Post on 26-Jun-2020
Performance and Aging of the BaBarDrift Chamber
Michael H. Kelsey
Stanford Linear Accelerator Center™
B
AB
AR
™&
©
L . de B r unhoff
Super B Factory Workshop in Hawaii
19–22 January 2004
DCH High Lumi
Outline
• Drift Chamber Design and Operation
• Tracking, dE/dx, and Physics
• Aging, Damage and Remediation
• Future Operations, Performance
• Summary and Outlook
Michael H. Kelsey SuperB 2
DCH High Lumi
BaBar Detector
Michael H. Kelsey SuperB 5
DCH High Lumi
BaBar Drift Chamber
Main tracking detector in BaBar
Surrounds beam pipe, final focus magnets, and
silicon vertex tracker
Michael H. Kelsey SuperB 6
DCH High Lumi
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)
Michael H. Kelsey SuperB 8
DCH High Lumi
DCH Operation
Gas mixture 80% helium, 20% isobutane,
3500–4000 ppm water vapor, ∼ 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)
Since January 2001 (85% of total data) at 1930V
Michael H. Kelsey SuperB 9
DCH High Lumi
Premature Aging
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
Michael H. Kelsey SuperB 10
DCH High Lumi
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 Since Startup (May 1999 - Present)
0
2.5
5
7.5
10
0
2.5
5
7.5
10
20000
2.5
5
7.5
10
20010
2.5
5
7.5
10
20020
2.5
5
7.5
10
20030
2.5
5
7.5
10
2004
Acc
umul
ated
Cha
rge
(mC
/cm
)
Total charge 12.2 mC/cm in nearly five years
Michael H. Kelsey SuperB 11
DCH High Lumi
Reconstruction Performance
Hit resolution 〈σ(resid)〉 ∼ 125 µm
Target: 140 µm in middle region of cell
Momentum σ(pT )/pT = 0.45% + 0.15% pT (GeV/c)
Target: 0.21% + 0.14% pT
Tracking > 95% matching with SVT tracks
dE/dx resolution ∼ 7.5%, ± (0.5-0.7)% bias
Early test results: 7.0%
Michael H. Kelsey SuperB 12
DCH High Lumi
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
p<0.
6 G
eV/c
Drift Chamber K/π Separation
0
50 π K
0.6<
p<0.
8
0
100π K
0.8<
p<1
0
100π 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.
Provides confirmation of DIRC, and coverage
outside of DIRC acceptance.
Michael H. Kelsey SuperB 16
DCH High Lumi
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
Michael H. Kelsey SuperB 17
DCH High Lumi
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
Michael H. Kelsey SuperB 18
DCH High Lumi
Gain vs. Time
G(Q) = {G0 + ∆G1|Q>Q1+ ∆G2|Q>Q2
+ . . .} exp(−AQ)
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 2.5 5 7.5 10
Aging rate: -0.549± 0.023 %/(mC/cm) over 12.17 mC/cm
Michael H. Kelsey SuperB 23
DCH High Lumi
Long-term Damage
Besides aging, “sudden damage” always possible
Transient discharges, voltage trips
Buildup of deposits on wires
Self-sustaining discharge (Malter effect)
Long-term studies of aging and 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 times BaBar lifetime charge
Michael H. Kelsey SuperB 27
DCH High Lumi
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
Michael H. Kelsey SuperB 28
DCH High Lumi
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
An
od
e C
urr
en
t (n
A)
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
Michael H. Kelsey SuperB 31
DCH High Lumi
Future Performance
Can we operate at ten times design luminosity?
DCH currents vs. Luminosity
0
1000
2000
3000
10 20 30 40Luminosity (1033 cm-2 s-1)
DC
H c
urre
nt, 1
930V
(µA
)
20002001
20022003
2004
2005
2006
20072008
250
500
750
1000
DC
H o
ccup
ancy
(Q
>50
)
High occupancy?
High currents?
High rates?
Aging problems?
DCH performance computed from beam currents and luminosity
By 2008, average occupancy, current, trigger rates
will be tripled from current (2003) conditions.
Michael H. Kelsey SuperB 34
DCH High Lumi
Tracking at High Luminosity
Mix Monte Carlo B → D(∗)D(∗) with real random-trigger data
Multiple triggers overlaid to match luminosity extrapolations
Evaluate physics quality relative to current performance
Compared to design 2 × 1034 4 × 1034 4 × 1034
3 × 1033 cm−2 s−1 (3× bkg) (5× bkg) (10× bkg)
Tracking eff. (%) 98.6 ± 0.1 ± 0.7 97.4 ± 0.1 ± 1.0
Momentum
σ(p)/p = 4.7×10−3+4.2 × 10−5 +5.5 × 10−5
D0→ K+π− (%) 96.0 ± 0.5 95.5 ± 0.5 80 ± 3
D0 Mass, σ
6.5 ± 0.2 MeV/c26.5 ± 0.2 6.4 ± 0.2 7.0 ± 0.3
D∗ → D0π (%) 84.4 ± 1.1 75.0 ± 1.3 25 ± 2
D∗ Mass, σ
0.80±0.03 MeV/c20.97 ± 0.04 1.50 ± 0.08 3.2 ± 0.8
Michael H. Kelsey SuperB 35
DCH High Lumi
High Rate Data Acquisition
Modular, parallel electronics
4-buffer pipeline per channel
16 elements per quadrant
via 1 GHz fiber to processor
FEA−3 180 ch
FEA−2 144 ch
FEA−1 96 ch
24 ch
16x FEE
to 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 hits each
=⇒ 45 hits requires 200 µs (5 kHz)
Michael H. Kelsey SuperB 37
DCH High Lumi
High Rate Data Acquisition
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
)-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
Deadtime when readout ∼ trigger rate
Expect 30–40% d.t. by 2006, 50+% by 2007
Michael H. Kelsey SuperB 38
DCH High Lumi
High Rate Data Acquisition
Redesign front-end with extreme parallelism
Three chips per logical “element”
≤ 24 channel serial readout
< 105–140 µs readout time, 7 kHz rate
Essentially no deadtime for normal running,
through lifetime of Babar.
Requires 20 fiber readout processors
Targeting installation in mid-2005
Michael H. Kelsey SuperB 39
DCH High Lumi
Effect of Aging on Gain
Integrate current to estimate accumulated charge
Include expected running year by year
Linear lumi improvement within years
DCH Projected Dose (1999 - 2009)
0
20
40
60
80
100
2000 2002 2004 2006 2008
Acc
umul
ated
Cha
rge
(mC
/cm
)
DCH Projected Gain (1999 - 2009)
0
0.25
0.5
0.75
1
0 20 40Accumulated Charge (mC/cm)
Est
imat
ed G
ain
(196
0V=
1)
Use fitted aging function to extrapolate gain
Assume 1930V operation, no gas changes
Michael H. Kelsey SuperB 40
DCH High Lumi
Compensating for Aging
By 2007, gain at 1930V could be >∼ 25% below
current performance
Significant impact on trigger, track finding
Non-uniform acceptance, efficiency
Compensate for gain loss by increasing voltage
Lower gain, same HV current as now
+10V ⇒ ∆G ∼ +0.09
Raise when G <∼ 0.65
E.g. 2006, 2008
DCH Projected Gain (1999 - 2009)
0
0.25
0.5
0.75
1
0 20 40Accumulated Charge (mC/cm)
Est
imat
ed G
ain
(196
0V=
1)
Michael H. Kelsey SuperB 41
DCH High Lumi
Summary and Outlook
BaBar Drift Chamber has been operating smoothly
since October 1999
Tracking performance up to design
dE/dx performance good, improvable
Excellent operational efficiency
Reasonable aging rate observed so far
Accumulated 12.2 mC/cm after five years
Gain fits well for simple aging 0.55%/(mC/cm)
Overall reduction 15% since startup
Comparable to other large experiments
Michael H. Kelsey SuperB 42
DCH High Lumi
Summary and Outlook
Expect reliable performance over 10-year lifetime
50–80 mC/cm total charge, 25% loss of gain
⇒ Well below limits found in test chambers
Minimal degradation of physics performance
Increasing data rate will require significant elec-
tronics upgrade
Damage and aging may be remediated with
additives
3500 ppm H2O should prevent discharges
Aging may be compensated by adjusting voltage
Michael H. Kelsey SuperB 43
DCH High Lumi
Supplemental Information
Michael H. Kelsey SuperB 44
DCH High Lumi
Michael H. Kelsey SuperB 3
DCH High Lumi
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 luminosity in ex-
cess of 6× 1033 cm−2 s−1
Over 165 fb−1 delivered to
BaBar (∼ 9% off resonance)
BaBar runs > 95% efficiency:
nearly 120 million BB pairs
Nov 1
Jan 1
1999
Mar 1
May 1
Jul 1 Sep 1 N
ov 1 Jan 1
2000
Mar 1
May 1
Jul 1 Sep 1 N
ov 1 Jan 1
2001
Mar 1
May 1
Jul 1 Sep 1 N
ov 1 Jan 1
2002
Mar 1
May 1
Jul 1 Sep 1 N
ov 1 Jan 1
2003 2004
0
10
20
30
40
50
60
70
80
90
100
110
120
130
140
150
160
Inte
grat
ed L
umin
osity
(fb
-1)
BA BA R
PEP-II Delivered 165.13/fbBABAR Recorded 157.78/fb
BABAR off-peak 14.65/fb
Michael H. Kelsey SuperB 4
DCH High Lumi
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
Michael H. Kelsey SuperB 7
DCH High Lumi
Track Fitting
Residuals of hits vs. distance from sense 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. Adjusted for angle through cell.
Michael H. Kelsey SuperB 13
DCH High Lumi
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% + 0.15% pT (GeV/c)
Design target: 0.21% + 0.14% pT
Michael H. Kelsey SuperB 14
DCH High Lumi
Tracking Efficiency
Polar Angle (radians)
Transverse Momentum (GeV/c)
Eff
icie
ncy
0.6
0.8
1.0
0.6
0.8
1.0
Eff
icie
ncy
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
Michael H. Kelsey SuperB 15
DCH High Lumi
Physics Performance (III)
D0 → K−π+ reconstruction efficiency vs. φ
ask David Williams for plot
Michael H. Kelsey SuperB 19
DCH High Lumi
Quantifying Gain
Normalize gain to absorb environmental effects
Pressure and temperature ⇒ density
Detailed gas mixture (He:i-C4H10, H2O, O2)
Precise operating voltage
Scale dE/dx from Bhabha-scattering events
[e+e− → e+e−(γ)]; normalization done ∼ hourly
Michael H. Kelsey SuperB 20
DCH High Lumi
Normalizing Gain
Most significant correlation with gas density
absgain(time)
DCH Gain vs. Density (1930V, Aug-Dec 2001)
0
500
0.68 0.735 0.79
dchdens()
0
500
3.34 3.41 3.48
P/T-3.43
Gai
n
0
1
-0.04 -0.02 0 0.02
14.24 / 48
A0 0.7307 0.1112E-02
A1 -0.9868 0.3940E-01
Density (P/T)
Gco
rr
0
1
3.35 3.4 3.45 3.5
nR/V = Pabs/Tabs
Several short time intervals
Jan–Jul 2000 (1900V)Jul–Dec 2000 (1960V)Mar–Jul 2001 (1930V)Aug–Dec 2001Feb–Jun 2002Feb–Jun 2003
Correct gain using slope of fit
Applying offset could obscure aging effects
Michael H. Kelsey SuperB 21
DCH High Lumi
Gain vs. Time
Continuous decrease G = G0 exp(−AQ) due to aging
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 2.5 5 7.5 10
A B C D
1 2 3 4 5
Steps due to operating changes (e.g., voltage)
Michael H. Kelsey SuperB 22
DCH High Lumi
Gain vs. Time Fit Details
G(Q) = {G0 + ∆G1|Q>Q1+ ∆G2|Q>Q2
+ . . .} exp(−AQ)
χ2/dof = 668.33 / 214
−A(%) = −0.549 ± 0.023
G0 = 0.975 ± 0.009
∆G1 = −0.429 ± 0.009 (Q1 = 0.3)
∆G2 = 0.432 ± 0.001 (Q2 = 1.2)
∆G3 = −0.276 ± 0.001 (Q3 = 2.8)
∆G4 = 0.053 ± 0.001 (Q4 = 4.4)
∆G5 = −0.035 ± 0.001 (Q5 = 8.7)
Michael H. Kelsey SuperB 24
DCH High Lumi
Systematic Checks
Accumulated Charge (mC/cm)
Cor
rect
ed G
ain
DCH Gain (showing error on means)
0.4
0.6
0.8
1
1.2
0 2.5 5 7.5 10
Aging rate: -0.574± 0.001 %/(mC/cm) over 12.17 mC/cm
Accumulated Charge (mC/cm)
Cor
rect
ed G
ain
DCH Gain (No data excluded)
0.4
0.6
0.8
1
1.2
0 2.5 5 7.5 10
Aging rate: -0.194± 0.024 %/(mC/cm) over 12.17 mC/cm
Accumulated Charge (mC/cm)
Gai
n
DCH Gain Since Startup (May 1999 - Present)
0.4
0.6
0.8
1
1.2
0 2.5 5 7.5 10
Aging rate: -0.747± 0.043 %/(mC/cm) over 12.17 mC/cm
No density correctionAccumulated 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 2.5 5 7.5 10
Aging rate: -0.565± 0.074 %/(mC/cm) over 12.17 mC/cm
Coarser binning (50 vs. 200 bins)
Michael H. Kelsey SuperB 25
DCH High Lumi
Comparative Aging
Aging measurements from other experiments
[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 12.2 0.680:20:0.4
From 2001 DESY Workshop presentations
Michael H. Kelsey SuperB 26
DCH High Lumi
Suppressing Damage
Lu Changguo, Princeton
Michael H. Kelsey SuperB 29
DCH High Lumi
Suppressing Damage
Lu Changguo, Princeton
Michael H. Kelsey SuperB 30
DCH High Lumi
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.
Michael H. Kelsey SuperB 32
DCH High Lumi
PEP-II Luminosity Upgrades
[1033cm−2 s−1] [mA] [mA] [µA] [raw/rec]
Year L I(e−) I(e+) DCH HV Hits/ev
2003 6.3 1140 1450 532 456/ 332
2004 12.1 1600 2700 973 686/ 483
2005 18.2 1800 3600 1380 898/ 621
2006 23.0 2000 3600 1665 1046/ 719
2007 33.0 2200 4500 2284 1368/ 930
2008 33.0 2200 4500 2284 1368/ 930J. Seeman/PEP-II, SLAC
Michael H. Kelsey SuperB 33
DCH High Lumi
Tracking at 4 × 1034cm−2 s−1
Momentum resolution
σ(p)/p
D∗ → D0π Mass
D* mass
0
25
50
75
100
2.002 2.004 2.006 2.008 2.01 2.012 2.014 2.016 2.018 2.02
568.8 / 66P1 0.4578 0.8226E-02P2 2.010 0.2885E-04P3 0.3429E-03 0.4997E-05P4 0.2012E-02 0.7171E-04P5 758.1 8.335
Michael H. Kelsey SuperB 36