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Quarkonia in CMS With First Year PbPb Data: Upsilon measurement

Vineet Kumar Prashant Shukla NPD BARC Mumbai

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Plan of Talk

Physics motivation of Quarkonia studies in heavy ion Collisions

Upsilon measurement in PbPb data

Cross section

Event selection

Acceptance and efficiency corrections

Upsilon yield extraction

Results

Summary

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Heavy Ion Collisions at Large Hadron Collider ( LHC)

LHC had Pb+Pb collisions at SNN

= 2.76 TeV. 8th November 2010 to 5th December 2010 , L ~ 7.28 b-1 Next run is expected at same energy but with high luminosity this year in Nov-Dec.

At large energy densities and / or high temperatures, a new form of matter exists, in whichthe relevant degree of freedom are quarks and gluons. Aim of Heavy Ion Collisions is to create such matter known as Quark Gluon Plasma(QGP). The final goal of HIC studies is to characterize and quantify the properties of QGP.

One of the most striking expected characteristic of QGP is suppressionOf quarkonium states (J/ ,',

c,1s,2s,2s)

due to color screening of strong interaction inQGP.

Different states are expected to dissociate at different temperatures, sequentially according to their binding energies

arXiv:0811:0337

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DiMuon mass spectrum with first year PbPb run: Nov2010-Dec 2010

We measure 37 Z0 with first year HI Data. Z0 will not be affected by QGP but canserve as standard candle for initial state effects (eg Shadowing ) 86 and 734 J/ are collected. It gives opportunity to do quarkonium physics in

detail is covered in this talkJ/ will be covered in Abdulla's talk.

PRL. 106, 212301 (2011)

arXiv:1105.4894v1 [nucl-ex]

Comming soon

Submitted to PRL

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Upsilon measurement

Yields of ϒ(1S) as function of pT, rapidity, and centrality of the collision

NQQ

: the number of measured ϒ in the μ+μ− decay channel N

MB : the number of minimum bias events sampled by the event selection

α : the geometric acceptance ε : the combined trigger and reconstruction efficiency Δy and ΔpT : the bin width in rapidity and p

T

TAA

: the nuclear overlap function ( varies with the centrality of the collision and has units of mb−1)

• Centrality bins: 0 - 10% , 10 - 20% , 20 - 100%• pT bins (GeV/c): 0 - 6.5 , 6.5 - 10 , 10 - 20• Rapidity bins: 0 < |y| < 1.2 , 1.2 < |y| < 2.4

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Event selection

Minimum bias collisions

L1 BscMinBiasThreshold1 (L1a36)

OR L1 HcalHfCoincidencePm (L1a44)Default offline HI PAG selection Coincidence of 3 HF towers above

threshold Selection of at least a two-track fitted

vertex Cluster-shape filter re-run offline

Reject BSC beam halo L1 technical

bits Dimuon trigger

HLT HIL1DoubleMuOpen

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Muon quality cuts

Extensive study to tune muon quality cuts using PYTHIA signal embedded in MBHYDJET background more in Abdulla Talk Final set of quality cuts

Is reconstructed as tracker muon as well as global muon p

T > 4 GeV

Tracker hits > 10 Hits in Pixel Layers > 0 Chi2 / ndf for inner track fit < 4.0 Chi2 / ndf for global fit < 20.0 D

xy < 3

Dz < 15

Probability of both tracks coming from common vertex is required to be better than 1%

For upsilon this set of cuts keeps 96.1% signal.

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Raw Yield for ns

ϒ(1S) raw yields: 86 ± 12

Signal•Crystall Ball functions•Resolution fixed from MCsimulation value• Peak separation fixed to PDG Background• Second order polynomial

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Acceptance Corrections

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Efficiency corrections

Efficiency corrections are based on MC. MC signal is generated using PYTHIA in various p

T bins.

This signal is embedded in HYDJET MB events. To calculate efficiency same selection criteria is applied as for raw yield determinationEfficiency include muon ID, Trigger and reconstruction efficiencies.Efficiency : [reconstructed signal passing all the analysis selections] / [generated signal]

mGeV/c2)

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Efficiency Corrections

Efficiency is flat with pT

, and rapidity. Small variation with centrality of collision. Only muons in the acceptance kinematic region are considered ϒ(1S) over all efficiency ~ 54.5%.

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Invariant Yield for s

• Centrality bins: 0 - 10% , 10 - 20% , 20 - 100%• pT bins (GeV/c): 0 - 6.5 , 6.5 - 10 , 10 - 20• Rapidity bins: 0 < |y| < 1.2 , 1.2 < |y| < 2.4

No obvious rapidity dependenceNo centrality dependence20-100% is not very peipheral.

Systematic uncertainties:Yield extraction: 8–14%. Acceptance: 1–5%. Efficiency: 14%. TAA: 4.3–15% Statistical uncertainties: 5–20%

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measurement in pp at 2.76 TeV

LHC have pp run at 2.76 TeV at the starting of this year.~225 nb-1 data is collected.

is measured using the same procedure in pp data also. R

AA is defined as ratio of yield in

AA collisions to yield in pp collisionsscaled by no of binary collisions.

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RAA

of (1s)

ϒ(1S) RAA in the most central 20%0.60 ± 0.12(stat.) ± 0.10(syst.)consistent with the suppression ofexcited states (50% feed-downcontribution measured by CDF)

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RAA

of (1s)

0-100% RAA

= 0.62 ± 0.11 ± 0.10No obvious rapidity dependenceHigh pT not as suppressed ?Waiting for more data next year

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Suppression of excited ϒ states in PbPb collisions at 2.76 TeV

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(2s+3s) vs (1s)

Measure the fraction of excited states ϒ(2S+3S) relative to ϒ(1S) Fraction extracted directly from the fit to the PbPb and pp data sample (both at 2.76 TeV)

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Double Ratio

Compare ratios of ϒ(2S+3S) relative to ϒ(1S) in PbPb & pp Extract double ratio directly from simultaneous fit to both samples Simultaneous fit results

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Systematics on Double Ratio

ϒ(2S+3S)/ϒ(1S) ratio in pp and PbPb benefits from cancellation of possible acceptance and efficiency differencesReconstruction and selection efficiencies: 0.5%Trigger efficiencies: negligible effectSystematic uncertainty from the fitting modelSignal shape: 0.9%Mass resolution: 3.7%Background PDF and fit range: 8.2%Sum: 9.1% Statistical uncertainty (dominant): 55%

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Conclusion 1

First observation of suppression of excited ϒ states

Double ratio

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Conclusion 2

ϒ(1S) invariant yields is measured as a function of centrality, pT, and y.ϒ(1S) is suppressed (In the most central collisions 20%, R

AA = 0.60 ± 0.12 ± 0.10)

Taken together these twoconclusions are consistentthe suppression of the ϒ(1S) is theresult of the excited ϒ statessuppression Comparing with prompt andnon-prompt J/ψ Prompt J/ψ suppressed the most,ϒ(1S) the least (in 0-20%)

Outlook We are working on finalization of J/ψ paper.Trigger menu for high luminosity run.

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Plan with second year data: Z0

First year Z0 measurement was the first ever measured Z0 in Heavy Ion Collisions.Only 36 Z0 . Large statistical errors. With improved statistics we will be able to constrain various inetial state effect.Z0 + Jet will be direct probe for energy loss of parton inside QGP.

Event display of Z0 + Jet event

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Plan with second year data: ssratio as a QGP signature

The dissociation of heavy quark resonances by color screening is one of the most promising signature of QGP formation. But cold nuclear matter effect and initial state effect can be trickyIn order to isolate pure QGP effect we proposed to study p

T

dependence of quarkonium ratioinstead of single quarkonium p

T

distributions.By doing so nuclear effects are washed out.

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Back Up slides

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Particle detection in CMS

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QCD calculations predict 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

Quarkonia in Heavy Ion Collisions

hadrons Quark and gluons

We study the QCD matter produced in HI collisions by seeing how it affects well understood probes as a function of the temperature of the system (centrality of the collisions) Color screening of strong interaction in QGP (Quark Gluon Plasma) is one of the earliest proposed signature of QGP phase transition Suppression of quarkonia is a longstanding classical prediction as QGP signature

Centrality Determination

2727

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Plan With Second Year Data

LHC will have high luminosity HI run in Nov 2011.We plan to contribute with muon trigger development for high luminosity conditions.High statstics for all quarkonia channelscan be used to constrain inetial state effects like shadowing of parton disstribution functions inside nucleus.Z0 + Jet will be direct probe for energy loss of parton inside QGP. can be measured in more centrality bins.