The STAR experiment

This page summarizes the effect of each major cut in the 2006 jet+charged pion analysis. Each plot is obtained by applying all other applicable analysis cuts except the one being illustrated.

Figure 1: Black is TPC z-vertex for all BJP1-triggered events, Green is the TPC z-vertex distribution for events in BBC timebins 6-9, and Red is the TPC z-vertex distributions for all charged pion tracks (inclusive, no trigger jet requirement).

It appears at first that the vz distribution of good tracks is broader than the BBC 6-9 distribution, but that’s not actually the case. Here’s the ratio of the red and green histograms from the above plot:

Figure 1b

The following histograms use positively charged pions from any spin state. Black lines are inclusive π+ passing all cuts except the one being shown, green lines are leading π+ opposite a trigger jet, and the filled green histogram shows the π+ accepted for the asymmetry analysis.

Figure 2: |η| < 1.0

Figure 3: |dcaG| < 1.0

Figure 4: nHitsFit > 25

Figure 5: nσ(π). It’s not possible to read off the efficiency from this histo because I actually use a time-dependent cut window based on the results of fill-by-fill fits to the nσ(π) distributions. Ideal world cut shown is nσ(π) [-1,2]

Here’s the ratio of the green and black histograms from that plot. The away-side spectrum has a relative lack of electrons but an increase in the p/K contamination:

Figure 5b

I should also add some more plots here documenting the cuts on jet pT, detector η, and N.E.F.

Asymmetries are defined as (Y,B):

Asymmetries are defined as (Y,B):

Attached is a list of jobs for run 9 with names of those volunteering to handle tasks.

Updated the dE/dx cut. Previous asymmetry calculations was using +/- 3σ in dE/dx. The following has a tighter cut on the lower end, varies with momentum bins.

1.0 MC Event Sample

1. Pythia event sample (pibero's gamma trees) w/ proper weighting for partonic pT bins
2. No offline trigger simulation
3. full EEMC acceptance

2.0 Definition of Isolation Cut

1. See You do not have access to view this node for definition of the 1-tower isolation cut and evaluation of rejection versus efficiency based on pythia events.
2. See You do not have access to view this node for data vs MC comparison, including trigger simulation.

Geometry used in simulation/embedding for hits projection

For embedding with SSD, we project GEANT hits on real geometry.

 The following plots are for data.

In order to estimate the order magnitude of the single spin Collins asymmetry at midrapidity I calcuated the following partonic components from jet reconstruction using the STAR PYTHIA + GEANT simu