Upload
others
View
0
Download
0
Embed Size (px)
Citation preview
08/03/12 1
Jet studies in PbPb collisionsPawan Kumar Netrakanti
BARC, MumbaiINDIA-CMS week 3rd-4th Aug 2012
PbPbpp
08/03/12 2
Outline:● Motivation● Jet selection and dataset● Analysis and results● Summary● Analysis related with this talk:
● Di-jet momentum imbalance (HIN-11-013)
PLB 710 (2012) 256● Gamma+jet (HIN-11-010) (submitted to PLB)● Jet RAA : HIN-12-004 (Approved)
08/03/12 3
Motivation : Heavy-ion collision
Jets :➔Good probes to understand the medium effects.
➔High pT particle suppression observed at RHIC (BNL).
➔Direct measure of the lost energy: γ+jet Z+jet
➔Constrains lot of theoretical modelsfor the energy loss mechanism in dense medium.
08/03/12 4
CMS Jets: PbPb and pp collisionspp 2.76 TeV data 2011 Luminosity 231/nb (HLT_Jet60_v1)PbPb 2.76 TeV data 2011 Luminosity 150/µb (HLT_HIJet80_v1)
pp MC : PYTHIA QCD dijet pT-hat 30+, 50+, 80+, 120+, 170+, 200+, 250+, 300+
PbPb MC : Above PYTHIA embedded into HYDJET for background.
Jet Selection: Jet Algorithm : Anti-k
T, Particle Flow jets, R = 0.3
(for systematics also used R=0.2 and 0.4)
Vertex : |vz|<15 cm
Jet p
T : > 100 GeV/c (sub-leading > 30 GeV/c)
Jet eta : |η|<2
pp jets are reconstructed with the PbPb tunned jet algorithm.
08/03/12 5
Centrality
Most peripheral 70-100%, 50-70%, 30-50%, 20-30%, 10-20%, 0-10% Most central
Npart : Number of participating nucleons in eventNcol l : Number of binary interactions in eventTransverse energy in the forward calorimeter is correlated to Npart
Rare probes occur more frequently in central events (Ncoll scaling)
08/03/12 6
Jet energy resolution and scale
08/03/12 7
Jet Background from PbPb
<Background pT> = (photonSum + neutralSum + chargedSum) – raw pT
08/03/12 8
Di-jet imbalance : centrality dependence
150 μb-1 ~ 20 times more data than in 2010!!! Able to perform same measurements differentially in pT
pp data at the same √s available, more statistics welcome!
https://twiki.cern.ch/twiki/bin/view/CMSPublic/PhysicsResultsHIN11013
PLB 712 (2011) 176
08/03/12 9
Energy loss apparent at all jet pT !
Reference itself has an increasing trend
No significant dependence on jet pT
pT-dependence of the dijet imbalance
08/03/12 10
Photon+Jet in PbPb
08/03/12 11
Isolated photon+jet momentum imbalance
Momentum ratio shifts/decreases with centralityRed/Shaded boxes try to indicate possible, anti-correlated systematic variations
https://twiki.cern.ch/twiki/bin/view/CMSPublic/PhysicsResultsHIN11010
Distribution consistent between pp and PYTHIA (Z2) + HYDJET
08/03/12 12
Width, mean and fraction
● Angular width σ (∆φJγ) is consistent, both PbPb to pp and PbPb
to PYTHIA tune Z2 + HYDJET
● Significant deviation of <XJγ> PbPb compared to PYTHIA
tune Z2 + HYDJET, significance of PbPb vs. pp is weaker
● The centrality dependence is mostly visible in RJγ (jet p
T shifting
below the 30 GeV/c threshold)
https://twiki.cern.ch/twiki/bin/view/CMSPublic/PhysicsResultsHIN11010
08/03/12 13
Inclusive jet spectra : 2.76 TeV
|η|<2
08/03/12 14
Nuclear Modification factor for inclusive jets (RAA
)
08/03/12 15
Comparison of inclusive jets (RAA
)
08/03/12 16
RAA
Vs. No. of participating nucleons
More suppression of jets in central collisions
08/03/12 17
RAA
: cross-checks
Smearing method
Systematics for Bayesian only. Different jet pT ranges averagedspectra and then take R
AA
08/03/12 18
pp PbPb
ConclusionsDi-jet:●Enhanced imbalance exists at all p
T.
●The fraction of the energy that a jet loses does not dramaticallychange with jet pT.
Isolated-photon + jet●First measurement of isolated prompt photon-jet in heavy-ion collisions
●Direct observation of jet energy loss vs. initial parton energy●Shift of associated jet towards lower jet p
T with centrality
Inclusive jets:●Observation of suppression of high p
T jets in central PbPb collisions
in comparison to peripheral collisions.●Consistent observation with jet quenching and high p
T charged
particle RAA
More details of the analysis can be found at:
Di-jet : AN-11-478 & HIN-11-013Isolated photon+jet : AN-11-435 & HIN-11-010Jet Raa : AN-11-393 & HIN-12-004
https://twiki.cern.ch/twiki/bin/view/CMS/HighPtFirstYear2011
08/03/12 19
High pT working group
BARC : P. K. Netrakanti, D. Dutta, D. K. Mishra and A.K. Mohanty
CERN : Y. J. Lee
LLR : M. Nguyen
MIT : Y. S. Lai, Y. Kim, F. Ma, Y. Yilmaz, D. Valicanu, I. A. Cali C. Roland, G. Roland, G. S. F. Stephans
UM : Y. Lu and M. Tjones
RU : J. Robels and S. Salur
VU : P. Kurt, Y. Mao and J. Velkovska
Current topics pursued in the group are: 1. Jet shape analysis 2. Jet track correlations 3. Photon-jet track correlations 4. b+jets 5. Fragmentation function analysis
One plenary and 6 parallel talks in Quark Matter – 2012 (Aug).
08/03/12 20
Back up
08/03/12 21
Isolated photon selection
08/03/12 22
Photon isolation in data