# Presentation: 862990

## BRAHMS Spin and p+p results

**BRAHMS** Spin and p+p results

- 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

## Single transverse Spin Asymmetry (SSA): Introduction

**Single 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?

## Beyond Naïve Parton Models to accommodate large SSA

- 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

## Determination of Single Spin Asymmetry: AN

-  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%)

## SSA 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

-  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:****“CC” (Cherenkov Radiators)**

## Particle 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%

## AN of  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

- 

- 

## Acceptance and Statistics in pT vs xF 

- FS(Front+Back) setting:
- 2.3o+2.3o
- 4o+4o

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

**A****N **

- 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

## 

**p****T**** dependent A****N**** of ************ and **********

- 

- 

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

## Data (+)

- Extrapolated to lower pT region
- Phys. Rev D59 014004 (98)

- Data (+)

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

- 

- 

## AN for Kaons

**A****N**** for Kaons**

- Anselmino and Murgia PLB442 (1998) 470-478

-  BKK FF rescaled

- BKK 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)

## AN of Kaon

**A****N**** 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-

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

- proton and pbar production
-      at high-y, pT
-      :Very different production mechanism (fragmentation vs. baryon transport)
- p/+ >> pbar/- (~x10)

**BRAHMS Preliminary**

## AN 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

## 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**

## Summary

- BRAHMS has obtained particle spectra and 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
- 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.

## BRAHMS 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.

## Theoretical 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

##                    The BRAHMS Collaboration

**I.Arsene****7****, I.G. Bearden****6****, D. Beavis****1****, S. Bekele****6**** , C. Besliu****9****, B. Budick****5****, **
**H. Bøggild****6 ****, C. Chasman****1****, C. H. Christensen****6****, P. Christiansen****6****, R. Clarke****9****, R.Debbe****1****, **
**J. J. Gaardhøje****6****, K. Hagel****7****, H. Ito****10****, A. Jipa****9****, J. I. Jordre****9****, F. Jundt****2****, E.B. Johnson****10****,**
** ****C.E.Jørgensen****6****, R. Karabowicz****3****, E. J. Kim****4****, T.M.Larsen****11****, J. H. Lee****1****, Y. K. Lee****4****,  **
**S.Lindal****1****1****, G. Løvhøjden****2****, Z. Majka****3****, M. Murray****10****, J. Natowitz****7****, B.S.Nielsen****6****, **
**D. Ouerdane****6****, R.Planeta****3****, F. Rami****2****, C. Ristea****6****, O. Ristea****9****, D. Röhrich****8****,  **
**B. H. Samset****11****, D. Sandberg****6****, S. J. Sanders****10****, R.A.Sheetz****1****, P. Staszel****3****, **
**T.S. Tveter****11****, F.Videbæk****1****, R. Wada****7****, H. Yang****6****, Z. Yin****8****,**** ****and I. S. Zgura****9**** **
**1****Brookhaven National Laboratory, USA, ****2****IReS and  Université Louis Pasteur, Strasbourg, France**
**3****Jagiellonian University, Cracow, Poland, **
**4****Johns Hopkins University, Baltimore, USA,**** 5****New York University, USA**
**6****Niels Bohr Institute,  University of Copenhagen, Denmark**
**7****Texas A&M University, College Station. USA, ****8****University of Bergen, Norway **
**9****University of Bucharest, Ro****mania,**** ****10****University of Kansas, Lawrence,USA   **
**11**** University of Oslo Norway **

**                   ****The BRAHMS Collaboration**

##                             Back-Up Slides

-                          **B**raod **RA**nge **H**adron **M**agnetic **S**pectrometers
- 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

## Kinematic 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*

## Relative luminosity L = L+ /L-  determination

- 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

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

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

## - Spin-Up/Spin-Down

## - / -xF