Ph.d. degree
INFN Ferrara, Italy, 2014

Riccardo Farinelli

Supervisor: Diego Bettoni

A cylindrical GEM detector for BES III

Keywords:

• triple-GEM
• micro-TPC
• Garfield

Abstract:

BESIII is a particle physics experiment located at the Institute of High-Energy Physics (BEPC-II) e + e − collider at IHEP in Beijing. It takes data in the τ − charm domain since 2009. Currently, the world largest samples of J/ψ, ψ(3686), ψ(3770) and ψ(4040) data have been collected. Among the many experimental results pub- lished so far, the large statistics accumulated at the Y (4260) and Y (4360) center of mass energies, allowed the discovery of the charged states Z c (3900) + and Z c (4020) − that are the first four-quark states observed and confirmed by different experiments. BESIII data taking will last until at least 2022. The Italian collaboration is leading the effort for the development of a cylindrical GEM (CGEM) detector with analog readout to upgrade the current inner drift chamber that is suffering early ageing due to the increase of the machine lumi- nosity. That will happen in either 2017 or in 2018. The new detector will match the requirements for momentum resolution (σ(p t )/p t ∼ 0.5% at 1 GeV) and radial resolution (σ(xy) ∼ 100 μm) of the existing drift chamber and will improve signif- icantly the spatial resolution along the beam direction (σ(z) ∼ 150μm) with very small material budget (about 1% of X 0 ). The project, that now involves also groups from Mainz, Uppsala and IHEP, has been recognised as a Significant Research Project within the Executive Programme for Scientific and Technological Cooperation between Italy and P.R.C. for the years 2013-2015, and more recently it has been selected as one of the projects funded by the European Commission within the call H2020-MSCA-RISE-2014. Within the CGEM project, this work aims to perform full detector simulation for the optimisation of the tracker geometry and its operational parameters. The goal is achieved by means of three different, but well connected, studies: a background estimation, a simulation of the detection elements and the data analysis of a beam test. My contribution to the work reported in this thesis was broad and continuos during the past 12 months. I participated to the construction of the cath- ode electrode, that was produced in Ferrara, helping during the assembling and manufacturing procedures. For the background studies and the detector simulation I took care both of the framework development and of the data analysis. Finally, I participated to installation and data taking of the beam test at CERN, and I was involved in the production of the reconstruction and analysis software. During and after the beam test I participated to the processing and analysis of the data.