The Strange Physics Occurring at RHIC

Helen Caines - Yale University

May 2004

The Strange Physics Occurring at RHIC

Workshop on Strangeness and Exotica R. Bellwied, H. Caines, C.Pinkenburg, J. Velkovska

RHIC & AGS Annual Users MeetingBNL

May 10-14th 2004

Helen Caines – May 2004 2

A theoretical view of the collision

Tc – Critical temperature for transition to QGPTch– Chemical freeze-out (Tch Tc) : inelastic scattering stopsTfo – Kinetic freeze-out (Tfo Tch): elastic scattering stops

1. Hadronic ratios.

2. Resonance production.

3. pT spectra.

4. Partonic collectivity.

High pT measurements.

4

31 2


Baryon transport to mid-rapidity

♦ Clear systematic trend with collision energy♦ Very similar trend between heavy ion and p-p

62.4 GeV data fits into patternR. Witt

E866 -


Resonance ratios

Thermal model [1]:Tch = 177 MeVB = 29 MeV

[1] P. Braun-Munzinger et.al., PLB 518(2001) 41 D.Magestro, private communication[2] Marcus Bleicher and Jörg Aichelin Phys. Lett. B530 (2002) 81-87. M. Bleicher, private communication

Need >4fm between Tch and Tfo

UrQMD [2]

Life time [fm/c] : = 40 * = 13 K* = 4

Small centrality dependence: little difference in lifetime!

Nch

/

TT chfoStable

Resonance

Stable

Resonance te

NOT ENOUGH

O. Barranikova


Resonance Feed-down

- - +n

Particle mass close to pdg value

Width ~ 10MeV

+ + +n

+ +p ?p misidentified asn

Phenix Preliminary

Might finally be able to answer question about contamination of

C. Pinkenburg


Measuring through both channels

Φ K+K- (min bias 200 GeV)

Mass and width agree within errors

with PDG values

PHENIXpreliminary

Yie

ldMass (GeV/c2)

Yie

ld PHENIXpreliminary

Mass (GeV/c2)

)()(5.24.5dy

dN : 4.3

8.2 sysstatee

K K : dN

dy2.010.22(stat) 0.52

1.01(sys)

Φ e+e- (min bias 200 GeV)

D. Mukhopadhyay


Modeling the Spectra♦ K0

s upper♦ lower♦ Centrality (0-5%)

♦ HIJING/BBar v2.0 right♦ HIJING v1.37 left

Also reasonable ratios as function of centrality

V. Topor-Pop

Need extra strings and rope breaking to obtain strange

particle yields


Low pT results

1)Tm

exp(

AdydmNd

m21

fit

TT

2

T

-1 for mesons+1 for baryons

Au+Au sNN = 200 GeV

PHENIX - open symbolsPHOBOS –closed symbols

Solid line = fit to PHENIX spectra

Dashed line = extrapolation of fit

This fit extrapolates smoothly to the low-pT points

No enhancement of low-pT particle yields

PHENIX spectra for mT < 1GeV/c2 fit with:

Low pT results are vital for getting spectral shapes

C. Henderson


pT vs Mass

♦ ISR parameterization fails for heavy particles♦ Same <pT> for p-p and Au-Au for heavy particles? Different <pT> with Nch, heavier particles different mult. bias R. Witt

STAR Preliminary


Phase space suppression less at RHIC

♦ See drop in “enhancement” at higher energy for ♦ Enhancement values not as predicted by model♦ Correlation volume not well modeled by Npart

130 GeV

STAR Preliminary 200 GeV

H. Oeschler

[Tounsi & Redlich: hep-ph/0111159]


Suppression of identified particlesTwo groups (2<pT<6GeV/c):

- K0s, K, K*, PHENIXhave mesons

- baryons

Rcp

Clearly not mass dependenceHigher stats. this run get and

Come together again at pT ~ 6 GeV?

“standard” fragmentation?

show different

behaviour to K

Suppression of K sets

in at lower pT

K

Mass or meson/baryon effect?

C. Mironov


Parton coalescence and medium pT

recombining partons:

p1+p2=ph

♦ When slope exponential: coalescence wins

♦ When slope power law: fragmentation wins

fragmenting parton:

ph = z p, z<1

recombining partons:

p1+p2+p3=ph

fragmenting parton:

ph = z p, z<1

♦Mesons

♦Baryons

♦ Recombination p(baryons) > p(mesons) > p(quarks) (coalescence from thermal quark distribution ...)♦ Pushes soft physics for baryons out to 4-5 GeV/c♦ Reduces effect of jet quenching

Do soft and hard partons recombine or just soft+soft ? Explore correlations with leading baryons and mesons C. Nonaka


v2 and coalescence model

Hadronization via quark coalescence: v2 of a hadron at a given pT is the partonic v2 at pT/n scaled by the # of quarks (n).♦ Works for K0

s, &

♦ v2s ~ v2

u,d ~ 7%

D. Molnar, S.A. Voloshin Phys. Rev. Lett. 91, 092301 (2003)V. Greco, C.M. Ko, P. Levai Phys. Rev. C68, 034904 (2003) R.J. Fries, B. Muller, C. Nonaka, S.A. Bass Phys. Rev. C68, 044902 (2003)Z. Lin, C.M. Ko Phys. Rev. Lett. 89, 202302 (2002)

Au+Au sNN=200 GeV

R. Seto


What about Strangeness in p-p?

p-p is not necessarily the best baseline Phase space suppression of strangeness in p-p

C. Mironov


Pentaquarks at RHIC

+n+K-

+ p +K0

p

Au-Au MinbiasSTAR Preliminary

Some possible peaks need more investigation

p-p

STAR Preliminary

STAR Preliminary

S. Kabana, C. Ko, L. Guo, C. Pinkenburg


Summary

0 1 2 3 4 5 6 7 8 9 10 11 12 GeV/c

pQCDReCo

Hydro

Different physics for different scales

Strange particles are useful probes for each scale

♦ All evidence suggest RHIC creates a hot and dense medium with partonic degrees of freedom.

♦ Only just beginning to understand the rich physics of RHIC.♦ Lots more to come and much already on TAPE!


Agenda

♦ STAR strangeness bulk properties – O. Barannikova♦ STAR strangeness pp results – R. Witt♦ Phi Production in PHENIX – D. Mukhopadhay♦ Strangeness production in PHOBOS – C. Henderson Break♦Thermal Model calculations for RHIC/SPS – H. Oeschler♦ HIJING model calculations – V.Topor-Pop♦ Intermediate pT results in PHENIX – R. Seto Lunch♦ Intermediate pT results in STAR – C. Mirinov♦ Recombination model calculations – C. Nonaka♦ Pentaquark results from JLAB – L. Guo♦ Pentaquark results from PHENIX – C. Pinkenburg Break♦ Pentaquark results from STAR – S. Kabana♦ Pentaquark production – theory input – C.M. Ko♦ Roundtable – What’s next for Strangeness – All Adjorn


BACK UP


Determining spin and parity K+ d + p

Intrinsic parity - + +? + K+ p + +

Intrinsic parity - + +? -

Parity Conserved 1= (-1)L n1n2

L = If – Ii L = Odd L = Even

K+ d + p spin 0 1 ½(?) ½

K+ p + + spin 0 1 ½(?) 0

L = 1 L = 0

L determines the decay angular distribution

Determination of spin and parity will help select between theories

Correlated quark & Chiral soliton models predicts Jpc=½+ (p-wave)Quark model naïve expectation is Jpc=½− (s-wave)


Interpretation of the +


Thermal model reproduces dataD

ata

– F

it (s

)

R

atio

Do resonances destroy

the hypothesis?Used in fit

Created a Large System in Local Chemical Equilibrium


Experimental Evidence for +

Currently 6 Experiments have identified a peak

Mass(nK+) GeV

CLAS p->+K*

Spring-8

DianaKXe->+N

Saphir

p->p-> ++ K Kss00

ITEPNe->K0

sp+

Hermes


Kinetic Freeze-out

,K,p: Tkin decreases with centrality

Tkin = const., coincides with Tch !

Large flow, lots of re-interactions, thermalization likely

*A. Baran et al.; nucl-th/0305075.

Tdec = 100 MeV

Kolb and Rapp,PRC 67 (2003)

044903.


<pT> Systematics in p-p at 200 GeV

p+p at 23 GeV

Mass dependence even in p-p. Not flow!


Temperature and Lifetime Centrality Dependence

Model includes: • Temperature at chemical freeze-out• Lifetime between chemical and thermal freeze-out• By comparing two particle ratios (no regeneration)

results between : T= 160 MeV => > 4 fm/c (lower limit !!!) = 0 fm/c => T= 110-130 MeV

(1520)/ = 0.034 0.011 0.013 K*/K- = 0.20 0.03 at 0-10% most central Au+Au

G. Torrieri and J. Rafelski, Phys. Lett. B509 (2001) 239

Life time:K(892) = 4 fm/c (1520) = 13 fm/c

preliminary

More resonance measurements are needed to verify the model and lifetimes

Blast wave fit of ,K,p (Tkin +Tchem

~ 6 fm/c (see poster Olga Barannikova)

does not change much with centralitybecause slight T reduction is compensated by slower expansion velocity in peripheral collisions.

UrQMD ~ 5-20 fm/c


Quantifying the Correlation Strength

Back sideBack side

dash lines indicate dash lines indicate estimated flow contributionestimated flow contribution

Trigger PT

Correlation difference defined as : Nsame - Nback

trigger

pairsback

N

NN

)49.2(

trigger

pairssame

N

NN

)65.0(

Trigger PT

Same sideSame side

Trigger PTrigger PTT

NNs

am

es

am

e -

N -

Nb

ac

kb

ac

k

trig: , assoc : charged hadrontrig: , assoc : charged hadron

• Suppression of as a function of pT is slightly different from the , K0

s and primaries. • Under investigation whether this is an experimental effect or whether there is indeed sensitivity to quenching or production mechanism effects

NNs

am

es

am

e -

N -

Nb

ac

kb

ac

k

Trigger PTrigger PTT

trig: , assoc : charged hadrontrig and assoc : charged hadrontrig: K0

s, assoc : charged hadron


What Does a RHIC Collision Look Like?

A Central Au+Au Collision: Npart sNN = 40 TeV

~ 6 Joule

Our Ears are sensitive to ~10-11 ergs= 10-18 Joule

= 10-12 Joule

If a RHIC Collision was converted solely into noise that‘s one BIG BANG!

HI Collisions converted into COPIOUS particle production


data data / power law

Au-Au

p-p

mT Scaling

In p-p

Not in Au-Au


Charged Particle Trends

<pT> [GeV/c]

dN/dy

K-

p

-

200 GeV130 GeV

200/130 ratios:Consistent with being flat:

<Nch> ratio: 1.190.05 (sys)

pt ratio: 0.99 0.02 (sys)

No increase of <pt> loss of early information?Maximum Missing Information thermalization?

Only true for , need detailed PID information…

STAR Preliminary


Hydro Calculation of v2

P. Kolb, J. Sollfrank, and U. Heinz Large v2 is an indication of early

thermalization

Heavy-Ion Collisions create a system which approaches hydrodynamic limit

A pressure build up -> Explosion zero for central events

self quenching

Elliptic flow observable sensitive to early evolution of system

Collective motion + large energy density ->Hydrodynamics Assumes continuum matter with local equilibrium, “thermalization”

Hydrodynamic model

Nch/Nmax

SPS

AGS

PRL 86 (2001) 402

V2

Equal Energy Density lines


Hadron Suppression for Identified Particles

STAR Prelimimary

s

Seem to come together at ~6GeV/c - “standard” fragmentation?

Is this a mass effect or a baryon/meson effect ?


Different Physics for Different Regions

pT

pQCDHydro

2-3 GeV/c 6-7 GeV/c ?

Soft Fragmentation and quenching

of jets

0

What do we think we know ?

What are the mechanism(s) atintermediate pT?


Baryon/Meson Ratios vs Collision Centrality

/K0s ratio increases with increasing centrality

peaks in the intermediate pT region. turns over and appears to tend to the

same value for all centralities for pT ~ 5-6 GeV/c.

Therefore pT range of baryon excess is

limited to < 5-6 GeV/c. Not yet down to level in pp data

Strong baryon/meson modification in Au + Au for in /K0s ratio as reco. predicts


The STAR Detector

MagnetMagnet

CoilsCoils

Central Central TriggerTriggerBarrel Barrel (CTB)(CTB)

ZCalZCal

Time Time Projection Projection

ChamberChamber(TPC)(TPC)

Year 2000Year 2000

Barrel EM Cal Barrel EM Cal (BEMC)(BEMC)

Silicon Vertex Silicon Vertex Tracker (SVT)Tracker (SVT)Silicon Strip Silicon Strip Detector (SSD)Detector (SSD)Vertex DetectorVertex Detector

FTPCFTPCEndcap EM CalEndcap EM CalFPDFPD

TOFp, TOFrTOFp, TOFr

Year 2001/2003Year 2001/2003

Year 2006+Year 2006+


Flow of multi-strange baryons

♦ , K, p: Common thermal freeze-out at Tfo ~ 90 MeV

<> ~ 0.60 c

♦ : Shows different thermal freeze-out behavior:

Tfo ~ 160 MeV

<> ~ 0.45 c

But: Already some radial flow!

Tfo ~ Tch Instantaneous Freeze-out of multi-strange particles?Early Collective Motion?

Higher temperatureLower transverse flowProbe earlier stage of collision?

Au+Au sNN=200 GeV

STAR Preliminary

68.3% CL 95.5% CL 99.7% CL

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The Strange Physics Occurring at RHIC