Transcript Scintillating Fibre Cosmic Ray Test Results Malcolm Ellis Imperial College London Monday 29th March 2004

Scintillating Fibre
Cosmic Ray Test Results
Malcolm Ellis
Imperial College London
Monday 29th March 2004
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Fibre Tracker Measurements
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Status at Abingdon Meeting
VLPC decoding
Trigger Timing
Reconstruction:
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–
–
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Pedestal and CMN
Clusters
Space Points
Tracking
• Dead Channels
• Track Residuals
• Light Yield
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Status at Abingdon
• 3 Station tracker had been assembled (in only a
few months) and data-taken at D0 test stand in
Fermilab
• First analysis of the data saw signals from the
tracker, however there were question marks over
the decoding of the data and less light seen than
anticipated.
• Initial estimates of efficiency and dead channel
rates were consistent with expectations, however
had large uncertainties...
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VLPC Decoding
• The tracker is read-out by one 1024 channel
VLPC cassette, through eight 128 fibre D0
connectors.
• Each of these is read out by a pair of multi chip
modules (MCMs).
• The ordering of the data in the output stream from
the MCMs was originally incorrect.
• This has been corrected, and two parallel
approaches to describing the full decoding from
electronics channel to station, plane and fibre
numbers now agree completely.
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Trigger Timing
• There is a particular window during which the
VLPCs are most sensitive to arriving photons.
• A delay between the trigger and VLPC read-out
needs to be adjusted in order to time the read-out
with respect to the trigger such that the light
arrives during this window.
• Studies of light yield versus timing have shown
that in 2003 this situation was not optimised.
• The data taken in March 2004 has included a
timing scan to optimise the read-out.
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Gain Settings and Calibration
• DAQ run with ramp trim set at two values:
– 0x150 (most data) gives gain of ~5 ADC/PE
– 0x350 (small amount) gives gain of ~14 ADC/PE
• Calibration of gains for each channel determined
from runs taken with LED.
• Not had enough time to sort out channels with
poor fits from 2003 data, so will only use 2004
data.
• Mean gain is 5.3 ADC/PE with a spread of about
12%.
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Pedestal and CMN
• Pedestals are typically around 30 ADC
counts.
• Common noise per MCM (64 channels)
creates a global shift of all 64 channels from
event to event.
• This CMN is subtracted event by event.
• Resulting distribution shows pedestal at 0
(width 2.9 ADC) with signal above.
• 3 times sigma of pedestal width is 1.95 PE. 7
Reconstruction - Clusters
• Most tracks go through one group of seven fibres,
and so a single electronic channel sees all the
light.
• A fraction go through the edges of two
neighbouring groups, and so the light is shared
between neighbouring channels
• A cluster is built from one or two channels, each
channel must have at least 1 PE and the sum must
have at least 2 PE.
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Space Points
• Triplets (a hit in all 3 projections) are built in
station B first. Clusters used in a triplet (or
triplets) are not used in the next stage.
• Duplets (pairs of clusters in two projections of a
station) are built from all remaining combinations
in all 3 stations.
• Due to DAQ restriction (only 1 cassette means
1008 out of 1512 channels read-out), active area in
3 stations is not the full 30cm circle.
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Tracking
• All combinations of points are tested, and that
with the best c2 is kept (assuming that the c2 is
small enough).
• 2003 data has 1670 tracks.
• 2004 data taken so far has 8484 (0x150) and 1679
(0x350) tracks.
• Space points in tracks are used to determine point
resolution.
• Light Yield determined by looking at distribution
of light in clusters that are included in a track.
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Our First Track:
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Dead Channels
• For each channel, determine the rate of hits above
4 PE on that channel.
• Plot rate versus channel number and look for
channels that are 0, or very low.
• No channels with exactly 0 hits, however 1 with a
very low rate, and another that is a little lower
than its neighbours.
• Worst case: 2 / 1008 = 0.2%
• G4MICE assumption is 0.25%
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Point Resolution
• Take two points in a track, use these to
determine expected position in third station.
• Point resolution is residual width after
extrapolation error is subtracted in
quadrature.
• Two options:
– Interpolation (Stations A and C)
– Extrapolation (Stations A and B or B and C)
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Point Resolution
• Subtracting extrapolation error from residual
widths (RMS or sigma) gives point resolution
(assuming all three X planes have the same
resolution).
• Resolution = 442 ± 4 (stat) ± 27 (syst) mm.
• Depending on definition of the width of one
channel (clusters complicate the issue slightly),
expected resolution is between 424 and 465 mm.
• Resolution measured in tracker agrees with
expectations.
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Light Yield
• 7 planes contain different amounts of 3HF:
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2500 ppm (1 plane)
3500 ppm (1 plane)
5000 ppm (4 planes)
One plane has a mixed composition and is not used for
this study.
• Proposal assumed a light yield of 8 PE.
• Due to non-linearity in gain at high signal,
gaussian fit to most-probable peak.
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5000 ppm 3HF
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3500 ppm 3HF
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2500 ppm 3HF
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Single Plane Efficiency
• Efficiency calculated in Station B, one plane each
of 2500, 3500 and 5000 ppm 3HF.
• Track built from 6 other planes and extrapolated to
plane under test.
• Road-width varied from 2 to 50mm.
• Systematic errors determined from variation with
road-width and runs on different sets of data.
• Algorithm will not over-estimate efficiency, but as
a result may slightly under-estimate it.
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Efficiency
• Efficiency expected due to Poisson:
– 8 PE: 98.62 %
– 9 PE: 99.38 %
– 10 PE: 99.72 %
• Efficiency measured (0x150 data):
– 5000 ppm 3HF: 97.45 ± 0.20 (stat.) ± 0.51 (syst.)
– 3500 ppm 3HF: 98.80 ± 0.14 (stat.) ± 1.11 (syst.)
– 2500 ppm 3HF: 99.26 ± 0.11 (stat.) ± 0.88 (syst.)
• Efficiency measured (0x350 data):
– 5000 ppm 3HF: 98.09 ± 0.39 (stat.)
– 3500 ppm 3HF: 99.29 ± 0.25 (stat.)
– 2500 ppm 3HF: 99.73 ± 0.16 (stat.)
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Conclusions
• Tracker performs at least as well as expected
based on expectations from D0 and design:
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–
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Light Yield better than 8 PE
Single Plane efficiency consistent with light yield
Dead channel rate lower than G4MICE assumption
Point Resolution as expected from design
• Performance currently being fed into G4MICE
(see talk on Wednesday)
• Only thing left is to build a couple of full trackers
for MICE…
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