Hardware
setup and settings
The multiwire proportional chamber is composed of two planes
of 128 wires, spaced by 2mm. The vertical plane defines the horizontal
coordinate x and the horizontal plane defines the vertical coordinate y.
When at least one wire fires, the chamber triggers. The software analysis
program then reconstructs clusters, defined to be a group of neighboring
fired wires in eachplane. It applies what is called dead-wire filling:
if a non-fired wire happensto be between two fired-wires, the program considers
it as fired, and build a cluster with this three wires (and eventually
others on each side of this cluster). The wires in each independant plane
are grouped in 8 discrimination cards connected each to 16 wires. The read-out
cables are connected to the discrimination cards, thus reading 16 wires
each (A1 to A8 in the horizontal plane and B1 to B8 on the vertical plane).
As seen from target, the wires arenumbered 1 to 128 from left to right
on the vertical plane, and 1 to 128 frombottom to top on the horizontal
plane. The center position (corresponding to x=0 and y=0 in the LG, is
located on vertical wire #67 (x=0), and horizontal wire #70 (y=0).
All the following results have been taken using run block #1. Here are
the settings which we used:
runs: 1429-1432
WC threshold: 1 V
WC high voltage: 2950 V
beam current: 10uA
No post-radiator
15cm LH2 target
calo angle: 35 degree
hadron arm angle: 34.86 degree (endpoint)
Efficiencies
calculation
The efficiency of the wire chanmer has been calculated with the following
ratio:
Efficiency = # of e- in small region of LG + anywhere in VETO +
at least 1 hit in the corresponding region of WC
_________________________________________
# of e- in small region of LG + anywhere in VETO
During the commissioning runs, only 4 discrimination cards were connected
on the horizontal plane (A3 to A6), and 6 on the vertical plane (B2 to
B7). We can thus determine 24 intersection regions, of 3cm*3cm. The efficiency
has been calculated in each of these intersection regions. A correlation
between the position calculated in the LG and the position of the
cluster is assured by considering only the small region of the LG facing
the studied intersection region of the WC. To make sure that any event
hitting the small region of the LG is detected, if detected, by the good
intersection region of the WC, the regions of the LG are a little bit smaller,
2.78cm*2.78cm. The difference, of 2.2mm is equal to half the resolution
on the position in the LG.
Since the threshold applied on the WC was low (1V), a lot of multiple
hits were recorded. It has been studied that rejecting the events with
more than 5 clusters in the vertical plane and more than 4 clusters in
the horizontal plane doesn't change the wire chamber efficiency. So only
lower multiplicity events have been kept.
Cuts
(cf. wc_cut.kumac)
The first cuts ($2 to $8) are on the veto detector. $8 requires at
least 1
hit in both plane of the Lucite Veto detectors.
Cuts $10 to $55 determine the region of the WC. Each cut corresponds
to a discrimination card. Then cuts in the $70's requires that at least
1 cluster fires the wires in the studied discrimination cards. Any combination
of one of the cuts $70 to $75 and one of the cuts $76 to $79 defines an
intersection region.
Cuts $60 to $69 define the corresponding region in the LG.
Cuts $85 and $86 reject high multiplicity events.
The last cuts ($95 and $96) are standard cuts for coincidence timing
between both arms, and particle ID.
Efficiencies
Vertical chamber:
| |
B2
|
B3
|
B4
|
B5
|
B6
|
B7
|
|
A6
|
(92.6%)
|
92.7%
|
95.5%
|
89.9%
|
88.0%
|
(92.5%)
|
|
A5
|
(92.6%)
|
89.7%
|
93.5%
|
88.9%
|
86.4%
|
(90.8%)
|
|
A4
|
-
|
92.4%
|
91.7%
|
82.3%
|
88.9%
|
(94.3%)
|
|
A3
|
(100%)
|
88.1%
|
88.5%
|
84.2%
|
84.4%
|
(88.5%)
|
Horizontal chamber:
| |
B2
|
B3
|
B4
|
B5
|
B6
|
B7
|
|
A6
|
(96.3%)
|
94.0%
|
91.6%
|
96.0%
|
94.2%
|
(93.4%)
|
|
A5
|
(85.2%)
|
94.7%
|
95.3%
|
95.5%
|
91.8%
|
(95.4%)
|
|
A4
|
-
|
94.3%
|
93.6%
|
92.5%
|
95.9%
|
(98.6%)
|
|
A3
|
(50%)
|
94.1%
|
94.3%
|
97.7%
|
97.8%
|
(88.5%)
|
Both planes:
| |
B2
|
B3
|
B4
|
B5
|
B6
|
B7
|
|
A6
|
(88.9%)
|
86.7%
|
88.8%
|
86.4%
|
83.0%
|
(86.3%)
|
|
A5
|
(85.2%)
|
87.6%
|
90.6%
|
85.4%
|
80.2%
|
(86.3%)
|
|
A4
|
-
|
88.6%
|
86.6%
|
76.9%
|
85.6%
|
(92.9%)
|
|
A3
|
(50%)
|
84.2%
|
86.2%
|
82.7%
|
82.1%
|
(82.0%)
|
The numbers given in brackets in the first and last columns are efficiency
calculated with low statistic, because of the absence of veto detector
facing these regions. The other numbers correspond to about 150 to 400
events each.
Conclusion
The average efficiency of the vertical chamber is about 88.5%,
and 94.6% for the horizontal chamber. The average both planes efficiency
drops to 85.1%.
There might be some more work to do to understand better why we end
up with so low efficiencies for the wire chamber.