Test for the CLAS12 RICH detector L. Barion, M. Contalbrigo, L.
Pappalardo (INFN Ferrara) V. Lucherini, M. Mirazita, P. Rossi (INFN
Frascati) M. Turisini (INFN Sanita) Aldo Orlandi, Angelo Viticchie
(INFN Frascati) for the preparation of the test set-ups CLAS
Collaboration meeting, October 12-15, 2011 Marco Mirazita Slide 2
Goals of the tests 1.Test MAPMT as single photon detectors H8500C
(normal glass) and H8500C-03 (UV glass) vs R8900 2.Validate Monte
Carlo simulations with a small scale RICH prototype - Laboratory
set-up using laser blue light - Hadron (pion) beam test of RICH
prototype Slide 3 MAPMT characterization as single photon detectors
1) Single photon response - distance between peak and pedestal -
peak width - threshold cut 2) Few photon response - distance
between peaks - width of the peaks 3) Behaviour with HV - lowest HV
for a given 1pe efficiency (80%? 90%?) 4) Uniformity of the PMT
response - comparison between border and central pixels 5) Cross
talk between pixels 6) Comparison between PMTs LASER BEAM LASER
BEAM Slide 4 Laser tests Slide 5 Test laser setup LASER PC trigger
IN trigger OUT fiber collimator filters MAPTM anode OUT 0 63 QDC
gate black box Laser intensity can be adjusted via the remote
control and using neutral density filters The fiber head can be
remotely moved in (x,y) to scan the PMT surface Conventional
electronics for data acquisition (CAEN V792) DAQ rate fixed at 100
Hz Slide 6 short flat cables laser controller motor controller
electronics Slide 7 fiber head + collimator + filters MAPMT H8500C
Slide 8 anode connections dynode output ground connections Slide 9
Noise measurement HV=-1125V on but PMT covered by its cap QDC 0 QDC
15 PMT H8500C Slide 10 Analysis of ADC spectra Poisson weights for
0,1,2,... p.e. pedestal = average number of p.e. N = max number of
p.e. photoelectron peaks Several shapes tried, gaussians provide
better results in terms of convergence of the fits and uniformity
of the parameters Slide 11 ADC spectrum HV = 1000 V pixel 25
(border) pixel 36 (centre) Fits with up to 5 p.e. peaks Slide 12
PMT response normalization constantaverage number of p.e. 1. p.e
gain (QDC channels) fraction of 1 p.e. loss PMT H8500C HV = 1000 V
Slide 13 Results for 10 MAPMTs HV = 1000 V points: mean of 64 pins
error bar: RMS of the 64 pins gain from data sheets (a.u.) Slide 14
ADC spectrum vs HV HV = 1000 V HV = 1040 V HV = 1075 V pixel 25
(border) pixel 36 (center) better pedestal/signal separation easier
threshold setting Slide 15 HV scan Up to a factor 2 increase in the
gain More than 85% detection efficiency for HV>1040 V
Recommended working range HV=900-1100 V Slide 16 Measurement in
magnetic field Compensating sextupolar magnet No field at the
center Up 50 gauss going toward the border Perpendicular to the
electron motion in the MAPMT HV=1040 V larger field smaller field
Slide 17 Magnetic field test Less than 15% gain loss Small decrease
in detection efficiency No major degrading in the MAPMT response HV
= 1040 V B=0 B>0 B=0 B>0 Slide 18 Cross-talk analysis Compare
the pixel response when - it is directly illuminated by the laser -
adjacent pixels are illuminated Threshold: 3 above pedestal Slide
19 Cross-talk contamination N = events above threshold i =
up,down,left,right = 2.1% = 2.0% = 2.1% = 2.6% For a given pixel:
Slide 20 Hadron beam test CERN, july 7-20, 2011 Slide 21 Slide 22
T9 Slide 23 The T9 hadron beam Magnet polarity set for negative
particles 400 ms 40 s Time structure of the beam: 3 short pulses
every 40 s duty cycle ~3% Transverse dimensions: few cm at the
entrance window of the hall focused after ~7.5m (close to our
setup) Hadron intensity particles per pulse N( ) ~ 60 N(K) Slide 24
The Experimental Hall Beam CLAS12 RICH GSI Glasgow Slide 25 The
Setup Beam Backward Scintillator 2x3 cm2 Two Forward Scintillators
~1x1 cm2 coinc. aerogel PMT Trigger of the DAQ: T beam *SC back *SC
forwH *SC forwV Two Reference Scintillators ~2x3 cm2 black box 60
cm Slide 26 The RICH prototype Slide 27 The PMT array 10 H85008
R8900 H8500-C H8500-C-03 H8500-C H8500-C-03 H8500-C H8500-C-03
H8500-C H8500-C-03 H8500-C H8500-C-03 Slide 28 The acquisition
electronics Maroc2 front end electronics 1 control board with 2
back planes up to 8 front end cards per back plane 64 channels per
card, 4096 total channels preamplifier, adjustable from 1/8 to 4
ADC, about 80fC per channel control board back planes MAROC front
end cards Visual C++ program to read the electronics (windows)
Event transfer to disk in single or multi event mode Slide 29
Preliminary test of the DAQ 2 reference scintillators for counting
normalization trigger rate measured with a scaler event rate
measured with DAQ system DAQ eff. = event rate / trigger rate 1.
scan of trigger rate by moving the box in or out of the beam 2.
take into account ~3% beam duty cycle black: single event buffering
red: multi-event buffering DAQ efficiency DAQ rate before (empty
symbols) and after (full symbols) duty-cycle correction DAQ rate
DAQ rate in one spill ~200Hz Slide 30 Run conditions Most of the 2
weeks of data taking to deal with the electronics - timing between
MAPMT signals and trigger - find stable conditions of low voltage
supply - optimization of preamp gain No stable conditions were
found with 12 MAPMT only 1 back plane was used 8 MAPMT H8500
(HV=1075 V) few preliminary data with R8900 (HV=970 V) preamp gain
= 4 E beam (GeV) Aerogel (cm) cm N. of triggers t (cm)n
1011.0535.111.2169k 102=1+11.0534.611.197k
103=1+1+11.0534.110.9100k 103=1+1+11.0348.812.090k
411.0349.812.241k Slide 31 ADC distributions R8900 gain = 0.5
PRELIMINARY RUN Slide 32 ADC distributions H8500 gain = 0.5
PRELIMINARY RUN Slide 33 ADC distributions H8500 gain = 4 FINAL
CONDITIONS Slide 34 ADC distributions threshold to remove pedestal
2.5% of the pedestal height = 0.05 Fit of the distribution
additional exponential background Slide 35 Hit distributions
aerogel n=1.05 aerogel n=1.03 1cm2cm 1cm 3cm integrated
distributions of hits above threshold Slide 36 Cerenkov ring
calculation Minimization of: Free parameters are the center
coordinates (X C,Y C ) and the radius R The problem can be solved
analitically Procedure : 1.Calculate center and radius with all
hits above threshold 2.If the distance of a hit from the ring is
bigger than 2 pixels (12mm) it is removed and a new calculation is
done 3.The iteration is stopped if no more hits have to be removed
or if N hits Conclusions and outlook Laser tests of MAPMTs has been
(are being) performed in Frascati measurements at 1000 V in
agreement with data sheets, but too low HV for reliable single
photon detection increasing HV (>~1040 V) sufficiently good
single photon detection efficiency can be obtained no large effect
from small magnetic field (preliminary) We had successful test at
CERN we saw pion Cerenkov rings close to what we expected there
things that need to be analyzed more in detail electronics is a
crucial point H8500 could be good single photon detectors Slide 48
Next RICH prototype Larger gap lenght ~ 1 m About 20 MAPMT to
accomodate in the prototype Radial geometry CLAS sector geometry
Slide 49 backup slides Slide 50 Pedestal measurements: stability
RMS (QDC channels) Run number QDC 0 QDC 63 0 2 Very low noise, high
stability over a week of measurements PMT H8500C Slide 51 ADC
fitting functions GAUSS SKEWED GAUSS peak distance Slide 52 Radius
resolution Larger thickness means: - larger uncertainty on the
emission point R/R = t/d 3 9 % -larger number of hits ~5.5 t=1 cm
~8.7t=3 cm / -30 % - more surfaces to cross ? - other effects? t=2
cm black: N 5 red: N H8500 border/center PMT Number of hits per
ring Number of pixels:N(center) = 40 N(border) = 24 R=1.7 Number of
hits:R>2 t=2 cm
