TPC track vs SVT hit Correlations
The first step towards matching the SVT hits to TPC tracks is to see if the
SVT hit multiplicity correlates with that of the TPC tracing. Fig 1 shows such a correlation. The tracks are primary tracks from events with vertices within +-20 cm.
Fig 1. Svt hits vs TPC tracks
A clear correlation is seen. That there are SVT hits even when there are zero tracks reconstructed in the TPC is a measure of the noise in the SVT. However there will also be some component from secondary tracks and from the TPC's own inefficiency (the TPC is also currently performing its own calibrations). However we believe the main component is noise. We know there are noisy anodes in the SVT which we will shortly blank out however it should be noted that there are 432 hybrids in the SVT so this offset corresponds to <1 noise hit per hybrid. It should also be noted that the left and figure was created before a bug in the software was fixed, this meant that the overall efficiency of the hit finder dropped dramatically, this is the reason that the total number of hits in the SVT is nowhere near the total number of tracks that hit the SVT. The right hand figure was made after the fix and shows number of SVT hits vs ALL TPC global tracks. You can see that now the numbers are ~ the same. This plot was made for central collisions and hence there is not much range in track density and the correlation is less clear.
Fig 2 below is with the corrected software using hte ssame events as the top
left plot above. You can see that the SVT hit reconstruction has dramtically
increased. There is still a large offset for zero tpc tracks. We now see that we find many more hits than Primary tracks but fewer the global. Care should be taken in comparing this plot to the right hand plot of Fig.1 as Fig 2 is for field off events and Right hand plot of Fig.1 is for field on.
SVT hits vs TPC tracks for B=0 events
Last modified: Sat Oct 13 20:39:05 EDT 2001