1. R&D for Future ZEPLIN M.J. Carson, H. Chagani, E. Daw, V.A. Kudryavtsev, P. Lightfoot, P. Majewski, M. Robinson, N.J.C. Spooner University of Sheffield Pawel Majewski, Univ. of Sheffield Cryogenic Liquid Detectors for Future Particle Physics; LNGS, 13-14 III 2006 D.B. Cline, W.C. Ooi, F. Sergiampietri(a), H. Wang, P. Smith(b), X. Yang Physics and Astronomy, UCLA, (a) Pisa, (b) RAL&UCLA J.T. White, J. Gao, J. Maxin, G. Salinas, R. Bissit, J. Miller, J. Seifert Department of Physics, Texas A&M University T. Ferbel, U. Schroeder (Chemistry), F. Wolfs, W. Skulski, J. Toke Department of physics and Astronomy, Rochester University Y. Gao Southern Methodist University, Texas

2. Presentation outline Introduction Detector geometry Principles of operation - characteristics of an event Light collection Signal readout - charge gain in liquid xenon Dark Matter limit Program for R&D Pawel Majewski, Univ. of Sheffield Cryogenic Liquid Detectors for Future Particle Physics; LNGS, 13-14 III 2006

3. Introduction Our goals: Large mass of sensitive LXe in a scale of Tonnes Simple detector geometry Very low background radiation Sensitivity to very low energy events - possibility of few photons detection - large surface photocathode - possibility of few electrons detection -> Both requires high gain in liquid Large mass with maximum surface acting as a photocathode : SPHERICAL GEOMETRY Pawel Majewski, Univ. of Sheffield Cryogenic Liquid Detectors for Future Particle Physics; LNGS, 13-14 III 2006

4. LXe physical properties Energy/scintillation photon W_ph =21.6 eV Scintillation Absorption length > 100 cm Energy/el-ion pair: W=15.6 eV Saturation velocity of electrons from E=3 kV/cm: v=2.6 mm/  s Threshold electric field for proportional scintillation: E=400-700 kV/cm Threshold electric field for electron multiplication: E~1 MV/cm Maximum charge gain measured 200-400 Pawel Majewski, Univ. of Sheffield Cryogenic Liquid Detectors for Future Particle Physics; LNGS, 13-14 III 2006 (table from T.Doke NIM 196 (1982) 87)

5. Spherical TPC filled with LXe Outer sphere Photocathode coated with CsI Central ball with charge readout Field shaping rings Pawel Majewski, Univ. of Sheffield Cryogenic Liquid Detectors for Future Particle Physics; LNGS, 13-14 III 2006

6. Detector structure Central ball 4  covered with charge collecting and amplifying micro-structure Sensitivity to single electron High readout segmentation for position information Requirements: Pawel Majewski, Univ. of Sheffield Cryogenic Liquid Detectors for Future Particle Physics; LNGS, 13-14 III 2006

7. Electric field distribution Can detector operate with a non uniform field ? Electron drift velocity = f (E) 3 kV/cm (L.S.Miller at al. Phys. Rev. Vol. 166, 1967) Pawel Majewski, Univ. of Sheffield Cryogenic Liquid Detectors for Future Particle Physics; LNGS, 13-14 III 2006

8. Charge and light yield = f (E) Measured charge and light yield for E<5 kV/cm Extrapolation to E<75 kV/cm (Thomas-Imel model Phys.Rev A 38 (1998) 5793) (T.Doke et al. Jpn.J.Appl.Phys. 41 (2002) 1538) Pawel Majewski, Univ. of Sheffield Cryogenic Liquid Detectors for Future Particle Physics; LNGS, 13-14 III 2006 (E.Aprile et al. astr-ph/0601552) E= 3 kV/cm 5e/keVr @ 2KV/cm

9. Charge and light readout Scintillation light photons converted into photoelectrons from the CsI photocathode - CsI QE ~ 30 % @ E>3 kV/cm (E.Aprile et al. NIM A 343, 1994) - 4  coverage except shadowing Ionisation electrons and photoelectrons readout with segmented charge amplifying device delivering energy and position information - low primary charge sensitivity with charge gain Pawel Majewski, Univ. of Sheffield Cryogenic Liquid Detectors for Future Particle Physics; LNGS, 13-14 III 2006

10. Charge amplification in LXE Conditions for electron multiplication and secondary scintillation in liquid xenon : Electric field threshold for avalanche development : ~ 1MV/cm Electric field threshold for proportional light: 100-150 kV/cm (B.A. Dolgoshein et al. JETP Lett. Vol. 6, 1967) 400-700 kV/cm (K.Masuda et al. NIM 160, 1979) Pawel Majewski, Univ. of Sheffield Cryogenic Liquid Detectors for Future Particle Physics; LNGS, 13-14 III 2006 H.Wang 1991, gain : 40

11. Event generation (1) Pawel Majewski, Univ. of Sheffield Cryogenic Liquid Detectors for Future Particle Physics; LNGS, 13-14 III 2006

12. Event generation (2) Interaction in the sensitive volume Pawel Majewski, Univ. of Sheffield Cryogenic Liquid Detectors for Future Particle Physics; LNGS, 13-14 III 2006

13. Event generation (3) Simultaneous creation of scintillation UV light and … Pawel Majewski, Univ. of Sheffield Cryogenic Liquid Detectors for Future Particle Physics; LNGS, 13-14 III 2006

14. Event generation (4) … creation of ionisation charge Pawel Majewski, Univ. of Sheffield Cryogenic Liquid Detectors for Future Particle Physics; LNGS, 13-14 III 2006

15. Event generation (5) Scintillation UV photons converted into photoelectrons Pawel Majewski, Univ. of Sheffield Cryogenic Liquid Detectors for Future Particle Physics; LNGS, 13-14 III 2006

16. Event generation (6) First pulse generated Pawel Majewski, Univ. of Sheffield Cryogenic Liquid Detectors for Future Particle Physics; LNGS, 13-14 III 2006

17. Event generation (7) Proportional scintillation UV photons converted into photoelectrons Pawel Majewski, Univ. of Sheffield Cryogenic Liquid Detectors for Future Particle Physics; LNGS, 13-14 III 2006

18. Event generation (8) Second pulse generated Pawel Majewski, Univ. of Sheffield Cryogenic Liquid Detectors for Future Particle Physics; LNGS, 13-14 III 2006

19. Event generation (9) First after–pulse generated Pawel Majewski, Univ. of Sheffield Cryogenic Liquid Detectors for Future Particle Physics; LNGS, 13-14 III 2006

20. Event generation (10) Second after–pulse generated and pulses generation continues … Pawel Majewski, Univ. of Sheffield Cryogenic Liquid Detectors for Future Particle Physics; LNGS, 13-14 III 2006

21. Light collection MC calculations Energy to produce UV photon: W= 21.6 eV Light attenuation length: 100 cm CsI QE : 20, 30 % Electron lifetime: 0.5, 1 and 5 ms Shadowing 3D example: Pawel Majewski, Univ. of Sheffield Cryogenic Liquid Detectors for Future Particle Physics; LNGS, 13-14 III 2006

22. MC calculations: results At R=50 cm, light collection = 4-7.5 phe/keV Pawel Majewski, Univ. of Sheffield Cryogenic Liquid Detectors for Future Particle Physics; LNGS, 13-14 III 2006

23. Charge amplification - wires S.E Derenzo et al. Phys. Rev. A Vol 9,1974 maximum gain : 400 M.Miyajima et al. NIM Vol 134,1976 maximum gain : 100 Pawel Majewski, Univ. of Sheffield Cryogenic Liquid Detectors for Future Particle Physics; LNGS, 13-14 III 2006 Readout wires

24. Problems with gain in liquid Slow motion of avalanche ions building space charge Local imperfections of the readout structure Purity of LXe Large amount of created UV photons causing after-pulses leading to discharge Bubble formation on the sharp edges of the readout electrode hence conducting path creation (J.G. Kim et al. NIM A 535 2004) Pawel Majewski, Univ. of Sheffield Cryogenic Liquid Detectors for Future Particle Physics; LNGS, 13-14 III 2006

25. Charge readout - microstructures Micropattern detectors : micromegas micro-dot MSGC (already used in LXe with gain =10) (A.P.L. Policarpo et al. NIM A 365 1995) Already used in LAr (no gain due to discharges) Cold field emission device: High electric field ~ 1MV/cm with small differential voltage (J.G. Kim et al. NIM A 535 2004) Pawel Majewski, Univ. of Sheffield Cryogenic Liquid Detectors for Future Particle Physics; LNGS, 13-14 III 2006

26. Charge readout – simulation (1) Tools: Garfield (Analytic) by R.Veenhof (CERN) Maxwell (FEM) by Ansoft Electric field near wire surface Recalculated LXe gain in single wire chamber Townsend coefficient from S. Derenzo et al. Phys. Rev. A Vol 9,1979 (large errors) Pawel Majewski, Univ. of Sheffield Cryogenic Liquid Detectors for Future Particle Physics; LNGS, 13-14 III 2006

27. Charge readout - simulation (2) Microstructure modelling What is needed : Local high electric field for high gain 100 % 4  charge collection Electric field < 400 kV/cm when V_cath=0 and E_drift = 75 kV/cm Drift field 75 kV/cm 5 kV/cm Pawel Majewski, Univ. of Sheffield Cryogenic Liquid Detectors for Future Particle Physics; LNGS, 13-14 III 2006

28. Charge readout – simulation (3) Simulated multiplication Electric field strength on the axis of the cell 75 kV/cm 0 V at the cathode Pawel Majewski, Univ. of Sheffield Cryogenic Liquid Detectors for Future Particle Physics; LNGS, 13-14 III 2006

29. How to avoid feedback pulses ? Using HV switch : When V_cath = 0 E_max < 400 kV/cm Field on the cell axis: Field at the cell entrance: Pawel Majewski, Univ. of Sheffield Cryogenic Liquid Detectors for Future Particle Physics; LNGS, 13-14 III 2006

30. Dark Matter Limit Assumptions: LXe mass: 1 Tonne Run period: 1 year Energy range: 4-50 keVnr O events detected 1O events detected Pawel Majewski, Univ. of Sheffield Cryogenic Liquid Detectors for Future Particle Physics; LNGS, 13-14 III 2006 Backgrund sources in 1 Tonne LXe detector: (M.Carson et. al. NIM A 548 (2005) 418) A)222 Rn events/year: 1.46*10^6 B) PMTs (Hamamatsu R8778) events/year: 3.65*10^5 C) 85 Kr events/year: 9.1*10^5

31. R&D program (goals to achieve) Study of the scintillation properties of LXe at high electric field (scintillation light and charge yield) Study of the electric field threshold for proportional light creation Explore possibility of the high gain in LXe using micro-structure devices (study of the limitations: maximum gain, stability in time, energy resolution) Work on the feedback pulses suppression Pawel Majewski, Univ. of Sheffield Cryogenic Liquid Detectors for Future Particle Physics; LNGS, 13-14 III 2006