E. Scapparone (INFN – Bologna, Italy) o n behalf of the ALICE Collaboration MIAMI 2012
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Transcript of E. Scapparone (INFN – Bologna, Italy) o n behalf of the ALICE Collaboration MIAMI 2012
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E. Scapparone (INFN – Bologna, Italy)on behalf of the ALICE CollaborationMIAMI 2012Fort Lauderdale, Dec. 17, 2012
Recent results from ALICE
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~ 1300 members from both NP and HEP communities 35 Countries 132 Institutes~ 160 MCHF capital cost (+ ‘free’ magnet)
Armenia Brazil Chile China Croatia Cuba Czech Republic Denmark Egypt Finland
France
Germany
Greece
Hungary
India
Italy
Japan Mexico Netherlands
Norway Pakistan Peru
Poland
Romania
Russia
Serbia
Slovakia
South Africa
South Ko-rea
Spain Sweden
Switzerland
Thailand Turkey Ukraine
United Kingdom
United States
The ALICE Collaboration
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Detector:Length: 26 metersHeight: 16 metersWeight: 10,000 tons
Collaboration:> 1000 Members> 100 Institutes > 30 countries
THE ALICE DETECTOR
Muon Spectrometer -2.5 > h > -4
V0 scintillators: h -1.7– -3.7, 2.8–5.1
PID:SPD, TPC (dE/dX)TOF (Time of Flight)TRD (e/p)HMPID (Cherenkov)
Centrality:V0ZDC
Tracking @ | |h < 1:ITSTPCTRD
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• particle identification (practically all known techniques)• extremely low-mass tracker ~ 10% of X0
• excellent vertexing capability• efficient low-momentum tracking – down to ~ 100 MeV/c
vertexingHMPID
ITS TPC
TRD
TOF
ALICE performance
ALICE performance
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Warning: this is not an exhaustive presentation on All ALICE results, but just a talk focusing on few selected ALICE results…
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A taste of pp results at √s=2.76 Tev and √s=7 TeV
J/y yield as a function of charged-multiplicity in pp collisions at √s=7 TeV
ATLAS
LHCb
CMS
ALICE mm
ALICE e+e-
J/y : the 4 LHC experiments
J/Y accompanied by high hadronic activity.
MPI for heavy quarks ?
Hard partonic scattering shows a different trend
Phys.Lett. B712 (2012) 165
The charged particle multiplicities measured in high-multiplicity ppcollisions at LHC energies ~ same order as those measured in heavy-ion collisions at lower energies. Are their production rates in high multiplicity pp collisions already exhibiting any effect like J/ψ suppression ?
Phys.Lett.B704 (2011) 442
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First measurement of J/y polarization at LHC
M.Butenschoen, A.Kniehl, arXiv:1201.3862
• Long standing puzzle with Tevatron results
• First result at the LHC: almost no polarization for the J/
• Crucial input for tuning NRQCD parameters
(Phys. Rev. Lett. 108 (2012) 082001)
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2010 run : L ~ 7 mb -1
2011 run : L ~ 100 mb -1
Heavy ions !
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Global properties
At LHC the fireball ishotter, larger and lasts more
Photon T = 304±51 MeV ~ 1.4 x TRHIC Lifetime: +20% wrt RHIC(~ 10 fm/c)
Phys. Lett. B 696 (2011) 328
Volume ~ 2 x RHIC (R3 ~ 300 fm3)
Phys. Lett. B 696 (2011) 328
tmdy
dN
AV
E
0
1)(
Energy density ~ 3 x RHIC~ 10 GeV/fm3
PRL 105, 252301 (2010)
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S. Das at QM2012
Hydro Calculation
RHIC
p
p
K
PbPb
pp
Radial flow pushes spectra depending on mass
Very strong radial flow, b ≈ 0.65 (2/3 of c!) even larger than predicted by most recent hydro
p-
Isotropic radial flow
P >> 0
P = 0
v0
v0
v0
Very significant changes in slope compared to RHIC, most dramatically for protons 10
Radial Flow- pressure P in center
drives expansion flow
velocity b=v0/c
- depends on f(P, t, EoS,)
momentum p = g m v0 =>
particles of different mass have
characteristic & different
momentum spectra
v0
v0
v0
What about Radial Flow @ LHC ?
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11arXiv: 1208.1272, accepted by PRL
Fit to the data with Blast-Wave modelSchnedermann et al., PRC 48, 2462 (1993)⟨βT ⟩ = 0.65 ± 0.02
Comparison with models:VISH2+1: viscous hydrodynamicsShen et al., PRC 84, 044903 (2011),p K ok up to 1.5 GeV/c, missing p lack of
hadron phase ?HKM: hydro + UrQMD(hadron particle Cascade), Karpenko et al., arXiv:1204.5351 improved p description (hadron cascade increases radial flow)Krakow: viscous corrections, lower effective Tch, Bozek, PRC 85, 034901 (2012)
Comparing to models
Model vs data comparison suggestsa hydrodynamic interpretation of the transverse momentum spectra at the LHC.
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flow" directed" cos1 v flow" elliptic" 2cos2 v
Fourier expansion of azimuthal distribution:
Flow: Correlation between coordinate and momentum space => azimuthal asymmetry of interaction region transported to the p T
® measure the strength of collective phenomena Large mean free path
particles stream out isotropically, no memory of the asymmetry extreme: ideal gas (infinite mean free path)
Small mean free pathlarger density gradient -> larger pressure gradient -> larger momentum extreme: ideal liquid (zero mean free path, hydrodynamic limit)
py
Py
Px
....2cos2)cos(212)( 21
0 RPRPRP
vvN
d
dN
x
yz
Azimuthal asimmetries
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• Collective behavior observed in Pb-Pb collisions at LHC (+30% wrt v2
RHIC) ideal fluid behavior (extremely low viscosity h » 0 )
• v2 as a function of pT not dramatically different wrt RHIC (few variations for identified hadrons, predicted by hydro models - see C. Shen et al arXiv:1105.3226) v2 increase with s from hadron <pT> increase• Testing hydrodynamical evolution
central
semi-central
PRL 105, 252302 (2010), > 250 citations (INSPIRE)
v2 Measurements at the LHC
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Viscous hydrodynamic model calculations reproduce the main features of v2 atlow transverse momentum:• mass dependence is better modelled for peripheral collisions;• for central collisions overestimate baryon flow;• Adding hadronic rescattering phase (VISHNU) improves the agreement with data Heinz, Shen, Song, AIP Conf. Proc. 1441, 766 (2012)
Hydrodynamic model predictions
Hydro not ok for baryons at 10-20%centrality
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Particles
STAR, S.Shu at QM2012 NCQ scaling goodbye….
NCQ scaling: partonic dof dominant; No scaling: hadronic dof dominant
NCQ scaling holds q
uite well at
any centralities a
t low energies..
Alice: stronger NCQ violation. Stronger radialflow or Jet quenching/rescattering, more important than coalescence ?
STAR, Phys. Rev. C 77 (2008) 54901
Dat
a/fit
PHENIX Phys. Rev. C85 064914(2012)
NCQ scaling at R
HIC holds in
0-10%
Centrality bin: d
eviations st
art at ~1GeV/c
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“ideal” shape of participants’ overlap is
~ elliptic; no odd harmonics expected participants’ plane coincides with event plane but fluctuations in the initial position of
the partecipant nucleons give:
- plane event plane
- v3 (“triangular”) harmonic appears
[B Alver & G Roland, PRC81 (2010) 054905]
and indeed, v3 0 !
ALICE: PRL 107 (2011) 032301
Fluctuations v3 ….(+ 3 v3 cos(3( -j y)))Sensitive to h/s
Similar v2 trend, mass ordering;
v3 has weaker centrality dependence than v2 when calculated wrt participants plane, v3 vanishes (as expected, if due to fluctuations…).
Progress in precision measurements of h/s
fluctuations discriminate & constrain models:large sensitivity to viscosity
arXiv:1205.5761v2
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- Less suppression wrt RHIC;- ALICE data flatter at high centralities: almost no centrality dependence for Npart > 100;- Evidence for c quark coalescence ?
2.5 < y < 4
1.2 < y < 2.2
J/Y in ALICE: the forward region
σ(cc)LHC ≈ 10 × σ(cc)RHIC
c
c
c
c
Colour screening @ work
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J/Y in ALICE: the pT dependence
- Nice agreement with CMS data;- Higher suppression at high pT
Predicted by coalescence model
Still uncertainties from shadowing run p-Pb coming soon
Does shadowing depends on the interaction centrality ?
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ψ’ should have a similar suppression at LHC energies wrt J/ψ (ψ’ melts at smaller T wrt J/ψ)
Tc ~ 160-170 MeVTAlice ~ 300 Mev
l ~ 0.15 fm > 0.29 fm (J/Y) > 0.56 fm (ψ’ )
ALICE not confirming CMS data(though at different rapidity)
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Hints for J/Y and D v2 ≠ 0
..hints for a strong coupling c - medium
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First pA Collision, Sep. 13th, 2012
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- Data favour models including shadowing- Saturation models predict too steep h dependence
Compatible with 1above 2-3 GeV/c→ binary scaling ispreserved, no (or small)initial state effectsNo sign ( or weak)Cronin effect
pT spectrum not reproduced by HIJING or DPMJET.Both saturation models and models with shadowing can reproduce data
p-Pb pilot run, Sep 2012
arXiv:1210.3615v1,arXiv:1210.4520v1
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Initial parton-parton scattering with large momentum transfer:
► calculable in pQCD
Particle jets follow direction of partons
Nucleus-nucleus collisions
► hard initial scattering
► scattered partons probe traversed hot and dense medium
► ‘jet tomography’
Hard Processes to Probe the Medium (Rutherford experiment...)
)(Yield
)(Yield)(
ppAACOLL
AAAA
T
TT pN
ppR
Medium modification quantified vianuclear modification factor RAA
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RAA(pT) for charged particles produced in 0-5% centrality range @ LHC:minimum for pT ~ 6-7 GeV/c then slow increase at high pTinterpreted as due to loss of energy of parton propagating through medium.A deeper inspection: selected hadrons in the medium: heavy quarks
Strong suppression for hadrons….
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Near side: compatible with PythiaBulk: p/p increase; overall baryon enhancement
Jet particle composition
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Energy loss in a dense medium proceeds mostly through gluon radiation:
- Gluon radiation higher for light quark than for heavy quark:
( dead cone: for q < MQ/EQ)
2) Gluon radiation stronger for gluons wrt quarks (higher colour charge);
Cr= 3
Summary: smaller DE expected for heavy quarks
L path in the medium
L
1)
q smaller for light quarks
..and heavy hadrons originate mostly from quark jets
Cr= 3/4 Cr= 1/2
<DE> as · Cr · q · L 2^
DEg > DEq> DEc > DEb
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Hint for smaller D0,D+,D- suppression for pt < 8 GeV/c ?
RAA for heavy flavours
ALICE: JHEP 09 (2012) 112
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New: DS !
Less suppression (s quark @ work) ?
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► Strong detector/physics efforts in view of the LHC upgrade
► Upgrade experiment to be able to run with 50 kHz Pb-Pb collision rates, several nb-1 per run (2 MHz proton-proton)
► Various new detectors being proposed (stregthen ALICE uniqueness at LHC)
ITS: B/D separation, heavy baryons, low-mass dielectrons
MFT: b-tagging for low pt J/psi and low-mass di-muons at forward y
VHMPID: New high momentum PID capabilities
FOCAL: Low-x physics with identified g/p0
The future: upgrade planning