Testing of CMS Endcap RPCs and the Testing of CMS Endcap RPCs and the Determination of Top Quark Mass Determination of Top Quark Mass

Using High Pt Jets at LHCUsing High Pt Jets at LHC

IJAZ AHMEDIJAZ AHMED

Physics Department QAU

Doctoral thesis

Supervisor: Prof. Hafeez R. Hoorani

PART 1PART 1

Top Quark Mass Reconstruction Using High Pt Top Quark Mass Reconstruction Using High Pt Jets in Ttbar Semi-leptonic Channel at LHCJets in Ttbar Semi-leptonic Channel at LHC

(CMS DETECTOR SIMULATION)(CMS DETECTOR SIMULATION)

PART 2PART 2

Resistive Plate Chamber (Resistive Plate Chamber (CMS Trigger DetectorCMS Trigger Detector))Beam test AND Cosmic testBeam test AND Cosmic test

OUTLINE OUTLINE (first part)(first part)

Motivations of Top PhysicsTopology of Lepton + Jets High Pt top basic idea3 methods for jets selectionTop quark mass reconstruction from jets Jets clustering in detectorClusters invariant masses Mtop

clus

Underlying Event (UEclus) estimation and subtraction

Summary

Integrated luminosity=10fb-1

Large Hadron Collider (LHC) Experiment

A

NfnNL 21

Compact Muon Solenoid DetectorCompact Muon Solenoid Detector

Top Quark Properties, production and decays at the Top Quark Properties, production and decays at the LHCLHC

9090

%%10%10%

~4.5%~4.5%~29%~29%

~66.5%~66.5%

need to reconstruct and identify muons b-jets light jets (u,d,c,s) missing ET(neutrinos)

NLO Cross-section for tt~ production at LHC is (tt)~830pb

Striking Features of top quarkStriking Features of top quark Heaviest particle (spin ½, charge 2/3)

Origin of mass, EWSB, Higgs

Short life time (top1/top, had=1QCD

No bound state

Yukawa coupling-unity

High PHigh Ptt Top Basic Idea Top Basic Idea

Highly boosted top quarks decay back-to-back, making two distinct hemispheres inside the detector.

When the top has a higher boost, one expects the opening angle between W and b (from top decay) to be smaller and as a consequence the decay products also have cone size smaller.

High Pt top quarks have decay angles close to the top flight direction and therefore the hadronic jets due to narrow cone size will have the probability of overlaping in space.

Calculate the invariant mass of the objects which are in larger cone around the top quark direction of flight and then is correlated with the real top mass. For this the top quark needs to have a larger Pt > 200 GeV.

Key elements of this analysisKey elements of this analysis

• This Topology reduces the combinatorial background as well as the backgrounds from other processes.

• The systematic effects due to jet energy calibration and gluon effects will be different from an analysis with standard jets.

• This technique has the potential to reduce the systematic errors, since it is less sensitive to the calibration of jets and to the intrinsic complexities of effects due to leakage outside the smaller cones, energy sharing between jets

• ******************************************************

******************************************************

1. With mt being reconstructed from the three jets in the one hemisphere (mt= mjjb)

2. Then mt is reconstructed summing up the energies in the calorimeter clusters in a large cone around the top direction.

Kinematical variables

• Invariant mass

• Transverse momentum

• Transverse mass

• Transverse energy

• Rapidity

• Pseudo-rapidity

• Jet cone radius

• Missing Transverse Energy

222 pEppm

222yxT ppp

)).((22222zzzTT pEpEpEpmm

T

z

z

z

m

pE

pE

pEy lnln

2

1

22 R

2tanln

sinEET

missTE

Tools and AlgorithmsTools and Algorithms

Minimum Bias Events (Pile-up) Triggering on isolated Muon Clusters reconstruction Jet reconstruction and Missing ET

B-tagging

1. Event generation (PYTHIA)

2. Simulation of the interaction of the generated particles with the detector (OSCAR, FAMOS)

3. Simulation of digitized phase (FAMOS, ORCA)

4. Local and global event reconstruction (FAMOS, ORCA)

5. Physics Analysis tools (PAW,ROOT)

Pre-selection cuts at Generator level

)( lblqbqbWbWtt

no of eventsWith pile-up

Int luminosityfb-1

X-sectionpb

49535 7.23 6.85

qqbbbWbWtt

Pttop > 200 GeV, || < 3.0

Ptanti-top > 200 GeV, || < 3.0

Pt > 30 GeV, || < 2.0

Ptq > 20 GeV, || < 2.5

)( lblqbqbWbWtt

X-section approximately 1% of the total tT cross-section

FAMOS_1_4_0 samples

165 Top mass point = 20K events

175 Top mass point = 50K events

185 Top mass point = 20K events

ORCA_8_7_3 sample (350K)

Pile-up events are included

Pttop MC top R(q,qbar) Pt

W

R(top,b-par) R(top,W) R(top, min W-quarks) R(top, max W-quarks)

Partonic Level Distributions

combined b-tag discriminator

leptonic W reco mass

• MET-> Missing Transverse Energy

•MET > 30 GeV

•At least 1 iso. muon, Pt>20 GeV, ||<2.0

combined b-tag disc. > log (1.0)

(60% b-tag efficiency)

Leading jets and muons Pt distributions

Leading light jets Pt

Ptjets > 20 GeV

Leading b-jets Pt

Ptb-jets > 20 GeV

Pttrks/Pt) < 5% R=0.01-0.2)

Efficiency > 92%

Muon IsolationPt > 30 GeV

Jet-Parton Matching (JPM)

2 light jets + 2 quarks from W

4 possible jet combinations take best combination

Correctly matched if R < 0.4

worst of 2 quarks

matching angles

(J1,j2), (q1, q2)

***************

(J1,q1), (j1,q2)

(j2, q1), (j2,q2)

R(j1,q1)

R(j1,q2)

R(j2,q1)

R(j2,q2)I1=Max (R(j1,q1),R(j1,q2))I2=Max (R(j2,q1),R(j2,q2))Min(I1, I2)<0.4

Introducing 3 approachesIntroducing 3 approaches

Three approaches to select events+ jet combination (for top direction)

Leading jets > = 2 b-tagged jets, > = 2 non b-tagged jets

Exactly 4 jets, =2 b-tagged jets, = 2 non b-tagged jets

> 2 leading b-jets, 2 light jets with mjj closest to W mass

Top quark selection from leading Top quark selection from leading jetsjets

Kinematical cuts Selection efficiency % No. of events

Before selection 100 49535

no of iso. muons 93.6 46370

1 iso muon Pt > 30 GeV 92.7 45920

1 reco light jets Pt > 20 GeV 91.1 45117

2 reco light jets | < 2.5 73.6 36484

1 b-jet Pt > 20 GeV 55.6 27543

2 b-jets | < 2.5 18.6 9214

|mjj – mWnom| < 20 GeV 8.5 4235

mWnom = 65.24 (gaussian fitted correctly jet-parton matching)

Nominal mass—fitted mass ~ 65 GeV

Same  mWnominal used in all selections

(JPM)

Top quark mass measurment from leading jetsReco W-boson purity with 2 quarks matched = 18.17%

Reco W-boson purity with 1 quark matched = 42.7%

b-jet with biggest

angle wr.t muon called

Hadronic b-jets

Top quark selection from four jets Top quark selection from four jets topologytopology

Kinematical cuts Selection efficiency %

No. of events

Before selection 100 49535

no of iso muons 93.6 46370

1 iso muon Pt > 30 GeV 92.7 45916

1 reco light jets Pt > 20 GeV

92.7 45915

Exectly 4 jets | < 2.5 21.3 10551

Exectly 2 light jets 8.0 3941

Exectly 2 b-jets 8.0 3941

|mjj – mW| < 20 GeV 3.9 1937

Di-jet invariant mass dist from four jets selection

Di-jet with associated b-jet invariant mass dist. from four jets selection

Reco W-boson purity with 2 quarks matched = 20.98%

Reco W-boson purity with 1 quark matched = 43.26%

Top quark selection from jjTop quark selection from jjWW

Kinematical cuts Selection efficiency %

No. of events

Before selection 100 49535

no of iso muons, Pt > 30 GeV < 2.0

92.7 45920

2 jj W, Pt > 20 GeV, < 2.5 73.6 36484

2 b-jets Pt > 20 GeV, < 2.5 18.6 9214

|mjj – mW| < 20 GeV 11.9 5917

W mass reconstruction jj---W

Reco W-boson purity with 2 quarks matched = 20.76 %

Reco W-boson purity with 1 quark matched = 40.6 %

Before b-jet selection After full selectionAll jets combinations

Top quark mass reconstruction from jjW

Right combinations

Wrong

Pt top dependence (leading jets approach)

Mjjb plots for all selections after calibration

Comments on mComments on mjjbjjb

Study based on shape of distributions for top direction determination

Explored three types of selection criteria for hadronic top mass reconstruction

Four jets selection results low efficiency with higher W purity

Jets with invariant mass close to W have higher efficiency with intermediate purity of W

Leading jets selection gives sharp and narrow dist. shape with less long tail behaviour and reasonable selection efficiency

Cluster Reco MethodCluster Reco Method

Once top direction determined,and Pt(jjb)= 200 GeV

Invariant mass of all calorimeters clusters

x around top direction

Ei represents total energy of the ith cluster

nDR runs over all clusters within selected cone size

Pi its 3-momenta vector

We know only E,, about clustersAssumptions:considering particles masseless

220 PEm cossinEPx sinsinEPy

cosEPz

2

7.0

2

7.0

222 )()()()( iiclusters

Rn

i

Rn

i

PEPERm

MMjjbjjb(P(PTTtoptop>200 GeV)>200 GeV)

Reco clusters pseudo-rapidy Calorimeters identifications

Et

Behaviour

on

jet

cone

size

Opening angle between reco. top and calorimeter clusters

Top mass reconstruction from calorimeter Top mass reconstruction from calorimeter clustersclusters

Underlying Event Estimation

Excluded

R > 0.7, Jet Isolation cut, excluding high Pt events

Jet Isolation cut

<Et> / cluster (MeV)

< no of clusters > / high Pt event

0.7

1.4

2.1

3.0

2.5 5.0

R = 0.7 201.2476

173.5981

102.26708

102.26708

53.99309

78.731383

R = 0.8 199.5066

172.5466

100.7166

100.7166

53.9966

77.4366

R = 0.9 198.5057

171.20146

99.28630

99.28630

54.01303

76.231285

R = 1.1 197.4641

168.08112

96.26546

96.26546

54.17295

73.791175

R = 1.5 192.9916

164.2755

91.25372

69.88922

54.77268

69.88922

LAYER # 01 (ECAL)

UE Estimation Method

LAYER # 02 (HCAL)

Jet Isolation cut

<Et> / cluster (MeV)

< no of clusters > / high Pt event

0.7

1.4

2.1 3.0 3.0 5.0

R = 0.7 626.8938

509.1988

445.77134

363.00229

236.77182

326.78352

R = 0.8 623.0733

503.1780

439.69125

356.43218

236.76181

321.3933

R = 0.9 618.4729

496.6673

433.11116

349.36180

236.69330

315.67208

R = 1.1 614.8522

485.2422

420.8222

335.5822

236.3522

304.6222

R = 1.5 599.838

459.4928

394.1156

306.64136

237.03169

283.05253

UE Estimation Method

Top mass MTop mass Mclusclustoptop and UE and UEclusclus subtraction subtraction

Before UE Subtraction After UE Subtraction

With 50,000 events which corresponds to 7.2 fb-1, one can expect a statistical uncertainty about m=1-1.5 GeV on top mass.

Summary Summary

• Analysis based (Pttop > 200GeV) with Full and Fast

Simulation of CMS detector is performed.• An alternate method for top mass reconstruction in

CMS is presented, strongly depends on Calorimeter.• A new method for Underlying event (UE) is developed• Statistical error 1-1.5 GeV on top mass is determined.

1. CMS IN-2007/023 -- Top Quark mass measurement in the lepton plus jets channel using large calorimeter clusters cone at LHC Authors: Ijaz Ahmed, Hafeez R. Hoorani, Martijin Mulders

2. CMS IN-2006/046 -- Study of High Pt Top Anti-Top Production at LHC Authors: Ijaz Ahmed, Hafeez R. Hoorani, Martijn Mulders

PART 2PART 2

The Resistive Plate Chamber (RPC)The Resistive Plate Chamber (RPC)

Bakelite resistivity 10 9- 10 10 cm Coated with linseed oil

• Gap width: 2 mm• HV electrodes : 100 m graphite • PVC Spacers (tolerance ± 200 m)• Graphite coating• Gas pressure : ~ 1 Atm• Gas mixture: 96% Freon, 3.5% iso-Butane, 0.5% SF6

BottomBottom

Top Wide

Top Wide

Top Top Narrow

Narrow

Station A B C D

RE2/2 1693 979 684 1687

RE2/3 1961 1323 981 1954

RE3/2 1693 979 684 1687

RE3/3 1961 1323 981 1954

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RE */1

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RE */3 RE */3

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Avalanche Mode RPC

RPC schematic diagram

ref: CMS NOTE 1997/004

20,10, 8

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dN

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Raether condition

d

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nsdn

sd

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GIF (Gamma Irradiation Facility)GIF (Gamma Irradiation Facility)Prototyping of RPCPrototyping of RPC

RPC Beam Test Set-up

At GIF SPS (CERN)-2003At GIF SPS (CERN)-2003

Environment for the Beam testEnvironment for the Beam test

Muon Beam – Momentum : 200 GeV/c (450 GeV max)– Flux : ~104 per SPS cycle (2.38sec)– Repetition peroid 14.4 sec– Area : 10 × 10 cm2

• Gas Mixture– C2H2F4 96% + Iso-C4H10 3.5% + SF6 0.5%

• Radiation Source– At 4m, Flux 0.86*105cm-2s-1

– 740 GBq(20Ci) 137Cs gamma ray (661keV)• Electronics

– LeCroy 2277 TDC (1 nsec/bit, multi-hit, common stop/start)

– 32-ch FEB, co-axial cables + Flate cables

RPC Test Beam Results

Beam Test ResultsBeam Test Results

Time Resolution

0

0

T

T

P

PHVHVeff

Correction is of the order of 1%

Power consumption =

(10.5kV*280 A)/1.169 m2 = 2.5W/m2

Dark current

HVeff = HV - RI

Beam Test ResultsBeam Test Results

Mean arrival time

)exp()( atatf

Efficiency

)1(

)(

s

st

ob

P

PNN

Beam Test ResultsBeam Test Results

Rate capability

Cluster size

tAN

NR

events

cl

Voltage drop = Vd = 2 <Qe> r s

<Qe>=1pC, r = 1000Hz/cm2, =1010cm, s = 0.2cm

RPC Cosmic Test Facility at NCP

NCP experimental test facility for RPC

Cosmic Test FacilityCosmic Test Facility

• Dimension – 195x20x1 cm can work up to 180 cm

• 18 scintillators• For the trigger we need 18 scintillators +

some spare• 2 layers – 8 scint. each + 2 additional scint.

Electronic Trigger Logic

TimingTiming

• Trigger– Cable 52 ns– Amplifier 26 ns– Discriminator 12 ns– Coincidence 16 ns– PMT 40 ns– Total Delay Trigger 146 ns

• RPC– RPC + FEE 16 ns– Cable 25 ns– Total Delay RPC 41 ns

Scintillator trigger is late by 100 ns compare to signal from RPC

RPC Cosmic Test ResultsRPC Cosmic Test ResultsDark Current Strip Occupancy

Chambers are rejected with current > A

More than 2 noisy strips are not accepted

Cosmic Test ResultsCosmic Test ResultsCluster size Efficiency

Summary (RPC)Summary (RPC)Characteristic

CMS Requirement

Test Results

Time Resolution < 3 nsec < 1.5 nsec

Efficiency > 95 % > 95 %

Rate Capability > 1 kHz/cm2 > 1 kHz/cm2

Power Consumption < 2~3 W/m2 < 2.5 W/m2

Plateau Region > 300 V 400-1000 V

• Production and the quality control for the CMS endcap RPCs (Nucl. Phys. B- Proc. Suppl. 158 : 103-107, 2006)

• Assembly and Quality Certification for the First Station of CMS Endcap RPCs (RE1) (Nucl. Phys. B- Proc. Suppl. 158 : 16-20, 2006))

• NOTE 2004/037)Beam test of the First Production Forward RPC

Publications

1) Production and the quality control for the CMS endcap RPCs (Nucl. Phys. B- Proc. Suppl. 158 : 103-107, 2006)

2) Assembly and Quality Certification for the First Station of CMS Endcap RPCs (RE1) (Nucl. Phys. B- Proc. Suppl. 158 : 16-20, 2006))

3) Beam test of the First Production Forward RPC (CMS NOTE 2004/037)

4) Study of High Pt Top Anti-Top Pair Production at LHC (CMS IN 2006/046)

5) Top Quark Mass Measurement in the Lepton Plus Jets Channel using Large Calorimeter Clusters cone at LHC (CMS IN 2007/023)

6) Test beam Results of Endcap RPC’s (submitted as CMS NOTE)

Talks DeliveredTalks Delivered• Talk given at “International Nathiagali Summer College in June 2002” titled, “Gas Gaps

required for the CMS Muon System”• Talk given at National Centre for Physics in 2003 titled “PYTHIA An introductory tutorial for

beginners”• Talk given at National Centre for Physics in 2003 titled “RPC based muon trigger system for

the CMS detector”• A demo based on CMS Endcap Resistive Plate Chambers delivered in CERN summer school in

July, 2003• Talk given at CERN Geneva, Switzerland in CMS-PRS Standard Model Meeting in 29 july, 2005

titled “High Pt top mass in the single lepton plus jets channel”• Talk given at CERN Geneva Switzerland in CMS-PRS Standard Model Meeting in 6 February,

2006 titled “Status report semi-leptonic Ttbar channel”• Talk given at CERN, Geneva, Switzerland in CMS-PRS Standard Model Meeting in 21 March,

2006 titled “Updates on the high Pt analysis in lepton plus jets channel”• Talk given at CERN, Geneva, Switzerland in CMS-PRS Week in 23 June, 2006 titled “Updates

of the high Pt top analysis in the lepton plus jets channel”• Talk given at CERN, Geneva, Switzerland in local group meeting titled “Top mass from high

Pt top samples”• Talk given at Quaid-i-Azam University, Physics department in the international “5th Particle

Physics Workshop” held 20-25 November 2006 titled “Top Quark Mass Reconstruction using High Pt Top in the Lepton + Jets Channel”

• Talk given at National Centre for Physics in the “LHC Data Analysis Workshop” from 27-28, November 2006 titled “PYTHIA, The Generator’s Physics”

• Talk given at National Centre for Physics in the “LHC Data Analysis Workshop” from 27-28, November 2006 titled “CMKIN-PYTHIA (Tutorial)”

• Talk given at National Centre for Physics in the “LHC Data Analysis Workshop” from 27-28, November 2006 titled “ROOT, An Object Oriented Analysis Framework”

• Talk given at National Centre for Physics in the “LHC Data Analysis Workshop” from 27-28, November 2006 titled “Introduction to OO CMS Softwares”

• Talk given at National Centre for Physics in the “LHC Data Analysis Workshop” from 27-28, November 2006 titled “ROOT, “Full Chain Simulation of CMS Detector”

BACK-UP SLIDESBACK-UP SLIDES

Calorimeter

(ECAL+HCAL)

clusters

distribution

UE subtracted top mass

<Mclusttop(fitted)>

(GeV)no UE subtraction

<Mclusttop(fitted)>

(GeV)UE subtraction

R=1.1 139.3 117.6

R=1.2 151.1 126.8

R=1.3 163.2 130.8

R=1.4 170.1 137.8

R=1.5 181.3 145

R=1.6 196.1 153.2

Clusters invariant masses

Top Mass Scale Calibration using Hight PTop Mass Scale Calibration using Hight PTT W W samplesample

RN

RW

clus

W

RTop

Rm

M

NC

1 )(

1

top

RN

R

topclustop CRm

RNm

1

)(1

Calibration Coefficient Formula

Top Mass determination

2mV=1 fC

Amplitude = 150 mV = 75 fC

Gas Gain = 106

mm-1

9.2mm-1

=-6.7mm-1

Fast Charge = 20%

Summary of Systematic Summary of Systematic

SourceOf uncertainity

mtop(GeV/c2)

Re-calibrationElectronic noiseISR on/offFSR on/offB-quark fragmentationUE estimate (+-10%)Cluster mis calibration:+-1(5)%Calorimeter: e/h=1.25 (1.63)

0.91.20.140.070.31.340.7(1.3)0.8(0.3)