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RHIC-STAR 实验

徐庆华， 邓建

2011.11.25

• RHIC-STAR 实验情况• STAR 上超子极化转移的测量• STAR forward upgrade plan & eRHIC (EIC)

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Relativistic Heavy Ion Collider (RHIC) at Brookhaven

-- also the first polarized pp collider

RHIC BRAHMSPHOBOS

PHENIXSTAR

AGS

TANDEMS

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What does RHIC do?

1) At 200 GeV top energy - Study medium properties, EoS - pQCD in hot and dense medium

2) RHIC beam energy scan - Search for the QCD critical point - Chiral symmetry restoration

Polarized spin program @ 200, 500 GeV - Study nucleon spin structure

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The RHIC spin program

Longitudinal spin program: determination of the helicity distributions:

• Gluon polarization ∆g(x) in the nucleon

-- inclusive jet, hadrons

-- di-jets, +jet

• Flavor separation: quark & anti-quark polarization

-- RHIC 500 GeV program (W prodction)

• Hyperons spin transfer

Transverse spin program:

• Single spin asymmetry AN (SSA) on 0,

• QCD mechanisms (Sivers, Collins, high-twist)

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Quark spin, Best known (~30%)-DIS

Gluon spin,Poorly known,RHIC

Orbital Angular MomentaLittle known

• Spin sum rule (longitudinal case):

Spin structure of nucleon

€

q(x,Q2) = q+(x,Q2)+q−(x,Q2)

€

−

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+

• Polarized parton densities:

-> Transversity: （ little know ）

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STAR group @ SDU

• 老师 : 徐庆华， 3 月－ 5 月在 BNL访问

邓 健 （ at BNL this year ）

Topic: Hyperon spin transfer in pp

• 研究生 : 李 璇 in BNL since 2009, 预计 2012 年毕业

Topic: Forward-Forward pi0 azimuthal correlation at STAR

研究生 : 张金龙， 2011 级硕士

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What is special with ?

decay parameter: 0.642(p-)

0.65 (n0)

Unit vector along proton momentum in ’s rest frame.

polarization vector

• polarization can be measured in experiment via weak decay:

Λ->p-(Br64%), Λ->n0(Br36%) , -T.D.Lee, C.N.Yang(1957)

• ’s contain a strange constitute quark, whose spin is expected to carry most of the spin:

spin <=> s quark’s spin

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Provide access to pol.p.d.f. and fragmentation functions

• Longitudinal spin transfer :

Longitudinal spin transfer in pp collisions

• Production of :

- DLL of is less sensitive to s, due to larger u and d quark frag. contributions.

- DLL of - should be sensitive to s, but need more integrated luminosity.

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BBCEast

Barrel EMC

BBC West

TPC

p

V0_vertex

V0_DCA

r_

Time Projection Chamber enables PID

Plus topological reconstruction:

4.2m

for ||<~1.3

• primary vertex

STAR 上的超子极化重建

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STAR, PRD80(R),111102(2009)

STAR 上的超子极化实验测量

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关于超子极化转移分析的进展及计划

邓健于 2011 年 8.23 －24, 11 月 9 － 18 参加了STAR合作组年会，并报告了利用新数据关于 超子纵向极化转移的新结果。

目前我们正在完善数据分析，包括 MC 模拟以及系统误差分析，明年参加国际会议报告结果，提交合作组准备发表。

已经开始探索其它超子如的极化，以及超子的横向极化。

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Forward-Forward pi0 correlation analysis

Xuan Li 12

CGC predicts suppression of back-to-back correlation.

STAR Collaboration Meeting, Nov. 15, 2011

(1) The suppression of the height of the away side peak in the central dAu collisions suggests forward-forward correlations at low x are consistent with gluon saturation in nuclei.(2) The degree of broadening is consistent with multi-parton scattering in central dAu collisions associated with saturation.

李璇 , Nov.15, 2011参加合作组会议，并报告分析结果。 PA of a STARpaper in preparation.

A Feasibility Experiment to Measure the Analyzing Power for Drell-Yan production at RHIC

(-ANDY experiment)

A critical test of QCD predictions

~2mr crossing ~1.6mr crossing

~0mr crossing angl

systematically increased thresholds for IP2

collisions

Data taken in 2011

-Xuan Li

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Future plan: Lambda polarization in the forward region & related upgrade in ~5 years

• Dec.12 － 16 ， STAR upgrade workshop at UCLA.

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Future plan: eRHIC ？ >2020

- EIC white paper, arXiv:1108.1713

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World data on pol. and unpol. deep-inelastic scattering

€

F2(x) = e i2

i

∑ xq i(x )