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 Delhi 28 th 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: v1[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 Peak No Peak, Excess over SM part

7 Matrix Element for qg  γ +Jet via q* SM Piece By: Prof. Debajyoti Choudhury

8 Background and X-sections Pt – hat GeV GeV GeV GeV GeV GeV >1500 GeV qg x x x10 -4 qqbar x x x x10 -4 gg x x x x x x10 -9 Cross Section (pb) for backgrounds in different P T -hat bin Type-1: SM γ+jet Background – Non-Reducible Interested above 200 GeV onwards.

9 Background and X-Section Pt –hat GeV GeV GeV GeV GeV GeV >1500 GeV Z(jj)+ γ x x x x x X10 -6 W(jj)+ γ x x x x x 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

10 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 P T  1.0 GeV (Inclusive jet i.e. neutrinos and muons are included in the jet definition)

11 Preliminary Distributions (I) Generation cuts: P T -hat ≥ 190 GeV on partons with no cut on η All plots are for L int =10 pb -1 Signal is qg  γ+jet via q*

12 Preliminary Distributions (II) Selection Cuts: P Tγ ≥ 200GeV, P T jet ≥200 GV | η γ | ≤ 2.5, |η jet | ≤ 2.5

13 Preliminary Distribution (III)

14 Preliminary Distribution (IV)

15 Preliminary Distribution (V) Backgrounds and signal separately Invariant Mass distribution without any isolation cuts

16 Preliminary Distribution (VI) Isolation variables: To decide track minimum P T to count them as track (final state, pi ±, e ±, p ± & K ± are considered as tracks )

17 Preliminary Distribution (VII) With Isolation cut: R iso ≤ 0.35, E T 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 28 th 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

21 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)

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

23 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: