# Presentation: 342193

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

_**[Transverse Single-Spin asymmetries for ](http://www.aps.org/meet/DNP04/baps/abs/S600.html#SBE.010)**__**[p](http://www.aps.org/meet/DNP04/baps/abs/S600.html#SBE.010)**__**[+ and ](http://www.aps.org/meet/DNP04/baps/abs/S600.html#SBE.010)**__**[p](http://www.aps.org/meet/DNP04/baps/abs/S600.html#SBE.010)**__**[- production from pp collisions at _](http://www.aps.org/meet/DNP04/baps/abs/S600.html#SBE.010)**__**[](http://www.aps.org/meet/DNP04/baps/abs/S600.html#SBE.010)**__**[S](http://www.aps.org/meet/DNP04/baps/abs/S600.html#SBE.010)**__**[NN](http://www.aps.org/meet/DNP04/baps/abs/S600.html#SBE.010)**__**[= 200 GeV](http://www.aps.org/meet/DNP04/baps/abs/S600.html#SBE.010)**_

- Introduction
- Measurements, Kinematic variables
- Corrections and checks
- Preliminary Physics results
- Conclusion and Prospects

**F.Videbaek**

- Single Spin Asymmetries in BRAHMS , DNP 2004

- October 27,   2004

**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.

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

- Single Spin Asymmetries in BRAHMS , DNP 2004

- October 27,   2004

## 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.

- +

- -

- 0

- Single Spin Asymmetries in BRAHMS , DNP 2004

- October 27,   2004

## The BRAHMS Spectrometer

- Single Spin Asymmetries in BRAHMS , DNP 2004

- October 27,   2004

## 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).

- Note the correlation between xF and pT as characteristic for a fixed angle spectrometer.
- The momentum resolution is p/p~1% at 22 GeV/c.

- Single Spin Asymmetries in BRAHMS , DNP 2004

- October 27,   2004

## Formula for raw asymmetries.

- Asymmetries are determined from An =  /P 
- The polarization P of the beams was ~40-45% in the RHIC Run-4
- With   = (N+ - N-) / (N+ + N+ where the yield of pions in a given kinematic bin with the beam spin direction is  N+ (up) and N- (down).
- For non-uniform bunch intensities
- = (N+ /L+ - N-/L-) / (N+ /L+ + N-/L-)
-   = (N+ - L*N-) / (N+ + L*N-) where L = L+ / L-
- 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 , DNP 2004

- October 27,   2004

## Event Selection Criteria

- Clean Track through spectrometer and in time with the RHIC 110 nsec clock.
- Momentum determined from 3 measurements.
- -30< 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 , DNP 2004

- October 27,   2004

**Notes:**
Low luminosity,

## PID using RICH

- Mass determined from momentum and Radius measured in a Ring Imaging Cherenkov Counter.

- P (GeV/c)

**PID using RICH**

- Single Spin Asymmetries in BRAHMS , DNP 2004

- October 27,   2004

## Individual bins for PID

**Individual bins for PID**

- The pion identification is clean up to 35 GeV.
**Now to results**

- R (cm)

- 

- K

- P

- Single Spin Asymmetries in BRAHMS , DNP 2004

- October 27,   2004

## +   vs. xF * 100

******+  ******** vs. x****F**** * 100**

******N**** **= +0.05 +- 0.005 +- [0.015]  in 0.17 < xF < 0.32

- BRAHMS preliminary

- Single Spin Asymmetries in BRAHMS , DNP 2004

- October 27,   2004

## -   vs. xF * 100

******-****  ******** vs. x****F**** * 100**

******N**** **= -0.08 +- 0.005 +- [0.015]  in 0.17 < xF < 0.32

- BRAHMS preliminary

- Single Spin Asymmetries in BRAHMS , DNP 2004

- October 27,   2004

##  -  and + with yellow Polarization pattern.

- BRAHMS preliminary

** ********-  ****and ********+ ****with yellow Polarization pattern.**

- This corresponds to negative xF, and is consistent with 0
- as expected.

- Single Spin Asymmetries in BRAHMS , DNP 2004

- October 27,   2004

**Notes:**
This plot is final in reagrd to sign

## The proton An is consistent with 0. Analyzing power

- BRAHMS preliminary

- e

- 

- Pl (GeV)

- Single Spin Asymmetries in BRAHMS , DNP 2004

- October 27,   2004

## Conclusions

- BRAHMS has obtained the first preliminary result for single spin asymmetries for + and - in 200 GeV pp collisions at RHIC in the xF range of 0.17 to 0.32.
- The value for + and - are significantly different with opposite sign, and the - < 0 at ~ 3 sigma level and at ~ 1.5 sigma level
- The sign of An is consistent with behaviour from lower energy.
- An at negative xF for + and - are consistent with 0 (as also found by STAR for 0)
- The protons are found to have AN ~0
- The upcoming Run-5 should enable BRAHMS to extend the measurements to xF ~ 0.45 and to get some information on p-dependence at xF~0.25

- Single Spin Asymmetries in BRAHMS , DNP 2004

- October 27,   2004

## Backup Slides

- Single Spin Asymmetries in BRAHMS , DNP 2004

- October 27,   2004

## Single-Spin Asymmetries at RHIC

- Large spin effects reported for 0 by STAR for *s* = 200 GeV *pp* collisions

**STAR PRL 92,06230(2004)**

- Single Spin Asymmetries in BRAHMS , DNP 2004

- October 27,   2004

## Measurement of AN for forward 0 production at s=200GeV

- Measurement of AN for forward 0 production at s=200GeV

**Positive A****N**** at large positive x****F **** has been confirmed**
** **Larger significance to be non-zero & positive than published data
**The**** ****first measurement of negative x****F**** A****N**** has been done, and is consistent with zero**
****** **Sensitive to twist-3 gluon-gluon correlation

**STAR Preliminary**

**Statistical error only for <********>=4.1**** **

- Single Spin Asymmetries in BRAHMS , DNP 2004

- October 27,   2004