Spin PWG

This is a feed of Drupal items targeting the "Spin" Audience.

Working Group Members

CDEV Monitoring

(Archived into Drupal from MIT servers in August 2008. Original analysis by Julie Millane and Bernd Surrow.)

CDEV Monitoring

(Archived into Drupal from MIT servers in August 2008. Original analysis by Julie Millane and Bernd Surrow.)


 Details for the 2006 RHIC run (Run 6)


 Details for the 2005 RHIC run (Run 5)

Beam Polarizations

The beam polarization of the proton beams is measured with a set of polarimeters at IP12.
Carbon polarimeters: fast measurement several times during a RHIC fill, two devices per beam



Invariant Mass and Width: Data-MC

Here I show the invariant masses and corresponding widths I obtain using my cross section binning. These are compared to MC values.

The Method:

Neutral Pions 2005: Frank Simon

Information about the 2005 Spin analysis (focused on A_LL and <z>, some QA plots for cross section comparisons) will be archived here. The goal is obviously the 2005 Pi0 spin paper.

Analysis Update for Spin PWG


Bernd and I are writing a paper with Yichun Xu and Zhangbu Xu from Spectra that extends STAR’s charged pion cross sections to 15 GeV/c and reports the inclusive charged pion A_{LL} measured using data from Run 5. We are targeting PRL. Yichun is also submitting a NIM paper detailing the methods used to correct the dE/dx distributions in the TPC at high pT. We don’t have a finished draft of the PRL available yet, but we do have a paper webpage.

Briefly, Yichun and Zhangbu use pions from K_{S} decays, protons from Λ decays, and electrons (and pions) identified using the BEMC to obtain a very precise relativistic dE/dx distribution for charged particles as a function of βγ. Their results deviate from the Bichsel function by up to ~3% (0.4σ) at large βγ, and are precise to better than 0.1σ. They also fit the e+/e- ratio as a function of pT to determine the momentum distortion due to space charge in the TPC. Finally, they use JP2 data from 2005 corrected using PYTHIA to obtain charge-separated pion cross sections out to 15 GeV/c that are in agreement with AKK, KKP, and DSS predictions. For more details, see Yichun’s talk at the Davis Collaboration meeting.

On the asymmetry side, I presented an update in April summarizing the 2005 inclusive result and my evaluation of some of the necessary systematic uncertainty checks. The major task left at that time was a study of pion fragmentation in trigger jets and away-side jets that could be used to assign an uncertainty to the < z > plot and hopefully reduce the trigger bias systematic uncertainty in the A_{LL} plot. That study is ongoing; I ended up rewriting most of my simulation analysis code in the process. I don’t have any final plots to show today.


My Run 6 data analysis is focused directly on the jet+pion A_{LL} measurement. I believe another inclusive measurement using this dataset is not as compelling, considering the additional bias introduced by the higher BJP1 trigger threshold. I’ve been using the BJP1 trigger so far, but I may also try to include the L2gamma trigger if there’s time. In the jet+pion measurement I have been identifying trigger jet(s) in each BJP1 event using the following cuts:

  • p_{T} > 3.5
  • -0.7 < detector η < 0.9
  • R_{T} < 0.92
  • jet axis within 36 degrees of triggered jetpatch center

and then counting the charged pions which are ΔR > π/2 away from a trigger jet axis. I suppose (based on Murad’s analysis note) that I should also check that the detector η of the jet is on the correct side of the barrel, with a 0.1 margin of error. Charged pions are identified using the same criteria as the 2005 inclusive measurement:

  • 2 < p_{T} < 10
  • |η| < 1.0
  • nFitPoints > 25
  • |dcaGlobal| < 1.0
  • recalibrated nσ(π) in [-1,2]

I’m using the list of 302 runs that passed the jet and luminosity QA, and I apply the standard 6 < BBC bin < 9 event cut. Just for fun, here’s the A_{LL} plots obtained using those cuts:

A<em>LL, pi-, Run 6 A</em>LL, pi+, Run 6

I’m evaluating the same suite of final-state-dependent systematic uncertainties (single-spin null tests, trigger bias, background from PID contamination, and false asymmetries from residual transverse polarization) that I checked in the inclusive A_{LL} measurement. I’ll need to fold in systematic uncertainties on the jet reconstruction as well.

SSA vs. pT
SSA vs. fill
A_{Σ} vs. pT

I expect to be able to release a preliminary jet+pion A_{LL} in time for the fall conferences. I don’t believe there will be any theoretical predictions for this measurement in that time frame, but I haven’t pressed our theorist friends on that front, either.

DIS 2008 proceedings

Here are my proceedings for DIS 2008

PWG Analysis Update

 Update on Run 5 charged pion A_{LL} for Spin PWG meeting.

DIS 2008 Presentation

Below you will find a link to a draft my DIS 2008 presentation.

Revised Eta Systematic

After some discussion in the spin pwg meeting and on the spin list, it appears I have been vastly overestimating my eta systematic as I was not properly weighing my thrown single etas.

Non-Longitudinal Beam Components Systematic


Documentation for a systematic uncertainty in the Run 5 charged pion A_{LL} based on non-longitudinal components in the beam polarization vector.

Energy Subtracted A_LL Calculation

For my single particle Monte Carlo studies, I argued (here) that I needed to ad

Alternate Calculation of Eta Systematic

At the moment I am calculating the systematic error on ALL from the presence of Etas in the signal reigon using theoretical predictions to estimate ALLeta.  Th

Mass Windows

The nominal mass window was chosen 'by eye' to maximize the number of pion candidates extracted while minimizing the backgrounds (see yield extraction page.)  I wanted to check to see how this

Single Spin Asymmetries

The plots below show the single spin asymmetries (SSA) for the blue and yellow beams, as a function of run index.  These histograms are then fit with flat lines.  The SSA's are consistent

Sanity Checks

Below there are links to various 'sanity' type checks that I have performed to make sure that certain quantities behave as they should