1 april 21 dis2006 j.h. lee (bnl) ssa in brahms j.h. lee (bnl) for brahms collaboration dis2006,...

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April 21 DIS2006 J.H. Lee (BNL)

SSA in BRAHMSSSA in BRAHMS

J.H. Lee (BNL)for BRAHMS Collaboration

DIS2006, Tsukuba, April 2006

• Short Introduction• Preliminary results on ,K,p SSA from RHIC/Run-5 • Summary/Prospects

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Single transverse Spin Asymmetry (SSA): IntroductionSingle transverse Spin Asymmetry (SSA): Introduction

• Large SSAs have been observed at forward rapidities in hadronic reactions: E704/FNAL and STAR/RHIC

• SSA is suppressed in naïve parton models (~smq/Q )

• Non-zero SSA at partonic level requires- Spin Flip Amplitude, and - Relative phase

• SSA: Unravelling the spin-orbital motion of partons?

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Beyond Naïve Parton Models to accommodate large Beyond Naïve Parton Models to accommodate large SSASSA

• Spin and Transverse-momentum-dependent parton distributions

-Final state in Fragmentation (Collins effect), -Initial state in PDF (Sivers effect) • Twist-3 matrix effects -Hadron spin-flip through gluons and hence the quark

mass is replaced by ΛQCD

-Efremov,Teryaev (final state) -Qiu,Sterman (initial state) • Or combination of above -Ji, Qiu,Vogelsang,Yuan…

Challenge to have a consistent partonic description: -Energy dependent SSA vs xF,pT,

-Flavor dependent SSA -Cross-section

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SSA measurements in BRAHMSSSA measurements in BRAHMS

BRAHMS measures identified hadrons (,K,p,pbar) in kinematic ranges of 0<Y<3.5 and 0.2 <pT<4

• pT dependent SSA in 0 < x < 0.35 (and

-0.35 < x < 0) utilizing blue (and yellow) beam (xF, pT, flavor dependent AN)

• Cross-section of hadron production (Theoretical consistency)Data: • Run-4: First SSA measurements in BRAHMS• Run-5: pp at √s = 200 GeV 2.5 nb-1 recorded (this Talk)• Run-6: pp at √s = 62 GeV planned (Energy dependence)This talk will focus on AN(,K,p,pbar) in 0.1 < x < 0.35 from Run-5

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Braod RAnge Hadron Magnetic Spectrometers• Designed to study nuclear reactions in broad kinematic range (y-pT)• 2 movable spectrometers with small solid angle measuring charged identified

hardrons precisely• Min-Bias Trigger Detector for pp (run05): ”CC” counter• Local polarimeter, SMD in Run-5 pp (analysis in progress)• 53 people from 12 institutions from 5 countries

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Kinematic Variables and AcceptancesKinematic Variables and Acceptances

• The kinematic variables used for SSA: Feynman-x (xF) and pT

• Shown is the BRAHMS acceptance for the data taken at = 2.3° and the maximum field setting (7.2 Tm).

• Strong xF-pT correlation due to

limited spectrometer solid angle acceptance

• The momentum resolution is p/p~1% at 22 GeV/c

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RICH Particle IdentificationRICH Particle Identification

Multiple settings

• PID for the analysis: Ring Image Cherenkov Counter• ,K identification < 30 GeV/c and proton,pbar > 17 GeV/c with efficiency ~ 97%

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• Covers ~70% of pp inelastic cross-section (41mb)• 3.25 < ||< 5.25 range• Vertex resolution (z)~ 1.6cm• Main relative luminosity monitor for SSA analysis • ±80cm in z used in the analysis

Min-Bias Trigger / Normalization Counter:Min-Bias Trigger / Normalization Counter:“CC” (Cherenkov Radiators)“CC” (Cherenkov Radiators)

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Determination of Single Spin Asymmetry: ADetermination of Single Spin Asymmetry: ANN

• Asymmetries are defined

AN = /P • For non-uniform bunch intensities

= (N+ /L+ - N-/L-) / (N+ /L+ + N-/L-) = (N+ - L*N-) / (N+ + L*N-) where L = relative luminosity = L+ / L-

and the yield of in a given kinematic bin with the beam spin direction is N+ (up) and N- (down).• The polarization P of the beam was ~50% in the RHIC Run-5 (Blue beam)• Beam polarization P from on-line measurements:(systematic uncertainty ~15%)

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Relative luminosity Relative luminosity L = L+ /L- determinationdetermination

• Using CC in spin scaler 80cm• Consistent with CC recorded in data stream• Relative luminosity calculated by Beam-Beam Counter and CC: < 0.3%• Systematic effect on bunch number dependent beam width: negligible

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AANN of of and and

• FS (Front+Back) setting: 2.3°+2.3° and 4°+4°• Statistical errors only• Systematic error estimated ~ 25%

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

• pT range is limited by PID and statistics

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Acceptance and Statistics in pAcceptance and Statistics in pTT vs x vs xF F

FS(Front+Back) setting:2.3o+2.3o

4o+4o

FS(Front+Back) setting:3o+2.3o

AN

Counts

• Statistically Challenging to do 2-d analysis

• Indication of pT dependence:

AN decrease with pT at fixed xF

• Lower field settings to cover lower pT and extending PID is in progress

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Twist-3 (initial state) calculations by Qiu and Sterman: Extrapolated to lower pT regionPhys. Rev D59 014004 (98)

Data (+)

Data vs Theory (Twist-3) for Data vs Theory (Twist-3) for ++

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AANN for Kaons for Kaons

Anselmino and Murgia PLB442 (1998) 470-478

BKK FF rescaledBKK FF

K+

K-

• Strong strangeness FF dependence in prediction

• If main contribution to AN at large xF is from valence quarks: AN(K+)~AN(+), K- ~0

• BKK (Binnewies, Kniehl, Kramer 1995)

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AANN of Kaon of Kaon

• AN(K): positive ~ AN(K): positive ≠ 0 for 0.2 <xF <0.3

• AN for lower and higher xF require including extended PID and lower field setting data: Work in progress but statistically challenging

• Consistent with un-scaled BKK FF: in disagreement with naïve expectations

K+

K-

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Forward proton and pbar production in pp at √s=200 Forward proton and pbar production in pp at √s=200 GeVGeV

• Very different production mechanism (baryon transport) for p and pbar at forward

• p/+ >> pbar/- (~x10)

BRAHM

S

Preliminary

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AANN of proton and pbar of proton and pbar

• AN(pbar) ≠ 0 and positive

• AN(pbar) ~ AN(K-)? Accidental?

• AN(p) ~ 0: At this kinematic region, protons are mostly from polarized beam proton, but only ones showing AN ~0

• Need theoretical inputs

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Charged Hadron production at Forward vs NLO pQCD Charged Hadron production at Forward vs NLO pQCD

• NLO pQCD describes data at forward rapidity at 200 GeV• - ,K- are described best by KKP (Kniehl-Kramer-Potter) than Kretzer

FF• pbar is described best by AKK (Albino-Kniehl-Kramer) FF (light flavor

separated) (NLO pQCD Calculations done by W. Vogelsang. mKKP: “modified” KKP for charge separations for and K)

BRAHM

S

Preliminary

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SummarySummary

BRAHMS has obtained preliminary results for single transverse spin asymmetries for ±,K±, p, and pbar in √s =200 GeV pp

collisionsat 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.

BRAHMS Also measured cross-sections for ±,K±, p, and pbar in the same kinematic ranges described by NLO pQCD (withupdated/modified FFs)

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BRAHMS SSA Measurement at 62 GeVBRAHMS SSA Measurement at 62 GeV

• BRAHMS will measure SSA at 62 GeV in RHIC/Run06

• Acceptance will reach kinematic limit, but SSA measurement up to xF~ 0.6 with statistical significance

• Measurements at 62 GeV offers an opportunity to address an intermediate energy (RHIC-FNAL) to clarify to what degree the SSA are describable by pQCD, or is a ‘soft’ physics effect.

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Theoretical ChallengesTheoretical Challenges

• BRAHMS xF, pT, flavor, and energy-dependent SSA and cross-section measurements:

ingredient for consistent (partonic) description at RHIC energy regime:

Exciting theoretical challenges

• We will work on our part: -Minimizing experimental systematic uncertainties -Extending kinematic coverage

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I.Arsene7, I.G. Bearden6, D. Beavis1, S. Bekele6 , C. Besliu9, B. Budick5, H. Bøggild6 , C. Chasman1, C. H. Christensen6, P. Christiansen6, R. Clarke9,

R.Debbe1, J. J. Gaardhøje6, K. Hagel7, H. Ito10, A. Jipa9, J. I. Jordre9, F. Jundt2, E.B.

Johnson10, C.E.Jørgensen6, R. Karabowicz3, E. J. Kim4, T.M.Larsen11, J. H. Lee1, Y. K.

Lee4, S.Lindal11, G. Løvhøjden2, Z. Majka3, M. Murray10, J. Natowitz7, B.S.Nielsen6,

D. Ouerdane6, R.Planeta3, F. Rami2, C. Ristea6, O. Ristea9, D. Röhrich8, B. H. Samset11, D. Sandberg6, S. J. Sanders10, R.A.Sheetz1, P. Staszel3, T.S. Tveter11, F.Videbæk1, R. Wada7, H. Yang6, Z. Yin8, and I. S. Zgura9

1Brookhaven National Laboratory, USA, 2IReS and Université Louis Pasteur, Strasbourg, France3Jagiellonian University, Cracow, Poland,

4Johns Hopkins University, Baltimore, USA, 5New York University, USA6Niels Bohr Institute, University of Copenhagen, Denmark

7Texas A&M University, College Station. USA, 8University of Bergen, Norway 9University of Bucharest, Romania, 10University of Kansas, Lawrence,USA

11 University of Oslo Norway

The BRAHMS CollaborationThe BRAHMS Collaboration

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Backup SlidesBackup Slides

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MRS: hMRS: h-- in 0.5<p in 0.5<pTT<1 GeV/c and 1<p<1 GeV/c and 1<pTT<1.5 GeV/c <1.5 GeV/c

1 april 21 dis2006 j.h. lee (bnl) ssa in brahms j.h. lee (bnl) for brahms collaboration dis2006,...

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