Space Charge Distribution

Updated on Thu, 2012-07-26 14:02. Originally created by dgarand on 2012-07-24 15:34.

To analyze the space charge distribution, we looked at 8 runs from the same fill of pp500 collisions. This allows us to look at variations as luminosity decreases.

In the following plots, Run# 1 corresponds to the earliest run being 13077066, and Run#8 corresponds to the latest run being 13078014.

We looked at how well the power fit (r^-N) and Howard's fit (howfit) match the charge distribution. In the first plot, I have the magnitude of N that best fits the data recorded for all acceptance, the second plot is broken into East acceptance and West acceptance. Besides an issue we are resolving for west acceptance in Run # 6 (13078001), we see the trend that as the fill progresses, later runs need a more negative N value to fit the distribution. (July 26 Note: It ends up the Fit had an abnormal termination due to running out of iterations, I ran the Fit several times and it reached a converged answer, plots have been updated.)

I also plotted the chisquare/ndf for the power fit and the howfit in the following plot. Next to it I have recorded the chisquare/ndf for East and West acceptance for the power fit. What we can see is the trend that the chisquare/ndf is decreasing with later runs, and that the chisquare/ndf is smaller for the howfit. These plots should only be used as trends since errors were not assigned.

We also looked at the azimuthal distribution of the charge. The following plots contain the charge distribution with the power fit subtracted from it. The rows are each specific runs, with the first plot being all acceptance (East+West), the second being West acceptance only, and the last being East acceptance only.

All Acceptance West East

Run # 13077066