“trends in heavy ion physics research” dubna may 22-24, 2008

Itzhak TserruyaItzhak Tserruya JINR, May 22, 2008JINR, May 22, 2008 11

““Trends in heavy ion physics research”Trends in heavy ion physics research” Dubna May 22-24, 2008 Dubna May 22-24, 2008

Itzhak TserruyaItzhak Tserruya

Hot and dense matter:Hot and dense matter:from RHIC to LHC from RHIC to LHC


““Trends in heavy ion physics research”Trends in heavy ion physics research” Dubna May 22-24, 2008 Dubna May 22-24, 2008


Hot and dense matter:Hot and dense matter:from RHIC to RHIC and LHC from RHIC to RHIC and LHC


OutlineOutline

Introduction

Highlights from RHIC Flow Charmonium Low-mass dileptons Thermal radiation High pT suppression

Summary


IntroductionIntroduction

Eight years of RHIC operationEight years of RHIC operationRHIC’s main goalsRHIC’s main goals– Nuclear collisionsNuclear collisions

To provide definitive experimental evidence for/against To provide definitive experimental evidence for/against Quark Gluon Plasma (QGP)Quark Gluon Plasma (QGP)

and study its properties under the much better conditions offered by RHICand study its properties under the much better conditions offered by RHIC

LargeLarge √s √s Access to reliable pQCD probes Access to reliable pQCD probes

– Polarized p+p collisionsPolarized p+p collisions

Accelerator complexAccelerator complex– Impressive machine performance:Impressive machine performance:

Routine operation at 2-4 x design luminosity (Au+Au)Routine operation at 2-4 x design luminosity (Au+Au)

– Extraordinary variety of operational modesExtraordinary variety of operational modesCollided four different species: Au+Au, d+Au, Cu+Cu, pCollided four different species: Au+Au, d+Au, Cu+Cu, p+p+p4 Energies: 20 GeV (Au+Au, Cu+Cu), 62 GeV (Au+Au,Cu+Cu, p4 Energies: 20 GeV (Au+Au, Cu+Cu), 62 GeV (Au+Au,Cu+Cu, p+p+p) , ) ,

130 GeV (Au+Au), 200 GeV (Au+Au, Cu+Cu, d+Au, p130 GeV (Au+Au), 200 GeV (Au+Au, Cu+Cu, d+Au, p+p+p))

55

PHENIX Run HistoryPHENIX Run HistoryYear Species √s [GeV ] ∫Ldt Ntot (sampled) Data Size

Run1 2000 Au - Au 130 1 µb-1 10 M 3 TB

Run2 2001/02 Au - Au 200 24 µb-1 170 M 10 TB

Au - Au 19 < 1 M

p - p 200 0.15 pb-1 3.7 B 20 TB

Run3 2002/03 d - Au 200 2.74 nb-1 5.5 B 46 TB

p - p 200 0.35 pb-1 6.6 B 35 TB

Run4 2003/04 Au - Au 200 241 µb-1 1.5 B 270 TB

Au - Au 62.4 9 µb-1 58 M 10 TB

Run5 2005 Cu - Cu 200 3 nb-1 8.6 B 173 TB

Cu - Cu 62.4 0.19 nb-1 0.4 B 48 TB

Cu - Cu 22.4 2.7 µb-1 9 M 1 TB

p - p 200 3.8 pb-1 85 B 262 TB

Run-6 2006 p - p 200 10.7 pb-1 233 B 310 TB

p - p 62.4 0.1 pb-1 10 B 25 TB

Run-7 2007 Au - Au 200 725 µb-1 4.6 B 570 TB

Run-8 2007/08 d - Au 200

p - p 200/500

Itzhak TserruyaItzhak Tserruya 66JINR, May 22, 2008JINR, May 22, 2008











Two small detectors, two large detectors Two small detectors, two large detectors – Complementary capabilities. Worked !Complementary capabilities. Worked !

77

Itzhak TserruyaItzhak Tserruya JINR, May 22, 2008JINR, May 22, 2008

RHIC and Its ExperimentsRHIC and Its Experiments

STARSTAR

88










Two small detectors, two large detectors Two small detectors, two large detectors – Complementary capabilities. Worked !Complementary capabilities. Worked !

ScienceScience– Unexpected results, major discoveriesUnexpected results, major discoveries– More than 170 papers in refereed literature, among them ~100 PRLMore than 170 papers in refereed literature, among them ~100 PRL

Future: RHIC and LHCFuture: RHIC and LHC– Key science questions identifiedKey science questions identified– Accelerator and experiment upgrade program underway to perform that scienceAccelerator and experiment upgrade program underway to perform that science– LHC to open a new energy frontier (increase by a factor of ~30!)LHC to open a new energy frontier (increase by a factor of ~30!) 99

1010

Geometry of Heavy Ion CollisionsGeometry of Heavy Ion Collisions

x

z

y

Non-central Collisions

Reaction plane

N_participants: number of incoming nucleons in the overlap region

N_binary: number of inelastic nucleon-nucleon collisions

Centrality of the collision expressed as percentile of the total cross

section.

N_participants:

N_collisions:

Centrality



FlowFlow(second major discovery at RHIC)(second major discovery at RHIC)


Flow: Evidence of Pressure and Collective Effects

Reaction plane

)(2cos)(21 2

2

RTT

pvdpd

Nd

Origin: In non-central collisions, the pressure converts the initial spatial

asymmetry (almond shape of overlap region) into azimuthal anisotropy of

particle emission

Collective effect

Absent in pp collisions

2v2

The flow is quantified by v2 (elliptic flow parameter) determined from the

azimuthal distribution of particles with respect to the reaction plane ψR


Every particle flows Mass hierarchy

Large v2 of heavier particles: d.

Even open charm flows (measured through single electrons)

Strong interactions at early stage early thermalization.


The “Flow” Is Perfect

as expected from “perfect fluid” hydrodynamics.as expected from “perfect fluid” hydrodynamics.

~~

mmmpmKE TTT 22

baryonsbaryons

mesonsmesons

1414

The mass hierarchy disappears if one uses the The mass hierarchy disappears if one uses the transverse kinetic energy:transverse kinetic energy:


The “Flow” knows quarks

baryonsbaryons

mesonsmesons

1515

Scaling the flow parameters by the valence quark content nq resolves the meson-baryon separation

All this makes the case for sQGP with early thermalization of partonic matter made of

constituent quarks and behaving like a perfect fluid

But there is a (conjectured) quantum limit:But there is a (conjectured) quantum limit:

““A Viscosity Bound ConjectureA Viscosity Bound Conjecture”, P. Kovtun, D.T. Son, A.O. Starinets, hep-th/0405231”, P. Kovtun, D.T. Son, A.O. Starinets, hep-th/0405231

Where do “ordinary” Where do “ordinary” fluids sit wrt this limit?fluids sit wrt this limit?


How Perfect is “Perfect” ?First hydrodynamic calculations for RHIC matter have all assumed zero viscosity First hydrodynamic calculations for RHIC matter have all assumed zero viscosity = 0= 0 “perfect fluid” “perfect fluid”

T=10T=101212 K K

Bks

4

RHIC “fluid” RHIC “fluid” mightmightbe at ~1 on this be at ~1 on this scale (!)scale (!)

1717

Open charm flows!Open charm flows!

Do bottom quarks flow too, or just charm? ANS: VTX in Run-11

Does thermalized charm contribute to J/ via recombination ?

i.e. does J/ flow too? ANS: Run-9 + Run-7!

Elliptic flow of heavy flavor via non-photonic electrons

PRELIMINARYRun-4

Run-7

Rapp & van Hees,

PRC 71, 034907 (2005)

minimum-bias



J/J/ψψ(the deconfinement probe?)(the deconfinement probe?)


Physics motivation

ccbarccbar predominantly produced by gluon fusion in the initial predominantly produced by gluon fusion in the initial parton collisions parton collisions probe the created medium : probe the created medium :

– ccbar (quarkonia) suppressed by color screening deconfinement

– open charm (or beauty) energy loss energy density

Anomalous J/ suppression seen at CERN SPS by NA50

At RHIC energy (10x√sNN ) expect much higher suppression

Color Screening

cc

T=0

T≠0

hadron size

confin

ement

color screening

Screening length

NA50 : Pb + Pb

√sNN ~ 17 GeV

nuclear absorption

σabs = 4.18 ± 0.35 mb


First surprise: RHIC vs SPS comparison SPS @ 0<y<1 :SPS @ 0<y<1 :

– √√s ~ 17 GeVs ~ 17 GeV– CNM = CNM = normal nuclear

absorption σabs = 4.18 ± 0.35mb

RHIC @ |y|<0.35 :• √√s = 200 GeVs = 200 GeV• CNM = CNM = shadowing + nuclear

absorption σabs from 0 to 3 mb from 0 to 3 mb (Vogt, nucl-th/0507027)(Vogt, nucl-th/0507027)

Very similar suppression at RHIC and SPS contrary to expectations.-

Second surprise: Rapidity dependence

Stronger suppression at forward rapidity compared to mid-rapidity


J/J/ Au+Au: suppression vs CNM Effects Au+Au: suppression vs CNM Effects

More forward suppression beyond CNM than at mid-rapidityMore forward suppression beyond CNM than at mid-rapidity

Large errors - need higher statistics d+Au data (Run 8)Large errors - need higher statistics d+Au data (Run 8)

J/ RAuAu 200 GeV (Run4)

arXiv:0711.3917|y| < 0.35

1.2 < |y| < 2.2

Cold nuclear matter (CNM) effects derived from d+Au data (run 3):

CNM = Shadowing(EKS) + Breakup = 2.8 mb+1.7

-1.4

J/J/ at RHIC: present status at RHIC: present status Suppression compensated by Recombination ?1) Models with only cold nuclear matter effects don’t quite have enough suppression2) Models with color screening (or comovers) have too much suppression3) Models with color screening (or comovers) AND recombination are in reasonable agreement with the data

J/ χc ’(2S)

ΔE [GeV] 0,64 ~ 0,22 0,05

Td/Tc 2,10 1,16 1,12

Dissociation temperature Td :

F. Karsch et al. (Nucl. Phys. A698(2002) 199c; hep-lat/0106019)

’ J/χc

Satz, J.Phys.G32:R25,2006

Sequential dissociation?

OR

J/J/: outlook: outlook

J/J/ from regeneration should from regeneration should inherit the large charm-quark inherit the large charm-quark elliptic flowelliptic flow

First J/First J/ flow measurement by flow measurement by PHENIX:PHENIX:

– vv22 = –10 ± 10 ± 2 ± 3 % = –10 ± 10 ± 2 ± 3 %

FVTX:

• 4x less ,K decays

• M: 170100 MeV Vertex detectors (VTX,FVTX) &

forward calorimeter (NCC) will give:

• ’ with reduced combinatoric background + sharper mass resolution

• precise open-charm measurements to constrain regeneration pictureLHC ? LHC ?


Low-mass dileptonsLow-mass dileptons(the chiral symmetry restoration probe)(the chiral symmetry restoration probe)

Origin of mass

1

10

100

1000

10000

100000

1000000

u d s c b t

QCD Mass

Higgs Mass X

Origin of mass:95% of the (visible) mass is due to the spontaneous breaking of the chiral symmetry.

Current quark masses generated by spontaneous

symmetry breaking (Higgs field)

Constituent quark masses generated by spontaneous chiral

symmetry breaking

Many models link the hadron masses to the quark

condensate.

At high T or density 0qq


Pioneering CERES results Pioneering CERES results at CERN SPS at CERN SPS

Strong enhancement of low-mass e+e- pairs in A-A collisions

(wrt to expected yield from known sources)

No enhancement in pp

nor in pA

Final CERES result

(from 2000 Pb run):Enhancement factor (0.2 <m < 1.1 GeV/c2 ):

2.58 ± 0.32 (stat) ± 0.41 (syst)± 0.77 (decays)


CERES and CERES and NA60NA60• Interpretation: thermal radiation from HG:

+- * e+e-

• Subtract the hadronic cocktail w/o the

* Both NA60 and CERES attribute excess to in-medium broadening of spectral shape (Rapp and Wambach) as opposed to dropping meson mass (Brown et al)

CERES Pb+Au

NA60 In+In

2929

Low-mass dielectrons at RHICLow-mass dielectrons at RHICarXiv:0706.3034

Significant enhancement of low-mass pairs

Different origin from SPS?

Limited by poor S/B ratio ( 1/200 at m=0.4 GeV/c2)

PHENIX

All pairsCombinatorial BGSignal


Hadron Blind Detector Hadron Blind Detector novel concept for e ID novel concept for e ID →→ Dalitz rejection Dalitz rejection

6 active panels2 side covers

with frame

2 vertical panels

window support

HV panels frame

Windowless Cherenkov detector

50 cm CF4 radiator

CsI reflective photocathode

Triple GEM with pad readout


Thermal RadiationThermal Radiation (the thermometer)(the thermometer)

Thermal PhotonsThermal Photons High energy density matter is formed at RHIC

If the matter is thermailzed, it should emit “thermal radiation”

The thermal photon spectrum provides a direct measurement of the temperature of the matter

Thermal photons are predicted to be the dominant source of direct photon for 1<pT<3 GeV/c at RHIC energies.

Higher pT: pQCD photon

Lower pT: from hadronic phase

Measurement is difficult since the expected signal is only 1/10 of photons from hadron decays

S.Turbide et al PRC 69 014903 S.Turbide et al PRC 69 014903


Alternative approach: virtual photons ( low-mass e+e- pairs)

Any source of real emits virtual * with very low mass

If the Q2 (=m2) of virtual photon is sufficiently small, the source strength is the same

The ratio of real photons and virtual photons can be calculated by QED

The real photon yield can be measured from the virtual photon yield, which is observed as low mass e+e- pairs

Excess of low-mass dileptons (wrt hadronic sources) is assigned to direct photons

..**

incl

direct

incl

direct

The idea of measuring direct photon via low mass lepton pair is not new one:

J.H.Cobb, et al, PL 78B, 519 (1978)

3434

TTinitinit via low mass, high p via low mass, high pTT dileptons dileptonsexp + TAA scaled pp

Fit to pp

NLO pQCD (W. Vogelsang)

Fit with exponential + TAA scaled p+p fit:

T = 221 ± 23 ± 18 MeV (central)

arXiv: 0804.4168

pp Au+Au min bias

M < 0.3 GeV/c2 pT = 1-5 GeV/c

JINR, May 22, 2008JINR, May 22, 2008


High pHigh pTT

suppressionsuppression(first major discovery at RHIC)(first major discovery at RHIC)

3636

Nuclear modification factorNuclear modification factor Zero hypothesis: scale pp to AA with the number of nn collisions Ncoll:

d2NAA/dpTd(b) = Ncoll d2Npp /dpTd = pp TAA(b) ?

d/dpd T

d/dpNd

/

/ )(pR

Tpp2

AA

TAA2

2

2

tAA ddpNdN

ddpNd

Tppcoll

TAA

Quantify “effect” with nuclear modification factor:

• If no “effect”:

RAA < 1 at low pT (soft physics regime)

RAA = 1 at high-pT (hard scattering dominates)

• If “jet quenching”:

RAA < 1 at high-pT

RAA = 1

RAA

RAA < 1

Ncoll /σinel pp


00 ppTT spectra at √ spectra at √ssNNNN = 200 GeV = 200 GeV

AuAu Run4

η=0

p-p

Excellent agreement between measured π0’s in p-p and measured π0’s in Au-Au peripheral collisions

scaled by the number of collisions over ~ 5 decades

70-80% peripheral

Ncoll =12.3 ± 4.0

Central Au-Au collisions yield significantly

suppressed relative to scaled pp yield

0-10% central

Ncoll =975 ± 94.0


Control: Photons shine, Pions don’t

Direct photons are Direct photons are notnot affected by hot/dense medium affected by hot/dense medium

Rather: Rather: shine shine through consistent with pQCD through consistent with pQCD 3838

Quantitative Analysis of Energy LossQuantitative Analysis of Energy Loss


Jet correlations in Au+Au Jet correlations in Au+Au Away side jet strongly modified in Au+Au compared to p+p collisions

Low/intermediate pT:

-broad away-side

-maxima at Δφ= π +/- 1 rad

High pT

-away-side shape like p+p

-but suppressed yield

•Current conjecture:•Head region -> jet modification (dominant at high pT)•Shoulder region -> medium response (dominant at intermediate pT)


Mach cone?Mach cone?☑ Jets travel faster than the Jets travel faster than the

speed of sound in the medium.speed of sound in the medium.

☑ While depositing energy While depositing energy via gluon radiation. via gluon radiation.

QCD “sonic boom” (?)QCD “sonic boom” (?)

To be expected To be expected in a in a dense fluiddense fluid which is which is strongly-coupledstrongly-coupled

Fluid Effects on Jets ?Fluid Effects on Jets ?

4141

62.4 GeV Au+Au

Summary and Outlook

Onset of heavy flavor energy loss? Emergence of opacity Onset of RHIC’s perfect fluid Energy Scans: where is the critical point? Low-mass dileptons Photon + Jets

Ambitious upgrade program underway RHIC RHIC II x40 luminosity increase Detectors and DAQ upgrades

RHIC has so far been very successful . Much is left to do to further characterize the properties of the “perfect fluid”

LHC is behind the corner. It will offer an unparalleled increase in √s. Will this still create a strongly coupled perfect fluid? Or will we approach the ideal QGP of free gas of quarks and gluons as originally sought?

Active pursuit via Dedicated experiment (ALICE) Targeted studies (CMS, ATLAS)

“trends in heavy ion physics research” dubna may 22-24, 2008

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