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Yoshitaka Kuno

Publications and source records attributed to Yoshitaka Kuno.

25 records · Page 2Linked to original sources
arXiv2004

A study of late decaying charged particles at future colliders

In models where the gravitino is the lightest supersymmetric particle (LSP), the next-to-lightest supersymmetric particle (NLSP) is long-lived. We consider an important charged NLSP candidate, the scalar tau $\tildeτ$. Slow charged NLSPs may be produced at future colliders and they may be stopped in a massive stopper which simultaneously serves as a detector for the NLSP and its decay products. We found the number of events at a 1 kton to O(10) kton detector could be significant enough to study the NLSP decays with lifetime shorter than $10^{10}$ sec at the LHC. The performance of existing 1 kton detectors may be good enough to do such studies at the LHC, if they can be placed close to the ATLAS/CMS detectors. At a future $e^- e^-$ collider, scalar electrons $\tilde{e}^-$s are copiously produced. Slow NLSPs may be produced from the $\tilde{e}^-$ decay. The number of stopped NLSPs at a future linear collider could be large enough to study rare decay modes of the NLSP.

hep-ph↗
arXiv2001

The matter effect to T-violation at a neutrino factory

We analyzed T-violation in neutrino oscillation by using perturbation methods with respect to $Δm_{21}^2L/2E$ and $δa(x)L/2E$, where $δa(x)$ represents the matter density fluctuation from its average value. We found that the matter contribution to T-violation arises from interferences between $Δm_{21}^2L/2E$ and $δa(x) L/2E$. In the 2nd order, the symmetric and asymmetric matter density fluctuations give effects to the $\sin δ$ (intrinsic) and the $\cos δ$ (fake) parts of T-violation. We give their analytic forms and analyze the matter contribution to the $\sin δ$ and $\cos δ$ terms. We found that, for L=3000km, both the symmetric and asymmetric matter density fluctuations give negligible contributions to T-violation, and that thus the constant (average) matter density gives a good approximation. On the other hand, we argue that, for L=7000km or longer length, T-violation turns out to become very small due to cancellation between the 1st and the 2nd order terms. This shows that the constant (average) matter approximation is not valid.

hep-ph↗
arXiv1999

Muon Decay and Physics Beyond the Standard Model

This article reviews the current theoretical and experimental status of the field of muon decay and its potential to search for new physics beyond the Standard Model. The importance of rare muon processes with lepton flavor violation is highly stressed, together with precision measurements of normal muon decay. Recent up-to-date motivations of lepton flavor violation based on supersymmetric models, in particular supersymmetric grand unified theories, are described along with other theoretical models. Future prospects of experiments and muon sources of high intensity for further progress in this field are also discussed.

hep-ph↗
arXiv1996

Background Suppression for $μ\to eγ$ with Polarized Muons

A search for the lepton-flavor violating $μ^{+}\rightarrow e^{+}γ$ decay using polarized muons is revisited in terms of suppression of the serious background arising from an accidental coincidence between a $e^{+}$ in the normal muon decay and a high energy photon in the radiative muon decay, $μ^{+} \rightarrow e^{+} ν\overlineν γ$. It is found that a high energy photon in $μ^{+} \rightarrow e^{+} ν\overlineν γ$ decay is preferentially emitted parallel to the muon spin direction, similarly to $e^{+}$ in the normal muon decay. The selective measurements of either $e^{+}$s or photons moving antiparallel to the muon spin direction would suppress the accidental background for $μ^{+} \rightarrow e^{+} γ$ with right-handed and left-handed $e^{+}$s respectively.

hep-ph↗
arXiv1996

Muon Polarization Working Group Report

We have examined the physics and the experimental feasibility at the AGS of various kaon decay processes in which the polarization of a muon in the final state is measured. Valuable information on CP violation, the CKM matrix or new physics can be obtained with these measurements and therefore they are well motivated. In particular, models of non-standard CP violation that produce the baryon asymmetry of the universe could also produce effects observable in these measurements. Limits from measurements such as the neutron and electron electric dipole moment, and epsilon-prime over epsilon in neutral kaon decays do not eliminate all of these models. We have made a more detailed examination of the measurement of the out of the plane muon polarization in Kmu3 decays. With our current knowledge of the AGS kaon beams and detector techniques it is possible to measure this polarization with an error approaching 10**-4. Such an experiment would be well justified since the sensitivity is well beyond the current direct experimental limit (5.3 times 10**-3) and the projected sensitivity (10**-3) of the currently running experiment at KEK in Japan.

hep-ex↗
arXiv1996

$μ\to eγ$ Search with Polarized Muons

A search for the lepton-flavor violating $μ^{+}\rightarrow e^{+}γ$ decay using polarized muons is proposed. By measuring the angular distribution of $e^{+}$s with respect to the muon spin direction, in particular antiparallel $e^{+}$s, the serious physics background from $μ^{+}\rightarrow e^{+}ν\overlineνγ$ as well as accidental background from normal muon decay accompanied by a high-energy photon can be suppressed significantly. In addition to the enhancement of the sensitivity, the angular distribution would discriminate among different extensions to the Standard Model, once the signal is observed.

hep-ph↗