RHICResults on Transverse Spin

Steve HeppelmannSteve Heppelmann

Penn State UniversityPenn State University

2nd Workshop on the QCD Structure of the Nucleon

June 12-16, 2006Villa Mondragone

Monte Porzio Catone, Rome, Italy

Three RHIC Experiments are producing results on Transverse Single Spin Asymmetries AN.

– BRAHMS: Small XF Small angle (Charged (+/-) pion, kaon, nucleon)

– PHENIX: Small angle Neutrons; Mid Rapidity 0, jets– STAR: Forward (larger XF) 0, jets, photons; Mid Rapidity

charged tracks, pions, jets

pp RUN05-06, PHENIX Integrated Luminosity (delivered)

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From Abhay Deshpande

STARSTAR detector layout (run 5)• TPC: -1.0 < < 1.0

• FTPC: 2.8 < < 3.8

• BBC : 2.2 < < 5.0

• EEMC:1 < < 2

• BEMC:0 < < 1

• FPD: || ~ 3.3/3.7/4.0

STAR Forward Calorimetry Recent History and Plans

• Prototype FPD – Run 2 polarized proton data

(published 2004 spin asymmetry and cross section)

Prototype FMS Run 6 (FPD++)2006 to present• Forward jet shape spin dependence.• Direct photon asymmetry (isolation)• High Statistics, High Polarization

FMS Forward MesonSpectrometer Run 7 2006

(hep-ex/0502040).

• FPD – Run 3-5 data – pp, dAu – (Preliminary An Results)

FMS DesignForward Calorimeters

FPD Run 3-5 (2003-2005)FPD++ Run 6 (2006)

FMS Run 7- (2006- )

AGS&RHIC Users Meeting -

200606065

Transverse spin runs at STAR with forward calorimetry: 2001→2006

~60~45~30~15

East FPD

West FPD++

full FPD

(8 matrices)

6 matrices

of FPD

EEMC

and FPD

prototypes

detector

6.80.10.250.15

±3.2/±3.7±3.7/±4.0±3.3/±4.03.8

Run6Run5Run3Run2

%,BEAMP

1, pbLdt

sampled

-1 0 1 2 -units

Barrel EMC EndcapEMC

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Reconstructed di-jets from EM calorimeter only trigger data:

kTx<0 kTx>0

Opening angle

2002- No charged track An Seen@Pt~1.5 GeV An < .01@Pt~4.5 GeV An < .16

2006- 3,000,000 dijets (-1<<2) will be sensitive to Sivers kT;measure predicted opening angletransverse spin dependence.

STAR Central RegionSTAR Central Region

Cross Sections and Analyzing Power published from RHIC Run 2

J. Adams et al. (STAR collaboration), Phys. Rev. Lett. 92 (2004) 171801 [hep-ex/0310058].

R.D. Klem et al., Phys. Rev. Lett. 36 (1976) 929;

W.H. Dragoset et al., Phys. Rev. D18 (1978) 3939;

S. Saroff et al., Phys. Rev. Lett. 64 (1990) 995;

B.E. Bonner et al., Phys. Rev. D41 (1990) 13;

K. Krueger et al, Phys. Lett. B459 (1999);

C.E. Allgower et al., Phys. Rev. D65 (2002) 092008.

Similar asymmetry to many lower energy

measurements. → But now, for the first time,in a region where NLO PQCD calculationsfairly accurately predict the cross section.

Caveats:Caveats: -RHIC CNI Absolute polarization -RHIC CNI Absolute polarization still preliminary. still preliminary. -Result Averaged over azimuthal -Result Averaged over azimuthal acceptance of detectors.acceptance of detectors. -Positive X-Positive XFF (small angle (small angle

scattering of the polarized proton).scattering of the polarized proton).

Run 2 Published Result.Run 2 Published Result. Run 3 Preliminary Result.Run 3 Preliminary Result. -More Forward angles.-More Forward angles. -FPD Detectors.-FPD Detectors.

Run 3 Preliminary Run 3 Preliminary Backward Angle Data.Backward Angle Data. -No significant Asymmetry -No significant Asymmetry seen.seen. ( Presented at Spin 2004: hep-ex/0502040)

Run 3 + Run 5 Preliminary Run 3 + Run 5 Preliminary <<>=3.7,4.0>=3.7,4.0(Presented SPIN 2005 Dubna Sept 27-Oct (Presented SPIN 2005 Dubna Sept 27-Oct 1)1)

pp π0 + X cross sections at 200 GeV

NLO pQCD calculations by Vogelsang, et al.

nucl-ex/0602011

STARSTAR

The error bars are statistical plus point-to-point systematic

Consistent with NLO pQCD calculations at 3.3 < η < 4.0

Data at low pT trend from KKP fragmentation functions toward Kretzer. PHENIX observed similar behavior at mid-rapidity.

Combined AN(pT) for xF > 0.4 from runs 3+5 (much higher statistic data recently collected)

Online calibration of CNI polarimeter

Data are consistent with the 1/pT expectation of pQCD

Run6 – STAR Forward physics objectives♦ Forward jet shape ♦ Asymmetry for jet-like events

♦ mapping ♦ ?

♦ Inclusive/direct photon measurements

),(A N0

TF px /J FPD++

hardware-level calibration

Analysis of jets and jet shape from already Analysis of jets and jet shape from already collected in 2006 will collected in 2006 will

•Greatly improve measurement of AGreatly improve measurement of ANN(X(XFF,p,pTT))•Determine if large asymmetry comes from Determine if large asymmetry comes from the jet axis or is produced within the jet.the jet axis or is produced within the jet.

BRAHMS Results

K+

K-

AN of proton and pbar

BRAHMS Summary (FROM DIS 2006)

BRAHMS has obtained preliminary results for single transverse

spin asymmetries for ±,K±, p, and pbar in √s =200 GeV pp collisions

at RHIC in the xF range of 0.1 to 0.35

• AN(): positive ~(<) AN(): negative: 5-10% in 0.1 < xF < 0.3

AN() for 0.2 <x in agreement with Twist-3 calculations

• First SSA Results on K, p in 0.1 < xF < 0.3

- AN(K) ~ AN(K): positive

- AN(p) ~0, AN(pbar): positive

AN(K) in disagreement with naïve expectation from valence quark fragmentation. Need more theoretical inputs.

Current 62 GeV run will allow Brahms to extend to higher XF.

The PHENIX DetectorThe PHENIX Detector• Philosophy

– high resolution & high-rate at the cost of acceptance

– trigger for rare events

• Central Arms– || < 0.35, ~ – , , e, +-, ... – Identified

– Momentum, Energy

• Muon Arms– 1.2 < || < 2.4

– Momentum (MuTr)

more on PHENIX analysis:more on PHENIX analysis:see: Christine Aidala (tomorrow)see: Christine Aidala (tomorrow)

Phenix Statistics s = 200 GeV

2001-2002 transverse P~15% L= 0.15 pb-1

2003 longitudinal-spin run P~30% L=0.35 pb-1 2004 longitudinal spin P~40% L=0.12 pb-1

2005 longitudinal-spin run P~45%

w/ short transverse run L=0.15 pb-1

2006 transverse (this run) (Radial polarization) P~55% L>2.4 pb-1

Very Forward Neutron～ 1800cm

10cm±3 mradDx magnetblue beam yellow beam

BBCZDC

3 modules: 150X0 5.1λI

Forward counter

SMD

1 ZDC

SMD

position measurementwith scintillators

Calculation of AN

RLRL

RLRLN

NNNN

NNNN

PPA

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• Square-root formula

• Smearing effect -- simulation

Without Minbias With Minbias

LARGE!!

neutron neutronchargedparticles

P~48%

0 and charged hadrons for y~0• Run2 result with ~0.15pb-1, P~15%• gg and qg processes are dominant (with small xB)

– transversity effect is suppressed• May provide infomation on gluon-Sivers effect

PRL 95 (2005)

202001

|| < 0.35

Update on charged pions

• Improved polarization ：　 P=15% in 2001/02, P=47% in 2005 while statistics is smaller. • AN is 0 within 1% interesting contrast with forward

pT (GeV/c)

AN

Conclusions From RHIC Transverse Running at √s=200 GeV

• Small pion/charged track AN asymmetry near y~0• Charged and Neutral Pion AN at Forward Angles large and qualitatively like E706

which took data at an order of magnitude lower energy. Corresponding backward º asymmetries small.

• Unlike Lower Energy, the cross sections are in general agreement with perturbative QCD calculations.

• Nature of forward AN (Collins/Sivers) to be examined with 2006 central di-jets and forward jet analysis.

• Large Neutron Asymmetry at very small forward angles.

•Central di-jet / di-hadron measurements (Sivers Effect) coming soon from Run 6 (STAR/PHENIX).•Forward Photon asymmetries, and Forward jet shape dependence coming soon from Run 6 (STAR). •Higher XF charged AN from BRAHMS (62 GeV running).•Run 7 ?? (STAR forward left/right dijets)