Motivation

1
Resonance Production in Heavy Ion Collisions
Christina Markert, Yale University

• Motivation
• Reconstruction
• Resonances in pp and AA
• STAR RHIC (and NA49 SPS)
• Results and Theory
• SummaryFuture

NATO ADVANCED STUDY INSTITUTE Structure and
Dynamics of Elementary Matter, 26 September,
Kemer, Turkey
2
Resonances

• Resonant state of ground state particles
• ? higher mass
• Same quark content
• Short lifetime in the order few fm/c (order of
  fireball)
• Decay strongly

? (uds)
?(1520) (uds) Spin Parity 1/2
3/2 Mass m
1115.7 MeV/c2 1519.5 MeV/c2 Width ?
lt 1 MeV/c2 15.6
MeV/c2 Lifetime ? 7.9 cm/c
12.8 fm/c
weak decay strong decay
Resonace K(892) ?(1385)
?(1520) ?(1530) Decay
channel K ? ? ?
p K ? ?
Branching Ratio 100.0
88.2 22.5
100.0 Width MeV 50.8
35.8 15.6
9.9 Life time fm/c
3.9 5.6 13
20
Sevil Salur Poster on ?(1385) Resonance Studies
in STAR
3
Resonances in Medium

• Short life time fm/c
• ? lt ? lt K lt ? lt ? lt ? lt ?
• 1.3lt1.7lt 4 lt 6 lt 13 lt 20 lt 40

Mass shift and width broadening ?

• Strangeness enhancement ?
• Temperature at chemical freeze-out ? ? Yield
  (Thermal models)
• Time between chemical and kinetic freeze-out ?
• Rescattering and regeneration of resonance
  decay particles
• ? Yield and pt spectra (Microscopic models
  UrQMD)

Comparison of pp and AA Collisions show effects
of interactions in an expanded reaction volume.
4
Rescattering and Regeneration of Decay Products
Rescattering
Detector
Regeneration
time
chemical freeze out end of inelastic
interactions T170 MeV particle multiplicities
thermal freeze out end of elastic
interactions T110MeV particle spectra, HBT
Between chemical and kinetic freeze-out
Rescattering gt Regeneration ? Resonance signal
loss
5
Rescattering and Regeneration of Decay Products
Predictions with a microscopic model
By Marcus Bleicher, Jorg Aichelin (SUBATECH,
Nantes). Jan 2002. hep-ph/0201123, private
communication
6
Resonance reconstruction in STAR TPC
?(1520)
?(1385)
End view
Front view
K(892) ? ?- K, ? K- ?(1520) ? p K- ,
p K
_
Sevil Salur Poster
7
Track Selection and Invariant Mass Reconstruction
Energy loss in TPC dE/dx
p
dE/dx
K
?
pp events
momentum p GeV/c
Invariant mass
8
Strange Resonances in pp at 200 GeV
K(892)
?(1520)
mass 1.516 ? 0.001 GeV width 18 MeV fixed
?
?(1385)
?(1530)
9
Pt Spectra in pp at 200 GeV
?(1520)
K(892)
preliminary
preliminary
T 210 ? 8 MeV
T 326 ? 42 MeV ltptgt 0.92 ?0.03 MeV
10
Mean pt in pp at 200 GeV
?(1520)
?(1385) ? ?(1530) ?
?
?
?
Helen SQM2003
ltptgt for high mass resonances in pp higher than
particles with same mass ?
11
Strange Resonance Production in AuAu Collisions
?(1520)
K(892)
?
?(1385)
No mass shift or width broadening visible in
integrated invariant mass spectra
12
L(1520) Production in pp and AuAu (I)
preliminary
Tch 175 MeV
Tch 120 MeV
Thermal description Late chemical freeze-out
close to kinetic freeze-out ? Temperature Tch
120 MeV ?
AuAu ?(1520)/? 0.034 ? 0.011 ? 0.013
Decrease from pp to AA at 200GeV 70 45
13
L(1520) Production in pp and AuAu (II)
preliminary
Microskopic model Time span between chemical
and kinetical freeze-out ?? 5-10 fm/c.
UrQMD Microscopic model
Decrease from pp to AA at 200GeV 70 45
14
K(892) Production in pp and AuAu
Thermal fit Tch 175 MeV K(892)/K ? 0.4
preliminary
K(892)/K 0.2 ? Tch ? 120MeV ?
K/K 0.19 ? 0.05 at 0-20 most central AuAu
P.Fachini QM2002
K(892)/K drop by a factor of 2 ? rescattering of
decay products ?
15
K(892) slopes in AuAu 200 GeV
K(892)
K-
Flow in AA
Inverse slopes are increasing in AA collisions.
UrQMD predicts more signal loss at low pt due to
more rescattering than regeneration ? Inverse
slopes are higher.
16
Temperature and life time from?(1520) /? and K/K
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
• Lifetime between chemical and
• thermal freeze out
• By comparing two particle ratios
• (no regeneration in this model)
• results between
• T 175 MeV gt ?? 4 - 6 fm/c
• ?? 0 fm/c gt T 110-130 MeV

preliminary
More resonances are needed to put additional
stringent conditions on T and ?? to verify this
model
?(1520)/? 0.034 ? 0.011 ? 0.013
K/K 0.19 ? 0.05 at 0-20 most central AuAu
17
?(1385) from Model predictions
G. Torrieri and J. Rafelski, Phys. Lett. B509
(2001) 239
At T160 MeV 50 of ?s are from ?(1385)
18
?(1520) Production in pp and AA at different
Energies
NA49 at SPS 17 GeV
STAR at RHIC 200 GeV
preliminary
preliminary
Thermal model Tch 175 MeV
V. Friese Nucl. Phys. A698 (2002) 487-49

19
First look at dAu Data in STAR
?(1385)
?(1530)
?(1520)
20
Summary Future

• Resonances are measured K(892), ?(1385), ?(1520)
  and ?(1530)
• High mean pt in pp for ? and ?(1520) .
• Strange resonance/non resonance ratio shows
  decrease in AuAu collisions
• compared to pp collisions. (also seen at SPS
  energies)
• ? Tch 120 MeV (thermal model) . or
• ? Time between chem. and kin. freeze-out ?
  5-10 fm/c (microscopic model).
• Including rescattering and regeneration after
  chemical freeze-out
• consistent with K slope increase from pp to
  AuAu (200 GeV).
• Time between chemical and thermal freeze out
  with Rafelskis model is
• 4-6 fm/c if there is only rescattering.
  (Regeneration makes it larger).
• Future
• More results from ?(1385) and ?(1530) and from
  dAu data are coming.
• Factor of 20 higher statistics from upcoming
  AuAu run.
• New detectors in STAR (TOF better PID) are
  coming.
• We need more theoretical calculations (thermal
  model UrQMD)