Jet Calibration in CMS: experience

1
Jet Calibration in CMS experience lot of
questions and few answersa work in
progress

• Attilio Santocchia
• INFN Perugia
• Frascati 2nd Workshop sui Monte Carlo, la
  Fisica e le Simulazioni a LHC
• 22.05.2006

2
Motivations

• ttH channel very challenging we have to optimize
  all the tools we need to use
• Which is the best Jet Algorithm to use for such a
  complex multi-jet final state rich with b-jets?
• I used to study the fully hadronic decay ? 8 jets
  (4 light 4 b jets)
• Honestly? Its a mess! And jets are the most
  important object I had to understand

3
Chosen Algorithm Data Sample

• 5 Different Iterative Cone Algorithm 3 KT
  inclusive
• ICA ?DeltaR0.30, 0.35, 0.40, 0.45 and 0.50
• KT ? r0.35, 0.40 and 0.45
• COMPHEPPYTHIA 6.215CTEQ4L
• ttH120 (200K)
• ttjj (1000K) 1.6M events
• ttbb (400K)
• ALPGEN2PYTHIA 6.325CTEQ5L
• tt1j exclusive (1000K)
• tt2j exclusive (560K)
• tt3j exclusive (68K)
• tt4j inclusive (97K)

1.725M events
4
Calibration

• To do physics we need to go back to parton energy
• 2 different aspect to be considered
• Detector Effects ? PARTICLE level correction
• Physics Model Effects ? PARTON level correction
• I tried to factorize the 2 effects
• 2 different set of Calibration functions are
  calculate for correction to JetMC Energy and to
  Parton Energy
• These functions are then applied to the raw jet
  energy in cascade to recover the initial Parton
  Energy

ET(raw) ? ET(MCjet) ? ET(parton)
5
Raw Jet

• Standard Jets from CMS simulreco software
• No Calibration
• Calorimeter Noise Cut are ET gt 0.5 GeV and E gt
  0.8 GeV
• Raw Jet ET gt 5 GeV
• All Jets are considered massless

6
MC Jets

• Built from stable generator particles and ET gt
  0.5 (1) GeV
• Muons and Neutrinos are included in the
  calculation
• Muons and Neutrinos are excluded in the
  calculation
• If you keep all particles ? Jet is the same
  (difference in ET below 5) but CPU time needed
  for ICA increases of a factor 2-3
• Jet is kept if ET(jet) gt 10 (20) GeV
• We need to b-tag MC jets to build flavored
  dependant calibration
• Each particle belonging to a jet is classified as
  daughter of a b-flavored unstable particle or not
• Define b-ratio as sum of energy from particles
  from b divided jet energy
• If b-ratio gt 0.20 then jet is tagged as a MC b-jet

7
Jet Costituents

• After ICA application, I can list all the
  particles used to form the Jet (Jet Components)
• Each Particle in the Jet can be associated either
  to the partons from the hard scattering or
  nothing
• Most of the time 100 of the particles within a
  jet comes from the same original parton
• But sometimes there is a mixing

8
Particles ? String ? Partons
9
Jet Classification - Example
JET 4 jet 4 EtJ33.731 EtaJ-1.211
PhiJ-0.899 EJ61.810 n 0 Npar192
Strg191 Part 4 EtP 6.883 EtaP-1.234
PhiP-0.864 EP12.832 dR 0.042 n 1
Npar193 Strg191 Part 4 EtP13.563
EtaP-1.249 PhiP-0.921 EP25.595 dR 0.044
n 2 Npar371 Strg191 Part 4 EtP 1.528
EtaP-1.243 PhiP-0.918 EP 2.873 dR 0.038
n 3 Npar373 Strg191 Part 4 EtP 1.604
EtaP-0.925 PhiP-0.825 EP 2.391 dR 0.295
n 4 Npar375 Strg191 Part 4 EtP 4.728
EtaP-1.204 PhiP-0.892 EP 8.606 dR 0.009
n 5 Npar376 Strg191 Part 4 EtP 1.334
EtaP-1.417 PhiP-1.046 EP 2.916 dR 0.254
n 6 Npar507 Strg191 Part 4 EtP 2.061
EtaP-1.067 PhiP-0.838 EP 3.351 dR 0.155
n 7 Npar508 Strg191 Part 4 EtP 2.061
EtaP-1.027 PhiP-0.890 EP 3.246 dR
0.184 JET 5 jet 5 EtJ25.726 EtaJ 1.639
PhiJ 2.254 ThetaJ 0.384 EJ68.962 n 0
Npar238 Strg 91 Part 0 EtP 3.739 EtaP
1.902 PhiP 2.357 EP12.810 dR 0.283 n
1 Npar258 Strg110 Part 3 EtP 3.686 EtaP
1.487 PhiP 2.340 EP 8.585 dR 0.174 n
2 Npar261 Strg110 Part 3 EtP 5.652 EtaP
1.518 PhiP 2.170 EP13.564 dR 0.147 n
3 Npar262 Strg110 Part 3 EtP 1.627 EtaP
1.466 PhiP 2.034 EP 3.716 dR 0.279 n
4 Npar422 Strg 91 Part 0 EtP 1.370 EtaP
1.977 PhiP 2.286 EP 5.042 dR 0.340 n
5 Npar438 Strg110 Part 3 EtP 3.864 EtaP
1.560 PhiP 2.246 EP 9.615 dR 0.079 n
6 Npar439 Strg110 Part 3 EtP 4.426 EtaP
1.622 PhiP 2.279 EP11.641 dR 0.031 n
7 Npar440 Strg110 Part 3 EtP 1.457 EtaP
1.665 PhiP 2.249 EP 3.990 dR 0.027

• First Jet is PURE all the particles comes from
  the same string the associated parton code is 4
  (a W)
• Second Jet is a mixing of t_bar (code 3) and
  something else (code 0)
• How can I treat this kind of situation?

10
Jet Classification An Event

• ttH fully hadronic ? CompHEP
• Iterative Cone Algo (Cone Size 0.4)
• ET(particles isthep1)gt1GeV
• Index 0 Jet 3 Et164.511 Eta-2.067
  Phi-2.742 RatioE0.800 Quark Higgs
• Index 1 Jet 0 Et147.849 Eta-2.614 Phi
  0.030 RatioE1.000 Quark top
• Index 2 Jet 2 Et105.950 Eta-2.131
  Phi-0.131 RatioE0.742 Quark W
• Index 3 Jet 1 Et102.842 Eta-0.176 Phi
  2.456 RatioE0.981 Quark top_bar
• Index 4 Jet 4 Et 33.731 Eta-1.211
  Phi-0.899 RatioE1.000 Quark W
• Index 5 Jet 5 Et 25.726 Eta 1.639 Phi
  2.254 RatioE0.741 Quark top_bar
• Index 6 Jet 7 Et 11.329 Eta-1.117 Phi
  1.326 RatioE1.000 Quark Higgs
• Index 7 Jet 8 Et 8.020 Eta-2.585
  Phi-2.695 RatioE1.000 Quark Higgs
• Index 8 Jet 9 Et 6.469 Eta 0.227 Phi
  2.937 RatioE1.000 Quark W-
• Index 9 Jet 10 Et 4.530 Eta-0.108
  Phi-3.023 RatioE1.000 Quark W-
• Index 10 Jet 6 Et 4.008 Eta-2.951 Phi
  0.251 RatioE1.000 Quark top
• Index 11 Jet 12 Et 3.490 Eta-1.442 Phi
  0.667 RatioE1.000 Quark Higgs
• Index 12 Jet 11 Et 2.566 Eta 0.574
  Phi-2.994 RatioE1.000 Quark W-
• Index 13 Jet 13 Et 1.797 Eta-2.101 Phi
  3.061 RatioE1.000 Quark Higgs
• Index 14 Jet 14 Et 1.566 Eta-3.743
  Phi-0.466 RatioE1.000 Quark top

11
How many MC jets?

• ltNjetgt distribution for different jet algo
• Black is ICA
• Red is KT
• In the table ltNjetgt
• red is maximum ltNjetgt
• 1st number is AllParticle 2nd is noMuNu
• Iterative Cone
• If ltNjetgt increase when DR increase ? I get more
  jets because of ET(jet)gt10GeV
• If ltNjetgt decrease when DR increase ? overlapping
• KT
• If ltNjetgt increase when r increase ? Again
  depends on ET(jet)gt10GeV
• If ltNjetgt decrease when r increase ? ???

tt1j All Particles ETgt10GeV
12
Jet Formation ? Overlapping
tt1j All Particles ETgt10GeV
Black is ICA Red is KT
Fractio of jets with jetRatio gt 0.80
Fractio of jets with jetRatio gt 0.90 ? 97.3
97.9
13
bJets and cJets Classification

• Look for each particle belonging to the jet
• Define b-Ratio and c-Ratio
• ratioParticle E(particle)/E(jet)
• If(decayFromBquark) ratioForBjetratioParticle
• elseIf(decayFromCquark) ratioForCjetratioParticl
  e
• A jet is a bJet if
• (ratioForBjetgtratioForCjet) (ratioForBjetgtCutBj
  etRatio)
• A jet is a cJet if
• (ratioForCjetgtratioForBjet) (ratioForCjetgtCutCj
  etRatio)
• What are CutBjetRatio And CutBjetRatio?
• See next slides

14
b-ratio Distribution
b-ratiogt0.2
b-ratiogt0.2
tt1j
Sample tt2j ICA 0.30?0.50 KT r0.35?0.45
ICA 0.40 sample tt1j tt4j
Percentuale di bJet taggabili! Sono meno di
quelli che mi aspetto (in percentuale!) I bJet
troppo soffici li perdo E il gluon splitting è
trascurabile
15
c-ratio Distribution
c-ratiogt0.2
c-ratiogt0.2

• Same criteria ? a jet is classified as a cJet
  when more than 20 of its energy comes from c
  haddrons (and there are no b in the decay chain)
• tt1j 11.2 are cJets
• tt2j 10.4 are cJets
• tt3j 9.8 are cJets
• tt4j 8.8 are cJets

16
Minimum Distance (b and c partons)
Fractio of jets nearer than 0.2 from a b(c)
parton in the hard scattering Jet Algo is ICA and
DR0.4
17
b Minimum Distance VS bRatio

• Example for tt2j and ICA cone 0.4
• Here we can evaluate the gluon splitting
• bJets with bRatiogt0.5 and minDistBgt0.5 are not
  coming from a b parton in the hard scattering ?
  6.2
• bJets with bRatiogt0.2 and minDistBgt0.8 are not
  coming from a b parton in the hard scattering ?
  4.0

18
Calibration Raw Jet? MC Jet

• Build jets from Full Reco (FR)
• Build jets from Generator (MC) particles list
• Match FR-MC jets minimizing SDRFR-MC keep jets
  where DRFR-MClt 0.3
• Fill 50h x 200ET histos with ET(FR)/ET(MC) for
  b-jets and not-b-jets in the range abs(eta)lt5 and
  ETlt600 GeV
• Gaussian Fit if Nentgt30
• For each Eta Value, fit the ET Ratio as a
  function of ET(raw) using the function

19
Calibration MC Jet? Parton

• Build jets from Generator (MC) particles list
• Match jets-Parton minimizing SDRMC-Parton keep
  jets where DRMC-Partonlt 0.15
• Fill 50h x 200ET histos with ET(MC)/ET(Parton)
  for b-jets and not-b-jets in the range abs(eta)lt5
  and ETlt600 GeV
• Gaussian Fit if Nentgt30
• For each Eta Value, fit the ET Ratio as a
  function of ET(MC) using the function

20
Single ET Ratio Distribution
Raw-MC jet Ratio Distribution
MC jet-Parton Ratio Distribution

• Example for 1 of the 10000 bins in which the
  eta-ET plane has been divided
• Red is b-jets - Black is not-b-jets
• Fit done in 2 steps
• First in the whole histo range 0,2 ? Get Mean
  and Sigma
• Second in the range mean-2.5sigma,mean2.5sigma
  

21
Ratio vs ET Distribution
Raw-MC jet Ratio Distribution
MC jet-Parton Ratio Distribution
ET(GeV)
ET(GeV)

• Eta Ring 0.5lthlt0.6
• Red is b-jets - Black is not-b-jets
• No needs to distinguish b-jets for MC-Parton
• Error Bar are defined as s/sqrt(N) where s is the
  width of the second fit and N is number of Entry
  (see slide 11)

22
Fitted Parameter Raw Jet? MC Jet
Parameter a
Parameter b
Parameter c
h
h
h
Here is the tracker Barrel-EndCaps Border!

• Fitted parameters as a function of eta
• Red is b-jets - Black is not-b-jets

23
Fitted Parameter MC Jet? Parton (DR0.5)
Parameter a
Parameter b
Parameter c
h
h
h

• Fitted parameters as a function of eta
• b-jets and not-b-jets are together
• Each parameter fitted with a streight line

24
Parton Calibration - Fitted Para Different
Cone All Particles
Light Jets
? ICA 0.30 ? ICA 0.35 ? ICA 0.40 ? ICA 0.45 ? ICA
0.50
h
h
h
bJets
h
h
h
25
Ratio vs ET DistributionInput Particles is NoMuNu
Eta0.5-0.6 ET51-54GeV
26
Ratio vs Eta Distribution (ET45-48 GeV)Input
Particles is NoMuNu and All Particles
h
h

• Here AllParticles and NoMuNu show differences
  (for low eta)
• But this is not a homogeneous functions
• Matching 0.15 is not enough? See also the Single
  distributions and the left tail

27
MCJet to ttH Comparison (cone 0.5)

• 3 different eta bin ? No major difference above
  40 GeV for not-b-jets and 60 GeV for b-jets
• Difference due to different Calibration
• MCJet is only particle level
• ttH is particle level and parton level
• Parton level correction important for low ET jets

28
MC Jet Definition what I learned

• Option Jet input list
• All Particles
• NoMuNu
• No major differences ? the difference in
  bJets/lightJets is minor (negligible?)
• Particle Calibration keeps the high difference
  btw bJets/lightJets
• Depends on the fragmentation used
• bJets charged spectrum different from lightJets
• To recover correctly the jet energy is mandatory
  to tag the jets and use 2 different corrections
  for bJets and lightJets
• Parton Calibration could be the same for all
  experiments (ATLAS/CMS)
• Providing the definition is the same for both od
  us
• All Particles keeps simple the definition for
  parton calibration

29
Invariant Masses ttH fully Hadronic

• To cross-check the quality of the calibration
  functions, invariant masses for the W,t and Higgs
  particles are used
• The 8 most energetic jets in the tracker are
  paired to the 8 partons in the final state using
  DR.
• All the events where alle the 8 jets are paired
  with DRlt0.3 have been selected
• Invariant mass are built using the calibrated
  jets for each algorithm-calibration

30
Invariant Masses ttH fully Hadronic from MC Jets

• 1000 events used for this exercise
• No DeltaR matching ? Look for configuration 332
  and correct JetRatio associations (see slide
  9-10)
• Cone 0.5 is the more ermetic OK but how many
  events survive the request 332?
• Cone 0.4 is better less ermetic but sigma is
  better, and Nevents is a lot better!

31
Invariant Masses ttH fully Hadronic
Minv(GeV)
Minv(GeV)
Minv(GeV)
Minv(GeV)
Minv(GeV)
Minv(GeV)

• Invariant Masses for (from left to right) W,t and
  Higgs
• Upper row is Standard CMS MC-Jet calibration and
  DeltaR0.5
• Lower row is ttH-calibration and DeltaR0.5

32
Invariant Masses full Results
CMS ICA 0.30 ICA 0.35 ICA 0.40 ICA 0.45 ICA 0.50 KT incl
MW 81,50 81,58 81,58 81,80 82,12 82,80 82,74
Mt 172,05 172,86 173,05 173,72 174,70 176,09 176,20
MH 105,54 108,85 109,29 109,92 110,72 111,15 112,20
sW 13,84 12,98 13,19 13,22 13,46 13,56 12,58
st 22,20 21,06 20,97 21,01 21,30 21,20 20,63
sH 19,29 18,83 19,05 19,04 19,12 19,33 18,58
RESW 0,170 0,159 0,162 0,162 0,164 0,164 0,152
RESt 0,129 0,122 0,121 0,121 0,122 0,120 0,117
RESH 0,183 0,173 0,174 0,173 0,173 0,174 0,166
Eff() 4,08 5,90 6,39 5,98 5,20 4,28 5,40

• Resolution is defined as s/M
• Numer of selected events and Resolution give a
  hint on the best algorithm to use
• ICA DR0.4 and inclusive KT seems good choice

33
Analysis from the CMS P-TDR ttH fully Hadronic

• Analysys based on c2mass for jet pairing
• 8 most energetic jets in hlt2.7
• Centrality Cuts (All and Higgs)
• The c2mass for 2W and 2tops within 3 sigma from
  expected values
• Different cut for Btag and ET jets
• Significance S/sqrt(N) and S/N used as benchMark

34
Same Analisys ? Different Parton Calibration
35
ConclusionsNon ci sono ancora! ma

• La parton calibration è necessaria per noi
  sperimentali
• La definizione di MCjet potrebbe essere uguale
  per tutti (ATLAS/CMS)
• In questo modo si potrebbe chiedere ai
  teorici/sperimentali di definire un unico oggetto
  che può essere usato da noi sperimentali per la
  particle calibration
• E dai teorici per la parton calibration che è
  uguale per tutti
• In ogni caso la particle calibration non può
  essere unica per tutti i jets
• Ma una distinzione tra bJets e lightJets è
  necessaria
• Non ho ancora guardato il KT mea culpa