z-vertexing using clustering


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In these plots, the z-resolution is determined by connectin points in the first and last planes hit, and finding the z-intercept. Events vertices are thrown between z=+-10cm. Top right shows the first and last hits in the r-z plane. Note the last plane is now at 36 cm.
The plots in the left column show the z-resolution under various conditions.
  • top: perfect tracking
  • positions 'integerized' according to the strip width
  • positions derived from hit strip clusters.
If an ADC threshold cut is made, it can remove strips from a cluster, the first or the last cluster member, or both. The right middle plot shows the cluster size after the threshold cut, and the bottom left plot also is after the threshold cut.

Analysis: resolution_both.C
Plots: res_cluster_both.C

Input: ancsvx_softlink.root -> ancsvx_143a-e.root
  
The threshold cut is expressed in terms of equivalent silicon thickness traversed. If we take 24000e/300um silicon, the correspondence is as shown:
Si path length # electrons
300 24000
125 10000
75 6000
50 4000
34 2720
25 2000
  
The table below shows the z-resolution using clustering, for various strip sizes and ADC threshold cuts. You can see that the resolution does not depend on the threshold cut, but that we can use this cut to lower the number od strips hit. The clustering recovers to a large extent what we lose by going to wider strips.

Some threshold cuts are in parentheses. This is because the cut level is larger than the strip width, wich means that high-angle tracks would be completely eliminated by such a threshold cut. (Maybe we want this?)

strip size 50 um   80 um   120 um
threshold cut 0 34 50 (75) (125)   0 25 34 50 75 (125)   0 25 50 75 (125)
strips/hit 3.18 2.74 2.53 2.19 1.61   2.37 2.19 2.09 1.96 1.74 1.32   1.91 1.77 1.63 1.49 1.21
z-resolution 221 224 221 218 204   240 249 244 242 225 241   272 261 241 244 291
pictures link link link link link   link link link link link link   link link link link link



Macros: res_vs_width.C and clsize_vs_width.C

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Last update 28 Mar 06 - HvH