An option for the SHiP Muon Detector: Scintillator bars with WLS fibers and SiPMs readout

Transcription

1 An option for the SHiP Muon Detector: Scintillator bars with WLS fibers and SiPMs readout M. Anelli, W. Baldini, P. Ciambrone, M. Dallavalle, F. Fabbri, G. Lanfranchi, A. Montanari INFN-LNF, INFN-Ferrara, INFN-Bologna First SHiP Workshop, Zurich, June th, 2014

2 Requirements: Goal: identify muons with high efficiency and reject hadrons/electrons from the decays of weakly interacting long-lived particles (mostly N 2,3 π µ for masses GeV, but also sgoldstinos ππ, µµ, LSP µµν, dark photons ee, µµ etc.) Inputs for the design: 1) momentum spectrum: low p-spectrum (p~10-20 GeV/c); large multiple scattering (moderate readout granularity: 5x5 cm 2 or 10x10 cm 2 ) 2) transverse dimensions, number of stations; 5x5 m 2, 2 (or more) stations per module 3) expected rates: driven by emulsions, ~ 0.4 Hz/cm 2, ~ 100 khz per station 4) High efficiency: >95% per station 5) Good time resolution (to be studied) help in rejecting combinatorial background from halo muons 6) Low cost, high performance, robust and simple construction, maintainance and operation of the detector 2

3 Muon detector: layout & granularity Active layers interleaved with muon filters, different possible configurations: A) M1 M2 B) M1 M2 ECAL δ 1 Muon Filter δ 3 ECAL Muon Filter δ 3 δ 3 C) ECAL filters M1 δ 2 M2 δ 3 Layout driven by sampling frequency Granularity δ driven by multiple scattering in material before the active layers: ECAL Shashlik Pb-scintillator: 22.5 X 0, 0.8 λ I, 40 cm thick δ 1 ~ 5 cm for p~20 GeV Muon filter 1 m of Fe: δ 3 ~ 10 cm for p ~ 20 GeV Active layers 3

4 Active layers: Scintillators bars with WLS fibers and SiPM readout Extruded scintillators produced (for example) at FNAL-NICADD facility extruded polystyrene core doped with blue-emitting fluorescent compounds and a co-extruded TiO2 coating (0.25 mm thick) for reflectivity. Scintillator bars of different shapes and dimensions are produced with embedded holes or surface grooves to host the WLS fibers. SiPM directly coupled to one or more fibers. FNAL NICADD facility Examples of experiments using this technology: MINOS (rectangular strips), MINERvA and NA62 (triangular strips); Muon system (IFR) of Super B 4

5 A possible layout for the SHiP Muon System: Rectangular scintillator bars with WLS fibers and SiPM readout SiPM A) Single sided- readout B ) Double sided- readout 5 m 5 m 5 m SiPM 5

6 Intense R&D program at Ferrara and Bologna for the first prototype of the Super B Muon system (IFR) Prototype Iro n Active Layers (Pizza Boxes) Iron: 60x60x92 cm 3, 9 slots for the active layers up to 9 active layers readout together 4 special modules to study different fibers or SiPM geometry Ac#ve Layer ( pizza box ) 6 6

7 Layout of a scintillating bar Active layers prepared in Ferrara 7

8 1. Prepare the supports and position the scintillators 2. fibers positioning 3. Putting silicone Sealant to fix fibers and keep optical glue inside the embedded holes 8

9 4. Labelling and collecting the fibers around the supports 6. Fill the machined grooves with optical grease and cover it with stripes of reflecting aluminum 5. Fill with optical glue the embedded holes Detailed view of the WLS fibers and the PCB hosting the SiPM 9

10 WLS fibers and SiPM characterization WLS fibers: Multi-clad WLS fibers from Saint Gobain (BCF92) or Kuraray (Y11-300): both have good attenuation length (λ ~ 3.5 m ) and trapping efficiency (ε~ 5%) Kuraray have higher light output (by 40%), BCF92 have faster time response (2.7 ns versus 9 ns of Kuraray) SiPM gain vs Vbias and T SiPMs Silicon Photomultipliers (SiPMs) from IRST-FBK and Multi Pixel Photon Counters (MPPCs) from Hamamatsu tested : Pros: - high gain (~ 10 5 ) - low bias voltage (< 100 V), - good detection efficiency (~ 30%), - fast response (rise time below ns), - very small (few mm 2 ) and insensitive to magnetic fields. Cons: - relatively high dark count rate (few 100 khz/mm 2 at 1.5 p.e.) and non-negligible sensitivity to radiation. 10

11 R&D results: measurements on prototypes Pedestal from: Dark noise Gain from: LED calibration Response to m.i.p. from: Cosmic muons 11

12 R&D results: optimization of number of fibers per scintillator strip 1, 2, 3 fibers grooved on the surface of strips 10 cm/5 cm wide, 1 cm thick factor 3 gain in light passing from 1 3 fibers per strip ~100 p.e. with 3 fibers on 5 cm wide strips (important for >2 m long strips) 12

13 R&D results: Light attenuation in long strips Attenuation is an issue on ~200 cm strip: ~50 % less light from far end, but still much larger than threshold (typical SiPM threshold: ~1-3 p.e., dark rate decreases by x10 each p.e.) Two possibilities: 1) Aluminize the free end with aluminum stripes; 2) Readout the fibers at both ends; 13

14 counts Time resolution has been measured as a function of the signal amplitude on a scintillator strip 4.5 cm wide, 1 cm thick, with one WLS fibre (Saint Gobain) 200 cm long, readout by SiPM (IRST-FBK) and Multi Pixel Photon Counters (Hamamatsu). Distance ~200 cm sigma 1.3 ns Distance ~200 cm sigma 1.8 ns We measured a time resolution at 200 cm: σ(t) ~ 1.3 ns (SiPM) σ(t) ~ 1.8 ns (MPPC) Strong dependence on the signal amplitude (eg number of photons collected). Time resolu7on (ns) Time resolu7on for different cut on ADC ch 150 cm 250 cm Time (ns) ADC ch 14

15 Test beam results: Test beam at FNAL with pions & muons beams of p=1-10 GeV/c Efficiency per active layer exceeds 95% Pion/muon separation WLS fibres 4 m long, SiPM threshold: 3.5 p.e. 15

16 Simulation Simulation with FLUKA of detector prototypes: Cosmic flux Trigger geometry Detector geometry and materials Muon energy loss Scintillator light response Light propagation inside scintillator Light collection by WLS fibers and light propagation inside fiber Optical coupling to SiPM Light detection by SiPM Simulation parameters tuned with data Important tool for the design of the SHiP Muon detector already available and working (INFN-Bologna) 16

17 Front End Electronics FEE design for SHiP can profit of the experience within INFN laboratories. Ex: FEE boards already designed, tested and produced in Frascati for the NA62 CHANTI detector (triangular scintillator bars); VME 9U FEE board for CHANTI CHANTI detector FEE VME 9U 32 channels board provides for each channel: - control of V bias with o(10 mv) accuracy,; - fast amplification (x25) and a fast, DC coupled, conversion to a Time Over Threshold-LVDS signal output; - temperature and/or a dark current (with na resolution) monitor for slow control adjustment of V bias. 17

18 (Rough) cost estimate Four stations, 5x5 m 2, x-y views, 10x10 cm 2 readout granularity, 3 WLS fibers/5 cm - Extruded plastic scintillator & WLS fibers m 2, 1 cm thick 2 tons of scintillators, 25$/kg 50,000 $ ~40 keuro m WLS fibers (Kuraray Y11): 12k$ ~ 10 keuro - SiPMs & FEE: 800 readout channels single-sided readout (1600 channels double-sided readout) - SiPMs: Hamamatsu S , photon detection efficiency~35%, G= Cost: 18 Euro (plastic) or 47 Euro (ceramic) assume ~50 Euro/SiPM 40 (80) keuro - FEE: cost of a 9U VME Board for NA62 was ~ 4 keuro/32 channels ~ 125 Euro/channel 100 (200) keuro per 800 (1600) channels - Support structures, cables Gran total: ~ 200 (350) keuro + support structures, cables 18

19 Conclusions Extruded scintillators with WLS fibers and SiPM readout are an excellent option for the SHiP muon detector due to: - High efficiency, good time resolution, flexibility in readout, fast timing, simple and robust construction, potential for distributed production, long-term stability, ease of calibration, low maintenance and high reliability; - very cost effective (no HV or gas systems, typically very expensive) A lot of work already done within the INFN laboratories: - for the IFR muon system of the Super B detector: full characterization of the response of modules instrumented with different type and number of fibers, SiPMs response, test beam results, detailed simulation - For the CHANTI detector of NA62 Design, test and production of the FEE boards Contact with FNAL-NICADD project leader (Anna Pla Dalmau) they are ready to collaborate also for the R&D phase SHiP dimensions (~ few tons of scintillators) fit well with the production capability of the facility (< 10 tons). 19