Resonance Production in RHIC collisions

Christina Markert

Kent State University

Motivation Resonance in hadronic phase

RAA, elliptic flow v2

Chiral symmetry restoration

(Future plans)

Summary

for the STAR Collaboration

I am going to talk about resonance production in heavy ion collisions. Let me stat with a motivation which addresses the measurements done by SPS and RHIC experiments.

The deconfinement conditions, chiral symmetry restoration and the time evolution of the hadronic phase.

At the end I would like to conclude with an brief outlook for the future measurements.

Why Resonances ?

Bubble chamber, Berkeley

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

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.

Invariant mass (K0+p-) [MeV/c2]

K*-(892)

640 680 720 760 800 840 880 920

Number of events

0 2 4 6 8 10

Luis Walter Alvarez

1968 Nobel Prize for

resonance particles

discovered 1960

K- + p K*-+ p

K0 + p-

K* from K-+p collision system

= h/t

STAR

Let me at first explain what a resonance is.

It is an exited state of a ground state particle with higher mass but same quark content.

It decays strongly with in a short lifetime on the order of a few fm/c which results in a width a natural spread of energy which can be described by at breit-wigner shape.

This resonances can be formed by their decay particles due to their finite width and lifetime.

The first resonance was discovered by Alvarez in 1968 by reconstructing the K*- from a K0 and a negative pion.

The surrounding hot and dense medium change due to Chiral symmetry breaking

Way do we measure resonances in relativistic heavy ion collisions?

The resonance lifetime is on the order of the lifetime of a heavy ion reaction.

The surrounding hot and dense medium change due to Chiral symmetry restoration

the resonance properties.

We expect at higher temperature a dropping of the mass which would result in a with broadening

and branching ratio changing

Thermal Models Describe Hadronic Yields

hadron-chemistry: particle ratios chemical freeze-out properties

Thermalized system of

hadrons can be described by

statistical model

(mass dependence)

~75% pions

~15% kaons

~10% baryons

STAR white paper

Nucl Phys A757 (05) 102

Average multiplicity of hadron j (Boltzmann)

Tch TC 165 10 MeVChemical freeze-out hadronization.s ~ u, d Strangeness is chemically equilibrated.

Tchemical

Tchemical

--- thermalization !!!!! Surprisingly good, except for resonances

Hadronic Re-scattering and Regeneration

Life-time [fm/c] :

L(1520) = 13

(1020) = 45

[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

L(1520) f

SPS (17 GeV) [1] 50% 26%

RHIC (200GeV) [2] 30% 23%

time

chemical freeze-out

f

L*

p

p

K

K

K

L*

K

K

p

p

signal lost

kinetic freeze-out

signal measured

late decay

signal measured

re-scattering

regeneration

(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/0310049]

Thermal model does not described

L(1520)/L ratio

UrQMD: rescattering of decay particle

signal loss in invariant mass reconstruction

(1520) = 50% , = 26%

Hadronic phase after chemical freeze-out

preliminary

I come back to the thermal model using the RHIC data

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

K(892)

(1520)

p+p

p+p

Au+Au

Au+Au

(1385)

p+p

Au+Au

(1020)

p+p

Au+Au

p+p

D++

K(892) K+

D(1232) p+

(1020) K + K

(1520) p + K

S(1385) L + p

Interactions of Resonance in Hadronic Nuclear Medium

K* and L* show rescattering

S* shows regeneration

Regeneration/Rescattering cross section:

s(K+p) < s (K+p) < s (L+p) ?

L* K* S*

[1] P. Braun-Munzinger et.al.,PLB 518(2001) 41,

priv. communication

[2] Marcus Bleicher and Jrg Aichelin

Phys. Lett. B530 (2002) 81.

M. Bleicher and Horst Stcker

J. Phys.G30 (2004) 111.

Life-time [fm/c] :

K(892) ~ 4.0

S(1385) ~ 5.7

L(1520) ~ 13

(1020) ~ 44

Preliminary

UrQMD Dt =103 fm/c

Dt

Temperature and Life-time fromK* and L* (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

L(1520) = 13 fm/c

Lifetime of Nuclear Medium

Dt > 4 fm/c

resonances

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 ?

Tchemical

Tchemical

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.

K(892)

flow

pT

D pT UrQMDK(892)140 MeVS(1385)90 MeVL(1520)35 MeV

p+p

Au+Au

Preliminary

RAA of Resonances (with rescattering)

K(892) are lower than Ks0 (and f)

pt < 2.0 GeV factor of 2

K(892) more suppressed in AA than Ks0

Nuclear Modification Factor RdAu

K* is lower than Kaons in low pt d+Au no medium no rescattering why K* suppression in d+Au ?S* follows h+- and lower than protons .

Mean pT early freeze-out ?

Resonance are regenerating close

to kinetic feeze-out

we measure late produced S(1385)

How is elliptic flow v2 effected ?

Resonances v2 and NCQ Scaling Test

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 freedom

Regenerated resonancesfinal state interactions

NCQ = 5 (S* = L +p =3+2)

C. Nonaka, et al.,

Phys.Rev.C69:

031902,2004

Elliptic flow v2

pT (GeV)

If the resonance in medium is mass modified, then collective medium properties such as the anisotropic flow v2 should be modified

As well for this resonance.

Here I show the mass dependency of v2 measured by phenix and sta.

Cleary a mass modified resonance would resonance would exhibits a different pt dependency as the unmodified resonance.

Detailed measurements of v2 of resonances would be one of our future priorities.

f elliptic flow v2 in minbias Au+Au 200 GeV

2(f-)

2( f-)

dN/d(f-)

dN/d(f-)

f signal

Bg of f invmass

v2=122%

v2=160.04%

f pT = 1.0-1.5 GeV

Inv mass (K+ K-)

Inv mass (K+ K-)

Kaon p < 0.6 GeV

Elliptic flow

Reaction plane

v2 of phi resonance in Au+Au 200GeV

f has long lifetime 45fm/c less rescattering or regeneration

Elliptic flow of -meson is close to Ks Delta resonance ?

STAR Preliminary

Resonance Response to Medium

Resonances 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/0505080Initial deconfinement conditions: Determine T initial through

J/Y and state (+resonance states) dissociation

Chiral symmetry restoration

Mass and width of resonances

( e.g. f leptonic vs hadronic decay,

chiral partners r and a1)

Hadronic time evolution

From hadronization (chemical

freeze-out) to kinetic freeze-out.

Tc

partons

hadrons

Baryochemical potential (Pressure)

Temperature

Quark Gluon Plasma

( perfect liquid)

Hadron Gas

T Freeze

Shuryak QM04

If you remember the phase diagram that I show you earlier in my talk. You see here extension of the diagram proposed by Shuryak 2 years ago.

The perfect liquid of the phase can be explained by the existents of partonic bound states above the critical temperature.

This states depending on their partonic structure and will dissociate at different temperature.

This states will therefore behave like heavy resonances above Tc.

So in addition to our studies of deconfinement and chiral symmetry restoration we will also look for exotic bound states using resonance methods.

We already obtained some data on this issue of J/si suppression.

So let me show you those and then elaborate a little more on the Chirality measurements at RHIC.

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 partners

Near critical temperature Tc

(e.g. r and a1)

Data: ALEPH Collaboration

R. Barate et al. Eur. Phys. J. C4 409 (1998)

a1 p + g

TOF cut |1/b-1| < 0.03

STAR:

electron hadron separation with Time of Flight upgrade

STAR Experiment

Until now the RHIC data do not show much evidence for chiral symmetry restoration due to low statistics in the leptonic decay of phi and rho.

An alternative idea was purposed by Rapp recently namely to measure chiral partners partner properties near the critical temperature.

The prime pair to study are the rho and a1. The a1 is difficult to measure because of its large width with very distinct decay channel.

The Detector has to have a good photon reconstruction capability which STAR has.

If the chiral symmetry is restored at Tc we would expect for the chiral partners which have the same quark content but different masses in vacuum, the same mass and width in medium.

Here are the two scenarios of a spectral function of the rho and a1 in medium.

Resonances from Jets to Probe Chirality

Bourquin and Gaillard

Nucl. Phys. B114 (1976)

L*

L*

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 ?

T=170 MeV, bT=0

Leading

hadrons

Medium

away

near

Heavy ion collision allows us to measure modified and unmodified resonances in the same event by triggering on leading resonances in a jet decay.

We can distinguish between unmodified resonances form jets and potentially modified resonances in the medium.

The left hand figure shows mean pt of pp collisions which show that resonances are predominantly produced in 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.

The main emphasis of research in the near future will be to study the hins of medium modification we found at SPS with the RHIC data.

Let me give you a little more detail.

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