Study of Quark compositeness in pp q + Jets at CMSindiacms/Talks/talks-2011/varun-22092011.pdf · Introduction INDIA CMS, Quark Compositeness Compositeness of Quarks is one such scenario

Brajesh Choudhary, Debajyoti Choudhury, Varun Sharma

University of Delhi, Delhi

Study of Quark compositeness in pp → q* → + Jets

at CMS

Sushil Singh Chauhan, Mani Tripathi University of California, Davis

INDIA CMS, Quark Compositeness September 22, 2011 1

Outline

INDIA CMS, Quark Compositeness

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

September 22, 2011 2

Motivation


Why Search ???

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?

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 !!!


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 If : A narrow resonance of excited particle can be observed on shell. If : Compositeness will manifest as 4-fermion Contact interactions.

s

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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 gi, Ga

iμν and Tai

are the corresponding gauge couplings, field strength tensors and generators respectively.

The dimensionless constants bi 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

o This is cured once suitable higher dimensional operators are included.

o Also by considering the bi to be form factors rather than constants.

o fi are the dimensionless constants related to bi.

o For Q2 = s, unitarity is restored as long as the constants ni ≥ 1.

The new physics contribution to the differential cross section thus depends on four parameters, namely f1 , f3 , Λ and the mass of the excited state Mq* . For this effective theory to make sense, Mq* < Λ.

Also as long as Λ >> s, one of f1,3 can be absorbed in Λ.

Model Setup


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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 via q* (a) Quark-antiquark annihilation

o via q* (b) gluon-gluon fusion

o (C)

Excited Quark Production


jetqq

jetqg (a)

(b)


ggg

(c)

Backgrounds


SM + jet production

Compton scattering o (a)

Pair annihilation o (b)

Gluon-gluon fusion o (c)

At the LHC energy the Compton

process dominates, other sub-processes

contributes only a small fraction.

For higher PT photon, annihilation process

can contribute up to ~ 20% of the total

background.

qqg

gqq

ggg (a)

(c)

(b)


QCD Dijet

When one of the jets fragment into a high ET π0, 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.


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.

(a)

(b) (c)

September 22, 2011 INDIA CMS, Quark Compositeness 9

CMS Detector

The CMS Detector


Electromagnetic Calorimeter Lead tungstate(PbWO4) Crystals

Radiation length 0.89 cm Moliere radius 2.0 cm Coverage : Barrel : |η| < 1.442 Endcaps : 1.479|η| < 3.0 Resolution

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 : 23–34 μm for r-φ measurement

230 μm for z measurement For TOB : 35–52 μm for r-φ measurement

530 μm for z measurement 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

Muon System 1400 muon chambers Drift tubes (250) Cathode Strip Chambers (540) Resistive Plate Chambers (610) Coverage : Barrel : |η| < 1.2 Endcap : |η| < 2.4

2222

26.012463.3

EEE


%5E

%100~

E

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.


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 (ΔRi = 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 ΔRi = 0.15 and an outer radius of ΔRo = 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 = 0.05. Low for photon, while high for jets as they carry both electromagnetic and

hadronic energy.

σiηiη 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 π0 it will tend to be larger.


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 Mq* = 1 TeV

Parameter Scale Parameter, 1000 Tev

Couplings f, f’, fs = 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



Samples Used : Background

QCD

/QCD_Pt_30to50_TuneZ2_7TeV_pythia6/Spring11-PU_S1_START311_V1G1-v1/AODSIM 5.312237e+07









/QCD_Pt_1000to1400_TuneZ2_7TeV_pythia6/Spring11-PU_S1_START311_V1G1-v1/AODSIM 3.321e-01

/QCD_Pt_1400to1800_TuneZ2_7TeV_pythia6/Spring11-PU_S1_START311_V1G1-v1/AODSIM 1.087e-02

/QCD_Pt_1800_TuneZ2_7TeV_pythia6/Spring11-PU_S1_START311_V1G1-v1/AODSIM 3.575e-04

PHOTON + JET

/G_Pt_15to30_TuneZ2_7TeV_pythia6/Spring11-PU_S1_START311_V1G1-v1/AODSIM 1.716832e+05







/G_Pt_470to800_TuneZ2_7TeV_pythia6/Spring11-PU_S1_START311_V1G1-v1/AODSIM 1.322870e-01



/G_Pt_1800_TuneZ2_7TeV_pythia6/Spring11-PU_S1_START311_V1G1-v1/AODSIM 2.935536e-07

Selection


Criteria Requirement

Vertex Selection

Vertex_z , |z| ≤ 24 cm

Vertex_ndof ≤ 4.0

Vertex_rho ≤ 2.0

Residual Spike (photon crystal timing) < 3 ns

HLT HLT_Photon75_CaloIDVI_IsoL_v* HLT_Photon90_CaloIDVI_IsoL_v*

> 100 GeV

< 1.44

> 100 GeV

< 1.5

ECAL Isolation < 4.2 + 0.006*PT

HCAL Isolation < 2.2 + 0.0025*PT

H/E Isolation 0.05

Trk Isolation < 2.0 + 0.0001*PT

σiηiη < 0.013

Track Veto No matching pixel seed

Cleaning Cuts

Trigger

Kinematic Cuts

Isolation Cuts


TP

|| jet

TP

|| jet


Efficiency Plot

N-1 Plots for Isolation variables


ECAL Isolation (in GeV) HCAL Isolation (in GeV)

4.2 + 0.006*PT 2.2 + 0.0025*PT

ECAL Iso HCAL Iso



Track Iso H/E Iso

HoE Trk Isolation (in GeV)

2.0 + 0.0001*PT H/E < 0.05


N-1 Plots for Isolation variables

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

Photon Pt and Eta


Jet Pt and Eta


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

Delta phi between Photon & Jet


Mass plot for Photon + Jet



Pt Cut Signal Bkg S/√B S/B

100 864.48 196.26 61.70 4.40

150 864.05 195.63 61.78 4.42

200 860.76 189.579 62.52 4.54

250 848.31 175.39 64.05 4.83

S/B for mass 915 – 1047 GeV with different Pt Cut

Fitted Mass plot for 1 TeV sample of signal

Not much difference in S/√B, So we can use higher PT selection.

Repeat this with official limit calculation tools but expect similar results. September 22, 2011

25

Different Mass samples of signal


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 PT 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.



Back up slides

Selection Efficiency (Cumulative)


Signal Photon+Jet(Bkg) QCD Dijet (Bkg)

Data

HLT 100 100 100 56.769

Vertex 100 99.99 99.99 55.986

Scrappy Event 100 99.99 99.99 55.986

No Cosmic 100 99.99 99.99 49.734

PhotonID 23.43 57.91 0.3942 6.782

Photon Pt 22.77 46.42 0.0610 4.111

Photon Eta 22.58 46.09 0.0610 4.035

Residual Spike 22.58 45.83 0.0601 4.034

Jet Pt 22.37 44.91 0.0598 2.337

Jet Eta 15.52 42.413 0.0568 1.837

Delta Phi 15.49 42.407 0.0504 1.829



Signal samples for different Mass point

0.7 TeV

1 TeV 1.2 TeV

1.5 TeV 1.7 TeV 2 TeV 2.5 TeV 3 TeV

PhotonID 26.73 23.43 21.37 19.60 18.17 17.12 15.22 14.49

Photon PT 25.17 22.77 20.83 19.06 17.60 16.53 14.59 13.84

Photon η 24.92 22.58 20.67 18.92 17.45 16.411 14.492 13.73

ResSpike 24.92 22.58 20.67 18.92 17.45 16.410 14.491 13.72

Jet PT 24.43 22.38 20.57 18.91 17.43 16.40 14.48 13.71

Jet η 15.87 15.52 15.04 14.79 14.16 13.73 12.59 12.67

Dphi 15.84 15.49 15.01 14.77 14.12 13.70 12.55 12.23

Selection Efficiency for signal sample of different mass points


Efficiency for Photon+Jet (Bkg) with different photon PT cut


Photon PT Cut

50 GeV

100 GeV

150 GeV

200 GeV

250 GeV

300 GeV

400 GeV

500 GeV

PhotonID 77.27 65.26 56.26 50.61 48.10 46.01 39.36 34.73

Photon PT 51.70 46.50 42.23 39.27 37.89 36.69 32.19 28.82

Photon η 51.23 46.18 42.01 39.11 37.74 36.56 32.12 28.78

ResSpike 50.96 45.91 41.74 38.84 37.47 36.30 31.85 28.51

Jet PT 45.66 44.99 41.60 38.82 37.47 36.29 31.85 28.51

Jet η 42.97 42.47 39.82 37.57 36.46 35.46 31.48 28.34

Dphi 42.94 42.44 39.81 37.56 36.44 35.44 31.47 28.32



Photon threshold PT in GeV


Documents

Study of Quark compositeness in pp q + Jets at CMSindiacms/Talks/talks-2011/varun-22092011.pdf · Introduction INDIA CMS, Quark Compositeness Compositeness of Quarks is one such scenario