FDIRC MC Studies:
PMT Coupling Options
Doug Roberts
University of Maryland
Overview
• Want to study the effect of PMT coupling options to
the Focusing Block
• Either just Air
• Or some type of optical coupling
• Just air would make PMT removal much easier
• But, we would lose some photons incident to the
PMT face at larger angles do to index mismatch
• How big of an effect is this on the resolution?
Momentum (GeV)
Number of P.E. vs Momentum and Cos(q)
Entries
234430
7
220
200
6.5
180
6
160
140
5.5
120
100
5
80
4.5
60
40
4
20
3.5
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
Studied with di-muon tracks
High momentum muons, generated over all dip angles
Full barrel detector simulation with magnetic field on
Hamamatsu H8500, 12 mm x 6 mm pixels
0.8
1
cos(q)
0
Photoelectrons vs. cosq
Average Number of P.E.
Number of P.E. vs. cos(q)
Entries 7437694
80
70
60
50
40
30
20
10
0
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
Average Number of P.E.
Ratio, WithAir/WithoutAir
0.8
1
cos( q)
Entries 1.731885e+07
1
0.95
0.9
0.85
0.8
0.75
0.7
0.65
0.6
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
cos( q)
Photoelectrons per Event
No Air Gap
<NPE> = 35
Number of PE per event
With Air Gap
<NPE> = 28
nGamEvent
Entries 234429
7000
Number of PE per event
nGamEvent
Entries 234425
10000
Mean
34.76
Mean
27.55
RMS
19.23
RMS
14.87
8000
6000
5000
6000
4000
4000
3000
2000
2000
1000
0
0
20
40
60
80
100
120
140
0
0
20
40
60
80
100
120
140
qX, No Air
thetaXNoAir
thetaXAir
Entries 5636243
7197759
Mean
0.4297
0.4991
RMS
0.3002
0.27
´103
100
80
60
40
20
0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
rad
Compare qX as photon leaves bar
Black = no air gap
Red = air gap
Actual angle at focal plane also a function of qY
Single g qC Resolution
No Air Gap
s = 8.834 mrad
DqC, No Time Correction
With Air Gap
s = 8.775 mrad
delTcNoCorr
´103
Entries
Mean
0.1082
RMS
20.58
N
8.712e+04 ± 6.236e+01
80000
8.834 ± 0.007
0.2366 ± 0.0004
p0
p1
9.332e-06 ± 2.881e-06
p2
-2.264e-05 ± 2.205e-07
0.5067
20.69
RMS
c2 / ndf
N
70000
0.1875 ± 0.0055
Sigma
3.071513e+07
Mean
2346 / 94
Mean
80
delTcNoCorr
Entries
3.869581e+07
c2 / ndf
100
DqC, No Time Correction
2344 / 94
6.452e+04 ± 5.227e+01
0.2295 ± 0.0063
Mean
8.775 ± 0.008
Sigma
60000
50000
p0
0.2552 ± 0.0005
p1
0.0002137 ± 0.0000033
p2
-2.918e-05 ± 2.543e-07
60
40000
40
30000
20000
20
-50 -40 -30 -20 -10
0
10
20
30
40 50
mrad
10000
-50 -40 -30 -20 -10
0
10
20
30
40 50
mrad
Event Resolutions
• What really matters is the single event resolution
• This is where losing photons will be seen
• Technique: Take qC measurements for all photons in
an event and fit to the profile of the single g qC
resolution with everything fixed except the mean
and normalization
• Probably not the optimal way to extract qC, but ok
for comparison?
Event qC Resolution
No Air Gap
s = 2.94 mrad
Fit Mean per Event
With Air Gap
s = 3.27 mrad
TcMeanEvent
16000
Fit Mean per Event
TcMeanEvent
Entries
234245
Entries
Mean
0.2365
Mean
RMS
3.244
RMS
c2 / ndf
4843 / 96
14000
12000
Mean
0.236 ± 0.006
Sigma
2.943 ± 0.006
0.203
3.535
c2 / ndf
Constant 1.546e+04 ± 4.377e+01
14000
234197
3867 / 97
Constant 1.395e+04 ± 3.903e+01
12000
Mean
0.214 ± 0.007
Sigma
3.272 ± 0.006
10000
10000
8000
8000
6000
6000
4000
4000
2000
2000
0
-25 -20 -15 -10
-5
0
5
10
15
20 25
mrad
0
-25 -20 -15 -10
-5
0
5
10
15
20 25
mrad
Conclusion
• There will be a degradation of resolution with an air
gap, roughly about ~10%.
• Trade-off with mechanical convenience
• In both cases, things can be improved with
timing/chromatic correction
• Analysis technique is probably non-optimal:
• Single photon resolution looks better than BaBar
• But single event resolution is a bit worse
• Blame analysis, I think