Testing of CMS Endcap RPCs and the Determination of Top Quark Mass Using High Pt Jets at LHC
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Transcript of Testing of CMS Endcap RPCs and the Determination of Top Quark Mass Using High Pt Jets at LHC
![Page 1: Testing of CMS Endcap RPCs and the Determination of Top Quark Mass Using High Pt Jets at LHC](https://reader035.fdocuments.net/reader035/viewer/2022062517/5681382c550346895d9fdc79/html5/thumbnails/1.jpg)
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
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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
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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
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Integrated luminosity=10fb-1
Large Hadron Collider (LHC) Experiment
A
NfnNL 21
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Compact Muon Solenoid DetectorCompact Muon Solenoid Detector
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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
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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.
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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.
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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
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m
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pE
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2tanln
sinEET
missTE
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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)
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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
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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
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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)
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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
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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
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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
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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)
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Nominal mass—fitted mass ~ 65 GeV
Same mWnominal used in all selections
(JPM)
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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
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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
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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%
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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
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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
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Top quark mass reconstruction from jjW
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Right combinations
Wrong
Pt top dependence (leading jets approach)
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Mjjb plots for all selections after calibration
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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
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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
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MMjjbjjb(P(PTTtoptop>200 GeV)>200 GeV)
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Reco clusters pseudo-rapidy Calorimeters identifications
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Et
Behaviour
on
jet
cone
size
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Opening angle between reco. top and calorimeter clusters
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Top mass reconstruction from calorimeter Top mass reconstruction from calorimeter clustersclusters
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Underlying Event Estimation
Excluded
R > 0.7, Jet Isolation cut, excluding high Pt events
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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
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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
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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.
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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
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PART 2PART 2
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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
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RE */1
RE */2 RE */2
RE */3 RE */3
=5/16, =0.1
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RPC schematic diagram
ref: CMS NOTE 1997/004
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GIF (Gamma Irradiation Facility)GIF (Gamma Irradiation Facility)Prototyping of RPCPrototyping of RPC
RPC Beam Test Set-up
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At GIF SPS (CERN)-2003At GIF SPS (CERN)-2003
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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
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RPC Test Beam Results
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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
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Beam Test ResultsBeam Test Results
Mean arrival time
)exp()( atatf
Efficiency
)1(
)(
s
st
ob
P
PNN
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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
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RPC Cosmic Test Facility at NCP
NCP experimental test facility for RPC
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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
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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
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RPC Cosmic Test ResultsRPC Cosmic Test ResultsDark Current Strip Occupancy
Chambers are rejected with current > A
More than 2 noisy strips are not accepted
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Cosmic Test ResultsCosmic Test ResultsCluster size Efficiency
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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
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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)
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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”
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BACK-UP SLIDESBACK-UP SLIDES
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Calorimeter
(ECAL+HCAL)
clusters
distribution
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UE subtracted top mass
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<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
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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
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2mV=1 fC
Amplitude = 150 mV = 75 fC
Gas Gain = 106
mm-1
9.2mm-1
=-6.7mm-1
Fast Charge = 20%
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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)