*(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

2

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

3

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.

4

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

5

*(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

6

*(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

7

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

8

*(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)

9

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

10

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

11

*(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

12

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.

13

14

15

16

17

Embedded Mc (1520) in min-bias AuAu events

18

Event azymuthal asymmetry effect correction

10% 10% - 40%

40% - 60% 60% - 80%

p+p

STAR note sn0446