Relativistic Heavy Ions: the UK perspective

STAR

Peter G. Jones

University of Birmingham, UK

NuPECC Meeting, University of Glasgow, 3-4 October 2008

The nuclear phase diagram

early universe

250 T 0 ≈ 4-5 T c (LHC) T 0 ≤ 2T c (RHIC) Location of critical point uncertain:

F. Karsch, BNL Workshop, 9-10 March 2006

.

Z. Fodor, S. Katz, JHEP 0203 (2002) 014, 0404 (2004) 050 C. R. Alton et al., Phys. Rev. D71 (2005) 054508 R. V. Gavai, S. Gupta, Phys. Rev. D71 (2005) 114014 200 critical point?

quark-gluon plasma

150 CERN-SPS BNL-AGS 100

hadron gas

GSI-SIS deconfinement chiral restoration 50 0 0 200 400

atomic nuclei

600 800 1000 Baryonic Potential  B [MeV] 1200 Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October 2008

neutron stars

2/20

UK participation

• Involved since the inception of the CERN Heavy Ion programme

16 O, 32 S 208 Pb 208 Pb, 197 Au 208 Pb

WA85 WA94 J. Kinson J.N. Carney O. Villalobos-Baillie M.F. Votruba R. Lietava A. Kirk

D. Evans (1992) J.P. Davies (1995) A.C. Bayes (1995) M. Venables (1997)

NA36 J.M. Nelson R. Zybert

P.G. Jones (1992) E.G. Judd (1993)

1987

WA97 NA57 J. Kinson D. Evans G.T. Jones O. Villalobos-Baillie I. Bloodworth P. Jovanovic A. Jusko R. Lietava

P. Norman (1999) M. Thompson (1999) R. Clarke (2004) P. Bacon (2005) S. Bull (2005)

NA49 J.M. Nelson R. Zybert P.G. Jones

H. Caines (1996) L. Hill (1997) T. Yates (1998) L. Barnby (1999) R. Barton (2001)

1994

ALICE J. Kinson D. Evans G.T. Jones O. Villalobos-Baillie A. Bhasin P. Jovanovic A. Jusko R. Lietava

R. Platt (2007) D. Tapia Takaki (2008) H. Scott

STAR J.M. Nelson P.G. Jones L. Barnby

M. Lamont (2002) J. Adams (2005) L. Gaillard (2008) A. Timmins (2008) T. Burton E. Elhahuli

1999

ALICE D. Evans P.G. Jones C. Lazzeroni G.T. Jones O. Villalobos-Baillie L. Barnby R. Lietava M. Bombara A. Jusko M. Krivda

Z. Matthews S. Navin R. Kour P. Petrov A. Palaha

2008

Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October 2008 3/20

Strangeness at the CERN-SPS

• Strangeness enhancement as a signature of QGP formation If T > T C ≈ m s , expect copious thermal s-quark production.

Gluon fusion shown to dominate over light quark annihilation.

Enhancement is measured relative to proton-proton collisions.

NA35/NA49 WA97 NA57 Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October 2008 4/20

Statistical/thermal models

• Hadrons are produced statistically – enhancement explained?

STAR  s strangeness  Strangeness saturation factor

N i



T

, 

B

, 

S V

  

s S

2

g i

 2   0

net

-baryon density 

B p

2   exp   

E i

 

B T ch

 

S

   1    1

dp

Chemical freezeout temperature

T ch

net

-strangeness density 

S

= 0 Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October 2008 5/20

Soft versus Hard QCD

• The advantage of high energy colliders  , K, N, …  , K, N, …  0 =  q  f Hadron gas  (  H )  s = 1?

QGP Light-cone trajectory Parton formation and thermalisation z  (  Q )  s = 0.4

Soft process e.g. strangeness

A

Hard process e.g. jets, charm

A Soft processes Hard processes

occur over the lifetime of the system.

occur at early times and serve as a “standard candle”.

Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October 2008 6/20

High p

T

particle production

• High p T jets are well described by perturbative QCD X.-N. Wang and M. Gyulassy,

Phys

.

Rev

.

Lett

.

68

(1992) 1480

key prediction

: jets are quenched Fragmentation Jet of high p T hadrons Leading hadron radiated gluons p TOT p T p L heavy nucleus

d



h pp dyd

2

p T



K



abcd



dx a dx b f a

(

x a

,

Q

2 )

f b

(

x b

,

Q

2 )

d



d

ˆ (

ab



cd

)

D

0

h

/

c



z c

Parton distribution functions Fragmentation function – initial state – pQCD calculable – final state Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October 2008 7/20

High-p

T

hadrons in A+A collisions

Central STAR: Phys. Rev. Lett.

89

(2002) 202301 STAR Central Peripheral Peripheral 

R AA

(

p T

) 

d

2

N T AA d

2 

AA

/

dp T d



NN

/

dp T d

 scale factor p+p reference Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October 2008 binary collisions 8/20

Measuring jets by two-particle correlations

STAR Trigger particle Associated (near-side) 8 < p T (trigger) < 15 GeV/c Df Associated (away-side) Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October 2008 STAR: Phys. Rev. Lett.

97

(2006) 162301 9/20

Away side broadening or quenching?

• Measure “jet” yields as a function of

z

T = p T (assoc)/p T (trig) STAR: Phys. Rev. Lett.

97

(2006) 162301 STAR Near-side | Df | < 0.63

Away-side | Df | < 0.63

No suppression Suppression by factor 4-5 in central Au+Au.

Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October 2008 10/20

Trigger particle

2-d ( DDf correlations

|| ~ 1  ~ 0 Trigger particle Df D Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October 2008 11/20

d+Au

2-d ( DDf correlations

Au+Au In vacuo (pp) fragmentation static medium broadening D Df flowing medium anisotropic shape Near-side Away-side (Armesto et al, PRL

93

, (2004); Eur. Phys. J. C

38

461) D Df Near-side Disappearance of

away-side

Modification of

near-side

correlation = jet quenching.

correlation = coupling of jet to the medium?

Away-side Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October 2008 12/20

Extracting near side “jet” yields

Au+Au 20-30% D 1 3 < p T,trig.

< 4 GeV/c and p T,assoc. > 2 GeV/c STAR 0  -1 Jet yield -2 0 2 Df (  ) 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 N part 13/20

ALICE at the LHC

Access to a wide range of observables in one experiment!

HMPID PID (RICH) @ high

p

t TOF PID TRD Electron ID PMD  multiplicity TPC Tracking, dEdx ITS Low

p

t tracking Vertexing PHOS  ,  0 MUON  -pairs Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October 2008 14/20

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 15/20

ALICE - Key Physics

• Study QCD on its natural (energy) scale T > T C ≈  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.

jets • 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 b b   c c   * l + Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October 2008 16/20 l – 

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) Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October 2008 17/20

ALICE – pp physics

• ALICE has a competitive programme of pp physics Precision measurements of inelastic cross-sections.

Particle production as a function of p T .

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?

STAR p + p   0 + X Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October 2008 18/20

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-p T 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 19/20

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 20/20

The nuclear phase diagram

early universe

250 T 0 ≈ 4-5 T c (LHC) T 0 ≤ 2T c (RHIC) Location of critical point uncertain:

F. Karsch, BNL Workshop, 9-10 March 2006

.

Z. Fodor, S. Katz, JHEP 0203 (2002) 014, 0404 (2004) 050 C. R. Alton et al., Phys. Rev. D71 (2005) 054508 R. V. Gavai, S. Gupta, Phys. Rev. D71 (2005) 114014 200 critical point?

quark-gluon plasma

150 SPS AGS 100

hadron gas

SIS deconfinement chiral restoration 50 0 0 200 400

atomic nuclei

600 800 1000 Baryonic Potential  B [MeV] 1200 Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October 2008

neutron stars

21/20

Expectations from lattice QCD

Central Au+Au √s NN = 200 GeV F Karsch: Quark Gluon Plasma 3 (World Scientific) RHIC LHC ?

 Energy density at RHIC  0  1 

R

2  0

dE T dy y

 0  5  15 GeV / fm 3 J D Bjorken: Phys. Rev. D 27 (1983) 40 RHIC: LHC: T 0 /T c = 1.5–2.0

T 0 /T c = 3.0–4.0

RHIC and LHC permit a detailed study of the high T phase of QCD Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October 2008 22/20

Surface bias

• R AA sets a lower bound on the density Wicks, Horowitz, Djordjevic and Gyulassy, nucl-th/0512076 Origin of surviving jets (p T = 15 GeV/c) More penetrating probes needed to explore the medium.

Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October 2008 23/20

Models of energy loss

Initial ideas based on collisional energy loss.

J D Bjorken, FERMILAB-Pub-82/59-THY 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)  Few hard(er) interactions Multiple soft interactions GLV formalism Opacity (twist) expansion  

L

  

glue L

Transport coefficient  For 1-d longitudinal expansion: BDMPS formalism D

E

ˆ  

C R



S

4

k T

2 ˆ 2

medium

  Static medium 

glue

D

E



L

Guylassy, Levai, Vitev, Wang, Wang, …  Baier, Dokshitzer, Mueller, Peigne, Schiff, Salgado, Wiedemann, … 24/20

Use R

AA

to determine the medium density

• Nuclear modification factor, R AA , for pions Eskola, Honkanen, Salgado, Wiedemann (2004) The medium is dense (30-50 x normal matter), but R AA provides limited sensitivity.

Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October 2008 25/20

ALICE – Observables

• ALICE is a general purpose detector Access to a wide range of observables in one experiment!

Peter G Jones, NuPECC Meeting, Glasgow, 3-4 October 2008 26/20