STAR

10-th Workshop on High Energy Spin PhysicsSeptember 16-21, 2003, Dubna, Russia

The STAR Spin Physics Program

Sandibek B. NurushevInstitute for High Energy Physics, Protvino,

Russia

(On behalf of the STAR Collaboration)

STAR

Introduction

The polarized RHIC Complex

STAR detector

Lessons of the first polarized beam runs

Main goals of the STAR Spin Physics Program

Hyperon polarizations

Summary

Contents

STARPoland:Warsaw Univ. of Tech.Russia:MEPHI - MoscowLPP/LHE JINR - DubnaIHEP - ProtvinoU.S. Laboratories:ArgonneBerkeleyBrookhavenU.S. Universities: Arkansas UniversityUC BerkeleyUC DavisUC Los AngelesCarnegie Mellon UniversityCreighton UniversityIndiana UniversityKent State UniversityMichigan State UniversityCity College of New YorkOhio State UniversityPenn. State UniversityPurdue UniversityRice UniversityTexas A&MUT AustinValparasio UniversityWashington UniversityWayne State UniversityYale University

Brazil: Universidade de Sao PauloChina: IHEP - BeijingIMP - LanzhouIPP - WuhanUSTCINR - ShanghaiTsinghua UniversityGrotia:University of ZagrebCzech Republic:NPI - AS CR RezGreat Britain: University of BirminghamFrance:IReS StrasbourgSUBATECH - NantesGermany: MPI – MunichUniversity of FrankfurtIndia:IOP - BhubaneswarPanjab UniversityUniversity of RajasthanJammu UniversityIIT - BombayVECC - KolcataNetherlands:NIKHEF

The STAR Collaboration

~ 500 Collaborators12 Countries

48 Institutions

STAR

Equipment to be

installed after FY03

Polarized RHIC Complex

STARSTAR – Solenoid Tracker At RHIC

Run0 Run1 Run2 and beyondSpin

Magnet Coils

B=0.25T

0.5T

Endcap EMC1< <2 = 2

Barrel EMC0< < 1 =2

|| < 1 = 2

Forward Pion Detector

(FPD) 3.1 < < 4.4+ upgrade

θ/2)] ln[tan(η

Time Projection

Chamber |<1.5

Silicon VertexTracker

Forward TPCs2.4 < || < 4.0

Beam-Beam Counters2 .4< || < 5.0

RICH: ||<0.3, =

Central Trigger Barrel |h| < 1

2 m

4.2 m

18 papers in NIM A499 (2003)

STAR

Left Right

Top

Bottom*BBC West

BBC East

InteractionVertex

3.3<||< 5.0

STAR uses observed asymmetry (AN ~0.006) in inclusive forward charged particle production in Beam-Beam Counters:

BBC - luminosity monitoring detector at STAR

Fast, highly-segmented scintillation counter serves many purposes in STAR:• Minimum Bias Trigger• Absolute Luminosity• Relative Luminosity• Measurement of Transverse Asymmetries

STAR upgrades for SpinSTAR

EndCapEMC (1/3)

EMC (Half) Barrel

Forward Pion Dets. (L,R,U,D on E; L,D on W)

STAR adding lots of EM calori-metry to detect high-energy , e, 0 plus Beam-Beam Counters for relative luminosity and polarization monitoring. EMC’s and FPD’s partially implemented for 2003 run, will be completed before 2005.

BBCWest

BBC EastTPC

See L. Bland talk

STARLessons of the first polarized beam runs

at s=200 GeV

1. BBC detector. It revealed the asymmetry of charged particles on the level AN(1±0.2)10-3 for each run. This is comparable to AN(CNI) (3±0.3)10-3 .

2. TPC. The asymmetry of the Leading Charged Particles (LCP) is close to zero on the level AN(1±1)10-2 up to pT 4 GeV/c for charged particles of both signs.

3. FPD. It detected inclusive 0 asymmetry on the level AN(0.2±0.07) at xF0.5.

STARThe Leading Charged Particle Asymmetry

Among the many complicated theoretical formulae the pQCDprediction for asymptotic quark asymmetry (polarization) is verysimple, namely

22T

TqsN mp

pmαA

Here mq is the quark mass, m is the final hadronic mass,

pT is the transverse momentum and

GeV 0.234Λ ,n3

211β ,

) /Λμ ln(β

4π)μ (α f022

0

2s

where nf is the number of flavors.

The asymptotic quark asymmetry

STARThe spin-orbital interaction

The soft scattering regime. It is well known from the dawn of the Spin Physics, that the spin orbital interaction (much smaller than the central potential) leads to the shift of the angular distribution of the scattered particles, so

θ Δ )) θ ( σ(ln dθ

d

) θ (σ) θ (σ

) θ (σ) θ (σAN

F.Halzen, Phys.Rev. 1962

STAR

This above expression was modified by M.G. Ryskin (Sov. Jour. Nucl. Phys. 48 (1988) 1114).

He assumed that two quarks in the colored string interact through the potential

The model of the quark polarization

GeV 0.1Hμδp

))(p (lnσdp

dδp) ) θ ( (lnσ

dθ

d

) θ (σ) θ (σ

) θ (σ) θ (σA

T

TT

TqN

,HμVμH

STAR

The inclusive pion versus quark asymmetry

onpolarizatiquark initial thex,q

P

2GeV60

s ,

0s3x)s(1

0sR

RAPA qNq

πN

3N

1/2qTT

108A

GeV 200s MeV, 100m 0.04, xGeV/c, 4p

The prediction can be verified at STAR

STAR

0.43 0.80 ΔG

0.03 0.09 - Δs

0.04 0.43- Δd

0.03 0.84 Δu

0.06 0.32 ΔΣ

0.01 0.1 1

0.0

0.1

0.2

0.3

0.4

PD(g1

NLO/F1

NLO)

x

xG(x)

0.01 0.1 1

-0.4

-0.3

-0.2

-0.1

0.0

x

-x(d+d)

0.01 0.1 1

-0.2

-0.1

0.0

x

-x(s+s)

0.01 0.1 10.0

0.1

0.2

0.3

0.4

x

PD (g1

NLO + HT)

-x(u+u)

Global NLO QCD analysis of DIS data SLAC (E142, E143, E154, E155)CERN (EMC, SMC)DESY (HERMES)

185 exp. points

E. Leader, A. Sidorov, D. Stamenov Phys. Rev. D67 (2003) 074017

22 GeV 1Q (JET), QCD NLO

G not well constrained not extracted

dΔ ,uΔ

Spin-dependent PDFs

dp,1

dp,1

dn,p,1 /Fg ,A

First moments at Q2 = 1 GeV2

STARSpin Physics Program at STAR

Gluon Polarization Direct Photon + jet Jet and DiJets Heavy flavor production (?)

Quark / Anti-Quark Polarization & Flavor Decomposition W production

Transversity & Transverse Spin Effects Single transverse spin asymmetries Transversity via Jet fragmentation Transversity via Dijet or Drell-Yan pairs

New Physics ? Parity violating asymmetries

qg q QCD Compton scattering

qg Jet Jet or gg Jet Jet

eWqq_

QQgg

STAR

Where is the spin

of the proton?

At present, the gluon contribution to the proton spin (G) is known only poorly from scaling violation in polarized deep inelastic scattering

STAR Spin goals: determine the gluon contribution to the proton’s spin determine the flavor decomposition of the quark (antiquark)

polarization probe transversity: the unknown, remaining leading-twist

structure function

STAR Parton distributions in proton

Helicity probes quark-gluon mixing qGq & G Probability to find longitudinal (z direction) polarized quarks & gluons in longitudinal polarized nucleon moving in the z direction.

Transversity probes dynamical chiral symmetry breakingq Probability to find transversely (x direction) polarized quarks in transversely

polarized nucleon moving in the z direction.

qqδq

GGΔG qqΔq

x

y

z

GGG qqq

Helicity average probes quark-gluon mixing q & G

q & G Probability density to find quarks in nucleon moving in the z direction

helicity difference

helicity flip

Quark chirality is conserved at all QCD and electroweak vertices, however quark chirality can flip in distribution function because they probe the soft regime where chiral symmetry is dynamically broken in QCD.

helicity average

STARALL(π0) Measurements at E704

The two-spin parameter ALL in inclusive π0 production by longitudinally-polarizedprotons and antiprotons on a longitudinally-polarized proton target has been measured

at 200 GeV Fermilab spin physics facility, for π0‘s at xF =0 with 1 ≤ pt ≤ 3 GeV/c. The

results exclude, at 95% confidence level, values of ALL(pp)>0.1 and < − 0.1, for π0‘s

produced by protons, and values of ALL(pp)>0.1 and < − 0.2 for incident antiprotons.The data are in good agreement with “conventional”, small or zero, gluon polarization.

A.Bazilevsky

π0 ALL from pp at s 1/2 =20 GeV

E704

STARALL(nγ) Measurements at E704

The double-spin asymmetry, ALL, for inclusive multi-γ pair production was measured with a 200 GeV/c longitudinally-polarized proton beam and a longitudinally-polarized proton target. The ALL values were found to be consistent with zero. The ALL values have been compared with theoretical predictions of gluon polarization, ΔG/G. The results put restrictions on the size of ΔG/G in the region of 0.05<x<0.35.

STAR STAR spin goals

Gluon spin-dependent distribution

function

Gluon contribution to proton spin

Sign of G

Jet, di-jet production

Measure of double-spin asymmetry ALL

with longitudinally polarized protons

L

LR

RNN

RNN

PP

1A

21LL

Xjetpp

Xjetjetpp

gq)(gqa)(xqe

)(xΔqe

)G(x

)ΔG(x

σσ

σσA LL

2i2i

2i2i

1

1LL

“ ..A priori not even the sign of Г is known, and it may be negative.” R.L.Jaffe

N – spin dep.yields of processL – yields of luminosity monitoring processR – relative luminosityP – beam polarization

STAR

gz

qz LLΔGΔΣ

2

1

2

1

STAR spin goals

Gluon spin-dependent distribution

function

Gluon contribution to proton spin

Sign of G

ΔsΔdΔuΔΣ

Direct productionjet correlation

Measure of double-spin asymmetry ALL

with longitudinally polarized protons

L

LR

RNN

RNN

PP

1A

21LL

Xjetγpp

Xγpp

1ΔΣ

0Δs γq)(gqa)(xqe

)(xΔqe

)G(x

)ΔG(x

σσ

σσA LL

2i2i

2i2i

1

1LL

N – spin dep.yields of processL – yields of luminosity monitoring processR – relative luminosityP – beam polarization

STARSTAR Spin Goals

))u(x(xd)(xd)u(x

))u(x(xdΔ)(xd)Δu(xA

2121

2121WL

XWpp

Separate quark - u, d , antiquark u, d helicity distribution functions

flavour andspin selects W

)u(x

)Δu(x

1

1

)(xd

)(xdΔ

1

1

21 xx

21 xx

Measure of parity violating asymmetry AL

with longitudinally polarized protons

L

LR

RNN

RNN

P

1AL

))d(x(xu)(xu)d(x

))d(x(xuΔ)(xu)Δd(xA

2121

2121WL

)d(x

)Δd(x

1

1

)(xu

)(xuΔ

1

1

21 xx

21 xx

N – spin dep.yelds of processL – yields of luminosity monitoring processR – relative luminosityP – beam polarization

¯ ¯

STAR STAR Spin Goals

GeV 20s

p

●0 - D.L. Adams, et al., Phys. Lett. B261(1991)201.●+/- - D.L. Adams, et al., Phys. Lett. B264(1991)462.

GeV/c 2.0p0.5 T

Transverse single pion asymmetry AN

from E704 to STAR

FNAL

AN increases with xF and reaches 40%

AN ≈ 0 at xF ≈ 0

sign(AN) – charge(correlation

AN (pp) ≈ – AN (pp)

RL

RLN σσ

σσA

LRLR

LRLR

P

1A

BN

Xπpp ,0

p_

STAR STAR Spin Goals Measure of double-spin

longitudinal ALL and transverse ATT

asymmetry for Drell-Yan pair production

LL22i

21i

2i

22i

21i

2i

LL a2)](1)Q,(xq)Q,(x[qe

2)](1)Q,(xq)Q,(xΔq [e

σσ

σσA

TT22i

21i

2i

22i

21i

2i

TT a2)](1)Q,(xq)Q,(x[qe

2)](1)Q,(xq)δQ,(xδq [e

σσ

σσA

Longitudinally polarized density q

Transverse polarized density q

Transversity distributions can not be measured in conventional DIS, semi-inclusive DIS is required. Transversity distributions are prime candidates for experiments at polarized proton collider.

Xllpp

Xllpp

STARSTAR Spin Goals

Measure of spin-transfer asymmetry

Spin-dependent fragmentation function

XΛpp ΛA

describes the transformation of a longitudinal polarized parton into

a longitudinal polarized (z)D(z)D(z)ΔD )Λ(

)i()Λ(

)i(Λi

hadronisation polarization transfer

)σ(σ)σ(σ

)σ(σ)σ(σA

)Λ()Λ()Λ()Λ(

)Λ()Λ()Λ()Λ(Λ

D. de Florian, M.Stratmann, W.VogelsangPRL 81 (1998) 530; PR D57 (1998) 5811

Sensitivity to flavour polarization transfer. Negative s (1), (u+d) (2), (s+u+d)(3) transmission of polarization to .

Phenomena exist but are not understandable

expected errors for STAR

STAR

Hyperon Polarization at STAR

STAR will be able after some upgrades to study a full set of the hyperon polarization parameters: I-diff. cross-section, P-polarization, AN-asymmetry, R, R’ -spin rotation parameters, A, A’ -longitudinal spin parameters, DNN -normal spin transfer parameters and Aij (i,j=n,s,l)-double spin parameters.

Hyperon polarization as a probe of the QGP.

STARSTAR Spin Goals

Measure of parity-violating spin asymmetry for one jet production

Standard Model test

)σ(σ)σ(σ

)σ(σ)σ(σAPV

LL

Xjetpp

New parity-violating interactions could lead to large modifications of the SM predictions

Asymmetry is nonzero due to electroweak QCD interference (g & Z0)

quark compositeness new short-range interactionSearch for

STARXjetγpp

BEMC

BEMC+EEMC

Compton

annihilation

N+(-) : Spin dependent event yield

R: Relative luminosity

P: Beam polarization

Double spin asymmetry:

RNN

RNN

PP

1A

21LL

RNN

)AP(P1

PP

1δA

2LL21

21LL

0ΔG

0ΔG

G.Skoro, M.T., hep-ph/0009028; E2-2001-40,JINR

G (x) determination via ALL

in p + p + jet + X

ALL

is sensitive to G

STAR

Simulation based on Pythia including trigger and and jet reconstruction efficiencies

Coverage of EMC (barrel) + EEMC (endcap) 0 < Φ < 2π and -1 < η < 2

Jet reconstruction: Cone algorithm

(seed = 1.5 GeV, R = 0.7) Luminosity: 320 pb-1

Polarization: 0.7 s = 200GeV

Sensitivity to Gluon Polarization at RHIC

xg , xq reconstruction G reconstruction

Comparison with other Comparison with other experimentsexperiments

STAR scans a wide range of xg=0.01-0.3

STAR

Xjetpp

Double spin asymmetry ALL: Inclusive jet production

Xdijetpp Simulation based on Pythia including jet

reconstruction efficiencies Coverage of EMC(barrel)+EMC(endcap)

0 < Φ < 2π and -1 < η < 2

Jet reconstruction: Cone algorithm (seed = 1.5 GeV, R = 0.7)

Luminosity: 8.1031 cm-2 s-1 s = 200 GeV Polarization: 0.7

Sign of ? ΔG

gz

qz LLΔGΔΣ

2

1

2

1

G.Skoro, M.T., M.ZupanNuovo Cim. A111(1998)353Nuovo Cim. A112(1999)809

0ΔG

0ΔG

0ΔG

0ΔG

G (x) determination via ALL in p + p jet+ jet + X

ALL

is sensitive to sign of G

STAR Flavor Decomposition of the proton’s spin

ALe(p p) d /d

ALe( p

p ) u /u

ALe (p p) u /u

ALe ( p

p ) d /d

Forward (backward) lepton measurement

p ( p)

p (p )

Blue beamtoward endcap

Yellow beamaway from endcap

Spin parity-violated asymmetry

Detect W ± in STAR via isolated high-pT daughter lepton, without away-side jet

u , d determination via AL

PV in p + p W ± + X @ s = 500 GeV

– –

STARSummary

Single spin asymmetry AN is measured by BBC. Precision is <10-3 allowing to control the transversal components of the beam polarization.

Significant single spin asymmetry in the inclusive 0 production is revealed by FPD in the polarized proton beam large xF region at s1/2 =200 GeV.

First single and double spin measurements in inclusive LCP production are made at STAR with transversally polarized protons. Measurements were done in the level of precision <10-2. Asymmetries are compatible with zero.

New measurements were done in this year with longitudinally polarized protons.

STAR at RHIC started a new generation of proton spin structure studies gluon contribution to the proton’s spin spin/flavor decomposition of the sea

double-spin asymmetries polarization transfer

transversity

STAR

• Measured cross sections consistent with pQCD calculations.

• Large spin effects observed for s = 200 GeV pp collisions, qualitatively

consistent with models extrapolating from FNAL E704 data at s = 20 GeV.

• Large normalization uncertainty on measured AN is reduced when Pbeam

calibration exp’t is done.

p + p “”+ X , s = 200 GeV

STAR Spin Results:STAR Spin Results:

Forward Pion Asymmetry and Cross SectionForward Pion Asymmetry and Cross Section

STAR PRELIMINARY