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Jet studies for PbPb and pPb collisions with CMS

Jet studies for PbPb and pPb collisions with CMS. Dipanwita Dutta Nuclear Physics Division, BARC, Mumbai India-CMS Meet, SINP, Kolkata 20 th Dec, 2012. 1. Jets : Probe of QGP in HI. Indirect jet quenching @ RHIC. Jet Quenching. QGP.

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Jet studies for PbPb and pPb collisions with CMS

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  1. Jet studies for PbPb and pPb collisions with CMS Dipanwita Dutta Nuclear Physics Division, BARC, Mumbai India-CMS Meet, SINP, Kolkata 20th Dec, 2012 1

  2. Jets : Probe of QGP in HI Indirect jet quenching @ RHIC Jet Quenching QGP Jets suppressed at Au+Au but not in pp or d+Au Direct jet quenching @ CMS, LHC • Confirm production of QGP @ LHC • Important probe to study QGP properties

  3. What do we expect for the jet shapes? r  Low- particles tend to be closerto the jet axis; high- particles extend to large distances (radii). low  =ln(pjet/p||track) high  Jet shape: pT-flow vs. - distancefrom the jet axis (r) Excess pT-flow is expected at largeradii, and no change at r0(compared to pp collisions). 3

  4. Background estimation Eta reflection Event mixing Dijet events are matched to randomly selected minimum bias events with consistent centrality, event-plane and position of the primary vertex. Then, the particles from minbias events falling into the jet axis are counted to estimate the average contribution from underlying event. pseudo-rapidity(η) of the background jet is determined by reflecting η of the original jet cone around η =0. phi (ϕ) of the background jet is the same as of the two leading jets. Δη<0.3 region is not used in order to avoid overlay between the leading jets and background jet. 4

  5. Changing jet shapes vs. centrality Pb Pb Pb Pb Compared to pp: same pT-flow close to the jet axis; more pT-flow at large radii; and a bit less in between. CMS PAS HIN-12-013 5

  6. Jet studies in pPb collisions Pb Pb p Pb p p pPb collisions run at s = 5.02 TeV in Jan-Feb 2013 • Have we created a medium in pPb collisions? ? 6

  7. Ridge observed in pPb pPb and pp ridge compared paper for “apples-apples” comparison pPb ridge much larger than pp Average over ridge region (2<|Δη|<4) 7

  8. Several unanswered question for pPb • What is the physics origin of ridge: • Collective effect? • Modification of jet structure? • Is there any medium produced in pPb • Jet quenching? ALICE result on ridge conclude: • Near side and away side same ridge • No pT dependence ( not from jet) • The ridge subtracted yield comparable for all multiplicities in pPb (5.02 TeV) and pp at 2.76 and 7 TeV, no change in jet structure observed - in contrast to RHIC result for dAu at 0.2 TeV 8

  9. Jet energy imbalance in PbPb Pb Pb pp p p Pb Pb • Parton energy loss is observed as a pronounced dijet energy imbalance in central PbPb collisions PRC 84 (2011) 024906 9

  10. Dijet asymmetry in pPb (pilot run) • Fake jets contribution with centrality • Centrality is determined by NTrack Lead Jet pT>40 GeV/c, SubLead pT>20 GeV/c Lead Jet pT > 60 GeV/c, SubLead pT >30 GeV/c Ruchi Chudasama 10

  11. Dijet asymmetry(contbn from fake jets) Fake jets contribution to Aj from side bands <1/3 Ruchi Chudasama 11

  12.  distribution for all jets

  13. Dijet asymmetry in pPb Lead Jet pT>40 GeV/c, SubLead pT>20 GeV/c Lead Jet pT > 60 GeV/c, SubLead pT >30 GeV/c Hijing Pythia AMPT Hydjet Ruchi Chudasama 13

  14. Future Plan • Study of fake jet contribution (fake pair from underlying events): • From side band in jet event (<1/3) • From mix event (jet from jet triggered event and paired with fake jets from min bias event) • Any other method • Efficiency correction and unfolding of jet distribution Acknowledgement: • Heavy ion High pT group • A. K. Mohanty 14

  15. Jet broadening can be studied in the differential shape through tot(r/R)/vac(r/R) Jets Shape : Theoretical study for LHC QGP effects are manifested as a suppression near the core and enhancement near the periphery for central collisions

  16. Back up Back up

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