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UK HEP Forum Roman Lietava, University of Birmingham
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ALICE Experiment
• Physics motivation
• Detectors
• Observables and Physics Performance
• Summary
Roman LietavaRoman LietavaUniversity of BirminghamUniversity of Birmingham
UK HEP Forum Roman Lietava, University of Birmingham
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SOUTH AFRICA
UKPORTUGAL
JINR
GERMANY
SWEDEN
CZECH REP.
HUNGARYNORWAY
SLOVAKIA
POLANDNETHERLANDS
GREECEDENMARK
FINLAND
SWITZERLAND
RUSSIA CERN
FRANCE
MEXICOCROATIA
ROMANIA
CHINA
USAARMENIA
UKRAINE
INDIA
ITALY
S. KOREA937 members (63% from CERN MS)
77 Institutions, 29 Countries
ALICE Collaboration
ALICE UK:6 members
University of Birmingham
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Collision Systems
Collision system
pp
PbPb
107
Run time
(s/year)
L0
(cm-2s-1)
√sNN
(TeV)
103114.0
106 10275.5
Other collision systems and energies: • pA, lighter ions (Sn, Kr, Ar, O) • pp @ 5.5 TeV
Year
April 2007
2007/2008
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Physics Motivation
The study of Quantum Chromodynamics:• A-A collisions: - physics of many particles interacting strongly, QCD phase transition• p-p and p-A collisions: - benchmark for AA collisions - specific aspects• Ultra peripheral AA collisions – physics• Cosmic ray physics
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QCD Phase Diagram
Lattice QCDLattice QCD
Nonperturbative phenomena
hep-ph/020516
PLB478(2000)447
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Space Time Evolution of the Collisions
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ALICE Physics Goals
Deconfinement: charmonium and bottomonium spectroscopy
Chiral symmetry restoration: neutral to charged ratios, res. decays
Fluctuation phenomena - critical behaviour: event-by-event particle comp. and spectra
Geometry of the emitting source: HBT, impact parameter via zero-degree energy flow
pp collisions in a new energy domain
Degrees of freedom as a function of T hadron ratios and spectra, dilepton continuum, direct photons
Global observables: Multiplicities, distributions
Early state manifestation of collective effects: elliptic flow
Energy loss of partons in quark gluon plasma: jet quenching, high pt spectra, open charm and open beauty
Large acceptance Good tracking capabilities Selective triggering Excellent granularity
Wide momentum coverage P.I.D. of hadrons and leptons Good sec. vertex reconstr. Photon Detection
Use a variety of experimental techniques!
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Alice Detector
• Tracking (B=0.2-0.5 T): - Inner Tracking System (ITS) – pixels,drift,strips - Time Projection Chamber (TPC)
- Transition Radiation Detector (TRD) • PID: - TPC - TRD - Time Of Flight (TOF) - High Momentum PID (HMPID)• Muons: dimuon arm• Calorimetry: - PHOton Spectrometer (PHOS) - Electromagnetic Calorimeter
(EMCAL) - under discussion
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Bat 40
ALICEALICE
ATLAS
CMS
From R.J.Cashmore,IOP Bham
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ALICE Detector Acceptance
Muon arm: 2.4<<4 PMD 2.3<<3.5 FMD: -5.4<<-1.6, 1.6<<3
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PT Resolution
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ALICE PID
, K, p identified in large acceptance (2 * 1.8 units ) via a combination of dE/dx in Si and TPC and TOF from ~100 MeV to 2 (p/K) - 3.5 (K/p) GeV/cElectrons identified from 100 MeV/c to 100 GeV/c (with varying efficiency) combining Si+TPC+TOF with a dedicated TRD In small acceptance HMPID extends PID to ~5 GeV Photons measured with high resolution in PHOS, counting in PMD, and in EMC
/K
0 1 2 3 4 5 p (GeV/c)
1 10 100 p(GeV/c)
TRD e / PHOS /
TPC+ITS
(dE/dx)
/K
/K
K/p
K/p
K/p
e /
e /
HMPID (RICH)
TOF
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ALICE Trigger (Birmingham)
Triggering on:
• collision centrality
• high pT muons
• high pT electrons
• jets
ALICE trigger features:• Global trigger selection• Past-Future protection• Different trigger rates for group of detectors• Dynamic suppression of common triggers
Rates and pile-up:• Pb-Pb collisions: 8 kHz interaction rate L=1027 cm-2 s-1 • 60 % pile-up probability
• p-p collisions: 200 kHz interaction rate L=3x1030 cm-2 s-1 • 100 % pile-up probability
• TPC drift time 90 s
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First ALICE trigger board (LTU)
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Observables
Medium characteristics
• Particle multiplicities• Particle spectra • Particle ratios• Flow• Particle correlation• Fluctuations
Hard probes
• Jets • Heavy quark and
quarkonium production• Direct photons and dileptons
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Multiplicity
(from K.Kajantie, K.Eskola)
dNch/d ~ 2500We can extrapolate from RHIC data:
What multiplicity do we expect?What multiplicity do we expect?
ALICE design: dN/dy=8000ALICE design: dN/dy=8000
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Transverse mass spectra
5% most central events
NA57 Pb-Pb at s=17GeV
rdrT
pI
T
mKmA
mym
N GRtt
TjTT
j
0 01
2sinhcosh
dd
d
)(tanh)( 1 rr
G
n
GS Rr
R
rr
)(
Transverse mass spectra
Freeze out temperatureTransverse flow
NA5NA577
FA - QM`04 Strangeness ReportRoman Lietava, University of Birmingham
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Hadron Ratios
Degree of chemical equlibrium: Constraint on timescales of flavour production mechanism
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Detection
• One year of ALICE running
(107 events) s up to pt = 12 GeV/c
• Topological signature, not reliant on identification of daughters
S/B 15.5 /event
S/B 15.5 /event
% of rec. s vs pt% of rec. s vs pt
Reconstructedpt spectrumReconstructedpt spectrum
M(p) (GeV/c2)
Ent
ries
%
pt (GeV/c)
pt (GeV/c)
Y
ield
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Hard Processes Modified by the Medium
• Jet quenching:– energy degradation of leading hadrons, pt dependence;
– modification of genuine jet observables;
– energy imbalance in dijet events
• Open charm/beauty production• c’onium & b’onium bound states production
Final state (medium) interaction versus initial state (Cronin,shadowing) interaction
p-p and p-A measurement are mandatory
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High pT Suppression
• High pt particles suppressed
in Au-Au relative to pp, d-Au.
RAB = d2N/dpTd
TABd2pp/dpTdSTAR results:
d-Au, Cronin effect
Au-Au, jet quenching
AA coll
pp collNumber of coll
J. Adams et al., Phys. Rev. Lett. 91, 072304 (2003).
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Di-jets
In central Au-Au events,although trigger jet is clearly visible, “away-side” jet is not visible, as predicted from strong absorption in a high colour charge density volume, e.g. that produced in a QGP
Mini-jets in Au+Au at RHIC (STAR)
Missing jet
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Jets Reconstruction in ALICE
• Jets are produced copiously.
• Jets are distinguishable from the HI underlying event.
pt (GeV)2 20 100 200
100/event 1/event 100K/year
100 GeV jet + HI event
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Heavy Quarks
• Initially produced quarks experience the full collision history:– Short time scale for production: 1/mQ
– Production suppressed at larger times: mQ»T– Long time scale for decay decay»QGP
• The large masses of c and b quarks make them qualitatively different probes ( massless partons)
Observables: • Total production rate• transverse momentum distribution• correlation between quark and antiquark
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Heavy Quarks D0 K-+ reconstruction in ALICE
Affected by main vertexresolution in p+p caseAffected by main vertexresolution in p+p case
D0 K-c= 123.7 0.8mBR: (3.83 0.09) %
D0 K-c= 123.7 0.8mBR: (3.83 0.09) %
cuts depend on D0 ptcuts depend on D0 pt
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Heavy Quarks D0 K-+ reconstruction in ALICE
PbPb: pT>1 GeV/cpp: pT>0 GeV/c
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Heavy QuarkoniaJ/ and via Dielectrons
Mass resolution for 100 MeV (B = 0.4T)Mass resolution for 100 MeV (B = 0.4T)
::
J/:J/:
Acceptance down to pt = 0 GeV/c !Acceptance down to pt = 0 GeV/c !
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Motivation for pp Study
• First insight in pp collisions in new energy domain (s 14 TeV), study of evolution of soft hadronic physics
• Contribution to knowledge of underlying minimum bias (background) pp events to complement other LHC physics programmes (Higgs search, Bphysics, etc.)
• Provide pp data as a reference for study of other collision systems (p-A, A-A)
• Low multiplicity data to commission and calibrate various components of ALICE
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ALICE Features for pp
Magnetic field (T) ALICE 0.2 0.5 ATLAS 2.0 CMS 4.0
Material thicknessX/X0 (%)
Minimal pion ()
momentum (MeV)Minimal kaon (K
)
momentum (MeV)ALICE 7 80 200ATLAS 30 130 305CMS 20 115 280
Excellent particle identification (TOF and HMPID)
pt cut-off
Magnetic field (but this could be lowered)
Material thickness (hard to change)
ATLAS and CMS have better -coverage
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Permanent closure of L3 door in RB26 (05/03/04)SummaryALICE experiment is getting ready:
- the detectors are being built
-the software is getting ready
... and so does the number of people involved
- the understanding of the physics potential grows …
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ALICE Setup
ITS
TPCTRD
TOFPHOS
HMPID
MUON SPEC.PMD
FMD
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Low pt Physics ExamplesResonances: K*
• Decay channel K* K+-
• Invariant mass distribution for 550 events
En
trie
s
Au+Au minimum bias
pT 0.2 GeV/c
|y| 0.5Statistical error only
STAR Preliminary
STAR data shows clear K* on
background
Other resonances (f0... ) are being
extracted
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HBTEvent-by-Event ++ HBT
• Single event
• Raw correlation function
– Uncorrected for Coulomb
– R = 8 fm, = 0.5
– Tracking with ITS+TPC, B = 0.2T
Qinv (GeV)C
(Qin
v)
Resolution for B=0.2T
d6N
d3p1d3p2
C(p1,p2)=d3N d3N
d3p1 d3p2
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Number of Participants
pA:
AA:
Participants Npart
SpectatorsNpart=+1
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Charged Particle Multiplicity 130 GeV AuAu 200 GeV AuAu
25-35%cent
0-6%cent
45-55%cent
Ntot
= 4100 ±210 Ntot
= 4960 ±250
dN/d
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EMCAL => trigger and -jet, + improve resolution on Ejet
2%
8%
jet
Collision axis
TPC
PHOS+EMCAL
Proposed EMCAL||<0.7 ~ 120o
-jet with PHOS+EMCAL + TPC
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Elliptic flow
dN(pT,b,y,)=A(1 + 2v1(pT,b,y) cos() + 2v2(pT,b,y)cos(2 ) +…)
- the angle relative to reaction plane
STAR Preliminary
scaled with n(quarks)
•v1=0 at y=0 by symmetry
•v2 – information about the information about the equation of state
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Why is elliptic flow interesting?
• Coordinate space configuration anisotropic (almond shape) however, initial momentum distribution isotropic (spherically symmetric)
• Only interactions among constituents generate a pressure gradient, which transforms the initial coordinate space anisotropy into a momentum space anisotropy (no analogy in pp)
• Multiple interactions lead to thermalization -> limiting behavior ideal hydrodynamic flow
y
x
py
px
coordinate space
Momentum space
12 , tan ( )cos 2( ) y
xrv
p
p
3 2
31
11 2 cos
2 n rnt t
d N d NE v n
d p p dp dy
Raimond Snellings
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Elliptic flow as a function of centrality
STAR Nucl. Phys. A698 (2002) 193
Non-flow considerable for central and peripheral events
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0 1 2 10 100
pt (GeV/c)
Bulk propertiesHard processes
Modified by the medium
ALICE
CMS&ATLAS
1+2 Experiments
PID
T=QCD Qs
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High pt RHIC Results
• RAA clearly different between mesons and baryons
• Importance of PID at high pt
• p+p baseline measurement!
tdpppdtdpAAd
collNtpAAR
)()(1)(
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Heavy QuarksOpen Charm via Hadronic Decays
Pb+Pb:Pb+Pb:
dN/dpt Significance
pt > 1 GeV/cpt > 1 GeV/c
p+p:p+p:
pt > 0 GeV/c !pt > 0 GeV/c !
dN/dpt SignificanceSignificance =
BSS /
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Heavy QuarksOpen Charm via Hadronic Decays
• Input to simulation
– cc: PYTHIA, tuned to NLO calculations, with CTEQ4L and nuclear shadowing EKS98
– Background: HIJING
• Reconstruction effects included
• PID with TOF
8437Significance
for107(109)evts
50 %11 %S/B
2000013000Signal
for107(109)evts
pp (14TeV)Pb-Pb (5.5TeV)System (s)
Pb+PbPb+Pb
minv = 12 MeV (B = 0.4T)minv = 12 MeV (B = 0.4T)
PbPb:pT>1 GeV;pp: pT>0
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Parton Energy Loss
- Reduction of single inclusive high pt particles
• Parton specific (stronger for gluons than quarks)
• Flavour specific (stronger for light quarks)
• Measure identified hadrons (, K, p, , etc.) + partons (charm, beauty) at high pt
– Suppression of mini-jets• same-side / away-side
correlations
– Change of fragmentation function for hard jets (pt >> 10 GeV/c)
• Transverse and longitudinal fragmentation function of jets
• Jet broadening reduction of jet energy, dijets, -jet pairs- p+p and p+A measurements crucial
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Parton Energy Loss
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Permanent closure of L3 door in RB26 (05/03/04)
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c/b Quarkonia
• 1 month statistics of PbPb √sNN=5.5 TeV;
Even
ts/1
00 M
eV
103
J/Y
5 10 15
102
dN/d=8000
M+- (GeV)
Even
ts/2
5 M
eV
104
J/Y
2 3 4 9 10 11 0
105
104
dN/d=5000
|| < 2.4 2.5 < < 4
via dimuons
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ALICE Pb-Pb central event
Nch(-0.5<<0.5)=8000
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The LHC facility
• Running conditions:
• + other collision systems: pA, lighter ions (Sn, Kr,
Ar, O) & energies (pp @ 5.5 TeV).
Collision system
pp
PbPb
√sNN
(TeV)
L0
(cm-2s-1)
<L>/L0
(%)
Run time
(s/year)
geom
(b)
14.0 1034* 107 0.075.5 1027 70-50 106 * * 7.7
April 2007
End 2007Early 2008 *Lmax(ALICE) = 1031 ** Lint(ALICE) ~ 0.7 nb-1/year
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Experimental Conditions @ LHC
• pp commissioning start April 2007
• wish list of the HI community for the LHC• Initial few years (1HI ‘year’ = 106 effective s, ~like at SPS)
– 2 - 3 years Pb-Pb L ~ 1027 cm-2s-1
– 1 year p - Pb ‘like’ (p, d or ) L ~ 1029 cm-2s-1
– 1 year light ions (e.g. Ar-Ar) L ~ few 1027 to 1029 cm-2s-1
plus, for ALICE (limited by pileup in TPC):
– reg. pp run at s = 14 TeV L ~ 1029 and < 3x1030 cm-2s-1
• Later: different options depending on Physics results
• Heavy Ion running part of LHC initial program, early pilot run expected by end of 2007