Tadashi Nomura (Kyoto U), KRare05 at Frascati, Italy Studies on High QE PMT Tadashi Nomura (Kyoto U.) Contents Motivation Performance of H7422P-40 Application to Scintillation counter with WLSF readout Summary May 26-27, 2005 Tadashi Nomura (Kyoto U), KRare05 at Frascati, Italy

Motivation Kpnn experiment needs hermetic veto system Signature = 2g + nothing Major KL decay modes KLp+p-p0 (13%) KLpen(g) (39%) These may fake the signal if charged particles are missed Cause of inefficiency p-pp0n (all neutrals and lost) e+ annihilated with materials Detection before these interactions (i.e. with low energy deposition) reduces the inefficiency Veto detectors surrounding Decay Region May 26-27, 2005 Tadashi Nomura (Kyoto U), KRare05 at Frascati, Italy

Simple Consideration of Inefficiency In case of loss due to p-pp0n reaction Cross section s(CH),max ~100mb (at the resonance peak: Ep~170MeV) Required inefficiency < 10-4 Energy deposit ~ 2MeV/cm Edeposit before Pint=10-4 ~ 40keV 6x1023[n/mol] / 104[g/mol] x 8[CH pair/n] x 1[g/cm3] x 100x10-27[cm2] x (thickness) = 10-4 thickness ~ 200mm, Energy deposit ~ 40keV (Note: Resultant p0 can be detected by photon veto detectors and thus inefficiency might be smaller) How many photoelectrons per 40keV can we obtain? High Quantum Efficiency (QE) PMT desired May 26-27, 2005 Tadashi Nomura (Kyoto U), KRare05 at Frascati, Italy

Example: KOPIO Downstream CPV Beam pipe liner inside pre-radiator / calorimeter Counter should be inside vacuum, but it’s desirable to locate PMT outside  Long WaveLength-Shifting-Fiber (WLSF)  Small light yield  Need High QE PMT May 26-27, 2005 Tadashi Nomura (Kyoto U), KRare05 at Frascati, Italy

High QE PMT : Hamamatsu H7422 H7422P-40 GaAsP photocathode Sensitive area: 5mm in diameter Metal channel dynode structure Price ~1.8k$ QE=30-40% for Green Measured QE using LEDs (relative to bi-alkali PMT) Expected QE GaAsP (H7422) Calculated from relative QE and bi-alkali catalog value Bi-alkali (H7415) Peak Wavelength of WLSF May 26-27, 2005 Tadashi Nomura (Kyoto U), KRare05 at Frascati, Italy

Tadashi Nomura (Kyoto U), KRare05 at Frascati, Italy Basic Properties of H7422 Stable upto 1MHz Rate dependence Light yield: 100 p.e. Linearity Gain~6x106 Sensitivity map gain drops above 200kHz Light yield: 1000 p.e. Gain~106 Linearity not so good (even within 100 p.e.) Improvement might be possible by optimizing base circuit Structure due to focusing mesh was seen… (~10% dip) May 26-27, 2005 Tadashi Nomura (Kyoto U), KRare05 at Frascati, Italy

High QE PMT + Scintillator + WLSF Test configuration PMT: H7422P-40 Scintillator: EJ-212 (ELJEN) 3mm-thick, 1m-long WLSF: Y11(200) (Kuraray) 1mm-diameter Machined groove, 1cm-pitch, bundle 7 fibers Wrapped by Aluminized mylar 90Sr (Edep~580keV) 70 p.e. / 0.58 MeV  120 p.e. / MeV Results: 70 p.e (both) with High QE PMT (x 3~3.5 larger than with Bi-alkali PMT) May 26-27, 2005 Tadashi Nomura (Kyoto U), KRare05 at Frascati, Italy

Tadashi Nomura (Kyoto U), KRare05 at Frascati, Italy WLSF attenuation Attenuation in WLSF alone with LED-excited, viewed by High QE PMT lL=6.1m AL/AS ratio decreases if measured by bi-alkali PMT (longer wavelength ~ longer attenuation) Attenuation in Scinti + WLSF Consistent well with WLSF alone In case of 4m long WLSF (1m in Scinti + 3m outside vacuum), Light yield will be 46% of our test result  120 x 0.46 x 40x10-3 = 2.2 p.e. / 40keV AS=9.0 , lS=1.0m AL=12.9 , lL=6.1m May 26-27, 2005 Tadashi Nomura (Kyoto U), KRare05 at Frascati, Italy

Further Effort to Increase Light Yield Use thicker WLS fiber Better acceptance of primary scintillation lights 1.0mm  1.5mm diameter 30% increase expected (by our measurement) Use clear fiber to transport light Longer attenuation 1m WLSF in Scintillator + 3m clear fiber (outside vacuum) 50% improvement expected Connection ~90% x attenuation ~75%  68% cf. 46% attenuation for WLSF Need large area PMT cathode to read a bundle of 7 fibers 5mm  8mm diameter May 26-27, 2005 Tadashi Nomura (Kyoto U), KRare05 at Frascati, Italy

Tadashi Nomura (Kyoto U), KRare05 at Frascati, Italy Summary (1) High Quantum Efficiency PMT Hamamatsu H7422P-40 (GaAsP photocathode) Basic properties QE : 30-40% for green light ~3 times larger than bi-alkali PMT Linearity : not so good if we use “default” base circuit Rate capability : stable upto 1MHz for 100 p.e. light Application to Scintillator + WLSF 120 p.e. / MeV (sum of both end) with 1m-long test counter ~3 times larger than bi-alkali PMT, as expected May 26-27, 2005 Tadashi Nomura (Kyoto U), KRare05 at Frascati, Italy

Tadashi Nomura (Kyoto U), KRare05 at Frascati, Italy Summary (2) Application to KOPIO DS Charged Particle Veto In case we use 4m long WLS fiber, 2.2 p.e. / 40keV (sum of both end) will be expected Threshold of 3 p.e. in both end, for example (6 p.e. in total) inefficiency will be 3x10-4 (without help by “backup” photon vetoes) Effort to increase light yield 1mm  1.5mm diameter fiber ( x 1.3 expected ) Use clear fiber to transport long distance Change reflection material (Aluminized mylar  Al evaporation?) May 26-27, 2005 Tadashi Nomura (Kyoto U), KRare05 at Frascati, Italy

Further High QE PMT issues Large sensitive area desired In order to use thicker fibers Need negotiation with the vendor (Hamamatsu) Linearity might be improved Not so good with “default” base circuit Optimize base circuit Life time of photocathode? Degradation of GaAsP ? Long-term test is planned May 26-27, 2005 Tadashi Nomura (Kyoto U), KRare05 at Frascati, Italy