mc digi for large angle vetoes
DESCRIPTION
MC Digi for Large Angle Vetoes. V. Palladino , T. Spadaro. MC Digi for Large Angle Vetoes. D etailed PMT simulation needed to assess efficiency @ low-energy Include and correctly treat: Gain fluctuations Optical g ’s path fluctuations Signal generation Time over threshold FEE. - PowerPoint PPT PresentationTRANSCRIPT
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MC Digi for Large Angle Vetoes
V. Palladino, T. Spadaro
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MC Digi for Large Angle Vetoes
8.0
6.4
1.6
3.2
4.8
Signal (mV)
1
2
3
4
Time (ns)
N photo electrons
Detailed PMT simulation needed to assess efficiency @ low-energyInclude and correctly treat:• Gain fluctuations• Optical g’s path fluctuations• Signal generation• Time over threshold FEEMC input parameters:• Gain at operation point
G = 1.1 ×106
• 1st dynode collection eff.e1 = 0.85
• Intra-dynode collection eff.
ed = 0.98• 1st dynode time fluctuations dT1 = 0.5 ns• Intra-dynode time fluctuations
dTd = 0.8 ns Large Angle Veto WG meeting – Mainz – 6/9/2011 2
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MC Digi: Data/MC agreement
Data/MC agreement comparing MIP muons and using test beam data
Further tests in progress
DataMC
Integrated charge (pC)
Evts
/0.5
pC
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MC Digi: effect of cable
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Cable effect correctly reproduced in standalone simulationWhether or not it has to be inserted in official code is under scrutiny
MIP signal
Reminder, total cable length:small LAV’s: 6.15 m, 7.15 m, intermediate LAV’s: 8.5 m, big LAV’s: >~10 m
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Data
Time over threshold (ns)
MC Digi: Data/MC agreement
Data/MC comparing test beam data to MIP muons, varying (nominal) threshold for dataFor MC use: 290 pF PMT capacitance, 10 mV threshold, 3 mV hysteresis
Inte
grat
ed c
harg
e (p
C)
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MC
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Data
Time over threshold (ns)
MC Digi: Data/MC agreement
For MC use: 290 pF PMT capacitance, 10 mV threshold, 3 mV hysteresisData/MC agreement: looking in detail, not really satisfying
Inte
grat
ed c
harg
e (p
C)
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MC
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MC default, CPMT = 250 pF, Vthr = 10 mV, Vhyst = 3 mV
ToT (ns)
Characterization of ToT curve: CPMTFor MC, study dependence of Q(ToT) on PMT capacitance
Inte
grat
ed c
harg
e (p
C)
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MC, CPMT = 300 pF
MC, CPMT = 200 pF
Below ~ 8pC, leading time contribution significantFor large signals, trailing time contribution dominates
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MC default, CPMT = 250 pF, Vthr = 10 mV, Vhyst = 3 mV
ToT (ns)
Characterization of ToT curve: VthrFor MC, study dependence of Q(ToT) on FEE threshold voltage
Inte
grat
ed c
harg
e (p
C)
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MC, Vthr = 9 mV
MC, Vthr = 11 mV
Uncertainty on nominal threshold, ~ 2mVSizeable variation: dToT/dVthr ~ 3ns/mV, for low charges
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MC default, CPMT = 250 pF, Vthr = 10 mV, Vhyst = 3 mV
ToT (ns)
Characterization of ToT curve: VhystFor MC, study dependence of Q(ToT) on FEE hysteresis voltage
Inte
grat
ed c
harg
e (p
C)
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MC, Vhyst = 4 mV
MC, Vhyst = 2 mV
Hysteresis uncertainty ~ several % (to be confirmed)Acting on trailing time only: dToT/dVhyst ~ 1 ns/mV for low Q
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Direct measurement of CPMTEquivalent circuit for the direct measurement of CPMT
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= 33Ω Transmission line
Rx
33 Ohm resistor introduced to correct for parasitic inductance (ringing)
Measure signal V(t) for Rx = 50, 100, 200ΩFit the time constant t = CPMT (R + Rx)
V(t)PMT
PMT Divider
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Direct measurement of CPMT
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Rx (Ω) Time constant t (ns)
CPMT (pF)
50 12.6(2) 152(2)100 20.4(3) 153(2)200 36.62(5) 157(2)
V(t) (mV/0.4 ns)
time(s)
Fit with p0 e-t/t
Rx = 50 Ohm
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Data
Time over threshold (ns)
Data/MC agreement: old...For MC use: 157 pF PMT capacitance, take into account the 33 Ohm resistor, 9.5 mV threshold, 2 mV hysteresisData/MC agreement: from the old situation....
Inte
grat
ed c
harg
e (p
C)
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MC
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Data
Time over threshold (ns)
... and presentFor MC use: 157 pF PMT capacitance, take into account the 33 Ohm resistor, 9.5 mV threshold, 2 mV hysteresisData/MC agreement: now much more satisfying
Inte
grat
ed c
harg
e (p
C)
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MC
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A first to-do listToT vs Q curve well reproduced for MIP’s
PMT capacitance value confirmed by direct measurement
Quantitative check satisfactoryCaveats:
agreement for extremely low values of ToT to be studied
Uncertainty on hysteresis to be determined
Cable modifications treated: relevant for biggest LAV’sinserted into digitization code
To-do list:check with electron datastudy of global LAV responsenew data acquisition campaign for better
assessment of data/MC agreement to be tested with known threshold and hysteresis values
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Precise threshold measurement
Precisely assess threshold and hysteresis, mandatory for Q vs T reliabilitySub-mV total uncertainty needed
Tried with a standard approach, such as efficiency profile: measure efficiency as a function of minimum signal voltage
Above approach would need clean environment: in presence of a 2-3 mV radiofrequency noise, width of efficiency profile depends on noise
Try to overcome this, by measuring crossing times
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Accurate mmt of threshold
The idea is to register a signal copy and the LVDS output with a flash ADC
The LVDS transition time, TL, can be correlated with the time TS(Vth) expected from signal, assuming a trial value Vth for the threshold
As Vth varies, the correct threshold value is found as the one for which the time difference TL-TS is independent of the signal amplitude
For this to work, the signal time characteristics have to be preserved as much as possible
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Setup for threshold mmtInput to PMT from Hamamatsu C10196, ultrashort light pulser, 70 ps FWHM
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Setup for threshold mmtUse LeCroy WaveSurfer 44Xs as 2.5 GS/s, 8-bit flash ADC
Signal from DC 50 Ohm For the moment, an improper treatment of LVDS
output: one polarity to signal, the other grounded via 100 Ohm resistor
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LVDS in
Home made
LVDS to LEMO
Sign
al in
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Problems for LVDS signalDue to this treatment, LVDS rise and fall times significantly worsened
time over threshold possibly affected: 10-90% time to 1-1.5 ns
but rise and fall time correlations expected to be maintained
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LVDS signal (V)
Time (ns)
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Time correlation measurements
Leading time correlations as a function of trial threshold valuesFor the true value of the threshold, dT should be independent from Vmin
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Thanks to Paolo Valente for the animated gif preparation
dT (leading) (ns)
Vmin
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Time correlation measurements
Rise time correlations as a function of trial threshold valuesFor the true value of the threshold, dT should be independent from Vmin
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Thanks to Paolo Valente for the animated gif preparation
dT (trailing) (ns)
Vmin
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Time correlation measurements
Not exactly true... effect of overdrive-dependent delay at the comparator must be subtracted for dT to be independent on Vmax
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Correlation factorCorrelation factor well suited to evaluate “best” threshold valueFor leading time, method sensitivity is on the order of 0.2-mVVle ~ -28.3 mV
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Correlation factor for leading times
Vth (V)
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Identification of optimal threshold:Correlation factor well suited to evaluate “best” threshold valueFor trailing time, method sensitivity is on the order of 0.1-mV Vth(trailing) ~ -30.7
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Correlation factor for trailing times
Vth (V)
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Compare with efficiency profile
Evaluation compared with that from efficiency profile
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e
Vmin
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Proposal for threshold validation
Work shown able to clarify important points, but for en-mass mmts:
To proceed in a reasonable time, need more channels
TDC treatment of LVDS must be taken into account
One may think:use a 32-channel, 5-GS/s, 8-bit flash-ADC with 1
Vpp at maxInclude in acquisition together with TDC
Above approach would work for old FEE boards, in which each channel has an independent analog copy in output
For new FEE’s, analog output are given for 4-fold and 16-fold sums only
Proposed solution:pulse individual channels in a round-robin fashioncan acquire with few channels of flash-ADCmight exploit 4-ch, 12-bit, 2-GS/s V1729 digitizer,
presently available
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Logical scheme for fast simulation
Particle generation and decay
Interactions in LAV volumeEnergy release, Cerenkov
Transport to the PMT
Photocathode emissionDynode amplificationSignal generationTransmission lineFEE: Threshold
discrimination
Optical g’s: number, direction of emission, position
Mimmo’s transport matrix
G4
Leading and trailing times
This work
Number, energy of optical photons at PMT cathode
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MC Digi: effect of cableCable induces RLC(G) filter
C ~ 100 pF/m, L ~ 2.4 10-7 H/mSilver copper steel, R ~ 86Ω/km
G varies withω, it is negligible for ω< 150 MHz, where signal lies
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|F(ω)|
ω (MHz)
Attenuation* cable data sheet, typical values for 30 m length
x x + dx
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MC Digi: effect of cableCable induces RLC(G) filter
C ~ 100 pF/m, L ~ 2.4 10-7 H/mSilver copper steel, R ~ 0.086Ω/m
G varies withω, it is negligible for ω< 150 MHz, where signal lies
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|F(ω)|, MIP signal Fourier transform
ω (MHz)