arXiv subjects

H. Tamura

Publications and source records attributed to H. Tamura.

At least 19 recordsLinked to original sources

arXiv2025

Measurement of $\Lambda$ Polarization in the $\pi^{-}p \to K^{0} \Lambda$ Reaction at $p_{\pi^{-}}=1.33$ GeV/$c$ toward a New $\Lambda p$ Scattering Experiment

This paper presents high-precision experimental data of the polarization of the $\Lambda$ hyperon in the $\pi^{-}p \to K^{0} \Lambda$ reaction, measured in the angular range $0.6<\cos \theta ^{CM}_{K0}<1.0$ with a fine bin width of $d\cos \theta ^{CM}_{K0}=0.05$. The data were obtained from the J-PARC E40 experiment at the K1.8 beamline in the J-PARC Hadron Experimental Facility. The observed average polarization of $\Lambda$ in the range $0.60<\cos \theta ^{CM}_{K0}<0.85$ was $0.932 \pm 0.058 \,(\text{stat}) \pm 0.028 \,(\text{syst})$, demonstrating the successful extraction of precise polarization observables. This result provides essential experimental input for partial wave analysis (PWA) of dynamical coupled-channel (DCC) models, which aim to uncover the underlying mechanisms of $N^{*}$ resonances that emerge in intermediate states of $\pi N$ and $\gamma N$ interactions. Besides, it indicates the feasibility of a strongly polarized $\Lambda$ beam suitable for future $\Lambda p$ scattering experiments (e.g., J-PARC E86).

nucl-ex↗

arXiv2024

Mini-Proceedings of the "Fourth International Workshop on the Extension Project for the J-PARC Hadron Experimental Facility (HEF-ex 2024)"

The mini proceedings of the "Fourth International Workshop on the Extension Project for the J-PARC Hadron Experimental Facility (HEF-ex 2024) [https://kds.kek.jp/event/46965]" held at J-PARC, February 19-21, 2024, are presented. The workshop was devoted to discussing the physics case that connects both the present and the future Hadron Experimental Facility at J-PARC, covering a wide range of topics in flavor, hadron, and nuclear physics related to both experimental and theoretical activities being conducted at the facility.

nucl-ex↗

arXiv2022

Measurement of differential cross sections for $\Sigma^+p$ elastic scattering in the momentum range 0.44-0.80 GeV/c

We performed a novel $\Sigma^+ p$ scattering experiment at the J-PARC Hadron Experimental Facility. Approximately 2400 $\Sigma^+ p$ elastic scattering events were identified from $4.9 \times 10^7$ tagged $\Sigma^+$ particles in the $\Sigma^+$ momentum range 0.44 -- 0.80 GeV/$c$. The differential cross sections of the $\Sigma^+ p$ elastic scattering were derived with much better precision than in previous experiments. The obtained differential cross sections were approximately 2 mb/sr or less, which were not as large as those predicted by the fss2 and FSS models based on the quark cluster model in the short-range region. By performing phase-shift analyses for the obtained differential cross sections, we experimentally derived the phase shifts of the $^3 S_1$ and $^1 P_1$ channels for the first time. The phase shift of the $^3 S_1$ channel, where a large repulsive core was predicted owing to the Pauli effect between quarks, was evaluated as $20^\circ<|\delta_{^3S_1}|<35^\circ$. If the sign of $\delta_{^3S_1}$ is assumed to be negative, the interaction in this channel is moderately repulsive, as the Nijmegen extended-sort-core models predicted.

nucl-ex↗

arXiv2021

Precise measurement of differential cross sections of the {\Sigma}-p --> {\Lambda} n reaction in momentum range 470-650 MeV/c

The differential cross sections of the {\Sigma}-p --> {\Lambda} n reaction were measured accurately for the {\Sigma}- momentum (p_{{\Sigma}}) ranging from 470 to 650 MeV/c at the J-PARC Hadron Experimental Facility. Precise angular information about the {\Sigma}-p --> {\Lambda} n reaction was obtained for the first time by detecting approximately 100 reaction events at each angular step of {\Delta}cos{\theta} = 0.1. The obtained differential cross sections show slightly forward-peaking structure in the measured momentum regions.The cross sections integrated for -0.7 < cos{\theta} < 1.0 were obtained as 22.5 +- 0.68 (stat.) +- 0.65 (syst.) mb and 15.8 +-0.83(stat.) +- 0.52 (syst.) mb for 470<p_{{\Sigma}}(MeV/c)<550 and 550<p_{{\Sigma}}(MeV/c)<650, respectively. These results show a drastic improvement compared to past measurements of the hyperon-proton scattering experiments. They will play essential roles in updating the theoretical models of the baryon-baryon interactions.

nucl-ex↗

arXiv2021

Development and application of CATCH: A cylindrical active tracker and calorimeter system for hyperon-proton scattering experiments

In this study, we developed a new proton detector system called CATCH, which was designed for a scattering experiment involving a $\Sigma$ hyperon and a proton (J-PARC E40). CATCH is a cylindrical detector system covering an inner target that can be used to measure the trajectory and energy of a proton emitted from the target for the kinematic identification of a $\Sigma$p scattering event. It comprises a cylindrical fiber tracker (CFT), a bismuth germanate (BGO) calorimeter, and a plastic scintillator hodoscope (PiID), which are coaxially arranged from the inner to the outer sides. The CFT is a tracking detector consisting of 5,000 scintillation fibers, and it has two types of cylindrical layers in which the fibers are arranged in straight and spiral configurations. 24 BGO crystals are placed around the CFT to measure the kinetic energy of the recoil proton. The PiID is used to determine whether the recoil proton is stopped in the BGO calorimeter. We performed proton-proton (pp) and proton-carbon (pC) scattering experiments using an 80 MeV proton beam to evaluate the performance of CATCH. The total energy resolution for the recoil proton was 2.8 MeV in $\sigma$ for the entire angular region after the energy calibrations of the BGO calorimeter and the CFT. The angular resolution of the CFT was 1.27 degrees in $\sigma$ for the proton, and the time resolution was more than 1.8 ns in $\sigma$. We also developed an analysis method for deriving the cross section of the pp scattering using CATCH. The obtained relative differential cross section for the pp elastic scattering was consistent with that obtained by reliable partial wave analysis, and the systematic error was maintained at below 10%. These performance results satisfy our requirements for a reliable detection system for the $\Sigma$p scattering experiment conducted at J-PARC .

physics.ins-det↗

arXiv2021

Measurement of the differential cross sections of the Sigma-p elastic scattering in momentum range of 470 to 850 MeV/c

A high statistics $\Sigma p$ scattering experiment has been performed at the J-PARC Hadron Experimental Facility. Data for momentum-tagged $\Sigma^{-}$ running in a liquid hydrogen target were accumulated by detecting the $\pi^{-}p \to K^{+}\Sigma^{-}$ reaction with a high intensity $\pi^{-}$ beam of 20 M/spill. Differential cross sections of the $\Sigma^{-}p$ elastic scattering were derived with a drastically improved accuracy by identifying the largest statistics of about 4,500 events from 1.72 $\times$ $10^{7}$ $\Sigma^{-}$. The derived differential cross section shows a clear forward-peaking angular distribution for a $\Sigma^{-}$ momentum range from 470 to 850 MeV/$c$. The accurate data will impose a strong constraint on the theoretical models of the baryon-baryon interactions.

nucl-ex↗

arXiv2021

First observation of a nuclear $s$-state of $\Xi$ hypernucleus, $^{15}_{\Xi}{\rm C}$

Bound-systems of $\Xi^-$--$^{14}_{}{\rm N}$ are studied via $\Xi^-$ capture at rest followed by emission of a twin single-$\Lambda$ hypernucleus in the emulsion detectors. Two events forming extremely deep $\Xi^-$ bound states were obtained by analysis of a hybrid method in the E07 experiment at J-PARC and reanalysis of the E373 experiment at KEK-PS. The decay mode of one event was assigned as $\Xi^-+^{14}_{}{\rm N}\to^{5}_{\Lambda}{\rm He}$+$^{5}_{\Lambda}{\rm He}$+$^{4}_{}{\rm He}$+n. Since there are no excited states for daughter particles, the binding energy of the $\Xi^-$ hyperon, $B_{\Xi^-}$, in $^{14}_{}{\rm N}$ nucleus was uniquely determined to be 6.27 $\pm$ 0.27 MeV. Another $\Xi^-$--$^{14}_{}{\rm N}$ system via the decay $^{9}_{\Lambda}{\rm Be}$ + $^{5}_{\Lambda}{\rm He}$ + n brings a $B_{\Xi^-}$ value, 8.00 $\pm$ 0.77 MeV or 4.96 $\pm$ 0.77 MeV, where the two possible values of $B_{\Xi^-}$ correspond to the ground and the excited states of the daughter $^{9}_{\Lambda}{\rm Be}$ nucleus, respectively. Because the $B_{\Xi^-}$ values are larger than those of the previously reported events (KISO and IBUKI), which are both interpreted as the nuclear $1p$ state of the $\Xi^-$--$^{14}_{}{\rm N}$ system, these new events give the first indication of the nuclear $1s$ state of the $\Xi$ hypernucleus, $^{15}_{\Xi}{\rm C}$.

nucl-ex↗

arXiv2021

Observation of Coulomb-assisted nuclear bound state of $Ξ^-$-$^{14}$N system

In an emulsion-counter hybrid experiment performed at J-PARC, a $Ξ^-$ absorption event was observed which decayed into twin single-$Λ$ hypernuclei. Kinematic calculations enabled a unique identification of the reaction process as $Ξ^{-} + ^{14}$N$\ \rightarrow\ ^{10}_Λ$Be + $^5_Λ$He. For the binding energy of the $Ξ^{-}$ hyperon in the $Ξ^-$-$^{14}$N system a value of $1.27 \pm 0.21$ MeV was deduced. The energy level of $Ξ^-$ is likely a nuclear $1p$ state which indicates a weak $ΞN$-$ΛΛ$ coupling.

nucl-ex↗

arXiv2019

Jump Markov Chains and Rejection-Free Metropolis Algorithms

We consider versions of the Metropolis algorithm which avoid the inefficiency of rejections. We first illustrate that a natural Uniform Selection Algorithm might not converge to the correct distribution. We then analyse the use of Markov jump chains which avoid successive repetitions of the same state. After exploring the properties of jump chains, we show how they can exploit parallelism in computer hardware to produce more efficient samples. We apply our results to the Metropolis algorithm, to Parallel Tempering, to a Bayesian model, to a two-dimensional ferromagnetic 4 x 4 Ising model, and to a pseudo-marginal MCMC algorithm.

math.ST↗

arXiv2019

Observation of a Be double-Lambda hypernucleus in the J-PARC E07 experiment

A double-$Λ$ hypernucleus, ${}_{ΛΛ}\mathrm{Be}$, was observed by the J-PARC E07 collaboration in nuclear emulsions tagged by the $(K^{-},K^{+})$ reaction. This event was interpreted as a production and decay of $ {}_{ΛΛ}^{\;10}\mathrm{Be}$, ${}_{ΛΛ}^{\;11}\mathrm{Be}$, or ${}_{ΛΛ}^{\;12}\mathrm{Be}^{*}$ via $Ξ^{-}$ capture in ${}^{16}\mathrm{O}$. By assuming the capture in the atomic 3D state, the binding energy of two $Λ$ hyperons$\,$($B_{ΛΛ}$) of these double-$Λ$ hypernuclei are obtained to be $15.05 \pm 0.11\,\mathrm{MeV}$, $19.07 \pm 0.11\,\mathrm{MeV}$, and $13.68 \pm 0.11\,\mathrm{MeV}$, respectively. Based on the kinematic fitting, ${}_{ΛΛ}^{\;11}\mathrm{Be}$ is the most likely explanation for the observed event.

nucl-ex↗

arXiv2018

Ultrafast carbon monoxide photolysis and heme spin-crossover in myoglobin via nonadiabatic quantum dynamics

Light absorption of myoglobin triggers diatomic ligand photolysis and spin crossover transition of iron(II) that initiate protein conformational change. The photolysis and spin crossover reactions happen concurrently on a femtosecond timescale. The microscopic origin of these reactions remains controversial. Here, we apply quantum wavepacket dynamics to elucidate the ultrafast photochemical mechanism for a heme--carbon monoxide (heme--CO) complex. We observe coherent oscillations of the Fe-CO bond distance with a period of 42 fs and an amplitude of $\sim$1 Å. These nuclear motions induce pronounced geometric reorganization, which makes the CO dissociation irreversible. The reaction is initially dominated by symmetry breaking vibrations inducing an electron transfer from porphyrin to iron. Subsequently, the wavepacket relaxes to the triplet manifold in $\sim$75 fs and to the quintet manifold in $\sim$430 fs. Our results highlight the central role of nuclear vibrations at the origin of the ultrafast photodynamics of organometallic complexes.

physics.chem-ph↗

arXiv2017

First Determination of Level Structure of an $sd$-Shell Hypernucleus, $\rm {^{19}_ΛF}$

We report on the first observation of $γ$ rays emitted from an $sd$-shell hypernucleus, $\rm ^{19}_ΛF$. The energy spacing between the ground state doublet, $1/2^{+}$ and $3/2^{+}$ states, of $\rm ^{19}_ΛF$ is determined to be $\rm 315.5 \pm 0.4 (stat) ^{+0.6}_{-0.5} (syst)~keV$ by measuring the $γ$-ray energy from the $M1(3/2^{+} \rightarrow 1/2^{+})$ transition. In addition, three $γ$-ray peaks were observed and assigned as $E2(5/2^{+} \rightarrow 1/2^{+})$, $E1(1/2^{-} \rightarrow 1/2^{+})$, and $E1(1/2^{-} \rightarrow 3/2^{+})$ transitions. The excitation energies of the $5/2^{+}$ and $1/2^{-}$ states are determined to be $\rm 895.2 \pm 0.3 (stat) \pm 0.5 (syst)~keV$ and $\rm 1265.6 \pm 1.2 (stat) ^{+0.7}_{-0.5} (syst)~keV$, respectively. It is found that the ground state doublet spacing is well described by theoretical models based on existing $s$- and $p$-shell hypernuclear data.

nucl-ex↗

arXiv2017

Missing-mass spectroscopy with the ${}^{6}$Li($π^{-}, K^{+}$)X reaction to search for ${}^{6}_Λ$H

We searched for the bound state of the neutron-rich $Λ$-hypernucleus ${}^{6}_Λ$H, using the ${}^{6}$Li($π^{-}, K^{+}$)X double charge-exchange reaction at a $π^{-}$ beam momentum of 1.2 GeV/c at J-PARC. A total of $1.4 \times 10^{12}$ $π^{-}$ was driven onto a ${}^{6}$Li target of 3.5-g/$\rm cm^2$ thickness. No event was observed below the bound threshold, i.e., the mass of ${}^{4}_Λ$H + 2n, in the missing-mass spectrum of the ${}^{6}$Li($π^{-}, K^{+}$)X reaction in the $2^{\circ}$ < $θ_{πK}$ < $20^{\circ}$ angular range. Furthermore, no event was found up to 2.8 MeV/$c^2$ above the bound threshold. We obtained the the double-differential cross section spectra of the ${}^{6}$Li($π^{-}, K^{+}$)X reaction in the angular range of $2^{\circ}$ < $θ_{πK}$ < $14^{\circ}$. An upper limit of 0.56 nb/sr (90% C.L.) was obtained for the production cross section of the ${}^{6}_Λ$H hypernucleus bound state. In addition, not only the bound state region, but also the $Λ$ continuum region and part of the $Σ^{-}$ quasi-free production region of the ${}^{6}$Li($π^{-}, K^{+}$)X reaction, were obtained with high statistics. The present missing-mass spectrum will facilitate the investigation of the $Σ^{-}$-nucleus optical potential for $Σ^{-}$-${}^{5}$He through spectrum shape analysis.

nucl-ex↗

arXiv2015

Observation of Spin-Dependent Charge Symmetry Breaking in $ΛN$ Interaction: Gamma-Ray Spectroscopy of $^4_{Λ}$He

The energy spacing between the ground-state spin doublet of $^4_Λ$He(1$^+$,0$^+$) was determined to be $1406 \pm 2 \pm 2$ keV, by measuring $γ$ rays for the $1^+ \to 0^+$ transition with a high efficiency germanium detector array in coincidence with the $^4$He$(K^-,π^-)$ $^4_Λ$He reaction at J-PARC. In comparison to the corresponding energy spacing in the mirror hypernucleus $^4_Λ$H, the present result clearly indicates the existence of charge symmetry breaking (CSB) in $ΛN$ interaction. It is also found that the CSB effect is large in the $0^+$ ground state but is by one order of magnitude smaller in the $1^+$ excited state, demonstrating that the $ΛN$ CSB interaction has spin dependence.

nucl-ex↗

arXiv2015

Precise determination of $^{12}_Λ$C level structure by $γ$-ray spectroscopy

Level structure of the $^{12}_Λ$C hypernucleus was precisely determined by means of $γ$-ray spectroscopy. We identified four $γ$-ray transitions via the $^{12}$C$(π^{+},K^{+}γ)$ reaction using a germanium detector array, Hyperball2. The spacing of the ground-state doublet $(2^{-}_{1},1^{-}_{1})$ was measured to be $161.5\pm0.3\text{(stat)}\pm0.3\text{(syst)}$\,keV from the direct $M1$ transition. Excitation energies of the $1^{-}_{2}$ and $1^{-}_{3}$ states were measured to be $2832\pm3\pm4$\,keV and $6050\pm8\pm7$\,keV, respectively. The obtained level energies provide definitive references for the reaction spectroscopy of $Λ$ hypernuclei.

nucl-ex↗

arXiv2014

Near threshold angular distributions of the $^2$H$(γ,Λ)$X reaction

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.

nucl-ex↗

arXiv2014

High-resolution search for the $Θ^{+}$ pentaquark via a pion-induced reaction at J-PARC

The pentaquark $Θ^+$ has been searched for via the $π^-p \to K^-X$ reaction with beam momenta of 1.92 and 2.01 GeV/$c$ at J-PARC. A missing mass resolution of 2 MeV (FWHM) was achieved but no sharp peak structure was observed. The upper limits on the production cross section averaged over the scattering angle from 2$^{\circ}$ to 15$^{\circ}$ in the laboratory frame were found to be less than 0.28 $μ$b/sr at the 90\% confidence level for both the 1.92- and 2.01-GeV/$c$ data. The systematic uncertainty of the upper limits was controlled within 10\%. Constraints on the $Θ^+$ decay width were also evaluated with a theoretical calculation using effective Lagrangian. The present result implies that the width should be less than 0.36 and 1.9 MeV for the spin-parity of $1/2^+$ and $1/2^-$, respectively.

nucl-ex↗

arXiv2014

Search for $^6_Λ$H hypernucleus by the $^6$Li$(π^-,K^+)$ reaction at $p_{π^-}$ = 1.2 GeV/$c$

We have carried out an experiment to search for a neutron-rich hypernucleus, $^6_Λ$H, by the $^6$Li($π^-,K^+$) reaction at $p_{π^-}$ =1.2 GeV/$c$. The obtained missing mass spectrum with an estimated energy resolution of 3.2 MeV (FWHM) showed no peak structure corresponding to the $^6_Λ$H hypernucleus neither below nor above the $^4_Λ$H$+2n$ particle decay threshold. An upper limit of the production cross section for the bound $^6_Λ$H hypernucleus was estimated to be 1.2 nb/sr at 90% confidence level.

nucl-ex↗