BRAHMS Spin and p+p results

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BRAHMSBRAHMS Spin and p+p Spin and p+p resultsresults

J.H. Lee (BNL)for BRAHMS Collaboration

• Short Introduction• Preliminary Results on ,K,p Single Spin

Asymmetries and Spectra from Run5 at high-xF/rapidities• Summary/Prospects

June 8th 2006 RHIC Users’ Meeting

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

• Asymmetries are defined as 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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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 pb-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 Run5

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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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Particle Identification using RICHParticle Identification using RICH

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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AANN of of and and

• FS (Front+Back) setting: 2.3°+2.3° and 4°+4°• Statistical errors only• Systematic error estimated ~ 25%• point-to-point variations include pT-dependence of AN

from <pT> variations in xF bins • 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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ppTT dependent A dependent ANN of of and and

• xF and pT dependence: increasing with xF and decreasing with pT

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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 FFK+

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

• proton and pbar production at high-y, pT

:Very different production mechanism (fragmentation vs. baryon transport)

• p/+ >> pbar/- (~x10)

BRAHMS

Preliminary

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AANN of proton and pbar of proton and pbar

• AN(pbar) ≠ 0 and positive • AN(p) ~ 0: At this kinematic region, protons are mostly from

polarized beam proton, but only ones showing AN ~0 • Need theoretical inputs

p

pbar

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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 mKKP (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)

BRAHMS

Preliminary

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SummarySummary

BRAHMS has obtained particle spectra and 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• Cross-section described by NLO pQCD (with updated/modified

FFs)• Proton production requires extra production mechanism in

addition to fragmentation even at high-pT • AN(): positive ~(<) AN(): negative: 5-10% in 0.1 < xF < 0.3 increasing with xF and decreasing with pT

AN() 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 of small sea quark polarization. Lack of understanding of p, pbar

polarization: Need more theoretical inputs.

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BRAHMS SSA Measurements at 62 GeVBRAHMS SSA Measurements at 62 GeV

• BRAHMS will measure SSA at 62 GeV in RHIC/Run6

• 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: -Expect to have interesting results from 62 GeV Run6 -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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Back-Up SlidesBack-Up Slides

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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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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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Anti-particle/Particle ratios at y~3 and NLO comparisons Anti-particle/Particle ratios at y~3 and NLO comparisons

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-- Spin-Up/Spin-Down Spin-Up/Spin-Down

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- - / -x/ -xFF