STAR

Jinhui Chen

for STAR Collaboration

Spin alignment of vector mesons (Φ, K*0) in Heavy-Ion C

ollisions at RHIC

QM06 Nov.14-20 Shanghai China 2Jinhui Chen

STAR Outline

Introduction

Analysis method and results

1) Spin alignment with respect to reaction plane

2) Spin alignment with respect to production plane

Summary and outlook

QM06 Nov.14-20 Shanghai China 3Jinhui Chen

STARIntroduction Spin alignment of vector mesons is a unique probe of particle produ

ction and dynamics[1,2]

1. Orbital angular momentum spin? 2. Coalescence/Fragmentation of polarized quarks? 3. Contributions to the significant collective flow observed at RHIC? Spin alignment of vector mesons is described by

We measure ρ00 through decayed products angular distribution in the rest frame of vector mesons:

111011

100001

111011

V

1. Z.T. Liang and X.N. Wang, PRL 94 102301 (05), PRL 96 039901 (06), PLB 629 (05) 20-26;

2. S.A. Voloshin nucl-th/0410089.

]cos)13()1[(4

3

cos*2

0000*

Norm

d

dN

Deviation of ρ00 from 1/3 manifests the alignment of vector mesons

spin density matrix (s=1)

QM06 Nov.14-20 Shanghai China 4Jinhui Chen

STAR Previous measurements

XBep Λ polarization Fermi-lab 1976 G

. Bu

nce

et a

l. PR

L 3

6 (1

97

6) 1

11

3 XKqqZee 0*

OP

AL

Co

l. PL

B 4

12

(19

97

) 2

10

ρ00

Xpp

J. Du

ryea

et a

l. PR

L 6

7 (1

99

1) 1

19

3

XAuAu

E8

96

Co

l. NP

A 6

98

(20

02

) 49

9

PΛ

QM06 Nov.14-20 Shanghai China 5Jinhui Chen

STARMeasurement from RHIC-STAR

STAR DetectorFeatures at RHIC:

Formation of bulk partonic matter

Hadronization from bulk partonic matter is different from fragmentation scheme

Constituent quark degree of freedom ? STAR Collaboration, NPA 757 (05) 102

x

y

beam

reaction plane

Measurements for:

Global hyperon polarization

Global vector meson spin alignment

QM06 Nov.14-20 Shanghai China 6Jinhui Chen

STAR

secondary vertec

27% Yi-Jin Pei, hep-ph/9703243.

x

y

beam

Hyperon polarization vs vector meson spin alignment

reaction plane

QM06 Nov.14-20 Shanghai China 7Jinhui Chen

STAR

]cos)13()1[(4

3 *20000 Norm

Fitting dN(pT)/d(cosθ*) with

to get the ρ00obs.

Analysis details (φ-meson)

Correct ρooobs with “reaction plane

resolution” to obtain ρ00.

Correct the dN(pT)/d(cosθ*) with

detector acceptance.

Using mixed event method to get the raw dN(pT)/dcos(θ*) distribution.

QM06 Nov.14-20 Shanghai China 8Jinhui Chen

STARρ00 vs pT

With statistical and systematical uncertainties, φand K*0 spin are not aligned w.r.t. reaction plane.

STAR Preliminary

|y|<1.0

QM06 Nov.14-20 Shanghai China 9Jinhui Chen

STAR

STAR Preliminary

ρ00 vs Npart

04.001.038.0:)(00 13.002.036.0:)( 0

00 K

Centrality 10-40%

With the data sample, we have not observed global spin alignment for φand K*0 at different centrality.

|y|<1.0

QM06 Nov.14-20 Shanghai China 10Jinhui Chen

STAR

Au+Au @ 200GeV (20-70%)

Au+Au @ 62GeV (0-80%)

Tp (GeV/c)

P

STAR Preliminary

What about Λ global polarization?

I. Selyuzhenkov’s talk

Section 3.4, Nov. 19

With statistical and systematical uncertainties, we have not observed global spin alignment for φ, K*0 and global polarization for Λ at mid-central collisions.

QM06 Nov.14-20 Shanghai China 11Jinhui Chen

STARSpin alignment w.r.t. production plane

Hyperons H produced in unpolarized p+p H+X or p+A H+X are transversely polarized w.r.t. production plane.

What about vector mesons?

transversely polarized? correlated with spin alignme

nt w.r.t. reaction plane?

|)()(|

)()(

pzp

pzpL

Tp ( )��������������

z

L��������������

*

K

K

production plane

QM06 Nov.14-20 Shanghai China 12Jinhui Chen

STAR

STAR Preliminary

ρ00 vs pT

Φand K*0 spin may be slightly aligned at low pT w.r.t. production plane.

05.001.042.0:)(00 05.004.044.0:)( 0

00 K

0.8<pT<1.2GeV/c

|y|<1.0

QM06 Nov.14-20 Shanghai China 13Jinhui Chen

STAR And p+p collisions ?

φ-meson spin alignment in p+p collisions needs more statistics to be conclusive.

STAR Preliminary

|y|<1.0

QM06 Nov.14-20 Shanghai China 14Jinhui Chen

STAR Compared with Au+Au

In current statistics, the spin alignment of φ-meson between Au+Au and p+p collisions are similar.

We are interested in possible difference in φ and K*0 spin alignment between Au+Au and p+p collisions due to different dynamics.

STAR Preliminary

QM06 Nov.14-20 Shanghai China 15Jinhui Chen

STAR

In our current analysis, We used kaons from TPC only.

KK

STAR Preliminary

Au+Au 200GeV

(0-80%)

Time of Flight detector upgrade

Full barrel ~ a factor of 10. J. Wu’s talk

Section 1.4, Nov.15

One tray will enhance the S/B ratio by a factor of 3.5 at intermediate pT.

Au+Au 200GeV KK

(0-80%)

STAR Preliminary

QM06 Nov.14-20 Shanghai China 16Jinhui Chen

STAR Summary and Outlook

Reaction plane: within statistics, we have not observed a global polarization for Λ and global spin alignments for and K*0.

Production plane: and K*0 spin may be slightly aligned in low pT

region.

No significant difference in spin alignments, w.r.t. production plane, between p+p and Au+Au collisions have been observed.

STAR Full Barrel Time-of-Flight detector upgrade will significantly enhance our capability for a conclusive measurement in the future.

Thanks!Thanks!