Jet Measurements in PbPb Collisions with the CMS Detector · Marguerite Tonjes (UMD) HPHD,...

Marguerite Tonjes (UMD) HPHD, Palaiseau, May 30 2011

Jet Measurements in PbPb Collisionswith the CMS Detector

Marguerite Belt Tonjesfor the CMS Collaboration

High pT Probes of High Density QCD at the LHC, Palaiseau, May 30-June 1, 2011 1


Compact Muon Solenoid (CMS)

2

EM and HAD calorimeters|η|< 5

Silicon tracker|η|< 2.4

Magnet yoke3.8 T

Muon chambers|η|< 2.5

HF2.9<|η|< 5.2

Beam Scintillator Counters(BSC)

±

±

CASTOR

ZDC±140m


Jet Finding in Heavy Ion Events

3

• Jet: localized collection of hadrons that come from a fragmented parton

a

b

c

d

hadrons

hadrons

Radius RJet

leading particle


Jet Finding in Heavy Ion Events

4

• Jet: localized collection of hadrons that come from a fragmented parton

• Problem: finding jet above significant soft background– dNcharged/dη ~1600 for 5%

most central events

• Approach: use pileup subtraction technique[*] to remove background underlying event

a

b

c

d

hadrons

hadrons

Radius RJet

leading particle

[*] O. Kodolova, et. al., Eur. Phys. J. C50 (2007) 117


CMS Jet Finding• CMS has non-linear calorimeter response in pT and η, need jet energy corrections (which are well understood in pp)– iterative cone 0.5: use corrections derived in pp (and

checked with pp data, including dijet asymmetry)

– anti-kT cone 0.3 with particle flow, heavy ion tracking: derive corrections using PYTHIA pp simulations ONLY

• Remove soft background (next slide)• Particle Flow !=anisotropy, but is instead a method to

utilize all subdetectors to the finest granularity: based on reconstructing all stable particles in the event to create higher level objects (jets)

5


Iterative Pileup Subtraction (Event by Event)

6

ϕ

η

2) Run IC5 jet finder on subtracted towers

ϕ

η

4) Re-run IC5 jet finder on subtracted towers

Eur. Phys. J. C 50 (2007) 117

ϕ

η

1) Calculate background in ieta slices

ϕ

η

3) Re-calculate background excluding jets

Exclude jets pT>10 GeV/c

ETtower-ETtower(η)-σTtower(η)

ETtower-ETtower(η)-σTtower(η)

Original towers


Background Studies• Study PYTHIA embedded into MinBias PbPb data• Study PYTHIA embedded in HYDJET

– See same jet finding resolution for both

• Study background fluctuations with MC and data– Agree closely, differences included in systematic

• Extra background distributed from quenching added to systematic

• Background subtraction method used removes most low pT content before it can contribute to jet– Soft fluctuations in background contribute little

– High pT fluctuations understood in jet resolution studies

7


Jet Efficiency and Dijet “Mismatch” Rate

8

Efficiency: fraction of reconstructed

jets which match a generator jet in

position

• Require leading jet pT> 100 GeV/c

• How often is an away-side jet not the

true dijet partner?

• Count all away-jets per leading jet which

do not match to PYTHIA jet

Smaller cone size less sensitive to background


Inclusive Jet Performance in PbPb

9

Resolution: σ of (reconstructed jet pT)/(generator level jet pT) for matched jets in ΔRResponse: Mean of (reconstructed jet pT)/(generator level jet pT) for matched jets in position ΔR

Particle flow improves response, especially at low pT

Pb Pb PbPb


Finding Dijets in PbPb Collisions• Trigger on jet collisions (35U or 50U)

– iterative cone 0.5 with iterative pileup subtraction in trigger

– U means energy before pT, η corrections applied

• Make sure they are minimum bias events– Also remove uncharacteristic detector signal events

• Select dijets with choices based on performance of jet finder in simulations, and trigger efficiency– anti-kT particle flow, iterative pileup subtraction

• leading pT>100 GeV/c, subleading pT>40 GeV/c

– iterative cone 0.5 calorimeter jet, iterative pileup subtraction

• leading pT>120 GeV/c, subleading pT>50 GeV/c

– and |η|<2; Δϕ1,2 > 2π/310


Finding Dijets in PbPb Collisions II• Check some fraction by eye in event display

11


Checking for Modification by PbPb

12

CMS: arXiv:1102.1957

Pb Pb PbPb

Note: spectra

not unfolded

Similar results

found with anti-kT3,particle

flowThe propagation of high pT partons in a dense nuclear medium does not lead to a visible angular decorrelation


Dijet pT Asymmetry

13

Pb Pb

PbPb

balanced dijets

unbalanced dijets

Similar results

found with anti-kT3,particle

flow

Parton energy loss is observed as a pronounced energy imbalance in reconstructed dijets



Dijet “Balanced” Fraction

14

partN0 50 100 150 200 250 300 350 400

< 0

.15)

J(A B

R

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7=2.76 TeVNNsPbPb

PYTHIAPYTHIA+DATA

CMS

> 120 GeV/cT,1

p

-1bµL dt = 6.7 ∫


Suppression clear outside systematic

uncertainty

0.15 ismedian AJ value from PYTHIA

RB(AJ) also includes apparent

'mono-jet' events

BalancedAll other events

Christof Roland 11 Quark Matter 2011, Annecy

!"12(rad)

Jet Angular Correlation

CalorimeterJets

PbPb PbPb PbPb PbPbpp

PbPb PbPb PbPbPbPb PbPbPbPb

R=0.5

Iterative Cone

1st lesson learned:

The propagation of high pT partons in a dense nuclear

medium does not lead to a visible angular decorrelation


!"12(rad)

Jet Angular Correlation

CalorimeterJets

PbPb PbPb PbPb PbPbpp

PbPb PbPb PbPbPbPb PbPbPbPb

R=0.5

Iterative Cone

1st lesson learned:

The propagation of high pT partons in a dense nuclear

medium does not lead to a visible angular decorrelation

Marguerite Tonjes (UMD) HPHD, Palaiseau, May 30 2011 15

Comparing the ATLAS and CMS dijet selection pT hat > 30 GeV

ATLAS Selection Pthat > 30 GeV

CMS Selection Pthat > 30 GeV

ATLAS vs CMS Dijet selection

• With the higher jet thresholds used for the CMS paper we are less sensitive to background fluctuations

– ATLAS 100/20, CMS: 120/50 for leading/sub-leading

Slide added from backup per morning’s discussion


Where Does the Missing Jet Energy Go?

16

• A large dijet energy imbalance is seen

in the calorimeters

• By using the track information, we have

an opportunity to do the first in-depth

studies of where the energy goes

• Look at sum of tracks near jet cone

• Investigate missing momentum using all

charged particle tracks


Jet-Track Correlations

17

Look at the sum pT of charged tracks in 3 different pT ranges

Plot against ΔR from the jet axis for both the leading

and subleading jet

Baseline is PYTHIA

+HYDJET where generator

information is available for all

charged particles

Background (Underlying Event) is subtracted using a cone at same ϕ, but

reflected in η (η ➞ -η)

pT distribution of tracks found in a ring of ΔR = √(Δϕ2 +Δη2), and width 0.08 around jet axes, then summed over all selected jets

jet2

cartoon

Σjets jet1



Asymmetry Dependence of Fragmentation

18


AJ

balanced jets unbalanced jets

Note: sum of tracks

Enhancement of low pT tracks at large cone,0.8 not enough to balance momentum


Missing pT||

• Explore momentum balance to low pT over all angles• Projection of pT onto leading jet axis:

• Defined such that tracks on away side give a positive contribution

• Calculated for all tracks with pT>0.5 GeV/c and |η|<2.4, and in various pT ranges

• Averaged over events• Allows us to see which pT range carries the balance of

the jet momentum• Note this is a sum of differences, we are interested in the direction of

excess (towards or away from leading jet)– Tracks could cancel out in some region

• No background subtraction needed19


Missing-pT||

arXiv:1102.1957 [nucl-ex]

0-30% Central PbPb


Missing pT||:

excess awayfrom leading jet

excess towardsleading jet

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

(a)

PYTHIA+HYDJET

30-100%

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40CMS

=2.76 TeVNNsPb+Pb -1bµL dt = 6.7 ∫

30-100%(c)

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

0.1 0.2 0.3 0.4

-40

-20

0

20

40 > 0.5 GeV/c

0-30%(b)

> 120GeV/cT,1

p

> 50GeV/cT,2p

π32> 1,2φΔ | < 1.61,2η|

0.1 0.2 0.3 0.4

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

0-30%(d)

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40


<pT||> vs. AJ

20

• For all tracks of pT> 0.5 GeV/c: momentum balance recoveredPb Pb PbPb

/

excess away from leading jet

excess towards leading jet

balanced dijets

unbalanced dijets

All tracks in event used

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

(a)

PYTHIA+HYDJET

30-100%

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40CMS


30-100%(c)

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

0.1 0.2 0.3 0.4

-40

-20

0

20

40 > 0.5 GeV/c

0-30%(b)

> 120GeV/cT,1

p

> 50GeV/cT,2p

π32> 1,2φΔ | < 1.61,2η|

0.1 0.2 0.3 0.4

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

0-30%(d)

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

Data

MC

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

(a)

PYTHIA+HYDJET

30-100%

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40CMS


30-100%(c)

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

0.1 0.2 0.3 0.4

-40

-20

0

20

40

> 0.5 GeV/c0.5 - 1.0 GeV/c1.0 - 2.0 GeV/c2.0 - 4.0 GeV/c4.0 - 8.0 GeV/c> 8.0 GeV/c

0-30%(b)

> 120GeV/cT,1

p

> 50GeV/cT,2p

π32> 1,2φΔ | < 1.61,2η|

0.1 0.2 0.3 0.4

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

0-30%(d)

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

(a)

PYTHIA+HYDJET

30-100%

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40CMS


30-100%(c)

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

0.1 0.2 0.3 0.4

-40

-20

0

20

40


0-30%(b)

> 120GeV/cT,1

p

> 50GeV/cT,2p

π32> 1,2φΔ | < 1.61,2η|

0.1 0.2 0.3 0.4

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

0-30%(d)

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

(a)

PYTHIA+HYDJET

30-100%

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40CMS


30-100%(c)

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

0.1 0.2 0.3 0.4

-40

-20

0

20

40


0-30%(b)

> 120GeV/cT,1

p

> 50GeV/cT,2p

π32> 1,2φΔ | < 1.61,2η|

0.1 0.2 0.3 0.4

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

0-30%(d)

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

(a)

PYTHIA+HYDJET

30-100%

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40CMS


30-100%(c)

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

0.1 0.2 0.3 0.4

-40

-20

0

20

40


0-30%(b)

> 120GeV/cT,1

p

> 50GeV/cT,2p

π32> 1,2φΔ | < 1.61,2η|

0.1 0.2 0.3 0.4

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

0-30%(d)

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

Only direction information is

towards or away from leading jet

Classify events by dijet asymmetry (AJ)

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

(a)

PYTHIA+HYDJET

30-100%

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40CMS


30-100%(c)

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

0.1 0.2 0.3 0.4

-40

-20

0

20

40> 0.5 GeV/c

> 8.0 GeV/c

0-30%(b)

> 120GeV/cT,1

p

> 50GeV/cT,2p

π32> 1,2φΔ | < 1.61,2η|

0.1 0.2 0.3 0.4

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

0-30%(d)

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40


<pT||> vs. AJ

21

High pT particles: Excess momentum towards leading jet with increasing AJ

Pb Pb PbPb

/

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

(a)

PYTHIA+HYDJET

30-100%

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40CMS


30-100%(c)

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

0.1 0.2 0.3 0.4

-40

-20

0

20

40> 0.5 GeV/c

> 8.0 GeV/c

0-30%(b)

> 120GeV/cT,1

p

> 50GeV/cT,2p

π32> 1,2φΔ | < 1.61,2η|

0.1 0.2 0.3 0.4

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

0-30%(d)

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40



balanced dijets

unbalanced dijets

Data

MC

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

(a)

PYTHIA+HYDJET

30-100%

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40CMS


30-100%(c)

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

0.1 0.2 0.3 0.4

-40

-20

0

20

40


0-30%(b)

> 120GeV/cT,1

p

> 50GeV/cT,2p

π32> 1,2φΔ | < 1.61,2η|

0.1 0.2 0.3 0.4

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

0-30%(d)

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

(a)

PYTHIA+HYDJET

30-100%

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40CMS


30-100%(c)

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

0.1 0.2 0.3 0.4

-40

-20

0

20

40


0-30%(b)

> 120GeV/cT,1

p

> 50GeV/cT,2p

π32> 1,2φΔ | < 1.61,2η|

0.1 0.2 0.3 0.4

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

0-30%(d)

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

(a)

PYTHIA+HYDJET

30-100%

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40CMS


30-100%(c)

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

0.1 0.2 0.3 0.4

-40

-20

0

20

40


0-30%(b)

> 120GeV/cT,1

p

> 50GeV/cT,2p

π32> 1,2φΔ | < 1.61,2η|

0.1 0.2 0.3 0.4

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

0-30%(d)

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

(a)

PYTHIA+HYDJET

30-100%

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40CMS


30-100%(c)

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

0.1 0.2 0.3 0.4

-40

-20

0

20

40


0-30%(b)

> 120GeV/cT,1

p

> 50GeV/cT,2p

π32> 1,2φΔ | < 1.61,2η|

0.1 0.2 0.3 0.4

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

0-30%(d)

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

There probably were some

high pT particles in

away side, just no Excess

(sum of differences)

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

(a)

PYTHIA+HYDJET

30-100%

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40CMS


30-100%(c)

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

0.1 0.2 0.3 0.4

-40

-20

0

20

40


0-30%(b)

> 120GeV/cT,1

p

> 50GeV/cT,2p

π32> 1,2φΔ | < 1.61,2η|

0.1 0.2 0.3 0.4

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

0-30%(d)

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40


<pT||> vs. AJ

22

Pb Pb PbPb

/

balanced dijets

unbalanced dijets



Central PbPb: missing pT found in low pT in away side, mainly carried by tracks < 2 GeV/c

Data

MC

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

(a)

PYTHIA+HYDJET

30-100%

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40CMS


30-100%(c)

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

0.1 0.2 0.3 0.4

-40

-20

0

20

40


0-30%(b)

> 120GeV/cT,1

p

> 50GeV/cT,2p

π32> 1,2φΔ | < 1.61,2η|

0.1 0.2 0.3 0.4

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

0-30%(d)

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

(a)

PYTHIA+HYDJET

30-100%

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40CMS


30-100%(c)

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

0.1 0.2 0.3 0.4

-40

-20

0

20

40


0-30%(b)

> 120GeV/cT,1

p

> 50GeV/cT,2p

π32> 1,2φΔ | < 1.61,2η|

0.1 0.2 0.3 0.4

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

0-30%(d)

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

(a)

PYTHIA+HYDJET

30-100%

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40CMS


30-100%(c)

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

0.1 0.2 0.3 0.4

-40

-20

0

20

40


0-30%(b)

> 120GeV/cT,1

p

> 50GeV/cT,2p

π32> 1,2φΔ | < 1.61,2η|

0.1 0.2 0.3 0.4

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

0-30%(d)

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

(a)

PYTHIA+HYDJET

30-100%

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40CMS


30-100%(c)

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

0.1 0.2 0.3 0.4

-40

-20

0

20

40


0-30%(b)

> 120GeV/cT,1

p

> 50GeV/cT,2p

π32> 1,2φΔ | < 1.61,2η|

0.1 0.2 0.3 0.4

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

0-30%(d)

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

MC: missing pT mostly carried by tracks > 2 GeV/c

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40 PYTHIA+HYDJET 0-30%

In-ConeR<0.8Δ

(a)

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40CMS 0-30%


In-Cone

R<0.8Δ

(c)

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

0.1 0.2 0.3 0.4

-40

-20

0

20

40 > 0.5 GeV/c

Out-of-Cone0.8≥RΔ

(b)

> 120GeV/cT,1

p

> 50GeV/cT,2p

π65> 1,2φΔ | < 1.61,2η|

0.1 0.2 0.3 0.4

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

Out-of-Cone

0.8≥RΔ

(d)

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40


Radial Dependence of <pT||>

23

/

PbPb

Out-of-cone: balance of momentum found

In-cone reproduces Calorimeter jet asymmetry

balanced dijets unbalanced dijetsCMS: arXiv:1102.1957



Out-of-ConeΔR≥0.8

In-ConeΔR<0.8

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20


In-ConeR<0.8Δ

(a)

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40CMS 0-30%


In-Cone

R<0.8Δ

(c)

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

0.1 0.2 0.3 0.4

-40

-20

0

20

40 > 0.5 GeV/c


(b)

> 120GeV/cT,1

p

> 50GeV/cT,2p

π65> 1,2φΔ | < 1.61,2η|

0.1 0.2 0.3 0.4

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

Out-of-Cone

0.8≥RΔ

(d)

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20


In-ConeR<0.8Δ

(a)

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40CMS 0-30%


In-Cone

R<0.8Δ

(c)

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

0.1 0.2 0.3 0.4

-40

-20

0

20

40 > 0.5 GeV/c


(b)

> 120GeV/cT,1

p

> 50GeV/cT,2p

π65> 1,2φΔ | < 1.61,2η|

0.1 0.2 0.3 0.4

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

Out-of-Cone

0.8≥RΔ

(d)

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

Data

MC

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20


In-ConeR<0.8Δ

(a)

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40CMS 0-30%


In-Cone

R<0.8Δ

(c)

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

0.1 0.2 0.3 0.4

-40

-20

0

20

40 > 0.5 GeV/c


(b)

> 120GeV/cT,1

p

> 50GeV/cT,2p

π65> 1,2φΔ | < 1.61,2η|

0.1 0.2 0.3 0.4

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

Out-of-Cone

0.8≥RΔ

(d)

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20


In-ConeR<0.8Δ

(a)

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40CMS 0-30%


In-Cone

R<0.8Δ

(c)

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

0.1 0.2 0.3 0.4

-40

-20

0

20

40 > 0.5 GeV/c


(b)

> 120GeV/cT,1

p

> 50GeV/cT,2p

π65> 1,2φΔ | < 1.61,2η|

0.1 0.2 0.3 0.4

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

Out-of-Cone

0.8≥RΔ

(d)

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20


In-ConeR<0.8Δ

(a)

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40CMS 0-30%


In-Cone

R<0.8Δ

(c)

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

0.1 0.2 0.3 0.4

-40

-20

0

20

40> 0.5 GeV/c

> 8.0 GeV/c


(b)

> 120GeV/cT,1

p

> 50GeV/cT,2p

π65> 1,2φΔ | < 1.61,2η|

0.1 0.2 0.3 0.4

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

Out-of-Cone

0.8≥RΔ

(d)

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40



24

/

PbPb

PbPb data: different high pT

MC balance is found out-of-cone but at higher pT (3rd jet)




balanced dijets unbalanced dijets


In-ConeΔR<0.8

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20


In-ConeR<0.8Δ

(a)

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40CMS 0-30%


In-Cone

R<0.8Δ

(c)

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

0.1 0.2 0.3 0.4

-40

-20

0

20

40 > 0.5 GeV/c


(b)

> 120GeV/cT,1

p

> 50GeV/cT,2p

π65> 1,2φΔ | < 1.61,2η|

0.1 0.2 0.3 0.4

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

Out-of-Cone

0.8≥RΔ

(d)

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20


In-ConeR<0.8Δ

(a)

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40CMS 0-30%


In-Cone

R<0.8Δ

(c)

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

0.1 0.2 0.3 0.4

-40

-20

0

20

40 > 0.5 GeV/c


(b)

> 120GeV/cT,1

p

> 50GeV/cT,2p

π65> 1,2φΔ | < 1.61,2η|

0.1 0.2 0.3 0.4

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

Out-of-Cone

0.8≥RΔ

(d)

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40MC

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20


In-ConeR<0.8Δ

(a)

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40CMS 0-30%


In-Cone

R<0.8Δ

(c)

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

0.1 0.2 0.3 0.4

-40

-20

0

20

40 > 0.5 GeV/c


(b)

> 120GeV/cT,1

p

> 50GeV/cT,2p

π65> 1,2φΔ | < 1.61,2η|

0.1 0.2 0.3 0.4

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

Out-of-Cone

0.8≥RΔ

(d)

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20


In-ConeR<0.8Δ

(a)

0.1 0.2 0.3 0.4

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eV/c

)Tp<

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40CMS 0-30%


In-Cone

R<0.8Δ

(c)

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

0.1 0.2 0.3 0.4

-40

-20

0

20

40 > 0.5 GeV/c


(b)

> 120GeV/cT,1

p

> 50GeV/cT,2p

π65> 1,2φΔ | < 1.61,2η|

0.1 0.2 0.3 0.4

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

Out-of-Cone

0.8≥RΔ

(d)

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40Data

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20


In-ConeR<0.8Δ

(a)

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40CMS 0-30%


In-Cone

R<0.8Δ

(c)

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

0.1 0.2 0.3 0.4

-40

-20

0

20

40



(b)

> 120GeV/cT,1

p

> 50GeV/cT,2p

π65> 1,2φΔ | < 1.61,2η|

0.1 0.2 0.3 0.4

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

Out-of-Cone

0.8≥RΔ

(d)

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40



25

/

PbPb

PbPb data: in-cone excess of high-pT tracks is balanced by out-of-cone low-pT tracks




0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20


In-ConeR<0.8Δ

(a)

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40CMS 0-30%


In-Cone

R<0.8Δ

(c)

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

0.1 0.2 0.3 0.4

-40

-20

0

20

40 > 0.5 GeV/c


(b)

> 120GeV/cT,1

p

> 50GeV/cT,2p

π65> 1,2φΔ | < 1.61,2η|

0.1 0.2 0.3 0.4

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

Out-of-Cone

0.8≥RΔ

(d)

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20


In-ConeR<0.8Δ

(a)

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40CMS 0-30%


In-Cone

R<0.8Δ

(c)

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

0.1 0.2 0.3 0.4

-40

-20

0

20

40 > 0.5 GeV/c


(b)

> 120GeV/cT,1

p

> 50GeV/cT,2p

π65> 1,2φΔ | < 1.61,2η|

0.1 0.2 0.3 0.4

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

Out-of-Cone

0.8≥RΔ

(d)

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

balanced dijets unbalanced dijets

MC

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20


In-ConeR<0.8Δ

(a)

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40CMS 0-30%


In-Cone

R<0.8Δ

(c)

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

0.1 0.2 0.3 0.4

-40

-20

0

20

40 > 0.5 GeV/c


(b)

> 120GeV/cT,1

p

> 50GeV/cT,2p

π65> 1,2φΔ | < 1.61,2η|

0.1 0.2 0.3 0.4

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

Out-of-Cone

0.8≥RΔ

(d)

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

0.1 0.2 0.3 0.4

> (G

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In-ConeR<0.8Δ

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0.1 0.2 0.3 0.4

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eV/c

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0

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40

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-40

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0

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In-Cone

R<0.8Δ

(c)

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-40

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0

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0.1 0.2 0.3 0.4

-40

-20

0

20

40 > 0.5 GeV/c


(b)

> 120GeV/cT,1

p

> 50GeV/cT,2p

π65> 1,2φΔ | < 1.61,2η|

0.1 0.2 0.3 0.4

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

Out-of-Cone

0.8≥RΔ

(d)

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40


In-ConeΔR<0.8

Data

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!(;<%(%)%.3/(,.5=#7%(#)'#8%

((((25.%(.%'%1+7%'($%&'(#)(,,

>%&?#)(>#710@(ABC;D(((((((((((((((((((((((E%&(F.031%)&0&#5)(F6)2&#5)'(#)(*+*+


Learned from <pT||>

26

/The momentum difference in the dijet is

balanced by low pT particles at large angles relative to the away side jet axis



Out-of-ConeΔR≥0.80.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20


In-ConeR<0.8Δ

(a)

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40CMS 0-30%


In-Cone

R<0.8Δ

(c)

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

0.1 0.2 0.3 0.4

-40

-20

0

20

40



(b)

> 120GeV/cT,1

p

> 50GeV/cT,2p

π65> 1,2φΔ | < 1.61,2η|

0.1 0.2 0.3 0.4

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

Out-of-Cone

0.8≥RΔ

(d)

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

0.1 0.2 0.3 0.4>

(GeV

/c)

Tp<

-40

-20

0

20


In-ConeR<0.8Δ

(a)

0.1 0.2 0.3 0.4>

(GeV

/c)

Tp<

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40CMS 0-30%


In-Cone

R<0.8Δ

(c)

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

0.1 0.2 0.3 0.4

-40

-20

0

20

40



(b)

> 120GeV/cT,1

p

> 50GeV/cT,2p

π65> 1,2φΔ | < 1.61,2η|

0.1 0.2 0.3 0.4

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

Out-of-Cone

0.8≥RΔ

(d)

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

balanced dijets unbalanced dijets0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20


In-ConeR<0.8Δ

(a)

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40CMS 0-30%


In-Cone

R<0.8Δ

(c)

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

0.1 0.2 0.3 0.4

-40

-20

0

20

40



(b)

> 120GeV/cT,1

p

> 50GeV/cT,2p

π65> 1,2φΔ | < 1.61,2η|

0.1 0.2 0.3 0.4

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

Out-of-Cone

0.8≥RΔ

(d)

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20


In-ConeR<0.8Δ

(a)

0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40CMS 0-30%


In-Cone

R<0.8Δ

(c)

JA0.1 0.2 0.3 0.4

> (G

eV/c

)Tp<

-40

-20

0

20

40

0.1 0.2 0.3 0.4

-40

-20

0

20

40



(b)

> 120GeV/cT,1

p

> 50GeV/cT,2p

π65> 1,2φΔ | < 1.61,2η|

0.1 0.2 0.3 0.4

-40

-20

0

20

40

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40

Out-of-Cone

0.8≥RΔ

(d)

JA0.1 0.2 0.3 0.4

-40

-20

0

20

40


Parton Fragmentation

27

• Momentum Fraction z• characteristic of the parton showering process • z=pT

hadron/pTparton


ξ=ln(1/z)

28


!=ln(1/z) Representation

z =

0.5

z =

0.1 Soft particles

pT < 1GeV/c


ξ=ln(1/z)

29


z =

0.5

z =

0.1 Soft particles

pT < 1GeV/c

!=ln(1/z) Representation

• Eliminate the underlying event contribution, pT > 4GeV/c

• Select particles in a "R=0.3 cone

Select particles with pT > 4GeV/c to eliminate the underlying event contribution


Particle Flow and Fragmentation

• Jet energy corrections are derived from inclusive jets in PYTHIA

• In real data response may differ due to:- Poor description of fragmentation

- Different fraction of quark vs gluons

- Possible jet quenching effects

30

Corrected response to quark and gluon jetswith heavy-ion Particle Flow configuration

Particle flow jets show reduced sensitivity to the fragmentation pattern


Fragmentation Functions in Data

31

• Particle Flow Jet Reconstruction– Anti kT, R=0.3– Fully efficient for pT > 40GeV/c– Good control of jet pT scale– Applied in pp and PbPb

• Dijet selection– pT

Jet1>100GeV/c– pT

Jet2>40GeV/c– Δφ>2π/3

• Compare Leading and Subleading Jet

pp 2.76 TeV Data from 2011


Fragmentation Functions

CMS-PAS-HIN-11-004

http://cdsweb.cern.ch/record/1354531?ln=en



Fragmentation Functions, pp & PbPb

32

pp as reference for PbPb: Smear pp to PbPb jet pT resolutionReweight jet pT spectrum to match PbPb


Fragmentation Functions

Christof Roland30Quark Matter 2011, Annecy

Fragmentation Functions, pp and PbPb

PbPbPbPbPbPbPbPb

pp as reference for PbPb: Smear pp to PbPb jet pT resolution

Reweight jet pT spectrum to match PbPb

pTJet (GeV/c)

dN

/dp

TJe

t

pTJet (GeV/c) pT

Jet (GeV/c)

CMS-PAS-HIN-11-004




Fragmentation Functions, pp & PbPb

33

Reconstructed PbPb leading and subleading jets fragment like jets of corresponding energy from pp collisions

CMS-PAS-HIN-11-004




Select by Dijet Imbalance

34

AJ

CMS-PAS-HIN-11-004




Note Different Jet pT Distributions

35CMS-PAS-HIN-11-004




Dijet Possibilities• Symmetric jets:

– Neither jet interacted with medium: emitted at surface

– Both jets quenched in medium ~ similar path length

– Medium transparent to jets

• Not the case, because we do observe quenching

• Asymmetric jets:– Jets had different path lengths, but both interacted with medium– One jet on surface (no interaction), other went through the

medium– Something not yet considered... ?

36


Fragmentation Function Lesson• The hard part of the fragmentation function gives the

same results for leading, subleading, symmetric, and balanced jets

• Any issues with surface bias or path length are not important for this measurement: the result is the same

37

Fragmentation pattern independent of energy lost in mediumConsistent with partons fragmenting in vacuum


Summary• Angular correlation of partons not affected by the

medium– Favors multiple soft interactions with medium

• Large dijet momentum imbalance observed– Direct observation of parton energy loss

• Momentum difference in the dijet balanced by low pT particles at large angles relative to the away side jet

• Measurement of jet fragmentation functions in PbPb– Jets in pp and in PbPb show a similar pattern

• High pT fragmentation pattern is independent of the energy lost in the medium

– Consistent with partons fragmenting in vacuum

38


Stop to Reflect

39

Musée D’Orsay 2008, photo by M. Tonjes


Fin


PbPb √sNN = 2.76 TeV


Calorimeter Imbalance Comparison

41

Comparison to Calorimeter Jet Imbalance

Matthew Nguyen (CERN) Jet Reconstruction with Particle Flow in HI Collisions 20

pp 50-100% 30-50%

20-30% 10-20% 0-10%

CMS Preliminary

Results are in good agreement with previous calorimeter measurement

PbPb @ 2.76 TeV pp @ 7 TeV (Calo) pp @ 2.76 TeV (PF)

Results are in good agreement with previous Calorimeter jet measurement


Dijet Imbalance ak3

42

Dijet Imbalance for PF Jets

Matthew Nguyen (CERN) Jet Reconstruction with Particle Flow in HI Collisions 19

Excess of unbalanced jets persists with PF, R=0.3 dijet selection


Jet-Track Correlations

43

Look at the sum pT of charged

tracks in 3 different pT

ranges

Plot against ΔR from the jet axis for both the leading

and subleading jet

Background (Underlying Event) is subtracted using a cone at same ϕ, but

reflected in η (η ➞ -η)

pT distribution of tracks found in a ring of ΔR = √(Δϕ2 +Δη2), and width 0.08 around jet axes, then summed over all selected jets

jet2

Σjets jet1


MCSeparate

into bins of dijet

asymmetry


Jet-Track Background• Background evaluated within R=0.8 cone symmetric about η• Avoids ϕ dependent variations due to detector effects and

event anisotropy• Single jets required to be within 0.8 < |η|< 1.6

– To contain 0.8 radius of tracks around jet axis

44

Edward Wenger - Slide

η-Reflection Method

30

Intro to Heavy Ions Analysis Methods Calorimeter Jet Imbalance Energy balance in charged tracks

- Background evaluated within R=0.8 cone symmetric about η- Avoids φ-dependent variations due to detector effects and hydrodynamic flow- Single jets required to be in 0.8 < |η| < 1.6

Signal Jet Cone

η-reflectedBackground Cone

Dijet Partner

Ed Wenger, Fermilab Seminar, 28 Jan. 2011


Asymmetry Dependence of Fragmentation

45

AJ

MC

Data



Linear scale Similar results found with anti-kt3, particle flow


Dijet Back-to-Back Fraction

46

partN0 50 100 150 200 250 300 350 400

> 3

.026

)12φ

Δ( BR

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7=2.76 TeVNNsPbPb

PYTHIAPYTHIA+DATA

CMS

> 120 GeV/cT,1

p

> 50 GeV/cT,2

p

-1bµL dt = 6.7 ∫

Δϕ12)

Back-to-BackAll other dijet pairs

RB(Δϕ): fraction of dijets well

balanced in azimuthal

angle

3.026 is median

value from PYTHIA

No angular decorrelation

beyond systematic uncertainties



Leading Jet pT dependence

47

120 140 160 180 200 220 240

>T,

1)/p

T,2

-pT,

1<(

p

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0.55

0.6

30-100%

(a)

(GeV/c)T

Leading Jet p120 140 160 180 200 220 240

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0.55

0.6

10-30%

(b) > 120 GeV/cT,1

p

> 50 GeV/cT,2

p

π32 >

12φΔ

120 140 160 180 200 220 2400.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0.55

0.6

=2.76 TeVNNsPb+Pb

PYTHIA

embedded PYTHIA

CMS-1bµL dt = 6.7 ∫

0-10%

(c)

120 140 160 180 200 220 240

>T,

1)/p

T,2

-pT,

1<(

p

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0.55

0.6

30-100%

(a)

(GeV/c)T

Leading Jet p120 140 160 180 200 220 240

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0.55

0.6

10-30%

(b) > 120 GeV/cT,1

p

> 50 GeV/cT,2

p

π32 >

12φΔ

120 140 160 180 200 220 2400.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0.55

0.6

=2.76 TeVNNsPb+Pb

PYTHIA

embedded PYTHIA

CMS-1bµL dt = 6.7 ∫

0-10%

(c)


Pb Pb PbPb

Fractional imbalance varies little with leading jet pT, even at highest leading jet pT


Iterative Pileup Subtraction Algorithm1. Make a tower of ECAL + HCAL energy2. Find average tower ET(η) and σT(η) at each η

ring in each event• Recalculate tower energy by subtracting mean energy

and dispersion, dropping negative towers3. Find jets with iterative cone algorithm and

corrected tower energy (ET> 10 GeV pedestal cut)4. Using original tower energy, calculate ET and σT

for those towers outside of the jets • Correct tower energy again, dropping negative towers

5. Find jets with iterative cone algorithm with current background subtracted energies

48


Parton Energy Loss

49


Parton Energy Loss

• Key ingredients of parton energy loss calculations:

• Components sensitive to– medium properties

– where and when the process happens

• Reconstructed dijets– full final state of hard scatterings

– study the individual components contributing

to the parton energy loss

Parton propagation in the nuclear medium

Radiative- Collisional-energy loss

Parton Showering

(Fragmentation)


What is Particle Flow?Hint: It’s got nothing to do with hydrodynamics

Particle flow reconstructs all stable particle in the event: h+/-, γ, h0, e, µ

• On average jets are: ~ 65% charged hadrons, ~ 25% photons, ~ 10 % neutral hadrons • Using the silicon tracker (vs. HCAL) to measure charged hadrons

o Improves resolution, avoids non-linearity o Decreases sensitivity to the fragmentation pattern of jets

• Used extensively in ALEPH, CMS and proposed for the ILC

50


Edward Wenger - Slide

PYTHIA Momentum Balance

22

Intro to Heavy Ions Analysis Methods Calorimeter Jet Imbalance Energy balance in charged tracks

For the ~10% of unbalanced PYTHIA dijets (Aj > 0.3), a 3rd jet provides most of momentum balance

pp

PYTHIA Momentum Balance

Winter Workshop on Nuclear Dynamics, 2011


Different Gaussian smearing

Cacciari, Salam, Soyez: arXiv: 1101.2878


PYTHIA+HYDJET

Cacciari, Salam, Soyez: arXiv: 1101.2878


PYTHIA + Fluctuations

• Apply ATLAS's selection on the smeared jets:– pT1 > 100 GeV, pT2 > 25 GeV, dphi > pi/2– GenJet pT > 0 GeV

• Applying a gaussian smearing to PYTHIA we can reproduce the results of the Salam paper.


Peak moving, widening

Ingredients

– Gaussian smearing of the leading jet makes the AJ distribution wider

• Select only Jets above pT = 3GeV

GaussianSmearing

True dijet

Smeared true dijet


Squeeze due toMany low pT jets

Ingredients II

– Adding many low pT jets, smeared to higher pT than the true away side jet, compresses the AJ distribution

• Tested by adding the 0-3GeV jets in the analysis

Smeared true dijet

Reconstructed dijet

Add low pT jets

Smear low pT jets

Select 2 leading jets


Number of genjets:Black: GenJet Pt >3 GeV Red: GenJet Pt >0 GeV

Ingredients III

• Balanced dijets + fluctuations can fake a wide AJ distribution– Needs a very large number (~100) of low pT jets per event

• Remember: dn/dηch ~6 in |eta| < 5 -> ~60 charged particles/event– And a very large σ (20GeV) for the smearing

• based on a Gaussian fit to the low pT part of the ATLAS min bias jet spectrum• ATLAS reports σ ~8 GeV for their background fluctuations


Hydjet

– The HYDJET AJ distribution is created by the same mechanism• The hard part of a central HYDJET event consists of ~300 unquenched PYTHIA

events with pThat of ~7GeV• Low pT jets smear the leading jets by superposition and cause a combinatorial

problem

Smeared true dijet

Reconstructed dijet

Add multi jet event

Select 2 leading jets


Is unquenched Hydjet a good background reference?

• PYTHIA embedded in real data, including all background fluctuations and resolution effects does not show a widened AJ distribution

– A cross check with pThat = 30GeV embedded in a large min bias data sample gave an identical reference distributions

– RAA shows a strong hadron suppression at 5-10GeV

– Low pT jets seem to be strongly suppressed

Aj

Eve

nt fr

actio

n - PYTHIA + Data

!"#$%&'()#$*+,-&(.//(+0('+11&$&0*(,&0*$#-+*+&2

345&067+&(8&&9:;<=((((((((((((((((((((>?,-&#$(:@'+1+,#*+@0(1#,*@$2(1$@A(*"&(!:B(&C)&$+A&0*(((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((D?#$E(:#**&$(3FGG(

HF6IFJ KF6HFJ LF6KFJ

GF6LFJ K6GFJ F6KJ

(((((( (((((( ((((((

!(M+)(2*$?,*?$&('&N&-@)+0%(#2(#(1?0,*+@0(@1(,&0*$#-+*O!(.

//(+0,$&#2&2(#2(#(1?0,*+@0(@1()

<(+0(*"&()

<PGF(Q&RS,($&%+@0

!"#$%&'()#$*+,-&(.//(+0('+11&$&0*(,&0*$#-+*+&2

345&067+&(8&&9:;<=((((((((((((((((((((>?,-&#$(:@'+1+,#*+@0(1#,*@$2(1$@A(*"&(!:B(&C)&$+A&0*(((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((D?#$E(:#**&$(3FGG(


GF6LFJ K6GFJ F6KJ

(((((( (((((( ((((((

!(M+)(2*$?,*?$&('&N&-@)+0%(#2(#(1?0,*+@0(@1(,&0*$#-+*O!(.

//(+0,$&#2&2(#2(#(1?0,*+@0(@1()

<(+0(*"&()

<PGF(Q&RS,($&%+@0

!"#$%&'()#$*+,-&(.//(+0('+11&$&0*(,&0*$#-+*+&2

345&067+&(8&&9:;<=((((((((((((((((((((>?,-&#$(:@'+1+,#*+@0(1#,*@$2(1$@A(*"&(!:B(&C)&$+A&0*(((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((D?#$E(:#**&$(3FGG(


GF6LFJ K6GFJ F6KJ

(((((( (((((( ((((((

!(M+)(2*$?,*?$&('&N&-@)+0%(#2(#(1?0,*+@0(@1(,&0*$#-+*O!(.

//(+0,$&#2&2(#2(#(1?0,*+@0(@1()

<(+0(*"&()

<PGF(Q&RS,($&%+@0

TAA uncertainty


Comparing the ATLAS and CMS dijet selection pT hat > 30 GeV

ATLAS Selection Pthat > 30 GeV

CMS Selection Pthat > 30 GeV

ATLAS vs CMS Dijet selection

• With the higher jet thresholds used for the CMS paper we are less sensitive to background fluctuations

– ATLAS 100/20, CMS: 120/50 for leading/sub-leading


ATLAS input

• The large σ (20GeV) smearing is based on a Gaussian fit to the low pT part of the ATLAS min bias jet spectrum

• ATLAS reports σ ~8 GeV for their background fluctuations


20GeV smearing closure test


Centrality definition• Determined by the total

energy from both HF calorimeters

• Split minimum bias events into centrality bins

• Relate to <Npart> with calculation based on a Glauber model (nucleon-nucleon scattering)– Finite detector resolution

effects from fully simulated Monte Carlo AMPT events

63

Sum HF Energy (TeV)0 20 40 60 80 100 120 140 160

Frac

tion

of m

inim

um b

ias

even

ts

-510

-410

-310

-210

-110 Minimum Bias TriggerJet Trigger

50%

- 10

0%

30%

- 50

%

20%

- 30

%

10%

- 20

%

0%

- 10

%

=2.76 TeVNNsCMS PbPb (a)

CMS: arXiv:1102.1957M.L. Miller et al., Glauber modeling in high energy nuclear

collisions, Ann. Rev. Nucl. Part. Sci 57 (2007) 205

Pb PbPbPb

• Selecting rare processes (high pT jets): bias towards central collisions


Jet Energy Scale• Match reconstructed CaloJet to GenJet within a cone ΔR = 0.3 (ΔR = √(Δϕ2

+Δη2)) – CaloJet: jet reconstructed from calorimeter towers after detector simulation– GenJet: jet reconstructed from PYTHIA Generator particles

• Leading Jet pT,1 > 120 GeV/c, |η|<2 → for this analysis• Subleading Jet (in same event) pT,2 > 50 GeV/c, |η|<2 → for this analysis• Residual not used to correct energy, but is included in systematic uncertainty• PYTHIA (QCD dijet) + DATA (PbPb Minimum Bias)

64

100 150 200

>G

enJe

tT

/pC

aloJ

etT

<p

0.8

1

1.2

1.4

1.6 50-100% CMS(a)(a) CMS

(GeV/c)GenJetT

p100 150 200

)G

enJe

tT

/pC

aloJ

etT

(pσ

0

0.2

0.4

50-100%(d) 100 150 2000.8

1

1.2

1.4

1.6 20-30%(b) 20-30%(b)

(GeV/c)GenJetT

p100 150 2000

0.2

0.4

20-30%(e) 100 150 2000.8

1

1.2

1.4

1.6 0-10%(c)PYTHIA+DATALeading Jet ResponseSubleading Jet Response

(GeV/c)GenJetT

p100 150 2000

0.2

0.4

0-10%(f)Leading Jet Resolution

Subleading Jet Resolution

Resolution in p+p

100 150 200

>G

enJe

tT

/pC

aloJ

etT

<p

0.8

1

1.2

1.4

1.6 50-100% CMS(a)(a) CMS

(GeV/c)GenJetT

p100 150 200

)G

enJe

tT

/pC

aloJ

etT

(pσ

0

0.2

0.4

50-100%(d) 100 150 2000.8

1

1.2

1.4

1.6 20-30%(b) 20-30%(b)

(GeV/c)GenJetT

p100 150 2000

0.2

0.4

20-30%(e) 100 150 2000.8

1

1.2

1.4


(GeV/c)GenJetT

p100 150 2000

0.2

0.4



Resolution in p+p

iterativeCone R=0.5 with pileup subtraction



Jet Resolution• Match reconstructed CaloJet to GenJet within a cone ΔR = 0.3• Resolution is standard deviation of Gaussian CaloJet/GenJet

response• Resolution degraded by ~30% due to heavy-ion background in

most central events• PYTHIA (QCD dijet) + DATA (PbPb Minimum Bias)

65

100 150 200

>G

enJe

tT

/pC

aloJ

etT

<p

0.8

1

1.2

1.4

1.6 50-100% CMS(a)(a) CMS

(GeV/c)GenJetT

p100 150 200

)G

enJe

tT

/pC

aloJ

etT

(pσ

0

0.2

0.4

50-100%(d) 100 150 2000.8

1

1.2

1.4

1.6 20-30%(b) 20-30%(b)

(GeV/c)GenJetT

p100 150 2000

0.2

0.4

20-30%(e) 100 150 2000.8

1

1.2

1.4


(GeV/c)GenJetT

p100 150 2000

0.2

0.4



Resolution in p+p

CMSiterativeCone R=0.5 with

pileup subtraction



Jet Finding Efficiency• Match reconstructed CaloJet to GenJet within a cone ΔR = 0.3

• Fully efficient for leading jet selection (pT,1>120 GeV/c)

• High efficiency for subleading jet selection (pT,2> 50 GeV/c)

• PYTHIA (QCD dijet) + DATA (PbPb Minimum Bias)

66

(GeV/c)GenJetT

p50 100 150 200

Eff.

(Mat

ched

Rec

o/G

en)

0

0.2

0.4

0.6

0.8

1

1.2

1.4CMS(a)

30-100%

(GeV/c)GenJetT

p50 100 150 200

0

0.2

0.4

0.6

0.8

1

1.2

1.4PYTHIA+DATA

Leading JetSubleading Jet

(b)

10-30%

(GeV/c)GenJetT

p50 100 150 200

0

0.2

0.4

0.6

0.8

1

1.2

1.4(c)

0-10%



PbPb Collision with CMS

67

PbPb event displays showed easily identified

jets above the soft background.

CMS tracker & Calorimeters: side viewECAL: red, HCAL: blue


http://cdsweb.cern.ch/record/1309898?ln=enCalorimeter towers = ECAL+HCAL

Δη x Δϕ = 0.087 x 0.087




PbPb Collision with CMS

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CMS tracker & Calorimeters: end viewECAL: red, HCAL: blue






Edward Wenger - Slide 37

ATLAS Dijet Asymmetry

pT,1 > 100 GeVpT,2 > 25 GeVΔφ1,2 > π/2|ηjet| < 2.8

ATLAS Dijet Asymmetry

Winter Workshop on Nuclear Dynamics, 2011


ϕ definition (for <pT||>)

70

Looking down the beam axis

Jet1 axis

+x: south; ϕ=0

+y: up; ϕ=π/2

CMSConventions

ϕ=-π/2

z

ϕjet1 ~ 110 degrees)pT measured at surface of detector pependicular to beam axis

https://twiki.cern.ch/twiki/bin/view/CMS/CMSConventions



Pictoral <pT||> Example

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Jet1 axis

ϕjet1 ~ 110 degrees

calculate change in angle from leading jet

)

+y: ϕ=π/2

+x: ϕ=0

ϕtrack2

Δϕtrack1

-30 degrees

)

)

115 degrees

pT_track2 = 7 GeV/c

ϕ=-π/2

pT measured at surface of detector pependicular to beam axis


Pictoral <pT||> Example

72

Jet1 axisΔϕtrack2

)

-7*cos(5°)-2*cos(-140°)= -7*0.99+2*0.77

ϕjet1 110 degrees

Sum = -3.8 excess towards leading jet

calculatefull <pT||>example

)Δϕtrack1

ϕ=-π/2

+y: ϕ=π/2

+x: ϕ=0

(-30-110)=-140 degreespT_track1= 2 GeV/c

pT_track2 = 7 GeV/c(115-110)=5 degrees

)


Result of the cos(ϕtrack-ϕjet1)

73

Looking down the beam axis

Jet1 axis

+x: south; ϕ=0

+y: up; ϕ=π/2

CMSConventions

ϕ=-π/2

cos: -

cos: +

cos: -

cos: +

cos will give you:+ or -

perpendicular to jets axis




-pT,track cos(ϕtrack-ϕjet1)

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Jet1 axis

-pTcos(Δϕ): +

-pTcos(Δϕ): -

-pTcos(Δϕ): +

-pTcos(Δϕ): -

cos will give you:+ or -

multiply by-pT,quadrantsreverse sign

Defined asnegative towards leading

perpendicular to jets axis

Jet Measurements in PbPb Collisions with the CMS Detector · Marguerite Tonjes (UMD) HPHD,...

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Transcript of Jet Measurements in PbPb Collisions with the CMS Detector · Marguerite Tonjes (UMD) HPHD,...