arXiv subjects

R. Valle

Publications and source records attributed to R. Valle.

6 recordsLinked to original sources

arXiv2013

New constraint on the existence of the mu+-> e+ gamma decay

The analysis of a combined data set, totaling 3.6 \times 10^14 stopped muons on target, in the search for the lepton flavour violating decay mu^+ -> e^+ gamma is presented. The data collected by the MEG experiment at the Paul Scherrer Institut show no excess of events compared to background expectations and yield a new upper limit on the branching ratio of this decay of 5.7 \times 10^-13 (90% confidence level). This represents a four times more stringent limit than the previous world best limit set by MEG.

hep-ex↗

arXiv2012

Development and commissioning of the Timing Counter for the MEG Experiment

The Timing Counter of the MEG (Mu to Electron Gamma) experiment is designed to deliver trigger information and to accurately measure the timing of the $e^+$ in searching for the decay $μ^+ \rightarrow e^+γ$. It is part of a magnetic spectrometer with the $μ^+$ decay target in the center. It consists of two sectors upstream and downstream the target, each one with two layers: the inner one made with scintillating fibers read out by APDs for trigger and track reconstruction, the outer one consisting in scintillating bars read out by PMTs for trigger and time measurement. The design criteria, the obtained performances and the commissioning of the detector are presented herein.

physics.ins-det↗

arXiv2011

New limit on the lepton-flavour violating decay mu -> e gamma

We present a new result based on an analysis of the data collected by the MEG detector at the Paul Scherrer Institut in 2009 and 2010, in search of the lepton flavour violating decay mu->e gamma. The likelihood analysis of the combined data sample, which corresponds to a total of 1.8 x 10**14 muon decays, gives a 90% C.L. upper limit of 2.4 x 10**-12 on the branching ratio of the mu->e gamma decay, constituting the most stringent limit on the existence of this decay to date.

hep-ex↗

arXiv2011

The Timing Counter of the MEG experiment: calibration and performance

The MEG detector is designed to test Lepton Flavor Violation in the $μ^+\rightarrow e^+γ$ decay down to a Branching Ratio of a few $10^{-13}$. The decay topology consists in the coincident emission of a monochromatic photon in direction opposite to a monochromatic positron. A precise measurement of the relative time $t_{e^+γ}$ is crucial to suppress the background. The Timing Counter (TC) is designed to precisely measure the time of arrival of the $e^+$ and to provide information to the trigger system. It consists of two sectors up and down stream the decay target, each consisting of two layers. The outer one made of scintillating bars and the inner one of scintillating fibers. Their design criteria and performances are described.

physics.ins-det↗

arXiv2010

A limit for the mu -> e gamma decay from the MEG experiment

A search for the decay mu -> e gamma, performed at PSI and based on data from the initial three months of operation of the MEG experiment, yields an upper limit on the branching ratio of BR(mu -> e gamma) < 2.8 x 10**-11 (90% C.L.). This corresponds to the measurement of positrons and photons from ~ 10**14 stopped mu-decays by means of a superconducting positron spectrometer and a 900 litre liquid xenon photon detector.

hep-ex↗

arXiv2008

Synthesis, crystal structure, microstructure, transport and magnetic properties of SmFeAsO and SmFeAs(O0.93F0.07)

SmFeAsO and the isostructural superconducting SmFeAs(O0.93F0.07) samples were prepared. Characterization by means of Rietveld refinement of X-ray powder diffraction data, scanning electron microscope observation, transmission electron microscope analysis, resistivity and magnetization measurements were carried out. Sintering treatment strongly improves the grain connectivity, but, on the other hand, induces a competition between the thermodynamic stability of the oxy-pnictide and Sm2O3, hence worsening the purity of the sample. In the pristine sample both magnetization and resistivity measurements clearly indicate that two different sources of magnetism are present: the former related to Fe ordering at 140 K and the latter due to the Sm ions that orders antiferromagnetically at low temperature. The feature at 140 K disappears in the F-substituted sample and, at low temperatures a superconducting transition appears. The magnetoresistivity curves of the F-substituted sample probably indicates very high critical field values.

cond-mat.supr-con↗