d Au collisions at s NN 200 GeV in STAR Xianglei Zhu Tsinghua U UCLA For the STAR Collaboration 1 Motivation I Strangeness enhancement Strangeness enhancement in A A collisions at RHIC energy ID: 636344
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Slide1
Strangeness production and Cronin effect in d+Au collisions at √sNN = 200 GeV in STAR
Xianglei Zhu (Tsinghua U / UCLA)For the STAR Collaboration
1Slide2
Motivation I : Strangeness enhancementStrangeness enhancement in A+A collisions at RHIC energy, a
s a QGP signature (see. A. Timmins’ talk)d+Au strangeness data will connect peripheral A+A and p+p, supplying the baseline for the study of strangeness enhancement in the deconfined matter.
2
Redlich
, JPG27
Redlich&Tounsi
, 02
From A. TimminsSlide3
Motivation II : Cronin effect
Cronin effect in p+A, d+Au collision
[Cronin1975], seen in nuclear
m
odification
factor R
AA
or
R
CP
< 1 for
p
T < Px > 1 for pT > Px approach 1 again when pT →
3
p
q
h
A
Traditional
models
[
Accardi
hep
-ph/0212148]
:
Multiple
parton
/
hardon
scatterings in initial state
Recombination/Coalescence
:
[
Hwa&Yang
03, 04]
Final state effect, modification of hadronization
What is the mechanism of Cronin effect?
traditional models: do not explicitly predict particle type dependence, but centrality dependence.
final state models: predict particle species dependence of Cronin effect
Measurements of particle type and centrality dependence of Cronin effect seem helpful to understand the effect.Slide4
Cronin effect in d+Au STAR
4 Cronin effect seen with identified particle RdAu
For 2<pT
<5GeV/c, R
dAu
of proton seems higher than
pions
.
With topological reconstruction, strange hadrons have good PID up to high p
T! Suitable for the study of particle type dependence of Cronin effect.
STAR, PLB637, PLB616Slide5
OutlineK
0s, L, X spectra in most central
d+Au
200GeV
Strangeness enhancement in most central
d+Au
Baryon enhancement at intermediate
p
T
(
L
/ K
0s)Cronin effect, particle type dependence of RdAu in most central d+AuSummary5Slide6
STAR Run 08 d+Au Experiment Setup
Time Projection Chamber
Forward TPCs
Vertex Position Detector to confine primary vertex within ±30 cm, together with east ZDC as minimum bias trigger
No inner silicon detectors
pion
,
kaon
, proton and electron : identified using ionization energy loss
in TPC.
6Slide7
The data set
STAR Run 8 d+Au
200GeV Minimum Bias data
Event Selection:
|
VertexZ
| < 30cm
~
32
M
events after the cuts.
Centrality definition in
d+Au
:
Provided by uncorrected # of
charged particles @ east
Forward TPC
(
Au side, -3.8<
<-2.8),
‘
refMult
’ in the
right plot
Currently, only the most central
(0-20%) events are well defined
by East FTPC.
7
STAR PreliminarySlide8
Strangeness reconstruction in STARStrange particles are reconstructed with their secondary TPC tracks through weak decay topology, thanks to TPC full
azimuthal coverage.
8
K
0
s
, |
y|<1
0.4 <pt<
0.6
Λ, |
y|<1
0.4 <pt< 0.6
Ξ
, |y
|<1
0.6 <pt<
1.0
STAR PreliminarySTAR Preliminary
STAR PreliminarySlide9
Spectra of K0s, Λ, Ξ
Λ(Λbar) corrected for weak decay feed-down from Ξ’sSpectra can be fitted with Levy function [Wilk&Wlodarczyk 00]
, low p
T
– exponential
high
p
T
– power law
fitting parameters:
percentage of
dN
/dy from extrapolation at low pT:K0s 10% ; Λ 17.5%; Ξ 29%9
d+Au 200 GeV
, 0-20%
dN
/
dyn
Tχ2/ndf
K0s
1.21±0.02
11.7±0.20.215±0.002
34.86/12Λ
0.402±0.00820.9±1.3
0.270±0.00510.81/10
Ξ0.058±0.003
14.0±1.30.275±0.011
3.52/5
STAR Preliminary
statistical error onlySlide10
Strangeness enhancement
Λ and K0s enhancement factor is almost the same in most central d+Au, lie in a trend with peripheral Cu+Cu and Au+AuΞ yield is consistent with that from most peripheral
Cu+Cu.strangeness enhancement factor is proportional to the strangeness content in
d+Au
too
10
dN
/
dy
/ <Npart> relative to pp
STAR Preliminary
statistical error only for
d+Au dataNumber of Participants NpartSlide11
Λ/K0s
Baryon enhancement at intermediate pT at STAR measured with Λ/K0sMost central
d+Au data is close to peripheral Au+Au
11
STAR Preliminary
p+p
data is from STAR PRC75Slide12
Nuclear modification factor RdAu
12STAR Preliminaryπ
,K,p
data is from STAR, PLB616, 637, statistical error only;
φ
data is from STAR arXiv:0809.4737;
p+p
K
0
s and
Λ
is from STAR PRC75
K0s agree with charged K at low pTΛ agrees with proton at intermediate pT (2 – 4GeV/c).Particle type (baryon/meson) dependence of RdAu for pT from 2.0 to 4 GeV/c; φ meson RdAu also falls into the meson band, for high statistical φ data, see C. Jena and X. Zhang’s postersSlide13
Summary
Measured productions for 3 identified particles(K0s
,
L
,
Ξ
) in most
central (0-20%)
d+Au
collisions at RHIC
Strangeness (
K
0s, L, Ξ) enhancement
in central
d+Au
.
Especially, we see
Ξ enhancement factor is also large in most central d+Au
L
/K
0
s
ratio
in
dAu
is close to
Au+Au
most peripheral (60-80%)
d+Au
Nuclear modification factor
seems
to show particle type (baryon/meson) difference (
K0s
,,φ vs. p, L), indicating that the hadronization scheme may have an impact on the Cronin effect13Slide14
backups14Slide15
Comparison of K0 to charged K spectraGood agreement of K0s
and charged K (from TPC dEdx) spectra at low pT.15
STAR PreliminarySlide16
RAA in low energy p+A collisions
s =27.4GeV
P.B Straub,PRL 68, 452(1992)
R
w/Be
in p+A collisions
W: tungsten Be: beryllium
s =38.8GeV
R
w/Be
:
Mesons
(2 quarks):
kaon and pion
~ 1.5;
Baryons
(3 quarks):
proton
~ 2.5
Particle-type dependence ??
~1.4
~1.5
~2.5
16