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DiMuon Analysis with CMS detector using 2011 Heavy Ion Data
Vineet KumarPrashant Shukla
Nuclear Physics DivisionBARC Mumbai
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Outline of Talk
Physics Motivation of quarkonia analysis in heavy ion collisions.
Dimuons with CMS in 2010 Pb+Pb run
ϒ measurement with 2011 Pb+Pb data : paper in FR
Signal Extraction
Corrections
Results
J/ψ measurement with 2011 Pb+Pb data : Approval Today
Summary and outlook
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QGP and Colour Screening of Quarkonia
P e r t u r b a t i v e V a c u u m
cc
C o l o r S c r e e n i n g
cc
QCD Calculations indicate that, at a critical temperature around 170 MeV, strongly interacting matter undergoes a phase transition to a new state where the quarks and gluons are no longer confined in hadrons. Aim of Heavy Ion Collisions at high energies is to create, characterize and quantify the properties of QGP.
Color screening in QGP is expected to prevent the formation of quarkonium states indeconfined matter Different quarkonia states J/, ',
c, 1S,2S,3S) are expected to dissociate at different
temperatures, sequentially according to their radius. Measurement of a suppressed quarkonium yield may provide direct experimental sensitivity to the temperature of the medium created in high energy nuclear collisions.
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Experimental Puzzle at Lower energies
PHENIX, PRL 98 (2007) 232301, PRC 84 (2011) 054912SPS from Scomparin @ QM06
Similar J/ψ suppression at theSPS and RHIC
RAA
(RHIC, |y|<0.35) ≈ RAA
(SPS)
New observation at RHIC:
Suppression is more in forward rapidity region
RAA
(|y|<0.35) > RAA
(1.2<|y|<2.2)
Possible processes Initial state effects Cold nuclear matter effects Regeneration
What happens at the LHC? higher energy + higher luminosity more charm (more regeneration?) more bottom → a new probe ϒ states can be measured
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Quarkonia results with 2010 Pb+Pb Run
PRL. 106, 212301 (2011) CMS AnNote (055) 2010
PRL. 107, 052302 (2011) CMS AnNote (062) 2011
JHEP 1205 (2012) 063, CMS AnNote (062) 2011
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Dimuons with 2011 Pb+Pb data
2011 Pb+Pb at 2.76 TeV Total Luminosity 150 (µ b)-1 (20 times more than 2010) Detail study of ϒ states with event centrality Detail study of J/ψ suppression in many bins.
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ϒ raw yield extraction
3 Crystal-ball: Gaussian core & power law tail Free parameters: yield, resolution and mass for ϒ(1S) Fixed parameters: Resolution forced to scale with PDG mass ratios Background : 2nd order polynomial (PP) , exponential x error function (PbPb)
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Efficiency Vs Centrality of collision
Corrections mainly based on MC. Cross checked with TnP. Reconstruction efficiency almost constant with centrality of collision. Similar values for PP and PbPb collision. Efficiency ratio flat within uncertainties with centrality.
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Nuclear Modification Factor (RAA
)
Lpp
= 231 nb-1 N
MB = 1.13 billion
Centrality dependence observed with ϒ(2S) more suppressed thanϒ(1S)
ϒ(1S): 0.41±0.05±0.04 (0-5%)→ 1.01±0.18±0.12 (50-100%)
ϒ(2S): 0.11±0.02±0.06 (0-5%)→ 0.30±0.07±0.16 (50-100%)
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Double Ratio : [ϒ(ns) / ϒ(1s)]PbPb
/ [ϒ(ns) / ϒ(1s)]PP
Measure the relative suppression of the excited states relative to the ground state
In absence (by cancellation) of cold nuclear matter effects, ϒ(2S) is five times more suppressed than ϒ(1S) Within uncertainties centrality dependance is not very clear, on an average more suppressed in central collisions.
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Comparison to RHIC and J/ψ CMS
STAR measured RAA
of ϒ(1S+2S+3S) combined. We can measure R
AA separately for Y(1S) and Y(2S).
Suppression pattern in most central collisions, as expected from sequential melting
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J/ψ measurement with 150 µb-1 Pb+Pb Data
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J/ψ measurement with 150 µb-1 Pb+Pb Data
8.5K J/ψ with 6.5<pT<30GeV/c, |y|<2.4
Triggered by HLT_HIL1DoubleMu0_HighQ
Prompt J/ψ 12 centrality bins: 0-5, 5-10, ... 50-60, 60-100%
4 pT bin: 6.5-8, 8-10,10-13, 13-30 GeV/c
Non-prompt J/ψ 6 centrality bins: 0-10, 10-20,... 50-100%
4 pT bin: 6.5-8, 8-10, 10-13, 13-30 GeV/c
Differential: centrality&rapidity, centrality&pT
CMS Analysis Note CMSAN(246) 2012
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Prompt J/ψ RAA
First measurement high pT J/ψ, 12 centrality bins at 2.76 TeV.
Strong centrality dependence (more suppressed in central collisions)
More suppressed at hight pT ?
Less at forward rapidity ?
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Non Prompt J/ψ RAA
Unique measurement of non prompt J/ψ
Show same trend with centrality although entirely different physics process
First signature of b quark energy loss in strongly interactive medium.
More suppressed at hight pT and forward rapidity ?
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Summary and Plan
ϒ measurement : Double Ratio: First separate measurement, in HI collisions, of the relative suppression of ϒ(2S) and ϒ(3S) excited states wrt to the ground state. Ratio indicate ϒ(2s) is five times more suppressed than ϒ(1s).
RAA: ϒ(1S): Decrease of suppression from ~0.4 in 0-5% to ~1 in 50-100% ϒ(2S): First time measured in HI collisions , more suppressed than the ground state and still suppressed in 50-100% centrality bin. ϒ(3S): Smaller than 0.1 (95% C.L.)Study finished paper in FR. Will be submitted to PRL.
J/ψ measurement : Detailed study of J/ψ R
AA with centrality, pT and rapidity for Prompt and non Prompt.
Prompt J/ψ shows strong centrality dependence of suppression. First indication of b quark energy loss in medium with non prompt J/ψ Preparation of p+Pb run in Feb 2013 : Trigger Menu + MC
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Back Up slides
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Summary 1
First separate measurement, in HI collisions, of the relative suppression of ϒ(2S) and ϒ(3S) excited states wrt to the ground state.
Suppression pattern as expected in the sequential melting scenario.
Ratio indicate ϒ(2s) is five times more suppressed than ϒ(1s).
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Summary 2
RAA
: ϒ(1S) detailed centrality study decrease of suppression from ~0.4 in 0-5% to ~1 in 50-100%
RAA
: ϒ(2S) first time measured in HI collisions more suppressed than the ground state and still suppressed in 50-100% centrality bin
RAA
:ϒ(3S) smaller than 0.1 (95% C.L.)
Analysis finished. Paper under final reading by collaboration.Will be submitted to PRL.
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Outlook
CMS Data : Update of J/ψ R
AA with 2011 data.
More centrality bins for non prompt J/ψ Centrality bins in two rapidity bins for prompt J/ψ
Preparation for P+Pb run No QGP is expected there Measurement of initial state effect at LHC Nuclear matter effect
Phenomenology kinetic model of J/ψ regeneration
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ϒ yield extraction Functions
Npart , Ncoll and Taa values
Centrality Determination
2323
Acceptance of quarkonia in CMS
Antishadowing in LHC
B Fraction
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ϒ raw yield extraction
3 Crystal-ball: Gaussian core & power law tail Free parameters: yield, resolution and mass for ϒ(1S)tail parameter α (transition Gaussian→power-law) Fixed parameters: n (MC) exponent for tail description, resolution forced to scale with PDG mass ratios Background : 2nd order polynomial (PP) , exponential x error function (PbPb)
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ϒ raw yield : Pb+Pb and PP data
Using Bjorken scaling model, the time dependence of the energy density in the QGP medium is
the r dependence of the energy density is
Then the time a which temperature drops to TD =
t0 – formation time T
0 – initial temperature
A bottonium pair can escape the screening region rS if
r is the position of creation
Which gives the survival probability of the bottonium states as
ε (t )=ε ( t=t0 )( tt0
)ε (r,t0 )=ε0 [1− r
R ]1 /3
∣r+τ F pT
M∣>r S