This blog investigates the cuts that will be necessary to select Au+Au collisions from the background in low energy collisions in 2010.

Background events consist of:

beam-pipe collisions

beam-gas collisions

out-of-time pile-up

shadow vertices (39 GeV only)

Parameters we can use to cut on:

Vx,Vy,Vz,average dip angle, # matches, # tracks matched to tof

39 GeV

This data set was run with the default Minuit Parameters for Rimpact,zDca and # of tracks of 1.5,3,5 which means that there is some shadow vertex contamination.  In order to examine this, we created a miniproduction of 39 GeV files with the 662 option.

11105011

file                                                   #events

st_physics_11105011_raw_2020001.daq 17804
st_physics_11105011_raw_3030001.daq 18000
st_physics_11105011_raw_4030001.daq 18152

11107012
st_physics_11107012_raw_2030001.daq 17940
st_physics_11107012_raw_4030001.daq 18172
st_physics_11107012_raw_3010001.daq 18317

Figure 1a: Average Dip Angle vs Vz for 39 GeV vertices.  slope=-3.93818e-03±5.51839e-05

Figure 1b: Average Dip Angle vs Vz for 39 GeV vertices with Vr<2cm. slope=-4.03368e-03±5.60170e-05. Note only 10 events were removed by the Vr cut.

Figure 1c: Average Dip Angle vs Vz for 39 GeV vertices with Vr<2cm and |Vz|<70cm. slope=-3.45137e-03±1.85872e-04