1. 2011 HV scan SF6 flow-meter accident 2011 Results 2010-2011 comparison RPC HV efficiency scan Pigi Paolucci on behalf of RPC collaboration

2. RPC – Why an HV scan ? 11/04/11 Pigi - RPC project - XEB 12 April 2 2010 pressure Δ P = 20 mbar 2010 efficiency Δε =10%  In 2010 we had not enough statistic to make a full efficiency scan  RPC system worked with 2 common HV working point 9.35 & 9.55 kV  RPC performance depends on P and T  We decided to do an HV scan per year: To define a WP per chamber in order to improve the performance and avoid to stress the detector. Choose a WP in the plateau region in order to avoid instability with pressure  RPC monitor stream is vital. Very high statistic in 1 hour at present L

3. HV scan – first 8 points RPC project - CMS GM 4 May 2011 3  18-19 March: HV scan (8 points – HV corrected with pressure )  27 March: full analysis completed  About 60% of the rolls have a very good efficiency sigmoid fit – more points needed !  An overall efficiency decrease of 3% seen in the only run comparable with 2011 WP !!! Pigi on behalf of RPC group plateau curves repository barrel endcap

4. HV scan – preliminary results 11/04/11 4 Pigi - RPC project - XEB 12 April Defined plateau region Knee 95% Working = knee + 150 V HV scan fit ε (HV) = ε max /(1 + e Slope (HV-HV50%) ) Working Point defined as Knee + 150 V taking into account the  P of 2010 We can reduce to 100 in case of rate problem and even less when we will correct the Effective HV with the pressure variations.

5. HV scan – 11 points RPC project - CMS GM 4 May 2011 5  15 April: 3 more points taken – scan completed (3.3 pb -1 BAD)  95% of the rolls have now a very good efficiency sigmoid fit Pigi on behalf of RPC group barrel endcap

6. HV scan – Chi2 distribution RPC project - CMS GM 4 May 2011 6 Pigi on behalf of RPC group

7. HV scan – all curves shifted RPC project - CMS GM 4 May 2011 7  it is now clear that was not an overall efficiency decrease but that  all curves were shifted forward about 120 ± 10 V (respect 2010) ??  We double checked HV, pressure, temperature, timing, Trigger,  selection checked  Everything seems to be ok – what about the GAS ? Pigi on behalf of RPC group Artificial shift of 110 Volts 2010

8. HV scan – curve shifted RPC project - CMS GM 4 May 2011 8 Pigi on behalf of RPC group HV scan 2010 Fit HV Scan 2011

9. HV scan – SF6 shift measurement RPC project - CMS GM 4 May 2011 9  16 April: Gas expert called  SF6 mass flow-meter replaced after few hours  18 April: System came back at nominal gas mixture  SF6 mass flow-control analyzed by Gas Group: not working properly - 30% more !!! 0.39% not 0.30% (flow-meter monitoring was stable and at 0.3%)  Only way to detect the failure was an external measurement with chromatograph  24 April: mini-scan in 2 sectors (39 rolls) to calibrate the shift due to the SF6 Pigi on behalf of RPC group  HV (0.39% SF6 – 0.30% SF6) at 50% eff HV 50% shifted of 100 Volts RMS is 19 Volts 100 Volts renormalization will be applied to all the curves

10. HV scan – working points RPC project - CMS GM 4 May 2011 10  30 April:  Rolls WP merged in chamber and then in HV channel (1 HV ch.  4 bi-gap rolls)  2011 final HV working point table is ready (average of 4 rolls WP)  System should be now more stable.vs. pressure  About 65% were working closer to the knee in the 2010 Pigi on behalf of RPC group Nominal voltage 2010 Nominal voltage 2010  P 2011  P

11. HV scan – final results I RPC project - CMS GM 4 May 2011 11  2172 (99%) fits are good (51 recovered deleting 1-2 bad points)  Only 23 OFF rolls are without plateau Pigi on behalf of RPC group All Barrel HV scan 2011 HV value at 50% eff Barrel RMS 64 Volts Endcap RMS 84 Volts

12. Pigi on behalf of RPC group RPC project - CMS GM 4 May 2011 12

13. Pigi on behalf of RPC group RPC project - CMS GM 4 May 2011 13 Cluster size noise Public results on WEB page

14. HV scan – final results I RPC project - CMS GM 4 May 2011 14  Also low efficiency rolls have a very nice plateau Pigi on behalf of RPC group barrel 1 Front End board broken

15. HV scan – final results II RPC project - CMS GM 4 May 2011 15 Pigi on behalf of RPC group 2010 2011 Average Effective voltage over 1 month kV P T cut > 0 GeV Effective voltage in 1 hour 9.35 & 9.55 kV P T cut > 7 GeV Systematic error of about 1%

16. ClusterSizeBarrel 2010 2011 Average Effective voltage over 1 month kV P T cut > 0 GeV Effective voltage in 1 hour 9.35 & 9.55 kV P T cut > 7 GeV Pigi on behalf of RPC group 16 RPC project - CMS GM 4 May 2011

17. Cluster size distribution at WP Pigi on behalf of RPC group RPC project - CMS GM 4 May 2011 17 Cluster size distribution at the 2011 HV channel WP Measurement will be re-done in 1 day after the TS = 1.6 RMS 0.23

18. HV scan – gas monitoring improvements RPC project - CMS GM 4 May 2011 18  Central gas group is helping a lot in understanding the SF6 flow-meter failure and in improving the monitoring of this crucial component – Thanks  SF6 flow-meter is today monitored by the gas group with a gas chromatograph until the automatic procedure will be ready (June)”  RPC Gas system review 3 May (today):  Gas Gain Monitor could be used to monitor the gas mixture (under study)  Gas monitor parameters alarm/warning have been reviewed  Instructions for the RPC shifter will be updated Pigi on behalf of RPC group

19. Conclusions Pigi on behalf of RPC group RPC project - CMS GM 4 May 2011 19  Barrel Gaps have been produced from 2003 and after 8 years  Stability and uniformity of 2172 bi-gap rolls is now evident:  All the efficiency curve fits are good – 23 (1%) rolls are OFF  Average efficiency ≈ 95% - stable in time (2010-2011)  Efficiency RMS = 5%  HV 50% distribution has RMS = 64 Volts and 84 Volts (very uniform set)  HV working point table is now ready. It will be uploaded after TS  Expected at WP are 95-96 % and more stable.vs. P & T  SF6 is a critical component for RPC detector 30% more corresponds to 110 Volts  Gas chromatograph automatic measurement needed to control the gas mixture  Online HV correction with pressure is needed to reduce the operating voltage and keep safe the detector (under-study) Final results WEB page