Download Presentation
## DCOPS Analysis

- - - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - - -

**DCOPS Analysis**• James N. Bellinger • University of Wisconsin at Madison • 9-February-2007 • DCOPS Data from MTCC2**Simple Analysis**• This is not a substitute for using COCOA, which is what we intend for the final determination of position. • Finding the absolute Z positions requires use of the Z-sensors.**DCOPS Sensor**The Line has 10 DCOPS, with a laser at each end CCD 3: RPhi CCD 2: Z CCD 4: Z CCD 1: RPhi**Piecing together lines for Z measurements**• Disk bending tilts the lasers • Field-off: laser offscale one way by #8 of 10 • Field-on: laser offscale other direction • By #9 the laser beam has vanished • Have to piece together incomplete lines**RPhi measurements**• Disk bending has little effect: beam reaches far side • Field off • Field on • RPhi is the crucial direction for momentum measurements**Analysis Approach**• Fit the measured positions with a straight line. The resulting residuals are independent of the laser direction and show the variation from an “average position” level. • Residuals can be refit, and the resulting new residuals will be the same as the old ones. I rely on that when piecing Z-measuring lines together.**Field-OFF ME+2/SLM1 Z measurements**• CCD2=+ • CCD4=* • PG=o ME+2 1/10 The positions are consistent with the shimming. The data was taken over several weeks, and is clearly stable. Photogrammetry is in good agreement**Field-ON ME+2/SLM1 Z measurements**• CCD2=+ • CCD4=* • Change from field OFF is consistent with disk bending estimates • Measurements are stable**Quality notes**• CCD2 profiles were somewhat shadowed in the 6’th and 7’th DCOPS, so the quality of the profiles’ fits are poorer. It shows in the distribution of residuals, and in the RMS of the following slide.**Z measurement stability**• Station CCD2 CCD4 • 0 92 51 • 1 78 52 • 2 30 35 • 3 41 26 • 4 88 65 • 5 28 126 • 6 261 104 • 7 44 11 • 8 140 26 • 9 155 31 CCD2 = 96 microns CCD4 = 53 microns Measurements were taken over 3 weeks Field is OFF**Rphi residuals: Field ON**• Laser 1= + • Laser 2= * • This is the direction critical for momentum measurement**Rphi measurement stability**• Station TP1 Laser TP4 Laser • TP1 10 40 • 1/2/O 10 106 • 1/2/I 5 49 • 2/3/O 11 49 • 2/3/I 12 32 • 2/20/I 19 22 • 2/20/O 13 113 • 1/10/I 22 22 • 1/10/O - 20 • TP4 33 26 Laser 1 = 15 microns Laser 2 = 48 microns Measured over weeks Field is ON, CCD1**Rphi residuals and photogrammetry**• Laser 1 OFF= + • Laser 2 OFF= * • PG =o • Agreement with photogrammetry is usually good • Laser 1 and 2 data are consistent**Rphi residuals Field OFF and ON**• Laser 1 OFF= + • Laser 2 OFF= * • Laser 1 ON = o • Laser 2 ON = x • CCD 3 data • Shifts are noticeable • Measurements are stable**Change in RPhi from OFF to ON**• Laser 1 = * • Laser 2 = o • The endpoints of each distribution on the previous slide were corrected to be 0 before subtracting to get these, so the endpoints have change=0 by construction. • This is a relative measure of the Rphi change when the field turns on, using CCD3**Summary**• The DCOPS system works and can locate misaligned chambers • COCOA should work • Disk bending is consistent with predictions • The ability to adjust the laser direction would help**Quality studies**• Although after solving the previous two problems I had reasonable-looking results for the fits, the histograms were plagued with fliers. • Hand scanning showed which CCDs were consistently bad (and I then always excluded these) and which “events” had unusually bad profiles. This can be made automatic later. So far it looks as though the absolute signal size [available] and signal to background [not available in MTCC data] are the most useful quantities.**Piecing together partial lines**• Fit one side’s data: 7 DCOPS worth • Fit the other side’s data: 7 DCOPS worth (there was sometimes more, but I was being conservative) • Fit the difference between the residuals of the above two fits in the overlap region. • Use this to extrapolate into the right-hand side’s data from the left and calculate residuals from this “virtual laser.” • Using the left side’s residuals and the extrapolated residuals, fit this set to a line and find the residuals from that fit.