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Register a new userPolarization measurements and their perspectives: PVLAS Phase II
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G. Cantatore
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We sketch the proposal for a PVLAS-Phase II experiment. The main physics goal is to achieve the first direct observation of non-linear effects in electromagnetism predicted by QED and the measurement of the photon-photon scattering cross section at low energies (1-2 eV). Physical processes such as ALP and MCP production in a magnetic field could also be accessible if sensitive enough operation is reached. The short term experimental strategy is to compact as much as possible the dimensions of the apparatus in order to bring noise sources under control and to attain a sufficient sensitivity. We will also briefly mention future pespectives, such as a scheme to implement the resonant regeneration principle for the detection of ALPs.
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The MEG experiment makes use of one of the worlds most intense low energy muon beams, in order to search for the lepton flavour violating process $mu^{+} rightarrow {rm e}^{+} gamma$. We determined the residual beam polarization at the thin stopping target, by measuring the asymmetry of the angular distribution of Michel decay positrons as a function of energy. The initial muon beam polarization at the production is predicted to be $P_{mu} = -1$ by the Standard Model (SM) with massless neutrinos. We estimated our residual muon polarization to be $P_{mu} = -0.85 pm 0.03 ~ {rm (stat)} ~ { }^{+ 0.04}_{-0.05} ~ {rm (syst)}$ at the stopping target, which is consistent with the SM predictions when the depolarizing effects occurring during the muon production, propagation and moderation in the target are taken into account. The knowledge of beam polarization is of fundamental importance in order to model the background of our ${megsign}$ search induced by the muon radiative decay: $mu^{+} rightarrow {rm e}^{+} bar{ u}_{mu} u_{rm e} gamma$.
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The GERmanium Detector Array (GERDA) experiment at the Gran Sasso underground laboratory (LNGS) of INFN is searching for neutrinoless double-beta ($0 ubetabeta$) decay of $^{76}$Ge. The technological challenge of GERDA is to operate in a background-free regime in the region of interest (ROI) after analysis cuts for the full 100$,$kg$cdot$yr target exposure of the experiment. A careful modeling and decomposition of the full-range energy spectrum is essential to predict the shape and composition of events in the ROI around $Q_{betabeta}$ for the $0 ubetabeta$ search, to extract a precise measurement of the half-life of the double-beta decay mode with neutrinos ($2 ubetabeta$) and in order to identify the location of residual impurities. The latter will permit future experiments to build strategies in order to further lower the background and achieve even better sensitivities. In this article the background decomposition prior to analysis cuts is presented for GERDA Phase II. The background model fit yields a flat spectrum in the ROI with a background index (BI) of $16.04^{+0.78}_{-0.85} cdot 10^{-3},$cts/(kg$cdot$keV$cdot$yr) for the enriched BEGe data set and $14.68^{+0.47}_{-0.52} cdot 10^{-3},$cts/(kg$cdot$keV$cdot$yr) for the enriched coaxial data set. These values are similar to the one of Gerda Phase I despite a much larger number of detectors and hence radioactive hardware components.
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