Study of Quark compositeness in pp q * at CMS

Transcription

1 Study of Quark compositeness in pp q * at CMS + Jets Brajesh Choudhary, Debajyoti Choudhury, Varun Sharma University of Delhi, Delhi Sushil Singh Chauhan, Mani Tripathi University of California, Davis 1

2 Outline Motivation Introduction Model setup Signal & background for the + jet final state The CMS detector: brief overview Photon identification and isolation Samples used Selection cuts Selection efficiency Data MC comparison Comparison with different samples Summary & future plans 2

3 Motivation Standard Model Most successful theory of particle physics, thoroughly tested at the experimental level. Still have some open questions Hierarchy problem Lots of free parameters Why their exist three identical generation of quarks & leptons? Why Search??? What is Fundamental? Definition stays tentative ~ Energy Scale Higher Energies Smaller Resolution TeV Scale Structure of Quarks & Leptons? ( ARE they fundamental? ) LHC, being a parton-parton resonance factory in a previously unexplored energy regime. Nature may surprise us with some new particle!!! 3

4 Introduction Compositeness of Quarks is one such scenario which can provide answers to some of the above problems. Other being SUSY, Extra-Dimensions, Technicolor etc. For compositeness Look for excited quarks. In such theories, fundamental constituent of matter is termed as preons. Below certain energy scale Λ, the interaction becomes strong and binds preons together to form quarks. Signature for this compositeness can be significant deviation in the measured cross-section (in certain final states) compared to the predictions of the SM. Compositeness study can be broadly categorized on the compositeness scales ŝ If : A narrow resonance of excited particle can be observed on shell. If ŝ : Compositeness will manifest as 4-fermion Contact interactions. 4

5 Model Setup Relevant part of the Lagrangian, namely the (chromo-) magnetic transition between ordinary and excited states. Where, i runs over three gauge groups viz. SU(3), SU(2) and U(1) and g i, G a iμν and T a i are the corresponding gauge couplings, field strength tensors and generators respectively. The dimensionless constants b i are a priori, unknown and presumably of order unity. Lagrangian being a higher dimension operator, the cross sections would typically grow with center-of-mass energy Violating Unitarity 2 o o int 1 * a a qr gibt i i Gi q 2 i This is cured once suitable higher dimensional operators are included. Also by considering the b i to be form factors rather than constants. o f i are the dimensionless constants related to b i. o For Q 2 = s, unitarity is restored as long as the constants n i 1. The new physics contribution to the differential cross section thus depends on four parameters, namely f 1, f 3, Λ and the mass of the excited state M q*. For this effective theory to make sense, M q* < Λ. Also as long as Λ >> s, one of f 1,3 can be absorbed in Λ. L h. c. q* q q* qg ee f Q n q 1 ( p) : n3 g f Q s 3 ( p) : 1 p T 2 1 p 5

6 Excited Quark Production Excited Quarks can be produced (if they exist!!!) in different channels in pp collisions with different final states namely, Photon + jet Dijet Diphoton Photon + jet Production Quark-gluon scattering (or Compton Scattering) o qg jet via q* (a) Quark-antiquark annihilation o qq jet via q* (b) gluon-gluon fusion o (C) gg g (a) 6 (c) (b)

7 Backgrounds SM + jet production Compton scattering qg q o (a) Pair annihilation qq g o (b) Gluon-gluon fusion gg g o (c) (a) (b) At the LHC energy the Compton process dominates, other sub-processes contributes only a small fraction. For higher P T photon, annihilation process can contribute up to ~ 20% of the total background. (c) 7

8 QCD Dijet When one of the jets fragment into a high E T π 0, which then decays into a pair of overlapping photons. (a) One of the jets brems a photon (b, c) Electromagnetic fraction of a jet can mimic a photon in the detector. (a) (b) (c) There is a small contribution from photon + dijet final state when one of the jet is either lost or mismeasured. Also when a γ +W/Z is produced where W/Z then decays to a pair of jets. 8

9 CMS Detector 9

10 The CMS Detector 10

11 Brief overview of CMS Detector Silicon Tracker Innermost layer of the Detector Reconstruct paths of high energy particles Consists of 3 regions One Pixel tracker Resolution : 10 μm for r-φ measurement 20 μm for z measurement Two Microstrip tracker Resolution For TIB : μm for r-φ measurement 230 μm for z measurement For TOB : μm for r-φ measurement 530 μm for z measurement Muon System 1400 muon chambers Drift tubes (250) Cathode Strip Chambers (540) Resistive Plate Chambers (610) Coverage : Barrel : η < 1.2 Endcap : η < Electromagnetic Calorimeter Lead tungstate(pbwo 4 ) Crystals Radiation length 0.89 cm Moliere radius 2.0 cm Coverage : Barrel : η < Endcaps : η < 3.0 Resolution Hadronic Calorimeter Hermetic coverage, Sampling calorimeter Layers of Brass/Steel interleaved with tiles of fluorescent scintillators. Special wavelength-shifting fibres. Coverage :HB : η < 1.4 HE : 1.3 < η <3.0 Resolution hr E E E 100% ~ 5% E E

12 Photon Identification Photon candidates are reconstructed from energy deposits in the ECAL called as superclusters. Superclusters are formed from the energy sum clustered in a rectangle of crystals 35 wide in φ and 5 wide in η Superclusters allows almost complete recovery of energy deposited by photons. It is required that the signals be in time with the collision. Sum of energy in the four adjacent crystals surrounding the central crystal should be at least 5% of the central crystal s energy. It is required to be in the pseudo rapidity acceptance of the tracker. It should not match pixel hits consistent with an electron or positron track from the interaction region. 12

13 13 Photon Isolation IsoECAL The sum of electromagnetic transverse energy of the crystals lying in a cone of ΔR = 0.4, centered around the super-cluster with a veto cone (ΔR i = 3.5 crystals) and eta-slice (Δη = 2.5 crystals) should be less than the threshold value. IsoHCAL The sum of hadronic transverse energy of all the particles in the HCAL towers in a hollow cone with an inner radius of ΔR i = 0.15 and an outer radius of ΔR o = 0.4 centered around the super-cluster should be less than a threshold value. IsoTrk The sum of transverse momenta of all the tracks in a full cone (ΔR = 0.4) centered around line joining the primary vertex to the cluster should be less than a threshold value. H/E The fraction of hadronic energy to the total electromagnetic energy inside a cone of ΔR = Low for photon, while high for jets as they carry both electromagnetic and hadronic energy. σ iηiη The transverse shape of the electromagnetic cluster. Trajectory of a photon in η is not affected by magnetic field, so its magnitude in η should be small, while for π 0 it will tend to be larger.

14 Samples Used Center of mass energy 7 TeV Luminosity used 1.14± 4% fb -1 Data /Photon/Run2011A-May10ReReco-v2/AODSIM /Photon/Run2011A-PromptReco-v5/AODSIM MC Samples Summer 11 samples Mass point for M q* = 1 TeV Parameter Scale Parameter, 1000 Tev Couplings f, f, f s = 1, SM couplings Considered u* & d* Also compared for different mass point samples viz. 1.2, 1.5, 1.7, 2, 2.5 TeV Backgrounds Photon+Jet QCD dijet 14

15 Samples Used : Background QCD /QCD_Pt_30to50_TuneZ2_7TeV_pythia6/Spring11-PU_S1_START311_V1G1-v1/AODSIM /QCD_Pt_50to80_TuneZ2_7TeV_pythia6/Spring11-PU_S1_START311_V1G1-v1/AODSIM /QCD_Pt_80to120_TuneZ2_7TeV_pythia6/Spring11-PU_S1_START311_V1G1-v1/AODSIM /QCD_Pt_120to170_TuneZ2_7TeV_pythia6/Spring11-PU_S1_START311_V1G1-v1/AODSIM /QCD_Pt_170to300_TuneZ2_7TeV_pythia6/Spring11-PU_S1_START311_V1G1-v1/AODSIM /QCD_Pt_300to470_TuneZ2_7TeV_pythia6/Spring11-PU_S1_START311_V1G1-v1/AODSIM /QCD_Pt_470to600_TuneZ2_7TeV_pythia6/Spring11-PU_S1_START311_V1G1-v1/AODSIM /QCD_Pt_600to800_TuneZ2_7TeV_pythia6/Spring11-PU_S1_START311_V1G1-v1/AODSIM /QCD_Pt_800to1000_TuneZ2_7TeV_pythia6/Spring11-PU_S1_START311_V1G1-v1/AODSIM /QCD_Pt_1000to1400_TuneZ2_7TeV_pythia6/Spring11-PU_S1_START311_V1G1-v1/AODSIM /QCD_Pt_1400to1800_TuneZ2_7TeV_pythia6/Spring11-PU_S1_START311_V1G1-v1/AODSIM /QCD_Pt_1800_TuneZ2_7TeV_pythia6/Spring11-PU_S1_START311_V1G1-v1/AODSIM e e e e e e e e e e e e-04 PHOTON + JET /G_Pt_15to30_TuneZ2_7TeV_pythia6/Spring11-PU_S1_START311_V1G1-v1/AODSIM /G_Pt_30to50_TuneZ2_7TeV_pythia6/Spring11-PU_S1_START311_V1G1-v1/AODSIM /G_Pt_50to80_TuneZ2_7TeV_pythia6/Spring11-PU_S1_START311_V1G1-v1/AODSIM /G_Pt_80to120_TuneZ2_7TeV_pythia6/Spring11-PU_S1_START311_V1G1-v1/AODSIM /G_Pt_120to170_TuneZ2_7TeV_pythia6/Spring11-PU_S1_START311_V1G1-v1/AODSIM /G_Pt_170to300_TuneZ2_7TeV_pythia6/Spring11-PU_S1_START311_V1G1-v1/AODSIM /G_Pt_300to470_TuneZ2_7TeV_pythia6/Spring11-PU_S1_START311_V1G1-v1/AODSIM /G_Pt_470to800_TuneZ2_7TeV_pythia6/Spring11-PU_S1_START311_V1G1-v1/AODSIM /G_Pt_800to1400_TuneZ2_7TeV_pythia6/Spring11-PU_S1_START311_V1G1-v1/AODSIM e e e e e e e e e-03 /G_Pt_1400to1800_TuneZ2_7TeV_pythia6/Spring11-PU_S1_START311_V1G1-v1/AODSIM e /G_Pt_1800_TuneZ2_7TeV_pythia6/Spring11-PU_S1_START311_V1G1-v1/AODSIM e-07

16 Selection Cleaning Cuts Criteria Vertex Selection Vertex_z, z Requirement 24 cm Vertex_ndof 4.0 Vertex_rho 2.0 Residual Spike (photon crystal timing) < 3 ns Trigger Kinematic Cuts HLT P T jet P T jet ECAL Isolation HCAL Isolation HLT_Photon75_CaloIDVI_IsoL_v* HLT_Photon90_CaloIDVI_IsoL_v* > 100 GeV < 1.44 > 100 GeV < 1.5 < *P T < *P T Isolation Cuts H/E Isolation 0.05 Trk Isolation < *P T σ iηiη < Track Veto No matching pixel seed

17 Efficiency Plot 17

18 N-1 Plots for Isolation variables ECAL Iso HCAL Iso *P T *P T ECAL Isolation (in GeV) HCAL Isolation (in GeV) 18

19 N-1 Plots for Isolation variables Track Iso H/E Iso *P T H/E < 0.05 Trk Isolation (in GeV) HoE 19

20 Effect of Pile-up reweighting on MC The Spring11 MC has been generated with a flat+poisson tail distribution for the number of pileup interactions which is meant to roughly cover, though not exactly match the conditions expected for 2011 data-taking. In order to factorize these effects, we reweight them with number of pileup interactions from the simulation truth. All MC Plots are normalized to Cross-section & reweighted with pileup Before reweighting After reweighting 20

21 Photon Pt and Eta 21

22 Jet Pt and Eta L2L3 Residual correction is not applied for jet energy correction (on data), which can have a effect of ~2%. 22

23 Delta phi between Photon & Jet 23

24 Mass plot for Photon + Jet 24

25 Fitted Mass plot for 1 TeV sample of signal Pt Cut Signal Bkg S/ B S/B S/B for mass GeV with different Pt Cut 25 Not much difference in S/ B, So we can use higher P T selection. Repeat this with official limit calculation tools but expect similar results.

26 Different Mass samples of signal 26

27 Summary & Future Plans Have studied the theory aspect of quark compositeness Learnt the details of the CMS detector Analysed 1.14 fb -1 of data Looked at various bkgs and techniques to filter these bkg. Compared the Data & MC for γ + jet samples. The data matches well with SM γ + jet and dijet production as estimated by MC. Compared different qstar mass point samples. Calculated S/ B for the signal at different P T cut. To do Estimate QCD background using data driven techniques using ratio method or fake rate method. Repeat the analysis with higher luminosity data. Setting up limit calculation tool and systematic study. Repeat the analysis for other samples with higher Mass points. Have a full analysis with data collected by the end of this year. 27

28 Back up slides 28

29 Selection Efficiency (Cumulative) Signal Photon+Jet(Bkg) QCD Dijet (Bkg) Data HLT Vertex Scrappy Event No Cosmic PhotonID Photon Pt Photon Eta Residual Spike Jet Pt Jet Eta Delta Phi

30 Selection Efficiency for signal sample of different mass points 0.7 TeV Signal samples for different Mass point 1 TeV 1.2 TeV 1.5 TeV 1.7 TeV 2 TeV 2.5 TeV 3 TeV PhotonID Photon P T Photon η ResSpike Jet P T Jet η Dphi

31 Efficiency for Photon+Jet (Bkg) with different photon P T cut Photon P T Cut 50 GeV 100 GeV 150 GeV 200 GeV 250 GeV 300 GeV 400 GeV 500 GeV PhotonID Photon P T Photon η ResSpike Jet P T Jet η Dphi

32 Photon threshold P T in GeV 32