Ken Read

Oak Ridge National Laboratory/

University of Tennessee

on behalf of the ALICE Collaboration

SESAPS 2008, Raleigh, NC

October 30, 2008

Research supported by the Office of Nuclear Physics, US Department of Energy

Heavy Ion Nuclear Physics Ultrarelativistic heavy ion nuclear physics Investigate properties of nuclear matter at high

temperature and density Improve understanding of strong force concerning deconfinement and

chiral symmetry breaking/restoration (transition from quark to hadronic matter)

Explore QCD in novel regimes. Study the phase diagram of QCD matter. Probe conditions of quark/hadron phase transition (universe at 10-6 s)

and fully characterize the properties of the novel produced matter

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spectators

participants

Heavy Ion Nuclear Physics

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Particles are flowing like an ideal hydrodynamical fluid. Viscosity/entropy ratio is lowest observed, near predicted quantum mechanical lower bound.

Suppression of particles with a high transverse momentum in Au+Au (but not d+Au) collisions as predicted to occur if QGP is formed (“jet suppression”). Opacity very high, effectively stops quarks and gluons.

Significant correlated emission of partons (“flow”) with shock-wave dynamics. Rapid thermalization of created medium, fluid expansion, even heavy quarks are swept up by flow.

RHIC Discoveries

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More protons than pions at high transverse momentum. Almost as many anti-protons as protons, which is another indication that conditions are favorable for the production of a Quark-Gluon Plasma.

Energy density in the center of the collision is about 30 times that of a normal nucleus. Conditions may be favorable for Quark-Gluon Plasma production.

The source of produced particles is large and short-lived. Modification of charm production measured via semileptonic

decays. Suggests that a new state of matter has been created at RHIC. Anti de Sitter space / Conformal Field Theory (AdS/CFT)

correspondence between QCD (quark gluon plasma) and string theory. The RHIC “fireball” can be “mapped” to a “gravity dual” (mathematical black hole) via this correspondence.

RHIC Discoveries

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Large Heavy ion Collider

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LHC Specifications LHC

p+p collisions at maximum energy of 14 TeV Pb+Pb at 5.5 TeV per nucleon pair Energy density 3 to 10 times higher than RHIC

ALICE is the dedicated heavy ion nuclear physics detector at the LHC. Sophisticated charged-particle tracking and particle identification capabilities.

ALICE-USA is primarily focused on the EMCal which provides a fast trigger on high-energy jets. SESAPS institutes (ORNL, Univ. Tennessee, …) are involved.

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LHC Specifications

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CollisionSystem

sNN (TeV) Luminosity (cm-2s-1)

Run Time (s/yr)

geom (b)

p+p 14.0 1034 107 0.07

Pb+Pb 5.5 1027 106 7.7

p+Pb 8.8 1029 106 1.9

Ar+Ar 6.3 1029 106 2.7

Integrated luminosity for Pb+Pb: 0.5 nb-1/yr

Denser and Hotter

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CentralCollisions

SPS RHIC LHC

s1/2 (GeV) 17 200 5500

(GeV/fm3) 3 5 15 – 60

initial T (MeV) 200 300 600

tQGP (fm/c) < 1 1.5 – 4.0 4 –10

Centrality

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spectators

participants

b

Lorentz-contracted ionsin center of mass frame

Centrality

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• Centrality corresponds to impact parameter• For a given b, Glauber model predicts Npart and Ncoll.• Hard processes tend to scale as ~ Ncoll

• Can classify events based on centrality class

15 fm b 0 fm

0 Ncoll 1200

0 Npart 394

Centrality

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Initial state spatial anisotropy of reaction zone leads to final state momentum anisotropy

Results in asymmetric particle emission Second component of Fourier decomposition, v2, indicates degree of

azimuthal anisotropy

Flow

13x

zy

Mas

ashi

Kan

eta

3 3

R30T T

2 R

2 cos

cos 2

nn

d N d NE v nd p p d dp dy

v

High transverse momentum particles probe the medium

Probes

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medium

Variables

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1

1

rapidity tanh ln tan pseudorapidity2

tanh Preserves shapes of distributions like .

zpyE

dNy y

dy

2

2

Nuclear modification factor:

1

/1( )

/

what you observe

what you would expect

Pb Pb

Pb Pbevt T T

PbPb T p p p pcoll coll Tp pinel T

d NN dp d dN dp

R pN d N dN dp

dp d

naively

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17Simulated Event

18The “L3” Magnet

19The “L3” Magnet

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ALICE: Dedicated Heavy Ion LHC Experiment31 Countries, 109 Institutes and more than 1000 members

ALICE Detect most (2 * 1.8 units ) of the hadrons (dE/dx + ToF), leptons

(dE/dx, TOF, transition radiation) and photons (high resolution EM calorimetry, conversions)

Track and identify from very low (< 100 MeV/c) up to very high pT (>100GeV/c)

Identify short lived particles (hyperons, D/B meson) through secondary vertex detection

Excellent particle ID up to ~ 50 to 60 GeV/c

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Time Projection Chamber Specifications

designed for dN/dη=8000 |η|<0.9, radius 0.9-2.5m 0.5 T Solenoidal Field 570k chan., 80Mb/event 3% radiation length Outer diameter 5 m, Length 5 m Largest ever

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TRD, TOF, HMPID Transition Radiation Detector

pT>1 GeV electron id, pT>3 GeV trigger

540 modules, 4.8cm radiator with 1.2M chan. MWPC readout

Time Of Flight Multi-gap Resistive Plate Chambers (MRPC) 50 ps resolution at ~5m |η|<0.85, Δφ=2π

High Momentum PID Proximity focused, Ring Imaging CHerenkov

RICH |η|<0.6, Δφ=π/3 PID 1<p<6 GeV

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PHOS PHOton Spectrometer

PbO4W crystal calorimeter ,0, for 1<p<100 GeV ||<0.12, = 100º L0 trigger at 900 ns σ(E)/E = 3%, σ(x,y)=4mm

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EMCal Specifications

Lead-scintillator sampling calorimeter 13 k towers Each tower ΔηXΔφ = 0.014 X 0.014 Shashlik geometry Avalanche phototodiodes Δη=1.4, Δφ=107º σ(E)=0.15/E + 0.02 L0 trigger at 900 ns for e, , and jets

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EMCal Specifications

High pT triggering possible on , 0, and electrons. EMCal will significantly improve the statistics and energy resolution of jets.

EMCal has good high pT electron ID, including above pT ~ 10 GeV/c (beyond TRD reach)

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Fiber bundles with attached photodiodes and preamps for 4 towers of an EMCal module

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ALICE EMCal Physics Study Initial hard parton scattering High energy jets, photons and heavy flavors → requires EMCal and

triggering Exploit large kinematic range of jets at LHC Measure jet structure & medium-induced jet modification Investigate energy loss Low energy particles correlated with trigger or quenched jet →

requires ALICE acceptance, robust tracking, & PID to low/high pT

Investigate energy propagation in medium to determine medium properties

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ALICE EMCal Physics Heavy flavor studies in ALICE will serve as sensitive probes of

parton energy loss and the level of collectivity of the medium formed in heavy ion collisions.

The ALICE EMCal will provide improved high-pT identification and triggering of non-photonic electrons.

The displaced vertex method used in conjunction with the EMCal can provide efficient and pure identification of semi-electronic decays of B mesons.

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Muon Spectrometer Single muon acceptance

p>4 GeV/c - 4.0 < η < - 2.5

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Forward Detectors FMD (Forward Multiplicity Detector)

3 planes Si-pad, -3.4<η<-1.7 , -1.7<η<5.0 T0

2-arrays 12 quartz Cherenkov counters, 30ps res.

V0 2 arrays, 32 scintillator tiles, centrality trigger,

0.6ns res. ZDC (Zero Degree Calorimeter)

2-neutron, 2-proton calorimeters, 116m from IP also 2 EM calorimeters at -7 m

PMD (Photon Multiplicity Detector) 2.3< η <3.5

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Readiness All detectors fully installed except TRD, PHOS, EmCal, HLT to be

completed TRD(25%, completion 2010) PHOS (60%, completion 2010) EMCAL (0%, completion 2011)

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Initial Program Fully commissioned detector & trigger

alignment, calibration available from pp

First 105 events: global event properties multiplicity, rapidity density elliptic flow

First 106 events: source characteristics particle spectra, resonances differential flow analysis Interferometry

First 107 events: high-pt, heavy flavors jet quenching, heavy-flavor energy loss charmonium production

Yield bulk properties of created medium energy density, temperature, pressure heat capacity/entropy, viscosity, sound velocity, opacity susceptibilities, order of phase transition

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Program Initial low luminosity run p+p 2 to 3 years (106 s/yr) Pb+Pb 1 year p+Pb 1 year Ar+Ar Following requests depend on observations

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Conclusions ALICE will start to collect p+p data next year Later will measure Pb+Pb collisions at unprecedented

energies Will study jet suppression at still higher energies than

measured at RHIC, as well as a broad program of related measurements concerning the produced matter.

Thanks to my colleagues on PHENIX and ALICE for contributed material.

See aliceinfo.cern.ch/Public

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