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Ultra fast SF57 based SAC

This meeting at Sapienza Università di Roma discussed the need for a fast and radiation-tolerant small angle calorimeter to measure photons from ~100 MeV. The use of SF57 as the material for the calorimeter, along with the Hamamatsu R9880U-110 PMT and CAEN V1742 readout board, was explored. Preliminary tests showed promising results for signal detection and measurement.

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Ultra fast SF57 based SAC

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  1. Ultra fast SF57 based SAC M. Raggi Sapienza Università di Roma Meeting INFN referee March 2017 LNF 17/3/2017

  2. PADME Small angle calorimeter • Need to measure photons from ~100 MeV • No need for high light yield material 0.1-2p.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 basedSAC • 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 Mauro Raggi - Sapienza Università di Roma

  7. 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 = 1.8467, 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

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

  9. 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

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

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

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

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

  14. 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

  15. 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

  16. 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 0.083 pe/MeV of incident energy (200MeV) to be corrected with MC for deposited energy Mauro Raggi - Sapienza Università di Roma

  17. 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 = 0.1/0.65 = 0.154 • Run 495 = 0.083/0.65 = 0.127 Mauro Raggi - Sapienza Università di Roma

  18. 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

  19. Lead-fluoride PbF2 vs SF57 Higher density, more compact showers, better l/X0 ratio.Better transparency down to ~250 nm 10x more radiation hard wrt SF57 SF57 arXiv:1412.5525v2 Mauro Raggi - Sapienza Università di Roma

  20. Radiation damage • Radiation damage 60Co:1) PbF2 after 200Gy of 60Co2) Lucite after 200Gy of 60Co3) 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:1412.5525v2 Mauro Raggi - Sapienza Università di Roma

  21. Results obtained with PbF2 G-2 arXiv:1412.5525v2 Mauro Raggi - Sapienza Università di Roma

  22. Improving current setup 20mm • Surface coverage of the PMT 9880-U110 too small • 0.4x0.4xp = 0.5 cm2 on 2x2 = 4cm2 just 12.5% coverage • No optical coupling crystal-PMT • Deep air gap due to borders in the PMT. • Can use silicon glue to get better optical coupling • PMT gain ~1.5x106 can be raised up to ~3x106 • 1inch R13478 hamamatsu PMT • Using 30x30mm2 front face for the crystals • 2.2x2.2xp = 0.5 cm2 on 3x3 = 9cm2just 42.% coverage 20mm 30 mm 30 mm Mauro Raggi - Sapienza Università di Roma

  23. Looking for the best PMT Hamamatsu PbF2

  24. Data for the PMT choice Transparency and Cherenkov do not match the Y scale just for comparison of wavelength regions involved Compute the convolution of PBf2*R13478UV-10*Cherenkov; PBf2*R13478Q-10*Cherenkov; PBf2*R9880U110*Cherenkov; To select the best solution 9880U-110 R13478Q R13478UV PbF2 transparency Cherenkov Possible PMTs for the SAC 400U= R13478UV-10/-11 = 640 Euro 400S = R13478Q-10/-11   = 1.024 Euro 9880U-110 ~ 600 Euro

  25. 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 = 289356 A.U. Integral R13478Q-10 = 282977 A.U. Integral 9880U110 = 408280 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

  26. R13478 Tapered or untapered 9880U110 comparing performance 9880U110

  27. 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 Singalwdt = 2 ns GTap=3.2E5 and GUnt=5.3E5 • R9880U: Npe = 0.1 p.e./MeV and Singalwdt = 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)

  28. Expected signal R13478UVtapered R13478UVuntapered R13478UVuntapered R9880U R9880U R13478UVtapered 1.43/21 = 6.8% Thanks to better gain x8 wrtR13478UV taperedeven R9880Uhas higher signal at nominal gain! 1.82/10.4 = 17.5% 0.88/13.2 = 6.7%

  29. The PBf2 Crystals • 2 crystals 30x30x150 mm3 obtained on loan from Fermilab G-2 currently at LNF ready for April test beam. • PMT for the test 9800U • Quotation asked to SICCAS for brand new crystals: • 30x30x150 mm3 ~ 2000$ • 3-6 month delivery time Mauro Raggi - Sapienza Università di Roma

  30. 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

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