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ALICE Status Report106th LHCC meeting - Open session
Andrea Rossi, on behalf of the ALICE collaboration
1
ALICE publications in pp collisions
2
• Multiplicity & distributions• 900 GeV; EPJC: Vol. 65 (2010) 111• 900,2.36 TeV; EPJC: Vol. 68 (2010) 89• 7 TeV EPJC: Vol. 68 (2010) 345
• pbar/p ratio (900 GeV & 7 TeV) PRL: Vol. 105 (2010) 072002• Momentum distributions (900 GeV) PLB: Vol. 693 (2010) 53• Bose-Einstein correlations (900 GeV) PRD: Vol. 82 (2010) 052001• Strangeness (K0, , , ,L X W f) at 900 GeV EPJC: Vol: 71, (2011) 1594• Identified charged particle spectra (900 GeV)
• http://arxiv.org/abs/1101.4110 accepted by EPJC• Pion Bose-Einstein correlations at 0.9 and 7 TeV
• http://arxiv.org/abs/1101.3665v1 submitted to Phys. Rev. D• J/Y production at 7 TeV :
• http://arxiv.org/abs/arXiv:1105.0380 submitted to Phys. Lett. B
In this talk, focus on PbPb
results
QM2011 J. Schukraft 3
ALICE Talks atPlenary:ALICE overview: J. SchukraftGlobal properties: A. ToiaHBT: A. KisielFlow: R. Snellings
RAA: H. Appelshaeuser
Identified Particles: M. Floris
Correlations (IAA): Jan Fiete GO
J/Psi: G. Martinez GarciaHeavy Flavour: A. Dainese
Correlations & FluctuationsElliptic flow: A. BilandzicTriggered dihadrons: A. AdareUntriggered dihadrons: A. TimminsDihadrons pp: Y. MaopT fluctuations: S. HeckelHBT: J. Mercado
HBT K0s pp: T. Humanic
Global & Collective
Nch, centrality: C. Loizides
'strong CP viol': P. Christakoglou
directed flow v1: I. Selyuzhenkov
elliptic flow high pt: A. Dobrin
elliptic flow PID: M. KrzewickiUltra-peripheral: C. OppedisanoDiffraction pp: M. Poghosyan
Heavy FlavourHF m: X. ZhangHF e: S. MasciocchiJ/Y pp: R. ArnaldiJ/ Y Pb: P. Pillot
D mesons RAA: A. Rossi
Identified hadronsPID methods: A. Kalweitp/K/p in pp: M. Chojnackip0,h in pp: K. ReygersResonances: A. PulvirentiL/K0: I. BelikovX, W pp Pb: D. Chinellato
RAA L/K0 : S. Schuchmann
, , r w f pp: A. de Falco
JetsJet reconstruction: C. Klein-Boesing
RAA charged: J. Otwinowski
RAA p0: G. Conesa Balbastre
ExperimentsUpgrades: T. Peitzmanncross section pp: K. Oyama
22-28 May
In this talk: focus on
highlights of PbPb results
2011 runs
4
2.76 TeV pp run statistics
5
System Energy (√sNN) Trigger Integr. Lum.
pp 2.76 Min. Bias* 1.37 nb-1
pp 2.76Muon
SPD high mult.EMCal
20 nb-1
*w/o SDD (0.65 nb-1 w/ SDD)
2.76 TeV pp run: … not only a fundamental reference for PbPb analyses
ongoing 7 TeV pp run now Lint>400 nb-1 with unlike
sign muon pair trigger
- min. bias- single muon trigger
(x10)
~ 71 nb-1
Study of the QGP expanding fireball
6
HIC complex system of strongly interacting matter• Extended size• Local thermodynamical equilibrium
25 years experimental research to answer fundamental questions like:How does the system evolve? How does the collision geometry manifest itself and what can we learn from it?Can we access medium global properties (energy density, temperature, size)?How is particle production modified?How do high energetic partons interact with the medium?
An expanding and cooling fireball
7
A challenging environment!
Particle Identification
8
TPC dE/dx Time Of Flight
ITS
Anti-Matter PID
9
Anti-Hypertriton
Study of the QGP expanding fireball
10
HIC complex system of strongly interacting matter• Extended size• Local thermodynamical equilibrium
25 years experimental research to answer fundamental questions like:How does the system evolve? How does the collision geometry manifest itself and what can we learn from it?Can we access medium global properties (energy density, temperature, size)?How is particle production modified?How do high energetic partons interact with the medium?
An expanding and cooling fireball
Triggered Azimuthal Correlations
11
• Triggered correlations: choose a particle from one pT region ("trigger particle") and correlate with particles from another pT region ("associated particles") where pT,assoc < pT,trig in bins of pT,trig and pT,assoc
• Lower pT
• Assess the bulk of the correlations• Dominated by hydrodynamics and flow• Ridge
• Higher pT
• Dominated by jets• Quenching/suppression, broadening
Away-side jet disappears
One of the main highlights
at Quark Matter 2011
Triggered Azimuthal Correlations
12
Clean double Hump (aka 'Mach Cone') appears for ultra-central(without any flow subtraction !)
Full correlation structure described by Fourier Coefficients v1,v2, v3, v4,v5 (for |h|>0.8)v3 very visible, indeed, v3 ≈ v2 for very central
'Mach Cone' & 'Near Side Ridge' shapes evolve smooth with magnitude of v2 and v3
2 Particle correlation C( )DhDf 'Near Side Ridge'
broad away side structurev2v3
Dh > 0.8
v1+v2+v3+v4+v5
Projection on Df for Dh > 0.8
Any function can be described with enough coefficients… can we interpret them?
Anisotropic transverse flow
13
Initial spatial anisotropy
py
py
€
dN
d(ϕ −ψ n )∝1+ 2 vn
n=1
∑ cos(n[ϕ −ψ n ])
Smooth matter distribution in the colliding nuclei
• Yn=YRP
• v2n+1 = 0 by symmetry
€
vn = cos(n[ϕ −ψ n ])
€
ε =y 2 − x 2
y 2 + x 2
€
v2 =py
2 − px2
py2 + px
2(elliptic flow)
Final momentum anisotropyReflected in azimuthal distribution
Anisotropic transverse flow
14
Initial spatial anisotropy
py
py
€
ε =y 2 − x 2
y 2 + x 2
€
v2 =py
2 − px2
py2 + px
2(elliptic flow)
Final momentum anisotropyReflected in azimuthal distribution
yRP
y2
y3
Smooth matter distribution in the colliding nuclei
• Yn=YRP
• v2n+1 = 0 by symmetry Fluctuations in the matter distribution
→ event by event fluctuation of the plane of symmetry around YRP
→ non negligible odd harmonics
v3,v5,.. magnitude regulated by shear viscosity to entropy density ratio (h/s)
Higher Order Flow v3,v4,..
15
arXiv:1105.3865Accepted by PRL
v2
v3{2} = <cos(3(f1-f2))>
22
22
}4{
}2{
nnn
nnn
vv
vv
v3{4} 4 particle cumulant
v3 relative to reaction & participant planes
v4{2} = <cos(4(f1-f2))>
V3:small dependence on centrality
v3{4} > 0 => not non-flow
v3{4} < v3{2} => geometry fluctuations !
V3{YRP} ≈ 0 => Y3 indep. fluctuations w.r.t. YRP
Flow & Triggered Correlations
16
Any function can be described with enough coefficients- But not if we impose factorization C(pT
trig, pTassoc)=v(pT
trig)*v(pTassoc) (or take coefficients from flow
analysis).
Correlations (|h|>0.8) can be described consistently with 'collective flow' hypothesis
for pT < 3-4 GeV ( consistent with 'collectivity ')
only partially or not at all for pT > 5 GeV
≈ coefficients from flow analysis
coefficients from C(PT1,PT2) analysis
v3 : explain the 'near side long range ridge' and the away side 'Mach cone’ for |h| > 0.8 and pT < 3-4 GeV !
'away side jet'
Triangular Flow v3
17
v3 shows mass splitting expected from hydro flow
Has the magnitude (and pT dependence) expected from geometry fluctuations
(and has different sensitivity to h/s than v2 )
v3 for p/K/p
p
p
v3 v4 v5 versus pT
v2
v3
v4
v5
Hydro calculation for v3
K
v3 : - Explain the 'near side long range ridge' and the away side 'Mach cone’ for |h| > 0.8 and pT < 3-4 GeV !- Compatible with hydrodynamic predictions- Induced by geometry fluctuations
More on v2: identified particle flow
p/K/p v2
RHIC
PID flow: - Mass splitting and ordering ≈ hydro - p and anti-p are 'pushed' further compared to
RHIC≈ expected from hydro (with larger radial flow)- p and K flow well described by hydro- anti-p flow not well described by hydro in more
central collisions
Centraliy 10%-20%
Centraliy 40%-50%
Study of the QGP expanding fireball
19
HIC complex system of strongly interacting matter• Extended size• Local thermodynamical equilibrium
25 years experimental research to answer fundamental questions like:How does the system evolve? How does the collision geometry manifest itself and what can we learn from it?Can we access medium global properties (energy density, temperature, size)?How is particle production modified?How do high energetic partons interact with the medium?
An expanding and cooling fireball
Transverse energy & energy density
20
ε t ≈16 GeV/(fm2c)factor 2.7 larger than RHIC
€
ε = 1
πR2τ
dETdy
R =1.12A1/ 3fm
Energy density (Bjorken)
Grow with power of CM system energy faster than simple logarithmic scaling extrapolated from
lower energy (similar trend than dNch/dh)
21
Hydro parameters from Blast Wave Fit
RHIC
Identified Particle spectra
Hydro Prediction
Very significant changes in slope compared to RHICMost dramatically for protons
Very strong radial flow, b ≈ 0.66 even larger than predicted by most recent hydro
RHIC
more central
-p
K-
K0
p-
22
Ratio at MaximumRHIC
L/K0
'Baryon anomaly': L/K0
Baryon/Meson ratio still strongly enhanced x 3 compared to pp at 3 GeV
- Enhancement slightly larger than at RHIC 200 GeV
- Still present at 6 GeV/c
- Maximum shift very little in pT compared to RHIC
despite large change in underlying spectra !
Recombination + Radial flow?
x 3
Study of the QGP expanding fireball
23
HIC complex system of strongly interacting matter• Extended size• Local thermodynamical equilibrium
25 years experimental research to answer fundamental questions like:How does the system evolve? How does the collision geometry manifest itself and what can we learn from it?Can we access medium global properties (energy density, temperature, size)?How is particle production modified?How do high energetic partons interact with the medium?
→ in-medium partonic energy loss → parton nature (quark/gluon), mass dependence?
An expanding and cooling fireball
24
Charged particle nuclear modification factor (RAA)
PLB 696 (2011) 30-39
Extrapolated reference=> large syst. error
€
RAA =# particle observed in Pb - Pb collisions
(#particle observed in pp collisions) × number of binary collisions
€
RAA (pt ) =d2Nch
AA /dηdptd2Nch
pp /dηdpt × Ncoll
Pb-Pb
pp reference
Charged Particle RAA: Ingredients
25
Measured reference, still needs extrapolation for pT> 30 GeV(but not in √s => smaller syst. error)
Note: measured spectrum somewhat different than previous extrapolation
(RAA goes down, but stays well within old systematic error bands)
pp spectrum
2.76 TeV
4-7 GeV
PHENIX
pT 4-7 GeV
<RAA > in pT bins vers. Nch
RAA: Results
26
Rise continues beyond 20 GeVGradual change of slope above 30-40 GeVNote: centrality dependence is independent of reference spectrum !
RAA versus pT
RCP L, K
L
K0
K ±
Identified particle RAA(K/L): - Interesting differences < 6 GeV
- RAA universal > 6 GeV
Charm RAA: Ingredients
QM2011 J. Schukraft 27
D0→ K- p+
D0→ K-p+ D+→ K-p+p+ D*+→ D0 p+
- charm in pp @ 7 TeV- subtract B feed down- absolute cross section- scale (FONLL) to 2.76 TeV- check with CDF & data @ 2.76 TeV- compare with other expts
pp 2.76 TeV
Total Charm cross section
ALICEATLASLHCb
- charm central in Pb-Pb!- subtract B feed down
- absolute cross section (TAA)
=> prompt charm RAA (pT, centrality)- check consistency D0, D+
Charm RAA: results
28
D0→ K-p+ D+→ K-p+p+
Charm RAA: results
29
Qualitative expectation: RAA Charm > RAA Mesons- DE gluon > DE quark (Casimir factor)- DE massless parton > DE massive quark ('dead cone')
Needs quantitative comparison with quenching calculations
- RAA prompt charm ≈ RAA pions for pT > 5-6 GeV
- RAA charm > RAA p for pT < 5 GeV ?
(p+ + p-) RAA
Strong suppression observed in central (0-20%) collisions,
factor ~4-5 for pt >5 GeV/c
little shadowing
Hot medium effect
p-Pb run at LHC crucial to understand the low-pt rise
Heavy Flavour decay muons
30
- single prompt muon cross section (c,b) pp @ 7 TeV
Inclusive Electrons pp
Background
Heavy Flavour Electrons
QM2011 J. Schukraft 31
Inclusive electron spectrum pp 7 TeVBackground 'cocktail' based on measured p±
subtract => heavy flavour electrons (c, b)consistent with pQCD (and measured charm!)
impact parameter cut => select beautyconsistent with pQCD
Beauty Electrons Beauty + Charm
pQCD
Heavy Flavour decay Electrons
32
Inclusive Electrons Pb
Data / Background => hint of excess around 2 GeVinteresting region (thermal radiation ? seen at RHIC…)
33
Heavy Flavour decay Electrons & Muons RAA
- pp reference: 7 TeV measurement scaled (FONLL) to 2.76 TeV
Resulting HFe RAA consistent wit HFm for pT > 3-4 GeV
Heavy Flavour RAA Comparison
QM2011 J. Schukraft 34
Consistent centrality dependence Muons ~ Electrons ~ CMS J/y from B (QM2011)
D mesons clearly lower (charm vs beauty?)
D0 pt > 6 GeV/c m pt > 6 GeV/c e pt > 4.5 GeV/c
J/y suppression: Ingredients
QM2011 J. Schukraft 35
7 TeV pp J/y → mm
2.76 TeV pp
pp J/y Cross Section
7 TeV
2.76 TeV
7 TeV pp 4 LHC expts
Atlas
LHCb
CMS
mm
e+e-
J/y cross section ds/dydpT
7 TeV & 2.76 TeVAgreement with pQCDAgreement among 4 LHC experiments (in region of overlap)
7 TeV
2.76 TeV
J/y suppression: Results
36
PbPb
0-10%
Rather small suppression & centrality dependence
Di-muon channel
pT > 0, 2.5 <y<4
RCP
e+e-
J/y suppression: Compared to..
37
RCP(Alice/Atlas): suppression stronger at high pT ??
Phenix mm
RAA
ATLAS
RCP
Complementary measurements
Surprisingly (?) : less suppression than RHIC !
Progressing analyses
38
pp exclusive analyses: - Resonances in pp- Event shape
characterization in pp
Pb-Pb exclusive analyses:- Identified particle
- Including nuclei andanti‐nuclei- Azimuthal anisotropy- vn
- Chiral magnetic effects
- Event-by‐event fluctuations- HBT vs centrality
Analyses in both systems: - RAA - J/ψ (paper on pp results submitted)
- study of polarization- Single electron from heavy-flavor
decays- Single muons- Open charm- π0 production cross-section & RAA
- Azimuthal correlations
- Λ/K0s
- Multi‐strange particles
Extra slides
39
ResonancesResonances & Hyperons
40
Hyperons
Data Samples
41
Beam Energy # of Events
pp 900 GeV 300 k MB 2009, analysis finished
pp 900 GeV ~ 8 M MB 2010, partially analyzed
pp 2.36 TeV ~ 40 k MB 2009, only ITS, dNch/dh
pp 7 TeV ~ 800 M MB~ 50 M muons
~ 20 M high Nch
2010
PbPb 2.76 TeV/N ~ 30 M MB 2010
pp 2.76 TeV ~ 70 M MB~ 20 nb-1 (rare triggers)
2011, analysis started
30 h only
User activity – month on month increase
Average 7100 (+27%), 280 users (+16%) 1/4 of CPU resources
Average 5000 jobs, 190 usersFactor x2.5 increase over 2010 average
Average 5600 (+ 12%), 240 users (+20%)
Running jobs per user
43
User activity – month on month increase
Two weeks before final review - 10000 jobs in average• 5-6 May – all grid resources freed for users – 80% job slots
utilization ONLY from chaotic user analysis
Average 7500 jobs, 290 users
Stress-test for the GRID & Offline …OK!
44
5x increase of read traffic from Jul-Aug 2010 to today
4545
Detector:Size: 16 x 26 metersWeight: 10,000 tons
Collaboration:> 1000 Members> 100 Institutes > 30 countries
ALICE
ACORDE (cosmics)V0 scintillator centrality| |:h 1.7-3.7, 2.8-5.1T0 (timing)ZDC (centrality)
FMD (Nch -3.4<h<5)
PMD (Ng, Nch)
Central Barrel2 p tracking & PID
Dh ≈ ± 1
Muon Spectrometer 2.5 < h < 4
46
Detector Status
PLC 20J. Schukraft46
Complete since 2008: ITS, TPC, TOF, HMPID,FMD, T0, V0, ZDC, Muon arm, Acorde PMD , DAQ
Partial installation (2010): 4/10 EMCAL* (approved 2009)7/18 TRD* (approved 2002)3/5 PHOS (funding) ~ 60% HLT (High Level Trigger)
2011 10/10 EMCAL10/18 TRD
TRD to be completed end 2011
*upgrade to the original setup
ITS
TPC
TRD
TOF
EMCAL
PHOS
HMPID
L3 Magnet
RCP
e+e-
J/y suppression: Compared to..
47
Surprisingly (?) : less suppression than RHIC !
RCP(Alice/Atlas): suppression stronger at high pT ??
Caveats:
- J/y (B) about 10% (LHCb) => RAA(prompt) lower by ≈ 0.05
- compare to Phenix e+e- ? => less difference, still significant
- shadowing(LHC) > shadowing(RHIC) ? => RAA goes up ?
- cold nuclear matter suppression ?
Phenix mm
RAA
ATLAS
RCP
shadowing range
Complementary measurements
More on v2 • Non-flow contribution (d)• Measure flow fluctuations (s)
• different cumulants
• Identified particle flow (sensitive to radial expansion)
Anisotropic transverse flow
Initial spatial anisotropy
py
py
€
ε =y 2 − x 2
y 2 + x 2
from last LHCC
€
v2{2} ≅ v22 +σ 2
2 + δ
v2{4} ≅ v22 −σ 2
2
Final momentum anisotropyReflected in azimuthal distribution
€
v2 =py
2 − px2
py2 + px
2(elliptic flow)
More on v2
v2 no eta gap between particles
v2 |h|>1
both v2 corrected for remaining non-flow(Hijing or scaled pp)
Non-Flow corrections
€
v2{2} ≅ v22 +σ 2
2 + δ
v2{4} ≅ v22 −σ 2
2
More on v2 v2 Fluctuations Non-Flow corrections
€
v2{2} ≅ v22 +σ 2
2 + δ
v2{4} ≅ v22 −σ 2
2
Flow fluctuations:- comparable to RHIC (driven mostly by geometry)
More on v2 v2 Fluctuations Non-Flow corrections
€
v2{2} ≅ v22 +σ 2
2 + δ
v2{4} ≅ v22 −σ 2
2
p/K/p v2
RHIC
Flow fluctuations:- comparable to RHIC (driven mostly by geometry)
PID flow: - Mass splitting and ordering ≈ hydro - p and p are 'pushed' further compared to RHIC ≈ expected from hydro (with larger radial flow)
Triggered correlation at high pt & jets: IAA
52
• Extract near and away-side jet yields from per-trigger yields• Compare central and peripheral
collisions ICP
• Compare Pb+Pb and pp IAA
• Non-jet component (baseline) needs to be removed (no known assumption-free methods… pedestal at p/2, ALICE flow… )
• Measure in a region where the signal dominates over pedestal and v2 modulation(8 GeV/c < pT,trig < 15 GeV/c)
near
away
53
Triggered correlation at high pt & jets: IAA
• Peripheral events consistent with unity
• Near-side of central events slightly enhanced
IAA ~ 1.2 … unexpected and interesting• Away side of central events suppressed:
IAA ~ 0.6 … expected from in-medium energy loss
central
central
peripheral
Near Side
Away Side
Multiplicity & system size
54
• Multiplicity at central rapidity (Ingredient for many models)
• Study of system “size” at decoupling & decoupling time (within hydrodynamic scenario) via HBT analysis (quantum interference of
identical bosons emitted close in phase space from a common source) Phys.Lett.B 696:328-337,2011
Multiplicity at forward rapidity Total multiplicity
} Last LHCCK. Aamodt et al. (ALICE), Phys. Rev. Lett. 105, 252301 (2010)K. Aamodt et al. (ALICE), Phys. Rev. Lett. 106, 032301 (2011)
~linear increase with Npart
Tracking & Vertexing
55
SDD at nominal resolution
p±,p0 RAA
56
p0 from reconstruction of gamma conversions Being cross-checked with p0 spectra measured with EMCal & PHOS calorimeters
RHIC
Pb-Pb: K/p
STAR (including feed down)
PHENIX, Brahms (feed down corrected)
p/p
Particle Ratios
57
- pp: Thermus thermal fit rather poor (wasn't this better for pp at lower energies ??)
- K/p grows slightly from pp value- p/p ≈ like pp
Pb: p/p off by factor > 1.5 from predictions !but very compatible with RHIC !!
?
pp: 900 GeV & 7 TeV
Range of Thermal model prediction
Before we can conclude anythingwe need more particle species..
Comparing vn with en
58
CGC
GlauberGlauber
CGCCGC
CGC
v2 Fluctuations
v2 & v3 ultra-central (0% →5%) v2 {2}/e{2} & v2{4}/e{4}
v2 /e2 & v3/e3
Glauber
Glauber
'Flow Tomography' has thepotential to constrain geometry
improved precision on h/swhen comparing full hydro to measurements
Heavy Flavour decay muons
59
- single prompt muon cross section (c,b) pp @ 7 TeV- scaled (FONLL) to 2.76 TeV
- RAA (pT, centrality) with inclusive muons
Semi-peripheralPb-Pb 40-80%
Central Pb-Pb0-10%
Geometry of AA collisions
60
Centrality
61
2.8<h<5.1
-3.7<h<-1.7
Charm RAA: results
62
Strong suppression observed in central collisions (0-20%) wrt TAA-scaled pp reference
Significant suppression also in semiperipheral (40-80%) wrt TAA-scaled pp reference
• Can LHC solve the puzzle (measuring J/y and U families) ?
– suppression only: suppression for Y'(2S) ≈ y', Y''(3S) ≈J/y– suppression + recombination: Y', Y'' ~unaffected, J/y less suppression than @ RHIC
J/y Suppression
63
QM 2008 (P. Seyboth)
y’ c Y’’(3S) Y’(2S) J/y Y
Td/Tc1-1.2 1-1.2 1.1-1.3 1.2-2 1.5-2.5 3-5
Lattice QCD based predictions
of 'melting' temperature Td
(a bit dated..)
SPS ≈ RHIC
T/TC 1/-r-
-
J/-, -’
-c
y’
-b’
-’’
4
2
1
LHC??
Chiral Magnetic Effect ('strong parity violation')
64
RP 2cos
B
+-
Same charge correlations positiveOpposite charge correlations negative
RHIC ≈ LHCsomewhat unexpected
should decrease with Nch
may decrease with √s
RHIC : (++), (+-) different sign and magnitude
LHC: (++),(+-) same sign, similar magnitude?
cos
+ -
B
?
RHIC
RHIC
Local Parity Violation in strong magnetic Field ?