Ion backflow studies in Micropattern Gaseous Detectors

• Grant number: 18/10494-4
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: July 01, 2018
• End date: May 31, 2019
• Field of knowledge: Physical Sciences and Mathematics - Physics - Nuclear Physics
• Principal Investigator: Pedro Hugo Ferreira Natal da Luz
• Grantee: Chiara Mesquita Cerino Carrillo Le Roux
• Host Institution: Instituto de Física (IF). Universidade de São Paulo (USP). São Paulo , SP, Brazil
• Associated research grant: 16/05282-2 - Development and applications of Micropattern gaseous detectors, AP.JP

Abstract

Gas Electron Multipliers - GEM - have been chosen for many High Energy Physics experiments due to their interesting features that include the possibility of very large sensitive areas and fair energy and position resolutions. One of the most interesting effects that influence the selection of these detectors for such scientific experiments is their intrinsic capacity to suppress the ion backflow (IB). IB is defined by the current of positive ions that drift in the opposite direction of the electrons. These ions can penetrate the holes of the multiple GEMs in the multiplication chain and reach the drift region, causing electric field non-uniformities in this region where it should be as uniform as possible. In Time Projection Chambers (TPC), the electric field non-uniformities in the drift region jeopardize the reconstruction of the trajectories of the particles, consequently compromising their identification. GEMs allow to reduce the IB to very low fractions. However, for an accurate determination of de/dx, it is necessary that the energy resolution of the detector is kept. The challenge in this type of studies is the competition between the processes that allow IB reduction against those that improve the energy resolution. There has been an exhaustive study of some geometries of GEM-based detectors in the frame of the ALICE experiment, which converged to a quadruple GEM stack operating in a neon-based mixture, reaching IB below 1 % and energy resolution below 12 % for a deposited energy of 5.9 keV. This Scientific Initiation project proposes to study new, simpler geometries, using more cost effective gaseous mixtures which can suppress IB without compromising the energy resolution. (AU)