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!
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