Position Sensitive SiPMs for Ring Imaging Cherenkov Counters

1. Position Sensitive SiPMs for Ring Imaging Cherenkov Counters C.Woody BNL January 17, 2012

2. Cherenkov Radiation Light emitted as a “shock wave” when a charged particle travels faster than the speed of light in a dielectric medium For Cherenkov radiation to be produced g Threshold velocity: p v =bc = particle velocity = phase velocity of photon Symmetric in f Light is emitted in a cone from a line source = refractive index = group velocity of photon • L.M.Frank and Ig.Tamm • C.R.Acad.Sci. USSR, 14 No.3 (1937) 109-114 • Ig. Tamm, J.Phys. USSR 1 (1939) 439 • J.V. Jelly, Cherenkov Radiation and it Applications (1958) Dispersion C.Woody, SiPMs for RICH, 1/17/12

3. Cherenkov Spectrum Differential Spectrum: Spectrum peaks in the deep (V)UV Note: Spectrum is UV divergent However, in real materials, n is dispersive and < 1 at short wavelength  Self absorption limits intensity at short wavelengths Integral Spectrum Where l1 and l2 are the wavelengths of transmission of the radiator material C.Woody, SiPMs for RICH, 1/17/12 3

4. Cherenkov Detectors • Two types of detectors • Threshold • Detects only the presence of light emitted by a particle with a velocity greater than bc • Ring imaging • Measures the ring produced by the light emitted into the Cherenkov cone • Can use a spherical mirror to focus the light from the line source into a ring • Detection efficiency depends on: • length of radiator • transmission of radiator • reflectivity of mirror (if any) • transmission of window (if any) • photon detection efficiency of photodetector • photoelectron detection efficiency Figure of Merit : C.Woody, SiPMs for RICH, 1/17/12 4

5. Threshold Cherenkovs Typically want to identify/separate p/K/p’s over some momentum range For a given radiator, each particle will have a different threshold momentum for producing Cherenkov light For particle id, p=mv = bgm0 e.g., for air, n=1.0003, bc = 1/n = 0.9997, gc=40.8 Threshold counting: Typically use two threshold counters with two different radiators for p/K/p separation over some momentum range C.Woody, SiPMs for RICH, 1/17/12 5

6. Ring Imaging Cherenkovs (RICHs) Measure the diameter of the ring produced by the cone of Cherenkov light Two ways of focusing the light into a ring: Proximity focused Mirror focused DIRC Detector p Detector g Window Expansion medium Window Uses trapped light (internally reflected) from proximity focused type radiator to form ring image Radiator Spherical mirror with detector plane at the focal distance RM/2 Combined C.Woody, SiPMs for RICH, 1/17/12 6

7. PHENIX RICH • Ring Imaging Cherenkov counter with large mirrors • and PMT readout • 5120 1-1/8” PMTs equipped with Winston Cones • Gas radiator (ethane) • Pion threshold = 3.7 GeV/c, ~ 20 g/ring • Ring resolution ~ 1° in f and h (R ~ 14.5 cm for p) • st < 1 ns C.Woody, SiPMs for RICH, 1/17/12 7

8. Particle ID with RICHs Measure the particle velocity and momentum independently  determine particle’s mass Figure of merit for a RICH detector: sq = total angular error per detected photon For two particles of mass m1 and m2 with momentum p well above threshold (b~1), their separation ns is given by: • T.Ypsilantis & J.Seguinot, NIM A343 (1994) 30-51 • Theory of Ring Imaging Cherenkov Counters • B. Ratcliff, NIM A502 (2003) 211-221 • Imaging Rings in Ring Imaging Cherenkov Counters BaBar DIRC (Radiator = quartz) C.Woody, SiPMs for RICH, 1/17/12

9. HERMES Dual Radiator RICH PMTs = 0.75” with Winston Cones N.Akopov et.al., Nucl. Inst. Meth. A479 (2002) 511-530 Angular Resolution Aerogel s~ 7.6 mrad C4F10 s~ 7.5 mrad C.Woody, SiPMs for RICH, 1/17/12

10. Photon Detection Efficiency with PMTs HERMES RICH Aerogel C4F10 C.Woody, SiPMs for RICH, 1/17/12

11. Detection of Internally Reflected Cherenkov Light DIRC Concept: Use Cherenkov radiator (quartz bar) to propagate internally reflected light to an image plane at the end of the radiator Use external tracking detectors to measure entry location and direction of incoming track Also to measure momentum and time Functions as an imaging detector - rectangular bar preserves angle information (qc ,fc) - ring is imaged onto xy (rf) plane of PMTs - measuring arrival time of photons gives 3rd z coordinate Must worry about chromatic dispersion I.Adam et.al., Nucl. Inst. Meth. A538 (2005) 281-357 B.Ratcliff, Nucl. Inst. Meth. A502 (2003) 211-221 ng(l)=n(l)-ldn(l)/dl Group Velocity kz = direction cosine in z-direction BaBar Experiment at SLAC C.Woody, SiPMs for RICH, 1/17/12 11

12. BaBar DIRC 1-1/8” PMTs n2= 1.346 (water) Used to minimize internal reflection at quartz-water interface <n1> = 1.473 (quartz) Bars need to be square (< 0.25 mrad) and smooth (roughness < 7.5Å) n3 = 1.0 (N2) Performance: N0 = 25 cm-1 <Npe> = 23 for b=1 particle C.Woody, SiPMs for RICH, 1/17/12 12

13. BaBar DIRC Angular Resolution Overall track resolution: XY sq=2.5 mrad • sn(l) = chromatic dispersion • scol = distortions due to light collection • sdet = detector resolution Consider contribution to detector resolution: Z 1-1/8” PMT @ 1.17m  sq ~ 7 mrad (single g) Assuming 23 p.e per ring  sq ~ 1.5 mrad HERMES RICH (single photon) C.Woody, SiPMs for RICH, 1/17/12

14. Photon Detection Efficiency with SiPMs Consider the Hamamatsu S11064-050P PDE  dE 4x4 array of 3x3 mm2 SiPMs 50 mm pixels, 3600 pixels per SiPM 61.5% fill factor Dark counts per channel (> 0.5 pe) - 6 MHz ~ 0.75 eV DE = 4.13 eV (300 nm)  1.38 eV (900 nm) = 2.75 eV C.Woody, SiPMs for RICH, 1/17/12

15. SiPM Angular Resolution Assume can locate the photon to 25 mm  sx = sy = 25 mm/12 = 7.2 mm To achieve the same angular resolution as BaBar, one could reduce the expansion length by a factor of 25 mm/25mm = 1000 ! Could also greatly reduce area coverage: Cross section of a BaBar radiator bar = 1.75 x 3.5 cm = 6 cm2  could cover entire end of bar with ~ 65 3x3 mm2 devices C.Woody, SiPMs for RICH, 1/17/12

16. MPPC Readout of Cherenkov Light E.Garutti, SiPM Workshop, CERN C.Woody, SiPMs for RICH, 1/17/12

17. Possible way to save and readout hit SPAD address 0 1 0 Readout Trig Latch 0 1 0 Bit Register Readout Bit Register SPAD Disc Latch 0 0 1 1 0 0 0 0 Trig C.Woody, SiPMs for RICH, 1/17/12

18. Noise ~ 1 MHz = 1 msec Trig (~ 1 ns) C.Woody, SiPMs for RICH, 1/17/12

19. SiPM Readout Chips C.Woody, SiPMs for RICH, 1/17/12

20. Summary and Challenges • Possibility to detect single photons with a spatial resolution ~ 25-50 mm • (this may be a first… and could possibly have many other applications) • Could potentially greatly improve the angular resolution for a RICH/DIRC • ( improved db/b) • Could greatly reduced expansion volume for a RICH or DIRC • (requires only modest area coverage) • Can provide fast timing (needed for DIRC or TOF RICH) • Need to integrate first level readout electronics onto the SPADs • Must detect single photoelectrons in the midst of very high noise • Device must be triggerable C.Woody, SiPMs for RICH, 1/17/12

21. Backup Slides C.Woody, SiPMs for RICH, 1/17/12

22. 0 0 0 0 0 0 4 4 4 4 4 4 8 8 8 8 8 8 Pion-Kaon separation Kaon-Protonseparation TOF s~100 ps 0 - 2.5 0 - 5 RICH n=1.00044 gth~34 5 - 17 17 - Aerogel n=1.007 gth~8.5 1 - 5 5 - 9 Combined Particle ID Using Threshold Cherenkov, RICH and Time of Flight (PHENIX) C.Woody, SiPMs for RICH, 1/17/12

23. PHENIX Time of Flight Counter PMT m-metal Base Scintillator Light Guide/miror 1000 finely segmented slats Read out on both ends with 2000 PMTs st < 96 ps (used with fast “Beam-Beam” counter to define start time) K/p separation to ~ 2 GeVc p/K separation to ~ 4 GeV/c C.Woody, SiPMs for RICH, 1/17/12 23