Observation of Spin-Dependent Charge Symmetry Breaking in ΛN\Lambda N Interaction: Gamma-Ray Spectroscopy of Λ4^4_{\Lambda }He

The energy spacing between the ground-state spin doublet of $^4_\Lambda$He(1$^+$,0$^+$) was determined to be $1406 \pm 2 \pm 2$ keV, by measuring $\gamma$ rays for the $1^+ \to 0^+$ transition with a high efficiency germanium detector array in coincidence with the $^4$He$(K^-,\pi^-)$ $^4_\Lambda$He reaction at J-PARC. In comparison to the corresponding energy spacing in the mirror hypernucleus $^4_\Lambda$H, the present result clearly indicates the existence of charge symmetry breaking (CSB) in $\Lambda N$ 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 $\Lambda N$ CSB interaction has spin dependence

Search for the Θ+\Theta^{+} pentaquark via the π−p→K−X\pi^-p\to K^-X reaction at 1.92 GeV/cc

The $\Theta^+$ pentaquark baryon was searched for via the $\pi^-p\to K^-X$ reaction in a missing-mass resolution of 1.4 MeV/$c^2$(FWHM) at J-PARC. $\pi^-$ meson beams were incident on the liquid hydrogen target with the beam momentum of 1.92 GeV/$c$. No peak structure corresponding to the $\Theta^+$ mass was observed. The upper limit of the production cross section averaged over the scattering angle of 2$^{\circ}$ to 15$^{\circ}$ in the laboratory frame was obtained to be 0.26 $\mu$b/sr in the mass region of 1.51$-$1.55 GeV/$c^2$.The upper limit of the $\Theta^+$ decay width using the effective Lagrangian approach was obtained to be 0.72 MeV/$c^2$ and 3.1 MeV/$c^2$ for $J^P_{\Theta}=1/2^+$ and $J^P_{\Theta}=1/2^-$, respectively.Comment: 5 pages, 3 figures, 1 tabl

Search for Λ6^6_\LambdaH hypernucleus by the 6^6Li(π−,K+)(\pi^-,K^+) reaction at pπ−p_{\pi^-} = 1.2 GeV/cc

We have carried out an experiment to search for a neutron-rich hypernucleus, $^6_{\Lambda}$H, by the $^6$Li($\pi^-,K^+$) reaction at $p_{\pi^-}$ =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 $^6_{\Lambda}$H hypernucleus neither below nor above the $^4_{\Lambda}$H$+2n$ particle decay threshold. An upper limit of the production cross section for the bound $^6_{\Lambda}$H hypernucleus was estimated to be 1.2 nb/sr at 90% confidence level.Comment: 6 pages, 5 figures, published versio

Acute Insulin Stimulation Induces Phosphorylation of the Na-Cl Cotransporter in Cultured Distal mpkDCT Cells and Mouse Kidney

The NaCl cotransporter (NCC) is essential for sodium reabsorption at the distal convoluted tubules (DCT), and its phosphorylation increases its transport activity and apical membrane localization. Although insulin has been reported to increase sodium reabsorption in the kidney, the linkage between insulin and NCC phosphorylation has not yet been investigated. This study examined whether insulin regulates NCC phosphorylation. In cultured mpkDCT cells, insulin increased phosphorylation of STE20/SPS1-related proline-alanine-rich kinase (SPAK) and NCC in a dose-dependent manner. This insulin-induced phosphorylation of NCC was suppressed in WNK4 and SPAK knockdown cells. In addition, Ly294002, a PI3K inhibitor, decreased the insulin effect on SPAK and NCC phosphorylation, indicating that insulin induces phosphorylation of SPAK and NCC through PI3K and WNK4 in mpkDCT cells. Moreover, acute insulin administration to mice increased phosphorylation of oxidative stress-responsive kinase-1 (OSR1), SPAK and NCC in the kidney. Time-course experiments in mpkDCT cells and mice suggested that SPAK is upstream of NCC in this insulin-induced NCC phosphorylation mechanism, which was confirmed by the lack of insulin-induced NCC phosphorylation in SPAK knockout mice. Moreover, insulin administration to WNK4 hypomorphic mice did not increase phosphorylation of OSR1, SPAK and NCC in the kidney, suggesting that WNK4 is also involved in the insulin-induced OSR1, SPAK and NCC phosphorylation mechanism in vivo. The present results demonstrated that insulin is a potent regulator of NCC phosphorylation in the kidney, and that WNK4 and SPAK are involved in this mechanism of NCC phosphorylation by insulin

Isoscaling in central Sn+Sn collisions at 270 MeV/u

Experimental information on fragment emissions is important in understanding the dynamics of nuclear collisions and in the development of transport model simulating heavy-ion collisions. The composition of complex fragments emitted in the heavy-ion collisions can be explained by statistical models, which assume that thermal equilibrium is achieved at collision energies below 100 MeV/u. Our new experimental data together with theoretical analyses for light particles from Sn+Sn collisions at 270 MeV/u, suggest that the hypothesis of thermal equilibrium breaks down for particles emitted with high transfer momentum. To inspect the system's properties in such limit, the scaling features of the yield ratios of particles from two systems, a neutron-rich system of ${}^{132}\mathrm{Sn}+{}^{124}\mathrm{Sn}$ and a nearly symmetric system of ${}^{108}\mathrm{Sn}+{}^{112}\mathrm{Sn}$, are examined in the framework of the statistical multifragmentation model and the antisymmetrized molecular dynamics model. The isoscaling from low energy particles agree with both models. However the observed breakdown of isoscaling for particles with high transverse momentum cannot be explained by the antisymmetrized molecular dynamics model

Search for the pentaquark at J-PARC

We have been searching for the Θ^+ pentaquark via the π^−p→K^−X reaction at the J-PARC hadron facility. No peak structure was observed in the missing mass spectrum obtained at 1.92 GeV/c beam momentum. The upper limit for the production cross section averaged over the scattering angle from 2° to 15° in the laboratory frame was derived to be 0.26 μb/sr. In order to make a more stringent constraint we have also performed a measurement at 2.0 GeV/c. Present analysis status of this new data is reported

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

The pentaquark $\Theta^+$ has been searched for via the $\pi^-p \to K^-X$ 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 $\mu$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 $\Theta^+$ 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.Comment: 12 pages, 9 figures; published versio

Measurement of differential cross sections for Σ⁺p elastic scattering in the momentum range 0.44–0.80 GeV/c

クォーク間の「芯」をとらえた --物質が安定して存在できる理由の理解に貢献--. 京都大学プレスリリース. 2022-09-05.We performed a novel Σ⁺+p scattering experiment at the J-PARC Hadron Experimental Facility. Approximately 2400 Σ⁺+p elastic scattering events were identified from 4.9 × 10⁷ tagged Σ⁺+ particles in the Σ⁺+ momentum range 0.44-0.80 GeV/c. The differential cross sections of the Σ⁺+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 ³S₁ and ¹P₁ channels for the first time. The phase shift of the ³S₁ channel, where a large repulsive core was predicted owing to the Pauli effect between quarks, was evaluated as 20° < |δ₃S₁| < 35°. If the sign of δ₃S₁ is assumed to be negative, the interaction in this channel is moderately repulsive, as the Nijmegen extended-sort-core models predicted