Nuclear physics. B, Proceedings, supplements最新文献

I first recall the relevance of the eighth-order and the tenth-order QED contributions to the muon $g-2$ in order to interpret the results to be obtained in the next-generation experiment of the muon $g-2$. We give the latest result of the numerical calculation of those contributions.

MuSIC is a new muon facility, which provides the world's highest intense muon beam with continuous time structure at Research Center of Nuclear Physics (RCNP), Osaka University. It's intensity is designed to be 10⁸ muons per second with only 0.4 kW proton beam. Such a high intense muon beam is very important for searches of rare decay processes, for example search for the muon to electron conversion.

We are developing a hybrid photo detector (HPD) for the Hyper-Kamiokande Project. Eight-inch HPDs were prepared to evaluate their performance. Based on the results from these measurements, HPDs achieve a better performance such as single photon separation than conventional PMTs. A verification study lasting a few years in a water tank is planned in 2013 to check their feasibility.

The COMET Experiment at J-PARC aims to search for a lepton-flavour violating process of muon to electron conversion in a muonic atom, ${\mu }^{-}N\to e^{-}N$, with a branching-ratio sensitivity of better than ${10}^{-16}$ in order to explore the parameter region predicted by most of well-motivated theoretical models beyond the Standard Model. The need for this sensitivity places several stringent requirements on both the beam-line and detector systems. The current R&D status and prospects of experiment are presented in addition to the experimental overview.

The aim of OPERA is to prove the existence of the ${\nu }_{\mu }\to {\nu }_{\tau }$ neutrino oscillation by detecting the τ lepton emitted in the ${\nu }_{\tau }$ CC interactions. Thanks to the sub-micron resolution of the emulsion technique, the τ decay topology is clearly identified. The accumulated number of neutrino events in the OPERA target until mid-September 2012 is about 16000. Among the sample of 4190 events analysed so-far, two candidate ${\nu }_{\tau }$ CC interactions have been identified. The first one was published in May 2010 and the second one was recently reported at the NEUTRINO 2012 conference in June 2012.

Recent studies of novel four-body lepton number violating decays of τ leptons and neutral B mesons are summarized and updated. These decays are assumed to be enhanced by the exchange of resonant Majorana neutrinos. It is shown that the ${\tau }^{-}\to {\pi }^{+}{l}^{-}{l}^{-}{\nu }_{\tau }$ decay channels, with $l=e$ or μ, can provide stronger constraints on the mixing vs. mass parameter space of resonant Majorana neutrinos than analogous three-body decays of charged B mesons.

A realistic model for the spin-one correlators guided by the large-$N_c$ limit of QCD is elaborated in terms of the meson decay constants, masses and energy-dependent widths, which are expanded in 1/n, where n is the radial excitation number. The matching onto OPE is performed up to NLO in 1/$N_c$. After applying the resulting constraints, the remaining free parameters are fitted to ALEPH and OPAL data on the related spectral functions. Excellent agreement with the data is found and the model yields, at large n, a spectrum of overlapping states coupling with essentially equal strength, in agreement with the large-$N_c$ predictions. This model provides a consistent and appropriate way to compute the impact of duality violations on the moments of the related spectral functions computed along the circle in the complex s-plane, and therefore to quantify its importance in the extraction of physical parameters like ${\alpha }_S\left(M_{\tau }^2\right)$.

We are searching for the $\mu \to e+\gamma$ in the MEG experiment. In order to improve the search sensitivity down to about 5 × 10⁻¹⁴, which is one order higher than the sensitivity goal of the current stage of the experiment. We are planning a major upgrade of the experiment including the upgrade of the liquid xenon (LXe) γ-ray detector. The main item of the upgrade of the xenon detector is a replacement of the current PMTs located on the γ-ray incident face with smaller photosensors such as MPPC. The energy and position resolutions are expected to be significantly improved, especially for the event where γ-ray converts at a shallow point in the LXe. Because the MPPC operational in liquid xenon is not yet commercially available, we are developing special MPPC in collaboration with Hamamatsu Photonics. The detection efficiency for LXe scintillation light is measured with prototype sensors and found to be already at the level necessary for the upgrade of the experiment.

An upgrade of the MEG experiment, which searches for the lepton flavor violating decay, $\mu \to e\gamma$, at the highest sensitivity ever, is planned in order to improve the sensitivity down to $\sim 5\times {10}^{-14}$. We plan to employ a stereo wire drift chamber with a unique volume for the tracking and a pixelated scintillation detector with silicon photomultiplier (SiPM) readout for the timing measurement with improved efficiency and resolutions. We will describe the expected performance and the R&D status of the new spectrometer especially focusing on the new timing counter, which is expected to contribute better resolution of the relative timing between positron and gamma-ray.