Old Studies

Outdated or obsolete studies are archived here

First Look at Charged Pion Trigger Bias

The charged pion A_LL analysis selects pions from events triggered by the EMC. This analysis attempts to estimate the systematic bias introduced by that selection.


  • Simulation files, database timestamps, and selection cuts are the same as the ones used in the 2005 Charged Pion Data / Simulation Comparison
  • Polarized PDFs are incorporated into simulation via the framework used by the jet group. In particular, only GRSV-std is used as input, since LO versions of the other scenarios were not available at the time.
  • Errors on A_LL are calculated according to Jim Sowinski's recipe.


The BBC trigger has a negligible effect on the asymmetries, affirming its use as a "minimum-bias" trigger. The EMC triggers introduce a positive bias of as much as 1.0% in both asymmetries. The positive bias is more consistent in JP2; the HT2 asymmetries are all over the map.



First Look at Single-spin Asymmetries

This is a study of 2005 data conducted in March 2006.  Ported to Drupal from MIT Athena in October 2007


Single-spin asymmetries for blue and yellow beams are calculated for each fill and sorted by particle charge and trigger ID. Each plot includes a legend that lists the value I calculate for the asymmetry when I integrate over pt bins. I fit each plot with a straight line and include the values of the fit parameters. The first page of the PDF is integrated over all data, and then fill-by-fill plots are available on subsequent pages. The basic structure of the PDF is as follows: each page contains all the plots for a given fill. Trigger IDs are constant for each column (mb,ht1,ht2,jp1,jp2). The top two rows are yellow and blue beam asymmetries for positively charged hadrons; the bottom two rows are the same plots for q=-1. This gives a total of twenty single-spin asymmetries for each fill.

I also increment 20 separate histograms with (asymmetry/error) for each fill and then fit the resulting distribution with a Gaussian. Ideally the mean of this Gaussian should be centered at zero and the width should be exactly 1. The results are in  asymSummaryPlot.pdf 

Finally, a summary of single-spin asymmetries integrated over all data. 2-sigma effects are highlighted in bold:

+ MB HT1 HT2 JP1 JP2
Y 0.0691 +/- 0.0775 0.0069 +/- 0.0092 -0.0038 +/- 0.0126 0.0086 +/- 0.0104 0.0116 +/- 0.0069
B -0.0809 +/- 0.0777 -0.0019 +/- 0.0092 -0.0218 +/- 0.0126 0.0067 +/- 0.0104 -0.0076 +/- 0.0069

- MB HT1 HT2 JP1 JP2
Y -0.0206 +/- 0.0767 -0.0193 +/- 0.0092 -0.0158 +/- 0.0130 -0.0035 +/- 0.0101 0.0061 +/- 0.0070
B 0.0034 +/- 0.0769 -0.0021 +/- 0.0092 0.0006 +/- 0.0130 -0.0164 +/-0.0101 -0.0147 +/- 0.0070

: The jet group sees significant nonzero single-spin asymmetries in Yellow JP2 (2.5 sigma) and Blue JP1 (4 sigma). I do not see these effects in my analysis. I do see a handful of 1 sigma effects and two asymmetries for negatively charged hadrons that just break 2 sigma, but in general these numbers are consistent with zero. I also do not see any significant dependence on track phi.

Inclusive Charged Pion Cross Section - First Look

Correction factors are derived from simulation by taking the ratio of the reconstructed primary tracks matched to MC pions divided by the MC pions. Specifically, the following cuts are applied:

Monte Carlo
  • |event_vz| < 60.
  • |eta| < 1.
  • nhits > 25
  • geantID == 8||9 (charged pions)

Matched Reco Tracks
  • |event_vz|<60.
  • |reco eta| < 1.
  • |global DCA| < 1.
  • reco fit points > 25
  • geantID of matched track == 8||9
The track yields and their associated yields are obtained from the minimc files that are produced automatically with each simulation request. I run a separate chain containing StEmcTriggerMaker on the MuDst simulation files to determine if each event would have satisfied EMC and BBC trigger conditions.

There is currently a bug in StDetectorDbMaker that makes it difficult to retrieve accurate prescales using only a catalog query for the filelist. This affects the absolute scale of each cross section and data points for HT1 and JP1 relative to the other three triggers. It's probably a 10%-20% effect for HT1 and JP1. With that in mind, here's what I have so far:

This plot is generated from a fraction of the full dataset; I stopped my jobs when I discovered the prescales bug.

The cuts used to select good events from the data are:
  • golden run list, version c
  • |vz| < 60.
  • Right now I am only using the first vertex from each event, but it's easy for me to change

The cuts used to select pion tracks are the same as the ones used for "Matched Reco Tracks", except for the PID cut of course. For PID I require that the dE/dx value of the track is between -1 and 2 sigma away from the mean for pions.

As always, comments are welcome.

Single-Spin Asymmetries by BBC timebin

This is a study of 2005 data conducted in May 2006.  Ported to Drupal from MIT Athena in October 2007

Hi jetters. Mike asked me to plot the charged track / pion asymmetries in a little more detail. The structure is the same as before; each column is a trigger, and the four rows are pi+/Yellow, pi+/Blue, pi-/Yellow, pi-/Blue. I've split up the high pt pion sample (2< pT < 12 GeV) and plotted single-spin asymmetries for timebins 7,8, and 9 separately versus pT and phi.  The plots and summaries are linked at the bottom of the page.

2 sigma effects are highlighted in yellow, 3 sigma in red. There are no 3 sigma asymmetries in the separate samples, although pi-/B/JP1 is 3 sigma above zero in the combined sample. Here's a table of all effects over 2 sigma:

B +2.07
9 - JP1 B +2.45
7-9 - JP1 B +3.15

If you compare these results with the ones I had posted back in March (First Look at Single-spin Asymmetries), you'll notice the asymmetries have moved around a bit for the combined sample. The dominant effect there was the restriction to the new version of Jim's golden run list. The list I had been using before had at least two runs with spotty timebin info for board 5; see e.g.,


and ensuing discussion. I'm in the process of plotting asymmetries for charged track below 2 GeV in 200 MeV pT bins and will post those results here when I have them.