arXiv subjects

T. Inagaki

Publications and source records attributed to T. Inagaki.

At least 19 recordsLinked to original sources

arXiv2024

Search for the $K_{L} \to \pi^{0} \nu \bar{\nu}$ Decay at the J-PARC KOTO Experiment

We performed a search for the $K_L \to \pi^{0} \nu \bar{\nu}$ decay using the data taken in 2021 at the J-PARC KOTO experiment. With newly installed counters and new analysis method, the expected background was suppressed to $0.252\pm0.055_{\mathrm{stat}}$$^{+0.052}_{-0.067}$$_{\mathrm{syst}}$. With a single event sensitivity of $(9.33 \pm 0.06_{\rm stat} \pm 0.84_{\rm syst})\times 10^{-10}$, no events were observed in the signal region. An upper limit on the branching fraction for the decay was set to be $2.2\times10^{-9}$ at the 90% confidence level (C.L.), which improved the previous upper limit from KOTO by a factor of 1.4. With the same data, a search for $K_L \to \pi^{0} X^{0}$ was also performed, where $X^{0}$ is an invisible boson with a mass ranging from 1 MeV/$c^{2}$ to 260 MeV/$c^{2}$. For $X^{0}$ with a mass of 135 MeV/$c^{2}$, an upper limit on the branching fraction of $K_L \to \pi^{0} X^{0}$ was set to be $1.6\times10^{-9}$ at the 90% C.L.

hep-ex↗

arXiv2022

Search for the Pair Production of Dark Particles $X$ with $K_L^0 \to XX$, $X \to \gamma\gamma$

We present the first search for the pair production of dark particles $X$ via $K_L^0\to XX$ with $X$ decaying into two photons using the data collected by the KOTO experiment. No signal was observed in the mass range of 40 - 110 MeV/c$^2$ and 210 - 240 MeV/c$^2$. This sets upper limits on the branching fractions as $\mathcal{B}(K_L^0 \to XX)$ $<$ (1-4) $\times$ 10$^{-7}$ and $\mathcal{B}(K_L^0 \to XX)$ $<$ (1-2) $\times$ 10$^{-6}$ at the 90% confidence level for the two mass regions, respectively.

hep-ex↗

arXiv2021

First Search for the $K_L \to π^0 γ$ Decay

We report the first search for the $K_L \to π^0 γ$ decay, which is forbidden by Lorentz invariance, using the data from 2016 to 2018 at the J-PARC KOTO experiment. With a single event sensitivity of $(7.1\pm 0.3_{\rm stat.} \pm 1.6_{\rm syst.})\times 10^{-8}$, no candidate event was observed in the signal region. The upper limit on the branching fraction was set to be $1.7\times 10^{-7}$ at the 90\% confidence level.

hep-ex↗

arXiv2021

Study of the $K_L \!\to\! π^0 ν\overlineν$ Decay at the J-PARC KOTO Experiment

The rare decay $K_L \!\to\! π^0 ν\overlineν$ was studied with the dataset taken at the J-PARC KOTO experiment in 2016, 2017, and 2018. With a single event sensitivity of $( 7.20 \pm 0.05_{\rm stat} \pm 0.66_{\rm syst} ) \times 10^{-10}$, three candidate events were observed in the signal region. After unveiling them, contaminations from $K^{\pm}$ and scattered $K_L$ decays were studied, and the total number of background events was estimated to be $1.22 \pm 0.26$. We conclude that the number of observed events is statistically consistent with the background expectation. For this dataset, we set an upper limit of $4.9 \times 10^{-9}$ on the branching fraction of $K_L \!\to\! π^0 ν\overlineν$ at the 90% confidence level.

hep-ex↗

arXiv2019

Dark Matter in logarithmic $F(R)$ gravity

The logarithmic $R^2$-corrected $F(R)$ gravity is investigated as a prototype model of modified gravity theories with quantum corrections. By using the auxiliary field method, the model is described by the general relativity with a scalaron field. The scalaron field can be identified as an inflaton at the primordial inflation era. It is also one of the dark matter candidates in the dark energy era. It is found that a wide range of the parameters is consistent with the current observations of CMB fluctuations, dark energy and dark matter.

gr-qc↗

arXiv2019

Search for $K_L \!\to\! π^0 ν\overlineν$ and $K_L \!\to\! π^0 X^0$ Decays at the J-PARC KOTO Experiment

A search for the rare decay $K_L \!\to\! π^0 ν\overlineν$ was performed. With the data collected in 2015, corresponding to $2.2 \times 10^{19}$ protons on target, a single event sensitivity of $( 1.30 \pm 0.01_{\rm stat} \pm 0.14_{\rm syst} ) \times 10^{-9}$ was achieved and no candidate events were observed. We set an upper limit of $3.0 \times 10^{-9}$ for the branching fraction of $K_L \!\to\! π^0 ν\overlineν$ at the 90% confidence level (C.L.), which improved the previous limit by almost an order of magnitude. An upper limit for $K_L \!\to\! π^0 X^0$ was also set as $2.4 \times 10^{-9}$ at the 90% C.L., where $X^0$ is an invisible boson with a mass of $135~{\rm MeV}/c^2$.

hep-ex↗

arXiv2016

A new search for the $K_{L} \to π^0 ν\overlineν$ and $K_{L} \to π^{0} X^{0}$ decays

We searched for the $CP$-violating rare decay of neutral kaon, $K_{L} \to π^0 ν\overlineν$, in data from the first 100 hours of physics running in 2013 of the J-PARC KOTO experiment. One candidate event was observed while $0.34\pm0.16$ background events were expected. We set an upper limit of $5.1\times10^{-8}$ for the branching fraction at the 90\% confidence level (C.L.). An upper limit of $3.7\times10^{-8}$ at the 90\% C.L. for the $K_{L} \to π^{0} X^{0}$decay was also set for the first time, where $X^{0}$ is an invisible particle with a mass of 135 MeV/$c^{2}$.

hep-ex↗

arXiv2016

Long-lived neutral-kaon flux measurement for the KOTO experiment

The KOTO ($K^0$ at Tokai) experiment aims to observe the CP-violating rare decay $K_L \rightarrow π^0 ν\barν$ by using a long-lived neutral-kaon beam produced by the 30 GeV proton beam at the Japan Proton Accelerator Research Complex. The $K_L$ flux is an essential parameter for the measurement of the branching fraction. Three $K_L$ neutral decay modes, $K_L \rightarrow 3π^0$, $K_L \rightarrow 2π^0$, and $K_L \rightarrow 2γ$ were used to measure the $K_L$ flux in the beam line in the 2013 KOTO engineering run. A Monte Carlo simulation was used to estimate the detector acceptance for these decays. Agreement was found between the simulation model and the experimental data, and the remaining systematic uncertainty was estimated at the 1.4\% level. The $K_L$ flux was measured as $(4.183 \pm 0.017_{\mathrm{stat.}} \pm 0.059_{\mathrm{sys.}}) \times 10^7$ $K_L$ per $2\times 10^{14}$ protons on a 66-mm-long Au target.

physics.ins-det↗

arXiv2015

Regularization dependence on phase diagram in Nambu-Jona-Lasinio model

We study the regularization dependence on meson properties and the phase diagram of quark matter by using the two flavor Nambu-Jona-Lasinio model. We find that the meson properties and the phase structure do not show drastically difference depending the regularization procedures. We also find that the location or the existence of the critical end point highly depends on the regularization methods and the model parameters. Then we think that regularization and parameters are carefully considered when one investigates the QCD critical end point in the effective model studies.

hep-ph↗

arXiv2014

Next to leading order calculation with dimensional regularization in Nambu--Jona-Lasinio Model

The Nambu--Jona-Lasinio model is investigated in the $1/N_c$ expansion with the dimensional regularization. At the four-dimensional limit the meson propagators have simple forms in the leading order of the $1/N_c$ expansion. Thus the next to leading order calculation reduces to an ordinary one loop calculation. Here we obtain an explicit form of the $1/N_c$ correction and numerically evaluate the $N_c$ dependence for the gap equation.

hep-ph↗

arXiv2013

Regularization parameter independent analysis in Nambu-Jona-Lasinio model

Nambu-Jona-Lasinio model used to investigate low energy phenomena is nonrenormalizable, therefore the results depend on the regularization parameter in general. A possibility of the finite in four-dimensional limit and even the regularization parameter (this is dimension in the dimensional regularization scheme) independent analysis is shown in the leading order of the 1/Nc expansion.

hep-ph↗

arXiv2012

Phase diagram of Nambu-Jona-Lasinio model with dimensional regularization

We investigate the phase diagram on temperature-chemical potential plane in the Nambu-Jona-Lasinio model with the dimensional regularization. While the structure of the resulting diagram shows resemblance to the one in the frequently used cutoff regularization, some results of our study indicate striking difference between these regularizations. The diagram in the dimensional regularization exhibits strong tendency of the first order phase transition.

hep-ph↗

arXiv2011

Nonet meson properties in Nambu-Jona-Lasinio model with dimensional regularization at finite temperature and chemical potential

The nonet meson properties are studied in the Nambu-Jona-Lasinio model at finite temperature and chemical potential using dimensional regularization. This study leads to the reasonable description which is mainly similar to one obtained in the model with the cutoff regularization. However, remarkable differences between the two regularizations are observed in the behavior of the chiral phase transition at finite chemical potential.

hep-ph↗

arXiv2011

Study of the K0(L) --> pi0 pi0 nu nu-bar decay

The rare decay K0(L) --> pi0 pi0 nu nu-bar was studied with the E391a detector at the KEK 12-GeV proton synchrotron. Based on 9.4 x 10^9 K0L decays, an upper limit of 8.1 x 10^{-7} was obtained for the branching fraction at 90% confidence level. We also set a limit on the K0(L) --> pi0 pi0 X (X --> invisible particles) process; the limit on the branching fraction varied from 7.0 x 10^{-7} to 4.0 x 10^{-5} for the mass of X ranging from 50 MeV/c^2 to 200 MeV/c^2.

hep-ex↗

arXiv2010

Search for the decay $K_L^0 \rightarrow 3γ$

We performed a search for the decay $K_L^0 \rightarrow 3γ$ with the E391a detector at KEK. In the data accumulated in 2005, no event was observed in the signal region. Based on the assumption of $K_L^0 \rightarrow 3γ$ proceeding via parity-violation, we obtained the single event sensitivity to be $(3.23\pm0.14)\times10^{-8}$, and set an upper limit on the branching ratio to be $7.4\times10^{-8}$ at the 90% confidence level. This is a factor of 3.2 improvement compared to the previous results. The results of $K_L^0 \rightarrow 3γ$ proceeding via parity-conservation were also presented in this paper.

hep-ex↗

arXiv2010

Nonet meson properties in Nambu--Jona-Lasinio model with dimensional versus cutoff regularization

Nambu--Jona-Lasinio (NJL) model with Kobayashi-Maskawa-'t Hooft (KMT) term is one of low energy effective theory of QCD which includes the $U_A(1)$ anomaly. We investigate nonet meson properties in this model with three flavors of quarks. We employ two type of regularizations the dimensional and sharp cutoff ones. The model parameters are fixed phenomenologically for each regularization. Evaluating the kaon decay constant, the $η$ meson mass and the topological susceptibility, we show the regularization dependence of the results and discuss the applicability of the NJL model.

hep-ph↗

arXiv2009

High density quark matter in the NJL model with dimensional vs. cut-off regularization

We investigate color superconducting phase at high density in the extended Nambu--Jona-Lasinio model for the two flavor quarks. Because of the non-renormalizability of the model, physical observables may depend on the regularization procedure, that is why we apply two types of regularization, the cut-off and the dimensional one to evaluate the phase structure, the equation of state and the relationship between the mass and the radius of a dense star. To obtain the phase structure we evaluate the minimum of the effective potential at finite temperature and chemical potential. The stress tensor is calculated to derive the equation of state. Solving the Tolman-Oppenheimer-Volkoff equation, we show the relationship between the mass and the radius of a dense star. The dependence on the regularization is found not to be small for these phenomena in the color superconducting phase.

hep-ph↗

arXiv2009

Search for a light pseudoscalar particle in the decay $K^0_L \to π^0 π^0 X$

We performed a search for a light pseudoscalar particle $X$ in the decay $K_L^0->pi0pi0X$, $X->γγ$ with the E391a detector at KEK. Such a particle with a mass of 214.3 MeV/$c^2$ was suggested by the HyperCP experiment. We found no evidence for $X$ and set an upper limit on the product branching ratio for $K_L^0->pi0pi0X$, $X->γγ$ of $2.4 \times 10^{-7}$ at the 90% confidence level. Upper limits on the branching ratios in the mass region of $X$ from 194.3 to 219.3 MeV/$c^2$ are also presented.

hep-ex↗