TTU Group MeetingMarch 20, 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

March 20, Outline The HF Detector Radiation Damage The Laser Monitoring System The Method Latest Results Plans

TTU Group MeetingMarch 20, The HF Detector

TTU Group MeetingMarch 20, HF Detector

Position of the HF TTU Group MeetingMarch 20, high eta region, 11m away from the IP, outside the B field

TTU Group MeetingMarch 20, HF construction HAD (143 cm) EM (165 cm) 5mm Iron calorimeter Covers 5 >  > 3 Total of 1728 towers,  x  segmentation (0.175 x 0.175) Outside the B field: use regular PMTs 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.

TTU Group MeetingMarch 20, HF detector HCAL readout is integrating charge over each 25ns interval, and then digitizing, continuously HBHEHF

TTU Group MeetingMarch 20, Location of Raddam Fibers ii 1 → fiber assigned to depth 1 2 → fiber assigned to depth 2 similar pattern in HF-

TTU Group MeetingMarch 20, Radiation Damage – The Concept With assistance from Jean-Pierre Merlo: CMS Week talk 9/28/2008 Nural Akchurin: HCAL DPG talk 3/8/2013

Intro (JP Merlo) HF quartz fibres (Polymicro FSHA 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. TTU Group MeetingMarch 20,

TTU Group MeetingMarch 20, 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.

Quartz Attenuation Profile TTU Group MeetingMarch 20,

Spectral Measurements Post Irradiation TTU Group MeetingMarch 20,

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 TTU Group MeetingMarch 20,

Estimated Dose at HF from 8 TeV Collisions Estimate of the dose in HF, probably optimistic TTU Group MeetingMarch 20,

Integrated Luminosity with Time TTU Group MeetingMarch 20,

Transmission Loss in Four Regions of HF TTU Group MeetingMarch 20,

Radiation Damage in First ~6 fb -1 - I TTU Group MeetingMarch 20,

Radiation Damage in First ~6 fb -1 - II IetadD/dt [rad/s] a (95% Conf. Bounds) [dB/m] b (95% Conf. Bounds) x (-1.36, 4.12)0.39 (0.21, 0.58) x (-0.46, 9.93)0.59 (0.47, 0.72) x (0.40, 4.45)0.72 (0.58, 0.86) x (0.75, 1.82)0.79 (0.68, 0.91) TTU Group MeetingMarch 20,

Recovery after the First ~6 fb -1 in 150 days TTU Group MeetingMarch 20,

Radiation Damage in Second ~6 fb -1 after Recovery TTU Group MeetingMarch 20,

Radiation Damage in First and Second ~6 fb -1 IetadD/dt [rad/s] a (95% Conf. Bounds) [dB/m] b (95% Conf. Bounds) x x (-1.36, 4.12) (-690, 716) 0.39 (0.21, 0.58) 0.69 (-4.9, 6.3) x x (-0.46, 9.93) 9.85 (-211, 230) 0.59 (0.47, 0.72) 0.75 (-2.1, 3.6) x x (0.40, 4.45) 7.76 (-7.4, 22,9) 0.72 (0.58, 0.86) 1.00 (0.62, 1.38) x x (0.75, 1.82) 1.99 (0.94, 3.06) 0.79 (0.68, 0.91) 1.07 (0.89, 1.25) TTU Group MeetingMarch 20,

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. TTU Group MeetingMarch 20,

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. TTU Group MeetingMarch 20,

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. TTU Group MeetingMarch 20,

TTU Group MeetingMarch 20, The Laser Monitoring System

Block Diagram TTU Group MeetingMarch 20,

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. TTU Group MeetingMarch 20, to PMT from laser

TTU Group MeetingMarch 20, The Method

Find S2/S1 stable region versus phase 1.Assemble digis for 56 RADDAM channels from raw data, convert from raw ADC to pedestal-subtracted femto-Coulombs (fC) 2.Find the two adjacent samples with max  fC amplitude, call the first S1 and the second S2. –allows for S2/S1 > 1 –Produces 25ns periodic function 3.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. TTU Group MeetingMarch 20,

Study S2/S1 versus time/luminosity 4.Collect ratio S2/S1 per run, per channel –S2/S1 = proxy for transmissivity of the fibers 5.Add in date and integrated luminosity for each run 6.Assess degradation/recovery as functions of eta, total dose received. TTU Group MeetingMarch 20,

List of 2012 Raddam Runs TTU Group MeetingMarch 20, List culled from ELOG, some runs eliminated for data quality

TTU Group MeetingMarch 20, The Latest Results

Sample Digis from Raddam channels TTU Group MeetingMarch 20,

Phase scan, Depth 1 channels TTU Group MeetingMarch 20, Blue = Laser TDC phase distributionRed = selected TDC phase window cut

Phase scan, Depth 2 channels TTU Group MeetingMarch 20, Blue = Laser TDC phase distributionRed = selected TDC phase window cut

S2/S1 over the year, select channels TTU Group MeetingMarch 20, (i , i  ) June TS

S2/S1 versus integrated lumi, select channels TTU Group MeetingMarch 20, (i , i  )

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

Cut on low amplitude pulses (   fC > 5000) TTU Group MeetingMarch 20, …eliminated some runs entirely!

  fC versus time TTU Group MeetingMarch 20, …the entire pulse is changing dramatically

…normalized to the first channel TTU Group MeetingMarch 20,

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

TTU Group MeetingMarch 20, Plans

Plans for continued analysis 1.Analyze the 2011 runs in the same way 2.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. 3.Write up an analysis note 4.Present at the next CMS week

Plans for HF Upgrade (Nural) 1.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. 2.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. 3.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. 4.If timing features of the new system allow with the new laser(s), measure transmission in the abort gap. 5.Automate the laser runs.