Update on TB 2007 Xtal Irradiation Studies at H4 Test-beam 2007 Analysis Meeting 24-10-07 Christopher Rogan California Institute of Technology

Christopher Rogan - TB 2007 Analysis Meeting 24-10-07 Introduction Irradiation studies at H4 TB 2007 A priori we assume that there is one alpha value that describes BTCP xtals and one for SIC xtals and that individual xtals have alpha values within some characteristic spread from these mean values The goal is to measure as many alpha values as possible in order to quantify the validity of this assumption Additionally, we can examine whether subsequent irradiations of single xtals yield the same alpha value Offline corrections using the laser monitoring require values of not only APD(VPT)/PN for each channel but also alpha. 11/27/2018 Christopher Rogan - TB 2007 Analysis Meeting 24-10-07

H4 TB 2007 irradiation data sets Pos 1: 131, 132, 151, 152 (BTCP) No pulser - 21038-21080 3 kHz pulser - 21245-21284 3 kHz pulser - 21393-21470 (collimator studies) 600 Hz pulser - 22019-22072 (VPT rate studies) 120, 600, 1000 Hz pulser for 152 Pos 2: 136, 137, 156, 157 (BTCP) No pulser - 20803-20817 3 kHz pulser - 21082-21196 3 kHz pulser - 21285-21325 Pos 3: 236, 237, 256, 257 (SIC) No pulser - 20952-21004 3 kHz pulser - 21199-21213 3 kHz pulser - 21326-21374 Pos 4: 336, 337, 356, 357 (BTCP) No pulser - 21007-21036 3 kHz pulser - 21213-21228 Pos 5: 437, 438, 457, 458 (BTCP) 3 kHz pulser - 21506-21521 Pos 6: x431, 432, 451, 452 (SIC) 3 kHz pulser - 21498-21505 Pos 7: 231, 232, 251, 252 (BTCP) 3 kHz pulser - 21838-21902 Pos 9: 422, 423, 442, 443 (BTCP) No pulser - 22073-22114 Pos 10: 127, 128, 147, 148 (SIC) No pulser - 22466-22490 Pos 11: 123, 124, 143, 144 (SIC) No pulser - 22718-22751 Pos 12: 174, 175, 194, 195 (BTCP) 1 kHz pulser - 22930-22962 11/27/2018 Christopher Rogan - TB 2007 Analysis Meeting 24-10-07

Shooting at ‘corners’ Xtal 137 Xtal 157 centered at raw hodo (-6.0, 4.5) centered at raw hodo (4.0, 4.5) x hodo xtal w/ maximum response profile Xtal 136 Xtal 156 centered at raw hodo (-6.0, -5.5) centered at raw hodo (4.0, -5.5) y hodo At each ‘position’ the beam is centered on the corner of 4 xtals 3 cm x 3 cm trigger reaches center of all 4 xtals 11/27/2018 Christopher Rogan - TB 2007 Analysis Meeting 24-10-07

Extracting ‘alpha’ values First strategy: use ‘correlation plot’ 4 mm x 4 mm hodoscope cut around point of maximum response ‘electron’ and ‘laser’ response values taken from distribution fit 1st irradiation no pulser xtal 152 120 GeV e- centered at raw hodo (4.0, 4.5) 11/27/2018 Christopher Rogan - TB 2007 Analysis Meeting 24-10-07

Extracting ‘alpha’ values Fitted Sigma as function of Alpha RMS as function of Alpha New strategy: minimize xtal energy resolution with respect to alpha value (see talk by C. Rogan in the Xtal PG meeting Sept 19 2007) Transparency changes affect electron responses - degrades energy resolution. Laser monitoring system (and optimal choice of alpha) is designed to minimize resolution Fitted (gaussian) sigma is not a smooth function of alpha Instead, use RMS of energy distribution with selected events - smooth function Problem become one dimensional minimization (for single xtal) Sigma / mean Sigma / mean E9 resolutions 2006 TB SM22 - xtal 168 120 GeV e- 11/27/2018 Christopher Rogan - TB 2007 Analysis Meeting 24-10-07

Extracting ‘alpha’ values New strategy: minimize xtal energy resolution with respect to alpha value (E25 approach, see XPG talk) 1st irradiation no pulser xtal 152 120 GeV e- centered at raw hodo (4.0, 4.5) sigma ~ 1.2 % Alpha is calculated in 25 different 2 mm x 2 mm hodoscope bins at the corner of the 3 cm x 3 cm trigger located in the center of the xtal 11/27/2018 Christopher Rogan - TB 2007 Analysis Meeting 24-10-07

First look at alpha values pos 12 pos 1 pos 2 pos 7 pos 4 pos 9 pos 5 BTCP alphas xtal No pulser pos 3 pos 11 pos 10 pos 6 3 kHz pulser 1 kHz pulser SIC alphas Here, xtal numbering is in ‘CMS frame For example: H4 148 = CMS 152 xtal 11/27/2018 Christopher Rogan - TB 2007 Analysis Meeting 24-10-07

Alpha extraction issues Run 20886, pos 2 hits hits xtal 136, 137 xtal 136, 156 xtal 156, 157 xtal 137, 157 x hodo position y hodo position The boxed regions above show the range of the 5 x 5 hodoscope bins for each xtal used for alpha extraction Trade-off between having bins closer to the center of xtals and # of events. Also, trade-off between # of hodo bins and # of events/per bin Binning should be optimized for each irradiation period to improve resolution of alpha values 11/27/2018 Christopher Rogan - TB 2007 Analysis Meeting 24-10-07

VPT instabilities Unstable VPT behaviour at SPS emulated in the lab ‘Measuring’ LEDs at 1 Hz: 1) Response stable to 0.5% as background illumination rate increased 2) Response rises by 26% as background illumination rate decreased 3) Response back to within 0.5% of ‘normal’ as background illumination rate increased again 10kHz of ‘250GeV’ events draws 7nA of Anode current – similar to max extra H4 in-spill current Points clustered together at 1, 10 & 100 Hz are at fixed frequency, but ordered in time for visibility < 0.1Hz points all have 0Hz of background 3 2 1 45 minutes From Ken Bell, ECAL Test-beam Meeting, July 6 2004 11/27/2018 Christopher Rogan - TB 2007 Analysis Meeting 24-10-07

In/out of high-rate VPT effects Run 20780 Run 20800 ~1% ~2% 8 min 3 min 6 min 1.5 min End high rate Begin high rate 1st irradiation no pulser xtal 132 120 GeV e- Clear ‘VPT effect’ going out of high rate with no pulser No visible ‘VPT effect’ going into high rate for any irradiations 11/27/2018 Christopher Rogan - TB 2007 Analysis Meeting 24-10-07

‘VPT effects’ Greater transparency change means less change in alpha Normalized VPT response, including xtal transparency change Normalized VPT/PN response, including xtal transparency change VPT/PN laser response VPT electron response (changing?) VPT gain factor During xtal transparency change, the relationship between the electron and laser response can be parameterized by: Changing VPT gain factor has this affect on measurement of alpha: Greater transparency change means less change in alpha The closer alpha is to 1, the less change in alpha Only a changing VPT gain factor during the irradiation period changes the alpha measurement 11/27/2018 Christopher Rogan - TB 2007 Analysis Meeting 24-10-07

‘VPT effects’ To validate the previous calculations regarding changing VPT gain factors, we consider a toy situation: Changing VPT gain factor Linearly changing VPT gain factor (total 1% change) 3% change in laser response ‘real’ alpha 1.05, ‘measured’ alpha 1.062 R - plot without changing VPT gain factor R - plot with changing VPT gain factor 11/27/2018 Christopher Rogan - TB 2007 Analysis Meeting 24-10-07

Xtal 137 (pos 2) Xtal 137 irradiated 3 different times Alpha measured to be close to one - insensitive to any potential VPT effects Repeated measurements of alpha give approximately the same value - first indication that repeated irradiations yield same value for xtals 1st irradiation - no pulser 2nd irradiation - 3kHz pulser 2nd irradiation - 3kHz pulser 11/27/2018 Christopher Rogan - TB 2007 Analysis Meeting 24-10-07

‘VPT effects’ Significant change in VPT gain factor necessary in order to change measured alpha, even for values of alpha not near 1: Changing VPT gain factor Linearly changing VPT gain factor (total .5% change) 10% change in laser response ‘real’ alpha 1.5, ‘measured’ alpha 1.525 R - plot without changing VPT gain factor R - plot with changing VPT gain factor 11/27/2018 Christopher Rogan - TB 2007 Analysis Meeting 24-10-07

Christopher Rogan - TB 2007 Analysis Meeting 24-10-07 Outlook Analysis of H4 TB 2007 irradiation data is well underway - expect about 80 alpha values in total Draft of note on H4 TB 2006 irradiation data will be completed in next few weeks Analysis of TB 2007 irradiation data will be completed by spring Toy Monte-Carlo demonstrating in situ alpha extraction with pi0 intercalibration will be completed by spring 11/27/2018 Christopher Rogan - TB 2007 Analysis Meeting 24-10-07

Christopher Rogan - TB 2007 Analysis Meeting 24-10-07 EXTRA SLIDES 11/27/2018 Christopher Rogan - TB 2007 Analysis Meeting 24-10-07

Energy resolution minimization Alpha vs. iteration Use iterative method to minimize energy resolution as a function of alpha For one xtal can, for example, use a parabolic interpolation minimization (Brent’s method) Algorithm converges quickly For selected events one can extract alpha with arbitrary precision Resolution vs. iteration SM22 - xtal 168 120 GeV e- 11/27/2018 Christopher Rogan - TB 2007 Analysis Meeting 24-10-07

Systematic error of the slope extraction Selects events within a ‘sigma window’ for fitted raw data Alpha value appears independent of ‘window’ size Small spread in alpha value distribution from different sets of events .008 .58% Alpha SM22 - xtal 168 120 GeV e- 11/27/2018 Christopher Rogan - TB 2007 Analysis Meeting 24-10-07

Resolution minimization summary Resolution of alpha parameter is closely related to magnitude of transparency change - should be taken into consideration for future irradiations Appreciable spread in alpha values between xtals - must calculate alpha in situ Dispersion of  for 35 BTCP crystals 2002 # Crystals 2003 mean = 1.538 /mean  6% 2004 (fall) 2004 (spring) 2006 (center)  alpha vs. % transparency change 2006 (neighbor)  11/27/2018 Christopher Rogan - TB 2007 Analysis Meeting 24-10-07