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HF Radiation Damage Evaluation (What, how, what to do about it, and what is next?)

HF Radiation Damage Evaluation (What, how, what to do about it, and what is next?). *Phil Dudero (TTU) ‏ Nural Akchurin March 20, 2013 TTU Group Meeting. Outline. The HF Detector Radiation Damage The Laser Monitoring System The Method Latest Results Plans. The HF Detector. HF Detector.

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HF Radiation Damage Evaluation (What, how, what to do about it, and what is next?)

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  1. TTU Group Meeting HF Radiation Damage Evaluation (What, how, what to do about it, and what is next?) *Phil Dudero (TTU)‏ Nural Akchurin March 20, 2013 TTU Group Meeting

  2. TTU Group Meeting Outline • The HF Detector • Radiation Damage • The Laser Monitoring System • The Method • Latest Results • Plans

  3. TTU Group Meeting The HF Detector

  4. TTU Group Meeting HF Detector

  5. Position of the HF • high eta region, 11m away from the IP, outside the B field March 20, 2013 TTU Group Meeting 5

  6. TTU Group Meeting HF construction 5mm HAD (143 cm) EM (165 cm) To cope with high radiation levels (>1 Grad accumulated in 10 years) the active part is Quartz fibers: the energy measured through the Cerenkov light generated by shower particles. • Iron calorimeter • Covers 5 > h > 3 • Total of 1728 towers, • h x fsegmentation (0.175 x 0.175) • Outside the B field: use regular PMTs

  7. TTU Group Meeting HF detector HBHE HF HCAL readout is integrating charge over each 25ns interval, and then digitizing, continuously

  8. TTU Group Meeting Location of Raddam Fibers 71 1 3 69 5 67 65 7 2 9 63 11 61 1 59 13 2 1 57 15 1 2 2 1 1 2 55 2 17 1 2 1 2 1 1 2 2 53 19 1 1 2 2 1 51 1 21 2 49 23 1 25 47 45 27 2 43 29 41 31 39 33 37 35 ij 1 → fiber assigned to depth 1 2 → fiber assigned to depth 2 similar pattern in HF-

  9. TTU Group Meeting Radiation Damage – The Concept With assistance from Jean-Pierre Merlo: CMS Week talk 9/28/2008 Nural Akchurin: HCAL DPG talk 3/8/2013

  10. TTU Group Meeting Intro (JP Merlo) • HF quartz fibres (Polymicro FSHA600630800 OH- 500ppm) when irradiated exhibit: • • Radiation damage increasing with dose, the light • absorption is high below 380nm, quite low near 450 nm, • rather high at 600 nm and negligible above 750 nm. • • Damage recovery when the irradiation stops. Maximum • effect near 450 nm. No recovery below 380 nm or above • 600 nm. 450 nm = mid zone of PMT’s sensitivity. • • With the recovery the calibration of a detector using • quartz fibres done after few days or weeks will appear • better than it was at the time of data taking.

  11. Why do we care? Reduced transmissivity → weaker detector response Changing detector response requires changing calibrations, or else Jets and missing energy get mismeasured HF becomes less useful to physics analyses …such as VBF Higgs, VBF diboson, etc. etc. where jets are expected in the forward region. March 20, 2013 TTU Group Meeting 11

  12. Quartz Attenuation Profile March 20, 2013 TTU Group Meeting 12

  13. Spectral Measurements Post Irradiation March 20, 2013 TTU Group Meeting 13

  14. Physics of Radiation Damage to Fused Silica - I • We “model” the effects of radiation on the fused silica fibers using binary molecular kinetics and the rate equations between these two (n=2) species thanks to Griscom. • The most important feature is that it gives us the prediction power where we can estimate the performance of the HF with dose/time. • Silica • Color Center March 20, 2013 TTU Group Meeting 14

  15. Estimated Dose at HF from 8 TeV Collisions • Estimate of the dose in HF, probably optimistic March 20, 2013 TTU Group Meeting 15

  16. Integrated Luminosity with Time March 20, 2013 TTU Group Meeting 16

  17. Transmission Loss in Four Regions of HF • 30 • 33 • 37 • 40 March 20, 2013 TTU Group Meeting 17

  18. Radiation Damage in First ~6 fb-1 - I • 30 • 33 • 37 • 40 March 20, 2013 TTU Group Meeting 18

  19. Radiation Damage in First ~6 fb-1 - II March 20, 2013 TTU Group Meeting 19

  20. Recovery after the First ~6 fb-1 in 150 days • 30 • 33 • 37 • 40 March 20, 2013 TTU Group Meeting 20

  21. Radiation Damage in Second ~6 fb-1 after Recovery • 30 • 33 • 37 • 40 March 20, 2013 TTU Group Meeting 21

  22. Radiation Damage in First and Second~6 fb-1 March 20, 2013 TTU Group Meeting 22

  23. Radiation Damage Profile in Depth (data) • These data were produced at 90 degrees (beam is perpendicular to the fiber axis). • We expect sourcing to provide similar information. • The previous (correlated) parametrization with a and b reproduces the shape of damage profile. March 20, 2013 TTU Group Meeting 23

  24. Radiation Damage Profile in Depth (data) • These data were produced at 90 degrees (beam is perpendicular to the fiber axis). • We expect sourcing to provide similar information. • The previous parametrization with a and b reproduces the shape of damage profile. March 20, 2013 TTU Group Meeting 24

  25. Comments • Made some progress towards understanding the basics of radiation damage to fused silica optical fibers • Small doses induce large effects • Dose rate matters • The damage parameters will likely to depend on r in HF • Relevance of the OTDR measurements on HF performance needs further investigation for the future. March 20, 2013 TTU Group Meeting 25

  26. TTU Group Meeting The Laser Monitoring System

  27. TTU Group Meeting Block Diagram

  28. TTU Group Meeting Fibers and pulses • - Inject 450 nm light through a capillary tube in a 2.5 m long fiber (two ends polished). 2.5 m = length of a regular fiber read by PMT. • - Reflection occurs at the two ends, signal S1 at the entrance and S2 at the far end. S2 coming 25 ns later. The reflected signals go to the PMT of a tower. • - The ratio R = S1 /S2 is related to the fiber transparency. R is stable when pulses are near the middle of the DAQ clocks. • - R depends on the accumulated dose D, and of post data taking time t for recovery). • - One Raddam fiber is installed at 7 pseudorapidity rings of 4 wedges for each HF. to PMT from laser

  29. TTU Group Meeting The Method

  30. Find S2/S1 stable region versus phase • Assemble digis for 56 RADDAM channels from raw data, convert from raw ADC to pedestal-subtracted femto-Coulombs (fC) • Find the two adjacent samples with max SfC amplitude, call the first S1 and the second S2. • allows for S2/S1 > 1 • Produces 25ns periodic function • Construct a metric that, when optimized, places the window size and position in the stable S2/S1 region versus laser phase with maximum statistics. • window optimization done per run, per channel • window size largely stable, but position drifts with the laser. March 20, 2013 TTU Group Meeting 30

  31. Study S2/S1 versus time/luminosity • Collect ratio S2/S1 per run, per channel • S2/S1 = proxy for transmissivity of the fibers • Add in date and integrated luminosity for each run • Assess degradation/recovery as functions of eta, total dose received. March 20, 2013 TTU Group Meeting 31

  32. TTU Group Meeting List of 2012 Raddam Runs List culled from ELOG, some runs eliminated for data quality

  33. TTU Group Meeting The Latest Results

  34. Sample Digis from Raddam channels March 20, 2013 TTU Group Meeting 34

  35. Phase scan, Depth 1 channels Blue = Laser TDC phase distribution Red= selected TDC phase window cut March 20, 2013 TTU Group Meeting 35

  36. Phase scan, Depth 2 channels Blue = Laser TDC phase distribution Red= selected TDC phase window cut March 20, 2013 TTU Group Meeting 36

  37. S2/S1 over the year, select channels (ih, ij) June TS March 20, 2013 TTU Group Meeting 37

  38. S2/S1 versus integrated lumi, select channels (ih, ij) March 20, 2013 TTU Group Meeting 38

  39. Why so jittery? Tightening phase cut didn’t help… S2/S1 with RMS spread per run shown March 20, 2013 TTU Group Meeting 39

  40. Cut on low amplitude pulses (S10 fC > 5000) …eliminated some runs entirely! March 20, 2013 TTU Group Meeting 40

  41. S10 fC versus time …the entire pulse is changing dramatically March 20, 2013 TTU Group Meeting 41

  42. …normalized to the first channel March 20, 2013 TTU Group Meeting 42

  43. Preliminary findings • There appears to be another source of event-to-event variations in pulse shape (phase?) other than laser jitter • There appears to be another part of the system affected by radiation than the embedded quartz fibers • Quartz fiber transmissivity appears to be roughly flat or slowly trending down. • System is sensitive to shutdowns and startups

  44. TTU Group Meeting Plans

  45. Plans for continued analysis • Analyze the 2011 runs in the same way • Establish a connection between the two years, a common normalization, since it is anticipated that a lot of the system dynamic response occurred in that year. • Write up an analysis note • Present at the next CMS week

  46. Plans for HF Upgrade (Nural) Purchase a new solid state laser with better triggering/timing features (~1 ns jitter at ~420 nm with reasonable power). It might be useful to use more than one laser/wavelength (420 nm 5XX nm?). The laser maybe located near the HFs. The pulse-to-pulse variation should be minimum but measured with PIN PDs or PMTs. There is no useful signal from the three PIN PD in CBOXs in HF racks. They were intended for normalization. Investigate if the raddam fibers can be changed/spliced to delay the reflected pulse such that there is one TS between the main and the reflected pulses. If timing features of the new system allow with the new laser(s), measure transmission in the abort gap. Automate the laser runs.

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