1. NEXT: A Neutrinoless 2  Experiment with a Gaseous XeTPC Thorsten Lux IFAE Barcelona in behalf of the NEXT Collaboration

2. What is the DB Decay? e–e– e–e– (A,Z) (A,Z+2) W W (A,Z)  (A,Z+2) + 2 e – + 2  e 2  Only possible if the neutrino is a Majorana particle (particle == anti-particle) e e–e– e–e– e (A,Z) (A,Z+2) W W (A,Z)  (A,Z+2) + 2 e – 0  rare SM process observed for several isotopes

3. Experimental signature is a small peak at the Q value. It does not look too bad until...... we use the correct normalization! Excellent energy resolution is a must! 3.5% FWHM 1% FWHM How can we measure it?

4. What is requiered? we need something scalable to large detector masses of a suitable isotope (~100 kg to several tons) the isotope should have a large Q value (> 2 MeV) -> larger decay rate its 2  lifetime should be long the detector must have an excellent energy resolution ( ≤ 1-2 % FWHM) the external BG has to be controlled and understood to few counts a year. Extra handles are important. Obviously it is difficult to get all our wishes fulfilled!

5. The NEXT Concept gaseous 136 Xe (100 kg, 80% enriched) TPC operated at high pressure ( 5 to 10 bar) first experiment in the new Canfranc Lab It could look like this... 1.4x1.4x1.4 m 3 (at 10 bar) inner volume filled with enriched Xe posibly an outer volume filled with a buffer gas. T 0 from prompt light Tracking and energy measurement separated

6. Electroluminescence between two parallel meshes (G1,G2) a voltage is applied operated below the point where charge amplification sets in linear production of light (~172 nm) -> better energy resolution light is read out by PMT/APD/MPPC/… used in DM experiments (XENON/LUX/…) gain of 1000-2000 photons per e- at 10 bar possible L.C.C. Coelho et al. NIM A 575 (2007) 444–448 <=1% should be achievable at 2.5 MeV

7. SOFT basic idea from Dave Nygren, evolved further by David Sinclair behind the cathode equipped with PMTs for T0 and energy measurement on the anode side EL meshes and tracking readout Cathode PMTs EL/Tracking plane Rectangular shape of the active volume requiered to achieve this homogenity -> number of PMTs (re-inforced XENON PMTs) can be reduced.

8. Tracking extra handle to reduce background from external gammas important argument to go for gaseous xenon BG: 1 e - → 1 blobS: 2 e - → 2 blobs Options for the tracking reaout: light readout with APDs or MPPCs MicroMegas readout

9. APDs modified standard product from Hamamatsu, available in 5x5, 10x10 and 18x18 mm2 in large quantities directly sensitive to DUV light (interesting for Ar and Xe applications, e.g. DM searches) price per sensor is not small Mesh voltage vs energy res./gain

10. MPPCs testing products from Hamamatsu and Sensl price per sensor very low and possibly simpler electronics very small (1x1 mm2) very limited dynamic range (~<= 1000 photons) not sensitive to DUV light, conversion via a WLS requiered

11. MicroMegas microbulk MMs produced at CERN various tests at up to 10 bar performed with Ar mixtures and up to 5 bar in Xe mixtures a “cheap” and simple solution for covering the whole readout plane operation in pure Xe at 10 bar and behind EL meshes?

12. NEXT Time Schedule The project has 4 phases: 1.NEXT-0 (2009-2010): operation of small setups for 1 or a few sensors 2.NEXT-1 (2010-2011): a 1 kg detector to prove on a larger scale the feasibility 3.NEXT-10 (2011-2012): 10 kg detector operated at Canfranc. Radiopure and scalable to 100 kg. 4.NEXT-100 (2013): operation of a 100 kg Xe detector in Canfranc The project received funding for 5 years and 6 million Euro by the Spanish government (CSD2008-00037) to build a 100 kg Xenon detector in the Canfranc underground lab.

13. Summary and Outlook the NEXT project aims to build a high pressure Xe TPC to measure the neutrioless DB decay detector concept is based on the SOFT idea: excellent energy resolution and sufficient tracking capabilities NEXT-100 will be an important step towards a 1 ton detector new collaborateurs are welcome to join this adventure In 5 years of operation of NEXT-100 one can cover the mass region down to 100 meV.