Study and design of the front-end and readout electronics for the tracking plane in the NEXT experiment

Abstract

The NEXT experiment is one of the most innovative ones looking for the neutrinoless double beta decay, which finding will answer one of the most important questions in the last years physics: is the neutrino its own antiparticle? Or in other words, is it a Majorana particle? With that purpose NEXT uses a TPC (Time Projection Chamber) filled with enriched xenon gas at high pressure, and two photosensors planes, one on each end. The first plane contains PMTs (PhotoMultiplier Tube), that collect the light emitted by the xenon when an event happens and precisely measures its energy. The second plane is a SiPM (Silicon PhotoMultiplier) matrix that allows to 3D-reconstruct the event track. Both planes together allows NEXT to have a great background rejection, which makes a difference with the other experiments aiming for the neutrinoless double beta decay. In addition, SiPMs are a new technology which nowadays is evolving to, in the future, displace the classical PMTs. For that reason the study of these sensors starts from zero, as there were not previous uses as pixel-tracking, and lead a new path in the physics detectors, for both high and low energy. This thesis is focused on the study and design of the electronics involving the tracking plane, which includes some technical solutions related also with mechanical issues. From the sensors placed inside the detector, the SiPMs, to the front-end electronic boards, there are few elements on the chain; as the support boards for the SiPMs which must satisfy severe outgassing and radiopurity levels. Also the inner and outer cabling has been designed, focusing on obtaining the best signal-noise ratio; and also the feedthrough for the tracking plane, which solved at low cost the huge problem of taking out about 4000 lines from the pressurized xenon to the outside. Finally, one of the most important elements on this chain and the one that this thesis is focused on, is the front-end board. Starting with the experience acquired with the first prototype, NEXT-DEMO, the electronics have been improved, able to condition, integrate and digitize the signals from all the tracking plane SiPMs; allowing the further acquisition and processing through an ATCA-based system (Advanced Telecommunications Computing Architecture). All the elements designed have been produced and assembled on the NEW detector, a large-scale prototype of the final detector, placed at the Laboratorio Subterra'neo de Canfranc, an underground laboratory at the aragonese Pyrenee.; El experimento NEXT es uno de los mas innovadores en la busqueda de la desintegracion doble beta sin neutrinos, cuyo hallazgo daria con la respuesta a una de las cuestiones mas importantes de la fisica en los ultimos anos: ?es el neutrino su propia antiparticula? O dicho de otro modo, ?es una particula de Majorana? Para ello NEXT hace uso de una TPC (Time Projection Chamber) llena de gas xenon enriquecido a alta presion, y con dos planos de fotosensores, uno en cada extremo. El primero de ellos esta formado por PMTs (Photo Multiplier Tube), que…