performance and aging of the babar drift chamber · 2008-02-13 · dch history babar drift chamber...

Performance and Aging of the BaBarDrift Chamber

Michael H. Kelsey

Stanford Linear Accelerator Center™

B

AB

AR

™&

©

L . de B r unhoff

2008 Super B Factory Workshop, SLAC

14–16 February 2008

DCH History

Outline

• Drift Chamber Design and Operation

• Aging and Wire Damage

• Tracking, dE/dx, and Physics

• Data Acquisition Upgrade

• Summary

Michael H. Kelsey SuperB 2008 2

DCH History

BaBar Drift Chamber

IP1618

469236

324 681015 1749

551 973

17.19ÿ20235

Dimensions in mm

24 cm inner radius

81 cm outer radius

2.8 m length

IP 37 cm behind center

Be & Al inner cylinder

Carbon fiber/Nomex outer

2.5 (1.2) cm Al end plates

All electronics on rear


DCH History

BaBar Drift Chamber

Small hex cells (1∼2 cm)

HEX2 - Wire 168 Isocrones every 50 ns HEX2 - Wire 185 Isocrones every 50 ns

10 superlayers of 4 layers each

Axial and stereo (∼ 4◦)

96–256 cells/superlayer

Sense wires 20 µm W-Rh (Au)

Field wires 120 µm Al (Au)

Guard wires 80 µm Al (Au)


DCH History

Construction

High-bay Class 1000 clean room at TRIUMF

Chamber volume enclosed in Class 100 clean tent

Measured at 10-20 particles/m3

No contact with wire in chamber or inner surfaces

Automated wire stringing

Operators attached wire from spool to steel rod

Pulled by robot (magnet grip) to opposite endplate

Feedthroughs, crimping outside clean tent


DCH History

Operating Parameters

Gas mixture 80% helium, 20% isobutane,

3500–4000 ppm water, ∼ 80 ppm O2

Designed to operate at 1960V

Initially operated without water vapor

Discharges observed in small region of chamber

Reduced to 1900V (October 1999–July 2000)

1930V January 2001–December 2006

1945V since January 2007


DCH History

Initial Damage

May 1999: 80:20, O2 < 10 ppm, H2O <∼ 100 ppm

28 July 1999: Large spikes in HV current

HV problem in SL6, OUT

Day in July 1999

Cur

rent

(µA

)

Minutes from 7/28/99 7 AM

Cur

rent

(µA

)

0

5

10

15

20

25

30

28 29 30

0

5

10

15

20

25

30

0 10 20 30 40 50 60

Hit Map High Charge

-100

-80

-60

-40

-20

0

20

40

60

80

100

-100 -80 -60 -40 -20 0 20 40 60 80 100

2000/05/31 11.02

x(cm)y(

cm)

October 1999: Turned off affected region, added water

=⇒ No discharges observed in chamber since


DCH History

Gain vs. Time

Expect continuous decrease G = G0 exp(−AQ) due

to aging (charge accumulation)

Accumulated Charge (mC/cm)

Cor

rect

ed G

ain

DCH Gain Since Startup (May 1999 - Present)

0.4

0.6

0.8

1

1.2

0 10 20 30

A B C D E F

1 2 3 4 5 6 7 8 9 10

Steps due to operating changes (voltage), transi-

tions between runs (gas mix), etc.


DCH History

Gain vs. Time

G(Q) = {G0 +∑

∆Gi|Q>Qi} exp(−AQ)

Accumulated Charge (mC/cm)

Cor

rect

ed G

ain

DCH Gain May 1999 - Feb 2008

0.4

0.6

0.8

1

1.2

0 10 20 30

Aging rate: -0.337± 0.006 %/(mC/cm) over 33.69 mC/cm


DCH History

Long-term Effects

Sudden damage always a concern, not observed

Transient discharges, voltage trips

Buildup of deposits on wires

Self-sustaining discharge (Malter effect)

Long-term studies of aging remediation

Lu Changguo (Princeton)

Pisa Frontier Detectors Meeting (2003)

Adam Boyarski (SLAC)

DESY Aging Workshop (2001)

IEEE NSS/MIC (2003)

Other groups (Colorado, Montreal, Novosibirsk, ...)

Accumulated several lifetime dose


DCH History

Suppressing Damage

Running chamber without water vapor allows

polymer (dielectric) buildup, increases likelihood

of discharges

Presumed mechanism for damage seen in July 1999

Princeton test chamber run dry up to 130 mC/cm,

saw discharges, high singles rate, 10% drop in gain

Adding 1500–4000 ppm H2O eliminated discharges

Gain stabilized at 0.9 of initial value, up to 300 mC/cm

Poor performance returned when water removed


DCH History

Reconstruction Performance

Hit resolution 〈σ(resid)〉 ∼ 125 µm

Target: 140 µm in middle region of cell

Momentum σ(pT )/pT = 0.45% + 0.13% pT (GeV/c)

Target: 0.21% + 0.14% pT

Tracking > 95% matching with SVT

dE/dx resolution ∼ 7.5%, ± (0.5-0.7)% bias

Early test results: 7.0%


DCH History

Physics Performance

Reconstruction of K0S → π+π− at large radii

)2Vtx+Y

2

Vtx(X√Decay Radius

2M

eV/c

0

2

4

6

8

10

12

0 10 20 30 40 50

RMS

hwhm

)2Vtx+Y

2

Vtx(X√Decay Radius

2M

eV/c

0

2

4

6

8

10

12

Bea

mP

ipe

Bea

mP

ipe

SV

TS

VT

Su

pp

ort

Su

pp

ort

DC

HD

CH

Fits in DCH comparable to

DCH+SVT

2) GeV/c

os)-M(K-π +πM(

)2Ev

ents/

(0.5 M

eV/c

0

50

100

150

200

250

300

350

25→Decay Radius 24. Entries = 4932oN

Sig. Events = 4460.50 MeV-0.045771

0.0458304mean = -0.156774RMS = 5.08925 MeV

/Ndof = 197.51/1922χhwhm = 2.38295 MeV

frac1 = 0.474382sigma1 = 3.8942 MeV

frac2 = 0.391389sigma2 = 1.5711 MeV

frac3 = 0.13423sigma3 = 11.4963 MeV

frac4 = 0sigma4 = 0.5 MeV

-0.05 0 0.05

“Jumps” due to material scattering uncertainty and fewer

hits per track fit


DCH History

High Rate Data Acquisition

Modular, parallel electronics

4-buffer pipeline per channel

16 elements per quadrant

via 1 GHz fiber to processor

Original 1995 design

FEA−3 180 ch

FEA−2 144 ch

FEA−1 96 ch24 ch

16x FEEto DIOM

Readout time set by single element’s occupancy

TDAQ = 8

{

8 +N

∑

(32mi + 4)

}

× 16.7 + 33 ns

N non-empty chips, mi = 1–8 wires (32 bytes) each

=⇒ 45 hits requires 200 µs (5 kHz)


DCH History


Replace multiplexer with modern FPGA

Implement feature extraction in firmware

Charge (waveform) integration

Leading edge (hit time) finding

Pedestal subtraction

Calibration constants in FPGA memory

Data volume reduced 32 → 6 bytes/channel

Identical data format used for reconstruction

Essentially no deadtime up to 10 kHz trigger rate


DCH History

Front-end Upgrade

New boards installed during Run 5 (Oct 2005)

Improved diagnostics, programmability vs. original

Firmware downloadable through FPGA to EPROM

via normal DAQ path

“Pass-through” firmware (emulates original front-

end) software selectable through DAQ command


DCH History

Summary

BaBar Drift Chamber operated for nine years

Tracking performance up to design

dE/dx performance good

Excellent operational efficiency

No substatial problems after startup

Excellent aging rate 0.3% / (mC/cm)

Clean-room construction, comprehensive QA/QC

procedures

Real-time monitoring of environment and data

quality

Electronics upgraded to support luminosity


DCH History

Supplemental Information


DCH History


DCH History

The PEP-II B Factory

Asymmetric e+e− collider: E(e+) = 3.1 GeV, E(e−) = 9 GeV

⇒ 10.58 GeV CMS: Υ(4S) → B+B−, B0B0

B decay length increased from ∼ 30 µm (CMS) to ∼ 250 µm

(lab), allowing precision time-dependent measurements

PEP-II delivers L > 1034 cm−2 s−1

(3× design)

433 fb−1 at Υ(4S), ∼ 9% off-peak

18 fb−1 at Υ(3S) =⇒ 30 fb−1 plan

BaBar operates at > 95% effi-

ciency

]-1

Inte

gra

ted

Lu

min

osi

ty [

fb

0

100

200

300

400

500

Delivered LuminosityRecorded LuminosityRecorded Luminosity Y(4s)Recorded Luminosity Y(3s)Off Peak

BaBarRun 1-7

PEP II Delivered Luminosity: 521.44/fbBaBar Recorded Luminosity: 501.38/fb

BaBar Recorded Y(4s): 432.74/fbBaBar Recorded Y(3s): 21.52/fb

Off Peak Luminosity: 47.11/fb

BaBarRun 1-7

PEP II Delivered Luminosity: 521.44/fbBaBar Recorded Luminosity: 501.38/fb

BaBar Recorded Y(4s): 432.74/fbBaBar Recorded Y(3s): 21.52/fb

Off Peak Luminosity: 47.11/fb

As of 2008/02/12 00:00

2000

2001

2002

2003

2004

2005

2006

2007

2008


DCH History

BaBar Detector


DCH History

BaBar Drift Chamber

Main tracking detector in BaBar

Surrounds beam pipe, final focus magnets, and

silicon vertex tracker


DCH History

Construction QA/QC

Continuous QA/QC monitoring

Tension measured during stringing

Before and after crimping

Daily evaluation of wires and feedthroughs

Replacement done during subsequent shift

Stringing completed in 3 months (Aug–Nov 1997)

Just 19 of 28,768 wires outside specification

Tension, crimps, continuity

Assembly fixture repositioned vertically

Wires removed and restrung in situ


DCH History

Commissioning

Tested at voltage with operating gas

Mixed in radioisotope (133Xe)

Pulses, singles rates measured for all 7,104 cells

Shipped fully operational, ready for comissioning

Commissioned at SLAC with production DAQ

system before installation in IR-2


DCH History

Accumulated Charge

Measure aging vs. accumulated charge per unit

wire length

276.4 cm × 7104 cells

= 19.6 km sense wire

400–600 µA w/beams

(0.25 nA/cm)

Recorded every second

DCH Dose May 1999 - Feb 2008

0

10

20

30

0

10

20

30

20000

10

20

30

20010

10

20

30

20020

10

20

30

20030

10

20

30

20040

10

20

30

20050

10

20

30

20060

10

20

30

20070

10

20

30

2008

Acc

umul

ated

Cha

rge

(mC

/cm

)

Total charge 33.7 mC/cm in nine years


DCH History

Quantifying Gain

Normalize to absorb environmental effects

Pressure and temperature ⇒ density

Detailed gas mixture (He:i-C4H10, H2O, O2)

Precise operating voltage

Compute dE/dx for tracks from Bhabha-scattering

events [e+e− → e+e−(γ)]

Relativistic plateau of Bethe-Bloch curve, fixed

average value

Normalization done ∼ hourly


DCH History

Gain vs. Time Fit Details

G(Q) = {G0 +∑

∆Gi|Q>Qi} exp(−AQ)

χ2/dof = 1789.58 / 418

−A(%) = −0.337 ± 0.006

G0 = 0.974 ± 0.001

∆G1 = −0.430 ± 0.001 (Q1 = 0.3)

∆G2 = 0.430 ± 0.001 (Q2 = 1.2)

∆G3 = −0.280 ± 0.001 (Q3 = 2.8)

∆G4 = 0.047 ± 0.001 (Q4 = 4.4)

∆G5 = −0.046 ± 0.001 (Q5 = 8.7)

∆G6 = 0.042 ± 0.001 (Q6 = 19.0)

∆G7 = 0.026 ± 0.001 (Q7 = 20.8)

∆G8 = −0.037 ± 0.001 (Q8 = 22.4)

∆G9 = 0.084 ± 0.001 (Q9 = 26.5)

∆G10 = −0.064 ± 0.001 (Q10 = 32.5)


DCH History

Other Chambers’ Aging

[mC/cm] [%/(mC/cm)]Experiment Gas Mix Charge ∆G/G Aging

CDF Ar:Eth:Alc 130 <1 ∼ 20(Run 2) 50:50:1

ZEUS Ar:Eth:CO2 100 <∼ 0.183:5:12

H1 Ar:Eth:H2O < 10 >∼ 150:50:0.1

HERA-B Ar:CF4:CO2 2300 ∼ none(test) 65:30:5

BaBar He:i-C4H10:H2O 33.6 0.380:20:0.4

From 2001 DESY Workshop presentations


DCH History

Suppressing Damage

Lu Changguo, Princeton


DCH History

Remediating Damage

Excess current can trigger self-sustaining discharges

Maximum safe current significantly reduced over time

0 20 40 60 80 100 120

Time (Min)

0

100

200

300

400

500

Ano

de C

urre

nt (

nA)

Adam Boyarski, SLAC

“Training” with oxygen (500 ppm) gradually raises current

limit to original construction. Maintained after O2 removed.

Further study underway to confirm long-term performance


DCH History

Remediating Damage

Additives (alcohol, water, oxygen) can suppress

discharges, allow running at higher currents

Before With Additive AfterAdditive (%) Imax Time (hr) Imax Imax Cured?

Methylal 4 0.3 ≈0 >8 No2 3 0.4 No

2-Propanol 1.0 ≈0.5 ≈0 >12 No0.5 >10 No0.25 >13 0.2 No

H2O 0.35 0.4 ≈0 >27 No0.18 >9 0.5 No

O2 0.10 0.5 1.5 >32 >40 Yes0.05 0.4 2 >29 >16 Yes0.02 0.9 10 >35 >14 Yes

CO2 5 0.4 35 >40 >27 Yes

O2+H2O 0.4 40 10 3 Partly(0.05+0.35)

Adam Boyarski, SLAC

Temporary 500–1000 ppm O2 running appears to

“cure” discharge problem. Current limit restored

to initial level.


DCH History

Track Fitting

Residuals of hits vs. distance from wire

0

0.005

0.01

0.015

0.02

0.025

-1 -0.75 -0.5 -0.25 0 0.25 0.5 0.75 1

Mean 125 µm

Signed distance from wire (cm)

Res

olut

ion

(cm

)

〈σ(resid)〉 ∼ 125 µm

Design target: 140 µm in middle region of cell

d(t): pair of 7th order Chebyshev functions, each side of

cell, corrected for angle and position in cell.


DCH History

Track Fitting

Momentum resolution from cosmic rays

0

1.0

2.0

0 4 8Transverse Momentum (GeV/c)

σ(p t

)/p t

(%

)

1-2001 8583A23

σ(pT )/pT = 0.45% + 0.13% pT (GeV/c)

Design target: 0.21% + 0.14% pT


DCH History

Tracking Efficiency

Polar Angle (radians)

Transverse Momentum (GeV/c)

Effi

cien

cy

0.6

0.8

1.0

0.6

0.8

1.0

Effi

cien

cy

0 1 2

3-2001 8583A40

1960 V

1900 V

a)

1960 V

1900 V

b)

0.0 0.5 1.51.0 2.0 2.5

“Pseudo-efficiency”

Count DCH+SVT tracks

vs. total SVT tracks

Measure acceptance in

momentum or pT

polar angle

azimuth (not shown)

DCH and SVT not independent


DCH History

dE/dx, Particle ID

dE/dx vs momentum

10 3

10 4

10-1

1 10Track momentum (GeV/c)

80%

tru

ncat

ed m

ean

(arb

itra

ry u

nits

)

eµ

π

K

p dBABAR

DCH dE/dx - dE/dx(K) (arb. units)

p<0.

6 G

eV/c

Drift Chamber K/π Separation

0

50

-600 -400 -200 0 200

π K


0.6<

p<0.

8

0

100

-600 -400 -200 0 200

π K


0.8<

p<1

0

100

-600 -400 -200 0 200

π K

DCH dE/dx - dE/dx(K)(arb. units)

p>1

GeV

/c

0

1000

-600 -400 -200 0 200

πK

Drift Chamber K/π Separation

BABAR

Good π/K separation up to ∼ 700 MeV/c

Confirms results in DIRC region, adds PID coverage outside

DIRC acceptance


DCH History

Physics Performance (II)

B → D(∗)D(∗), D∗+ → π+D0, D0 → K−π+

(Monte Carlo generated events)

Momentum σ(p)/p 4.7 × 10−3

D0 → K−π+ σ(mass) 6.5 ± 0.2 MeV/c2

D∗ → π+D0 σ(mass) 0.80 ± 0.03 MeV/c2


DCH History


Readout time scales with HV current, luminosity

(uniform occupancy)

IDCH (µA)

Rea

do

ut

tim

e (µ

s)

0

50

100

150

200

0 100 200 300 400 500 600 700 800

M. Cristinziani, 2004

)-1 s-2 cm33

Luminosity (x 100 5 10 15 20 25 30 35 40

Dea

dti

me

(%)

0

20

40

60

80

100

Deadtime Projection

Existing DAQ

With upgrade

2003

2004

2005

2006

2007-2010

C. Jessop, 2004

Readout ∼ trigger rate =⇒ non-linear deadtime


performance and aging of the babar drift chamber · 2008-02-13 · dch history babar drift chamber...

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