arXiv subjects
Publications and source records attributed to B. Beckford.
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.
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.
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 $135~{\rm MeV}/c^2$.
A large-acceptance spectrometer, Neutral Kaon Spectrometer 2 (NKS2), was newly constructed to explore various photoproduction reactions in the gigaelectronvolt region at the Laboratory of Nuclear Science (LNS, currently ELPH), Tohoku University. The spectrometer consisted of a dipole magnet, drift chambers, and plastic scintillation counters. NKS2 was designed to separate pions and protons in a momentum range of less than 1 GeV/$c$, and was placed in a tagged photon beamline. A cryogenic H$_{2}$/D$_{2}$ target fitted to the spectrometer were designed. The design and performance of the detectors are described. The results of the NKS2 experiment on analyzing strangeness photoproduction data using a 0.8--1.1 GeV tagged photon beam are also presented.
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/$c^{2}$.
A study of the $^2$H$(γ,Λ)$X reaction was performed using a tagged photon beam at the Research Center for Electron Photon Science (ELPH), Tohoku University. The photoproduced $Λ$ was measured in the $p{π^{-}}$ decay channel by the upgraded Neutral Kaon Spectrometer (NKS2+). The momentum integrated differential cross section was determined as a function of the scatting angle of $Λ$ in the laboratory frame for five energy bins. Our results indicated a peak in the cross section at angles smaller than cos$θ^{LAB}_Λ$ = $0.96$. The experimentally obtained angular distributions were compared to isobar models, Kaon-Maid (KM) and Saclay-Lyon A (SLA), in addition to the composite Regge-plus-resonance (RPR) model. Both SLA(r$K_{1}K_γ$ = $-1.4$) and RPR describe the data quite well in contrast to the KM model, which substantially under predicted the cross section at the most forward angles. With the anticipated finalized data on $Λ$ integrated and momentum dependent differential cross sections of $^2$H$(γ,Λ)$X~\cite{Kaneta_Beckford}, we present our findings on the angular distributions in this report.
The collection efficiency for Cherenkov light incident on a wavelength shifting plate (WLS) has been determined during a beam test at the Proton Synchrotron facility located in the National Laboratory for High Energy Physics (KEK), Tsukuba, Japan. The experiment was conducted in order to determine the detector's response to photoelectrons converted from photons produced by a fused silica radiator; this allows for an approximation of the detector's quality. The yield of the photoelectrons produced through internally generated Cherenkov light as well as light incident from the radiator was measured as a function of the momentum of the incident hadron beam. The yield is proportional to sin$^2$$θ_c$, where $θ_{c}$ is the opening angle of the Cherenkov light created. Based on estimations and results from similarly conducted tests, where the collection efficiency was roughly 39%, the experimental result was expected to be around 40% for internally produced light from the WLS. The results of the experiment determined the photon collection response efficiency of the WLS to be roughly 62% for photons created in a fused silica radiator and 41% for light created in the WLS.
An experiment was carried out with the NKS2+ in 2010 at the Research Center for Electron Photon Science (ELPH), in which tagged photon beams in the range of 0.8 $\le$ $E_γ$ $\le$ 1.1 GeV were impinged on a liquid $^2$H target positioned at the center of the NKS2+. The produced $Λ$ was subsequently detected by the $p{π^{-}}$ decay channel. Integrated cross sections of the $^2$H$(γ,Λ)$X in the angular region of 0.9 $\le$ $\cosθ_Λ^{LAB}$ $\le$ 1.0 was derived and compared with preceding experimental results of the NKS2 collaboration. In addition, the momentum spectra for two photon energy regions were also procured. The $Λ$ angle dependent cross sections as a function of the scattering angle in the laboratory system was additionally deduced. We present the latest results on the excitation function of $Λ$ photoproduction, the momentum distributions, angular distributions, and polarization.
An experiment designed to investigate the strangeness photoproduction process using a tagged photon beam in the energy range of 0.90 -1.08 GeV incident on a liquid deuterium target was successfully performed. The purpose of the experiment was to measure the production of neutral kaons and the lambda particles on a deuteron. The generation of photo produced particles was verified by the measurement of their decayed charged particles in the Neutral Kaon Spectrometer 2. The reconstructed invariant mass distributions were achieved by selecting events where two or more particles tracks were identified. Preliminary results are presented here.