1. Studies on Module 0 HAC V. Fascianelli, V. Kozhuharov, M. Martini, T. Spadaro, D. Tagnani

2. Outline Reminder: HAC insertion in NA62: why/how Module 0 HAC tests at BTF@LNF, for: – obtaining order-zero measurement of light yield – assessing possible FEE readout schemes First data/MC comparison studies: – simple digitization/reconstruction algorithms implemented, following FEE scheme assumed 8/27/132Photon veto meeting - Liverpool

3. HAC: why, how From the work by Ruggiero (23/5/2012) and Spasimir (06/02/2013): – need a new detector to reject O(10) residual background events from K->  +  +  - / year – events with  - lost (due to nuclear interaction), and a  + escaping detection through the hole, grazing the pipe, emerging at various depths in the range 247 < z < 255 m – need to efficiently veto  of ~40 GeV, with a detector at z = 253.35 m, while sustaining a muon halo rate of ~4 MHz (dominated by  +   + decays downstream GTK3) – bad energy resolution expected due to lateral leakage – total rate reduced by x10 if E>100 MeV is required – O(<1ns) time resolution to correctly match HAC information with the rest of event 8/27/133Photon veto meeting - Liverpool

4. HAC: why, how A single HAC channel collects light from 6 scintillator tiles (4 mm wide) alternating to 16-mm Pb layers Lights from each scintillator collected by a green-centered 1-mm 2 WLS fibers Tentative detector setup: 9 modules, each with 10 channels along the longitudinal direction 8/27/134Photon veto meeting - Liverpool From F. Hahn

5. RO: order of magnitude cost estimate Consider 90 channels in total SiPM case: 100 E/SiPM, 150 E / amplifier + Voltage bias electronics (evaluation scaling from CHANTI board, 4000 E/32 ch’s): 22500 E Digitizer (GANDALF, 12 bit 500 MS/s): 60000 E for 96 channels Grand total: 82 500 E PMT case: 400 E/PMT, 200 E/HV-ch: 54000 E The GANDALF is a common solution for both setups Grand total is 115 000 E 8/27/135Photon veto meeting - Liverpool

6. HAC studies Order-0 questions: is the scintillator performance still valid and is the light collection enough? Order-1 questions: can it be instrumented with SiPM’s or we have to consider PMT’s? Order-2 question: can it be readout with Flash ADC’s? 8/27/136Photon veto meeting - Liverpool

7. Measurement of HAC response rates Order-0 questions: are the scintillator performance and the light collection still OK? Data taken with SiPM at nominal bias voltage Trigger set at ~30 mV (~7 photoelectrons), rates in dark of ~20 Hz Use a Cs 137, 0.18 MBq, 30.07 years radioactive source Study trigger rates as the source is moved along the longitudinal direction 8/27/137Photon veto meeting - Liverpool

8. Measurement of HAC response rates Order-0 questions: are the scintillator performance and the light collection still OK? Measurement from each position repeated 4 times Expect spacing of 4 + 16 mm, OK 6 peaks spotted, rates span a range of x3... need cosmic-ray characterization, to be done 8/27/138Photon veto meeting - Liverpool no source Counts from channel 3 / 10 s Longitudinal Position (cm)

9. BTF runs Trigger setup with two positive signals from scintillator paddles Electron beam, 50 Hz, O(1) electron multiplicity Readout via Flash ADC, CAEN module V1751, 8 ch’s, 10 bit, 1 GS/s: – from signal shape, evaluate maximal voltages, integrated charge around the maximum, event-by-event pedestal, time of the maximum HAC runs: 570-MeV beam impact head-on onto channel 0 region at the center Expect some lateral leakage due to beam angular dispersion: the HAC is placed ~ 1 m downstream the pipe end 8/27/139Photon veto meeting - Liverpool

10. BTF runs: e- beam multiplicity, Q’s 8/27/1310Photon veto meeting - Liverpool Integrated Charge horizontal paddle (C) Integrated Charge vertical paddle (C) -- 0 electrons -- 1 electron -- 2 electrons -- 3 electrons

11. BTF runs: e- beam multiplicity Poisson distribution fit:  = 0.94(1),  2 = 1.8/1 8/27/1311Photon veto meeting - Liverpool

12. HAC readout Interface 6+1 (for calibration) fiber bundle at module end with 3x3 mm 2 prototypal high-density SiPM, Hamamatsu MPPC 15  m x15  m pixels: – Gain of 2.5 10 5, at 69.3 V bias at room termperature – 57,600 15 x 15  m 2 pixels in 3x3 mm 2 active area – ~ 370 pF capacitance – Gain lower than available SiPM’s by ~x3, but better time resolution expected, since novel corrections due to delay for far pixels are present (TSV, Through Silicon Via, no wire bonding, see http://kicp- workshops.uchicago.edu/ieu2013/depot/talk-ghassemi- ardavan__1.pdf) Voltage supply and amplification during run with electronics tuned for a 70 pF SiPM: time performance not reliable Runs were acquired with a PMT readout, as well 8/27/1312Photon veto meeting - Liverpool

13. HAC response: sampling a signal 8/27/1313Photon veto meeting - Liverpool Signal amplitude [mV] Time [ns] SiPM readout PMT readout

14. HAC response: maximal amplitude 8/27/1314Photon veto meeting - Liverpool Amplitude (mV) -- 0 electrons -- 1 electron -- 2 electrons -- 3 electrons

15. HAC Response: charge 8/27/1315Photon veto meeting - Liverpool -- 1 electron -- 2 electrons -- 3 electrons Integrated charge (C)

16. HAC Response: maximum amplitude 8/27/1316Photon veto meeting - Liverpool  (V)/V  V> [mV] Nominal impact energy (MeV)

17. HAC Response: charge 8/27/1317Photon veto meeting - Liverpool  (Q)/Q  Q> [C] Nominal impact energy (MeV)  (E)/E ~ 35%/Sqrt(E[GeV])

18. SiPM characterization in dark SiPM signals sampled in laboratory at fixed temperature and with no input source FEE electronics adapted from project developed for Mu2e (Martini, Tagnani, Corradi) performing accurate APD preamplification FEE electronics providing x97, while being matched to the SiPM capacitance – The value correspond to optimal matching and lowest noise Bias voltage provided via linear power supply Study of the V-I characteristics 8/27/1318Photon veto meeting - Liverpool Bias voltage (V) Current (  A) V op

19. SiPM characterization in dark Apply a 3 mV threshold, corresponding to < 1 pe (see after) Use oscilloscope as a Flash ADC Sampling frequency, 1 sample every 0.4 ns 8/27/1319Photon veto meeting - Liverpool ~8 ns rise time ~20 ns fall time pedestal evaluation region FADC channel # = T [0.4 ns]

20. SiPM in dark: the analog signal 8/27/1320Photon veto meeting - Liverpool Vbias = 71.4 V Amplitude (10 mV / division) Trigger Time (10 ns / division)

21. SiPM characterization in dark Evaluate maximum of SiPM signals and the related population Fit the first 3 peaks, corresponding to n, n+1, n+2 photoelectrons Perform a single fit allowing the peak-to-peak distance as free parameter 8/27/1321Photon veto meeting - Liverpool Repeat the above steps in a wide range of voltage bias: 69.3 V (nominal + 0.3V)  71.8 V

22. SiPM characterization in dark Change of the single-photoelectron voltage with the bias, as expected Single photoelectron ranges from 4.5 mV to 8.5 mV as Vbias varies from 69.3 to 71.8 V 8/27/1322Photon veto meeting - Liverpool peak to peak distance (V) bias voltage (V)

23. SiPM characterization in dark Change of the single-photoelectron voltage with the bias, as expected Single photoelectron ranges from 4.5 mV to 8.5 mV as Vbias varies from 69.3 to 71.8 V Result confirmed by the position of the first peak 8/27/1323Photon veto meeting - Liverpool position of first peak (V) bias voltage (V)

24. SiPM characterization in dark Change of the poissonian probability, ranging from ~0.2 to ~0.6 as the bias voltage varies Probably an effect linked to PDE variation 8/27/1324Photon veto meeting - Liverpool bias voltage (V)

25. SiPM characterization in dark Evaluate charge of SiPM signals and the related population Fit the first 3 peaks, corresponding to n, n+1, n+2 photoelectrons Perform a single fit allowing the peak-to-peak distance as free parameter Repeat the above steps in the bias range: 69.3 V (nominal + 0.3V)  71.8 V 8/27/1325Photon veto meeting - Liverpool Charge (pC)

26. SiPM characterization in dark Gain evaulation within the expectation: 10 5  2 10 5, after correcting for the FEE amplification of 100 (actually 97) Position of 1st peak confirms that the distribution is due to 1, 2, 3 photoelectrons 8/27/1326Photon veto meeting - Liverpool bias voltage (V) Gain = 10 5 Gain = 1.8 10 5

27. MC HAC Digitization Complement the MC made by Spasimir with digitization and reconstruction The following assumptions are used: – Scintillator produces 10 4 photons / MeV – 10 -3 of the produced photons reach the SiPM – SiPM PDE = 0.6 – The SiPM Gain is 10 6 (it will be changed in future) – With a FEE electronics amplification of 10, a single photo-electron produces a 4-mV peak with a 8 ns rise time and a 20 ns fall time 8/27/1327Photon veto meeting - Liverpool

28. HAC MC: energy release 8/27/1328Photon veto meeting - Liverpool  (E)/E  E> [MeV] Electron energy (MeV) electrons head-on impact

29. HAC MC: electrons MC reconstructed 8/27/1329Photon veto meeting - Liverpool  (V)/V  V> [mV] Electron energy (MeV) electrons head-on impact

30. HAC Data/MC comparison: electrons data 8/27/1330Photon veto meeting - Liverpool -- Data -- MC reco -- MC truth Fractional resolution Electron energy

31. Conclusions 8/27/1331Photon veto meeting - Liverpool Experience with HAC basically shows a working detector: Satisfactory operation with electron beam at Frascati BTF SiPM characterization in dark in agreement with Hamamatsu specifications Benefiting of previous work by Spasimir on MC, a simple procedure for digitization/reconstruction added (at the moment the code is kept private) Good linearity of energy response observed Agreement between data and MC after digitization has to be proved with cosmic rays: data with 2-3 electrons probably affected by lateral leakage SiPM operation + Flash ADC readout satisfactory To-do list: improved description of MC digitization (pileup of scintillator signals) Complete development of the low-noise voltage regulator cosmic ray tests and additional acquisitions with radioactive source test of final electronics (at the moment, in production) Channel by channel intercalibration studies Final design of readout on-board electronics and mechanical interface