# Presentation: 008378

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

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

**F.Videbaek**

- Single Spin Asymmetries in BRAHMS

- June 21,   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.

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

- Single Spin Asymmetries in BRAHMS

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## 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

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## The BRAHMS Spectrometer

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## 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

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## New Min-Bias Counter for pp 

**New Min-Bias Counter for pp **

- “CC” Counter –
-       Cherenkov Counter
- Installed for pp05
- Covers ~70% of pp inelastic cross-section
- Vertex resolution
-       ~ 2cm

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## 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

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## BRAHMS acceptance

- The acceptance is not *straight* in angle or . Illustrated in this plot. Thus care should be taken when comparing to both other experiments (STAR) and to theory.

- 

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## Determination of raw asymmetries.

- Asymmetries are determined from An =  /P 
- The polarization P of the beam was ~42% in the RHIC Run-4 (Blue beam)
- 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

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## 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

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**Notes:**
Low luminosity,

## Vertex determination

- Vertex Calculated from timing measurements in sets of counters INEL position on each side of IP covering roughly 2 < || < 5.2.
- Z-resolution is ~ 10 cm in Run-4
- The spectrometer accepts track weighted towards negative Z

- Single Spin Asymmetries in BRAHMS

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## Bunch Pattern Selection

- Bad bunches with different intensity outside norm is rejected.
- L+/L- ~ 1.05-1.15 typical factors
- Current run-5 have more systematic check with varying patterns.

- Single Spin Asymmetries in BRAHMS

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## PID using RICH

- Mass determined 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

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## Yields that can be used for analysis

|  | positive | negative |
| --- | --- | --- |
| pion | 219K | 216K |
| kaon | 46K | 26K |
| proton | 165K | 17K |

- Integrated yields of ,K and proton in xF range 0.15-0.35

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## Data of AN for +  and - 

******N**** **= -0.08 +- 0.005 +- [0.02]  in 0.17 < xF < 0.32

******N**** **= +0.05 +- 0.005 +- [0.015]  in 0.17 < xF < 0.32

- Polarization was ~42% for ******+**** **measurements and ~38% for ******-****.**
- Systematic scale error on P ~ 20-30%. Will improve final final analysis of CNI and Gas Jet data.

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##  -  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

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

## The proton An is also consistent with 0. 

- The proton An is also consistent with 0.

- BRAHMS preliminary

- e

- 

- Pl (GeV)

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

- Extrapolated to lower pT

- 2.3 deg

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## Comparison to data within acceptance.

- Single Spin Asymmetries in BRAHMS

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## SSA calculations by U.Alesio & F.Murgia PRD70,074009(04); hep-ph/0412317 & private comm.

- pQCD approach, including Sivers functions determined from the E704 data.
- Asymmetry for pi+,pi-.
- Data indicates the opposite trend.

- Single Spin Asymmetries in BRAHMS

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## Current RHIC Run

- RHIC Run-5 is just underway.
- Increased luminosity
- Polarization ~45-55%
- New vertex detector with Z ~ 2 cm.
- Additional bunch luminosity measures.

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## 2.3 deg

- Goal

- 4 deg

- 3/2.3

- Calculated by min-bias trigger (“CC trigger”)
-  covering ~70% of pp inelastic cross-section
- Goal Assumed:
-  -Recorded/Delivered ~0.5
-  -Blue Polarization = 45%

- Reference spectra

- 2.3 deg pi-

- 2.3 deg pi+

- 3/2.3 – high xF/Pt

- 2.3 deg K+/K-

- Ref spectra revisited

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## Preliminary Run-5 Data

- Very preliminary data from Run-5 confirms the run-4 measurements.
- Data from just  1(2) stores. Total statistics ~10-20 times this.

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## PT-xF acceptance

- The measurements at 4 deg in addition to 2.3 deg will allow for some pt coverage.

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## Expectations for 4 deg

- Statistics obtained for one run

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## 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 AN 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 behavior 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

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## Summary

- The ongoing 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
- RICH operating mode was be changed to get K+/K- out to about 35 GeV/c (xF ~ 0.4)

- Single Spin Asymmetries in BRAHMS

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## The BRAHMS Collaboration

**I.Arsene****10****,I.G. Bearden****7****, D. Beavis****1****, S.Bekele, C. Besliu****10****,,**
** ****B. Budick****6****,H. Bøggild****7 ****,C. Chasman****1****, C. H. Christensen****7****, P. Christiansen****7****,**
**J.Cibor****4****,R.Debbe****1****, E.Enger,J. J. Gaardhøje****7****, ****M. Germinario****7****, K. Hagel****8****,**
**  ****H. Ito****1****, A. Jipa****10****, E.B.Johnson, J. I. Jordre****10****, F. Jundt****2,**** C.E.Jørgensen****7****, R.Karabowisz, **
**E. J. Kim****5****, T. Kozik****3****, T.M.Larsen****12****, J. H. Lee****1****, Y. K.Lee****5****,S.Lindahl, R.Lystad, **
**G. Løvhøjden****2****, Z. Majka****3****, M. Murray****8****,**
** ****J. Natowitz****8****,B.S.Nielsen****7****, D. Ouerdane****7****, R.Planeta****4****, F. Rami****2****, **
**D. Roehrich****9****, C.Ristea, O.Ristea, B. H. Samset****12****, S. J. Sanders****11****, R.A.Sheetz****1,**** **
**P. Staszel****7****, T.S. Tveter****12****, F.Videbæk****1****, R. Wada****8**** ,H.Yang, Z. Yin****9, ****I. S. Zgura****10**
**1****Brookhaven National Laboratory, USA, ****2****IReS and  Université Louis Pasteur, Strasbourg, France**
**3****Jagiellonian University, Cracow, Poland, ****4****Institute of Nuclear Physics, Cracow, Poland**
**7****Niels Bohr Institute, Blegdamsvej 17, University of Copenhagen, Denmark**
**8****Texas A&M University, College Station. USA, ****9****University of Bergen, Norway **
**10****University of Bucharest, Ro****mania,**** ****11****University of Kansas, Lawrence,USA   **
**12**** University of Oslo Norway**** **

- - 12 institutions-

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## What is sensitivity to fragmentation.

- From same paper:
- SSA calculations by U.D’Alesio & F.Murgia PRD70,074009(04);
- Small differences- possibly not distinguishable within our data stat and systematic.

- For STAR kinematic acceptance.

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## +   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

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## -   vs. xF * 100

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

******N**** **= -0.08 +- 0.005 +- [0.02]  in 0.17 < xF < 0.32

- BRAHMS preliminary

- Single Spin Asymmetries in BRAHMS

- June 21,   2005