Author
Shintaro Ito
Bio: Shintaro Ito is an academic researcher from KEK. The author has an hindex of 1, co-authored 1 publications receiving 1 citations.
Papers
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TL;DR: In this article, the first 90% C.L.L upper bound on branching ratios was obtained for weakly interacting boson with mass (X) l1.6.
Abstract: From analysis of data produced by the BABAR experiment, the first upper bounds (90% C.L.) were obtained on the branching ratios $\mathrm{Br}(\ensuremath{\tau}\ensuremath{\rightarrow}e\ensuremath{\gamma}\ensuremath{\gamma})l2.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ and $\mathrm{Br}(\ensuremath{\tau}\ensuremath{\rightarrow}\ensuremath{\mu}\ensuremath{\gamma}\ensuremath{\gamma})l5.8\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$. In addition, improved upper bounds (95% C.L.) were found on branching ratios $\mathrm{Br}(\ensuremath{\tau}\ensuremath{\rightarrow}eX)l1.4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ and $\mathrm{Br}(\ensuremath{\tau}\ensuremath{\rightarrow}\ensuremath{\mu}X)l\phantom{\rule{0ex}{0ex}}2.0\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$, where $X$ is an undetected weakly interacting boson with mass ${m}_{X}l1.6\text{ }\text{ }\mathrm{GeV}/{c}^{2}$.
6 citations
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TL;DR: In this article , the authors present an overview of searches for violation of lepton flavor universality with a focus on low energy precision probes using π, K, τ, and nuclear beta decays.
Abstract: We present an overview of searches for violation of lepton flavor universality with a focus on low energy precision probes using π, K, τ, and nuclear beta decays. We review the current experimental results, summarize the theoretical status within the context of the Standard Model, and discuss future prospects (both experimental and theoretical). We review the implications of these measurements for physics beyond the Standard Model by performing a global model-independent fit to modified W couplings to leptons and four-fermion operators. We also discuss new physics in the context of simplified models and review Standard Model extensions with a focus on those that can explain a possible deviation from unitarity of the Cabibbo–Kobayashi–Maskawa quark mixing matrix.
5 citations
TL;DR: In this paper, the authors studied the sensitivity of the Belle-II experiment to lepton flavor violation associated with a light leptophilic axion-like particle (ALP) in the tau decay.
Abstract: We study charged lepton flavor violation associated with a light leptophilic axion-like particle (ALP), $X$, at the $B$-factory experiment Belle II. We focus on production of the ALP in the tau decays $\tau \to X l$ with $l=e,\mu$, followed by its decay via $X\to l^- l^+$. The ALP can be either promptly decaying or long-lived. We perform Monte-Carlo simulations, recasting a prompt search at Belle for lepton-flavor-violating $\tau$ decays, and propose a displaced-vertex (DV) search. For both types of searches, we derive the Belle~II sensitivity reaches in both the product of branching fractions and the ALP coupling constants, as functions of the ALP mass and lifetime. The results show that the DV search exceeds the sensitivity reach of the prompt search to the relevant branching fractions by up to about a factor of 40 in the long decay length regime.
5 citations
TL;DR: In this article , the authors study the bounds that the ArgoNeuT experiment can put on the parameter space of two specific scenarios: leptophilic axionlike particles and Majorons.
Abstract: Axionlike particles are among the most studied extensions of the standard model. In this Letter we study the bounds that the ArgoNeuT experiment can put on the parameter space of two specific scenarios: leptophilic axionlike particles and Majorons. We find that such bounds are currently the most constraining ones in the (0.2--1.7) GeV mass range.
1 citations
TL;DR: In this article , an effective field theory analysis was performed to correlate the charged lepton flavor violating processes and derive model-independent upper bounds on the rates for these processes, which are about three orders of magnitude stronger than the direct bounds from current searches.
Abstract: We perform an effective field theory analysis to correlate the charged lepton flavor violating processes ${\ensuremath{\ell}}_{i}\ensuremath{\rightarrow}{\ensuremath{\ell}}_{j}\ensuremath{\gamma}\ensuremath{\gamma}$ and ${\ensuremath{\ell}}_{i}\ensuremath{\rightarrow}{\ensuremath{\ell}}_{j}\ensuremath{\gamma}$. Using the current upper bounds on the rate for ${\ensuremath{\ell}}_{i}\ensuremath{\rightarrow}{\ensuremath{\ell}}_{j}\ensuremath{\gamma}$, we derive model-independent upper limits on the rates for ${\ensuremath{\ell}}_{i}\ensuremath{\rightarrow}{\ensuremath{\ell}}_{j}\ensuremath{\gamma}\ensuremath{\gamma}$. Our indirect limits are about three orders of magnitude stronger than the direct bounds from current searches for $\ensuremath{\mu}\ensuremath{\rightarrow}e\ensuremath{\gamma}\ensuremath{\gamma}$, and four orders of magnitude better than current bounds for $\ensuremath{\tau}\ensuremath{\rightarrow}\ensuremath{\ell}\ensuremath{\gamma}\ensuremath{\gamma}$. We also stress the relevance of Belle II or a Super Tau Charm Facility to discover the rare decay $\ensuremath{\tau}\ensuremath{\rightarrow}\ensuremath{\ell}\ensuremath{\gamma}\ensuremath{\gamma}$.
1 citations
TL;DR: In this paper , the authors consider charged lepton flavor violating transitions mediated by the diphoton effective interactions and explore which processes can probe them better, finding that currently the best limits are provided by the loop-induced $\ell_i\to\ell_j\gamma$ processes.
Abstract: We consider charged lepton flavor violating transitions mediated by the diphoton effective interactions $\ell_i\ell_j\gamma\gamma$ and explore which processes can probe them better. Our analysis includes single and double radiative decays, $\ell_i\to\ell_j\gamma(\gamma)$, as well as $\ell_i\to\ell_j$ conversions in nuclei for all possible flavor combinations, which we compute for the first time for $\ell\to\tau$ conversions in this framework. We find that currently the best limits are provided by the loop-induced $\ell_i\to\ell_j\gamma$ processes, while the best future sensitivities come from $\mu\to e$ conversion in aluminum and from potential $\tau\to \ell\gamma\gamma$ searches at Belle II or at the Super Tau Charm Facility. We also motivate the search for $\mu\to e\gamma\gamma$ at the Mu3e experiment as a complementary probe of these operators.