Exploring Hot QCD Matter with ALICE PHENO11, Madison WIHot QCD Matter in ALICE1 Heavy Ion...
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Transcript of Exploring Hot QCD Matter with ALICE PHENO11, Madison WIHot QCD Matter in ALICE1 Heavy Ion...
Exploring Hot QCD Matter with ALICE
PHENO11, Madison WI Hot QCD Matter in ALICE 1
• Heavy Ion Collisions: what are we after?• ALICE Overview• ALICE results from 2010 Pb+Pb run• Putting together RHIC and LHC:
What have we learned about hot QCD matter ?
Peter Jacobs, Lawrence Berkeley National Laboratoryfor the ALICE Collaboration
QCD Phase Diagram: qualitative view
PHENO11, Madison WI Hot QCD Matter in ALICE 2
Tem
pera
ture ~170
MeV
Baryon chemical potential µB
~few hundred MeV
Deconfined Quark-Gluon Plasma
QCD thermodynamics: calculation
PHENO11, Madison WI Hot QCD Matter in ALICE 3
42
30TgDOF
4T
T [MeV]
QCD on the lattice (B=0)
Cross-over, not sharp phase transition (like ionization of atomic plasma)
Slow convergence to non-interacting Steffan-Boltzmann limitWhat are the quasi-particles? “Strongly-coupled” plasma?
RHIC LHC?
4Hot QCD Matter in ALICE
ALICE is the comprehensive heavy ion experiment at the LHC
Design optimized for huge particle multiplicities of nuclear collisions
ALICE
PHENO11, Madison WI
ALICE vs ATLAS/CMS
PHENO11, Madison WI Hot QCD Matter in ALICE 5
Requirements for heavy ion physics:• measure large-scale collective phenomena:
reconstruct complex hadronic events• precise measurements of heavy flavor, photons, leptons, jets and jet fragments• energy scale
→ robust tracking ~ 100 MeV – 100 GeV→ calorimetry ~ 200 GeV
• low material budget near vertex• particle ID: multiple detector technologies
Requirements for Higgs/SUSY searches:• missing energy signatures: hermetic coverage• energy scale 10 GeV – 1 TeV• tiny cross sections: high rate and rejection capabilities
ALICE favors robust tracking, precision, and low mass over large acceptance, high rate, and huge dynamic range
November 7 2010: First Pb+Pb collisions at √sNN=2.76 TeV
PHENO11, Madison WI Hot QCD Matter in ALICE 6
PHENO11, Madison WI 7
Particle ID: TPC dE/dx
Hot QCD Matter in ALICECopious production of anti-nuclei
Tomography via -conversions
PHENO11, Madison WI Hot QCD Matter in ALICE 8
Inner material understood better than 10%
Compare data and MC
NLO(W. Vogelsang)
M
Charm in Pb+Pb
PHENO11, Madison WI 9Hot QCD Matter in ALICE
J/ψμ+μ-
D+K-
D0K-+
Heavy flavor in p+p: consistency check
PHENO11, Madison WI Hot QCD Matter in ALICE 10
Compare directly measured electrons and electrons calculated from D-decay
good agreement at low pt (charm dominant)
Measuring collision geometry I
PHENO11, Madison WI Hot QCD Matter in ALICE 11
Nuclei are “macroscopic”characterize collisions by impact parameter
Correlate particle yields from ~causally disconnected parts of phase space
correlation arises from common dependence on collision impact parameter
Measuring collision geometry II
PHENO11, Madison WI Hot QCD Matter in ALICE 12
For
war
d ne
utro
ns
Charged hadrons ~3
• Order events by centrality metric• Classify into percentile bins of “centrality”
HI jargon: “0-5% central”
Glauber modeling• Nbin: effective number of binary nucleon collisions (~5-10% precision)• Npart: number of (inelastically) participating nucleons
ALICE Results I: hadron multiplicityPRL, 105, 252301 (2010), arXiv:1011.3916
√sNN=2.76 TeV Pb+Pb, 0-5% central, |η|<0.5
2 dNch/dη / <Npart> = 8.3 ± 0.4 (sys.)PHENO11, Madison WI 13Hot QCD Matter in ALICE
dNch/dη: model comparisons
pp extrapolation
pQCD-based MC
Saturation
PRL, 105, 252301 (2010), arXiv:1011.3916
dNch/dη = 1584 ± 76 (sys.)
√sNN=2.76 TeV Pb+Pb, 0-5% central, |η|<0.5
Energy density estimate (Bjorken):
PHENO11, Madison WI 14Hot QCD Matter in ALICE
dNch/dη: Centrality dependencePRL, 106, 032301 (2011), arXiv:1012.1657
Interpolation between 2.36 and 7 TeV pp
Pb+Pb, √sNN=2.76 TeV
2.5% bins
|η|<0.5
ALICELH
C s
cale
RH
IC scaleRHIC
peripheral central
PHENO11, Madison WI 15Hot QCD Matter in ALICEStriking centrality-independent scaling RHICLHC
dNch/dη vs. centrality: modelsPRL, 106, 032301 (2011), arXiv:1012.1657
Two-component models Soft (~Npart) and hard
(~Ncoll) processes
Saturation-type models Parametrization of the saturation
scale with centrality
Comparison to data DPMJET (incl. string fusion)
stronger rise than data HIJING 2.0 (no quenching)
Strong centrality dependent gluon shadowing
Fine-tuned to 0-5% dN/dη Saturation models [12-14]
Most have too much saturation
Pb+Pb, √sNN=2.76 TeV
Albacete and Dumitru (arXiV:1011.5161):• Most sophisticated saturation model:
evolution, running coupling• Captures full centrality dependence…?
PHENO11, Madison WI 16Hot QCD Matter in ALICE
Collective Flow of QCD Matter
PHENO11, Madison WI Hot QCD Matter in ALICE 17
Initial spatial anisotropy
xy z
py
px
22
22
xy
xy
22
22
2
yx
yx
pp
ppv
Elliptic flow
Final momentum anisotropy
Interaction of constituents
Elliptic flow v2: LHC vs RHIC
PHENO11, Madison WI Hot QCD Matter in ALICE 18
PRL 105, 252302 (2010)PRL 105, 252302 (2010)
Striking similarity of pT-differential v2 at RHIC and LHC
19Hot QCD Matter in ALICE
Shear viscosity in fluids
PHENO11, Madison WI
Shear viscosity characterizes the efficiency of momentum transport
Large quasi-particle interaction cross section Strongly-coupled matterSmall shear viscosity”perfect liquid”
AdS/CFT and kinetic theory: absolute lower bound
Elliptic flow: data vs. viscous hydrodynamic modeling
PHENO11, Madison WI Hot QCD Matter in ALICE 20
e.g. Song, Bass, and Heinz, arXiv:1103.2380
pT-differentialpT-integrated
peripheralcentral
Preferred values: /s(RHIC)=0.16, /s(LHC)=0.20
Shear viscosity: expectations from QCD
PHENO11, Madison WI Hot QCD Matter in ALICE 21
Analytic: Csernai, Kapusta and McClerran PRL 97, 152303 (2006)Lattice: H. Meyer, PR D76, 101701R (2007)
pQCD w/ running coupling
Chiral limit,resonance gas
1/4 Lattice QCD
Temperature (MeV)
If TLHC > TRHIC, expect /s(LHC) > /s(RHIC)
Jet quenching
22
Total medium-induced energy loss:
Plasma transport coefficient:
Apr 4, 2011 LHC News - Sonoma State
Radiative energy loss in QCD (multiple soft scattering):
Jet quenching via leading charged hadron suppression
PHENO11, Madison WI Hot QCD Matter in ALICE 23
Phys. Lett. B 696 (2011)Phys. Lett. B 696 (2011)
peripheral
central
pTpT
p+p reference at 2.76 TeV: interpolated
Jet quenching: RHIC vs. LHC
Apr 4, 2011 LHC News - Sonoma State 24
Phys. Lett. B 696 (2011)Phys. Lett. B 696 (2011)
Qualitatively similar, quantitatively different
Where comparable, LHC quenching is larger
higher color charge density
0 vs charged hadrons/RHIC vs LHC
PHENO11, Madison WI Hot QCD Matter in ALICE 25
RHIC 0, , direct
RHIC/LHC charged hadrons
High pT dependence qualitatively different:• different quenching mechanisms?• consequence of steeper incl spectrum at RHIC? (near phase space limit…)
Jet quenching: comparison to pQCD-based models
Apr 4, 2011 LHC News - Sonoma State 26
X-F Che et al.,arXiv1102.5614 Horowitz and Gyulassy, arXiv1104.4958
Several formalisms different treatments of medium, radiative/elastic e-lossModels calibrated at RHICScale energy density with charged multiplicity (factor~2)
Models systematically predict too much quenching….?• must measure p+p reference at 2.76 TeV (data now on tape)• something missing in the formalism?
Summary and Outlook
PHENO11, Madison WI Hot QCD Matter in ALICE 27
Initial LHC heavy ion run: machine and ALICE worked superbly
First task is to rediscover and compare to the striking heavy ion phenomena found at RHIC
• qualitative similarities but quantitative differences• consistent picture of strongly-coupled (low viscosity) fluid with high color-charge density (opaque to jets)
• discrepancies with models: requires some rethinking
Next for ALICE: qualitative quantitative• quarkonia (deconfinement signature)• charm• full jets (newly commissioned large EMCal)• correlations of many kinds…