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

C.Woody, SiPMs for RICH, 1/17/122 Cherenkov Radiation Light emitted as a “shock wave” when a charged particle travels faster than the speed of light in a dielectric medium v =  c = particle velocity = group velocity of photon = refractive index = phase velocity of photon Dispersion For Cherenkov radiation to be produced Threshold velocity: Symmetric in  Light is emitted in a cone from a line source  p L.M.Frank and Ig.Tamm C.R.Acad.Sci. USSR, 14 No.3 (1937) Ig. Tamm, J.Phys. USSR 1 (1939) 439 J.V. Jelly, Cherenkov Radiation and it Applications (1958)

C.Woody, SiPMs for RICH, 1/17/123 3 Cherenkov Spectrum Spectrum peaks in the deep (V)UV Differential Spectrum: Integral Spectrum Note: Spectrum is UV divergent However, in real materials, n is dispersive and < 1 at short wavelength  Self absorption limits intensity at short wavelengths Where 1 and 2 are the wavelengths of transmission of the radiator material

C.Woody, SiPMs for RICH, 1/17/124 4 Cherenkov Detectors Figure of Merit : Two types of detectors Threshold Detects only the presence of light emitted by a particle with a velocity greater than  c 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

C.Woody, SiPMs for RICH, 1/17/125 5 Threshold Cherenkovs Typically want to identify/separate  /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 =m v =  m 0 e.g., for air, n=1.0003,  c = 1/n = ,  c =40.8 Threshold counting: Typically use two threshold counters with two different radiators for  /K/p separation over some momentum range

C.Woody, SiPMs for RICH, 1/17/126 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 focusedMirror focused DIRC Combined Uses trapped light (internally reflected) from proximity focused type radiator to form ring image Spherical mirror with detector plane at the focal distance R M /2 Radiator Window Expansion medium Detector  p

C.Woody, SiPMs for RICH, 1/17/127 7 PHENIX RICH Ring Imaging Cherenkov counter with large mirrors and PMT readout /8” PMTs equipped with Winston Cones Gas radiator (ethane) Pion threshold = 3.7 GeV/c, ~ 20  /ring Ring resolution ~ 1° in  and  (R ~ 14.5 cm for  )  t < 1 ns

C.Woody, SiPMs for RICH, 1/17/128 Particle ID with RICHs Measure the particle velocity and momentum independently  determine particle’s mass Figure of merit for a RICH detector: T.Ypsilantis & J.Seguinot, NIM A343 (1994) Theory of Ring Imaging Cherenkov Counters B. Ratcliff, NIM A502 (2003) Imaging Rings in Ring Imaging Cherenkov Counters For two particles of mass m 1 and m 2 with momentum p well above threshold (  ~1), their separation n  is given by: BaBar DIRC (Radiator = quartz)   = total angular error per detected photon

C.Woody, SiPMs for RICH, 1/17/129 HERMES Dual Radiator RICH PMTs = 0.75” with Winston Cones Aerogel C 4 F 10 Angular Resolution  ~ 7.6 mrad  ~ 7.5 mrad N.Akopov et.al., Nucl. Inst. Meth. A479 (2002)

C.Woody, SiPMs for RICH, 1/17/1210 Photon Detection Efficiency with PMTs HERMES RICH Aerogel C 4 F 10

C.Woody, SiPMs for RICH, 1/17/1211 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 (  c,  c ) - ring is imaged onto xy (r  ) plane of PMTs - measuring arrival time of photons gives 3 rd z coordinate Must worry about chromatic dispersion I.Adam et.al., Nucl. Inst. Meth. A538 (2005) B.Ratcliff, Nucl. Inst. Meth. A502 (2003) n g ( )=n( )- dn( )/d Group Velocity k z = direction cosine in z-direction BaBar Experiment at SLAC

C.Woody, SiPMs for RICH, 1/17/1212 BaBar DIRC = (quartz) Bars need to be square (< 0.25 mrad) and smooth (roughness < 7.5Å) n 3 = 1.0 (N 2 ) n 2 = (water) Used to minimize internal reflection at quartz-water interface Performance: N 0 = 25 cm -1 = 23 for  =1 particle 1-1/8” PMTs

C.Woody, SiPMs for RICH, 1/17/1213 BaBar DIRC Angular Resolution   =2.5 mrad  n( ) = chromatic dispersion  col = distortions due to light collection  det = detector resolution Overall track resolution: 1-1/8” 1.17m    ~ 7 mrad (single  ) Assuming 23 p.e per ring    ~ 1.5 mrad XY Z HERMES RICH (single photon) Consider contribution to detector resolution:

C.Woody, SiPMs for RICH, 1/17/1214 Photon Detection Efficiency with SiPMs Consider the Hamamatsu S P 4x4 array of 3x3 mm 2 SiPMs 50  m pixels, 3600 pixels per SiPM 61.5% fill factor Dark counts per channel (> 0.5 pe) - 6 MHz ~ 0.75 eV  E = 4.13 eV (300 nm)  1.38 eV (900 nm) = 2.75 eV PDE  dE

C.Woody, SiPMs for RICH, 1/17/1215 SiPM Angular Resolution Assume can locate the photon to 25  m  x =  y = 25  m/  12 = 7.2  m To achieve the same angular resolution as BaBar, one could reduce the expansion length by a factor of 25 mm/25  m = 1000 ! Could also greatly reduce area coverage: Cross section of a BaBar radiator bar = 1.75 x 3.5 cm = 6 cm 2  could cover entire end of bar with ~ 65 3x3 mm 2 devices

C.Woody, SiPMs for RICH, 1/17/1216 MPPC Readout of Cherenkov Light E.Garutti, SiPM Workshop, CERN

C.Woody, SiPMs for RICH, 1/17/1217 Trig Readout Bit Register Latch SPAD Disc Possible way to save and readout hit SPAD address

C.Woody, SiPMs for RICH, 1/17/1218 Noise ~ 1 MHz = 1  sec Trig (~ 1 ns)

C.Woody, SiPMs for RICH, 1/17/1219 SiPM Readout Chips

C.Woody, SiPMs for RICH, 1/17/1220 Summary and Challenges Possibility to detect single photons with a spatial resolution ~  m (this may be a first… and could possibly have many other applications) Could potentially greatly improve the angular resolution for a RICH/DIRC (  improved  ) 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, 1/17/1221 Backup Slides

C.Woody, SiPMs for RICH, 1/17/ n=1.007  th~8.5 Aerogel n=  th~34 RICH  ~100 ps TOF Kaon-Proton separation Pion-Kaon separation Combined Particle ID Using Threshold Cherenkov, RICH and Time of Flight (PHENIX)

C.Woody, SiPMs for RICH, 1/17/1223 PHENIX Time of Flight Counter 1000 finely segmented slats Read out on both ends with 2000 PMTs  t < 96 ps (used with fast “Beam-Beam” counter to define start time) K/  separation to ~ 2 GeVc p/K separation to ~ 4 GeV/c Scintillator Base PMT  -metal Light Guide/miror