sili_endcap_type   =  0,           no endcaps (barrel only) 
sili_endcap_type   =  1,           for the lampshade configuration,  or 
sili_endcap_type   =  2,           for the flat configuration.

The flat version is mechanically simpler, and it allows the study of small stereo angle strips.

This is the current situation, with the lampshade panels tilted by 22°. The big shades have 5+6 chips, the medium shades 5+3 chips, and the small one 5 chips per panel, and 24 panels per lampshade.
In the 'flat' configuration, the panels have been rotated so they are perpendicular to the beam axis. The small panel was pushed as close to the IP as possible, and the outer panels were moved close to the end in +-z. The middle two were then spaced equally in between. (z-positions are 18.7, 25.1, 31.5 and 37.9 cm respectively). This spacing also turned the 'medium shade' into a big one, with 5+6 readout chips. The tipping of the panels forced me to make the outer enclosure a little bigger, by 7mm in radius.
The existing overhang of the silicon was such that there still is sufficient overlap at the outer radius of the big panels:
To see if there is a difference, I re-ran the residual study. Particles at theta=19°, phi=3.75°, run 138
Same, for the umbrellas, run 139
Residuals:
The differences are small, as expected. Since the residuals scale with z, they observed difference is largely due to the different z's of the hits.	5 GeV mu+ residuals (um)   run the phi zvertex side view 9 10 11 12 comments 138 19° 4° 0 picture 41 65 89 118 flat endcaps 139 19° 4° 0 picture 44 58 80 104 umbrella endcaps
Resolution: Next, I extrapolated these tracks back to the z-axis using hits in the first and last endcap. 'Perfect tracking' (top plots) uses the hits in the silicon directly, thus seeing only the effects of multiple scattering, and in the bottom plots the hits are moved to the middle of 50-micron strips, causing additional blurring. Run 138 (flat planes, left column) is marginally better than run 139 (umbrella stations). Note that these runs use the same algorithm that assumes a single strip is hit, and moves the measured coordinate to the center of the 50 um strip. More on that below
Charge sharing: Silicon is 300um thick, and strips are 50 um wide. When the mean angle of incidence is not zero, more than one strip will be hit by each track. I spray 5 GeV muons into the top of the N arm, for z = -10, -5, 0 (shown above), +5 and +10cm. This distribution shows the distance in r between the entry and exit coordinates of tracks in the silicon. 50-micron intervals are marked in red. Most tracks hit 2 or 3 strips. A hit in 3 or 4 endcap planes is required. A single particle file used: 5 GeV muons, theta, phi = 24°, 3.75°, spread 29°. Root macro resolution_flat.C. Run ancsvx_140a-c.root
Same for the cones: A hit in 3 or 4 endcap planes is required. These tracks are mostly normal to the silicon, and thus the cluster size is typically 1. Root macro resolution.C. Run ancsvx_141.root
Multiple strips -> tracking resolution. Having a cluster of hit strips rather than a single hit strip improves the point resolution. Just taking the center of a cluster as an estimator of the track crossing coordinate is better than the single-strip center: cluster size sigma (um) 1 3.6 2 10.1 3 9.9 4 9.7 weighted avg. 9.9 For comparison (5th plot m29), sigma is 18.6 for normal-incident, single-strip hits. Also note that this distribution is flat, and making the assumption of a gaussian error distribution will negatively affect track fitting algorithms that assume measurement errors are gaussian. Since all this depends on angle of incidence, I added for this section 5 runs, with z-vertices at -10, -5, 0, 5 and 10cm. Further resolution improvements will result from making ADC threshold cuts, and ADC-weighted cluster fits. bigger version of these plots-->

Occupancy The typical cluster size for the flat planes is 2-3, which means the strip occupancy will go up by that factor. Q1: Are clusters still sufficiently separated in central AuAu so that track finding is not adversely affected? The plots show tracks per cm^2 for one central AuAu event (actually the average of 10 events from /phenix/data02/rhphemds/events/hjievt_600auaucentsq08_042298.dat), which has impact parameter b = 0-2 fm At the innermost radius of 38mm, there are 50 tracks in the first 1mm ring, which translates to 21/cm^2/event. For 50 um strips in 24x2x2 segments per 2pi, this translates to a track occupancy of 2.6%. Q2: Can the readout electronics handle a factor 2-3 more strips on?

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