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Jet R AA Studies with Pb-Pb data @2.76 TeV

Jet R AA Studies with Pb-Pb data @2.76 TeV. Dipanwita Dutta Nuclear Physics Division , BARC. R AA over two decades of P T. Jets in CMS: Excellent probe. Jet Quenching. QGP. Direct jet quenching @ CMS. Jet quenching via large dijet energy imbalance. D. Dutta , India CMS Meet.

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Jet R AA Studies with Pb-Pb data @2.76 TeV

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  1. Jet RAA Studies with Pb-Pb data @2.76 TeV DipanwitaDutta Nuclear Physics Division , BARC

  2. RAA over two decades of PT Jets in CMS: Excellent probe Jet Quenching QGP Direct jet quenching @ CMS Jet quenching via large dijetenergyimbalance D. Dutta , India CMS Meet

  3. Motivation RAA > 1 (enhancement) RAA = 1 (no medium effect) RAA < 1 (suppression) Binary scaling pp reference 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 D. Dutta , India CMS Meet, BARC, Mumbai , 28-29 July 2011

  4. Jet analysis : RAA twikipage 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)--DipanwitaDutta 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 pTmeetings (EVO) D. Dutta, India CMS Meet, BARC, Mumbai , 28-29 July 2011

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

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

  7. Jet analysis: Vertex z-distribution Pb-Pb Nov.- Dec . Run 2010 , sNN=2.76 TeV No. of Pb-Pb events = 20743 7 D. Dutta , India CMS Meet, BARC, Mumbai , 28-29 July 2011 7

  8. Jet analysis: PT distribution HLT: Jet35U Cut <2 8 D. Dutta, India CMS Meet, BARC, Mumbai , 28-29 July 2011 8

  9. Jet analysis:  and  distribution Black- icpu5calo jets Red- akpu3pf jets Cut <2 9 D. Dutta, India CMS Meet, BARC, Mumbai , 28-29 July 2011 9

  10. Jet analysis:  vs  distribution Cut <2 akpu3pf jets icpu5calo jets 10 D. Dutta, India CMS Meet, BARC, Mumbai , 28-29 July 2011 10

  11. Jet analysis: d and d distribution Cut <2 icpu5calo jets akpu3pf jets blue- without cut; black- leading jet pT>100 GeV/c - subleading jet pT>40 GeV/c 11 D. Dutta, India CMS Meet, BARC, Mumbai , 28-29 July 2011 11

  12. Outlook • Jet RAA analysis • Unfolding of jets • Jet Identification Analysis group : PawanNetrakanti DipakMishra L. M. Pant A. K. Mohanty RAA analysis group : GuntherRoland (MIT) Christof Roland (MIT) Yen-Jie Lee (MIT) Mathews Nguyen (CERN) Marguerite Tonjes (UMD), Ying Lu (UMD) Thank you 12 12 D. Dutta, India CMS Meet, BARC, Mumbai , 28-29 July 2011 12

  13. Back up slides

  14. CMS detector EM and HAD Calorimeter <5 Beam Scintillator Counter HF Silicon Tracker <2.4 D. Dutta , India CMS Meet, BARC, Mumbai , 28-29 July 2011

  15. Calorimeter Jets

  16. Particle Flow Jets Particle flow reconstructs all stable particle in the event: h+/-, γ, h0, e, μ with 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 D. Dutta et al., India CMS Meet, BARC, Mumbai , 28-29 July 2011

  17. Inclusion Of Jet Triggers Jet energy distribution Charged particle distribution Jet triggers are used to enhance the pT reach and to have low fake A. Yoon, QM2011 D. Dutta et al., India CMS Meet, BARC, Mumbai , 28-29 July 2011

  18. Studies on Dijet in CMS • Dijet selection: •  <2.0 • leading jet pT>100 GeV • Sub-leading jet pT>40 GeV • >2*/3 Dijet Asymmetry Dijet Fragmentation fn: Striking enhancement of asymmetry in data with increased centrality Fragmentation pattern independent of energy lost in medium M. Tonjes, QM2011 CMS: arXiv:1102.1957 D. Dutta et al., India CMS Meet, BARC, Mumbai , 28-29 July 2011

  19. Jet Algorithms • Collinear- and Infrared-Safe • collinear splitting shouldn’t change jets • soft emissions shouldn’t change jets Collinear-Safety Infrared-Safety • •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) • FastJet implementation • C++ library providing fast (!) JA • Implementation • kT, Cambridge/Aachen, Anti-kT, • SISCone • Sequential Clustering: yielding bit identical results w.r.t. prior • implementations featuring • dramatically improved performance

  20. Jet Correction Required Corrections Optional Corrections Pile-up subtracted Reconstructed Jets Offset L1 Rel L2 Abs pT L3 Callibrated jets EMF Flavour UE Parton • 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 be included 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 tower thresholds for calorimeter towers included in the jet Both pile-up and electronic noise produce an energy offset

  21. Jet reconstruction in heavy ions Background subtraction 1. Event-by-event subtraction of theheavy-ion background2. Jet energy corrections (JEC) based onGEANT simulation of PYTHIA jets3. Validation of the BG subtraction + JECfor PYTHIA jets embedded in HYDJET M. Naguyen, QM2011 D. Dutta et al., India CMS Meet, BARC, Mumbai , 28-29 July 2011 21

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