Efficiency from Pair Production Analysis

In order to determine the efficiency of detecting charged particles with the Veto detectors, I analyzed one pair production data run. The run number was 4865 which contained events from the ⁹Be target.

The following cuts were applied to isolate the true pairproduction events from the background in the data

• Number of clusters in HYCAL bank : 2
• Absorber exclusion: sqrt(x² + y²)>4.0cm
• Energy conservation : |(E₁+E₂)/E_gamma -1 | < 0.1
• dPhi : 170.0 <= Phi₁ - Phi₂ <= 190.0

The figure below shows the energy and dPhi distributions with the green region are events accepted by the cuts.

The next set of plots show the x-y distributions from the HYCAL detector for all clusters(left), after the energy cut(middle), and after energy and dPhi cuts.(right).

The next set of plots show the x-y distributions from the HYCAL detector for clusters without a Veto hit(left column) and clusters with a Veto hit(right column). The top two plots are from matching the x-position of HYCAL with that of the Veto paddles. The bottom row has x-position matching as well as a +/-10ns timing match between the Veto time and the photon time.

These two plots show the energy sharing of the two clusters. The left plot is cluster energy divided by the photon energy for cluster 1(x-axis) vs 2(y-axis. The right plot is of HYCAL x-position vs cluster energy where red(blue) is for cluster 1(2).

Next I tried to ignore the Veto paddles which strddle the beamline since they have more beam related background. Aslo I looked at clusters which were within +/-3cm of the center of the paddle in x. This cut is to avoid edge effects in the scintillators. Here are the plots as above

Summary table of the statistics for clusters with and without hits in the Veto detectors.

Update from Feb. 3, 2005

I found a problem with the x-position in the Veto reconstruction. I was applying the wrong sign to the x-position given the Veto paddle number. Here are the new charged-particle detection efficiencies.