Calibration of the new Particle Identification Detector (PID) Tom Jude, Derek Glazier, Dan Watts

Talk overview A brief description of the new PID. Energy corrections for light loss in the PID. Calibration of energy deposition in the PID by comparison with simulated data. Particle identification and reconstruction of missing masses using the PID.

Description of the PID The PID is a cylinder of 24 plastic scintillators, surrounding the target and parallel to the beam. The PMTs for light collection from the plastic scintillators is upstream from the target. The PID can be used for particle identification via  E-E plots (Figure 1). Figure 1. Example of a  E-E plot Figure 2. PID cross-section

Correcting for light loss in the PID At forward angles, protons stop further from the PMTs in the PID elements. Less scintillation light from these protons reach the PMT. Figure 3. Light loss corrections. Mean energy of minimum ionised pions vs. . Red points are without light loss correction, blue with the correction. A 3 rd order polynomial was fitted to the data. A cut on the minimum ionised pions that punch through the Crystal Ball was made. The mean energy was plotted as a function of  A 3 rd order polynomial was fitted and the parameters used to correct for light loss in the Crystal Ball reconstruction software.

Calibration of the PID A Geant4 simulation was used to simulate Pion and Proton detection.  E-E plots of the energy in the Crystal Ball Vs. the energy in the PID. Sliced into 50 intervals across the Crystal Ball energy axis. Projected as one dimensional histograms onto the PID axis. Two Gaussian functions fitted, giving peaks over the pions and protons. Figure 4. A projected slice of the  E-E plot of experimental data. First peak is the slice from the pion curve, second peak the slice from the proton curve. Two Gaussian peaks are fitted to the data.

Figure 5. Means of the proton peaks from projections. Experimental Vs. simulated data. /MeV

Figure 6.  E-E plot at forward angles where a curve of kaons can be seen.

Graphically cutting on the  E-E plots Figure 7. Graphical cuts on proton, kaon and pion curves

Strange meson production The reaction channels in Equations 1 and 2 were reconstructed using the graphical cuts on the previous slide (Figure 6).   mesons were identified from their decay into two photons. Other decay channels were avoided by vetoing on charged particles. (1) (2)

First look at K + in the Crystal Ball Figure 8. Missing mass measurements for strange decay channels. In (a),(b) and (c) red lines are simulated data. (a) K + missing mass (b) K + and  0 combined missing mass (b)  angle between measured and expected recoil from missing 4 momentum (c) K+ missing mass V s. K +,  0 combined missing mass Expected missing masses:   = 1193 MeV  = 1116 MeV n = 940 MeV

Summary As a first approximation, the PID was calibrated using simulated data. Energy corrections for light loss in the PID were incorporated into the reconstruction software and shown to enhance  E-E plots. Graphically cutting on  E-E plots and vetoing charged particles successfully reproduced missing masses from strange meson production channels.