1 Nondestructive Measurement of Charged Particles Kensuke Homma / Kazuhiro Hosokawa Hiroshima University １． A novel principle of charged particle sensing ２． Verification of the detection principle in a static condition ３. Future prospects

2 Principle of charged particle detection  Conventional principle developed so far utilizes local inelastic processes such as ionizations and excitations with the typical energy loss above 1eV.  Can we use a quasi elastic process such as macroscopic polarizations with an extremely small energy loss? It opens up a novel charged particle sensing without changing velocities of charged particles.  Is the macroscopic polarization detectable by visible rays? Crystals with the Electro-Optical property combined with the laser readout are suitable for the purpose.

3 Novel principle e-e- Measure instantaneous variation of refractive index in Electro-Optical crystal by external electric fields. e-e- z z x y y x R Phase retardation

4 How to extract small phase retardation ? df Lens  (x 0,y 0 ) y z x  (x 1,y 1 )  (x 2,y 2 ) Fraunhoffer diffraction at an infinite distance can be obtained by lens at a short distance. at a focal point The diffraction pattern at a focal point corresponds to Fourier transformation of input shape of a refractive media.

5 Diffraction patterns with a thin wire of 50  m  Horizontal wire Tilted wireVertical wire Pictures taken by wide dynamic range CMOS camera No wire Fourier transformation of Gaussian is Gaussian with smaller waist. Narrowing the wire width makes diffraction pattern extend more outside. Diffraction pattern keeps vector information on the projection. Gaussian profile

6 Verification with LiNbO 3 in quasi static state Electron current: ~1nA Electron beam diameter: ~50  m(FWHM) Electron kinetic energy: 4keV Electron beam distance: ~300  m Laser intensity: 1W Laser wave length: 532nm Focal length of lens: 10cm CMOS camera dynamic range: 103dB CMOS camera exposure time: 20  sec CMOS camera pixel size: 45 x 45  m 2 y [  m] Expected # of photons along y-axis  ~ E 1 =E 2 =0, r 13 =8.7 pm/V Sampling here Index ellipsoid of LiNbO3 crystal Local phase retardation z x y E3E3 e-e-

7 Experimental setup Wide dynamic range CMOS camera CW Laser injection Plastic Scintillater + PMT for e- monitor 凸 Lens Flexible optical fiber bundle DC e - gun Coupling to Optical fiber bundle LiNbO 3 crystal Location of fiber bundle Auto stage +y +x

8 Shot by shot intensity profiles at focal plane BKG(e-off) BKG(e-off)-BKG(e-off) SIG(e-on)-BKG(e-off) Focal point +y

9 Future prospect toward single charged particle detection Soviet Physics – Solid State Vol.8, No. 11 (1967) Ferroelectrics, 2002 Vol.272, pp Large electro-optical coefficient Fast rise and not too long duration time compared to effective impact time KH 2 PO 4 (KDP) KD 2 PO 4 (DKDP) KH 2 PO 4 (KDP)  T=14.2K  T=4.2K  T=1.3K LiNbO 3

10 Expected diffraction pattern by single electron Developed eclipse flexible fiber bundle Mask here

11 Summary The novel remote sensing technique with laser diffraction readout was qualitatively verified at a static condition. In ideal case, even remote sensing of non-relativistic single electron is possible with cooled DKDP crystal and the test experiment is on going. If single charged particle is detectable, it would open up many applications like; end-point determination in beta decays with the nondestructive ToF measurement, mass spectroscopy of ionized protein beam and so on.

12 Backup slides

13 x y z  = 1mm  = 0.1mm Diffraction with square aperture Merits at a focal point: 1.S/N can be greatly improved compared to conventional interferometry 2.Incident photon intensity can be lowered 3. Size can be extremely compact 4. Pattern is simple compared to grating optics

14 One more step x y e - DKDP crystal Profile of scanning laser Linear polarization z e-e- y z x Scanning laser y’ x’ z

15 Ultimate goal of this study E end Count rate m e Big issue in particle physics Absolute scale of neutrino mass Big issue in cosmology Are there relic neutrinos ？ Lepton number asymmetry btw.  and ？ Can we achieve energy resolution beyond 1eV limit by a novel method ？ E end Count rate m e << 1eV Kinetic energy measurement of beta decay is a key measurement p ne-e- e n e-e- e p 3 body decay2 body interaction 2 body Neutrino temperature eV Electron kinetic energy 3 body

16 Spectrometer for end-point measurement LOI of KATRIN experiment (hep-ex/ ) under adiabatic field change Phase space in the last 1eV just below E 0 is 2x H source is ~10 13 Bq Bmax Bmin Bmax B field -eU 0 Mainz

17 B1B1 B2B2 B3B3 B4B4 S1S1 S2S2 S3S3 S4S4 ToF sectionMCP plane Source plane Detector element Electrostatic potential of E 0 -10eV at analyzing plane eV resolution to 10eV electron with 10m ToF section may be achievable.

18 R vtvt dr rd(tan  ) r  v dd Energy loss per single element Energy loss strongly depends on R: If R is small, phonon excitations cause typically meV order energy loss If R is large, polarization variation may be caused by not accompanying phonon excitations due to structural phase transition of DKDP crystal. In such a case, energy loss would be expressed as E loss ~0.8x10 -7 eV for  1, K~10 3 and R~1  m.

19 LiNbO 3 結晶の電気光学効果を利用した 非破壊測定の成功例 hep-ex 電荷量の依存性距離の依存性 time (ns) 40MeV/c electrons with 40ps bunch length

20 Time response of KDP Ferroelectrics, 2002 Vol.272, pp KDP crystal

21 Shot by shot intensity profiles at focal plane BKG(e-off) BKG(e-off)-BKG(e-off) SIG(e-on)-BKG(e-off) Focal point +y