  NEXT (Neutrino Experiment with a Xenon TPC) is an experiment to search
neutrinoless double beta decay processes (bb0nu) in Xe136. The NEXT technology
is based in the use of time projection chambers operating at a typical pressure
of 15 bar and using electroluminescence to amplify the signal (HPXE). The main
advantages of the experimental technique are: a) excellent energy resolution;
b) the ability to reconstruct the trajectory of the two electrons emitted in
the decays, which further contributes to the suppression of backgrounds; c)
scalability to large masses; and d) the possibility to reduce the background to
negligible levels thanks to the barium tagging technology (BATA). The NEXT
roadmap was designed in four stages: i) Demonstration of the HPXE technology
with prototypes deploying a mass of natural xenon in the range of 1 kg, using
the NEXT-DEMO (IFIC) and NEXT-DBDM (Berkeley) prototypes; ii) Characterisation
of the backgrounds to the bb0nu signal and measurement of the bb2nu signal with
the NEW detector, deploying 10 kg of enriched xenon and operating at the LSC;
iii) Search for bb0nu decays with the NEXT-100 detector, which deploys 100 kg
of enriched xenon; iv) Search for bb0nu decays with the BEXT detector, which
will deploy masses in the range of the ton and will introduce two additional
handles, only possible in a HPXE: a) A magnetic field, capable of further
enhancing the topological signal of NEXT; and b) barium-tagging (a technique
pioneered by the EXO experiment which is also accessible to NEXT).
