The Gotthard and MUNU TPCs From the past to the future? Jean-Luc Vuilleumier, LHEP Bern

1. The Gotthard and MUNU TPCs From the past to the future? Jean-Luc Vuilleumier, LHEP Bern TPC symposium, Paris, 18-19 dec. 2008

2. Caltech-Neuchâtel-PSI, Gotthard underground laboratory (3000 mwe)‏ Search for 0n double beta decay in 136Xe TPC, 62.5 % enriched 136Xe (+5% CH4) at 5 bar (180 l fiducial, 5.3 kg) E0=2.48 MeV Anode and x-y plane vD=1.36 cm/s pitch 3.5 mm Gas purification Pb -HV(65kV)‏

3. Sum spectrum of 2-electron events 2 electron event: Single continuous track with enhanced energy (blob) at both ends, inside fiducial volume (radial)

4. (E)/E=0.13 % at 2.48 MeV ! Energy resolution F=0.19, W=22 eV Gotthard 5 bar xenon  (from cathode), 210Po (238U chain)‏ quenching (/e-)=1/6.5 (E)/E=1.1 % at 2.48 MeV ! e-, 232Th (E)/E=3.4 % at 1.59 MeV (E)/E= 2.7 % at 2.48 MeV

5. MUNU (Grenoble, Neuchâtel, Padova, Zurich) Study of scattering at the Bugey nuclear reactor (2.7 GWth)

6. MUNU in Bugey x-y pick-up plane (pitch 3.5 mm)

7.  - proton EM shower MUNU

8. X,Y = 1.7mm 1.7mm 870 keV electron MUNU x 10 cm y 10 cm cm z MUNU measures reacand Te

9. Single forward electron spectrum, • background subtracted • (66.6 days live time) • Single forward electron: • continuous track with one blob • inside fiducial volume (radial) • not vetoed • reconstructed En>0

10. The MUNU veto/anti-Compton proved valuable. • But more is needed to go to larger DBD, solar n detectors • What can/must be improved? • reliability: Micromegas • absolute z: primary scintillation light for t0 3-D fiducial volume, most background comes from the walls • (Gotthard: cathode, MUNU: anode!) • also required for optimal energy resolution, to compensate for charge loss along drift • spatial resolution: segmented Micromegas? • better event selection, discrimination between blobs and d-electrons

11. Test of Micromegas in mini-TPC in Neuchâtel Bern 10 cm diameter, xenon+CF4, 1 bar (CF4 is transparrent to light) grid with spacer 75 mm high, every 1 mm (R. Oliveira, CERN) plain copper anode Edrift =200 V/cm/bar 5.9 keV L. Ounalli et al., JINST

12. Also works at higher pressure Amplification must be increased according to pressure Gain in Ar(90)CH4(10) at 1, 2, 3, 4 bar 75 mm gap 225 mm gap Gain of 103 in Xe(98)CF4(2) at 4 bar

13. Can be procured in larger sizes Gotthard, 50 cm diameter Micromegas, 70 cm drift distance 1 bar Ar(90)CH4(10) Exposure to 241Am and 133Ba sources s(E)/E=4.2% at 228 keV, averaged over anode area Similar results in CF4

14. Xenon, argon, CF4 scintillate And TPB is an efficient WLS from UV to blue can be doped to polystyrene, evaporated to form thin films on light guides fluorescence efficiency 40 % (D.N. McKinsey et al., NIM A516(2004)475) J. Jortner et al., J. Chem. Phys. 42(1965)4250

15. Schematic layout TPB-polystyrene coated light guide for primary scintillation MicromegasTPC xenon+2% CF4, 5-10 bar anti.-Compton scintillator 5 m Anti-Compton also catches 511 keV gammas from e+ annihilation

16. Spatial resolution: segmented Micromegas anode (I. Giomataris, R. Oliveira, CERN) • Patterns produced by microelectronics technologies • Great flexibility in the geometry. Several configurations will be tested in Bern • Standard x-y strips, made from interconnected pixels • Zones subdivided in pixels, read out individually and multiplexed (less ambiguity)

17. TPCs are 34 years old, but there is still much room for improvements for use in low energy particle physics!