1. Ultra Cherenkov based SAC
M. Raggi Sapienza Università di Roma
Meeting INFN referee July 2017
Sapienza 10/07/2017

2. PADME Small angle calorimeter
Need to measure photons from ~100 MeV
No need for high light yield material 0.5-2p.e./MeV more than enough
Need to cope with very high rate several ~10 e+ per 100ns
Avoid scintillation mechanism if possible (t too long)
Need a good time resolution ~200 ps
Need very fast photosensors with low transit time spread
Need to be radiation tolerant (oder 1Gy per 1013 e+ on target)
Mauro Raggi - Sapienza Università di Roma

3. PADME SF57 based SAC Inefficiency for electrons at BTF
Very fast Cherenkov signal
Few100MHz rate capability
Low light yield expected
Need ~0.5 p.e./MeV
Very good time resolution ~200ps
Need very fast photosensors with low transit time spread
Inefficiency for electrons at BTF
NA62 (from OPAL) lead glass (Schott SF57)
Mauro Raggi - Sapienza Università di Roma

4. The PMT Hamamatsu R9880U-110 Compact ultra fast High Gain PMT
Diameter 16 mm only 8 mm sensitive area
Only 0.57 ns rise time and 0.2 ns transit time spread
Typical gain 2x106
Mauro Raggi - Sapienza Università di Roma

5. Read out board CAEN V1742 CAEN V1742 Sampling frequency 5Gs/s
12bits for 1V dynamic
1024 samples (200ns)
Mauro Raggi - Sapienza Università di Roma

6. First Small Angle Calorimeter test
R9880U-110
First tests during November calorimeter beam-time
Just one lead-glass bar, 20×20×200 mm3,
Wrapped in Teflon no optical coupling
Hamamatsu R9880U-110, operated at 950V (G~1.5x106)
Readout with CAEN V1742 digitizer set to 5 GS/s
Obtained 0.15 p.e/MeV with 20x20x200mm3 SF57 crystals
Mauro Raggi - Sapienza Università di Roma

7. Improving crystal LY SF57
Can we found a glass with better transparency in the UV region?
SF57 seems to have a bad fall down at ~400 nm
Important gain is expected in the light yield due to better matching with Cherenkov spectrum
Mauro Raggi - Sapienza Università di Roma

8. Lead-fluoride PbF2 vs SF57
Density
7.77
5.51 X0
0.93
1.54
Moliere radius
2.12
2.61
Interaction Length (l)
22.1
20.6
l/X0
23.65
13.3 n
1.8
Higher density, more compact showers, better l/X0 ratio. Better transparency down to ~250 nm
10x more radiation hard wrt SF57
SF57
arXiv: v2
Mauro Raggi - Sapienza Università di Roma

9. Looking for the best PMT
Hamamatsu
PbF2

10. Data for the PMT choice
Transparency and Cherenkov do not match the Y scale just for comparison of wavelength regions involved
Cherenkov
PbF2 transparency
R13478Q
R13478UV
9880U-110
Compute the convolution of
PBf2*R13478UV-10*Cherenkov;
PBf2*R13478Q-10*Cherenkov;
PBf2*R9880U110*Cherenkov;
To select the best solution
Possible PMTs for the SAC
400U= R13478UV-10/-11 = 640 Euro
400S = R13478Q-10/-11   = Euro
9880U ~ 600 Euro

11. Convoluted spectra PBf2*R13478UV-10*Cherenkov;
PBf2*R13478Q-10*Cherenkov;
PBf2*R9880U110*Cherenkov;
Due to the PbF2 transparency there is no difference in between R13478UV R13478Q
Integral R13478UV-10 = A.U.
Integral R13478Q-10 = A.U.
Integral 9880U = A.U.
Diff=2.2%
Diff=30%
9880U-110
R13478UV
R13478Q
We don’t need the more expensive UV PMT we can buy R13478Q-10

12. R13478 Tapered or untapered 9880U110 comparing performance

13. Expected signals with different solutions
Comparing signals obtained from R13478UV tapered and untapered dividers with R9880U
Assuming the following
R13478UV: Npe = 1 p.e./MeV and Singal wdt = 2 ns GTap=3.2E5 and GUnt=5.3E5
R9880U: Npe = 0.1 p.e./MeV and Singal wdt = 1 ns
Using the following formula:
Signal(V) = Qtot/SWDT*Rload = (Npe*Eg*G*Qe)/SWdt*50W
Signal(Q) = Qtot = (Gaus(Npe*Eg,sqrt(Npe*Eg)) *G*Qe)

14. Expected signal R13478UV untapered R9880U R13478UV tapered
Thanks to better gain x8 wrt R13478UV tapered even R9880U has higher signal at nominal gain!
1.43/21 = 6.8%
1.82/10.4 = 17.5%
0.88/13.2 = 6.7%

15. Transparency spectrum comparisons
PbF2 sample 30x30x140 mm3 measured by Atomiki Lab in Debrecem
SF57 sample 20x20x200 mm3 measured by Atomiki Lab in Debrecem
Results in agreement with expectation from literature
SF57 Atomiki measurement
PbF2 Atomiki measurement
PbF2 Literature

16. Comparing different materials
SF57 Atomiki
PbF2 Atomiki
PbF2 Literature
Integral a.u.
Integral a.u.
Integral a.u.
Diff % 0
Diff % wrt to SF57
Diff % wrt to SF57
Convolution=TranspSF57(nm)*QE_UV(nm)*Cherenkov(nm)
Convolution=TranspPbF2(nm)*QE_UV(nm)*Cherenkov(nm)
Convolution=TranspPbF2Lite(nm)*QE_UV(nm)*Cherenkov(nm)

17. The PBf2 Crystals test beam
1 crystals 30x30x140 mm3 obtained on loan from Fermilab G-2 used at LNF test beam.
2x9800U PMT used during the test
Coverage is only 11% of the surface
We will reach 42% with the new PMT
All the crystal is black tapered
Quotation asked to SICCAS for brand new crystals:
30x30x150 mm3 ~ 2000$
3-6 month delivery time
Some issues on transmittance for longer 180mm samples.
30 mm
30 mm
Mauro Raggi - Sapienza Università di Roma

18. Surface coverage Surface coverage of one PMT 9880-U110
30 mm
Surface coverage of one PMT 9880-U110
0.4x0.4 x p = 0.5 cm2 on 3x3=9cm2 just 5.5% coverage
Surface coverage of 2 PMT 9880-U110
0.4x0.4 x p = 0.5 cm2 on 3x3=9cm2 just 11.% coverage
Experiment setup 1inch R13478 hamamatsu PMT
Using 30x30mm2 front face for the PbF2 crystals
2.2x2.2xp = 0.5 cm2 on 3x3 = 9cm2 just 42.% coverage
Roughly a factor 4 improvement in LY expected
30 mm
30 mm
30 mm
Mauro Raggi - Sapienza Università di Roma

19. First look at June test beam data
Structures observed in laser pulses as well maybe a characteristic of this fast PMT
Naïve reconstruction:
QCh[i] = sum samples in the interval [-1.5ns,1.5ns] wrt maximum sample
TCh[i] = position of the signal maximum
Mauro Raggi - Sapienza Università di Roma

20. Different PMT charges Ch[0] Ch[1]
Mauro Raggi - Sapienza Università di Roma

21. Comparing signals Ch[0] Ch[1]
Ch[0] seem to have really smaller signals
Mauro Raggi - Sapienza Università di Roma

22. Charge for >1e- 450 MeV Ch[1] Ch[0]
Difference in charge seems to be related to a gain difference
Tubes where having the same HV setting with no equalization.
Difference in resolution is not that important:
Ch(1)= 3.2/9.9=32%
Ch(0)= 1.39/4.35=32%
Mauro Raggi - Sapienza Università di Roma

23. Charge correlation
Mauro Raggi - Sapienza Università di Roma

24. Preliminary efficiency
Mauro Raggi - Sapienza Università di Roma

25. Preliminary random veto (noise)
Mauro Raggi - Sapienza Università di Roma

26. TCh[0] TCh[1] correlation
Very good time correlation in between the two PMT!
Evidence for out of bunch particles leakage
Mauro Raggi - Sapienza Università di Roma

27. Preliminary time resolution
Just the peak position is used
Expected time resolution per single block <100ps with 5Gs sampling rate!
T0 of V1742 digitizer ~ 50ps in between adjacent channels.
Mauro Raggi - Sapienza Università di Roma

28. Conclusions
Cherenkov radiator coupled with a R9880-U100 PMT can provide extremely fast signal
RMS~600ps have been measured with electrons at BTF
Reasonably high light yield ~0.15 p.e. MeV can be reached
Even higher performance ~1p.e. MeV can be achieved using PbF2
Interesting solution to be explored PbF2
10x higher radiation hardness wrt SF57
4-5x higher light yield
More compact calorimeter (X0 only 0.93 cm)
Two samples of PbF2 received from mu2e are ready to be tested
Cherenkov radiators maybe a suitable technology for PAMDE SAC detector
Mauro Raggi - Sapienza Università di Roma

29. SPARE SLIDES
Mauro Raggi - Sapienza Università di Roma

30. SF57+R9880-U110 Very short signals!
3 peaks in ≈5 ns
Black tape at end
1.5 ns pulse
Black tape
20 ns
Light reflections?
n = , speed of light≈16 cm/ns, 40 cm=2.5 ns
Number of events with multiple peaks reduced by rotating the crystal by ≈ 60° wrt the beam direction
Much better results by placing black tape absorber on the crystal front face.
Technology choice SF57+R9880U-110 seem ok!
Mauro Raggi - Sapienza Università di Roma

31. Long beam pulses 150 ns 150 ns 200 ps 200 ps
Mauro Raggi - Sapienza Università di Roma

32. Automatic peak fitting
Signal wdt = 3.5 samples
Means 3.5*0.2 = 700ps
Very short signals!!
200 ps
Root macro able to identify multiple peaks and measure the position (time)
Can be used to measure the double pulse resolution of the detector.
Integral of fit function to compute charge under development.
Mauro Raggi - Sapienza Università di Roma

33. Multi peak event Two real peak identified and position measured 200 ps
Mauro Raggi - Sapienza Università di Roma

34. Signal amplitude and time
Mauro Raggi - Sapienza Università di Roma

35. Npeaks and TDiff
Minimum Tdiff 2.5ns means that we can distinguish peaks 2.5 ns apart!
Mauro Raggi - Sapienza Università di Roma

36. Run 490 high multiplicity long bunch
200 ps
Run 490 was a long pulse high multiplicity run
Mauro Raggi - Sapienza Università di Roma

37. Amplitude and time Several overlapping particles
Signal up to 140 ns but distribution not very flat.
SAC can be used to monitor beam bunch structure
Mauro Raggi - Sapienza Università di Roma

38. 200 MeV run 494 (one peak charge)
No Black tape
Spectrum fitted with a Landau distribution
MPV = 5.2 pC
Q=5.2 pC= eNpeG ⇒ Npe=Q/(eG)= 5.2E-12/(1.6E-19*1.5E6)~21.6 p.e.
Order 0.1 p.e./MeV of incident energy (200MeV) to be corrected with MC for deposited energy
Mauro Raggi - Sapienza Università di Roma

39. 200 MeV run 495 (one peak charge)
Black tape
Spectrum fitted with a Landau distribution
MPV = 4 pC
Q=4pC= eNpeG ⇒ Npe=Q/(eG)= 4E-12/(1.6E-19*1.5E6)~17.2 p.e.
Order pe/MeV of incident energy (200MeV) to be corrected with MC for deposited energy
Mauro Raggi - Sapienza Università di Roma

40. Energy deposit simulation 200 MeV
Simulated single crystal of SF57
20x20x200 mm3
Incident electrons energy 200MeV
Radius of the beam spot 3mm.
Energy deposit ~ 130 MeV
Fraction of deposit ~65%
Renormalizing LY of the SF57
Run 494 = 0.1/ = 0.154
Run 495 = 0.083/0.65 = 0.127
Mauro Raggi - Sapienza Università di Roma

41. Radiation damage
Radiation damage 60Co: 1) PbF2 after 200Gy of 60Co 2) Lucite after 200Gy of 60Co 3) SF5 after 200Gy of 60Co
PbF2 damage after high dose
No effect up to 100Gy
Serious damage at 1KGy
~1Gy is the expected dose at PADME
arXiv: v2
Mauro Raggi - Sapienza Università di Roma

42. Results obtained with PbF2 G-2
arXiv: v2
Mauro Raggi - Sapienza Università di Roma