The STAR experiment

Analysis of all setC4 events using geant tracks and vertices

In this analysis, I looked at all QCD background events from setC4 as well as W events from setC2 Wprod detailed here. I used version 3.0 of my analysis code which uses geant vertices and tracks instead of reconstructed vertices and tracks as version 2.5 did. I have also made changes to the quantities I make cuts on, see below. All transverse energy is event ET and an energy scaling factor of 1.23 is used.

Cuts:

I make 14 cuts described below. Plots of the cut spectra can be found here. Pages 1-11 show the cut spectra after 3 preliminary phase space cuts have been made (spectra of the first 3 cuts are not shown). Every event must pass the first three cuts to be considered. Pages 12-18 show cut spectra 8-14 after cuts 1-7 have been applied. Pages 19-29 show cut spectra after all cuts but its own have been applied. Pages 30-32 show a possible alternative cut.

1. Cut 1: Require that the geant vertex be in the region [-70,-50]
2. Cut 2: Require that the trigger patch ET > 20GeV
3. Cut 3: Require that the high tower not be in eta bin 1 or 12
4. Cut 4: Isolation cut - Ratio of the ET in the trigger patch to the ET in an iso cone with r=0.45. Require > 0.96 to pass
5. Cut 5: Track iso cut - Number of geant charged tracks with pT>0.5GeV in an iso cone with r=0.7. Require < 3 to pass
6. Cut 6: Awayside isolation cut - ET in a region Pi +/- 0.7 radians from the high tower in phi. Require < 6.0 to pass
7. Cut 7: Awayside track cut - Number of geant charged tracks with pT>0.5GeV in same region as cut 6. Require < 7 to pass
8. Cut 8: Track near high tower - Number of geant charged tracks with pT>5.0GeV in an iso cone with r=0.7. Require < 2 to pass
9. Cut 9: Ratio of energy in two highest towers in trigger patch to energy in all towers in trigger patch. Require > 0.9 to pass
10. Cut 10: Ratio of energy in 7 highest adjacent U strips under the patch to the energy in all U strips under the patch. Require > 0.7 to pass
11. Cut 11: Ratio of energy in 7 highest adjacent V strips under the patch to the energy in all V strips under the patch. Require > 0.7 to pass
12. Cut 12: Number of hit U strips in sector containing the trigger patch. Require < 48 to pass
13. Cut 13: Number of hit V strips in sector containing the trigger patch. Require < 48 to pass
14. Cut 14: Ratio of energy in patch post-shower layer to full energy in patch. Require < 0.0005 to pass

I have also made several 2-D plots of other quantities which may provide good electron/hadron discrimination. These plots can be found here.

1. Page 1 is a plot of the trigger patch energy Vs. the post shower energy
2. Page 2 is a plot of the energy in both the U and V strips under the trigger patch Vs. the energy in all post shower layers in the trigger patch
3. Page 3 is a plot of the energy in both the U and V strips under the trigger patch Vs. the energy in all 2nd pre-shower layers in the trigger patch
4. Page 4 is a plot of the trigger patch energy Vs. the energy in all 2nd pre-shower layers in the trigger patch

Spectra

The plots showing the effect of the various cuts on the trigger patch ET spectrum can be found here. Pages 1-14 show the effect that the first 3 cuts plus the individual cut has on the trigger patch ET spectrum. So, for example, page 7 shows the spectrum after cuts 1, 2, 3, and 7. Pages 15-26 shows the effects that a number of cuts applied sequenitally has on the spectrum. In all plots the black curve is the detected ET spectrum before any cuts have been made and the red curve is the ET spectrum after the cuts in question have been applied.

Fig 1: This plot shows the effects of all the cuts applied in sequence on the trigger patch ET spectrum

Fig 2: This plot shows the final trigger patch ET spectra after all cuts have been applied. The QCD background is in black and the W signal is in red.