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K. Itahashi

Publications and source records attributed to K. Itahashi.

At least 37 records · Page 2Linked to original sources
arXiv2018

Missing-mass spectroscopy of the ${}^{12}{\rm C}(p,d)$ reaction near the $η^\prime$-meson production threshold

Excitation-energy spectra of $^{11}$C nuclei near the $η^\prime$-meson production threshold have been measured by missing-mass spectroscopy using the $^{12}$C($p$,$d$) reaction. A carbon target has been irradiated with a 2.5 GeV proton beam supplied by the synchrotron SIS-18 at GSI to produce $η^\prime$ meson bound states in $^{11}$C nuclei. Deuterons emitted at $0^\circ$ in the reaction have been momentum-analyzed by the fragment separator (FRS) used as a high-resolution spectrometer. No distinct structure due to the formation of $η^\prime$-mesic states is observed although a high statistical sensitivity is achieved in the experimental spectra. Upper limits on the formation cross sections of $η^\prime$-mesic states are determined, and thereby a constraint imposed on the $η^\prime$-nucleus interaction is discussed.

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arXiv2016

Measurement of excitation spectra in the ${}^{12}$C$(p,d)$ reaction near the $η'$ emission threshold

Excitation spectra of $^{11}$C were measured in the $^{12}$C$(p,d)$ reaction near the $η'$ emission threshold. A proton beam extracted from the synchrotron SIS-18 at GSI with an incident energy of 2.5 GeV impinged on a carbon target. The momenta of deuterons emitted at 0 degrees were precisely measured with the fragment separator FRS operated as a spectrometer. In contrast to theoretical predictions on the possible existence of deeply bound $η'$ mesic states in carbon nuclei, no distinct structures were observed associated with the formation of bound states. The spectra were analyzed to set stringent constraints on the formation cross section and on the hitherto barely-known $η'$-nucleus interaction.

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arXiv2016

First application of superconducting transition-edge-sensor microcalorimeters to hadronic-atom x-ray spectroscopy

High-resolution pionic-atom x-ray spectroscopy was performed with an x-ray spectrometer based on a 240-pixel array of superconducting transition-edge-sensor (TES) microcalorimeters at the piM1 beam line of the Paul Scherrer Institute. X-rays emitted by pionic carbon via the 4f->3d transition and the parallel 4d->3p transition were observed with a full-width-at-half-maximum energy resolution of 6.8 eV at 6.4 keV. Measured x-ray energies are consistent with calculated electromagnetic values which considered the strong-interaction effect assessed via the Seki-Masutani potential for the 3p energy level, and favor the electronic population of two filled 1s electrons in the K-shell. Absolute energy calibration with an uncertainty of 0.1 eV was demonstrated under a high-rate hadron beam condition of 1.45 MHz. This is the first application of a TES spectrometer to hadronic-atom x-ray spectroscopy and is an important milestone towards next-generation high-resolution kaonic-atom x-ray spectroscopy.

physics.ins-det↗
arXiv2016

Structure near $K^-$+$p$+$p$ threshold in the in-flight $^3$He$(K^-,Λp)n$ reaction

To search for an S= -1 di-baryonic state which decays to $Λp$, the $ {\rm{}^3He}(K^-,Λp)n_{missing}$ reaction was studied at 1.0 GeV/$c$. Unobserved neutrons were kinematically identified from the missing mass $M_X$ of the $ {\rm{}^3He}(K^-,Λp)X$ reaction in order to have a large acceptance for the $Λpn$ final state. The observed $Λp n$ events, distributed widely over the kinematically allowed region of the Dalitz plot, establish that the major component comes from a three nucleon absorption process. A concentration of events at a specific neutron kinetic energy was observed in a region of low momentum transfer to the $Λp$. To account for the observed peak structure, the simplest S-wave pole was assumed to exist in the reaction channel, having Breit-Wigner form in energy and with a Gaussian form-factor. A minimum $χ^2$ method was applied to deduce its mass $M_X\ =$ 2355 $ ^{+ 6}_{ - 8}$ (stat.) $ \pm 12$ (syst.) MeV/c$^2$, and decay-width $Γ_X\ = $ 110 $ ^{+ 19}_{ - 17}$ (stat.) $ \pm 27$ (syst.) MeV/c$^2$, respectively. The form factor parameter $Q_X \sim$ 400 MeV/$c$ implies that the range of interaction is about 0.5

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arXiv2016

Absolute Energy Calibration of X-ray TESs with 0.04 eV Uncertainty at 6.4 keV in a Hadron-Beam Environment

A performance evaluation of superconducting transition-edge sensors (TESs) in the environment of a pion beam line at a particle accelerator is presented. Averaged across the 209 functioning sensors in the array, the achieved energy resolution is 5.2 eV FWHM at Co $K_α$ (6.9 keV) when the pion beam is off and 7.3 eV at a beam rate of 1.45 MHz. Absolute energy uncertainty of $\pm$0.04 eV is demonstrated for Fe $K_α$ (6.4 keV) with in-situ energy calibration obtained from other nearby known x-ray lines. To achieve this small uncertainty, it is essential to consider the non-Gaussian energy response of the TESs and thermal cross-talk pile-up effects due to charged-particle hits in the silicon substrate of the TES array.

physics.ins-det↗
arXiv2015

Spectroscopy of $η'$-nucleus bound states at GSI and FAIR --- very preliminary results and future prospects ---

The possible existence of η'-nucleus bound states has been put forward through theoretical and experimental studies. It is strongly related to the η' mass at finite density, which is expected to be reduced because of the interplay between the $U_A(1)$ anomaly and partial restoration of chiral symmetry. The investigation of the C(p,d) reaction at GSI and FAIR, as well as an overview of the experimental program at GSI and future plans at FAIR are discussed.

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arXiv2015

Measurement of the strong interaction induced shift and width of the 1s state of kaonic deuterium at J-PARC

The antikaon-nucleon interaction close to threshold provides crucial information on the interplay between spontaneous and explicit chiral symmetry breaking in low-energy QCD. In this context the importance of kaonic deuterium X-ray spectroscopy has been well recognized, but no experimental results have yet been obtained due to the difficulty of the measurement. We propose to measure the shift and width of the kaonic deuterium 1s state with an accuracy of 60 eV and 140 eV respectively at J-PARC. These results together with the kaonic hydrogen data (KpX at KEK, DEAR and SIDDHARTA at DAFNE) will then permit the determination of values of both the isospin I=0 and I=1 antikaon-nucleon scattering lengths and will provide the most stringent constraints on the antikaon-nucleon interaction, promising a breakthrough. Refined Monte Carlo studies were performed, including the investigation of background suppression factors for the described setup. These studies have demonstrated the feasibility of determining the shift and width of the kaonic deuterium atom 1s state with the desired accuracy of 60 eV and 140 eV.

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arXiv2015

Search for η'(958)-nucleus bound states by (p,d) reaction at GSI and FAIR

The mass of the η' meson is theoretically expected to be reduced at finite density, which indicates the existence of η'-nucleus bound states. To investigate these states, we perform missing-mass spectroscopy for the (p, d) reaction near the η' production threshold. The overview of the experimental situation is given and the current status is discussed.

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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.

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arXiv2012

Formation of eta-prime(958)-mesic nuclei by (p,d) reaction

We calculate theoretically the formation spectra of eta'(958)-nucleus systems in the (p,d) reaction for the investigation of the in-medium modification of the eta' mass. We show the comprehensive numerical calculations based on a simple form of the eta' optical potential in nuclei with various potential depths. We conclude that one finds an evidence of possible attractive interaction between eta' and nucleus as peak structure appearing around the eta' threshold in light nuclei such as 11C when the attractive potential is stronger than 100 MeV and the absorption width is of order of 40 MeV or less. Spectroscopy of the (p,d) reaction is expected to be performed experimentally at existing facilities, such as GSI. We also estimate the contributions from the omega and phi mesons, which have masses close to the eta' meson, concluding that the observation of the peak structure of the eta'-mesic nuclei is not disturbed although their contributions may not be small.

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arXiv2012

Search for the $Θ^{+}$ pentaquark via the $π^-p\to K^-X$ reaction at 1.92 GeV/$c$

The $Θ^+$ pentaquark baryon was searched for via the $π^-p\to K^-X$ reaction in a missing-mass resolution of 1.4 MeV/$c^2$(FWHM) at J-PARC. $π^-$ meson beams were incident on the liquid hydrogen target with the beam momentum of 1.92 GeV/$c$. No peak structure corresponding to the $Θ^+$ 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 $μ$b/sr in the mass region of 1.51$-$1.55 GeV/$c^2$.The upper limit of the $Θ^+$ decay width using the effective Lagrangian approach was obtained to be 0.72 MeV/$c^2$ and 3.1 MeV/$c^2$ for $J^P_Θ=1/2^+$ and $J^P_Θ=1/2^-$, respectively.

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arXiv2010

Three- and four-nucleon absorption processes observed in the $K^-$-$^4$He reaction at rest

Correlations of back-to-back coincident $Λd$ and $Λt$ pairs from the stopped $K^-$ reaction on $^4$He had been investigated, thereby $Λd$ and $Λt$ branches of non-mesonic three- and four-nucleon absorption processes of antikaon at rest were identified as well-separable processes, respectively. The branching ratio of the three-nucleon process, ($^4$He-$K^-$)$_{atomic} \rightarrow Λd "n"$, is estimated to be $(0.9 \pm 0.1 (stat) \pm 0.2 (syst)) \times 10^{-3}$ from the normalized $Λd$ spectrum in a $Λd n$ final state, while the fraction of the four-nucleon process, ($^4$He-$K^-$)$_{atomic} \rightarrow Λt$, is obtained to be $(3.1 \pm 0.4 (stat) \pm 0.5 (syst)) \times 10^{-4}$ per stopped $K^-$.

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arXiv2009

Spectroscopy of 32Ne and the Island of Inversion

We report on the first spectroscopic study of the N=22 nucleus 32Ne at the newly completed RIKEN Radioactive Ion Beam Factory. A single gamma-ray line with an energy of 722(9) keV was observed in both inelastic scattering of a 226 MeV/u 32Ne beam on a Carbon target and proton removal from 33Na at 245 MeV/u. This transition is assigned to the de-excitation of the first J^pi = 2+ state in 32Ne to the 0+ ground state. Interpreted through comparison with state-of-the-art shell model calculations, the low excitation energy demonstrates that the Island of Inversion extends to at least N=22 for the Ne isotopes.

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arXiv2007

$Λd$ correlations from the $^4$He(stopped-$K^-$,$d$) reaction

We have observed an intense high-energy component in an inclusive $^4$He(stopped $K^-$, $d$) spectrum. For back-to-back $Λd$ pairs a prominent event cluster has been found just below the $m_{^4\textrm{He}}+m_{K^-}-m_{n}$ mass threshold in the $Λd$ invariant mass spectrum of $Λdn$ events, which is evidence for a three-nucleon absorption process of $K^-$ in $^4$He. In addition, an appreciable strength is revealed below $\sim$3220 MeV/$c^2$. Well separated $Σ^0 dn$ events show a peak similar to the case of $Λdn$.

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arXiv2007

$ΛN$ correlations from the stopped $K^-$ reaction on ${}^4$He

We have investigated correlations of coincident $ΛN$ pairs from the stopped $K^-$ reaction on ${}^4$He, and clearly observed $Λp$ and $Λn$ branches of the two-nucleon absorption process in the $ΛN$ invariant mass spectra. In addition, non-mesonic reaction channels, which indicate possible exotic signals for the formation of strange multibaryon states, have been identified.

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arXiv2007

Search for strange tribaryon states in the inclusive ^4He(K^{-}_{stopped}, p) reaction

A search for tribaryon states was performed at KEK-PS. We adopted the $^4$He($K^-_{stopped}, p)$ reaction to populate the states with strangeness -1, charge 0 and isospin 1. No significant narrow structure was observed in the mass region from 3000 to 3200 MeV/c^2 in an inclusive missing mass spectrum. The upper limit of the formation branching ratio was determined to be ($1\sim3)\times 10^{-4}$, ($0.7\sim2)\times 10^{-3}$ and ($2\sim8) \times 10^{-3}$/($stopped K^{-}$) with 95 % confidence level for narrow states with an assumed width of 0, 20 and 40 MeV/c^2, respectively.

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arXiv2007

Precision measurement of the $3d \to 2p$ x-ray energy in kaonic $^4$He

We have measured the Balmer-series x-rays of kaonic $^4$He atoms using novel large-area silicon drift x-ray detectors in order to study the low-energy $\bar{K}$-nucleus strong interaction. The energy of the $3d \to 2p$ transition was determined to be 6467 $\pm$ 3 (stat) $\pm$ 2 (syst) eV. The resulting strong-interaction energy-level shift is in agreement with theoretical calculations, thus eliminating a long-standing discrepancy between theory and experiment.

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