E895 Trigger Bias Determination

The first step in the impact parameter cut analysis was to use the scalers to determine the cross section of the events which were selected by the trigger (trigger bias). Below is included a table which details which runs were used for the determination of the inclusive trigger cross section for the minimum bias runs and the measured cross sections. The inclusive cross section is calculated using all interaction triggers and the total measured beam rate (ratio of scaler 9 to scaler 5 for the 6,8 AGeV data, or 9 to 8.live for the 2,4 AGeV data). A normalization factor which inlcudes target thickness allows us to quote these trigger cross sections in millibarns.
The column refering to target-related tigger cross section removes that fraction of the trigger cross section which is rejected by a vertex selection on the events. This number is estimated by comparing the multiplicity distributions both with and without an event vertex cut. We have not yet used a direct comparison of identical run sets and therefore the numbers we provide for target-related trigger bias should be considered preliminary.
The multiple listings of various run sets are included because these trigger bias studies were preformed twice at UCD. Once by MDH and then later repeated by WC. Both numbers are included for completeness. Errors are included where there was sufficent documentation in the log books to calculate an uncertainty.
A parallel study has been completed by Dieter Best. A comparison of the results is discussed here.

Runs Used Inclusive Trigger Cross-Section (Maximum Impact Parameter) Target-related Trigger Cross-Section (Maximum Impact Parameter)
2 AGeV r1205q0,q2,q4
3325 mb (10.3 fm)
2060 mb (8.1 fm)
2 AGeV r1234q4
3345 mb (10.3 fm)
N/A
4 AGeV r1140-r1145, q0,q2,q4
2620 +/- 360 mb
(9.1 +/- 0.5 fm)
1860 mb (7.7 fm)
6 AGeV r1260q0,q2,q4
7645 mb (15.6 fm)
To be determined
6 AGeV r301q0,r311q0
7340 +/- 305 mb
(15.3 +/- 0.3 fm)
N/A
8 AGeV r1060q0,q2,q4
5230 mb (12.9 fm)
2835 mb (9.5 fm)
8 AGeV r1170q0,r1166q0
5350 +/- 250 mb
(13.05 +/- 0.3 fm)
N/A

Note: The measured total reaction cross section for Au+Au at 10.6 AGeV is 6.78 barns. The geometric cross section for two gold nuclei of radius 7.1 fm would be 6.33 barns.

Last update: 09-Aug-99.

Email: cebra@physics.ucdavis.edu

A link is provided to W. Caskey thesis, Appendix E -- Impact Parameter which provides additional details of this study and of the methods used to determine the impact parameter for E895.

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