1 Quark Compositeness With Di-Photon Final State at LHC :Update Prof. Debajyoti Choudhury, Dr. Satyaki Bhattacharya & Prof. Brajesh C. Choudhary Department of Physics & Astrophysics University of Delhi, India Sushil S. Chauhan India-CMS meeting 21 st -22 nd 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., Λ QCD 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  γ γ contribution 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 P T (hat) >190 GeV  (TeV) M* (TeV)  ª ( fb ) SM >  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

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 ) For Next-To-Leading Photon Candidates of (  +Jet sample) φ ( radians) η Δη & Δφ Distributions Δφ ( radians) Δη

10 Discriminating Variables Variables considered:  E T sum in a cone around photon  # of stable charge tracks around photon in a cone (from  +/-, p +/-, K +/-, e +/- )  P T of the highest track in a cone around photon  P T sum of tracks in a cone around photon  Vector P T sum of tracks in a cone around photon  P T of first few nearest tracks in a cone around photon Have studied these variables for a number of cone sizes

11 E T Sum

12 # of Tracks

13 Highest P T Track

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

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 ( Λ, M=0.5 TeV), L= 10 fb fb fb -1 1 TeV5σ5σ>5 σ 2 TeV99 % C.L.> 5 σ 3 TeV94 % C.L.99 % C.L.> 5 σ

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

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, P T 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 (P T 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 ~ m at LHC with this channel ( ~ 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!!! interface with CMKIN_6_1_0. Available at,

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

28  Those events where EGamma Super Clusters < Generated EGamma Super Clusters Generator Level Reconstruction Vs FAMOS cont..

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

30 Available Literature For Quark & Lepton compositeness: Dijet channel ( Phys.Rev. D-03110, Robert Harris hep- ph/ ) Drell -Yan (S. Jain et. al.hep-ex/ ) Gamma+Jet final State: ATLAS collaboration ( ATL –PHYS ). ( 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* –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=f s =1, q*  q  ) Limits from Tevatron:

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

33 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 ( 88.6 % )56.98( % )56.09( % )50.79 ( % ) Total Background ( %)55.32 ( 8.58 %)63.62 ( 9.87 %)42.66 ( 6.62 %) S/B  + Jet 6.63 ( 1.10 %)14.51 ( 2.40 %)23.49 ( 2.40 %)6.35 ( 1.05 %) gg   1.96 ( %)2.17 ( %)2.151 ( %)1.91 ( %) qqbar   ( %)38.63 ( %)37.98 ( %)34.39 ( %) So far best variables to discriminate the signal from background are, Cut A: R iso < 0.35, E Tsum < 5.0 GeV Cut B: R iso < 0.35, Highest Tracks P T < 4.0 GeV Cut C: R iso < 0.10, # of Tracks < 2 For L= 1 fb -1 Event Type without isolation cutsTotal # of Events for L=1fb -1 Signal58 Total Background  + Jet q-qbar   gg  

34 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 (88.6% ) ( % ) ( 95.36%)48.17 ( % ) Total Background (6.815%) ( 6.86 %)63.62 ( 9.87 %) ( 6.22 %) S/B  + Jet 6.63 ( 1.10%)7.57 ( 1.25 %)23.49 (2.409%)5.64 ( 0.93%) gg   1.96 ( 85.73%)1.93 ( %)2.151 ( 93.96%)1.80 ( %) qqbar   ( 88.84%)34.74 ( 87.38%)37.98 ( 95.53%)32.65 ( %) Cut A: R iso < 0.35, E Tsum < 5.0 GeV Cut B: R iso < 0.35, Highest Tracks P T < 2.0 GeV Cut C: R iso < 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 P T

37 P T Sum of Tracks