full electromagnetic simulation of multi-strip detectors
DESCRIPTION
full electromagnetic simulation of multi-strip detectors. Diego González-Díaz (GSI-Darmstadt) A. Berezutskiy (SPSPU-Saint Petersburg), G. Kornakov (USC-Santiago de Compostela), M. Ciobanu (GSI-Darmstadt), Y. Wang (Tsinghua U.-Beijing), J. Wang (Tsinghua U.-Beijing). - PowerPoint PPT PresentationTRANSCRIPT
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Diego González-Díaz (GSI-Darmstadt)
A. Berezutskiy (SPSPU-Saint Petersburg), G. Kornakov (USC-Santiago de Compostela), M. Ciobanu (GSI-Darmstadt), Y. Wang (Tsinghua U.-Beijing), J. Wang (Tsinghua U.-Beijing)
Darmstadt, November 24th
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Some references used in this talk
[1a] H. Alvarez Pol et al., 'A large area timing RPC prototype for ion collisions in the HADES spectrometer', NIM A, 535(2004)277.[2a] A. Akindinov et al., 'RPC with low-resistive phosphate glass electrodes as a candidate for CBM TOF', NIM A, 572(2007)676.[3a] J. Wang et al., paper in preparation.[4a] L. Lopes et al., 'Ceramic high-rate RPCs', Nuclear Physics B (Proc. Suppl.), 158(2006)66.[5a] D. Gonzalez-Diaz et al., 'The effect of temperature on the rate capability of glass timing RPCs', NIM A, 555(2005)72.[6a] A. Ammosov et al., talk at XIII CBM collaboration meeting, Darmstadt, Germany.[7a] L. Nauman et al., talk at XIV CBM collaboration meeting, Split, Croatia.[1] A. Mangiarotti et al., 'On the deterministic and stochastic solution of Space-Charge models and their impact in high resolution timing' talk at RPC Workshop Seoul, 2005.[2] G. Chiodini et al., 'Characterization with a Nitrogen laser of a small size RPC', NIM A 572(2007)173.
[3] A. Colucci et al., 'Measurement of drift velocity and amplification coefficient in C2H2F4-isobutane mixtures for avalanche-operated
resistive-plate counters', NIM A, 425(1999)84. [4] W. Riegler et al., 'Detector physics and simulations of resistive plate chambers', 500(2003)144 .[5] E. Basurto et al., 'Time-resolved measurement of electron swarm coefficients in tetrafluoretane (R134a)', Proc. to 28th ICPIG, Prague, 2007.[6] P. Fonte, V. Peskov, 'High resolution TOF with RPCs', NIM A, 477(2002)17.[7] P. Fonte et al., 'High-resolution RPCs for large TOF systems', NIM A, 449(2000)295.[8] A. Akindinov et al. 'Latest results on the performance of the multigap resistive plate chamber used for the ALICE TOF', NIM A 533(2004)74.[9] G. Aielli et al., 'Performance of a large-size RPC equipped with the final front-end electronics at X5-GIF irradiation facility', NIM A
456(2000)77. [10] S. An et al., 'A 20 ps timing device—A Multigap Resistive Plate Chamber with 24 gas gaps', NIM A 594(2008)39. [11] A. Blanco et al., 'In-beam measurements of the HADES-TOF RPC wall', NIM A 602(2009)691.[12] W. Riegler, D. Burgarth, 'Signal propagation, termination, crosstalk and losses in resistive plate chambers', NIM A 481(2002)130.[13] T. Heubrandtner et al., NIM A 489(2002)439.
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Dipolemagnet
The Compressed Baryonic Matter Experiment
Ring ImagingCherenkovDetector
Transition Radiation Detectors
ResistivePlate Chambers(TOF)
Electro-magneticCalorimeter
SiliconTrackingStations
Tracking Detector
Muondetection System
Projectile SpectatorDetector(Calorimeter)
VertexDetector
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The CBM-TOF wall. Design requirements
● Overall time resolution (including start time) σT = 80 ps.
● Occupancy < 5 % for Au-Au central collisions at E=25 GeV/A.
● Space resolution ≤ 5 mm x 5 mm.
● Efficiency > 95 %.
● Pile-up < 5%.
● Rate capability = 20 kHz/cm2.
● Multi-hit capability (low cross-talk).
● Compact and low consuming electronics (~65.000 electronic
channels).
● Multi-strip design in the outer region, due to the very
low occupancies. Why? -> Why not?. If electrically
possible it is mechanically much more easy.
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In order to accommodate the different granularities as a function of the polar angle, five different regions were defined:
➔Pad region (1): 2.0 x 2.0 cm2 ( 27072 channels,
~10 m2) ➔Strip region (2): 2.0 x 12.5 cm2 ( 3840 x 2 channels, ~10
m2)➔Strip region (3): 2.0 x 25.0 cm2 ( 5568 x 2 channels, ~30
m2)➔Strip region (4): 2.0 x 50.0 cm2 ( 6150 x 2 channels, ~60
m2 )➔Strip region (5): 2.0 x 100.0 cm2 ( 2900 x 2 channels, ~60
m2 )
TOTAL ( ~65000 channels, ~170 m2)
The CBM-TOF wall. Simulation based on occupancies
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A multi-gap RPC in general. Here a differential RPC ('a la' STAR), just for the sake of 'electrical elegance'
Rin
standard PCBwith read-outstrips on oneside
HV insulatorwith Vbreak>10-15 kV
HV coating withR~100 MΩ/□
+V
-V
differential pre-amplifier
at least 4 gas gaps (~0.3 mm thick)
float glass
particle
*parameters not from STAR
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More electrical schemes are (un)fortunately possible
ALICE-LHC
V
-V
-V
STAR-RHIC
V
-V
V
HADES-SIS
-V
-V
FOPI-SIS
-V
V
all these schemes are equivalent regarding the underlying avalanche dynamics... but the RPC is also a strip-line, and this is manifested after the avalanche current has been induced. And all these strip-lines have a completely different electrical behavior.
-V
V
V
-V
V
S. An et al., NIM A 594(2008)39 [10]
!
HV filtering scheme is omitted
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Generation + induction + transmission + FEE. Sketch
generation + induction
1transmission
2
FEE response
3
multi-strip
4
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Avalanche generation. A simple avalanche model
• The stochastic solution of the avalanche equation is given by a simple Furry law (non-equilibrium effects are not included).
• Avalanche evolution under strong space-charge regime is characterized by no effective multiplication. The growth stops when the avalanche reaches a certain
number of carriers called here ne,sat.
• The amplifier is assumed to be slow enough to be sensitive to the signal charge and not to its amplitude. We work, for convenience, with a threshold in charge
units Qth.
log 1
0 n e
lect
rons
~7
to t
space-charge regime
exponential-growthregime
~7.5
tmeas
avalanche Furry-typefluctuations
~2
Raether limit 8.7
exponential-fluctuationregime
threshold
0
simplifying assumptions
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continuous line: data from Basurto et al.
in pure Freon [5]
α extrapolated to mixture by using Freon's partial pressure:
αmixture = αFreon(E/fFreon) fFreon
vd directly taken from Freon (inspired on microscopic codes)
vd,mixture = vd,Freon
Parameters of the gas used for input: α* (effective Townsend coefficient), vd (drift velocity), no (ionization
density)
HEED(from Lippmann[4])
n o [m
m-1]
little dependencewith mixture!
*purely phenomenological!
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results for wide-pad detectors
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MC results. Efficiency and resolution for 'wide-pad' detectors
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qinduced, prompt [pC]
qinduced, total [pC]
1-gap 0.3 mm RPC standard mixture
simulated
measured
Eff = 74%
Eff = 60%
Eff = 38%
measured
simulated
ne,sat= 4.0 107 (for E=100 kV/cm)
qinduced, prompt [pC]
assuming space-charge saturation at
4-gap 0.3 mm RPC standard mixture
data from Fonte, [6,7]
MC results. Prompt charge distributions for 'wide-pad' detectors
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multi-strip detectors
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Generation + induction + transmission + FEE
generation + induction
1transmission
2
FEE response
3
multi-strip
4
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Induction and weighting field Ez
(t)nedzvEti )( t=2.5 mm
w=22 mm HV
read-out
wide-pad limit t << w
gap
totz C
C
gE
1
additionally when g<<t (typicalsituation) Ez does not depend on the position –z- along the gap
g=0.3 mm
ws-s ~0 mm
T. Heubrandtner et al. NIM A 489(2002)439
We adapted to multi-gap the formulas from: problem: under-estimation of Ez
for large inter-strip separations
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Cross-talk in a 2-strip RPC modeled as a loss-less transmission-line (I)
om
mo
CC
CCC
om
mo
LL
LLL
om
moc ZZ
ZZZ
1ˆ TvTLZc
112 ˆ)ˆ(ˆ TLCTv
momo LLCC
20
02
vv
vv
v
cc
o
m
co
mc
c
ZZC
C
ZC
CZ
Z
roo
cCLv
1
)(3moom LCLCvv
cCC
LZ r
oo
oc
1
two different modes in the transmission line!. This causes 'modal dispersion' unless:
o
o
m
m
L
C
L
C true for
homogeneous transmission lines!
a 4-gap RPC seen as a transmission-line
om
mo
RR
RRR
dominated by skin-effect:small for typical dimensionsand rise-times
om
mo
GG
GGG
very small, due to the presence of gas and glass
)(ˆ CC
for typical materials (glass)
loss-less line!
W. Riegler, D. Burgarth, NIMA 481(2002)130 [12]see
if
1)
2) 0, mm LC
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)(]9ln22)(
[)(2 v
ztI
tv
z
v
v
RZ
RZtI o
rise
o
inc
inmtc
for exponential signals
)(4
)(2,1v
ztItI o
tc
low-frequency /small distance/ non-dispersivelimit
high-frequency /large distance/ dispersivelimit
1
rise
o
tv
z
v
v
1
rise
o
tv
z
v
v
small dispersion
very large dispersion
zo = position along the strip where the signal is induced
see also [12]
the 2 modes are fullydecoupled
Cross-talk in a 2-strip RPC modeled as a loss-less transmission-line (II). Limits.
in
mg
mm
c
m
mgc
mg
mm
mg
RZ
Z
CC
C
L
L
Z
Z
CC
LZ
CC
C
L
L
v
v
CCLv
det
det
0
0
0
1
0
2
2
1
)(
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Cross-talk influence in the timing of a coincident (double) hit. A simple derivation (I).
log[i(t)]
t
ith
variations in base-line due to cross-talk
variations in time at threshold due to cross-talk 2talkcrossrms
space-charge
exponential regime
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Assumptions: Within the same primary collision cross-talk extends up-to infinite time. It does not depend on position. Fluctuations in time of cross-talk signal are smaller than fluctuations coming from the avalanche charge distribution. Pick-up strips are separated by a typical distance bigger than the area of influence of the avalanche. Charge sharing during induction can be neglected!. Cross-talk is small, given by Fct.
Tctth
ctriseq
th
Fq
qF
t
q
rms
q
qrms
~
9lntalkcross
q
qF thct
cross-talk is expected to affect timing when
Cross-talk influence in the timing of a coincident (double) hit. A simple derivation (II).
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History revisited: 1.6m-long 2-strip RPC (P. Fonte et al., 2002)
width = 5cm
strip separation = 1mm
glass = 3mm
gap = 0.3mm
length= 1.6m
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Cross-talk in Fonte multi-strip RPC
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Cg=521 pF/m
Cm=88 pF/m
Fct=50% !
BW=1.5 GHzRin=50 Ω
very dispersive!
experimental conditions:Π, E=3.5 GeV, low rates, trigger width = 2 cm
Fct=40%
'fine-tunning'
80%-90% measured cross-talk levels reproduced
Zc~13 Ω
transverse scan
Cross-talk in Fonte multi-strip RPC
HV=5.7 kV
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x10
->increase stripseparation
Cg
Cm
Δv/v
trise
Minimizing cross-talk (I)
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x6 /2.5
/6
->increase strip/widthseparation->reduce glass thicknessCg
Cm
Δv/v
trise
Minimizing cross-talk (II)
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x6 /2.5
/6
BW/10
->increase strip/widthseparation->reduce glass thickness->reduce band-width
Cg
Cm
Δv/v
trise
low couplinglow dispersion
Minimizing cross-talk (III)
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guard strip
->put guard strip
Cg
Cm
Δv/v
trise
Minimizing cross-talk (IV)
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not mirrored
->use only two electrodes
Cg
Cm
Δv/v
trise
(it flips!)
Minimizing cross-talk (V)
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not mirrored
coupling to PCB
->use only two electrodes->couple locally to groundCg
Cm
Δv/v
trise
low couplingNO dispersion
Minimizing cross-talk (VI)
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Minimizing cross-talk + detector response (I)
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x10
Minimizing cross-talk + detector response (II)
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x6 /2.5
/6
Minimizing cross-talk + detector response (III)
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x6 /2.5
/6
BW/10
Minimizing cross-talk + detector response (IV)
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not mirrored
coupling to PCB
Minimizing cross-talk + detector response (V)
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Ideal case: no cross-talk + perfect tracking
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'some' of the new CBM prototypes(preliminary short compilation)
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35-cm long wide-strip, mirrored and shielded
... ...
Zc~18 Ω
BW=260 MHzRin=100 Ω
Fct=11%little dispersive
experimental conditions:~mips from p-Pb reactions at 3.1 GeV, low rates, trigger width = 2 cm
Fct=19%
'fine-tunning'inter-strip regiondominated by trigger width
probability of pure cross-talk:1-3%
Analysis with high resolution tracking on-going.
transverse scan
Cg
Cm
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1-m long counter, 6-strip RPC, 12-gap, mirrored and shielded
... ...
experimental conditions:~mips from p-Pb reactions at 3.1 GeV, low rates, trigger width = 2 cm (< strip width)long run. Very high statistics.
No simulations available yet
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no double hitdouble-hit in any of 1st neighborsdouble-hit in any of 2nd neighborsdouble-hit in any of 3rd neighbors
1-m long counter, 12-gap, mirrored and shielded
No simulations available yet
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1-m long counter, 12-gap, mirrored and shielded
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conclusions and outlook
• Multi-strip design of timing RPCs at 1-m scale with acceptable cross-talk, small cluster size and small deterioration of time resolution seems doable.
• Further optimized structures based on simulations are on the way (Fct~1%).
• For making a multi-strip fully robust against streamer-crosstalk there is still a long way to go (maybe impossible).
-> Detailed optimization based on physics performance soon to follow. Then we will know if cross-talk is 'high' or not.
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Appendix
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Multi-strip-MRPC (MMRPC)
1.1 mm
Glass: ε=7.5, strip width = 1.64 mm, strip gap = 0.9 mm, strip length = 900 mm
1.1 mm
0.5 mm
0.22 mm
copper (20 μm)
8 gaps
The FOPI counter
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Induction. Example FOPI case.
n(t)dwvEtI )(
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cathode 150 anode 1
50
50
50
cathode 250 anode 2
50
50
50
cathode 350 anode 3
50
50
50
cathode 4anode 4 50
50
cathode 550 anode 5
50
50
50
Cross-talk in an un-terminated line
signal from BC420scintillator (used as current generator)
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cathode 150 anode 1
50
50
50
cathode 250 anode 2
50
50
50
cathode 350 anode 3
50
50
50
cathode 450 anode 4
50
50
50
cathode 550 anode 5
50
50
50
Cross-talk in a terminated line
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Cross-talk and signal shape
cross-talkconstant, very independent from the signal shape
low dispersion counter, typical working conditions, BW=260 MHz
Take as a typical shape the one of an avalanche produced at the cathode
Even for dispersive counters it is reasonable since most of the charge is coming from that region
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The FOPI counter (11th strip)
50 anode 0 50
50 anode 1 50
50 .......... 50
anode 11 50
50 anode 12 50
50
cathode
50 anode 13 50
50 anode 14 50
50 50anode 15
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The FOPI counter (9th strip)
50 anode 0 50
50 anode 1 50
50 .......... 50
anode 9 50
50 anode 10 50
50
cathode
50 anode 11 50
50 anode 12 50
50 .......... 50
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50-cm long, mirrored and not shielded
... ...
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~1-m long, non-mirrored and shielded
... ...
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several electrons (I)
•An ionizing particle at fixed energy creates an average number of ionizations no randomly distributed along the gap, with each cluster having a (1/ne in cluster)2 probability to produce more than 1 electron. This is very easy to generate. Then each cluster can be made to fluctuate according to Furry law.
HEEDcalculation
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A parentheses: rate capability of various CBM prototypes
for small fluxes and in a simple DC-model
gappergapper dqg
EE1
)(
see for instance: D. Gonzalez-Diaz et al. Nucl. Phys. B (Proc. Suppl.) 158(2006)111
dqAoTT ,)(
dqBo )(
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A parentheses: rate capability and DC-model systematics
In first order, it fits! dqAoTT ,)(
dqBo )(
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prompt (e-) component
Slow (ion) component
g/ve ~ 1 ns g/vi ~1 μs
E=ΔV/g
ev
D
/1
p
particle
e--I+
How (we believe) is the avalanche produced?
vtwo eEqti )(
ith
space-chargelimitation
Eav~E
avalanche growth
decreases!
τg ~ 1 s (glass relaxation time)
see [4],for instance
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More electrical schemes are (un)fortunately possible
ALICE-LHC
V
-V
-V
STAR-RHIC
V
-V
V
HADES-SIS
-V
-V
FOPI-SIS
-V
V
all these schemes are equivalent regarding the underlying avalanche dynamics... but the RPC is also a strip-line, and this is manifested after the avalanche current has been induced. And all these strip-lines have a completely different electrical behavior.
-V
V
V
-V
V
S. An et al., NIM A 594(2008)39 [10]
!
HV filtering scheme is omitted
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First of all... what is a strip?
In this talk:
A strip is a read-out structure that must be described (due to the phenomena under study) like a transmission-line. In the simplest single-strip description, it is something characterized by 2 magnitudes: a transmission coefficient and a propagation velocity.
This is a definition based on the electrical properties of the structure.
In standard language:
- strip: something read-out in two ends/something 'quite rectangular'- pad: something read-out in one end/something 'quite squared'
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Induction + transmission + FEE. Sketch (II)
Five stages in order to get a predictive result
• Avalanche generation with the previous code.
[->Comparison with eff vs V and fine-tune, if needed, of threshold value. This approach seems to be flexible enough.]
• Induction, based on analytical formulas from [13], extrapolated to multiple-gaps by using the effective series permittivity of the corresponding group of layers.
• Propagation based on HF simulator APLAC (http://web.awrcorp.com/Usa/Products/APLAC/).
[-> Validation of APLAC for the structure of interest with a pulse generator (nowadays we do not need this step anymore)]
• Termination and other circuit elements are included, together with FEE, simulated also with APLAC.
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A 2-strip RPC as a loss-less transmission-line. Example (III)
2-strip geometry and signal taken from [12]
injected signal cross-talk signal
non-dispersive limit(zo=0)
dispersive limit (zo->∞)
->Continuous line is the exact analytical solution from [12].->Dashed and dotted lines are the numerical solution from APLAC used later in this work.
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Measurements of cross-talk with RPC mockup
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Typical plots where to look at
• Transverse profile of the efficiency, with and w/o valid charge.
• Cross-talk probability. Integral and as a function of the charge in the main strip.
• Resolution when a second hit is present in the module.
• Cluster sizes (not shown here).
• Dependence with HV of the above observables (not shown here).
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50-cm long wide-strip, mirrored and not shielded
... ...
probability of pure cross-talk: 1-3%
similar cross-talk levels than in previous case
experimental conditions:~mips from p-Pb reactions at 3.1 GeV, low rates,
trigger width = 2 cm (< strip width)
BW=260 MHzRin=100 Ω
Zdet~20 Ω
Cm=18 pF/m
Cg=276 pF/m
dispersiveCm/Cg =6.5%
Fct=11.5%
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30-cm long narrow strip, differential
... ...
Cm=20 pF/m
Cdiff=23 pF/m
Fct=9%
experimental conditions:~mips from p-Pb reactions at 3.1 GeV, low rates, high resolution (~0.1 mm) tracking
probability of pure cross-talk:1-3%
intrinsic strip profile is accessible!
Zdiff=80 Ω
dispersive
transverse scan