MC Digi for Large Angle Vetoes

V. Palladino, T. Spadaro

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

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

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)

Large Angle Veto WG meeting – Mainz – 6/9/2011 5

MC

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)

Large Angle Veto WG meeting – Mainz – 6/9/2011 6

MC

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

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)

Large Angle Veto WG meeting – Mainz – 6/9/2011 8

MC, Vthr = 9 mV

MC, Vthr = 11 mV

Uncertainty on nominal threshold, ~ 2mVSizeable variation: dToT/dVthr ~ 3ns/mV, for low charges

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)

Large Angle Veto WG meeting – Mainz – 6/9/2011 9

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

Direct measurement of CPMTEquivalent circuit for the direct measurement of CPMT

Large Angle Veto WG meeting – Mainz – 6/9/2011 10

= 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

Direct measurement of CPMT

Large Angle Veto WG meeting – Mainz – 6/9/2011 11

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

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)

Large Angle Veto WG meeting – Mainz – 6/9/2011 12

MC

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)

Large Angle Veto WG meeting – Mainz – 6/9/2011 13

MC

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

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)

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

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

Large Angle Veto WG meeting – Mainz – 6/9/2011 21

Thanks to Paolo Valente for the animated gif preparation

dT (trailing) (ns)

Vmin

Time correlation measurements

Not exactly true... effect of overdrive-dependent delay at the comparator must be subtracted for dT to be independent on Vmax

Large Angle Veto WG meeting – Mainz – 6/9/2011 22Reminder: for old (new) voltage at comparator is amplified x5 (x3) wrt original signal

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)

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

Large Angle Veto WG meeting – Mainz – 6/9/2011 24

Correlation factor for trailing times

Vth (V)

Compare with efficiency profile

Evaluation compared with that from efficiency profile

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e

Vmin

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

Large Angle Veto WG meeting – Mainz – 6/9/2011 S1

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

Large Angle Veto WG meeting – Mainz – 6/9/2011 S2

|F(ω)|

ω (MHz)

Attenuation* cable data sheet, typical values for 30 m length

x x + dx

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

Large Angle Veto WG meeting – Mainz – 6/9/2011 S3

|F(ω)|, MIP signal Fourier transform

ω (MHz)