Heavy-Ion Physics with CMS

Heavy-Ion Physics with Heavy-Ion Physics with CMSCMS

Aneta IordanovaAneta Iordanova

University of Illinois at ChicagoUniversity of Illinois at Chicago

Moriond QCDMoriond QCDHeavy-Ion SessionHeavy-Ion Session

Aneta IordanovaAneta IordanovaUniversity of Illinois at ChicagoUniversity of Illinois at Chicago

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Expected energy densityat the LHC

CMS Heavy-Ion programCMS Heavy-Ion program

Study of QCD matter Study of QCD matter under extreme conditionsunder extreme conditions Pb+Pb @ Pb+Pb @ √s√sNNNN==5.5 TeV5.5 TeV

Bulk observablesBulk observables

(soft physics)(soft physics) Hard probesHard probes Ultra peripheral collisionsUltra peripheral collisions

Proton-proton programProton-proton program First measurements of First measurements of

bulk observablesbulk observables Analysis exerciseAnalysis exercise

“…presents the capabilities of the CMS experiment to explore the rich heavy-ion physics programme offered by

the CERN Large Hadron Collider (LHC) .”

dET/d → ϵBj J.D.Bjorken, Phys.Rev.D27(1983) 140

J. Phys. G: Nucl. Part. Phys. 34 (2007) 2307-2455



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The CMS detectorThe CMS detectorce

ntra

l det

ecto

rstr

ansv

erse

slic

e

Global Event Characterization:Global Event Characterization: Silicon tracker: (Silicon tracker: (±±, K, K±±, p) , , p) , , K, K00 (via (via

displaced vertices)displaced vertices) Infer energy density, freeze-out Infer energy density, freeze-out

temperatures and chemical potential...temperatures and chemical potential...

Specific Probes:Specific Probes: Calorimetry: eCalorimetry: e±± , , and ha and hadronic jetsdronic jets

probe of early times and jet-medium probe of early times and jet-medium interactions, energy loss…interactions, energy loss…

Muon Chambers: Muon Chambers: μμ±± (from J/ (from J/ψψ, , )) (heavy) quark energy loss and (heavy) quark energy loss and

sensitivity to QGP temperature…sensitivity to QGP temperature…



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The CMS detectorThe CMS detectorde

tect

or

cov

erag

e

Silicon tracker: |Silicon tracker: ||<2.5|<2.5 Momentum resolution <2% for Momentum resolution <2% for

ppTT<100GeV and |<100GeV and ||<0.5.|<0.5.

Calorimetry: ECal |Calorimetry: ECal ||<3, HB,HE,HF ||<3, HB,HE,HF ||<5, |<5, Castor 5<|Castor 5<||<7, ZDC ||<7, ZDC ||>8|>8

Wide energy-space range measure of jets and Wide energy-space range measure of jets and METMET

Muon Chambers: Muon Chambers: |||<2.5|<2.5 Precise measure of position/momentum and fast Precise measure of position/momentum and fast

L1 response L1 response



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Soft physics:Soft physics:Global Event Characterization Low-momentum trackingLow-momentum tracking

dE/dx measurement using dE/dx measurement using the inner silicon layersthe inner silicon layers

PID for PID for ±±, K, K±± (p<0.8 GeV/ (p<0.8 GeV/cc) ) and protons (p<1.5 GeV/and protons (p<1.5 GeV/cc))

Good efficiency and Good efficiency and resolutionresolution Central PbPb collisions Central PbPb collisions

occupancy of pixel layers occupancy of pixel layers ~2%~2%

p-p @ 14 TeV (Pythia)



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Soft physics:Soft physics:Global Event Characterization

Particle identificationParticle identification Charged hadrons from Charged hadrons from

dE/dxdE/dx Neutral hadrons from decay Neutral hadrons from decay

topology (topology (, K, K00)) Multistrange baryons (Multistrange baryons (−−,,−−) )

Freeze-out parameters:Freeze-out parameters: Chemical potential (Chemical potential (BB) and ) and

temperature temperature From identified particlesFrom identified particles

Kinetic freeze-out Kinetic freeze-out temperature and radial flowtemperature and radial flow From particle spectraFrom particle spectra

Baryon transport and Baryon transport and strangeness productionstrangeness production

Particle identification

K p

p-p @ 14 TeV(Pythia)



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Hard probes:Hard probes:energy loss in the mediumMotivationMotivation RHIC Physics ResultsRHIC Physics Results

High-pHigh-pTT suppression suppression →→ medium induced parton medium induced parton energy lossenergy loss

Initial gluon medium density Initial gluon medium density dNdNgg/dy/dy

Medium diffusion properties Medium diffusion properties (transport coefficient q)(transport coefficient q)

Disappearance of back-to-Disappearance of back-to-back jetsback jets

RHIC RHIC →→ LHC: Increased hard LHC: Increased hard scattering cross section and scattering cross section and luminosityluminosity CMS detector and triggering CMS detector and triggering

capabilities provide extended capabilities provide extended ppTT reach for charged hadrons reach for charged hadrons and for fully reconstructed jets and for fully reconstructed jets



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Large acceptance calorimetry (ECal+HCal) Fully reconstruct jets in

heavy ion collisions Photon reconstruction in

ECal

4T magnetic field Momentum resolution

<2% Low fake rates

High-Level Triggering Online inspection of all

events provides 20 to 300 times statistical reach

PbPb background[HYDJET 010 dN/d~2400]

190 GeV photon [PYTHIA]

quenched jet [PYQUEN]

Full CMS sim reco

Hard probes:Hard probes:CMS Capabilities

minimum bias HLTriggeredPbPb dNch/d|y=0=3500



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Hard probes:Hard probes:Reconstructing Jets Inclusive jet spectraInclusive jet spectra

utilizes Hcal and Ecalutilizes Hcal and Ecal

Iterative cone (R=0.5) + Iterative cone (R=0.5) + Background subtractionBackground subtraction High efficiency and purity for High efficiency and purity for

EETT>50 GeV jets>50 GeV jets Good energy resolution for Good energy resolution for

EETT>100 GeV>100 GeV Jet spectra reconstructed up Jet spectra reconstructed up

to Eto ETT~ 0.5 TeV~ 0.5 TeV Estimated for one “year” of Estimated for one “year” of

running PbPb 0.5 nbrunning PbPb 0.5 nb-1-1

(or 3.9x109 events,106 sec)



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Hard probes:Hard probes:-Jet Direct probe for in-medium Direct probe for in-medium

energy loss, energy loss, E=EE=E-E-Ehjethjet

ReconstructionReconstruction Photon ID: combine Photon ID: combine

Ecal/Hcal/tracker to form Ecal/Hcal/tracker to form isolation cutsisolation cuts Use of Multivariate analysisUse of Multivariate analysis ForFor = 60%, fake = 60%, fake = 3.5%, = 3.5%,

S/B=4.5S/B=4.5 Away-side jet selection

ET > 30 GeV, ||< 2, ,jet > 1720

Calculate dN/dξ Charged tracks in R=0.5 cone

around jet axis



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Hard probes:Hard probes:-Jet Direct probe for in-medium Direct probe for in-medium

energy loss, energy loss, E=EE=E-E-Ehjethjet

Final Measurement Reconstruction using non-

quenched and quenched MC Fragmentation functions differ

Medium modification of fragmentation functions can be discriminated with high significance

Significant difference between

Non-quenched and QuenchedAnalysis method has discriminatory power



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Heavy Flavor:Heavy Flavor:J/ and ’ Direct probe of QGP Direct probe of QGP

formationformation ““Step suppression” of Step suppression” of

charmonium/bottomonium charmonium/bottomonium resonancesresonances

Sensitive to QGP Sensitive to QGP temperaturetemperature

Reconstruction performanceReconstruction performance Excellent dimuon mass Excellent dimuon mass

resolutionresolution ~1% of the quarkonium mass ~1% of the quarkonium mass

for full for full Best Signal/Background at LHCBest Signal/Background at LHC

Clean separation of the statesClean separation of the states Broad Broad -coverage and high-p-coverage and high-pTT

reachreach Using HLT selectionUsing HLT selection

NJ/~1.8×105

Di-m

uon

mas

s re

cons

truc

tion

1-ye

arst

atis

tical

rea

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Broad coverage

PbPb=2500

J/y=35MeV/c2

||<2.4

S/B~1.2

J/ acceptance

p T (

GeV

/c)



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Heavy Flavor:Heavy Flavor: family

PbPb=2500S/B~1

N~2.5 104D

i-muo

nm

ass

reco

nstr

uctio

n

1-ye

arst

atis

tical

rea

ch

Broad coverage

p T (

GeV

/c)

Direct probe of QGP Direct probe of QGP formationformation ““Step suppression” of Step suppression” of

charmonium/bottomonium charmonium/bottomonium resonancesresonances

Sensitive to QGP Sensitive to QGP temperaturetemperature

Reconstruction performanceReconstruction performance Excellent dimuon mass Excellent dimuon mass

resolutionresolution ~1% of the quarkonium mass ~1% of the quarkonium mass

for full for full Best Signal/Background at LHCBest Signal/Background at LHC

Clean separation of the statesClean separation of the states Broad Broad -coverage and high-p-coverage and high-pTT

reachreach Using HLT selectionUsing HLT selection



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Ultra peripheral collisionsUltra peripheral collisions photo-production At LHC the accelerated Pb nucleus can

produce strong electromagnetic field due to the coherent action of the Z = 82

proton charges

Equivalent photon flux Emax ~ 80 GeVPb: cm Emax ≈ 1. TeV/n (~3×e+p HERA): cm Emax ≈ 160 GeV (~LEP)

Measure the gluon distribution function in the nucleus (Pb)

low background simpler initial state

Pb→ photo-production in CMS Unexplored (x,QUnexplored (x,Q22) regime:) regime: Pin down amount of low-x suppression Pin down amount of low-x suppression

in the Pb nuclear PDF (compared to the in the Pb nuclear PDF (compared to the proton PDF)proton PDF)

dAu eA



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SummarySummary

CMS has a broad and exciting heavy ion program, CMS has a broad and exciting heavy ion program, including:including: Bulk observables (soft physics)Bulk observables (soft physics)



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SummarySummary

CMS has a broad and exciting heavy ion program, CMS has a broad and exciting heavy ion program, including:including: Jet physics Jet physics Quarkonia and heavy-quarksQuarkonia and heavy-quarks Ultra peripheral collisionsUltra peripheral collisions



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Backup slidesBackup slides



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Soft PhysicsSoft PhysicsCharged particle tracking

Pixel triplets+vertex+stripsPixel triplets+vertex+strips reconstructing down to preconstructing down to pTT=0.075 GeV/c with high efficiency (~80-90%) and =0.075 GeV/c with high efficiency (~80-90%) and

acceptanceacceptance The pThe pTT resolution is about 1-2% in the barrel region resolution is about 1-2% in the barrel region Fake track rateFake track rate

around per mille level in p+p, below 10% in central Pb+Pb for pT > 0.4 GeV/caround per mille level in p+p, below 10% in central Pb+Pb for pT > 0.4 GeV/c Steps at 1 and 2 GeV/c are due to stricter requirements (points on track)Steps at 1 and 2 GeV/c are due to stricter requirements (points on track) Close to flat and smooth in the mid-rapidity regionClose to flat and smooth in the mid-rapidity region



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Jet quenchingJet quenching At RHIC, suppression of leading At RHIC, suppression of leading

particlesparticles Interpretated by “parton energy Interpretated by “parton energy

loss” models in the mediumloss” models in the medium Loose energy by gluon –strahlungLoose energy by gluon –strahlung transport coefficient hˆqi, transport coefficient hˆqi,

characterizing the scattering characterizing the scattering power of the mediumpower of the medium

GLV: Gyulassy M, Levai P and Vitev I nucl-th/0006010,hep-ph/0209161

BDMPS:Baier R, Dokshitzer Y L, Mueller A H, Peigne S and Schiff

hep-ph/9608322, hep-ph/0002198, hep-ph/0005129, hep-ph/0302184



2020

+Jet:In medium modified +Jet:In medium modified fragmentation functionfragmentation function



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Generated eventsGenerated events



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Reconstruction/Photon IDReconstruction/Photon ID



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Jet finding biasJet finding bias

Setting working point Jet finding (away side)

Main contribution to systematic uncertaintyBiased to parton with high ET (high pt particles)

Heavy-Ion Physics with CMS

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