# Presentation: 363186

## Single Spin Asymmetries for charged pions. Overview

- One physics slide
- What is measured, kinematic variables
- Corrections and issues
- Polarization
- Bunch dependent luminosities
- Systematic errors
- Experimental Checks
- Preliminary Physics results
- Will value your comments to analysis and results.
- Results will be presented at DNP by me on Thursday and was also shown at the *forward physics workshop* in Lawrence last week.

- Single Spin Asymmetries

- October 14,   2004

**Notes:**
Not a physics talk

## Transverse Single-Spin Asymmetries

- Low energy data (FNAL) show clear differences between  +- and 0. At higher energies the models used to describe the data differ.Large spin effects reported for 0 by STAR for *s* = 200 GeV *pp* collisions

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

- Single Spin Asymmetries

- October 14,   2004

## What does the measurement consist of

- An = (+ - -) / (+ + -)
- Where the spin cross section is determined with the spin direction defined by kb x kpi
- The k are the momenta of the beam and detected particle respectively. In the BRAHMS FS thus the spin direction point down.
- Experimentally this is determined from
- An = 1/P 
- With   = (N+ - N-) / (N+ + N-) where the is the yield of pion in a given kinematic bin with the beam spin direction (up). The normal RHIC definition of + thus is down just to confuse you.

- Single Spin Asymmetries

- October 14,   2004

## The kinematic variables of interest are Feynman x (xF) and pT.
The BRAHMS acceptance in these variables are
Nominal coverage for 2.3, 3 and 4 deg in xF-pT space.
Thus is in range of 1-3 GeV/c
All data here from 2.3 deg and Maximum Field setting 
.

- The BRAHMS acceptance in these variables are
- Nominal coverage for 2.3, 3 and 4 deg in xF-pT space.
- Thus is in range of 1-3 GeV/c
- All data here from 2.3 deg and Maximum Field setting
- .

- Population for - (negative Polarization.

- Single Spin Asymmetries

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## Bunch information

- The bunch information comes from 3 sources.
- A V124 module is coded to provide a 7-bit counter 0...60
- The bunch 1 from Blue and Yellow are recorded in a pipeline TDC. This time can be converted into bunch number.

- The bunch distribution from run 11880 is shown here. Notice the Gap on 16-20. This corresponds to the gap in the yellow beam
- The bunch 10 in each beam is probed by beam diagnostics and has bad luminosity , vertex information and will be discarded.
- Other bunches may have low luminosity due to poor filling ,...

- Single Spin Asymmetries

- October 14,   2004

## Formula for raw asymmetries.

- = (N+ - N-) / (N+ + N-) equation assumed that each bunch has same luminosity.
- This needs need not be the case and the generalized equation is
- = (N+ /L+ - N-/L-) / (N+ /L+ + N-/L-)
- = (N+ - L*N-) / (N+ + L*N-) where L = L+ / L-
- The Polarisation pattern is +-+-+-... for the Blue beam
- And ++--++--++--++--... for the Yellow beam (away from spectrometer).
- For all the data runs used in the last ~4 days of the RHIC run the polarization is ~45%. There are some issue with the measurements of Blue polarization using the CNI.

- Single Spin Asymmetries

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## Slide 7

- Single Spin Asymmetries

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## Typical vertex plots.

- Inel vertex from Bad bunches. The satelite peak is mainly from the **gap** bunches, I.e single beam background due to interaction in Ring2 left.
- This data are from runs 11803-11834

- Inel vertex from runs 11880 and 11882, all bunches, trigger 2 only
- Below vertex from all good bunches (11803--)

- Inel St 2

- Single Spin Asymmetries

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## Track Selection Criteria

- Trigger 2 events exclusively
- Momentum from FS track
- SwimD1 status == 1
- -40< InelVertex <40
- |trackProjection-InelVtx|<45
- -2<Ty<2
- Good Bunches Only (selected per store)
- 0< Mass < .400 (or .350)
- Data above >= .35 has been excluded (statistics). For these typically <pt> and <xf> are somewhat different for + and – bunches.

- Single Spin Asymmetries

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## PID using RICH

- Single Spin Asymmetries

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## Individual bins for PID

- Single Spin Asymmetries

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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

- Single Spin Asymmetries

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## Checks for data

- For singles stores explored changing several data cuts
- Vertex cuts (40->20, even outside the nominal by mistake)
- PID limits (.350 , .450)
- Using different luminosity measure (ZDC rather than BBC)
- Have overlapped results from individual stores
- Have not looked at subsets of Blue Pol bunches e.g. randomly selecting half of up and down bunches.

- Single Spin Asymmetries

- October 14,   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

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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

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##  + with yellow Pol.

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

- BRAHMS preliminary

- 

- Pl (GeV)

- Single Spin Asymmetries

- October 14,   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

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## Conclusions

- BRAHMS has obtained the first preliminary result for single spin asymmetries for p+ and p- in 200 GeV pp collisions at RHIC in the xF range of 0.17 to 0.32.
- The value for + and - are significantly different from each other and the - < 0 at ~ 3 sigma level and at ~ 1 sigma level
- The  negative xF for pions are consistent with 0 (as also found by STAR)
- The protons is found to have An ~0.
- Have some data at 1⁄2 Field and from 4 deg, but with less statistics
- The upcoming run-5 should enable BRAHMS to extend the measurements to xF ~ 0.45 and to get some information on pt-dependence at xF~0.25

- Single Spin Asymmetries

- October 14,   2004