Position Sensitive SiPMs for Ring Imaging Cherenkov

Counters

C.Woody

BNL

January 17, 2012

C.Woody, SiPMs for RICH, 1/17/12 2

Cherenkov Radiation

nc

1cos

Light emitted as a “shock wave” when a charged particle travels faster than the speed of light in a dielectric medium

kp

v

p

cn

v

v =c = particle velocity

= group velocity of photon

= refractive index

dk

dn

n

ck

n

c

dk

dg

2

v

= phase velocity of photon

Dispersion

cn

c v

For Cherenkov radiation to be producedtn

ctg v

n

cp v

Threshold velocity:nc

1

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) 109-114• Ig. Tamm, J.Phys. USSR 1 (1939) 439• J.V. Jelly, Cherenkov Radiation and it Applications (1958)

C.Woody, SiPMs for RICH, 1/17/12 33

Cherenkov Spectrum

22

21

sin2

cdxd

Nd

Spectrum peaks in the deep (V)UV

12

22

11sin2

cddxd

Nd

dx

dN

Differential Spectrum:

Integral Spectrum

2

22 11cos1sin

ncc

Note: Spectrum is UV divergentHowever, 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

137

12

c

e

C.Woody, SiPMs for RICH, 1/17/12 44

Cherenkov Detectors

2

2 )(sin)(2 d

LN cpe

dEEeVcmd

cmN )()(370)(2)( 112

10

cpe NLN 20 sin

peWMR PDETRT )()()()()(

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

2

2

)(

11)(sin

nc

C.Woody, SiPMs for RICH, 1/17/12 55

Threshold Cherenkovs

Air Aerogel Water Quartz PbGl PbF2

Density (g/cm3) 1.2x10-3 0.2-0.4 1.00 2.2 6.3 7.77Index of refraction 1.0003 1.01-1.10 1.33 1.46 1.8 1.78

Radiation Length (cm) 3.1x104 68-136 36 12.3 1.26 0.93Npe/cm for N0=100 0.06 9 43 53 69 68

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=mv = m0

e.g., for air, n=1.0003, c = 1/n = 0.9997, c=40.8

21

1

Particle m0 (MeV) pthresh (GeV) 140 5.7K 494 20.2p 938 38.3

Threshold counting:

Typically use two threshold counters with two different radiators for /K/p separation over some momentum range

C.Woody, SiPMs for RICH, 1/17/12 66

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 focusedDIRC

Combined

Uses trapped light (internally reflected) from proximity focused type radiator to form ring imageSpherical mirror with detector

plane at the focal distance RM/2

Radiator

Window

WindowExpansion

medium

Detector

Detector

p

C.Woody, SiPMs for RICH, 1/17/12 77

PHENIX RICH

Ring Imaging Cherenkov counter with large mirrorsand PMT readout

• 5120 1-1/8” 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, 1/17/12 8

Particle ID with RICHsMeasure the particle velocity and momentum independently determine particle’s mass

Figure of merit for a RICH detector:

pe

rNLN

nk

tan

0

• 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

rkp

mmn

2

21

22

2

||

For two particles of mass m1 and m2 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, 1/17/12 9

HERMES Dual Radiator RICH PMTs = 0.75” with Winston Cones

Aerogel C4F10

Angular Resolution

~ 7.6 mrad ~ 7.5 mrad

N.Akopov et.al., Nucl. Inst. Meth. A479 (2002) 511-530

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 1111

Detection of Internally Reflected Cherenkov LightDIRC

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 3rd z coordinate

Must worry about chromatic dispersion I.Adam et.al., Nucl. Inst. Meth. A538 (2005) 281-357B.Ratcliff, Nucl. Inst. Meth. A502 (2003) 211-221

z

gp ck

Lnt ng()=n()-dn()/d Group Velocity

kz = direction cosine in z-directionBaBar Experiment at SLAC

C.Woody, SiPMs for RICH, 1/17/12 1212

BaBar DIRC

<n1> = 1.473 (quartz)

Bars need to be square(< 0.25 mrad) and smooth (roughness < 7.5Å)

n3 = 1.0 (N2)

n2= 1.346 (water)

Used to minimize internal reflection at quartz-water interface

Performance:

N0 = 25 cm-1

<Npe> = 23 for =1 particle

1-1/8” PMTs

C.Woody, SiPMs for RICH, 1/17/12 13

BaBar DIRC Angular Resolution

=2.5 mraddet22

)(2 coln

• n() = chromatic dispersion• col = distortions due to light collection• det = detector resolution

Overall track resolution:

1-1/8” PMT @ 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, 1/17/12 14

Photon Detection Efficiency with SiPMs

Consider the Hamamatsu S11064-050P

4x4 array of 3x3 mm2 SiPMs50 m pixels, 3600 pixels per SiPM61.5% fill factorDark counts per channel (> 0.5 pe) - 6 MHz

1110 277)(370 cmdEEeVcmN

~ 0.75 eV

E = 4.13 eV (300 nm) 1.38 eV (900 nm) = 2.75 eV

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

Photon Energy (eV)

PD

E*d

E

PDE dE

C.Woody, SiPMs for RICH, 1/17/12 15

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/25m = 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

Trig

Trig

Readout

ReadoutBit Register

Bit Register

Latch

LatchSPAD Disc

0 0

0 01

0 01

0

0

0

0

11

Possible way to save and readout hit SPAD address

C.Woody, SiPMs for RICH, 1/17/12 18

Noise~ 1 MHz = 1 sec

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 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, 1/17/12 21

Backup Slides

C.Woody, SiPMs for RICH, 1/17/12 22

5 - 91 - 5 n=1.007

th~8.5

Aerogel

17 -5 - 17 n=1.00044

th~34

RICH

0 - 50 - 2.5 ~100 psTOF

Kaon-Protonseparation

Pion-Kaonseparation

0 4 8

0 4 8

0 4 8 0 4 8

0 4 8

0 4 8

Combined Particle ID Using Threshold Cherenkov, RICH and Time of Flight

(PHENIX)

C.Woody, SiPMs for RICH, 1/17/12 2323

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 GeVcp/K separation to ~ 4 GeV/c

ScintillatorBasePMT-metal

Light Guide/miror