heavy-ion physics with cms
DESCRIPTION
Heavy-Ion Physics with CMS. Aneta Iordanova University of Illinois at Chicago. Expected energy density at the LHC. CMS Heavy-Ion program. J. Phys. G: Nucl. Part. Phys. 34 (2007) 2307-2455. Study of QCD matter under extreme conditions Pb+Pb @ √s NN = 5.5 TeV Bulk observables - PowerPoint PPT PresentationTRANSCRIPT
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
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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
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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
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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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Aneta IordanovaAneta IordanovaUniversity of Illinois at ChicagoUniversity of Illinois at Chicago
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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
Moriond QCDMoriond QCDHeavy-Ion SessionHeavy-Ion Session
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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
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+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)