Characterization and simulation of drift chambers prototypes for the MEG II experiment
In: http://etd.adm.unipi.it/theses/available/etd-06242014-111434/, 2014
academicJournal
Zugriff:
The MEG experiment, located at the Paul Scherrer Institut near Zurich (Switzerland), searches for the lepton flavour violating decay μ+ → e+ + γ (1) The MEG collaboration has recently published a new upper limit on the branching ratio BR(μ+ → e+ + γ) < 5.7 · 10−13 (90% C.L.) The Standard Model does not predict violation of the flavour of charged-leptons, that means the decay (1) is forbidden by this theory, unless the recently discovered neu- trino oscillations are incorporated in the Standard Model: in this case, an experimentally unattainable branching ratio ∼ 10−55 is expected. Some Super-Symmetric extensions to the Standard Model predict the decay (1) in the range 10−11 − 10−14 , making the search worthwhile with a new upgraded apparatus. The MEG II experiment aims to reach a ten times lower limit on the branching ratio BR(μ+ → e+ + γ) < 6.0 · 10−14 in 3 years of data taking; studies on the upgrade have already started and will continue until 2015, then a first test run is expected to be done at the end of 2015. In order to achieve this result, an improvement of the detectors resolutions is mandatory: the two main detectors involved in the upgrade process are the magnetic spectrometer and the LXe calorimeter which, respectively, measure momentum and emission point of the positron and the photon energy, as well as the position of the photon conversion. The new improved drift chamber is designed with more than a thousand wires in a stereo configuration, immersed in a helium-isobutane gas mixture as active medium. The cham- ber allows for a 3-dimensional reconstruction of the positron trajectory. An increase by a factor 3 of the MEG muon-stopping rate is also foreseen in the MEG II upgrade, but it will affect the drift chamber performances during the detector operation. Fragmentation of the gas molecules in the avalanches causes formation of deposits along the wires, with a reduction of the gas gain or, in the extreme case, continous discharge of the chamber: this phenomenon is called ‘ageing’. The ...
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Characterization and simulation of drift chambers prototypes for the MEG II experiment
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Autor/in / Beteiligte Person: | ZERMINI, ALFREDO ; Grassi, Marco |
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Zeitschrift: | http://etd.adm.unipi.it/theses/available/etd-06242014-111434/, 2014 |
Veröffentlichung: | Pisa University, 2014 |
Medientyp: | academicJournal |
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