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Christina Markert 22nd Winter Workshop, San Diego, March 2006 1

Christina Markert Kent State University

Resonance Production in RHIC collisions

• Motivation• Resonance in hadronic phase RAA, elliptic flow v2• Chiral symmetry restoration (Future plans)• Summary

for the STAR Collaboration


Why Resonances ?

2212

21 ppEEminv

Bubble chamber, BerkeleyM. Alston (L.W. Alvarez) et al., Phys. Rev. Lett. 6 (1961) 300.

Invariant mass (K0+) [MeV/c2]

K*-(892)

640 680 720 760 800 840 880 920

Num

ber o

f eve

nts

0

2

4

6

8

10

Luis Walter Alvarez 1968 Nobel Prize for

“ resonance particles ” discovered 1960

K* from K-+p collision system Kp p

K

Resonances are: • Excited state of a ground state hadron.• With higher mass but same quark content.• Decay strongly short life time (~10-23 seconds = few fm/c ), width = reflects lifetime • Can be formed in collisions between the hadrons into which they decay.

Why Resonances?:• Short lifetime decay in medium • Surrounding nuclear medium may change resonance properties• Chiral symmetry restoration: Dropping mass -> width, branching ratio

RHIC: No strong indication of medium modification (mass, width)But: Indication of extended lifetime of hadronic medium.

= h/t

STAR


Thermal Models Describe Hadronic Yieldshadron-chemistry: particle ratios chemical freeze-out properties

• Tch ≈ TC ≈ 165 ± 10 MeVChemical freeze-out ≈ hadronization.

• s ~ u, d Strangeness is chemically equilibrated.

Thermalized system of hadrons can be described by

statistical model(mass dependence)

~75% pions~15% kaons~10% baryons

STAR white paperNucl Phys A757 (05) 102

Average multiplicity of hadron j (Boltzmann)

)/exp2

12 223

3 TmppdJ

n jj

j

TchemicalTchemical


Hadronic Re-scattering and Regeneration

Life-time [fm/c] :(1520) = 13 (1020) = 45

time

chem

ical

free

ze-

out

p

pp

signal lost

kine

tic fr

eeze

-out

signal measured late decay

signal measured

re-scattering

regeneration

[1] Soff et al., J.Phys G27 (2001) 449[2] M.Bleicher et al. J.Phys G30 (2004) 111

Depends on:• hadronic phase density • hadronic phase lifetime Regeneration: statistical hadronic recombination

UrQMD:Signal loss in invariant mass reconstruction (1520) SPS (17 GeV) [1] 50% 26%RHIC (200GeV) [2] 30% 23%


(1520) Results in p+p and Pb+Pb at SPS (1520)/ in p+p and Pb+Pb

C. Markert for the NA49 collaboration, QM2001

NA49 Experiment

Fit to NA49 data[Becattini et al.: hep-ph/0310049hep-ph/0310049]Thermal model does not described

(1520)/ ratio

UrQMD: rescattering of decay particle

signal loss in invariant mass reconstruction

(1520) = 50% , = 26%

Hadronic phase after chemical freeze-out

preliminary


Resonance Signals in p+p and Au+Au collisions from STAR

K(892)

(1520)

p+p

p+p

Au+Au

Au+Au (1385)

p+pAu+Au

(1020) p+p

Au+Au

p+p

K(892) K+

(1232) p+ (1020) K + K(1520) p + K(1385) +


* and* show rescattering * shows regenerationRegeneration/Rescattering cross section:p)

Interactions of Resonance in Hadronic Nuclear Medium

[1] P. Braun-Munzinger et.al.,PLB 518(2001) 41, priv. communication[2] Marcus Bleicher and Jörg Aichelin Phys. Lett. B530 (2002) 81. M. Bleicher and Horst Stöcker J. Phys.G30 (2004) 111.

Life-time [fm/c] :

Preliminary

UrQMD =10±3 fm/c


Temperature and “Life-time” fromK* and * (STAR)

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

Lambda1520 T= 160 MeV > 4 fm/c K(892) T = 160 MeV > 1.5 fm/c

(1520)/ = 0.039 0.015 at 10% most central Au+Au

K*/K- = 0.23 0.05 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


Lifetime of Nuclear Medium

TchemicalTchemical

t > 4 fm/cresonances

t ~ 10 fm/c(HBT)

Partonic phase < 6 fm/c

C. Markert, G. Torrieri, J. Rafelski, hep-ph/0206260 + STAR delta lifetime > 4fm/c

Lifetime from:Balance function ?


Signal Loss in Low pT Region

Inverse slope increase from p+p to Au+Au collisions. UrQMD predicts signal loss at low pT due to rescattering of decay daughters. Inverse slopes T and mean pT are higher.Flow would increase pT of higher masse particles stronger.

pT UrQMD 140 MeV 90 MeV 35 MeV

p+p

Au+Au

K(892)

flowpT

Preliminary


RAA of Resonances (with rescattering)

K(892) are lower than Ks0 (and

pt < 2.0 GeV factor of 2K(892) more suppressed in AA than Ks0


Nuclear Modification Factor RdAu

1. K* is lower than Kaons in low pt d+Au no medium no rescattering why K* suppression in d+Au ?

* follows h+- and lower than protons .


Mean pT ≠ early freeze-out ?

Resonance are regenerating close to kinetic feeze-out we measure late produced (1385)How is elliptic flow v2 effected ?


Resonances v2 and NCQ Scaling TestEl

lipti

c flo

w v

2

pT (GeV) Fluid dynamics calculations (zero viscosity) describe data pT < 2 GeV Do Resonances show same mass splitting ? Number of Constituent Quark (NCQ) scaling at intermediate pT (2= mesons, 3= baryons) indication of partonic degrees of freedomRegenerated resonances–final state interactions NCQ = 5 (* = + =3+2)

C. Nonaka, et al.,Phys.Rev.C69:031902,2004


elliptic flow v2 in minbias Au+Au 200 GeV

2(-)

2( -)

dN

/d(

-)

dN/

d(-

)

signal

Bg of invmass

v2=12±2%

v2=16±0.04%

pT = 1.0-1.5 GeV

Inv mass (K+ K-)

Inv mass (K+ K-)

Elliptic flow

)](2cos[21 2 RvddN

Reaction plane

Kaon p < 0.6 GeV


v2 of phi resonance in Au+Au 200GeV

has long lifetime 45fm/c less rescattering or regenerationElliptic flow of Φ-meson is close to Ks Delta resonance ?

STAR PreliminarySTAR Preliminary


Resonance Response to Medium

Tc

par

tons

ha

dron

s

Baryochemical potential (Pressure)

Temperature

Quark Gluon Plasma ( perfect liquid)

Hadron Gas

T Freeze

Shuryak QM04Resonances below and above Tc: Gluonic bound states (e.g. Glueballs) Shuryak hep-ph/0405066 Survival of mesonic heavy quark

resonances Rapp et al., hep-ph/0505080 Initial deconfinement conditions:

Determine T initial through J/ and state (+resonance states)

dissociation Chiral symmetry restoration Mass and width of resonances ( e.g. leptonic vs hadronic decay, chiral partners and a1) Hadronic time evolution From hadronization (chemical freeze-out) to kinetic freeze-out.


Chiral Symmetry Restoration

Ralf Rapp (Texas A&M) J.Phys. G31 (2005) S217-S230

Vacuum At Tc: Chiral Restoration

Hendrik van Hees (talk)Measure chiral partnersNear critical temperature Tc (e.g. and a1)

Data: ALEPH Collaboration R. Barate et al. Eur. Phys. J. C4 409 (1998)

a1 +

TOF cut |1/-1| < 0.03

STAR: electron hadron separation with Time of Flight upgrade

STAR Experiment


Resonances from Jets to Probe Chirality

Bourquin and GaillardNucl. Phys. B114 (1976)

T=170 MeV, T=0 Leadinghadrons

Mediumaway

near

• In p+p collisions resonances are predominantly formed as “leading particles” in jets. • Comparison of mass, width and yield of resonances from jets (no medium) with resonances from bulk (medium)

jets ?


Summary

• Hadronic resonances help to separate hadronic from partonic lifetime

• Ranking of rescattering over regeneration cross section in medium.

•Low pt RAA behavior confirms rescattering hypothesis. (RdAu puzzle?)

• v2 of long lived resonances seems to follow stable particle trends (confirmation of NCQ scaling)

• Exciting future program: resonance in jets.