Resonances in Heavy Ion Collisions

Zhangbu Xu (BNL) SQM2003 1

Resonances in Heavy Ion Collisions

• Introduction– History/Techniques

• Particle Yield– Thermal Description– Strangeness Enhancement

• In-medium Effect• Time Scale Measurement• pT Spectra

– Flow Effect– High pT Phenomenon

O. Barannikova, M. Bleicher, G. Brown, P. Fachini, L. Gaudichet, T. Hallman,H. Huang, F. Laue, H. Long, R. Longacre, J. Ma, C. Markert , S. Salur, J. Sandweiss, E. Shuryak, A. Tai, G. Torrieri, T. Ullrich, N. Xu, E. Yamamoto, H. Zhang


A little bit of historyWith the establishment of the hydrogen bubble-chamber, entirely new possibilities for research into high-energy physics present themselves. Results have already been apparent in the form of newly-discovered elementary particles. The first, very short-lived, so called, "resonance particle" was found in 1960. The Nobel Prize in Physics 1968

First time Invariant Mass was used (bump hunting)

(1952?)(1385) (1960)(892) (1961)(1405)

1411 (1967)


Measurement Technique

• Mixed-event, Like-sign Background subtraction

• P-Wave Breit-Wigner function or Modified BWH. Zhang (STAR)

ISR STAR PreliminaryK*0 from p+p Collisions


How Many Resonances?


How are we doing so far?e+e-: 50 particlesAA: 16Including stable particles

How Many Measured?


Experiments

Exp 2 4* 0 f0 4* 2* 4

NA49 1 1 1

NA50 1

PHENIX 2

STAR 1 4 1 1 4 2 2


What do we do with it?

)/)(exp(

)/exp(22

2

uss

q

qihbind

mm

m

mMEi

Y.J. Pei, hep-ph/9610329

More advanced: Thermal model

e+e-


Significance of Feeddown

0.18K 0.30

0 0.50

K* 0.60

1.00f0(980) 1.00

p, 0.20

++ 0.80

* 1.00

* 0.80

Hadron Primordial Fraction


• Brown-Rho Scaling• Rho Broadening• Low Mass Dilepton

measuring properties

Last Call for RHIC PredictionsNucl.Phys. A661 (1999) 205-260

• Chiral UA(1) symmetry restoration (J. Schaffner, D. Kharzeev, et al.)

Medium Effect in Dense Nuclear Matter

R. Rapp, et al


How to Probe Early Stage?

• Modification in medium

• Decay quicklymatter exists 10-23s

• Small or no FSIleptons, photons, neutrino

Golden: J/

q

q

l

l

s

Small Branching Ratio(10-4), Low Production Rate


-Production: Hadronic versus Leptonic Decay Channel

• Different decay channels:– NA49: -+

– NA50: -+

• Transverse momentum spectrum– fit: 1/mTdn/dmT ~ exp(-mT/T)

(NA49: 3.0<y<3.8)

significant differences in slopes and yields

Dieter Röhrich, QM02


Vector Meson at RHIC

• AMPT: (l+l-)/(K+K-)=1.5• Experiments’ comparison

c=50fm

K

K

l+l-

K+K-

AMPT, STAR

Nucl-th/0202086

130GeV


hadronic/leptonic decay

)()(22.001.2dy

dN : 01.1

52.0 sysstatKK

PHENIX Preliminary

eeKK

PHENIX Preliminary

)()(5.24.5dy

dN : 4.3

8.2 sysstatee

e+e-

K+K-

200GeV

J. Nagle, QM02

Sensitivity Reach


Dileptons at SPS

Conventional cocktail of particles Underpredicts dilepton production

Mass shifted??


Last Call for RHIC PredictionsNucl.Phys. A661 (1999) 205-260

Cleaner Way of Detecting Modification?

Hadronic Decay at Late Stage

• Lower Density

• Lower Temperature

• Smaller Effect

• Hadronic Decay

• Larger Signal

• Extrapolation


+ - Invariant Mass Distribution from Data at QM2002

• 2.1106 Au+Au minimum bias events and 4.7106 pp events

• Breit-Wigner fixed width 0 = 150 MeV and f0 = 75 MeV fixed f0 masse 0.98 GeV (AuAu) and 0.96 GeV (pp)

0 mass = 0.698 ± 0.013 GeV (AuAu)

0 mass = 0.729 ± 0.006 GeV (pp)

AuAu 40% to 80%0.2 pT 0.9

GeV/c

|y| 0.5

0

f0

K0S

K*0

STAR Preliminary

STAR Preliminary

0

f0

K0S

K*0

0.2 pT 0.8 GeV/c

|y| 0.5

pp

Statistical error only Statistical error only

sNN = 200 GeV

New: pT dependenceP. Fachinia (STAR)


K*0 Mass and Width Distribution

K*0 Mass shift in p+p and Au+Au at low pT possible in-medium dynamiceffect modified K*0 mass and the line shape

K*0 width matches the MC prediction

STAR Preliminary

H. Zhang (STAR)


What Effects?

• Rescattering

• Phase Space

• Interference

• Modification

Ron Longacre, et alWork in progress


Probe Freeze-out Dynamics

Strange Hadron Resonances as a signature of freeze-out dynamics

hep-ph/0103149

Basic Idea:: Two parameters two measurements:

e-m/TSurviving possibility Thermal factor

e-t/c


M. Bleicher QM02

Difference (t) may be SmallEffect is Large

Initial Production

Final Production

Transport ModelUrQMD


All that Matters: X-section

Different by 5

Rescattering>Regeneration at later stage

Chemical freeze-out

Kinetic freeze-out

K*

lost

K*

measured

K

K* K

K*

K*

K

K*

K K K*

measured


Yield and pT Spectra

STAR Preliminary

K*0/K in AuAu is a factor of 2 lowerthan in STAR pp rescattering

H. Zhang (STAR)J. Ma (STAR)

STAR Preliminary


Flow/pQCD Effect

Gyulassy, etc.

Leading Quark Effect


Particle Spectra

STAR Preliminary

T=156MeVpp: 63GeV

ISR Vector Mesons


Power Law Spectra

mT-m0

STAR Preliminary

In AuAu Preliminary

In pp Preliminary

Power lawmT Exponential


What Puzzles?

At pT ~ 2-3 GeV/c, yields approach each other. Heavier mass particles show stronger collective flow effects !

? When did the collectivity developed at RHIC


Spectra Meet at 2GeV/c

130GeV

Proton Puzzle???

2GeV/c PUZZLE? dN/(dypTdpT)=constant |pT=2GeV/c

, different (rare particles)Low production Cross section Small Scattering X-sectionLess flow from hadronic stage???


<p<pTT> centrality dependence> centrality dependence

1) , K, p mean transverse momentum <pT> increase in more central collisions;2) Heavier mass particle <pT> increase faster than lighter ones as expected from hydro type collective flow;

Star preliminary

1) , K, p mean transverse momentum <pT> increase in more central collisions;2) Heavier mass particle <pT> increase faster than lighter ones as expected from hydro type collective flow;3) -meson seems flow differently.

J. Ma (STAR)


Resonance Elliptic Flow v2

Coordinate phase space

K*

K

K*

K

X

Y

Ky

x

py

Px

22

22

xy

xy )(tan,2cos 12

x

y

p

pv

(A.M.Poskanzer and S.A.Voloshin, Phys. Rev. C 58, 1671 (1998))

Coordinate-space-anisotropy Momentum-space-anisotropy

Momentum phase space

K*K*

K

X

Y

Nuclei Non-central Collisions Hot System Elliptic Shape

• partonic flow?

• Daughters re-scattering K*0

v2 sensitive to coordinate phase space


K*0 , Elliptic Flow v2

Statistical error only

Statistical error only

STAR Preliminary

• Observed Significant K*0, Elliptic Flow v2 vs. Centrality and pT

• Need more statitics


Summary

• Resonances are Important Tools in Heavy Ion Physics– Particle Production – Matter Properties (particle properties)– Hadronic Decay Probes Freeze-out Dynamics– Flow/High pT Effect


More Conventional Approach

J. Kapusta QM02

CERES

Hadronic channels consistent??


)1385(

)1520(

)(

)(

)(

0

0

'

0

*

pK

p

KK

N

K

K

S

Hadronic Decay Mode


Statistical models

T. Ullrich QM02

Dieter Röhrich, QM02

Statistical Model: Work Reasonably wellMore Resonance Data Coming

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Resonances in Heavy Ion Collisions