Studies on High QE PMT

Transcription

1 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 1

2 Motivation K πνν experiment needs hermetic veto system Signature = 2γ + nothing Veto detectors surrounding Decay Region Major K L decay modes K L π + π - π 0 (13%) K L πeν(γ) (39%) These may fake the signal if charged particles are missed Cause of inefficiency π - p π 0 n (all neutrals and lost) e + annihilated with materials Detection before these interactions (i.e. with low energy deposition) reduces the inefficiency May 26-27, 2005 Tadashi Nomura (Kyoto U), KRare05 at Frascati, Italy 2

3 Simple Consideration of Inefficiency In case of loss due to π - p π 0 n reaction Cross section σ (CH),max ~100mb (at the resonance peak: Eπ~170MeV) Required inefficiency < 10-4 Energy deposit ~ 2MeV/cm Edeposit before P int =10-4 ~ 40keV 6x10 23 [n/mol] / 104[g/mol] x 8[CH pair/n] x 1[g/cm 3 ] x 100x10-27 [cm 2 ] x (thickness) = 10-4 thickness ~ 200µm, Energy deposit ~ 40keV (Note: Resultant π 0 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 3

4 Example: KOPIO Downstream CPV Beam pipe liner inside pre-radiator / calorimeter Beam Innercounter Outer counter Pre-radiator KOPIO DSCV Scintillator&Fiber Option Calorimeter Y11Fiber HQE PMT 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 4

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

6 Basic Properties of H7422 Linearity Gain~6x10 6 Sensitivity map Rate dependence Light yield: 100 p.e. Stable upto 1MHz Light yield: 1000 p.e. Gain~10 6 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) gain drops above 200kHz May 26-27, 2005 Tadashi Nomura (Kyoto U), KRare05 at Frascati, Italy 6

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

8 WLSF attenuation Attenuation in WLSF alone with LED-excited, viewed by High QE PMT λ L =6.1m A L /A S 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 x A exp + A λs x exp λ = S L L May 26-27, 2005 Tadashi Nomura (Kyoto U), KRare05 at Frascati, Italy 8 f ( x) A S =9.0, λ S =1.0m A L =12.9, λ L =6.1m

9 Further Effort to Increase Light Yield Use thicker WLS fiber Better acceptance of primary scintillation lights 1.0mm 1.5mm diameter Need large area PMT cathode to read a bundle of 7 fibers 5mm 8mm 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 May 26-27, 2005 Tadashi Nomura (Kyoto U), KRare05 at Frascati, Italy 9

10 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 10

11 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 11

12 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 12