*(1520) and *(1385) resonance production in Au+Au and p+p collisions at RHIC energy
(200 GeV)
Motivation and models
Data analysis
p+p and Au+Au results
Summary
Ludovic Gaudichet SUBATECH, NantesFor the STAR collaboration
Strange Quark Matter 2003
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Resonance production in heavy ion collisions
thadronizationbegins
Chemicalfreeze-out
Thermalfreeze-out
Resonance decay inside the hot and dense mediumMass shift, width broadening, …
Daughter rescattering inside the mediumSpectra modification, signal loss, …
1.3 fm/c
K* 4 fm/c
(1385) 5 fm/c
(1520) 13 fm/c 40 fm/c
Medium effects on resonance and their decay products
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Strange hadron resonances and freeze-out within a statistical model
Including the signal suppression due to freeze-out conditions :
Association of at least two resonances could allow the calculation of chemical freeze-out temperature and the interacting phase lifetime between chemical and thermal freeze-out.
Giorgio Torrieri and Johann RafelskiPhys.Lett.B509:239-245, 2001
The model should take into account resonance regeneration.
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Probing Freeze-out via UrQMD
Rescattering probabilities of the resonance decay products are studied.
The microscopic study show also a chemical freeze-out followed by a thermal freeze-out. The dynamics is described in term of inelastic and (pseudo)elastic collision rates.
UrQMD predicts a relative supression of reconstructable resonances compared to thermal estimation, and a modification of their spectra.
Marcus Bleicher and Jörg AichelinPhys.Lett.B530:81-87, 2002Marcus Bleicher, private communication
Au+Au at 200 GeV
Au+Au at 200 GeV
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*(1520) and *(1385) reconstruction in STAR
(1385)
-
-
p
*(1385) + -*(1385) + +
*(1520) p+K-
Invariant mass reconstruction
*(1520) original mass distribution in p+p
Combinatorial background reproduced by event mixing.
(1520)
K- p
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*(1520) in p+p collisions
anti-*(1520)/ *(1520) = 0.90 ± 0.11 (not corrected from anti-proton absorption)
Event mixing technique,(similar results from like sign mixing)and Breit-wigner fit :
*(1520) M = 1518 ± 2 MeV /c² = 24 ± 5 MeV /c²
Anti *(1520) M = 1517 ± 2 MeV /c² = 26 ± 5 MeV /c²
Same event mixing technique :anti-/ = 0.822 ± 0.008
Particle Data Group:Mass: 1519.5 1.0 MeV/c2
Width : 15.6 1.0 MeV/c2
STAR preliminary p+p at 200 GeV
Yields via bin counting, statistical error only
STAR preliminary p+p at 200 GeV
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p+p Mt spectrum
T
236 ± 7 MeV
(1520) 326 ± 42 MeV
dN/dy = 0.0039 ± 0.0003slope = 326 ± 42 MeV < Pt > = 0.95 ± 0.07 GeV/c
*(1520)/ = 0.082 ± 0.007 T
)mm(
0TT
2
T
0Te)Tm(m2
dydNdydm
Ndm21
Exponential fit :
2)1520()1520( anti
STAR preliminaryp+p at 200 GeV
from event mixing, same limited Mt range than *(1520)
Only statistic error shown, ~30% systematical error
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*(1520) in Au+Au minimum Bias collisions
80% - 60% 60% - 40%
M = 1514 ± 3 MeV/c²= 21 ± 10 MeV/c²
M = 1515 ± 3 MeV/c² = 11 ± 6 MeV/c²
Measure the yield in the limited Mt range and extrapolate to the dN/dy, assuming a temperature derivated from results.
<Npart>
*(1520)/ ratioSTAR preliminary
Yields extracted by bin counting,statistical errors only, ~30% sys.uncertainties.
40%-10%(upper limit)
10% most central(upper limit)
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pT: 1.0-2.0 GeV
*(1520) Invariant Mass in central Au+Au Collisions
1.7 M events
preliminary
thermal model dN/dy = 1.2
Entries: 17460 6324extracted via bin counting and subtracting BG fitAcceptance: 35% 5% for y = |0.5| T=350 50 MeVBG uncertainty = 30% of yield
(1520) dN/dy =0.58 0.21 35%
Breit-Wigner-Fit + linear BGMass: 1519.2 1.3 MeV/c2
Width : 12.9 9.6 MeV/c2
pT: 1.2-1.4 GeV
preliminary
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STARCentral point
* (1520) over ratio
• AuAu min-bias data and central point are consistent.• Suppression of observed lambda*, already in peripheral event• Show the same trend as the K* (Haibin Zhang, Sun)
071.0)1520(*
P.Braun-Munzinger et al, PLB 518 (2001) 41D. Magestro, private communication
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*(1385) signal in p+p
Raw yields : *-+*++*-+*+ = 7500 ± 100(- + -) & (++ +) = 3000 ± 60
Sevil Salur, poster session
Statistical error is shown. ~20% systematic uncertainty comes from normalization of the background for the yields.Corrected spectra should come soon.
M(-) = 1321 ± 1 MeV/c²(-)= 5.8 ± 0.7 MeV (gaussian fit)
M(*) = 1381 ± 2 MeV/c²(*)= 57.5 ± 7.3 MeV (Breit-Wigner)
STAR preliminary
Nen
trie
s
Minv (*) [GeV/c²]
Ratios :/ = 0.90 ± 0.07*/* = 0.89 ± 0.04
3 particle event mixing.
Nen
trie
s
Minv (*) [GeV/c²]
STAR preliminary p+p at 200 GeV
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Summary
• Clear signal of * (1520) and *(1385) is visible in p+p collisions in STAR data at sNN = 200 GeV.
• First results on the production of * (1520) are given in p+p collisions.
• * (1520) signal in peripheral minimum bias events of Au+Au collisions is observed in two centrality bins : 80% to 60% and 60% to 40%. *(1520) signal in central data is also consistent with peripheral points.
• A comparison of * (1520)/ ratio in p+p and Au+Au collisions shows a decrease of this ratio, already in peripheral Au+Au collisions. This decrease could be explained by the rescattering of daugthers particles between a chemical and thermal freeze-out.
* (1520) and *(1385) resonances could give us a unique chance of probing the rescattering phase of Au+Au collisions and providing information on the collision dynamics.
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Embedded Mc (1520) in min-bias AuAu events
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Event azymuthal asymmetry effect correction
10% 10% - 40%
40% - 60% 60% - 80%
p+p
STAR note sn0446