Jet RAA Studies with Pb-Pb data @2.76 TeV

Dipanwita DuttaNuclear Physics Division , BARC

Jets in CMS: Excellent probeJet Quenching

QGP

Direct jet quenching @ CMS

RAA over two decades of PT

D. Dutta , India CMS Meet 2

Jet quenching via large dijet energy imbalance

3

• To study the Nuclear Modification factor for inclusive jets

• Gives Information: Medium modification of jets, jet broadening, Initial state effect• Challenges and interest:

Jet unfolding : subtraction of huge HI background, underlying events (UE) produced simultaneously with hard nucleon-nucleon collision- properly subtracted to get “true” momentum

Jet identification: implementation of proper Jet quality criteria to remove fake jets arising from noise, important in HI

Motivation

D. Dutta , India CMS Meet, BARC, Mumbai , 28-29 July 2011

RAA > 1 (enhancement)

RAA = 1 (no medium effect) RAA < 1 (suppression)

Binary scaling pp reference

4

Jet analysis : RAA twiki page

D. Dutta, India CMS Meet, BARC, Mumbai , 28-29 July 2011

• Discussed with Jet RAA Analysis group:• Gunther Roland (former HI spokes person, MIT), Christof Roland (MIT), Yen-Jie Lee (MIT)- (co-ordinator of high pT group), Mathew Ngyuan, Marguerite Tonjes (UMD), Ying Lu (UMD)

•Twiki page• https://twiki.cern.ch/twiki/bin/viewauth/CMS/HIJetRAA• Some initial plan is discussed and mentioned in RAA page

Pb –Pb :• Make raw and corrected jet pT spectrum for iC5pu (7/19/11.pdf)--Dipanwita Dutta and akpu3pf • Find where RecoJetpT of two algorithms is fully efficient for trigger• Check Jet energy scale, jet response, jet resolution for both algorithms • Jet unfolding • Study JetID and Include JetID in analyzer

• Both pp and Pb-Pb analysis will use same analyzer • Presenting results and discussion in high pT meetings (EVO)

5

Jet analysis • Data: Pb-Pb Run Nov. –Dec. 2010 and pp Run 2011 @ s=2.76 TeV • Simulations : Pythia jets embedded + Hydjet and Pythia QCD Dijets (to be done)• Integrated Luminosity: Pb-Pb : 7.2 b-1 and pp : 231 nb-1

• Jet Trigger: HLT from calorimeter towers, • Pb-Pb: Trigger threshold pT=35 GeV/c

D. Dutta, India CMS Meet, BARC, Mumbai , 28-29 July 2011

1. Calorimeter jets • Calorimeter based Jet Finder

(IC5)– Iterative Cone Algorithm– R = 0.5

Tag: icpu5calo

2. Particle Flow Jets • Particle Flow Jet Finder (PF)

– Anti-kT Clustering Algorithm– R = 0.3

Tag: akpu3pf

6

Jet analysis

D. Dutta, India CMS Meet, BARC, Mumbai , 28-29 July 2011 6

• Jet Trees are reconstructed from RECO data (PAT on fly) (used by HI group for Dijet analysis ) by the working analyzer Data: hidata/HIRun2010/HIAllPhysics/RECO/• Analyzer involve : (1) Reco-Extra (Heavy ion track reconstruction) (2) Heavy ion background subtraction (3) PAT-Jet and Ana-step• Tree Variables are :

vx, vy, vz: vertex position n, jtpt, corrpt, jteta, jtphi: inclusive jet kinematics for each event refpt, refeta, refphi: matched genjet kinematics ntrack, trackpt, tracketa, trackphi: track kinematics nPFcand, candId, candpt, candeta, candphi: particle flow candidate kinematics (pfid: 1 = charged hadrons, 4 = photons)

• For inclusive jet RAA study : Low pT jets, need sophisticated back-ground subtraction and jet identification: new PAT analyzer to be introduced.

77D. Dutta , India CMS Meet, BARC, Mumbai , 28-29 July 2011 7

Jet analysis: Vertex z-distribution

No. of Pb-Pb events = 20743

Pb-Pb Nov.- Dec . Run 2010 , sNN=2.76 TeV

8

Jet analysis: PT distribution

8D. Dutta, India CMS Meet, BARC, Mumbai , 28-29 July 2011 8

HLT: Jet35U Cut <2

99D. Dutta, India CMS Meet, BARC, Mumbai , 28-29 July 2011 9

Jet analysis: and distributionCut <2Black- icpu5calo jets

Red- akpu3pf jets

10

Jet analysis: vs distribution

10D. Dutta, India CMS Meet, BARC, Mumbai , 28-29 July 2011 10

Cut <2

icpu5calo jets akpu3pf jets

11

Jet analysis: d and d distribution

11D. Dutta, India CMS Meet, BARC, Mumbai , 28-29 July 2011 11

Cut <2icpu5calo jets

akpu3pf jets

blue- without cut; black- leading jet pT >100 GeV/c - subleading jet pT>40 GeV/c

12

Outlook

1212D. Dutta, India CMS Meet, BARC, Mumbai , 28-29 July 2011 12

• Jet RAA analysis

• Unfolding of jets

• Jet Identification

Analysis group :

Pawan Netrakanti Dipak MishraL. M. Pant A. K. Mohanty

RAA analysis group :

Gunther Roland (MIT)Christof Roland (MIT)Yen-Jie Lee (MIT) Mathews Nguyen (CERN)Marguerite Tonjes (UMD), Ying Lu (UMD)

Thank you

13

Back up slides

CMS detector

Silicon Tracker<2.4

D. Dutta , India CMS Meet, BARC, Mumbai , 28-29 July 2011 14

EM and HAD Calorimeter

HF

<5

Beam Scintillator Counter

15

Calorimeter Jets

16

Particle flow reconstructs all stable particle in the event: h+/-, γ, h0, e, μwith thorough combination of all sub-detectors in CMS

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

Particle Flow Jets

D. Dutta et al., India CMS Meet, BARC, Mumbai , 28-29 July 2011

17

Inclusion Of Jet Triggers

Jet triggers are used to enhance the pT reach and to have low fake

Jet energy distribution Charged particle distribution

D. Dutta et al., India CMS Meet, BARC, Mumbai , 28-29 July 2011

A. Yoon, QM2011

18D. Dutta et al., India CMS Meet, BARC, Mumbai , 28-29 July 2011

Dijet Asymmetry

Striking enhancement of asymmetry in data with increased centrality

CMS: arXiv:1102.1957

Dijet selection: <2.0leading jet pT>100 GeVSub-leading jet pT>40 GeV>2*/3

Dijet Fragmentation fn:

Studies on Dijet in CMS

Fragmentation pattern independent of energy lost in medium

)/(ln trackT

jetT pp

ddN /

M. Tonjes, QM2011

19

Collinear- and Infrared-Safe• collinear splitting shouldn’t change jets• soft emissions shouldn’t change jets

Jet Algorithms

•Cone-Type Algorithms Midpoint Cone (Tev), Iterative Cone (CMS), SISCone (LHC)

• Typically not Infrared- & Collinear-Safe (exception: SISCone)• Typically complex, invoving several (non-phyiscal) parameters• Favored at hadron colliders (computational performance?)• Strongly disfavored by theorists

•Sequential Clustering Algorithms• kT, Cambridge/Aachen, Anti-kT• Infrared- & Collinear-Safe by construction• Clean & Simple Algorithms• Strongly favored by theorists• Not widely used at hadron colliders in the past

‣ computational performance (SOLVED) ‣ jet area not trivially accessible (SOLVED)

Collinear-Safety Infrared-Safety

FastJet implementationC++ library providing fast (!) JAImplementation• kT, Cambridge/Aachen, Anti-kT,SISCone• Sequential Clustering: yielding bit identical results w.r.t. priorimplementations featuringdramatically improved performance

20

• Plan: the jet corrections will be factorized- Correcting for each factor in a fixed sequence up to a level chosen by the user.

✦ Factorization facilitates the use of data-driven corrections- Breaking the correction into pieces that are naturally measured in collider data:

• Offset: pile-up and noise measured in zero-bias events.• Relative: jet response vs. η relative to barrel found using dijet balance.• Absolute: jet response vs. PT found in barrel using γ / Z + jet.

- Allows data-driven corrections as they emerge to easily replace MC truth ✦ Pile-up

-Refers to the energy from additional proton-proton collisions,occurring close enough in time to the hard scatter to beincluded in the calorimeter energy within the jet-Statistically independent: not correlated with hard scatter-Increases with luminosity-The additional energy amounts to 2.5 GeV/10 GeV/200 GeV in a cone of radius 0.5 in the barrel for low luminosity pile-up, high luminosity pile-up and heavy ion collisions, respectively.

Calorimeter noise-Refers to any noise above the calorimeter cell and towerthresholds for calorimeter towers included in the jet

Both pile-up and electronic noise produce an energy offset

Reconstructed Jets

OffsetL1

Rel L2

Abs pT

L3

Required Corrections Optional CorrectionsJet Correction

EMF Flavour UE Parton Callibrated jets

Pile-up subtracted

21D. Dutta et al., India CMS Meet, BARC, Mumbai , 28-29 July 2011 21

M. Naguyen, QM2011

1. Event-by-event subtraction of theheavy-ion background

2. Jet energy corrections (JEC) based onGEANT simulation of PYTHIA jets

3. Validation of the BG subtraction + JECfor PYTHIA jets embedded in HYDJET

Jet reconstruction in heavy ionsBackground subtraction