherently to the q* signal

Compositeness scale Λ and mass of q*, M* are free parameters of the theory

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Feynman Diagrams :Background

All these backgrounds have the same final state and very large cross

section compared to q* signal

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Event Generation with PYTHIA

For generation of events the matrix element has been included in PYTHIA (CMKIN) with showering and hadronization effects

Cross-Section for q* Signal with PT (hat) >190 GeV

(TeV) M* (TeV) ª ( fb )1. 0.7 0.5 106.902. 1.0 0.5 95.413. 2.0 0.5 81.944. 3.0 0.5 78.695. 5.0 0.5 77.116. 100.0 0.5 76.04 7. SM ------------------------------------- > 76.04 For fixed values of M* & sqrt (s) the x-section decreases

with increasing Λ, hence it becomes difficult to extract the signal

ª For standard parametrization

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X-section with Λ

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Photon Finding Algorithm

• Using 10x10 clustering algotithm to “reconstruct” the photon at the generator level Select a seed with P,e±

T> 5GeV and Look around the seed in 10x10 crystal size in φ and η

directions Where Δφ=0.09 and Δη=0.09 Add the 4-momentum vectorialy Only e+/e- and are selected as seed and inside 10x10

crystal size around the seed Vector additions provides EGamma Super-Cluster or Photon

Candidate

Compare this algorithm with actual detector simulation for fake and direct photons - found to be in good agreement

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Generator Level Resonstruction Vs Detector level Simulation

For leading Photon Candidates ( +Jet sample)

For Next-To-Leading Photon Candidates of (+Jet sample)

φ ( radians)η

Δη & Δφ Distributions

Δφ ( radians)

Δη

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Discriminating Variables

• Variables considered:ET sum in a cone around photon# of stable charge tracks around photon in a cone

(from +/- , p+/- , K+/-, e+/-)PT of the highest track in a cone around photonPT sum of tracks in a cone around photonVector PT sum of tracks in a cone around photonPT of first few nearest tracks in a cone around photon

• Have studied these variables for a number of cone sizes

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ET Sum

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# of Tracks

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Highest PT Track

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Selection of Cuts: Track min. PT

Highest PT Track

(Histograms are normalized to unity) Signal Efficiency increases with increase

in min. Pt of track by ~ 50 % for Ntrk =0

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Final cuts

• Kept gamma+Jet nearly ~1 % & large signal efficiency

• Analysis points for signal are chosen which have similar x-section as SM process

With these cuts JJ background estimated to be ~ 3.5 events* at Lum. of 1 fb-1

(* if we assume same efficiency as gamma +Jet background)

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Confidence Limit Calculations

• Due to statistical fluctuation we can not say whether the data is from signal or from background. We interpret results in terms of “ Confidence Limits (CL)” and test whether data is consistent with signal or background from theory

• Using Frequentist approach

• Hypothesis: (S+B) -Type OR B-Type only. The observed data can be of S+B type or B type.

• Generating “Gedenken” experiment to put 95 % CL and “5σ Discovery Limit”.

• Estimator is Log Likelihood Ratio (LLR):

LLR= - 2 * ln X

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Signal vs Background Distributions

Kinematical variables can be used to estimate the CL

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Some Results

( Λ , M=0.5 TeV), L= 10 fb-1 30 fb-1 100 fb-1

1 TeV 5σ >5 σ >5 σ

2 TeV 99 % C.L. > 5 σ >5 σ

3 TeV 94 % C.L. 99 % C.L. > 5 σ

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Exclusion: Λ- Mq* Parameter Space

Work in Progress: Generating points for 300 fb-1 of luminosity

Cos ө* used as test variable

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Systematic

• Scale variation: We varied the scale by a factor of 0.5 and 2.0 from the central scale. Also estimated x-section with other scales like t-hat, PT etc. The maximum variation found to be 1.6 % in the cross-section

• PDF uncertainty: We have used CTEQ5L. Taking CTEQ6M as reference we compared CTEQ5M1, MRST2001 & CTEQ5L. The maximum uncertainty of ~7 % found with CTEQ5L. MRST2001 and CTEQ5M1 shows 2.3 % and 3.5 % of uncertainty

• Luminosity error: Expected to be 3 % above 30 fb -1

• Effect of systematic on C.L : Still to be done

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Summary & Plans

• Combining two discriminating variable (PT and Cos ө* ) will give better limits (3-6 % CL ). Effect of systematic need to be evaluate

• Preliminary results show that we can probe up to a distance scale of ~ 10-20 m at LHC with this channel

( ~10-19 m excluded by Tevatron: ATLAS-TDR )

• Propose this channel in BSM group, some results were presented at the BSM meetings at CERN in Nov. 06

• Publication: To be subimmited very soon

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Thank you!

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Backup Slide

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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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Signal vs Background Distributions

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Could be Useful!!!

• MC@NLO interface with CMKIN_6_1_0.

Available at,

http://schauhan.web.cern.ch/schauhan/MCNLO_Interface/mcatnlocmk.tar.gz

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Generator Level Reconstruction Vs FAMOScont..

For Next-To-Leading Photon Candidate

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Those events where EGamma Super Clusters < Generated EGamma Super Clusters

Generator Level Reconstruction Vs FAMOScont..

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Matrix Element for q-qbarq* γ γ

For Standard Parametrization f1=1, n1=1. Is the compositeness scale and m is the mass of q*

SM Piece

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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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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:

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Motivation

• Are quarks fundamental particles? OR Do they have sub-structure?

• Replication of three generation of quarks and leptons suggests the possibility that may have composite structures made up of more fundamental constituents

• Large Hadron Collider (LHC) will explore physics “Beyond the Standard Model” @ the TeV scale

• Excited quark state represents signal for substructure of quarks and physics beyond the SM

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Effects of Different Cuts

Events Type Cut A# events (efficiency)

Cut B# events (efficiency)

Cut C# events efficiency)

Cut A+Cut B+Cut C# events (efficiency)

Signal Events 52.13 ( 88.6 % ) 56.98( 96.87 % ) 56.09( 95.36 % ) 50.79 ( 86.35 % )

Total Background

43.91 ( 6.815 %) 55.32 ( 8.58 %) 63.62 ( 9.87 %)

42.66 ( 6.62 %)

S/B 1.18 1.03 0.88 1.19

+ Jet 6.63 ( 1.10 %) 14.51 ( 2.40 %) 23.49 ( 2.40 %) 6.35 ( 1.05 %)

gg 1.96 ( 85.73 %) 2.17 ( 94.94 %) 2.151 ( 93.96 %) 1.91 ( 83.41 %)

qqbar 35.324 ( 88.84 %)

38.63 ( 97.18 %) 37.98 ( 95.53 %) 34.39 ( 86.51 %)

So far best variables to discriminate the signal from background are,

Cut A: Riso< 0.35, ETsum< 5.0 GeVCut B: Riso< 0.35, Highest Tracks PT < 4.0 GeVCut C: Riso< 0.10, # of Tracks < 2

For L= 1 fb-1

Event Type without isolation cuts Total # of Events for L=1fb-1

Signal 58

Total Background+ Jet

q-qbargg

644

602

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04

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Effects of Different Cuts …..

Events Type Cut A# events (efficiency)

Cut B# events (efficiency)

Cut C# events (efficiency)

Cut A +Cut B+ Cut C# events (efficiency)

Signal Events

52.13 (88.6% ) 51.11 ( 86.90 % ) 56.09 ( 95.36%) 48.17 ( 81.90 % )

Total Background

43.91 (6.815%) 44.24 ( 6.86 %) 63.62 ( 9.87 %) 40.09 ( 6.22 %)

S/B 1.18 1.15 0.88 1.20

+ Jet 6.63 ( 1.10%) 7.57 ( 1.25 %) 23.49 (2.409%) 5.64 ( 0.93%)

gg 1.96 ( 85.73%) 1.93 ( 84.34 %) 2.151 ( 93.96%) 1.80 ( 78.70 %)

qqbar 35.32 ( 88.84%) 34.74 ( 87.38%) 37.98 ( 95.53%) 32.65 ( 82.12 %)

Cut A: Riso< 0.35, ETsum< 5.0 GeVCut B: Riso< 0.35, Highest Tracks PT < 2.0 GeVCut C: Riso< 0.10, # of Tracks < 2

For L= 1 fb-1

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Why Two photon final state?

• Two photon final state provides a cleaner signal compared to other channels

• CMS ECAL energy resolution is very good• Not much studies have been done with this

channel without detector effects • Disadvantages with other channels, like energy

correction scale with jets• Large background with lepton final state e.g.,

Drell -Yan etc.

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Nearest Track PT

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PT Sum of Tracks