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Thoughts on Changing the Effective Radius of the SSD

Thoughts on Changing the Effective Radius of the SSD. Jim Thomas May 1, 2009 Lawrence Berkeley National Laboratory. The SSD is a beautiful detector . The SSD is thin 1% - double sided Si The SSD lies at an ideal radius 23 cm - midway between IP and IFC The SSD has excellent resolution

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Thoughts on Changing the Effective Radius of the SSD

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  1. Thoughts on Changing the Effective Radius of the SSD Jim Thomas May 1, 2009 Lawrence Berkeley National Laboratory

  2. The SSD is a beautiful detector • The SSD is thin • 1% - double sided Si • The SSD lies at an ideal radius • 23 cm - midway between IP and IFC • The SSD has excellent resolution • (rumor says better than design) • The SSD is too large to be replaced • The money is better spent, elsewhere

  3. SSD ~ 60 cm The SSD as we know it now … • Double sided Si wafers 300 mm thick with 95 mm x 4.2 cm strips • Crossed at 35 mrad – effectively 30 mm x 900 mm • One layer at 23 cm radius • 20 ladders, 67 cm long • air cooled •  < 1.2 • 1 % radiation length @  = 0

  4. Assumptions and Worst Case Scenarios • Use the Fast MC model to calculate single particle efficiencies • Assume idealized detectors which have 100% acceptance • Show results without including the TPC efficiency or the SSD geometric acceptace • Usually assumed to be 75%, combined. • Ignore crossed strip design of the SSD • Do worst case analysis with 4 cm long strips • Show only results for pions • Kaons decay and so it can be confusing which effect is which • Calculates results with and without the SSD • We are primarily interested in what happens when the IST fails and the SSD is the only active ladder in this region

  5. SSD performance versus radius • Blue – IST and SSD in nominal positions • IST active • Magenta – SSD at 23 cm • IST not active • Red – SSD at 20 cm • IST not active • Blue – SSD 86% efficient, IST 99%, PXL2 96%, PXL1 97% = 79% @ 750 • Magenta – SSD 86% efficient, PXL2 88%, PXL1 98% = 74% @ 750 MeV/c • Red – SSD 81%, PXL2 91%, PXL1 98% = 72% @ 750 MeV/c

  6. Additional Detail • Enter a new detector configuration • vtx pxl1 pxl2 ist1 ist2prime tpc end kBlue • Radius Thickness PointResOn PointResOnZ DetRes DetResZ Density Efficiency • 0.229 0.0100 1067 1132 27 11520 0.21 0.86 • 0.140 0.0100 193 1291 17 1728 0.57 0.99 • 0.080 0.0028 121 1149 9 9 4.55 0.96 • 0.025 0.0028 61 166 9 9 44.99 0.97 • The single track efficiency (all layers combined) is 79.0504 percent. • vtx pxl1 pxl2 ist2prime tpc end kMagenta • Radius Thickness PointResOn PointResOnZ DetRes DetResZ Density Efficiency • 0.229 0.0100 1067 1132 27 11520 0.21 0.86 • 0.080 0.0028 321 1421 9 9 4.55 0.88 • 0.025 0.0028 59 126 9 9 44.99 0.98 • The single track efficiency (all layers combined) is 74.3411 percent. • vtx pxl1 pxl2 ist2 tpc end kRed • Radius Thickness PointResOn PointResOnZ DetRes DetResZ Density Efficiency • 0.200 0.0100 1140 1181 27 11520 0.28 0.81 • 0.080 0.0028 257 1407 9 9 4.55 0.91 • 0.025 0.0028 60 130 9 9 44.99 0.98 • The single track efficiency (all layers combined) is 72.0211 percent.

  7. Conclusions • Moving the SSD from 23 cm to 20 cm causes a loss in efficiency of about 5% for a single particle (worst case analysis) • This translates to about a 10% loss in efficiency for D0s • The exact amount of loss is pT dependent, and even particle species dependent • The hit density on the SSD goes up from .21 / cm2 to .28 / cm2 • Note that having 19 ladders active at 23 cm radius represents about the same efficiency as 18 ladders operating at 20 cm radius (both represent a 5% loss for single particles).

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