Resonance Production in RHIC collisions

1
Resonance Production in RHIC collisions
Christina Markert Kent State University
for the STAR Collaboration

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

2
Why Resonances ?

• 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.

Bubble chamber, Berkeley M. Alston (L.W.
Alvarez) et al., Phys. Rev. Lett. 6 (1961) 300.
3
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)
Average multiplicity of hadron j (Boltzmann)
STAR white paper Nucl Phys A757 (05) 102
75 pions 15 kaons 10 baryons
4
Hadronic Re-scattering and Regeneration
Life-time fm/c L(1520) 13 ? (1020)
45

• 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
1 Soff et al., J.Phys G27 (2001) 449 2
M.Bleicher et al. J.Phys G30 (2004) 111
5
?(1520) Results in pp and PbPb at SPS
?(1520)/? in pp and PbPb
NA49 Experiment
preliminary
C. Markert for the NA49 collaboration, QM2001
UrQMD rescattering of decay particle ? signal
loss in invariant mass reconstruction
?(1520) 50 , ? 26 ? Hadronic phase after
chemical freeze-out
Fit to NA49 data Becattini et al.
hep-ph/0310049 Thermal model does not described
L(1520)/L ratio
6
Resonance Signals in pp and AuAu collisions
from STAR
pp
?
pp
AuAu
K(892)
?(1385)
AuAu
K(892) ? K ? D(1232) ? p ? ? (1020) ?
K K ?(1520) ? p K S(1385) ? L p
D
pp
?(1020)
pp
?(1520)
pp
AuAu
AuAu
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Interactions of Resonance in Hadronic Nuclear
Medium
Life-time fm/c K(892) 4.0 S(1385)
5.7 L(1520) 13 ? (1020)
44
Dt
Preliminary
UrQMD Dt 103 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.
K and L show rescattering S shows
regeneration Regeneration/Rescattering cross
section s(Kp) K S
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Temperature and Life-time fromK 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 ? ?? 4 fm/c
• K(892)
• T 160 MeV ? ?? 1.5 fm/c

?(1520)/? 0.039 ? 0.015 at 10 most central
AuAu
K/K- 0.23 ? 0.05 at 0-10 most central AuAu
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Lifetime of Nuclear Medium
Dt 4 fm/c resonances
Lifetime from Balance function ?
t 10 fm/c (HBT)
Partonic phase ?? C. Markert, G. Torrieri, J. Rafelski,
hep-ph/0206260 STAR ? delta lifetime 4fm/c
10
Signal Loss in Low pT Region
K(892)
flow ?pT?
Inverse slope increase from pp to AuAu
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.
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RAA of Resonances (with rescattering)
K(892) are lower than Ks0 (and f) pt factor of 2
K(892) more suppressed in AA than Ks0
12
Nuclear Modification Factor RdAu

• K is lower than Kaons in low pt dAu no medium
  ? no rescattering why K suppression in dAu ?
• S follows h- and lower than protons .

13
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 ?
14
Resonances v2 and NCQ Scaling Test
C. Nonaka, et al., Phys.Rev.C69 031902,2004

• Fluid dynamics calculations (zero viscosity)
• describe data pT
• 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 32)

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f elliptic flow v2 in minbias AuAu 200 GeV
f pT 1.0-1.5 GeV
v2122
dN/d(f-?)
f signal
2(f-?)
Inv mass (K K-)
v2160.04
dN/d(f-?)
Bg of f invmass
2( f-?)
Inv mass (K K-)
Kaon p 16
v2 of phi resonance in AuAu 200GeV
STAR Preliminary
f has long lifetime 45fm/c ? less rescattering or
regeneration Elliptic flow of F-meson is close to
Ks Delta resonance ?
17
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/0505080
• Initial 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.

18
Chiral Symmetry Restoration
Vacuum
At Tc Chiral Restoration
Data ALEPH Collaboration R. Barate et al. Eur.
Phys. J. C4 409 (1998)
Hendrik van Hees (talk) Measure chiral
partners Near critical temperature Tc (e.g. r
and a1)
a1 ?p g
Ralf Rapp (Texas AM) J.Phys. G31 (2005)
S217-S230
19
Resonances from Jets to Probe Chirality
L
jets ?
?
L
Bourquin and Gaillard Nucl. Phys. B114 (1976)

• In pp 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)

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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.