Available Theses

Master's Theses

The following theses are available within the MEG II experiment:

• Calibration of the drift velocity for the drift chamber of the MEG II experiment

Even small variations in the electron drift velocity close to the cell anode can significantly degrade the spatial resolution of the drift chamber. In MEG II, a small monitoring chamber, positioned downstream of the drift chamber, tracks the stability of both the gain and drift velocity using two radioactive ionization sources (Fe55 and Sr90). The first stage of the thesis involves analyzing the monitoring chamber signals to determine variations in drift velocity and gain. The next step is to study temporal fluctuations in the spatial resolution of the drift chamber and investigate possible correlations with the variations observed by the monitoring chamber. Finally, based on the identified trends, corrections to the drift chamber's tXY tables can be determined. The last phase consists of assessing the performance improvements achieved in Michel muon decay.

• Improvement of the positron tracking algorithm in the MEG II experiment

The positron track reconstruction algorithm in MEG II is based on the Kalman Filter, a recursive algorithm that estimates the "state" of a dynamic system, in this case the position and momentum of the positron, using a series of noisy measurements. The measurements are the "hits" recorded by the drift chamber cells, while the noise is due to multiple Coulomb scattering and energy losses. The Kalman filter assumes a Gaussian distribution for the expected hit position in a given cell, but this is a simplification of reality. Better algorithms, such as the Gaussian Sum Filter (GSF), use a sum of Gaussians instead of a single Gaussian. The thesis involves implementing the GSF in the MEG II reconstruction code using neural networks, along with the optimization of its parameters. In the second phase, the improvement achieved will be assessed by studying the resolution in momentum and angles for positrons from simulated events and real data (Michel positrons that perform double loops in the drift chamber).

The MEG Rome group is also involved in the construction of the muonEDM experiment, which aims to search for the muon's electric dipole moment. A nonzero result would be evidence of new physics. The following thesis projects are available:

• Simulations of the Time Projection Chamber for the muonEDM experiment

The muonEDM experiment will use a Time Projection Chamber (TPC) to measure the injection angle and momentum of the muon. To ensure proper muon trapping within the detector magnet, an angular resolution of a few milliradians and a momentum resolution of 0.5% are required. The goal of this thesis is to develop a full Geant4 simulation of a TPC within the relevant experimental setup while optimizing its design based on the achievable resolutions and the constraints imposed by the experiment's geometry.

• Characterization of the high-rate GridPix detector

The GridPix detector enables high-granularity and high-resolution readout of gaseous detector signals. The combination of a Time Projection Chamber (TPC) with GridPix is a promising solution for detecting positrons and muons with momenta in the tens of MeV range. This thesis aims to characterize this setup, focusing particularly on the efficiency achievable at high rates, as required by high-intensity beam experiments. The work involves measuring efficiency using a TPC + GridPix prototype with a high-intensity Fe55 source as ionization source.

• Characterization of the Time Projection Chamber for the muonEDM experiment

Once the design optimization phase is complete, the muonEDM TPC will be built. The aim of this thesis is the "commissioning" phase of this detector, which involves determining the working point and characterizing the signals using different ionization sources (cosmic rays, lasers, etc.).

The MEG-Roma group is also part of an international group studying future experiments for the search or measurement of decay processes in the context of future high-intensity muon beams, which will be available at major currently operating facilities (PSI, Fermilab). The following thesis projects are available:

• Characterization of innovative mixtures for future muon experiments

The aim of this thesis is to propose and characterize innovative gas mixtures for future muon experiments. Specifically, the goal is to replace isobutane, which promotes aging, with alternative gases that are eco-friendly, in line with the growing focus on sustainability in particle physics experiments at accelerators. Several potentially suitable mixtures have been identified, and the thesis involves using them to perform measurements similar to those described in the thesis "Characterization of the drift chamber mixture in the MEG II experiment."

• Simulation of a future experiment for the search of \( \mu^+ \to e^+ \gamma \)

The aim of this thesis is to develop components of a Geant4 simulation code for a future experiment searching for \( \mu^+ \to e^+ \gamma \), focusing on positron tracking using silicon detectors and photon reconstruction through their conversion into \( e^+ e^- \) pairs. In particular, it will be necessary to develop the code components that describe the geometry of the detectors and the generation of electronic signals within them.