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APEX High Rate VDC Analysis
Seamus RiordanUniversity of Massachusetts, Amherstsriordan@physics.umass.edu
Mathew Graham, SLACOle Hansen, Jefferson Lab
Mike Paolone, University of South Carolina
December 8, 2010
Seamus Riordan — Hall A Analysis Meeting, Dec 2010 APEX VDC 1/22
Outline
HRS VDCs
APEX Calibration
High Rate Tracking Performance
Seamus Riordan — Hall A Analysis Meeting, Dec 2010 APEX VDC 2/22
HRS Vertical Drift Chambers
45O
Side view
Top view
nominal particle trajectory
Upper VDC
Lower VDC
2118 mm
288 mm
nominal particle trajectory
d =335mmv
d =335mmu
v2
d =26mmuv1
d =26mmuv2
v1
u1
u2
U1
V1
U2
V2
Nominal Characteristics
U/V angle ±45◦
Sense wires/plane 368Wire Spacing 4.24 mm
Pos. Res ∼ 100 µmAng. Res ∼ 0.5 mrad
Seamus Riordan — Hall A Analysis Meeting, Dec 2010 APEX VDC 3/22
Basic VDC Operation
Tracks enter nominally 45◦, produce signals on 3-7 wires
Drift time patterns among several wires matched to construct“cluster”
2 U-plane and 2 V-plane clusters fit to recreate full 3D track
Ci+4
Ci+3
Ci+2
Ci
Ci+1
di+2
crossover
point
id
di+3 d
i+4
D=13mm
wire plane
4.24mm
"pivot wire"
τslope
di+1
(HV) plane
cathode
(HV) plane
cathode
particle trajectory
Drift Time (ns)-50 0 50 100 150 200 250 300 3500
200
400
600
800
1000
1200
1400
1600
1800
2000
2200
Drift Time Spectrum, U1
Seamus Riordan — Hall A Analysis Meeting, Dec 2010 APEX VDC 4/22
APEX PAC Concerns
Requested for test run by PAC:Prove that the vertical drift chambers (VDCs) can operate at arate higher that 20 kHz/wire (that, according to the TAC report, isthe maximum Hall A has operated till now).
VDCs had not been run at such high rate (for extended period oftime)
Required to go to ∼ 5 MHz (75 kHz/wire)
Requires hardware modifications to run efficiently without severeaging
Seamus Riordan — Hall A Analysis Meeting, Dec 2010 APEX VDC 5/22
VDC Modifications
Modifications for performance up to 5 MHz (full experimentluminosity).
Standard APEX High RateHV −4.0 kV −3.5 kVDisc. LeCroy (Ith = 8 µA) JLab Custom (Ith = 1 µA)Gas 60-40 Ar/CH2 60-40 Ar/CH2
Max Rate 500 kHz 5 MHzGain 20×103 2.5×103
Max VDC current draw I/wire/cm ∼ 5 nA
For APEX, QVDC < 0.1 C (no serious aging)
Seamus Riordan — Hall A Analysis Meeting, Dec 2010 APEX VDC 6/22
Timing Offset Calibration
VDC requires software offsets for drift time
Calibrated in groups of 16 wires (discriminator inputs)
500 600 700 800 900 1000 1100 1200 1300 14000
20
40
60
80
100
120
140
u1 TDC grp 8u1 TDC grp 8
Calibration done by fitting time dist. peak and fixed at 1.4 σearlier from peak (arbitrary)
Seamus Riordan — Hall A Analysis Meeting, Dec 2010 APEX VDC 7/22
Timing Offset Calibration Results
Calibration is done to ∼ ns level
Offsets may be different for different triggersMinimized in hardware to ∼ 10 ns level, fully corrected in software
wire group number0 2 4 6 8 10 12 14 16 18 20 22 24
Mea
n P
eak
Pos
ition
(ns
)
15
16
17
18
19
20
21
22
23
24
25
time (ns)-50 0 50 100 150 200
Nor
mal
ized
ent
ries
0
50
100
150
200
250
300
350
400Trigger1
Trigger2
Trigger3
Trigger4
Trigger5
Trigger6
Seamus Riordan — Hall A Analysis Meeting, Dec 2010 APEX VDC 8/22
Drift Time-to-Distance
Drift time-to-distance conversion follows form:
Theta dependence:
v2t < 0 : d = v2t
0 < v2t < a1 : d = v1t = v2t
(
1+a2
a1
)
a1 < v2t : d = v2t +a2
a1 and a2 carry tanθ =∆z∆r dependence (r = u or v )
a1 =
3
∑i=0
a1,i tani θ
a2 =
3
∑i=0
a2,i tani θ
Seamus Riordan — Hall A Analysis Meeting, Dec 2010 APEX VDC 9/22
TTD Calibration
No serious differences between high and low rate data
Restricting to slice in incident angle θ:
Low Rate, 0.4 MHz
Drift Time (ns)-50 0 50 100 150 200 250 300
Drif
t Dis
tanc
e (m
)
0
0.002
0.004
0.006
0.008
0.01
0.012
0.014
TTD Function
|<5 mradfpθTTD, low current, |
High Rate, 4.6 MHz
Drift Time (ns)-50 0 50 100 150 200 250 300
Drif
t Dis
tanc
e (m
)
0
0.002
0.004
0.006
0.008
0.01
0.012
0.014
TTD Function
|<5 mradfpθTTD, high current, |
Small recalibrations for θ dependence are necessary
Seamus Riordan — Hall A Analysis Meeting, Dec 2010 APEX VDC 10/22
TTD Calibration
Requires some θ dependence re-fitting
Discrepancies are in the tail on the level of 20 µm
(rad)fpθ-0.1 -0.05 0 0.05 0.1
Res
idua
l (m
)
-0.002
-0.0015
-0.001
-0.0005
0
0.0005
0.001
0.0015
0.002
fpθU1 Residual vs.
Seamus Riordan — Hall A Analysis Meeting, Dec 2010 APEX VDC 11/22
Tracking Algorithm - Clustering
Ci+4
Ci+3
Ci+2
Ci
Ci+1
di+2
crossover
point
id
di+3 di+4
D=13mm
wire plane
4.24mm
"pivot wire"
τslope
di+1
(HV) plane
cathode
(HV) plane
cathode
particle trajectory
→
Wire Number160 162 164 166 168 170
Drif
t Tim
e (n
s)
-50
0
50
100
150
200
VDC U1
Algorithm scans for ’V’ shaped clusters in time
Hits in each cluster must be within reasonable time constraints
Allow for gaps of 1 wire, must have 3 ≤ wires in cluster ≤ 7
Time of the cluster is offset, calculated through fit based ontime-to-drift distance mapping
Time resolution from fit on σt ≈ 15 ns
Seamus Riordan — Hall A Analysis Meeting, Dec 2010 APEX VDC 12/22
Advanced Scanning
Wire Number0 50 100 150 200 250 300 350
Drif
t Tim
e (n
s)
-100
0
100
200
300
400
500
VDC U1
Multihit TDC information used since rates are highEarliest hits used to fit clustersSeveral passes over data taken to maximize clusters found whenseparated in time, but not space
Seamus Riordan — Hall A Analysis Meeting, Dec 2010 APEX VDC 13/22
Tracking Algorithm - UV Association
Cut on U cluster - V cluster time difference, ±40 ns
Cluster positions must be in chamber active area
Time Difference (ns)-100 -80 -60 -40 -20 0 20 40 60 80 1000
500
1000
1500
2000
2500
VDC U-V Cluster Time Difference
Select clusters
near in time
VDC U-V Cluster Time Difference
Ambiguity prevents uniqueassociation between U-V clusters
If ambiguity in UV association, end tracking
Seamus Riordan — Hall A Analysis Meeting, Dec 2010 APEX VDC 14/22
Tracking Algorithm - Track Fitting
All chamber 1 - chamber 2 UV clustersbuilt
Sort by χ2 based on angularinformation from drift time fit
Accept as many χ2 clusters untilmaximum found
Seamus Riordan — Hall A Analysis Meeting, Dec 2010 APEX VDC 15/22
Tracking Resolutions
Track resolutions found through residuals of full χ2 fit
Residual (m)-0.003 -0.002 -0.001 0 0.001 0.002 0.003
0
2000
4000
6000
8000
10000
12000
14000
mµRes. = 354.0
U1 Residual
Second, broader Gaussian distribution appears for high rate data
Average width of central peak goes from 320 µm to 360 µmbetween low and high rate data
Seamus Riordan — Hall A Analysis Meeting, Dec 2010 APEX VDC 16/22
Tracking Efficiency
Tracking efficiency found in left arm for:Left arm s2m scintillator triggerHigh preshower+shower calorimeter signal (e−)
Low rate, 0.3 MHz
Cluster Size2 3 4 5 6 7 8
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
u1 Cluster size - 2uA Tantalum
Highest rate, 5 MHz
Cluster Size2 3 4 5 6 7 8
0
2000
4000
6000
8000
10000
u1 Cluster size - High Current Lead
Average wires in clusters become smaller at high rate due toefficiency
Seamus Riordan — Hall A Analysis Meeting, Dec 2010 APEX VDC 17/22
Tracking Efficiency
Tracking efficiency found in left arm for:Left arm s2m scintillator triggerHigh preshower+shower calorimeter signal (e−)
Low rate, 0.3 MHz
N Clusters0 2 4 6 8 10
0
1000
2000
3000
4000
5000
6000
7000
8000
+/- 40ns
No abiguity
Used in track
u1 - Clusters in 40 ns - Low rate Ta
Highest rate, 5 MHz
N Clusters0 2 4 6 8 10
0
2000
4000
6000
8000
10000
12000+/- 40ns
No abiguity
Used in track
u1 - Clusters in 40 ns - Highest Current Lead
Average wires in clusters become smaller at high rate due toefficiency
Seamus Riordan — Hall A Analysis Meeting, Dec 2010 APEX VDC 17/22
Hit Efficiency
Hit efficiency drops at higher rate
Non-uniform due to non-uniform event distribution
Wire Number0 50 100 150 200 250 300 350 400
Hit
Effi
cien
cy
0.86
0.88
0.9
0.92
0.94
0.96
0.98
1
2uA Lead
30uA Lead
Left arm U1 efficiency
Seamus Riordan — Hall A Analysis Meeting, Dec 2010 APEX VDC 18/22
Tracking Efficiency
Losses come from:UV association ambiguityNo clusters found (bad timing structure, overlapping, hitinefficiency)
Trigger Rate (MHz)0 1 2 3 4 5 6
Fra
ctio
nal L
oss
0
0.1
0.2
0.3
0.4
0.5 Total Loss
Loss from Ambig.
Loss from No Clusters
Event Loss
Loss goes up to 40% for highest current runningSeamus Riordan — Hall A Analysis Meeting, Dec 2010 APEX VDC 19/22
Event distribution
Event distribution has small distortions due to non-uniformefficiency
Xdet
(m)detx-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1
0
50
100
150
200
250
300
350
310×
0.4 MHz, Lead
4.6 MHz Lead
Detector X Distribution, S2m trigger (T1), Normalized to charge and prescales
Ydet
(m)det
y-0.06 -0.04 -0.02 0 0.02 0.04 0.06
0
100
200
300
400
500
600
700
800
900
310×
0.4 MHz, Lead
4.6 MHz Lead
Detector Y Distribution, S2m trigger (T1), Normalized to charge and prescales
Seamus Riordan — Hall A Analysis Meeting, Dec 2010 APEX VDC 20/22
Efficiency Improvements
Tracking Work To Do:
UV ambiguity may be broken through use of other detectors, χ2
fitting, geometry considerations, event distribution considerations
Some clusters from “no cluster” events may be recovered throughbetter cluster searching code
Efficiency improvents to 75% (from 60%) with improved analysisas estimate
Seamus Riordan — Hall A Analysis Meeting, Dec 2010 APEX VDC 21/22
Conclusion
HRS VDC provide high resolution, hit based tracking
PAC condition met: VDCs were able to perform tracking at highrates with appropriate hardware modifications
Tracking efficiency is about 60% at 5 MHz trigger, optimization ofbeam current must be performed
Seamus Riordan — Hall A Analysis Meeting, Dec 2010 APEX VDC 22/22
BACKUP SLIDES
Seamus Riordan — Hall A Analysis Meeting, Dec 2010 APEX VDC 23/22
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