K*(892) Resonance Production in Au+Au and Cu+Cu Collisions at sNN = 200 GeV & 62.4 GeV

Motivation

Analysis and Results

Summary

1

Sadhana DashInstitute of Physics, Bhubaneswar

(For STAR Collaboration)

Outline:

Neutral K* -meson :

Mass : 896.10 +/- 0.27 MeV Width : 50.70 +/- 0.60MeVDecay Modes : K ~ 100 %Decay Modes for present study K+

K-

BR ~ 66% ……….. Life time : ~ 4 fm Quark Structure : d s d s

Features of K* Meson

2

Charged -meson :

Mass : 891.66 +/- 0.26 MeV Width : 50.80 +/- 0.90 MeVDecay Modes : K ~ 100 %Decay Modes for present study K0

S

K0 S

BR ~ 23% ……….. Life time : ~ 4 fm Quark Structure : K*+ u s K*- u s

Importance of K* studies

3

K*/, /K* information on interplay of rescattering and regeneration effects .

Modification in K* Mass , Width and pT

spectra in-medium dynamical effects

v2 and RCP

measurements of K* provide important information on its production mechanism in the hot/dense phase of heavy ion collisions.

K* lifetime ~4fm/c, sensitive to the properties of hot and dense medium created.

K* thermally produced at the chemical freeze-out stage

K*lost

K

K*

K*

K K K*

reconstructed

Regeneration Effect compensatesagainst lost K* yield

Chemical freeze-out

Thermal freeze-out

K*

time

K*

K

Daughter particles’ Rescattering Effect destroys part of K* signal

K

Regeneration and Rescattering Effects

4

We study K*/K ratio in p+p and A+A collisions to understand rescattering effect.

K*

reconstructed

5

STAR Time Projection Chamber was used to select kaons and pions.

STAR Experiment

STAR DATA (Run IV & V)Au+Au 62.4 GeV ~ 7e+6 eventsAu+Au 200 GeV ~ 13e+6 eventsCu+Cu 62.4 GeV ~ 10e+6 eventsCu+Cu 200 GeV ~ 8e+6 events

The signal was obtained by subtracting the combinatorialbackground distribution (generated using mixed event technique) from the kaon-pion invariant mass distribution.

K* Invariant Mass Spectrum

0

02

02/4] Signal : Simple Breit-Wigner

6

Background : Linear functionM0 and Gamma

Phys. Rev. C 71 (2005) 064902

MinBiasMinBias

K*0 Mass and Width Distribution

7

K* mass and width are consistent with PDG values

Centrality Dependence of Transverse Mass Spectra

Exponential Fit function:

8

d2N dN/dy 2πmT dmTdy 2 πmT(m0+T)

1exp {-(mT-m0)/T}

K*0 dN/dy and <pT>

The integrated yields of K* scale with charged particle multiplicityfor Au+Au and Cu+Cu collisions at 62.4 GeV and 200 GeV.

9

K* 200GeV (Run II) : Phys. Rev. C 71 (2005) 064902

No significant centrality dependence of <pT> for both Au+Au and Cu+Cu collisions at a given energy.

There is a suppression of (K*/K-)A+A

/(K*/K-)p+p

ratio with centrality => rescattering effect predominates over regeneration . 10

Rescattering crosssection> 5 times the regeneration cross-section,

Phys. Rev.D 9, 1872(1974)

Particle Ratio (K*/K-)

(/K*)

A+A/ (/K*)

p+p ratio increases with centrality favouring

rescattering effect: more K* are destroyed than regenerated.

Particle Ratio (Φ/K*)

11

Nuclear Modification Factor

Baryon-meson effect is favored in particle production

12

Run IV

RCP

of K* is smaller than and K

S at lower p

T => strong

rescattering of daughter particles.

K* v2

13

Scaled particle momentum elliptic flow is same for different species.

Number of quarks is found to be 2.0 +- 0.3 which implies hadronic regeneration process contributes little to the final observed K*

Phys. Rev Lett.92(2004)052302

Number of quarks from v2 scaling = 4 => K*regenerationPhys.Rev.C69 ,031902(2004)

Au+Au at 200 GeV

STAR Preliminary

K*(896) resonance production has been measured at sNN=62.4 GeV and sNN=200 GeV in both Au+Au and Cu+ Cu collisions by STAR at RHIC.

Measurements of K*0/K and /K*0 ratio, v2, and K* R

CP at low pT are primarily

formed at hadronization.

K*0 integrated yield scales with dNch

/d in both Au+Au and Cu+Cu collision systems.

<pT> shows no significant centrality or system size dependence in Au+Au and Cu+Cu collisions.

Summary

14

At intermediate pT , RCP measurements support

baryon -meson effect over mass effect of particle production .A non-zero K* elliptic flow v2 was measured in Au+Au collisions at 200 GeV .

At intermediate pT , the number of quark constituents is found to be 2.0+-0.3 which suppports quark recombination model of particle production.

Summary (contd)

15

Typical Invariant Mass Spectrum

The signal was obtained by subtracting the combinatorialbackground distribution (through mixed event technique) from the kaon-pion invariant mass distribution.

0

02

02/4]

Fit function :

0

: K* width

0 : K*

massSTAR PRELIMINARY

Au+Au 62GeV

Signal : Simple Breit-Wigner

Background : Linear functionSTAR PRELIMINARY

18

STAR TPC was used to selectkaons and pions.

STAR DATA (Run IV & V)Au+Au 62.4 GeV ~ 7e+6 eventsAu+Au 200 GeV ~ 13e+6 eventsCu+Cu 62.4 GeV ~ 10e+6 eventsCu+Cu 200 GeV ~ 8e+6 eventsQM-08 Sadhana Dash Jaipur, Feb 04 - 10

K* <pT> in comparison with other species

19