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