Resonance Production in RHIC collisions
Christina Markert
Kent State University
•
•
•
•
Christina Markert
for the STAR Collaboration
Motivation
Resonance in hadronic phase
RAA, elliptic flow v2
Chiral symmetry restoration
(Future plans)
Summary
22nd Winter Workshop, San Diego, March 2006
1
Number of events
10
8
6
Why Resonances ?
Resonances are:
K*-(892)
• 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
 = h/t
• Can be formed in collisions between
the hadrons into which they decay.
2
4
Luis Walter Alvarez
1968 Nobel Prize for
“ resonance particles ”
discovered 1960
0
minv 
640
680
720
E1  E2 2  p1  p 2 
2
760
800
840
880
920
Invariant mass (K0+p) [MeV/c2]
STAR
K* from K-+p collision system
K  p  K* p
 K0  p
Bubble chamber, Berkeley
M. Alston (L.W. Alvarez) et al., Phys. Rev. Lett. 6 (1961) 300.
Christina Markert
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.
22nd Winter Workshop, San Diego, March 2006
2
Thermal Models Describe Hadronic Yields
hadron-chemistry: particle ratios  chemical freeze-out properties
T
Tchemical
chemical
Thermalized system of
hadrons can be described by
statistical model
(mass dependence)
Average multiplicity of hadron j (Boltzmann)
STAR white paper
Nucl Phys A757 (05) 102
~75% pions
~15% kaons
~10% baryons
Christina Markert
nj 
•
•
2 J
j
 1
2p 
3
3
 d p exp

p 2  m 2j / T )

Tch ≈ TC ≈ 165 ± 10 MeV
Chemical freeze-out ≈ hadronization.
s ~ u, d
Strangeness is chemically equilibrated.
22nd Winter Workshop, San Diego, March 2006
3

p
p
L*
re-scattering
p
L*
K
kinetic freeze-out
chemical freeze-out
Hadronic Re-scattering and Regeneration
K
K
signal measured
late decay
K
signal lost
p
K
signal measured
regeneration
time
UrQMD:
Signal loss in invariant mass reconstruction
L(1520) 
SPS (17 GeV) [1]
50%
26%
RHIC (200GeV) [2]
30%
23%
Depends on:
• hadronic phase density
• hadronic phase lifetime
Regeneration:
statistical hadronic
recombination
[1] Soff et al., J.Phys G27 (2001) 449
[2] M.Bleicher et al. J.Phys G30 (2004) 111
Christina Markert
Life-time [fm/c] :
L(1520) = 13
 (1020) = 45
22nd Winter Workshop, San Diego, March 2006
4
L(1520) Results in p+p and Pb+Pb at SPS
L(1520)/L in p+p and Pb+Pb
NA49 Experiment
preliminary
C. Markert for the NA49 collaboration, QM2001
UrQMD: rescattering of decay particle
 signal loss in invariant mass reconstruction
L(1520) = 50% ,  = 26%
 Hadronic phase after chemical freeze-out
Christina Markert
Fit to NA49 data
[Becattini et al.: hep-ph/0310049]
Thermal model does not described
L(1520)/L ratio
22nd Winter Workshop, San Diego, March 2006
5
Resonance Signals in p+p and Au+Au
collisions from STAR

p+p
p+p
Au+Au
(1385)
K(892)
Au+Au
K(892)  K+ p
D(1232) 
 (1020) 
L(1520) 
(1385) 
p+p
p+ p
K+K
p +K
L+p
D
(1020)
L(1520)
p+p
Au+Au
Christina Markert
p+p
22nd Winter Workshop, San Diego, March 2006
Au+Au
6
Interactions of Resonance in
Hadronic Nuclear Medium
Life-time [fm/c] :
K892
~ 4.0
1385 ~ 5.7
L1520 ~ 13
 1020 ~ 44
Dt
Preliminary
UrQMD Dt =10±3 fm/c
[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.
Christina Markert
K* and L* show rescattering
* shows regeneration
Regeneration/Rescattering cross section:
sKp) < s Kp < s Lp ?
L*
K*
*
22nd Winter Workshop, San Diego, March 2006
7
Temperature and “Life-time” from
K* and L* (STAR)
Life time:
K(892) = 4 fm/c
L(1520) = 13 fm/c
G. Torrieri and J. Rafelski,
Phys. Lett. B509 (2001) 239
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  Dt > 4 fm/c
K(892)
T = 160 MeV  Dt > 1.5 fm/c
L(1520)/L = 0.039  0.015 at 10% most central Au+Au
K*/K- = 0.23  0.05 at 0-10% most central Au+Au
Christina Markert
22nd Winter Workshop, San Diego, March 2006
8
Lifetime of Nuclear Medium
Tchemical
Tchemical
Dt > 4 fm/c
resonances
Lifetime from:
Balance function ?
t ~ 10 fm/c
(HBT)
Partonic phase Dt < 6 fm/c
C. Markert, G. Torrieri, J. Rafelski, hep-ph/0206260 + STAR  delta lifetime > 4fm/c
Christina Markert
22nd Winter Workshop, San Diego, March 2006
9
Signal Loss in Low pT Region
K(892)
Preliminary
Au+Au
p+p
D pT UrQMD
K892
140 MeV
1385
90 MeV
L1520
35 MeV
flow
pT
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.
Christina Markert
22nd Winter Workshop, San Diego, March 2006
10
RAA of Resonances (with rescattering)
K(892) more suppressed in AA than Ks0
Christina Markert
22nd Winter Workshop, San Diego, March 2006
K(892) are lower than Ks0 (and 
pt < 2.0 GeV factor of 2
11
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 ?
2.
* follows h+- and lower than
protons .
Christina Markert
22nd Winter Workshop, San Diego, March 2006
12
Mean pT ≠ early freeze-out ?
Resonance are regenerating close
to kinetic feeze-out
 we measure late produced (1385)
How is elliptic flow v2 effected ?
Christina Markert
22nd Winter Workshop, San Diego, March 2006
13
Elliptic flow v2
Resonances v2 and NCQ Scaling Test
C. Nonaka, et al.,
Phys.Rev.C69:
031902,2004
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 freedom
Regenerated resonances–final state interactions
NCQ = 5 (* = L +p =3+2)

Christina Markert
22nd Winter Workshop, San Diego, March 2006
14
 elliptic flow v2 in minbias Au+Au 200 GeV
dN
 1  2v2 cos[ 2(  R )]
d
 pT = 1.0-1.5 GeV
dN/d(-)
v2=12±2%
Elliptic flow
Reaction plane
 signal
2(-)
dN/d(-)
v2=16±0.04%
Inv mass (K+ K-)
Bg of  invmass
2(
-)
Kaon p < 0.6 GeV
Christina Markert
22nd Winter Workshop, San Diego, March 2006
Inv mass (K+ K-)
15
v2 of phi resonance in Au+Au 200GeV
STAR Preliminary
 has long lifetime 45fm/c  less rescattering or regeneration
Elliptic flow of Φ-meson is close to Ks
Christina Markert
22nd Winter Workshop, San Diego, March 2006
Delta resonance ?
16
Resonance Response to Medium
Temperature
partons
Shuryak QM04
(e.g. Glueballs) Shuryak hep-ph/0405066
Quark Gluon Plasma
( perfect liquid)

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
Tc
T Freeze
hadrons
Resonances below and above Tc:
 Gluonic bound states
 Chiral symmetry restoration
Mass and width of resonances
( e.g.  leptonic vs hadronic decay,
chiral partners r and a1)
Hadron Gas
 Hadronic time evolution
Baryochemical potential (Pressure)
Christina Markert
From hadronization (chemical
freeze-out) to kinetic freeze-out.
22nd Winter Workshop, San Diego, March 2006
17
Chiral Symmetry Restoration
Vacuum
TOF cut |1/b-1| < 0.03
At Tc: Chiral Restoration
STAR Experiment
Data:
ALEPH Collaboration
STAR:
R. Barate
et al.
Eur. Phys.
J. C4 409 with
(1998)
electron
hadron
separation
Time of
Flight upgrade
Hendrik
van Hees (talk)
Measure chiral partners
Near critical temperature Tc
(e.g. r and a1) a1 p + g
Christina Markert
22nd Winter Workshop, San Diego, March 2006
Ralf Rapp (Texas A&M)
J.Phys. G31 (2005) S217-S230
18
Resonances from Jets to Probe Chirality
T=170 MeV, bT=0

L*
jets ?
near
Leading
hadrons
away
Medium
Bourquin and Gaillard
Nucl. Phys. B114 (1976)
Christina Markert
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)
22nd Winter Workshop, San Diego, March 2006
19
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.
Christina Markert
22nd Winter Workshop, San Diego, March 2006
20