STARSTAR William Christie, BNL

Mini-symposium on Orbital Motion of Quarks in Hard Scattering I

2005 2nd Joint Meeting of the Nuclear Physics Divisions of the APS and the Physical Society of Japan

September 21, 2005.

Transverse Spin Results from STAR

Outline

• Physics motivation

• Brief introduction to the STAR Detector

• STAR Transverse polarization Data sets

• Cross section measurements

• Forward 0 asymmetry

• Future measurements

• Summary

STARSTAR

500+ collaborators52 institutions14 countries

Austria: Bern Brazil: Sao Paolo

China: IHEP-Beijing, IMP-Lanzhou, Shanghai INR, Tsinghua, USTC, IPP-Wuhan Croatia: Zagreb

Czech Republic: Nuclear Physics Institute-AS-CR

England: Birmingham France: IReS - Strasbourg, SUBATECH-Nantes

Germany: Frankfurt, MPI-Munich India: Bhubaneswar, Jammu, IIT, Panjab, Rajasthan, VECC-Kolkata Netherlands: NIKHEF Poland: Warsaw U. of Technology Russia: JINR - Dubna, IHEP – Protvino, MEPHI - Moscow S. Korea: Pusan

U.S.: Argonne, Berkeley, Brookhaven National Laboratories UC Berkeley, UC Davis, UCLA, CalTech, Creighton, Carnegie-Mellon, Indiana, Kent State,

Michigan State, CCNY, Ohio State, Penn State, Purdue, Rice, Texas, Texas A&M, Valparaiso, Washington, Wayne State, Yale Universities

The STAR Collaboration

STARSTARPhysics Motivation

It has been determined, through polarized deep inelastic scattering experiments, that the quarks alone can not account for the spin of the proton (i.e.

To account for the spin of the proton, either the gluons are polarized and/or there are significant contributions to the protons spin from the orbital motion of its constituents.

Would like to unravel the contributions to transverse spin asymmetries (an area of intense recent theoretical development) from:

a) quark transverse spin preferences in a transversely polarized proton (p)

“transversity” quark property decoupled from gluons

b) quark and gluon transverse motion preferences in p

spin-kT correlation related to quark/gluon orbital ang. mom.

1

2

1

2G + L

Quark spin Gluon Spin Angular momentumProton Spin:

STARSTARBarrel EM Calorimeter

-1<η< 1

STAR Detector

=0

Forward Pion Detector

Endcap EM Calorimeter

Beam-Beam Counters

Time Projection Chamber

-1<η< 1

1<η< 2-4.1<η< -3.3

2<|η|< 5

Solenoidal MagneticField (5 kG) analyzestransverse momentumpT of charged particles

=2= -1

Tracking 200320042005

Triggering

Triggering

- ln(tan(/2) Lum. Monitor Local Polarim.

ForwardTPC

2.8 < < 3.8

Central TriggerBarrel

SiliconVertex

Tracker

STARSTARTransverse Polarization Data sets and FPD Configurations

2002 Run: <Pb> ~ 15%, Lint = 0.3 pb-1

2003 Run: <Pb> ~ 30%, Lint = 0.5 pb-1

Upgraded Forward Detector (FPD)

• Pb-glass EM calorimeter

(from IHEP Protovino, used in E704)

• Shower-Maximum Detector (SMD)

• Preshower

Forward Detector (FPD, aka pEEMC)

- 24 layer Pb-scintillator sampling calorimeter

- 2 orthogonal planes of finely segmented triangular scintillator strips (Shower-Maximum Detector, or SMD)

- 2 Preshower layers

East of STAR

Top

Bottom

North

South

STARSTAR

Polarization Pattern at STAR: Spin Up Spin Down Unpolarized

Spin asymmetries in proton-proton collider

Double Spin Asymmetries (F.o.M = P4L)

A 1P

N RN

N RN R L

L

=1P

NL NR

NR NL

NL NR

NR NL

Single Spin Asymmetries (F.o.M = P2L)

A 1P1P2

N RN

N RN R =L

L

N = spin dependent yields of process interestN = spin dependent yields of process interestL = yield of luminosity monitoring process L = yield of luminosity monitoring process R = relative luminosity between different spin configuration R = relative luminosity between different spin configuration P = beam polarization(s) from polarimeter at RHICP = beam polarization(s) from polarimeter at RHICAlso need direction of polarization vector at IRAlso need direction of polarization vector at IR

AN with left-right symmetric detectors

Requires 3 different process/measurements “Bunch/Spin sorting” Up to 120 bunches in RHICBunch Spacing 107nsec (9MHz)Alternating spin patternBunch/Spin sorted scaler system

bunch crossing number at STAR IR

inte

ract

ions

(kH

z)/c

ross

ing

STARSTAR

Left Right

Top

Bottom*BBC West

BBC East

InteractionVertex

3.3<||< 5.0 (inner tiles)

BBC’s register hits for ~50% of tot (pp); EW coinc. discriminates against beam-gas bkgd. for good L monitoring; segmentation local polarimeter with AN

obs.~0.006.

1

L

LR

Example of R

• Statistical uncertainty: dRstat ~10-4 -10-3

• Systematic uncertainty ( beam-gas background ) < 10-3

BBC gives triggering, (Rel.) Luminosity, and local polarimetry.

Negative xFPositive xF

• = BBC L/R asym.

= BBC T/B asym.

Time [Run Number]

2.1 <||< 5.0

R 1 and time dependent!

05/16/03 05/30/03

BB

C

YCNI B

CNI

STARSTAR

<z>

<xq>

<xg>

NLO pQCDJaeger,Stratmann,Vogelsang,Kretzer

p p 0, 3.8, s 200GeV

Forward 0 production in a hadron collider

• Large rapidity production ~4 probes asymmetric partonic collisions

• Mostly high-x valence quark + low-x gluon

• 0.3 < xq< 0.7

• 0.001< xg < 0.1

• <z> nearly constant and high 0.7 ~ 0.8

• Large-x quark polarization is known to be large from DIS

• Directly couple to gluons = A probe of low x gluons

pd

pAu

q

g

Q2 ~ pT2

s 2EN

ln(tan(2

))

xq xF / zEN

xqpxgp

xF 2E

s

z E

Eq

xg pT

se g

EN

(collinear approx.)

STARSTAR2002 STAR Forward Detector (aka pEEMC)

M

reconstruction atE=20~80GeV, 1 <pT < 4 GeV 3<<4

EventDisplay

SMD

EMC

o Cluster separation in shower maximum detector and measured calorimeter energy serves as input to the 0 mass determination.

STARSTARRun 2 Results: Forward Inclusive Cross Section

STAR data consistent with Next-to-Leading Order pQCD calculations

in contrast to data at lower s (Bourrely and Soffer, Eur.Phys.J. C36 (2004) 371-374)

• STAR data at

= 3.8 (hep-ex/0310058, Phys. Rev. Lett. 92 (2004) 171801)

• = 3.3 (hep-ex/0403012, Preliminary)

• NLO pQCD calculations at fixed with equal factorization and renormalization scales = pT

• Solid and dashed curves differ primarily in the g fragmentation function

STARSTARRun 2 Results: Large Analyzing Powers at RHIC

First measurement of AN for forward π0 production at s=200GeV

Similar to FNAL E704 result at s = 20 GeV

In agreement with several models including different dynamics:

Sivers: spin and k correlation in initial state (related to orbital angular momentum?)

Collins: Transversity distribution function & spin-dependent fragmentation function

suppressed? (hep-ph/0408356)

Qiu and Sterman (initial-state) / Koike (final-state) twist-3 pQCD calculations

STAR collaboration, hep-ex/0310058, Phys. Rev. Lett. 92 (2004) 171801

STARSTAR

First shown at spin2002

• pT dependence?

• xF<0?

•AN with mid-rapidity correlation?

• Spin dependence in jet?

STARSTARRun 3 Results: AN for forward & backward 0 production at s=200GeV

Positive AN at large positive xF has been confirmed Larger significance to be non-zero & positive than published data

The first measurement of negative xF AN has been done, and is consistent with zero

Sensitive to twist-3 gluon-gluon correlation

STAR Preliminary

Statistical error only for <>=4.1

STARSTAR

Different position for FPD relative to the beam, relative to already accumulated 2002 data, allows mapping of AN in xF and pT plane to begin

xF and pT range of the data

Run 3 Results: Add 0 cross sections at = 4.0

STARSTAROutlook

• Disentangling the dynamics of AN via

• Higher precision AN measurement vs xF and pT

• AN with mid rapidity correlation

• Forward jet• Proposal for forward calorimeter upgrade

• Heavy mesons and direct photons • Low x gluons in nuclei

• Mid rapidity jets

• Di-jet kT balance gluon Sivers function

• Inside jet particle correlation Collins function * Transversity

~2.4m square~1500 cells

=4.2

=3.2

=2.5

Current FPD

STARSTARSummary

• Forward hadron production at hadron-hadron collider selects high-x (thus high polarization) quark + low-x gluon scatterings

• Inclusive cross section is consistent with NLO pQCD calculations and PYTHIA(LO pQCD + parton showers)

• Analyzing power for forward 0 mesons at large positive xF was found to be large and positive

• The first measurement of negative xF AN has been done, and is consistent with zero

• Accumulation of significant (O 10 pb-1, P 50%) transverse polarization data set expected in upcoming FY06 RHIC run. Expect to start extracting information on dynamics responsible for transverse spin asymmetries.

STARSTAR

Backup

STARSTARCoincidence Transverse Spin Measurements Should Unravel Coincidence Transverse Spin Measurements Should Unravel

Transversity, Collins, Sivers EffectsTransversity, Collins, Sivers Effects

p

p

q

g

Jets with 2 hadrons detected

+

+ …

p

p q

q

Study transversity by exploiting chiral-odd fragment’n “analyzing powers” (Collins or interference frag. fcns.) calibrated at BELLE

Search for spin-dependent transverse motion preferences inside proton (related to parton Lorbit ) via predicted leading-twist spin-dependent deviation from back-to-back alignment of di-jet axes study unique to RHIC spin

STAR projections for 30 pb1, Pbeam=70%

parton kT

AN

pp dijet + X s = 200 GeV 8 pT(1,2) 12 GeV |(1,2)| 1.0

D. Boer & W. Vogelsang predictions

p spin

STARSTAR

kPS

)k(PS)k(x,ƒΔ

21

)k(x,ƒ)s,k(x,ƒPP

pPq

NqqPq

s

2EX

0πF

D. Boer and W. Vogelsang,Phys.Rev. D 69 (2004) 094025

Analyzing Powers at Mid-RapidityDo processes invoked in forward scattering show up at large angles?

Sivers Function – correlation between kT and spin

For given parton at some x kT

L=kTR

Jet

Jet

DijetDijet

DijetDijetN

YY

YY

Pol1

A

Measure

STARSTAR

STAR Collab. Phys. Rev. Lett. 92 (2004) 171801

STARSTAR4.1 x 10 -4

Partonic kT from Dijet Analysis

kT = <kT>2 = ET sin (σ)

ET = 13.0 ± 0.7sys → Trigger Jet

0.030.05

σ =0.23 ± 0.02±

AN8 < pT1,2 < 12 GeV

|η1,2 | < 1

Sivers Effect Prediction

STAR agrees well with World

Data on Partonic kT

D. Boer and W. Vogelsang,Phys.Rev. D 69 (2004) 094025

• Curves are for various gluonic Sivers functions

• Connection to partonic orbital angular momentum

• Suppressed by Sudakov effect

kT distribution

STARSTAR

T. Henry