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

2. 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

3. H4 TB 2007 irradiation data sets
Pos 1: 131, 132, 151, 152 (BTCP)
No pulser
3 kHz pulser
3 kHz pulser (collimator studies)
600 Hz pulser (VPT rate studies)
120, 600, 1000 Hz pulser for 152
Pos 2: 136, 137, 156, 157 (BTCP)
No pulser
3 kHz pulser
3 kHz pulser
Pos 3: 236, 237, 256, 257 (SIC)
No pulser
3 kHz pulser
3 kHz pulser
Pos 4: 336, 337, 356, 357 (BTCP)
No pulser
3 kHz pulser
Pos 5: 437, 438, 457, 458 (BTCP)
3 kHz pulser
Pos 6: x431, 432, 451, 452 (SIC)
3 kHz pulser
Pos 7: 231, 232, 251, 252 (BTCP)
3 kHz pulser
Pos 9: 422, 423, 442, 443 (BTCP)
No pulser
Pos 10: 127, 128, 147, 148 (SIC)
No pulser
Pos 11: 123, 124, 143, 144 (SIC)
No pulser
Pos 12: 174, 175, 194, 195 (BTCP)
1 kHz pulser
11/27/2018
Christopher Rogan - TB 2007 Analysis Meeting

4. 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

5. 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

6. 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 )
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

7. 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

8. 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

9. 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

10. 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
11/27/2018
Christopher Rogan - TB 2007 Analysis Meeting

11. 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

12. ‘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

13. ‘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

14. 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

15. ‘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

16. 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

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

18. 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

19. 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

20. 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