Drift Chambers and Pattern recognisation

1
Drift Chambers and Pattern recognisation

• Fabrizio Cei Pattern recognition ideas INFN
  Pisa University
• Hajime Nishiguchi Kapton foils for DC cathode
• University of Tokyo
• Johny Egger DC status and tests
• PSI

2
DC Status and Tests

• Hood and inner cathodes
• Print foils
• pM1 test
• Drift time measurement
• Cathode read out
• Next future

3
Cathode hood
Delivery and first tests second half of July
4
Inner cathodes

• measurement of deformation with applied forces
• simulate forces (level arm) with wires through
  the gas holes
• eventually stabilize free edges with tiny foam
  support(rohacell)

5
Print foils
Good results of pM1 tests
hood-foil tests with mounting tool Inner cathode
foil mounting test
possible foil pattern deformations
Final design of the foil pattern
Ordering if all requests
are satisfied by the manufactory
6
H. Nishiguchi
Kapton foils for DC cathodes
Requirements Low-Mass reduce resolution
deterioration due to multiple scattering Kapton
film 12.5 µm thick Aluminum deposition 50 nm
thick (NOT copper !! ) Accuracy precise position
reconstruction with vernier pad method
requires manufacture accuracy 20 µm and
deposition by Etching. Situation Sample foils
with 3 Japanese companies suffered from many
problems, but a sample foil which satisfies all
requests (except cost) was built. Contacts with
european factories under way from PSI group.
7
pM1 test with the 4 test chambers
Anode 1, 2 plan 0 to 4 digital Scope 8
channels 500 MHz 500 points, 8 bits
Cathodes of anode 2 plan 2,3 FLASH ADC 8
channels 100 MHz 500 points, 8 bits
24 Cathodes Anode 1,(2,3) LRS ADC 24 double
channels
Anode 3 plan 0 to 4 AD811
Read out
8
Parallel beam tilted chambers
Not staggered
9
DC tilted by a1
No Field P 158 258 MeV/c
1.00 .60 Tesla P 158 258 MeV/c D
parallel
DC tilted by a2
s .21 ns
10
Behavior of amplifiers in the 1 Tesla magnetic
field

• no measurable difference on induced test pulses
• time definition Dt .12 ns ( s .8 ns)
• pulse integral DI

• -no measurable effect in the magnetic field even
  with magnetic SMD capacitors and resistances (
  contacts)
• approximate the field distortion with the new
  non magnetic SMD elements, cables, connectors

11
Drift time
Subtract y b1 b2(sinw(t-t0)) fit of the
225 first points pM1 run w 2p 50 MHz Look
for the first n4,5 adjacent points above
threshold Linear fit of first n signal points and
n last background points (0)
threshold
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(Fit-measured time) against drifttime
Drift time
t3 against t0
Sqrt( S(Fit-measured time)2 ) 2.0 ns 2.8
ns(.1 mm)
1.0 ns
Difference between 2 colors in t1 shows
misalignment of anode w2p1 of .1 mm
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Cathode readout
Anode has a shielding effect of a few percents
Cathode u1 n1Anode (1c2 sinc3x e
c2 sin2 c3x) Cathode u2 n2 Anode (1-c2
sinc3x - e c2sin2 c3x) Cathode d1
n3 Anode (1c2 cosc3x e c2cos2
c3x) Cathode d2 n4 Anode (1-c2
cosc3x - e c2cos2 c3x) e value for
traces on 1 side of the anode is the opposite of
the value for traces on the other side
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e and the cathode normalization factors ni are
correlated in the calibration procedure
Calibration procedure not yet optimal
distributions are not flat 0.34 mm
s(Fit-measured value)
s(Fit-measured value)
June 27
July 8
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Cross talks

• a) to next plane
• b) To adjacent anode 1) small on integrals
• 2) important for timimg
• c) to near cathode of adjacent anode Important
• Corrections to b) and c) well defined by
  measurement of events without signal on the
  adjacent anode ? ?
• Domino read out on all channels is important
• 1000 points, 500 MHz, 10 bits is ideal

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Present and near future plane

• Analysis of pM1 run (rich sample of data)
• Magnetic field
• Anode shielding, cross talk
• Exotic events
• Tests
• Foils
• Amplifiers and prints
• High rates
• Ordering
• Foils
• Frames and prints
• Amplifiers and cables
• Construction
• Test with first elements (maybe within this
  year)

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Positron Tracker
2002
2003
2004
2005
Medium Prototype
Charge division Cosmics
Full Prototype
FP
FP
Full Detector (18 DC)
Test
Milestone
Assembly
Design
Manufactoring
18
Fabrizio
Ideas for pattern recognition
Pattern recognition problem in MEG DC
integration time 1 ms Positron rate on drift
chambers 5 MHz Some superimposed tracks in
each DC readout.
Two turns (a rather frequent case)
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Assumptions

• Chambers are formed by two independent sensitive
  elements
• From each of them a three-dimensional
  information of the
• crossing point (hit) can be extracted
• DC signals were already analysed up to this
  level
• Wires and signal formation not simulated.

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Strategy outline

• Define a segment of track as two pairs of hits
  (or a pair and an isolated hit) within two
  adjacent chambers (one wedge)
• Perform a fast and reliable estimation of the
  positron momentum associated to any segment
• Look at any couple of segments which have the
  same pair of hits (or the same isolated hit) as
  end (one segment) and beginning (the other)
• Select the couples of segments having compatible
  momentum components and total momentum
• Within this sample, join the couples of segments
  which satisfy the geometrical requirements for a
  good track
• Save all tracks formed by a minimum number of
  segments (4 or 5)
• Absolute timing information not used (by now).

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Not enough time for details only
Fast momentum estimation
Technique principal component analysis in
quadratic approximation
Minimize
to determine ai, bij. hi one of the three
spatial coordinates of one hit. Sum over the hits
(3 or 4) in one wedge associated to a
segment. Training by MC events sample of 5 x 105
Michel positron tracks, corresponding to (1
? 3) x 104 tracks in each wedge.
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Tracks with ? 4 segments
Momentum reconstruction in one segment minus true
value

N.B. This is NOT a momentum reconstruction.
py
px
Black true Red estimated
pz
p
pz
MeV
Total momentum
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Linking segments

• Any chamber (except 1 and
• 17) is a part of twowedges
• we can link two segments in
• adjacent wedges requiring that
• they have one common point.
• Further selections
• compatibility of momentum vectors in adjacent
  segments
• compatibility of new segment
• with extrapolated track.

Segments with the same starting point.
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Example of reconstructed tracks
25
Algorithm performances
Michel positrons in the solid angle covered by
the spectrometer or isotropically over the whole
detector no significant differences positron
momentum 30 MeV
of correctly reconstructed
tracks Efficiency
of generated tracks
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A by-product momentum estimation
Not a momentum reconstruction, but a reasonable
starting point for more refined tracking
algorithms (like MINUIT).
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Conclusions

• Algorithm looks to work well e 95 for 5
  mixed tracks 91 for 10 more efficient for
  higher momentum tracks (encouraging !).
• Performances be only slightly ( 1 ) affected by
  worsening the
• z resolution or reversing the scanning
  direction.
• Technical note soon.
• Suggestions (to investigated)
• begin the search from outermost radii try
  to recover isolated hits.
• Possible improvements
• perform a cuts fine tuning
• follow all possible links between segments
• use absolute timing information as linking tool
• perform a better track extrapolation
• include random noise
• insert signal propagation in the simulation code
  

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pM1 tests with four test chambers and various
readout (digiscope 500 MHz, flash other ADCs
..)
No Field P 158 258 MeV/c
1.00 .60 Tesla P 158 258 MeV/c D
parallel Measurement of four DC times
DC tilted by a1
DC tilted by a2
s .21 ns
Trigger timing resolution