Proposed Change to CLCT Pretrigger

1. Proposed Change to CLCT Pretrigger • Proposal: • Study changing from 2- to 3-layer pretrigger for CLCT • Study the same for ALCT • Possible benefits: • Lower rate of CLCT pretriggers lowers deadtime at high luminosity • Lower rate of CLCT pretriggers decreases SCA occupancy • The change MAY improve CLCT efficiency • The change MAY improve CLCT timing • Cartoon: highly angled track: 2-layer but not 3-layer pretrigger Also will cut away pretriggers from 2-layer neutron hits CSC DPG/Commissioning Meeting Jay Hauser

2. CLCT Efficiency • From Elog entry 59743 (20-May-09): • “Past Slice Test studies (August 2007) indicated that this may improve cathode trigger efficiency by a small fraction of a percent. A plot of this effect is attached.” Disclaimer: ‘the "efficiencies" shown in the plot attached use the CLCT in n-layer trigger mode, so that when the ALCT fires, any combination of n layers hit will trigger the CLCT. This is a way of getting an algorithmic efficiency that can be gleaned from TMB counters information online. The slight loss of efficiency (on the order of 1%) may be largely due to hits at the ends of the wires (last 5mm on each end), where cathode strip coverage within the chamber is incomplete.’ CSC DPG/Commissioning Meeting Jay Hauser

3. High-luminosity effect • Electronics effect of a CLCT pretrigger: • Causes SCA blocks to be frozen in CFEBs • Causes cathode trigger deadtime of a few bx  trigger ineff. • Plot from Khotilovich May 13-15, 2009 CMS upgrade workshop, 400 pile-up events/bx from L=1035/cm2s: Efficiency loss is significant for ME1/1 Note: the simulation of CLCT-ALCT matching has been improved (Valuev) since this plot CSC DPG/Commissioning Meeting Jay Hauser

4. ALCT and CLCT Details • ALCT and CLCT both work the same way: • Hits arrive over 2-3 bx due to drift time variations. • Hits are made “persistent” for several bunch crossings. • Coincidence level>=2 layers in a pattern (“pretrigger”) defines TIME. • Fixed “drift delay”, then coincidence level>=4 layers in a pattern validates the LCT (“trigger”) and defines SPACE position • Current parameters: • (same for all chambers) Too long, 4 bx better matched to 2 bx drift delay CSC DPG/Commissioning Meeting Jay Hauser

5. Test runs: 100K events each in quick succession CLCT 2/4, and ALCT 2/4 planes (baseline) Same as previous but change clct_hit_persist from 64 bx CLCT 3/4, and ALCT 2/4 planes (CLCT changes) CLCT 3/4, and ALCT 2/4 planes (ALCT changes) CLCT 3/4, and ALCT 3/4 planes (both change) Should NOT measurably affect CLCT or ALCT or matched LCT rates with cosmic rays Study performance with DQM and offline ALCT-CLCT relative timing accuracy CLCT efficiency Etc. Must then agree on such a change Trivial to implement – parameters in XML configuration files Some tuning possible: CLCT will be later relative to ALCT by ~6 ns (0.25 bx). Should not affect LCT timing to SP. Detailed Proposal CSC DPG/Commissioning Meeting Jay Hauser

6. Update June 2: Test run data collected 26-May-09 • About 200K events per run • Run 97511 ALCT=2, CLCT=2 layers baseline • Run 97557 change to CLCT hit persistence=4 bx • Run 97563 ALCT=2, CLCT=3 layers • Run 97568 ALCT=3, CLCT=2 layers • Run 97574 ALCT=3, CLCT=3 layers • Run 97577 ALCT=2, CLCT=2 return to baseline, long run • Next slide: results from offline CSC DQM for one chamber • ME-3/2/28 at bottom so “collision-like” muon angles CSC DPG/Commissioning Meeting Jay Hauser

7. ALCT: 2 CLCT: 2 ALCT: 2 CLCT: 3 ALCT: 3 CLCT: 2 ALCT: 3 CLCT: 3 ALCT-CLCT timing with pretrigger layers 2, 3 CSC DPG/Commissioning Meeting Jay Hauser