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  1. Quark Compositeness With Di-Photon Final State at LHC:Update Sushil S. Chauhan Prof. Debajyoti Choudhury, Dr. Satyaki Bhattacharya & Prof. Brajesh C. Choudhary Department of Physics & Astrophysics University of Delhi, India India-CMS meeting 21st -22nd January 007

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

  3. 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

  4. Feynman Diagrams: Signal • For signal one need to add SM q-qbar qγγcontribution coherently to the q* signal • Compositeness scale Λ and mass of q*, M* are free parameters of the theory

  5. Feynman Diagrams :Background All these backgrounds have the same final state and very large cross section compared to q* signal

  6. 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 ) • 0.7 0.5 106.90 • 1.0 0.5 95.41 • 2.0 0.5 81.94 • 3.0 0.5 78.69 • 5.0 0.5 77.11 • 100.0 0.5 76.04 • 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 ªFor standard parametrization

  7. X-section with Λ

  8. 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

  9. Generator Level Resonstruction Vs Detector level Simulation For leading Photon Candidates ( +Jet sample) Δη & Δφ Distributions Δη For Next-To-Leading Photon Candidates of (+Jet sample) Δφ ( radians) η φ( radians)

  10. 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 photon • PT sum of tracks in a cone around photon • Vector PT sum of tracks in a cone around photon • PT of first few nearest tracks in a cone around photon • Have studied these variables for a number of cone sizes

  11. ET Sum

  12. # of Tracks

  13. Highest PT Track

  14. Selection of Cuts: Track min. PT Highest PT Track Signal Efficiency increases with increase in min. Pt of track by ~ 50 % for Ntrk =0 (Histograms are normalized to unity)

  15. 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)

  16. 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

  17. Signal vs Background Distributions Kinematical variables can be used to estimate the CL

  18. Some Results

  19. Exclusion: Λ- Mq* Parameter Space Cos ө* used as test variable Work in Progress: Generating points for 300 fb-1 of luminosity

  20. 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

  21. 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

  22. Thank you!

  23. Backup Slide

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

  25. Signal vs Background Distributions

  26. Could be Useful!!! • MC@NLO interface with CMKIN_6_1_0. Available at, http://schauhan.web.cern.ch/schauhan/MCNLO_Interface/mcatnlocmk.tar.gz

  27. Generator Level Reconstruction Vs FAMOScont.. For Next-To-Leading Photon Candidate

  28. Generator Level Reconstruction Vs FAMOScont.. • Those events where EGamma Super Clusters < Generated EGamma Super Clusters

  29. Matrix Element for q-qbarq*γγ SM Piece For Standard Parametrization f1=1, n1=1.  Is the compositeness scale and m is the mass of q*

  30. 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)

  31. 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  )

  32. 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

  33. Effects of Different Cuts So far best variables to discriminate the signal from background are, Cut A: Riso< 0.35, ETsum< 5.0GeV Cut B: Riso< 0.35, Highest Tracks PT < 4.0 GeV Cut C: Riso< 0.10, # of Tracks < 2 For L= 1 fb-1

  34. Effects of Different Cuts ….. Cut A: Riso< 0.35, ETsum< 5.0GeV Cut B: Riso< 0.35, Highest Tracks PT < 2.0GeV Cut C: Riso< 0.10, # of Tracks < 2 For L= 1 fb-1

  35. 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.

  36. Nearest Track PT

  37. PT Sum of Tracks