Spin Physics Progress with the STAR Detector at RHIC

• Spin related hardware improvements to STAR• Important constraints on G along the way – jets and 0s• Sivers Functions from jets at mid-rapidity

J. Sowinskifor the

STARSTAR

Collaboration

Detector

=0

Forward Pion Detector

Endcap EM Calorimeter

Beam-Beam Counters

Time Projection Chamber-1.6<η< 1.6

Barrel EM Calorimeter

-1<η< 1

1<η< 2-4.1<η< -3.3

2.2<|η|< 5

Solenoidal MagneticField 5kG

=2= -1

Tracking

Lum. Monitor Local Polarim.

200320042005

Triggering

Triggering

= - ln(tan(/2)

STARSTAR

See talk by J. Kiryluk

• Pb Scintillator sampling calorimeter – 21 rad. lengths• 720 Towers give EM energy• Shower Max. Detector for 0/ discrimination• Pre- and post-shower det’s for e/h discrimination• 9,792 channels read out• High Tower and Jet Patch triggers

Endcap ElectroMagnetic Calorimeter

2003 1/3 Towers2004 All

Towers . 1/3 SMD

2005 Fully Instr.

SMD profiles for a 9 GeV 0 candidate

Charged tracks matched to fired EEMC towers for a 62 GeV Au+Au event. 2004 DataMIPs ~ 0.3GeV

Online tower-only 0 reconstruction, 200 GeV Au+Au

All eventsMixed events

Difference

[200 GeV p+p (2003)]U V

8 cm

7 cm

Inv. Mass

Scinti. + Pb sandwich sampling EMC• 4800 projective towers (2in, -1< <1)• Shower Max Detector-gas detector-18K strips• Pre Shower Detector (first 2 layers)• High tower trigger & 1x1 (η, φ) jet trigger

Barrel ElectroMagnetic Calorimeter

pT>3GeV

24 modules FY0260 modules FY0390 modules FY04All modules (plan all elect.)FY05

One module = 40 towers

#120 – the last one!August 2004

Sz = ½ = ½ + G + Lzq + Lz

g

First Moments at Q02=1 GeV2:

(MS) = 0.19 ± 0.05 ± 0.04

(AB) = 0.38

G(AB) = 0.99

(just one example of many)

+ 0.03 + 0.03 + 0.03 0.03 0.02 0.05

+ 1.17 + 0.42 + 1.43 0.31 0.22 0.45

—

SMC Analysis, PRD 58, 112002 (1998)

The Proton Spin Structure - G

Quark pol. well known from DISBut only a small fraction of p helicity

Gluon polarization poorly determined

Orb. Ang. Mom.unknown

G is accessible and a high priority at RHIC and STAR!

STARSTAR

A ~ P P a LL g part LL^

pQCD

MeasureKnow from DIS

“G”

G via partonic scattering from a gluon

• Dominant reaction mechanism

• Experimentally clean reaction mechanism

• Large a• But jet and 0 rates are

sufficient to give significant G const. in 2005 data

Prefer

LL^

-jet coinc. rare

STARSTAR

Heavy flavor rare

Jets and 0s

STARSTARSees and reconstructs jetsLarge solid angle is crucial

But signal is mixture of multiple partonic subprocesses 0 5 10 15 20 25 30

0.2

0.4

0.6

0.8

1.0

0.0

gg qq

qg

Inclusive Jets :LOW. Vogelsang

pT (GeV)

Fra

ctio

n

Leads to small but significant ALL in 2005

(~1/10 of these stats from 2004 currently being processed)

Polarized Proton Operation at RHIC

Year 2002 ~2007

s = 200 GeV

Improving L and Pol.

2002 2003 2004 2005 2006 2007• L (s-1cm-2) 0.5x1030 2x1030 3x1030 8x1030

17x1030 48x1030

• Int. L (pb-1) (T/L) 0.3/0.0 0.5/0.4 0.5/0.4 4/7 28 86 • Pol. 0.2 0.3 0.40 0.45 0.65 0.70

Spin flipper

Transverse/LongitudinalSpin running

T/L DivisionTo be decided

Jager, Stratmann, Vogelsang NLO pQCD calculations

hep-ph/0404057~1/3 of the jet energy is EMUse EM cals for triggering jets0s carry ~same physics

-1<<1

EEMC 1<<2

Significant const. on G expected in 2005 data (~1/10 stats. from ’04 being analyzed)(error bar estimates too small pT<6 GeV)

-1<<1 BEMC

• Only STAR can track vs. – EMCs+FPD– Different partonic contributions– Large small x

dab

d

Simulation

EEM/Ejet

pT

frac

tion

STARSTAR Quark – Gluon Compton Scatteringp p Direct Jet

• Compton scattering dominates competing qq g mechanism

• Coinc. – jet relatively clean exp. signature

• E, and jet determine

xq, xg,• Allows extraction of g(x)

^

Simulated full data set

Source: F.H. Heinsius, DIS 2004

SMC:PRD70, 012002(2004) HERMES: PRL 84, 2584 (2000)

xg

Eventually gives best determ. of g(x) for existing experiments.

Will get started in 2005 & 2006but need L of 2007+ and 500 GeV for g(x)

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?

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

See A. Ogawatalk on fwd 0s

Sivers Function – Initial state correlation between kT and spin

4.1 x 10 -4

Partonic kT from Dijet Analysis

kT = <kT>2 = ET sin ()

ET = 13.0 0.7sys GeV Trigger Jet

0.030.05

= 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, Quark Matter 2004, J. Phys. G

kT

S

Conclusions (Beginnings;-)• RHIC will provide increasing L and P

• STAR EM calorimeters complete– Triggering– Large solid angle EM coverage– See poster on future upgrades

• Important constraints on G expected in ‘05– 0s– Jets– Direct s – longer term

• Investigations of transverse spin effects

STARSTAR