BBC / VPD Vertex Investigation

The purpose of this study is to determine how well the Z vertex of an event can be found using the BBC or VPD detector. This is an important issue when analyzing data from the trigger block files because there is no tracking information to determine a vertex. The event vertex is needed to get true jet transverse energy and Eta. These quantities in turn are needed to reconstruct the partionic momentum fractions.

To study the effectiveness of BBC and VPD vertex finding I have done studies using a set of fastOffline MuDsts from the 200GeV run. Using the MuDsts allows me to compare the vertex found from tracking to the vertex found from the BBC and VPD. I used approximately one fastOffline run from each day in the data set (set A, info here) I am analyzing. The lists of fastOffline files I've used are here (Reversed Full Field) and here (Full Field).

I have split my study into three phases: In the first phase I look at the relationship between the VPD and BBC online time difference values and the PPV vertex as well as calculating the vertex directly using Bill Lope's formula (time diff between first TDC on each side * 0.017 * c/2). I did this analysis on the Reversed Full Field and Full Field data seperately to look for discrepencies and could find none. In the second phase I use the fits from the PPV vs time difference plots to calculate the vertex using VPD and BBC time differences and then compare these vertices to the tracking vertices. The plots can be found here. In the third phase I access the L2jet output from the MuDsts and look at the ET, Eta, Phi, Eta sum, and Eta difference distributions using the tracking vertex as well as the VPD and BBC vertices found from Bill's formula and the online time difference fits made in the previous step. I also look at the difference between the kinematic quantities when using the tracking vertex as opposed to the four other BBC / VPD vertex methods. The plots are here.