Unexpectedly large 3He loss in TORCH radiator
Black-Blue difference: this much 3He was lost between sc1 and sc2
Blue-Red difference: this much 3He was lost between sc2 and sc3
t11
sqrt(sc1l_q*sc1r_q)
Entries
Mean
RMS
2500
55878
322.9
85
2000
1500
•
top: sc1 pulse height, middle: sc2 pulse height,
bottom: sc3 pulse height
•
Blue - He3 identified by using sc1&sc2, Red He3 identified using sc1&sc2&sc3
•
43.8k 3He reached sc2, 21.7 k 3He reached
sc3.
•
about 50% of 3He lost in the torch radiator!?
•
This is large; from interaction cross section, I
expected about 15% loss.
1000
500
0
0
50
100
150
200
250
300
350
400
450
500
t21
sqrt(sc2l_q*sc2r_q)
Entries
Mean
RMS
5000
55878
173.5
47.23
4000
3000
2000
1000
0
0
50
100
150
200
250
300
350
400
450
500
t31
sqrt(sc3l_q*sc3r_q)
Entries
Mean
RMS
16000
55878
139.1
66.6
14000
12000
10000
8000
6000
4000
2000
0
0
50
100
150
200
250
300
350
400
450
500
A closer look at the situation
black: identified as 3He on sc1
red: identified as 3He on sc3
a1
sc1 vs sc2
Entries
Mean x
Mean y
RMS x
RMS y
500
450
400
450
400
350
300
300
250
250
200
200
150
150
100
100
50
50
50
100
150
200
250
300
350
400
450
500
Entries
Mean x
Mean y
RMS x
RMS y
500
350
0
0
a2
sc1 vs sc3
55878
173.5
322.8
47.17
85.08
0
0
50
100
150
200
250
300
350
400
a3
sc2 vs sc3
Entries
Mean x
Mean y
RMS x
RMS y
500
450
400
55878
139.5
173.4
66.67
47.24
450
55878
139.1
322.8
66.57
85.11
•
top-left: sc1 pulse height vs sc2 PH;
top-right: sc1 PH vs sc3 PH
•
Interesting figure is bottom-left: sc2
PH vs sc3 PH.
500
•
The particles in the blue box were identified
as 3He on sc2, but only those in the red box
survived as 3He to sc3.
•
The clusters to the left of 3He are deuterons
and protons produced by 3He interaction in
the Torch radiator.
350
300
250
200
150
100
50
0
0
50
100
150
200
250
300
350
400
450
500
blue: identified as 3He on sc2
red: identified as 3He on sc3
TORCH pulse height vs hit position
Detected photoelectron per PMT / photon_sum
PMT
n-2
PMT
n-1
PMT
n
PMT
n+1
PMT
n+2
•
Use Drift chamber to determine
the hit position on TORCH
radiator, and look at the pulseheight distribution of PMT#7.
(origin is the center of PMT#7)
•
Pulse height (normalized to
photon_sum) is nearly gaussian,
with a width (sigma) of ~13 mm.
•
Three “hit patterns” expected
from this distribution are shown
at bottom
0.6
0.5
Width (!)= 12.65 ± 5.08 mm
0.4
0.3
0.2
0.1
0
-50
-40
-30
-20
-10
0
10
20
30
40
50
Hit position (mm)
•
left: hit in between two PMT’s
•
middle: hit at the center of a PMT
•
right: hit at 4.25mm away from the PMT
center
Typical (expected) hit patterns
A typical event
•
h1
TORCH
Entries
16
Mean
80
6.287
RMS
!2 / ndf
70
height
mean
80.84 ! 7.438
6.124 ! 0.06413
const -0.9196 ! 0.2875
30
20
0
6
8
10
12
14
converted to the number of
photoelectrons, assuming 1 photon=4
ADC channels (LED calibration aimed
to achieve this)
•
A typical event looks as shown
here (PMT # vs photoelectron
count)
•
Constant+gaussian fit -> peak
height, position and width
determined for each event
10
4
•
1.603
40
2
pedestal & pre-sampling ADC value
subtracted from the raw torch ADC
value.
0.9921
sigma 0.8427 ! 0.04371
50
•
3.393 / 12
Prob
60
Used Miki’s analysis, i.e.,
16
chi2 distribution (gaussian fit to TORCH hit pattern)
•
Chi2 distribution
(gaussian+constant fit to TORCH
hit pattern), 16-4=12 dof.
•
he3 events with good track
reconstruction have been
selected
•
The distribution peaks at a much
smaller chi2 value, indicating
the estimate of fit weight (error)
is not quite right. I will look into
this.
•
We can remove spurious hits,
etc., based on the chi2 value.
htemp
Entries
2573
Mean
6.929
RMS
4.595
poschi2 {(poschi2<50&&chimin<.2&&abs(newdcx)<100)&&((((sqrt(sc1l_q*sc1r_q)>200)&&(sqrt(sc2r_q*sc2l_q)>150))&&(sqrt(sc3r_q*sc3l_q)>170))&&(photon_sum>50))}
120
100
80
60
40
20
0
0
5
10
15
20
25
30
Peak height & peak width vs hit position
pospeak:newdcx {((((sqrt(sc1l_q*sc1r_q)>200)&&(sqrt(sc2r_q*sc2l_q)>150))&&(sqrt(sc3r_q*sc3l_q)>170))&&(photon_sum>50))&&(chimin<.2&&abs(newdcx)<100&&poschi2<15)}
a1_pfx
Entries
2402
Mean
-2.363
RMS
56.54
100
•
80
60
40
Top: Peak height (as determined
by the fit) plotted against hit
position.
20
0
-100
-50
0
50
possigma*17:newdcx {((((sqrt(sc1l_q*sc1r_q)>200)&&(sqrt(sc2r_q*sc2l_q)>150))&&(sqrt(sc3r_q*sc3l_q)>170))&&(photon_sum>50))&&(chimin<.2&&abs(newdcx)<100&&poschi2<15)}
20
Bottom: peak width (sigma, mm)
plotted against hit position
100
a3_pfx
Entries
2402
Mean
-2.363
RMS
56.54
•
both peak height and width are
nearly flat (good!)
•
slight position-dependent
variations are due to PMT gain
(mis)adjustment
18
16
14
12
10
8
6
4
2
0
-100
-50
0
50
100
Peak pulse height vs resolution
(this page will be updated later, after the chi2 shape is understood)
possigma*17:1/sqrt(pospeak) {((((sqrt(sc1l_q*sc1r_q)>200)&&(sqrt(sc2r_q*sc2l_q)>150))&&(sqrt(sc3r_q*sc3l_q)>170))&&(photon_sum>50))&&(chimin<.2&&abs(newdcx)<100&&poschi2<15)}
20
•
Top: 1/Sqrt(peakheight) vs peak width (sigma)
bottom: profile spectrum
•
There is a clear linear correlation, i.e., position
resolution depends on photon statistics.
•
A crude linear fit gives
18
16
14
12
10
8
6
4
2
0
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
12.2
σ(mm) = !
Nphoton
a4_pfx
possigma*17:1/sqrt(pospeak) {((((sqrt(sc1l_q*sc1r_q)>200)&&(sqrt(sc2r_q*sc2l_q)>150))&&(sqrt(sc3r_q*sc3l_q)>170))&&(photon_sum>50))&&(chimin<.2&&abs(newdcx)<100&&poschi2<15)}
Entries
2402
Mean
0.1066
RMS
0.006655
16
14
12
10
8
6
4
2
0
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
i..e, for peak photoelectron count of 100, the
position resolution is 1.2mm.