study of quark compositeness in pp q + jets at cmsindiacms/talks/talks-2011/varun-22092011.pdf ·...
TRANSCRIPT
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
INDIA CMS, Quark Compositeness
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 !!!
September 22, 2011 3
Introduction
INDIA CMS, Quark Compositeness
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
s
September 22, 2011 4
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
INDIA CMS, Quark Compositeness
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September 22, 2011 5
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
INDIA CMS, Quark Compositeness
jetqq
jetqg (a)
(b)
September 22, 2011 6
ggg
(c)
Backgrounds
INDIA CMS, Quark Compositeness
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)
September 22, 2011 7
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.
INDIA CMS, Quark Compositeness September 22, 2011 8
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)
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
INDIA CMS, Quark Compositeness
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
September 22, 2011 11
%5E
%100~
E
Photon Identification
INDIA CMS, Quark Compositeness
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.
September 22, 2011 12
Photon Isolation
INDIA CMS, Quark Compositeness
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.
September 22, 2011 13
Samples Used
INDIA CMS, Quark Compositeness
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
September 22, 2011 14
INDIA CMS, Quark Compositeness September 22, 2011 15
Samples Used : Background
QCD
/QCD_Pt_30to50_TuneZ2_7TeV_pythia6/Spring11-PU_S1_START311_V1G1-v1/AODSIM 5.312237e+07
/QCD_Pt_50to80_TuneZ2_7TeV_pythia6/Spring11-PU_S1_START311_V1G1-v1/AODSIM 6.359119e+06
/QCD_Pt_80to120_TuneZ2_7TeV_pythia6/Spring11-PU_S1_START311_V1G1-v1/AODSIM 7.842652e+05
/QCD_Pt_120to170_TuneZ2_7TeV_pythia6/Spring11-PU_S1_START311_V1G1-v1/AODSIM 1.151335e+05
/QCD_Pt_170to300_TuneZ2_7TeV_pythia6/Spring11-PU_S1_START311_V1G1-v1/AODSIM 2.426283e+04
/QCD_Pt_300to470_TuneZ2_7TeV_pythia6/Spring11-PU_S1_START311_V1G1-v1/AODSIM 1.168494e+03
/QCD_Pt_470to600_TuneZ2_7TeV_pythia6/Spring11-PU_S1_START311_V1G1-v1/AODSIM 7.022e+01
/QCD_Pt_600to800_TuneZ2_7TeV_pythia6/Spring11-PU_S1_START311_V1G1-v1/AODSIM 1.555e+01
/QCD_Pt_800to1000_TuneZ2_7TeV_pythia6/Spring11-PU_S1_START311_V1G1-v1/AODSIM 1.844e+00
/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_30to50_TuneZ2_7TeV_pythia6/Spring11-PU_S1_START311_V1G1-v1/AODSIM 1.669495e+04
/G_Pt_50to80_TuneZ2_7TeV_pythia6/Spring11-PU_S1_START311_V1G1-v1/AODSIM 2.721839e+03
/G_Pt_80to120_TuneZ2_7TeV_pythia6/Spring11-PU_S1_START311_V1G1-v1/AODSIM 4.471971e+02
/G_Pt_120to170_TuneZ2_7TeV_pythia6/Spring11-PU_S1_START311_V1G1-v1/AODSIM 8.417146e+01
/G_Pt_170to300_TuneZ2_7TeV_pythia6/Spring11-PU_S1_START311_V1G1-v1/AODSIM 2.264012e+01
/G_Pt_300to470_TuneZ2_7TeV_pythia6/Spring11-PU_S1_START311_V1G1-v1/AODSIM 1.492849e+00
/G_Pt_470to800_TuneZ2_7TeV_pythia6/Spring11-PU_S1_START311_V1G1-v1/AODSIM 1.322870e-01
/G_Pt_800to1400_TuneZ2_7TeV_pythia6/Spring11-PU_S1_START311_V1G1-v1/AODSIM 3.480984e-03
/G_Pt_1400to1800_TuneZ2_7TeV_pythia6/Spring11-PU_S1_START311_V1G1-v1/AODSIM 1.269863e-05
/G_Pt_1800_TuneZ2_7TeV_pythia6/Spring11-PU_S1_START311_V1G1-v1/AODSIM 2.935536e-07
Selection
INDIA CMS, Quark Compositeness
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
September 22, 2011 16
TP
|| jet
TP
|| jet
N-1 Plots for Isolation variables
INDIA CMS, Quark Compositeness
ECAL Isolation (in GeV) HCAL Isolation (in GeV)
4.2 + 0.006*PT 2.2 + 0.0025*PT
ECAL Iso HCAL Iso
September 22, 2011 18
INDIA CMS, Quark Compositeness
Track Iso H/E Iso
HoE Trk Isolation (in GeV)
2.0 + 0.0001*PT H/E < 0.05
September 22, 2011 19
N-1 Plots for Isolation variables
Effect of Pile-up reweighting on MC
INDIA CMS, Quark Compositeness
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
September 22, 2011 20
Before reweighting After reweighting
Jet Pt and Eta
INDIA CMS, Quark Compositeness September 22, 2011 22
L2L3 Residual correction is not applied for jet energy correction (on data), which can have a effect of ~2%.
INDIA CMS, Quark Compositeness
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
Summary & Future Plans
INDIA CMS, Quark Compositeness
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.
September 22, 2011 27
Selection Efficiency (Cumulative)
INDIA CMS, Quark Compositeness
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
September 22, 2011 29
INDIA CMS, Quark Compositeness
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
September 22, 2011 30
Efficiency for Photon+Jet (Bkg) with different photon PT cut
INDIA CMS, Quark Compositeness
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
September 22, 2011 31