Data Collection

• MB || JP1 || JP2
• BBC timebin in {7, 8, 9} -- roughly equivalent to 60 cm offline vertex cut (see BBC Vertex)
• spinDB QA team throws out occasional bxings

Pion Cuts

• |eta| < 1.0
• |global DCA| < 1.0
• nFitPoints > 25
• originated from highest-ranked primary vertex
• nSigmaPion in range [-1,2] ( no corrections applied yet)

Relative Luminosities

• obtained from BBC scalar board 5
• integrate counts from timebins 7,8,9 to get per spin state per run
• detailed QA by Murad Sarsour -- see http://cyclotron.tamu.edu/star/2005Jets/scalers/

Polarizations

• analysis by CNI group -- we just get the numbers
• documentation at http://www4.rcf.bnl.gov/~cnipol/pubdocs/Run05Offline/

Preliminary Result

SPIN 2006 Preliminary Result

Trigger Bias

A key question for this analysis is of course the use of BEMC jet patch triggers to select charged pions.  The triggers preferentially select jets with large neutral energy components, so the charged pions on the trigger side are artificially low <z>.  For the preliminary result we estimated the effect of this trigger bias by mocking up PYTHIA as a polarized event generator.  The basic idea is:

• assign an asymmetry weight to each MC based on its partonic kinematics.
• use an emulator for the jet patch triggers to determine if each MC event would have passed the trigger.
• sum up events to get an estimate of the double spin asymmetry for charged pion in minbias events and in triggered events separately
• calculate the asymmetry difference between minbias and triggered for a variety of input gluon polarization scenarios

In the end we assigned a pT-dependent systematic based on the average asymmetry difference for GRSV-STD and GRSV-MIN scenarios.  Here are a couple of plots from those earlier studies

A new set of grid are now available offering much more detailed coverage of the phase space:

http://www.star.bnl.gov/protected/spin/staszak/2006/Sims/newGrids/newGrids.html

I'm in the process of running those and repeating the original analysis now.  Just need another day or two.

We also examined the double-spin asymmetry when we restricted the data sample to pions opposite the jet that triggered the event.  Details are at

Asymmetries for near-side and away-side pions

The asymmetries were surprisingly consistent.

Other Systematic Studies

In the preliminary result we also assigned systematic uncertainties for the following:  non-longitudinal beam polarization components, uncertainties in the relative luminosity measurements, PID contamination, and beam background.  These can very likely be knocked down further.  The uncertainty on A_LL of 2.2e-3 was based on an uncertainty of 1.0e-3 in the relative luminosities; further analysis by the jet group has knocked this down by a factor of 4:

http://cyclotron.tamu.edu/star/2005Jets/epswBBCtbCor/jan5_2007/

The original PID contamination systematic was documented at Background from PID Contamination, but this should be refined for sure. 

The non-longitudinal beam polarization systematic was taken from the jet group since there were insufficient statistics in the Run 5 transverse polarization data to obtain a measurement of the double transver spin asymmetry A_sigma.  Kasia's documentation for this preliminary systematic of 3.0e-3 is at

http://www.star.bnl.gov/protected/spin/kowalik/2005/sigma/summary.html

The final value for this systematic in the recently submitted jet PRL is now 1.8e-3.  Nailing this down still requires a bit of work on my end.