New CHOD tests with SiPM readout in Napoli

F.Ambrosino, G. Anzivino, P. Cenci, V. Duk, P. Massarotti, M. Mirra, M. Napolitano, M. Piccini

Goals of the test

• Joint effort from Napoli and Perugia people to test the Mainz prototype with a SiPM readout and CHANTI electronics to power SiPMs and amplify signals

• Assess feasibility, compare (if possible) with Mainz results, thus– Use Mainz prototype– Use Mainz trigger system (but w/o CFD…)

[many thanks to R. Wanke !]

• Tests in Napoli: climatic chamber, experience with SiPM, availability of CHANTI electronics

Test setup• Trigger system: 2 x scintillator pads w PMT readout. No CFD,

discriminated signals in AND• 12 +12 fibers detector from Mainz (w BCF-92 1.2 mm round

fibers) actually 11+11 …• SiPM Hamamatsu 50 mm cell, 6 x 6 mm2 w low (1.6 MHz)

darkrate (≲ 150 euro each for low quantity order) • Dedicated fibers –SiPM coupling designed and realized in Napoli

(L. Roscilli)• Tests in climatic chamber• Readout w 2GHz bandwidth scope 5 Gs/s

– Can emulate, in software both CFD and ToT– Charge determination to assess Npe– Full signal shape to study rise and fall times

Mainz prototype (out of the box)

Fibers-SiPM coupling system

Prototype assembled

Response and efficiency

Q1(pC)

Q2(

pC)

• SiPM characterized to find 1pe charge ≈4 pC– Difficult to estimate precisely due to RF noise

problems . Uncertainty at 10-20% level.• Signals integrated to obtain typical response

All events

Response and efficiency

Q1(pC)

Q2(

pC)

• SiPM characterized to find 1pe charge ≈4 pC– Difficult to estimate precisely due to RF noise

problems . Uncertainty at 10-20% level.• Signals integrated to obtain typical response

Peak around 100 pC i.e.

>20 pe

Peak region

Response and efficiency

Q1(pC)

Q2(

pC)

• SiPM characterized to find 1pe charge ≈4 pC– Difficult to estimate precisely due to RF noise

problems . Uncertainty at 10-20% level.• Signals integrated to obtain typical response

10% fake triggers due

to acceptance mismatch

Single «view» truly inefficient

events ≲ 1%

Lowresponse region

Acceptance issues

• Dedicated study to better understand trigger problems

• Analog signals from trigger collected• Clear evidence for anticorrelated signals: inclined

tracks touching marginally one of the palettes due to small misalignment (and/or signals generated into the light guide) these will not hit the detector

• Need to re-run with higher trigger thresholds and better mechanics to avoid this

[N.B. waiting for Physics Department to re-open after summer closing! Data was taken August 2-3 and analysed during following days…]

Time studies

• Correct time walk using «software» CFD on each collected waveform.

T vs Q raw

Time studies

• Correct time walk using «software» CFD on each collected waveform.

T vs Q software CFD

Apparent «early» signal tails due to (late) small trigger signals:

remember, no CFD for trigger!

Time resolution (1)

Single view resolutions• Include trigger jitter• «software» CFD• «Early» tails visible

s=1.02 (1) ns

s=1.03(1) ns

Time resolution (2)Time difference among two views• Trigger jitter cancels out• Compares driectly to Mainz

PMT result (s=1.19 ns)s=1.059 (9) ns

s=0.845(8) ns

Time average of two views• Includes trigger jitter• «Early» tail is correlated in

both views (and thus is present in the average) because is a (common) trigger walk effect

Time resolution (preliminary)

– Trigger «core» resolution about 700 ps (checked independently)– Single view intrinsic resolution about 750 ps– Two views time average resolution about 530 ps– Slightly better than PMT result (but missing real CFD

electronics fluctuations)– Handles to improve further:

• Thicker scintillator (the one used is 15 mm thick)• Better noise shielding (signals are amplified 25X…)• Better fiber-SiPM coupling (the one used is still preliminary)• Better reflective wrapping of the detector

The full picture is consistent with:

Efficiency at high rates

Eff2(Dt)/ <acceptance>

Dt(ns)

SiPM signals have a typical «core» with FWHM of O(20-30) ns and a long (>120 ns) tail-> possible issue at high rates!

However device efficiency is almost restored before the tail of the signal is over->see CHANTI presentation for details

Here we show only one plot obtained with the CHANTI at the BTF: evidence of e≈97% to detect a second particle hitting the detector between 30 and 80 ns after a first one is obtained. Assuming 100% inefficiency for first 30 ns and 97% efficiency for remaining 120 ns one gets 2% average dead time for a 550kHz rate in a single tile, the long tail contributing for only 10% to the overall dead time.

Conclusions

• Preliminary tests of Mainz prototype with Hamamatsu SiPM readout compare well with the PMT results showing SiPMs to be a viable solution for the new CHOD readout

• Preliminary results with CHANTI@BTF show that the long tail of the SiPM signal seems not an issue at the maximum rates foreseen for new CHOD. (but beware! the SiPM is not the same…)