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Relativistic Heavy Ions:the UK perspective
Peter G. Jones
University of Birmingham, UK
NuPECC Meeting, University of Glasgow, 3-4 October 2008
STAR
Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October 2008 2/20
The nuclear phase diagram
Baryonic Potential B [MeV]
Chemical Temperature Tch [MeV]
0
200
250
150
100
50
0 200 400 600 800 1000 1200
quark-gluon plasma
hadron gas
neutron stars
early universe
deconfinementchiral restoration
Lattice
QCD
atomic nuclei
Location of critical point uncertain:F. Karsch, BNL Workshop, 9-10 March 2006.Z. Fodor, S. Katz, JHEP 0203 (2002) 014, 0404 (2004) 050C. R. Alton et al., Phys. Rev. D71 (2005) 054508R. V. Gavai, S. Gupta, Phys. Rev. D71 (2005) 114014
critical point?
GSI-SIS
chemical freeze-out curve
BNL-AGS
CERN-SPS
T0 ≤ 2Tc (RHIC)
T0 ≈ 4-5 Tc (LHC)
Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October 2008 3/20
UK participation•Involved since the inception of the CERN Heavy Ion programme
WA85WA94WA85WA94
NA36NA36 NA49NA49 STARSTAR
ALICEALICE
WA97NA57WA97NA57
J.M. NelsonR. ZybertP.G. Jones (1992)E.G. Judd (1993)
J.M. NelsonR. ZybertP.G. JonesH. Caines (1996)L. Hill (1997)T. Yates (1998)L. Barnby (1999)R. Barton (2001)
J.M. NelsonP.G. JonesL. BarnbyM. Lamont (2002)J. Adams (2005)L. Gaillard
(2008)A. Timmins (2008)T. BurtonE. Elhahuli
D. EvansP.G. JonesC. LazzeroniG.T. JonesO. Villalobos-
BaillieL. BarnbyR. LietavaM. BombaraA. JuskoM. KrivdaZ. MatthewsS. NavinR. KourP. PetrovA. Palaha
J. KinsonJ.N. CarneyO. Villalobos-BaillieM.F. VotrubaR. LietavaA. KirkD. Evans (1992)J.P. Davies (1995)A.C. Bayes (1995)M. Venables (1997)
J. KinsonD. Evans G.T. Jones O. Villalobos-BaillieI. BloodworthP. JovanovicA. JuskoR. LietavaP. Norman (1999)M. Thompson (1999) R. Clarke (2004)P. Bacon (2005)S. Bull (2005)
ALICEALICE
J. KinsonD. Evans G.T. Jones O. Villalobos-BaillieA. BhasinP. JovanovicA. JuskoR. LietavaR. Platt (2007)D. Tapia Takaki (2008)H. Scott
1987 1994 1999 2008
16O, 32S 208Pb 208Pb, 197Au 208Pb
Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October 2008 4/20
Strangeness at the CERN-SPS•Strangeness enhancement as a signature of QGP formation
If T > TC ≈ ms, expect copious thermal s-quark production.
Gluon fusion shown to dominate over light quark annihilation.
Enhancement is measured relative to proton-proton collisions.
NA35/NA49NA35/NA49
WA97NA57WA97NA57
Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October 2008 5/20
Statistical/thermal models•Hadrons are produced statistically – enhancement explained?
€
Ni T ,μ B ,μ S( )V
= γ sS gi
2π 2p2 exp
− Ei − μ B − μS( )Tch
⎡
⎣ ⎢
⎤
⎦ ⎥±1
⎡
⎣ ⎢
⎤
⎦ ⎥
0
∞∫
−1
dp
Chemical freezeout temperature Tch
net-baryon density BStrangeness saturation factor
net-strangeness density S = 0
strangeness
s
STARSTAR
CERN-pp
CERN-pp
CERN-AA
CERN-AA
RHIC–AA
RHIC–AA
Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October 2008 6/20
Soft versus Hard QCD•The advantage of high energy colliders
Hadron gas
Parton formation and thermalisation
z
, K, N, …
f
(H)
(Q)
QGP
A A
0 = q
Light-cone trajectory
s = 0.4
s = 1?
Soft processe.g. strangeness
Hard processe.g. jets, charm
, K, N, …
Soft processes occur over the lifetime of the system.Hard processes occur at early times and serve as a “standard candle”.
Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October 2008 7/20
•High pT jets are well described by perturbative QCD
High pT particle production
pT
pL
pTOT
€
dσ pph
dyd2 pT
= K dxa∫ dxbabcd∑ fa (xa ,Q2) fb(xb,Q2)
dσ
dˆ t (ab → cd)
Dh /c0
π zc
Parton distribution functionsHard scattering cross-sectionFragmentation function
– initial state
– pQCD calculable
– final state
Fragmentation Leading hadron
heavy nucleus
radiatedgluons
key prediction: jets are quenchedX.-N. Wang and M. Gyulassy, Phys. Rev. Lett. 68 (1992) 1480
Jet of high pT hadrons
Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October 2008 8/20
High-pT hadrons in A+A collisions
Central
Peripheral
STAR: Phys. Rev. Lett. 89 (2002) 202301
p+p reference
€
RAA (pT ) =d 2N AA /dpTdη
TAAd 2σ NN /dpTdη
€
RAA (pT ) =d 2N AA /dpTdη
TAAd 2σ NN /dpTdη
scale factor
Central
Peripheral
binary collisions
STARSTAR
Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October 2008 9/20
Measuring jets by two-particle correlations
Trigger particle Associated (near-side)
Associated (away-side)
8 < pT(trigger) < 15 GeV/c8 < pT(trigger) < 15 GeV/c
STAR: Phys. Rev. Lett. 97 (2006) 162301
STARSTAR
Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October 2008 10/20
Away side broadening or quenching?•Measure “jet” yields as a function of zT = pT(assoc)/pT(trig)
Near-sideNear-side Away-sideAway-side
No suppressionNo suppression
|| < 0.63 | | < 0.63
Suppression by factor 4-5 in central
Au+Au.
Suppression by factor 4-5 in central
Au+Au.
STAR: Phys. Rev. Lett. 97 (2006) 162301
STARSTAR
Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October 2008 11/20
2-d ( correlations
~ 1 ~ 0 Trigger particle
Trigger particle
Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October 2008 12/20
2-d ( correlations
d+Au Au+Au
Near-side
Away-side
Disappearance of away-side correlation = jet quenching.Modification of near-side correlation = coupling of jet to the medium?
In vacuo (pp)fragmentation static medium
broadening
flowing mediumanisotropic shape
(Armesto et al, PRL 93, (2004); Eur. Phys. J. C Eur. Phys. J. C 38 38 461461)
Near-side
Away-side
Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October 2008 13/20
0
Extracting near-side “jet” yields
Au+Au 20-30%
yield,
)
3 < pT,trig. < 4 GeV/c and pT,assoc. > 2 GeV/c3 < pT,trig. < 4 GeV/c and pT,assoc. > 2 GeV/c
()2-2
-1
1
0
Npart
Jet yield
Ridge yield
STARSTAR
Birmingham analysis: particle-type composition of the jet/ridge.Strange particles now being used as a diagnostic tool.
Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October 2008 14/20
ALICE at the LHCAccess to a wide range of observables in one
experiment!
ITSLow pt trackingVertexing
ITSLow pt trackingVertexing
TPCTracking, dEdxTPCTracking, dEdx
TRDElectron IDTRDElectron ID
TOFPIDTOFPID
HMPIDPID (RICH) @ high pt
HMPIDPID (RICH) @ high pt
PHOS,0 PHOS,0
MUON -pairs MUON -pairs
PMD multiplicityPMD multiplicity
Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October 2008 15/20
UK–ALICE•Birmingham’s role in ALICE
The ALICE central trigger system.
Only major subsystem which is the responsibility of a single university group.
Strong involvement in the science (Physics Performance Reports).
Now one of the largest university groups in ALICE.
•ALICE trigger
Up to 60 inputs (every 25 ns)
24 L0 – 1.6 s (100 ns decision time)
24 L1 – 6 s
12 L2 – 90 s
50 trigger classes / 6 detector clusters
Pb-Pb collisions: 8 kHz interaction rate
p-p collisions: 200 kHz interaction rate
David Evans / ALICE trigger
Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October 2008 16/20
ALICE - Key Physics•Study QCD on its natural (energy) scale T > TC ≈ QCD.
•Explore quark and gluon dynamics in a hot medium.
•Hot topics:
Collective behaviour – sQGP.
Opacity to jets – gluon density.
Heavy flavour production – Debye screening.
•Some new theoretical developments:
AdS/CFT correspondance
Connection between string theory and ...
… strongly-coupled gauge theories.
Provides an alternative to (lattice) QCD.
Some (limited) success so far.
K
l+
l–
jets
b
cc
b
Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October 2008 17/20
New ideas in Hadronization
David d'Enterria (CERN)David Evans (Birmingham)Nick Evans (Southampton)Nigel Glover (IPPP)Peter Jones (Birmingham)Frank Krauss (IPPP)Kasper Peeters (MPI)Marija Zamaklar (Durham)
David d'Enterria (CERN)David Evans (Birmingham)Nick Evans (Southampton)Nigel Glover (IPPP)Peter Jones (Birmingham)Frank Krauss (IPPP)Kasper Peeters (MPI)Marija Zamaklar (Durham)
Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October 2008 18/20
ALICE – pp physics•ALICE has a competitive programme of pp physics
Precision measurements of inelastic cross-sections.
Particle production as a function of pT.
Test of QCD calculations.
Study of diffractive events.
Probes nucleon structure.
•Advantages of ALICE
Low transverse momentum coverage.
Particle tracking.
Particle identification.
•More speculative …
Multiplicity: pp (LHC) = CuCu (RHIC)
QGP in pp collisions?
p + p 0 + Xp + p 0 + X
STARSTAR
Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October 2008 19/20
UK–ALICE Physics•First physics
Multiplicity and transverse momentum distributions.
Initial tests of QCD; input to fragmentation functions.
Are parton distributions sufficiently well understood?
•Correction for trigger biases
Important for all papers reporting cross-sections (All).
•Longer term proton-proton physics – Pb-Pb physics
Resonances – sensitive to hadronic phase (Villalobos-Baillie).
Charmonium ( J/) production – Debye screening (Lazzeroni).
High-pT and jet physics – energy loss (Barnby, Bombara, Evans, Lietava).
Anomalous high multiplicity pp events? – (Jones).
Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October 2008 20/20
Outlook and Summary
Unclear whether there will be a Pb-run in 2009.
From 2010, expect 1 month of Pb per year.
First few years, Pb-Pb collisions @ 5.5 TeV per nucleon.
Option of changing beam species/energy in subsequent years.
e.g. p-Pb, symmetric light ions, lower energy(ies).
LHC will achieve first collisions in March 2009.
ALICE has a full physics programme.
UK is helping to shape that programme.
First physics proton-proton collisions Pb-Pb collisions.
Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October 2008 21/20
The nuclear phase diagram
Baryonic Potential B [MeV]
Chemical Temperature Tch [MeV]
0
200
250
150
100
50
0 200 400 600 800 1000 1200
AGS
SIS
quark-gluon plasma
hadron gas
neutron stars
early universe
deconfinementchiral restoration
Lattice
QCD
chemical freeze-out curve
SPS
atomic nuclei
Location of critical point uncertain:F. Karsch, BNL Workshop, 9-10 March 2006.Z. Fodor, S. Katz, JHEP 0203 (2002) 014, 0404 (2004) 050C. R. Alton et al., Phys. Rev. D71 (2005) 054508R. V. Gavai, S. Gupta, Phys. Rev. D71 (2005) 114014
critical point?
T0 ≤ 2Tc (RHIC)
T0 ≈ 4-5 Tc (LHC)
Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October 2008 22/20
Expectations from lattice QCD
€
0 =1
πR2τ 0
dET
dyy=0
= 5 −15 GeV /fm3
€
0 =1
πR2τ 0
dET
dyy=0
= 5 −15 GeV /fm3
Energy density at RHIC
Central Au+Au √sNN = 200 GeV
RHIC: T0/Tc = 1.5–2.0LHC: T0/Tc = 3.0–4.0RHIC: T0/Tc = 1.5–2.0LHC: T0/Tc = 3.0–4.0
RHIC and LHC permit a detailed study of the high T phase of QCD
J D Bjorken: Phys. Rev. D 27 (1983) 40
F Karsch: Quark Gluon Plasma 3 (World Scientific)
RHIC
LHC ?
Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October 2008 23/20
Surface bias•RAA sets a lower bound on the density
Wicks, Horowitz, Djordjevic and Gyulassy, nucl-th/0512076
Origin of surviving jets(pT = 15 GeV/c)
More penetrating probes needed to explore the medium.
Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October 2008 24/20
Models of energy loss
Initial ideas based on collisional energy loss.Initial ideas based on collisional energy loss.
Radiative energy loss was found to be dominant for light quarks.Radiative energy loss was found to be dominant for light quarks.
Soft gluon emission suppressed (Landau, Pomeranchuk, Midgal effect).Energy loss is independent of parton energy, E,
and becomes a function of the path length L in the medium.
Two example approaches (others exist)Two example approaches (others exist)
Few hard(er) interactionsFew hard(er) interactions Multiple soft interactionsMultiple soft interactions
€
E ≈CRα S
4ˆ q L2
€
ˆ q =kT
2
medium
λ∝ ρ glue
For 1-d longitudinal expansion:
Static medium
€
χ =Lλ
= σρ glueL
Opacity (twist) expansion
€
E ∝ L
Transport coefficient
GLV formalism BDMPS formalism
J D Bjorken, FERMILAB-Pub-82/59-THY
Guylassy, Levai, Vitev, Wang, Wang, …
Baier, Dokshitzer, Mueller, Peigne, Schiff,Salgado, Wiedemann, …
Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October 2008 25/20
Use RAA to determine the medium density
•Nuclear modification factor, RAA, for pions
The medium is dense (30-50 x normal matter), but RAA provides limited
sensitivity.
Eskola, Honkanen, Salgado, Wiedemann (2004)
Eskola, Honkanen, Salgado, Wiedemann (2004)
Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October 2008 26/20
ALICE – Observables•ALICE is a general purpose detector
Access to a wide range of observables in one experiment!