The first two years of RHIC: predictions vs. reality

Summary of the workshop:Who wins the wine, and why?

And, by the way,

What did we learn from the exercise?

Particle yields and spectra

global quantities hadron distributions

What do the data say?

dNch/d = 640

G. Roland

Rises somewhat faster than Npart

Rapidity distribution

PHOBOS

dN/dy ~ 220-230 per chargedNK+/dy ~ 40dNp/dy ~ 28Net baryon density at mid-y small, but not 0 B small

PHENIX preliminary

PHENIX preliminary

Transverse energy

ET/particle~ 0.9 GeV

Similar cent.dependence as <pt>

But <pt> goesup with s by20% whileET is constant particle mixis changing

Anti-particle/particle ratios

BRAHMS 200 GeV

At mid-rapidity:Net-protons: dN/dy 7proton yield: dN/dy 29 ¾ from pair-production

p+p collisions

I. Bearden

ISRextrapolation

Ratios similar to those in p+p!

What model can reproduce the net baryons?

Net baryon central plateau (y=0 to ~ y=2)

Cannot (yet) differentiate AMPT vs. HIJING/BJ

AMPT - CheMing Ko

Ingredients:HIJING, ZPC parton cascade, ART hadronic rescatting

ET = 750 GeV at y=0 (50% off *)data say: 3.3 GeV x (300/2) = 495 GeV

80 baryons at y= 3.9 (data say 34 at y=3.5)at y=0: 14 p, 10 pbar; pbar/p = 0.6 (data say 29, 22, 0.74)

(ratio is within 25% of data ***) dNch/d ~ 800 (dNch/d within 25% ***)

430 , 60 K per unit y at mid-y (data say 640 ,230, 40) Central plateau |y|<1.5 for mesons

(pion data says 1.5 *****)

Degree of difficulty = 3.5

Total score: 3.5 + 10.5 + 10.5 + 17.5= 42

What did we learn?

To get proper particle yields must tweak model so it no longer agrees with pp collisionsChanged fragmentation function to match lower s

data, rationale: fragmentation in dense matter

Must add a partonic phase with large scattering cross sections to reproduce v2 and HBT

To reproduce K-/K+ need additional hadronic rescattering channelsThen get K+K- correct in s = 130 GeV/A data

LEXUS – Joe Kapusta

Ingredients: parameterized p+p collision results, Glauber, NN hard collision probability parameter = 0.6

Minimalist approach, which works at SPS Net proton density = 13 (data say 7 *) dNch/dy = 1200, but should have been 950 using p+p at

proper s Correcting by 15% for y, get 1020 or 800(800 is within 25% of data, but –1 for p+p oops **)

Particle spectra are too steep, but missing power law tail proton <pT> ~ 0.925 GeV/c (data say 0.94 *****)

Degree of difficulty = 2

Total score: 2 + 4 + 10 = 16

(so their next model will be a Bentley…?)

What did we learn?

Create more hadrons in LEXUS than in wounded nucleon model, since wounded nucleons are not sterile in LEXUS. Overprediction some destructive interference among stopped nucleons at mid-y?

Total multiplicity is fixed by energy conservation Baryon density fixed by y in each collision

Minimalist picture works ~ OK for the simplest observables, but not for more complex ones

Caution in interpreting scaling with Ncoll or Npart !

Particle Spectra @ 200 GeV

Feed-down matters !!!

BRAHMS: 10% centralPHOBOS: 10%PHENIX: 5%STAR: 5%

QM2002 summary slide (Ullrich)

<pT> vs. Npart

open symbol : 130 GeV data

•Systematic error on 200 GeV data (10 %), K (15 %), p (14 %)

• Increase of <pT> as a function of Npart and tends to saturate < K < proton (pbar)• Consistent with hydrodynamic expansion picture.

<p

T>

[G

eV

/c]

<p

T>

[G

eV

/c]

J. Velkovska

Radial flow

<pT> prediction with Tth

and <> obtained from blastwave fit (green line)

<pT> prediction for Tch = 170 MeV and <>=0pp no rescattering, no flowno thermal equilibrium

STAR

preliminaryF. Wang

<pT> of and from exponential fits in mT

Do they flow ? Or is <pT> lower due to different fit function?

Does it flow? Fits to Omega mT spectra

M. van Leeuwen (NA49) C. Suire (STAR)

SPS/NA49

RHIC

STAR preliminary

T is not well constrained !

• At SPS and are now found to be consistent with common freeze-out• Maybe and are consistent with a blastwave fit at RHIC• Need to constrain further more data & much more for v2 of

UrQMD - Bleicher

Ingredients: excitation and fragmentation of color strings, formation and decay of hadronic resonances, hadronic rescattering

dET/d = 600, dNch/d = 750, ET/Nch = 0.85 GeVData say 495, 640, 0.9 Get ET to 20%, Nch to 17% *** and ***

y=0: 12 net protons, 400 -, 45 K+Data: 7, 230, 40 *, *, and ****

<pT> = 375, 500, 780 for , K, pData: 400, 650, 940 ****

not enough radial flow! v2 ~ 1% (way too low as the strings don’t collide)

Dense set of non-interacting strings… a problem…

Degree of difficulty = 2

Score = 32

We learned that

Need QGP-type equation of state to get the v2 and radial flow correctly UrQMD has insufficient initial pressure as the strings

don’t scatter.

Mass shifts of resonances very sensitive to breakup dynamics. Resonances are not dissolved implies fast freeze-out

Statistical model summary - Magestro

Johanna: chemical equilibrium with T=170 MeV, B = MeV

Johann: sudden freezeout with incomplete chemical equilibrium

Degree of difficulty = 1

0.58

0.75

0.90

0.66

0.660.890.95

STAR PHENIX

0.021

0.0015

Exptl. (130 GeV)

0.074

0.15

Predictions (200 GeV)

0.19

0.95

0.75Exptl. (200 GeV)

0.076

0.15

Scores:Johanna – within ~15%

****Johann - within ~ 40%

**

eVB MeV

Lessons from statistical analyses

See chemical equilibrium populations at RHIC as at SPSB is lower, but not as low as predictedNo anomalous strangeness enhancement

Simple thermal emission produces proton spectra flatter than pion spectra, so they must cross someplace!Of course the big question is where and why there??

Elliptic flow

Centrality dependence of v2

STAR

v2=0.05

130 GeV: 0.075< pt < 2.0 200 GeV: 0.150< pt < 2.04-part cumulants

200 GeV: 0.2< pt < 2.0

Preliminary

200 GeV: Preliminary

Note possible dependence on low pt cut

- Consistent results- At 200 GeV better pronounced decrease of v2 for the most peripheral collisions.

STARPreliminary

QM2002 summary slide (Voloshin)

Adler et al., nucl-ex/0206006

A puzzle at high pT

Still flowing at pT = 8 GeV/c? Unlikely!!

Nu Xu

Au+Au at sNN=200GeVv2 of mesons & baryons

v2

1) High quality M.B. data!!!

2) Consistent between PHENIX and STAR

pT < 2 GeV/c v2(light) > v2(heavy)

pT > 2.5 GeV/c v2(light) < v2(heavy)

Model: P.Huovinen, et al., Phys. Lett. B503, 58 (2001)

Hydrodynamics – Ulrich Heinz, Peter Kolb

Ingredients: thermal with some initial conditions, QGP EOS early with transition to resonance gas, geometry + Glauber, hydrodynamics

Predictions:Thermalization by 0.6 fm/c at RHICv2 as function of pion multiplicity density (to fix initial cond.)v2 has a dip (~5%) due to phase transition softening EOS

RHIC is near this point (data says v2 ~ 6%)v2 vs. pT increases to 2 GeV/c v2(mesons) > v2 (baryons)spectra (once initial condition is fixed)

Lessons: v2 requires early rescattering! Hadronization follows thermalization by 5-7 fm/c. But, final state decoupling needs work (get HBT wrong)

Predictions of major importance!

Hydrodynamics –Teaney & Shuryak

Ingredients: hydrodynamics + RQMD for hadronic state and freeze-out

Predictions:RHIC should be near softest point in EOSs dependence of v2 correctly predicted for b=6 fm fixed initial conditions, then got spectra correctPredict particle yields without rescalingInitial entropy too high, HBT radii too large!

Lessons: hydro good to pT ~ 1.5 GeV/cViscosity corrections may be important; cause v2 to

bend over at 1 GeV/c pT (compared to ideal gas). Also helps reduce HBT radii. Maybe small viscosity early, but increases in hadron gas phase?

Parton transport theory – Denes Molnar

Next step beyond hydro – calculate parton transport, fixing (i.e. transport opacity )

Predictions & insights:ET loss due to pdV work so (ET)cent < (ET)peripheral

ET results require small (3 mb)can’t easily fix up with inelastic collisions need parton subdivision to avoid numerical “viscosity”

Can reproduce v2 if dNgluon/dy very large or el= 45 mbBut large opacity underpredicts HBT spectra!

pQCD fixes dNgluon/dy at large pT

pQCD fixes parton at large Q2 Picture doesn’t want to hang together!

Degree of difficulty = 5

Next, jets and high pT

summary fromThomas Peitzmann,

QM2002

Preliminary sNN = 200 GeV

Preliminary sNN = 200 GeV

C. Roland, PHOBOS Parallel Saturday

200 GeV results from all experiments

Shape changes from peripheral central

Charged Hadron Spectra

p/ at high pT

Vitev & Gyulassy nucl-th/0104066

Can explain by combination ofhydro expansion at low pT withjet quenching at high pT

Higher than in p+pcollisions or fragmentationof gluon jets in e+e-collisions

Jet Quenching – Gyulassy, Wang, Vitev, Levai

HIJING: Beam jets @ pt<2 GeV (LUND), pQCD mini jets @ pt>2 GeV (PYTHIA), geometry (Glauber), 1D expansion, conservation laws; tuned to pp data 10-103 GeV

+ nuclear shadowing and parton energy loss “knobs”

gL / OpacityExpansion

GLV “Thin” Plasma Limit

BDMS “Thick” Plasma Limit

Degree of difficulty = 5

No Shadow, No QuenchNo Shadow, dEg/dx=0.5

GeV/fmDefault: Shadow,

dEg/dx=2.0

Npart/2

Nbinary

PHENIX 130

BRAHMSPRL88(02)

? 2003 ?

STAR 130

hch

15% too many particles, baryons over-quenched, but predicted the suppressionBUT: dE/dx =2 GeV/fm or 0.5 GeV/fm or not linear with x?

Vitev: they can get v2 right

C. Adler et al. [STAR Collab.], arXiv: nucl-ex/0206006

K. Filimonov [STAR Collab.],arXiv: nucl-ex/0210027

b=7 fmb~7 fm

• There is a quantitative difference Calculations/fits with flat or continuously growing

2 .v const 2 / .ln Tv p

Check against high-pT data (200 AGeV)

Same for 0-50%

• The decrease with pT is now supported by data• For minimum bias this rate is slightly slower

See: N.Borghini, P.Dinh, J-Y.Ollitrault, Phys.Rev. C 64 (2001)

Other penetrating probes

Open Charm J/ Dileptons

Need (a lot) more statistics in the dataBut getting a first sniff of physics already

J/

Energy/Momentum

Data consistent with:Hadronic comover breakup (Ramona Vogt) w/o QGPLimiting suppression via surface emission (C.Y. Wong)Dissociation + thermal regeneration (R. Rapp)

Open charm - Lin

about x2 within predicted curveswith or w/o energy loss

no x4 suppressionfrom peripheral to central,as predicted fordE/dx=-0.5GeV/fm

But - Is 40-70% peripheral enough? error bars still big!

Some old things and some new things

HBT High pT baryons Dijets vs. monojets

Well, there was a prediction but for 10x the pT

Parton saturation

HBT – lots of questions

• How to increase R without increasing Rout/Rside? EOS, initial T and r profiles (Csőrgó), emissivity?

• Why entropy looks low?Low entropy implies equilibrated QGP ruled out

Panitkin, Pratt

Baryons at high pT Jia, Sorenson

Meaning of Ncoll scaling?Accident? Complex hard/soft interplay?Medium modified jet fragmentation function?

Yields scale with Ncoll near pT = 2 – 3 GeV/c

Then start to fall

protons

, h

Away-side Jet Suppression

trigger-jetnot much modification (the trigger particles from jets!)

Away side:strong jet suppression

Strong jet suppression surface emission of jets?Color glass back-to-back jets simply not created…

D. Hardtke

Parton saturation

Hadron multiplicities imply a coherent initial stateInitial NN interactions are NOT independent!High parton density weak coupling CGC

Saturation at y=0, and even more so at forward yaffects QCD evolution, even at Q2 > Qs

2

causes multiplicity to scale with Npart, even at high pT

hard parton scattering suppressed by CGC monojets does saturation set in already at s ~ 20GeV? I doubt this! Should measure in forward y in p+A, where Qs is larger

and CGC is magnified.This should clarify initial vs. final state effect in AA!

Dima Kharzeev, Jamal Jalilian-Marian

conclusions

Have early pressure buildup – high dNg/dy & they scatter! success of hydro, need for string melting, large …

High pT, high mass data look like pQCD + somethingJet quenching works; surface emission??Baryon flow is a nuclear effect!Color glass is intriguing, but where does the collectivity

come from? Event generators (still) a valuable tool to investigate

sensitivity of observables to physics ingredients Integrated quantities are simple (conservation laws!)

Caution in interpreting scaling with Npart or Ncoll

e+e- scaling with Npart is arbitrary, agreement irrelevant

Experiments: homework to allow quantitative comparisons (multiple 15% factors = sloppy interpretations!)

And the winners are…

Best predictions of general features by event generatorAMPT (Ko, Lin, Zhang)

Novel approach, theoretically intriguing (+ agrees with data)Baryon junctions (Kharzeev, Vance, Gyulassy, Wang)

Important prediction with potential great insights to QGPHydrodynamics (Heinz & Kolb, Teaney & Shuryak, Bass &

Dumitru, Ollitrault for “inventing” v2 analysis)

Much promise for understanding properties of QGPJet energy loss (Gyulassy,Wang, Vitev, Levai)

yield in AuAu vs. p-p collisions

70-80% PeripheralNcoll =12.3 ±4.0

PHENIX Preliminary

pp

centralbinarycentral

Yield

NYield /

D. d’Enterria

Yield ratio s=200/130 GeVConsistent at at high pT withpQCD predictions (STAR)

kT dependence of R

Centrality is in top 30%

•Broad <kT> range : 0.2 - 1.2 GeV/c •All R parameters decrease as a function of kT consistent with collective expansion picture. • Stronger kT dependent in Rlong have been observed.

kT : average momentum of pair

Comparison of kaon to pion

In the most 30% central

Comparison with hydrodynamic model

Recent hydrodynamic calculation by U.Heinz and P. F. Kolb(hep-ph/0204061)

kT dependence of Rlong indicates the early freeze-out?

Hydro w/o FS

Hydro at ecrit

• Assuming freeze out directly at the hadronization point. (edec = ecrit)

• Standard initialization and freeze out which reproduce single particle spectra.

Centrality is in top 30%

kT dependence of Rout/Rside

A. EnikizonoQM2002

C.M. Kuo, QM2002 poster (PHOBOS) 200 GeV:

.)(25.009.016.1 syst @0.25 GeV/c

HBT PUZZLE

P.Kolb

Small Rout implies small

Large Rside implies large RSmall Rbeam impliessmall breakup ~10 fm/c

Jet Evidence in Azimuthal Correlations at RHIC

near-side correlation of charged tracks (STAR)trigger particle pT = 4-6 GeV/c distribution for pT > 2 GeV/c

signature of jets

also seen in (0) triggered events (PHENIX)trigger particle pT > 2.5 GeV/c distribution for pT = 2-4 GeV/c

M. Chiu, PHENIX Parallel Saturday

QM2002 summary slide (Peitzmann)

Identifying Jets - Angular Correlations

Remove soft background by subtraction of mixed event distribution

Fit remainder:Jet correlation in ; shape taken from PYTHIAAdditional v2 component to correct flow effects

PHENIX Preliminaryraw differential yields

2-4 GeV

Verify PYTHIA using p+p collisions

(neutral E>2.5 GeV + 1-2 GeV/c charged partner)

||<.35 ||>.35

ake cuts in to enhance near or far-side correlationsBlue = PYTHIA

In Au+Au collisions

1-2 GeV partner

(neutral E>2.5 GeV + charged partner)

||<.35 ||>.35

1/N

trig d

N/d

1/N

trig d

N/d

Correlation after mixed event background subtraction

Clear jet signal in Au + AuDifferent away side effect than in p+p

Jet strengthSee non-zero jet strength as partner pT increases!

jets or flow correlations? fit pythia + 2v2vjcos(2)

partner = .3-.6 GeV .6-1.0 GeV/c 2-4 GeV/c

1/N

trig d

N/d

v2vj

1-2 GeV/c

How do protons scale with Ncoll/Npart?

Scale with Ncoll (unlike )?!

High pT baryons scale with Ncoll!

Low pT near Npart scaling

But baryons with pT > 2 GeV/cbehave very differently!From jets? Unsuppressed??

J. Velkovska

Charm cross section at RHIC

Centrality dependence of charm

peripheralbinaryperipheral

centralbinarycentral

NYield

NYield

//

Homework assignment (PHENIX & STAR)

Charged larger than 0

But difference not same as for RAA

PHENIX and STAR RAA

not the same

Different reference in each case!

Systematic difference between experiments

Charged hadron correlations - small

•Fit charged correlations with v2 + Gaussian (fixed pT)•Jet signal visible via

Width of near-side Gaussian decreases with pT

No significant centrality dependence on near-side

Cor

rela

tion

wid

th

jT

pT Correlation width jT/pT

How do high pT yields scale?

vs. binary collisions:continuous decrease as

function of centralityfactor ~ 3.5 from

peripheral to central vs. participants:

first increase, then decrease as function of centrality

for Npart > 100 have 3 change (scaling or no?)

surface emission? re-interactions?accident?

18% scaling uncertainty from corrections

dN/dy

K+

p

Positive Negative

PHENIX Preliminary PHENIX Preliminary

• Similar centrality dependence 130 GeV and 200 GeV

open symbol : 130 GeV data

Au+Au at sqrt(sNN) =200GeV Au+Au at sqrt(sNN) =200GeV

K-

pbar

dN

/dy

/ (0

.5 N

pa

rt)

Npart Npart

Opaque, expanding source would mean:

2222222 2)()( xtso YXRR

)(outX

)(sideY

29.13

5)(

)(

spheres

shellhalfs

R

R

65.012

5)(

)(

sphereo

shellhalfo

R

R

Opaque Expanding

Rischke RIKEN workshop (2002): Such strong xt correlations probably require a lack of boost-invariance...

Energy Dependence

Assumptions:in Lab in C.M.

Energy density (Bjorken):

2% most central at sNN=200 GeV:

5.5 GeV/fm3

From AGS, SPS to RHIC:

Transverse energy and charged particle multiplicity densities per participant consistent with logarithmic behaviour

ddX

dy

dX

ddX

dy

dX2.1

dy

dE

Rt

2

1

cfm

AfmR

/1

18.1 3/1

PHENIX preliminary

PHENIX preliminary

P spectra from Star

High quality data over 9 centrality selections

Shape described by

blast wave fit

K-/K+ and p/p from AGS to RHIC

I. Bearden (BRAHMS)

Becattini caluclation usingstatistical model: T=170, s=1 (weak dependency)

vary B/T K+/K- andp/p

K- /K+=(p/p)1/4 is a empirical fit to the data points

KK driven by s

~ exp(2s/T)

p/p driven by B

~ exp(-2B/T)

s = s (B) since <S> = 0BUT: Holds for y 0 (BRAHMS y=3)

QM2002 summary slide (Ullrich)

The K*0 story

K*0/K suppressed in AA versus pp /K*0 appears enhanced versus pp

STAR QM Talks: E. Yamamoto and P. Fachini

STAR Preliminary

pp uncorrected for trigger bias and vertex finding efficiency

min bias 200 GeV Au+ Au

v2 at high pT

Centrality dependence of p/pi

+

-

•Ratios reach ~1 for central collisions

•Peripheral collisions lower, but still above gluon jet ratios at high pT

•Maybe not so surprising 1)“peripheral” means 60-91.4% of total

2) p/pi = 0.3 at ISR

Note pbar/p behavior

Centrality dependence only for pT > 3 GeV/c

Peripheral collisions have quite a few protons at mid-y