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Tesi etd-09032013-171715

Thesis type
Tesi di laurea magistrale
A cosmic ray telescope for the test of the upgraded MEG tracker
Corso di studi
relatore Nicolò, Donato
relatore Galli, Luca
Parole chiave
  • Nessuna parola chiave trovata
Data inizio appello
Riassunto analitico
The MEG experiment has been looking for the decay of the muon in the ultra rare lepton<br>flavour violating channel μ → eγ since 2009 and will conclude the data taking at the end of<br>summer 2013. This decay channel is forbidden by the minimal Standard Model of particle<br>interactions, which preserves lepton flavour. Extensions of the model predict μ → eγ, some<br>of them with a branching ratio close to the MEG sensitivity. The MEG collaboration recently<br>published the result of the analysis of the data collected in the years 2009-2011 setting an upper<br>limit to the branching ratio equal to 5.7 · 10−13 at 90% confidence level.<br>The MEG analysis consists in the reconstruction of the momentum of photons and positrons<br>coming from the muon decay at rest. The photons are detected by a scintillation electromagnetic<br>calorimeter which uses liquid xenon as a scintillating medium, while the positrons trajectories<br>are reconstructed through a set of drift chambers in a non homogeneous magnetic field and a<br>set of scintillation bar placed at the end of the tracker for the timing measurement.<br>The MEG upgrade will preserve the beam and target used by MEG while the calorimeter,<br>the timing counter and the tracking system will be subject to modification, especially the drift<br>chamber will have a totally new design. It will be a unique volume filled with a mixture of helium<br>and isobutane with more than 2000 wires almost two meters long. The required resolution of<br>the point of closest approach to the wire for the new drift chamber is of about 100 μm so that<br>a more sensitive tracking system is useful to test the effective performance of the chamber and<br>of the reconstruction algorithm. For this purpose a cosmic ray telescope has been set up.<br>The sensitive part of the telescope is made by four spare modules of the BaBar silicon vertex<br>tracker, the resolution of the hits on each plane depend on the pitch of the strips, 100 μm along<br>one direction and 50 μm along the other. The resolution at the height of the detector under<br>test, given by the errors on the fit parameters, is around 20 μm low enough to characterize the<br>MEG drift chamber prototypes.<br>In this thesis are described the steps needed to set the telescope in operating condition. The<br>programming of the FPGA and the microprocessor used to manage the communication (com-<br>mand and data transfer) between the PC and the SVT frontend chips. The noise analysis and<br>the investigation of the environmental conditions that affect the performance of the detectors.<br>Finally a description of the calibration, data acquisition, and data analysis software.<br>This cosmic ray telescope has a trigger rate around 0.3 Hertz, collecting more than 1500<br>reconstructed tracks per day, so that a sufficient statistic will be accumulated in a few day of<br>data acquisition.<br>The telescope will remain as a facility of the INFN section of Pisa available to test in house<br>any moderately compact detector.<br>