Transcript Slide 1

Measuring transparency change and gain change with
two wavelengths
Test-beam 2007 Analysis Meeting 21-11-07
Christopher Rogan
California Institute of Technology
Introduction
 Goal: To study the systematics of using a second wavelength
to disentangle simultaneous xtal transparency changes and VPT
gain changes
 Modeling transparency change
 Simulating the monitoring scheme
 Studying monitoring systematics
 The choice of
affects monitoring precision through LED
(laser) system precision and in the value of
7/17/2015
Christopher Rogan - TB 2007 Analysis Meeting 21-11-07
2
Modeling transparency change
• Recovery time constant:
• Damage time constant:
• Increased dose-rate results in
smaller damage time constant
• Each color-center has
and
values; dynamics of color center
density independent of other
color centers
•Similar to model used in
CMS RN 2004/001
7/17/2015
Christopher Rogan - TB 2007 Analysis Meeting 21-11-07
3
Modeling transparency change
• Data suggests two pairs of time constants:
@ 100 rad/h:
•Values of
CMS RN 2004/001
and
are subsequently estimated
Ren-yuan Zhu, CMS ECAL Week DPG, Nov. 3, 2005
7/17/2015
Christopher Rogan - TB 2007 Analysis Meeting 21-11-07
4
Modeling transparency change
• Total damage related
R = 25.6 rad/h
to
from previous
slide and dose-rate
•‘steady-state’
fluctuations’ magnitude
depends on interplay
between damage and
recovery time constants
and LHC fill cycle time
10 hour LHC
fill cycle
~ .65 %
• higher dose-rate =>
greater transparency
change
•
small =>
larger ‘steady-state’
fluctuations
7/17/2015
Christopher Rogan - TB 2007 Analysis Meeting 21-11-07
5
Monitoring simulation
R = 25.6 rad/h
(barrel)
1000 evenly distributed
‘electron’ events
R = 300 rad/h
(endcap)
Laser and LED points
every 20 min.
Assumptions:
•
•
•
normalized blue laser response
normalized red laser (LED) response
normalized ‘electron’ response
•
•
• ‘Real’ LED and ‘electron’ responses
can be calculated from simulated
laser response
7/17/2015
Christopher Rogan - TB 2007 Analysis Meeting 21-11-07
6
Monitoring simulation
R = 25.6 rad/h
‘Noise’ is added to the
‘real’ responses. For the
laser and LED, ‘noise’
refers to monitoring
precision. The nominal
values used for this
study are:
•
•
•
The nominal value of
is set at 1.5
The nominal value of
is estimated from xtal
absorption and
transmittance spectra to
be 3.0 for
7/17/2015
Christopher Rogan - TB 2007 Analysis Meeting 21-11-07
7
VPT gain changes
R = 25.6 rad/h
VPT gain changes are simulated
as a sinusoid with nominal
oscillation magnitude of 1 %
Normalized VPT gain factor
The ‘measured’ laser and LED
responses are given by:
The VPT gain change can be calculated from the
‘measured’ laser and LED responses. The
responses corrected with
are shown in
green:
7/17/2015
Christopher Rogan - TB 2007 Analysis Meeting 21-11-07
8
Corrected ‘electron’ response
R = 25.6 rad/h
• Transparency change and changing VPT
gain factor severely degrades ‘electron’
resolution
• Correction, with nominal values described
earlier, gives ~.2 % error, where the error is
the nominal ‘electron’ resolution subtracted in
quadrature from the measured resolution
‘Measured’ ‘electron’
response:
RMS ~ .73 %
RMS ~ 1.1 %
RMS ~ .55 %
Corrected ‘electron’
response:
7/17/2015
Christopher Rogan - TB 2007 Analysis Meeting 21-11-07
9
Monitoring systematics
R = 300 rad/h
Transparency change 5 %
LED monitoring precision (%)
For these studies, 1000 ‘electron’ points used to measure
resolution. 1000 iterations with new random numbers for
each set of parameters
Resulting resolution is very sensitive to the value of
(1.5)
7/17/2015
Christopher Rogan - TB 2007 Analysis Meeting 21-11-07
as it approaches
10
Monitoring systematics
R = 300 rad/h
Error is independent of
magnitude of VPT gain change
and
decrease with transparency change. Fixed
and
implies error increases with magnitude of transparency change
7/17/2015
Christopher Rogan - TB 2007 Analysis Meeting 21-11-07
11
Monitoring systematics
R = 25.6 rad/h
Transparency change 5 %
Laser monitoring precision (%)
For monitoring with one wavelength in the barrel:
Dependency on laser noise and transparency change is qualitatively the
same as for two wavelength scheme
7/17/2015
Christopher Rogan - TB 2007 Analysis Meeting 21-11-07
12
Resolution of alpha
w/ all other noise removed
constant 5% transparency
change
10% error in alpha
Only error in the
mean considered
here
uncorrected
Error in the alpha parameter yields two types
of error in measurements
Firstly, it shifts the mean of the corrected
‘electron’ response. Intercalibration constants
must take this in to account.
7/17/2015
Christopher Rogan - TB 2007 Analysis Meeting 21-11-07
13
Resolution of alpha
R = 25.6 rad/h
Transparency change 5 %
Secondly, error in alpha degrades
the resolution of the corrected
‘electron’ response.
Error sensitivity to alpha resolution
increases with increased
transparency change
corrected ‘electron’ resolution
7/17/2015
Christopher Rogan - TB 2007 Analysis Meeting 21-11-07
14
Resolution of alpha
R = 300 rad/h
w/ VPT gain
change
Transparency change 5 %
with two wavelengths:
Error is less
sensitive to
due to
7/17/2015
Christopher Rogan - TB 2007 Analysis Meeting 21-11-07
15
Conclusion
 The choice of
systematically affects the monitoring precision in
two distinct ways:
 How far
is in the infrared affects how much light the VPT’s see, and as
a result the precision of monitoring with the LED

determines the value of
. All the errors in a two wavelength
scheme are inversely proportional to
 Systematic uncertainty in the monitoring system depends on
 Laser and LED monitoring precision
 Damage and recovery time constants along with LHC fill cycle times
 The magnitude of transparency change
 Uncertainty the alpha parameters for both wavelengths
 This study illustrates the importance of understanding the values of
alpha for xtals.
7/17/2015
Christopher Rogan - TB 2007 Analysis Meeting 21-11-07
16
EXTRA SLIDES
7/17/2015
Christopher Rogan - TB 2007 Analysis Meeting 21-11-07
17
Monitoring systematics
Monitoring with two-wavelengths:
All errors go as
7/17/2015
Christopher Rogan - TB 2007 Analysis Meeting 21-11-07
18
Monitoring systematics
5% transparency change, R = 300 rad/h
Error independent of VPT gain change magnitude
7/17/2015
Christopher Rogan - TB 2007 Analysis Meeting 21-11-07
19
Monitoring systematics
R = 300 rad/h
5% transparency change
Error independent of VPT gain change magnitude
7/17/2015
Christopher Rogan - TB 2007 Analysis Meeting 21-11-07
20
Monitoring systematics
Monitoring with one wavelength:
7/17/2015
R = 25.6 rad/h
Christopher Rogan - TB 2007 Analysis Meeting 21-11-07
21