Christina MarkertHirschegg, Jan 16-22, 2005

1
Resonance Production in Heavy Ion Collisions
Christina Markert, Kent State University
Resonances in Medium Rescattering and
Regeneration Time Scale Phi Puzzle
at SPS Conclusions
2
Resonances in Medium
Life-time fm/c ? 1.7
K(892) 4 S(1385) 5.7 L(1520)
13 ? (1020) 44
Hadronization Hadrons are formed from
quarks Chemical freeze-out T170MeV end of
inelastic interactions particle yields Kinetic
freeze-out T100MeV end of elastic
interactions particle spectra
3
Rescattering and Regeneration
Life-time fm/c r 1.3 ?
1.7 K(892) 4.0 S(1385)
5.7 L(1520) 13 ? (1020) 45

• Proposed measurements
• Collision systems
• pp and AA collisions
• Leptonic and hadronic channels
• e.g. f,( r) ? ee- , mm- , KK-

4
Resonance Reconstruction in STAR TPC
Energy loss in TPC dE/dx
End view STAR TPC
p
dE/dx
K
?
e
momentum GeV/c

• Identify decay candidates
• (p, dedx, E)
• Calculate invariant mass

K(892) ? ? K ? (1020) ? K K ?(1520) ?
p K S(1385) ? L p X(1530) ? X p
5
Invariant Mass Reconstruction in pp
Invariant mass
?(1520)
original invariant mass histogram from
K- and p combinations in same event.
normalized mixed event histogram from K-
and p combinations from different events.
(rotating and like-sign background) Extractin
g signal After Subtraction of mixed event
background from original event and fitting signal
(Breit-Wigner).
STAR Preliminary
?(1520)
6
Resonance Signal in pp collisions
STAR Preliminary
STAR Preliminary
pp
K(892)
F?KK-
Statistical error only
STAR Preliminary
?
?(1385)
7
Resonance Signal in AuAu collisions
X?X
K(892)
S(1385)
S ?S
?(1520)
?(1020)
STAR Preliminary
STAR Preliminary
8
Resonance momentum Spectra
K(892)
S(1385) and L(1520)
Integrated momentum distribution ? yields
9
Rescattering and Regeneration
Life-time fm/c ? 1.7
K(892) 4 S(1385) 5.7 L(1520)
13 ? (1020) 45
K and L show rescattering D and S show
regeneration Regeneration cross section s(kp) lt
s (kp) lt s (pp), s (Lp) ? L
K D S
P. Braun-Munzinger et.al., PLB 518(2001) 41
Marcus Bleicher and Jörg Aichelin Phys. Lett.
B530 (2002) 81. M. Bleicher and Horst Stöcker
J. Phys.G30 (2004) 111.
10
Particle spectra from Thermal Model
W. Florkowski, SQM2004
T 165.7 MeV
µB 27.9 MeV
Signal loss for K in low momentum region due to
rescattering Regeneration also in low momentum
region (D,r)
11
pT changes due to rescattering (UrQMD)
Marcus Bleicher and Jörg Aichelin Phys. Lett.
B530 (2002) 81-87. M. Bleicher and Horst Stöcker
.Phys.G30 (2004) 111.
L(1520)
K(892)
MeV T all T obs ?pT? all ?pT ?obs D ?pT?
r(770) 125 190 490 640 150
D(1232) 250 230 665 765 100
K(892) 160 230 550 690 140
S(1385) 200 240 730 820 90
L(1520) 230 250 845 870 35
f(1020) 175 190 610 645 35
12
Signal Loss in low pT Region
?pT? UrQMD
D(1232) 100 MeV
K(892) 140 MeV
f(1020) 35 MeV
Inverse slope increase from pp to AuAu
collisions. UrQMD predicts signal loss at low pT
due to rescattering of decay daughters. ?
Inverse slopes and mean pT are higher. UrQMD has
long lifetime (Dt 5-20fm/c)
13
Temperature and Life-time fromK and L (STAR)

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)
• results between
• T 160 MeV gt ?? gt 4 fm/c
• (lower limit !!!)
• ?? 0 fm/c gt T 110-130 MeV

?(1520)/? 0.034 ? 0.011 ? 0.013
Does not work for S, D, f (STAR)
K/K- 0.20 ? 0.03 at 0-10 most central AuAu
14
Temperature, Life-time from Particle Spectra
p,K and p
Tch freeze-out
Tch from Thermal model, Tkin and b from
Blast-Wave-Fit to p, K and p
Tkin freeze-out
Life-time nearly constant in peripheral and
central AuAu collisions
Go to smaller systems volume ? Life-time dAu ,
SiSi , CuCu
15
f Meson puzzle at SPS
CERES f ? KK-, ee- A. Marin SQM2004
Hadronic channel less signal in low pt lower
yield (factor 2-4)
Carlos Lourenço
Yield?
16
Hadronic Phase after Chemical Freeze-out
signal loss in low momentum region ? Increase of
inverse slope

• Signal loss in UrQMD 26
• Data yield factor of 2-4 difference
• for hadronic to leptonic channel.
• Additional in medium modification
• of resonance at early stage ?

• Theory can describes data
• K. Haglin et. al, E. Kolomeitsev et.al
• f shorter lifetime in medium
• decay rate increased with in-medium kaons
• ? f? mm- from early decay
• ? f? KK- from late decay

UrQMD Marcus Bleicher and Jörg Aichelin Phys.
Lett. B530 (2002) 81. M. Bleicher and Horst
Stöcker .Phys.G30 (2004) 111.
17
Time from Hadronic and Leptonic Channel
UrQMD

• all decay
• - measured

ll-
pp-
Leptonic signal ? signal from early
decay Hadronic signal ? signal from late decay
18
Delta Resonance in dense Matter
STAR preliminary 30-50 AuAu
?
PDG
Minv pp GeV/c2

• nucleon propagation in medium
• fireball conditions (T, r )
• (1232) from Tkin100 MeV
• (1232)? width increase

Hendrik von Hees HotQuarks2004 (Hees and Rapp
nucl-th/0407050) Medium Modifications of the
Delta Resonance at RHIC
19
Feed down from Resonances

• Thermal modelSTAR data
• Tch160 MeV
• 32 primary Lambdas
• 26 primary Protons

• Large fraction of stable particles
• come from resonance decays.
• Rescattering and regeneration
• Less primary particles
• Momentum distribution changes

Regeneration increases the number of primary
particles that get used by a resonance
20
Resonances from Jets in pp ?
Thermal ltpTgt prediction for T 170 MeV, b0
High mass particles from more jet like events
21
Resonances in Medium (Jets vs Bulk Matter)

• Resonances as
• Particle in jet
• Bulk particle
• same side/away side

Snap shot from early stage of collision
Resonance in jet
Resonance from bulk
High luminosity, large acceptance, particle id up
to 30 GeV. R2D detector for RHIC II Talk by
Rene Bellwied
22
Conclusions

• Strong interacting hadronic medium after
• chemical freeze-out.
• ? Thermal models do not describe all resonance
  yields.
• ? Rescattering and regeneration of resonances.
• ? Regeneration probes hadronic cross sections
  of heavy baryons.
• ? Life-time between freeze-outs gt 4 fm/c
• Medium modification of resonances.
• ? f yield in leptonic and hadronic channel at
  SPS
• give indication of width broadening of phi
  in medium.
• ? Width broadening of D observed at RHIC
  energies in
• AuAu collisions ? medium modification.
• Large fraction of particles coming from
• resonance decays
• ?Could affect kinematics of primordial
  particles.