# Presentation: 342212

## Transverse Single-Spin asymmetries for p+ and p- production from pp collisions at _S =  200 GeV

- Introduction
- Experimental setup and considerations
- Preliminary Physics results
- Conclusion and Prospects

**F.Videbaek**

- Single Spin Asymmetries in BRAHMS

- PANIC, October 27,   2005

**Notes:**
Not a physics talk Polarization
Bunch dependent luminosities
Systematic errors
Experimental Checks

## Introduction

- Early  (naive) QCD predicted this effect to be small
- Non-zero Single Transverse Spin Asymmetry (SSA/ An) requires
- Spin Flip Amplitude and phase difference in intrinsic states
- Such studies may clarify  properties of transverse quark structure of the nucleon
**Sivers effect ****[Phys Rev D41 (1990) 83; 43 (1991) 261]**
-       Flavor dependent correlation between the proton spin , momentum  and transverse momentum  of the un-polarized partons inside the proton.
**Collins effect ****[Nucl Phys B396 (1993) 161]**
-      Correlation between the quark spin, momentum and transverse momentum  of the pion.

- An = (+ - -) / (+ + -)
- Where the spin cross section is determined with the spin direction defined by kb x kpi

- Single Spin Asymmetries in BRAHMS

- PANIC, October 27,   2005

## Background

**Background**

- Low energy data (FNAL E704 ) show clear differences between  +- and 0.

- D.L.Adams (E704) Phys.Lett B264,462(1991); Phys.Rev. D53, 4747 (1996).
- Recent STAR results on 0 also shows a significant SSA/ An at RHIC energies.
- Preliminary BRAHMS data was shown at DIS05.

- +

- -

- 0

- Single Spin Asymmetries in BRAHMS

- PANIC, October 27,   2005

**Notes:**
Add STAR data??

## RHIC beam transversely polarized at BRAHMS detector

- Single Spin Asymmetries in BRAHMS

- PANIC, October 27,   2005

**Notes:**
RHIC complex

## The BRAHMS Spectrometer

- Single Spin Asymmetries in BRAHMS

- PANIC, October 27,   2005

## Kinematic Variables

- The kinematic variables of interest are Feynman x (xF) and pT.
- Shown is the BRAHMS acceptance for the data taken at = 2.3 deg and the maximum field setting (7.2 Tm).
- The acceptance is not *straight* in angle or . Illustrated in this plot. Thus care should be taken when comparing to both other experiments and to theory.

- The momentum resolution is p/p~1% at 22 GeV/c.

- Single Spin Asymmetries in BRAHMS

- PANIC, October 27,   2005

## Determination of Asymmetries.

- Asymmetries are determined from
- An = (+ - -) / (+ + -)
- Experimentally determined from
- An = /P (N+ - L*N-) / (N+ + L*N-),
-  where L = L+ / L-
- Need to know
-  **Beam Polarization**
-  Bunch Luminosities
-  Pion rates in spectrometer

- Single Spin Asymmetries in BRAHMS

- PANIC, October 27,   2005

## Bunch Polarization

- These are obtained from the CNI online polarimeter normalized to a Gas Jet Target measurements

- Single Spin Asymmetries in BRAHMS

- PANIC, October 27,   2005

## Determination of Asymmetries.

- Asymmetries are determined from
- An = (+ - -) / (+ + -)
- Experimentally determined from
- An = /P (N+ - L*N-) / (N+ + L*N-),
-  where L = L+ / L-
- Need to know
-  Beam Polarization
-  **Bunch Luminosities**
-  Pion rates in spectrometer

- Single Spin Asymmetries in BRAHMS

- PANIC, October 27,   2005

## Bunch Luminosities

- Bad bunches with different intensity outside norm is rejected.
- L+/L- ~ 1.05-1.15 typical factors
- Run-5 have more systematic check with varying patterns.
- Since the up and down spin patterns alternate most time-dependent systematic errors are small. The main issue is determination of the L+  and  L-.

- Single Spin Asymmetries in BRAHMS

- PANIC, October 27,   2005

## Luminosityvariation vs. runs

- Single Spin Asymmetries in BRAHMS

- PANIC, October 27,   2005

## Determination of Asymmetries.

- Asymmetries are determined from
- An = (+ - -) / (+ + -)
- Experimentally determined from
- An = /P (N+ - L*N-) / (N+ + L*N-),
-  where L = L+ / L-
- Need to know
-  Beam Polarization
-  Bunch Luminosities
-  **Pion rates in spectrometer**

- Single Spin Asymmetries in BRAHMS

- PANIC, October 27,   2005

## PID using RICH

**PID using RICH**

- Good track are selected in spectrometer; determining momenta.
- Pions identified from momentum and radius measured in a Ring Imaging Cherenkov Counter.
- The pion identification is clean up to 35 GeV.
- Measured radius vs. calculated showing the selected pions

- p

- P GeV/c

- Single Spin Asymmetries in BRAHMS

- PANIC, October 27,   2005

## Hadron Spectra

-  pp - spectrum over 7 orders of magnitude
- Spectra for other charged hadrons are forth coming
- Such spectra will provide a testing ground for pQCD

- Single Spin Asymmetries in BRAHMS

- PANIC, October 27,   2005

## AN measurements for -

- Measurements at 2.3 and 4 degrees.
- Results averages of pT range in each setting.

- Pz

- Single Spin Asymmetries in BRAHMS

- PANIC, October 27,   2005

## Summary of pT dependence

- 0.15-0.30 in Xf
- AN(pi-) 0.078+-0.002 low pT
- AN (pi-) 0.045+-0.003 higher pT
- AN (pi+) 0.066+-0.002 low pT

- Systematic errors from online polarization is (presently estimated at ~20% [scale] )

- Single Spin Asymmetries in BRAHMS

- PANIC, October 27,   2005

## Twist 3 (initial state) calculations by J.Qiu and G.Sterman, Phys.ReV.D59,014004(98)

- Extrapolated to lower pT

- 2.3 deg

- Single Spin Asymmetries in BRAHMS

- PANIC, October 27,   2005

## Comparison to data within acceptance.

- The AN  for + in the theory is ~ AN for - with opposite sign
- The theory does predict a lowering at higher pTand a nearly flat distribution with xF in the acceptance.

- Single Spin Asymmetries in BRAHMS

- PANIC, October 27,   2005

## Other results.

- Using polarization from opposite beam (yellow), we obtain AN equivalent to asymmetries for negative xF

- Brahms will also access other charged hadrons; p+-, K+-.

- Single Spin Asymmetries in BRAHMS

- PANIC, October 27,   2005

## Conclusions

- BRAHMS has obtained the preliminary result for single spin asymmetries for + and - in 200 GeV pp collisions at RHIC in the xF range of 0.17 to 0.35
- The AN values for + and - are significantly different with opposite sign
- The absolute AN value for - decrease with increasing pT
- The sign of An is consistent with behavior from lower energy data
- An at negative xF for + and - are consistent with 0 The protons are found to have AN ~0

- Single Spin Asymmetries in BRAHMS

- PANIC, October 27,   2005

## The BRAHMS Collaboration

**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****6,9****, 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****12**** **
**1****Brookhaven National Laboratory, USA, ****2****IReS and  Université Louis Pasteur, Strasbourg, France**
**3****Jagiellonian University, Cracow, Poland,  ****12****Institute of Space Science,Bucharest**
**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 **
**48 physicists from 11 institutions**

**The BRAHMS Collaboration**

- Single Spin Asymmetries in BRAHMS

- PANIC, October 27,   2005

## Backup

- Single Spin Asymmetries in BRAHMS

- PANIC, October 27,   2005

## Backup- STAR RHIC data

- Single Spin Asymmetries in BRAHMS

- PANIC, October 27,   2005

## Event characterization

**Global Detectors in use for luminosity measures, and inelastic pp cross section**
**Triggers are defined with the CC,Inel ZDC and BB; p+p collisions were triggered with the INEL/CC detectors**.

**Event characterization**

- Single Spin Asymmetries in BRAHMS

- PANIC, October 27,   2005

## Vertex determination

- Vertex Calculated from timing measurements in sets of counters CC position on each side of IP covering roughly 2 < || < 5.2.
- Z-resolution is ~ 2 cm in Run-4
- The spectrometer accepts track weighted towards negative Z

- Single Spin Asymmetries in BRAHMS

- PANIC, October 27,   2005

## Event Selection Criteria

- Clean track through spectrometer and in time with the RHIC 108 nsec clock.
- Momentum determined from 3 measurements.
- -40< Z_Vertex <30 (Vertex from collision) determined from global detectors (INL, BB, ZDC)
- Track points to collision vertex (in Z and Y)
- Good Bunches Only (selected per store)
- Select pions using RICH for particle identification.

- Single Spin Asymmetries in BRAHMS

- PANIC, October 27,   2005

**Notes:**
Low luminosity,

- Single Spin Asymmetries in BRAHMS

- PANIC, October 27,   2005