Rhic results on transverse spin
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2nd Workshop on the QCD Structure of the Nucleon June 12-16, 2006 Villa Mondragone Monte Porzio Catone, Rome, Italy. RHIC Results on Transverse Spin. Steve Heppelmann Penn State University. Three RHIC Experiments are producing results on Transverse Single Spin Asymmetries A N.

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RHIC Results on Transverse Spin

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2nd Workshop on the QCD Structure of the Nucleon

June 12-16, 2006

Villa Mondragone

Monte Porzio Catone,

Rome, Italy

RHICResults on Transverse Spin

Steve Heppelmann

Penn State University


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


From Abhay Deshpande


STAR 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

  • FPD

    • Run 3-5 data

    • pp, dAu

    • (Preliminary An Results)

FMS Forward Meson

Spectrometer

Run 7 2006

(hep-ex/0502040).


FMS Design

Forward Calorimeters

FPD Run 3-5 (2003-2005)

FPD++ Run 6 (2006)

FMS Run 7- (2006- )


y

Barrel EMC

Endcap

EMC

x

-1

0

1

2

-units

Opening angle

kTx>0

kTx<0

STAR Central Region

Reconstructed di-jets from

EM calorimeter only trigger data:

Run 2

PRELIMINARY

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 angle

transverse spin dependence.


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].

Similar asymmetry to many lower energy

measurements. →

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.

But now, for the first time,

in a region where NLO PQCD calculations

fairly accurately predict the cross section.


Caveats:

-RHIC CNI Absolute polarization still preliminary.

-Result Averaged over azimuthal

acceptance of detectors.

-Positive XF (small angle

scattering of the polarized proton).

Run 2 Published Result.

Run 3 Preliminary Result.

-More Forward angles.

-FPD Detectors.

Run 3 Preliminary

Backward Angle Data.

-No significant Asymmetry

seen.

( Presented at Spin 2004:

hep-ex/0502040)

Run 3 + Run 5 Preliminary <>=3.7,4.0

(Presented SPIN 2005 Dubna Sept 27-Oct 1)


STAR

pp  π0 + X cross sections at 200 GeV

nucl-ex/0602011

  • 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.

NLO pQCD calculations by Vogelsang, et al.


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

FPD++

hardware-level calibration

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

    • Greatly improve measurement of AN(XF,pT)

  • Determine if large asymmetry comes from the jet axis or is produced within the jet.


BRAHMS Results


p+

AN of proton and pbar

p-

K+

K-


BRAHMS Summary (FROM DIS 2006)

BRAHMS has obtained preliminary results for single transverse

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

at RHIC in the xF range of 0.1 to 0.35

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

    AN(p+) 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 Detector

  • Philosophy

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

    • trigger for rare events

  • Central Arms

    • |h| < 0.35, Df ~ p

    • g, p0, e, p+-, ... – Identified

    • Momentum, Energy

  • Muon Arms

    • 1.2 < |h| < 2.4

    • Momentum (MuTr)

more on PHENIX analysis:

see: Christine Aidala (tomorrow)


Phenix Statisticss = 200 GeV

2001-2002 transverseP~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


ZDC

Forward counter

SMD

1 ZDC

3 modules: 150X0 5.1λI

Very Forward Neutron

~1800cm

10cm

blue beam

yellow beam

±3 mrad

Dx magnet

SMD

BBC

position measurement

with scintillators


charged

particles

neutron

neutron

Calculation of AN

P~48%

  • Square-root formula

  • Smearing effect -- simulation

LARGE!!

Without Minbias

With Minbias


p0 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

|h| < 0.35

PRL 95 (2005)

202001


Update on charged pions

AN

pT (GeV/c)

  • Improved polarization: P=15% in 2001/02, P=47% in 2005

  • while statistics is smaller.

  • AN is 0 within 1%  interesting contrast with forward p


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)


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