low_hsbeta

Do low hsbeta fire the Cerenkov? (03/23/05)

John A. said that we will need to know if these events fire the HMS Cerenkov. There are two scenarios, the first is the pions undergo a hadronic interaction and are deflected, but still have enough velocity to fire the Cerenkov. The low hsbeta would be due to the increased path length between the scintillators due to the scattering. The second is that the pion velocity is reduced by the interaction, and it no longer fires the Cerenkov.

By making separate cuts on (1) events with low hsbeta and (2) events very close to hsbeta =1 (+- 0.03). Events from (1) and (2) could be compared with the fraction of times that they fire the Cerenkov.

Hydrogen runs were used so that a tight mmx cut could be used to select pions. In addition, there were acceptance cuts in both the HMS and SOS, and PID cuts in the SOS. It was found that the fraction of events from (1) and (2) that fire the Cerenkov was unchanged (0.9338 and 0.9321 respectively). Here is the kumac used to generate these results.

There is also a third scenario, that the reconstruction of pions fails for some fraction of the events. Dave said that Peter Bosted has a new "prune" method for selecting tracks that may be an improvement over the chisq and tof selection procedure. This method may also fix the events with low hsbeta also.

Fraction of events with low hsbeta (03/23/05)

Dave asked me during the collaboration meeting to find the fraction of events that do not pass a tight beta cut.

Using a hydrogen run, 49549, a tight mmx cut to select pions in the HMS could be made. This is shown in the first plot. The second plot shows hsbeta vs cointime with PID and acceptance cuts in both arms, and the magenta lines shows a cut that is about to be applied.

The third plot is the same as the second, except that it has a wonky cut (magenta) and a loose hsbeta cut (red). The fourth is the same except that it has a tight hsbeta cut.

The efficiency of the tight hsbeta was calculated from the last two plots:
Events in loose hsbeta cut = 2299
Events in tight hsbeta cut = 2195
Efficiency = 95.5%

It was also found after generating these plots that the fraction of events near hsbeta=0 with cointime near -59ns was 0.5% of the events in the loose hsbeta cut.

Events with low hsbeta (03/23/05)

It was brought up by Dave at the collabration meeting that events with low hsbeta are due to hadronic interactions of the pion with the scintillators, Cerenkov, or other material. Here is an image showing these events (inside and to the left and right of the orange box).