arXiv subjects

Y. Akaishi

Publications and source records attributed to Y. Akaishi.

18 recordsLinked to original sources

arXiv2019

Write-ups for workshop on the project for the hadron experimental facility of J-PARC, Partial collection of LOIs at the extended hadron hall and the related topics

This write-up document is a summary of International workshop on the project for the extended hadron experimental facility which was held from March 26 to 28, 2018 at KEK Tokai Campus. This document is a collection of Letter Of Intents (LOIs) related to the proposed beam lines in the extended hadron experimental facility at J-PARC.

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arXiv2019

Kaonic Nuclear Clusters --- a New Paradigm of Particle and Nuclear Physics ---

Lambda*=Lambda(1405) plays an essential role in forming kaonic nuclear clusters (KNC). The simplest KNC, K-pp, has the structure Lambda*p=(K-p){I=0}p, where a real kaon migrates between two nucleons, mediating super-strong Lambda*-p$ attraction. Production data of K-pp have been accumulated by DISTO, J-PARC E27 and J-PARC E15 experiments. In the case of K-K-pp, the attractive covalent bond of Lambda*Lambda* is doubly enhanced compared to the Lambda*-p one. As a consequence, a m-th Lambda* multiplet, (Lambda*)m, with m(m-1)/2 bonds becomes more stable than its corresponding neutron aggregate, (n)m, with m=8 ~ 12. This may suggest the possible existence of stable Lambda* matter. The production of K-K-pp by high-energy pp or heavy-ion collisions is awaited as a doorway to so-far unknown Lambda* matter.

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arXiv2018

Single-pole Nature of the Detectable Lambda(1405)

We have investigated the single-pole nature of the detectable Lambda(1405) in detail, by employing a chiral model having double poles of a KbarN-piSigma coupled channel T-matrix. The effects of the 1st pole and the 2nd pole on the observed piSigma mass spectrum in the Lambda(1405) region were analyzed separately by means of the Generalized Optical Potential. It is concluded that the 1st pole is responsible for both peak structures seen in the T(piSigma leftarrow KbarN)(T(21)) and T(piSigma leftarrow piSigma)(T(22)) invariant-mass spectra, and the 2nd pole due to an energy-dependent chiral interaction provides continuum amplitudes affecting the shape of peak structures in experimentally observable spectrum of the Lambda(1405).

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arXiv2017

Clear indication of a strong I=0 Kbar-N attraction in the Lambda (1405) region from the CLAS photo-production data

Possible existence of deeply bound kaonic nuclear systems was proposed Akaishi and Yamazaki (2002} more than a decade ago, based on an ansatz that the Lambda* = Lambda(1405) mass is 1405 MeV/c2, where the Lambda* is a Kbar-N quasi-bound state decaying to Sigma-pi. Recently, a large number of data on photo-production of Lambda(1405) in the gamma p to K+ pi{0+-} Sigma{0-+} reaction were provided by the CLAS collaboration Moriya et al.(2013}, and double-pole structure of the Lambda* has been intensively discussed by chiral dynamics analyses {Roca (2013),Mai 2015}, whereas we show that a Lambda* mass of 1405 MeV/c2 is deduced from the same CLAS data.

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arXiv2012

Analysis of heavy hyperhydrogen 6^H_Lambda

We have revisited the possible existence and the binding mechanism of heavy hyperhydrogen 6^H_Lambda. This Lambda hypernucleus is enriched in information about Lambda hypernuclear dynamics which would shed a light on significant role of coherent Lambda-Sigma coupling effect in neutron-rich nuclear medium, discussed by the authors. Recently, reports on an experimental evidence of 6^H_Lambda with theoretical comparison have appeared, wherein the significance of the coherent coupling in 6^H_Lambda has been criticized. In this report, we are revising our previous work and give further theoretical analysis to confirm the influence of the Lambda N - Sigma N coupling effect in the binding mechanism of 6^H_Lambda.

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arXiv2011

Resonant formation of Lambda(1405) by stopped-K- absorption in deuteron

To solve the current debate on the position of the quasi-bound K^-p state, namely, "Lambda(1405) or Lambda*(1420)", we propose to measure the T_{21} = T_{Sigma-pi \leftarrow Kbar-N} Sigma-pi invariant-mass spectrum in stopped-K- absorption in deuteron, since the spectrum, reflecting the soft and hard deuteron momentum distribution, is expected to have a narrow quasi-free component with an upper edge of M = 1430 MeV/c^2, followed by a significant "high-momentum" tail toward the lower mass region, where a resonant formation of Lambda(1405) of any mass and width in a wide range is revealed. We introduce a "deviation" spectrum as defined by DEV = OBS (observed or calculated) / QF (non-resonant quasi-free), in which the resonant component can be seen as an isolated peak free from the QF shape.

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arXiv2010

Feshbach Resonance due to Coherent Lambda-Sigma Coupling in Lambda_He^7

Coherent Lambda-Sigma coupling effect in Lambda_He^7 is analyzed within three-body framework of two coupled channels, Lambda-t-t and Sigma-tau-t, where tau represents trinucleon which is either H^3 or He^3. The hyperon-trinucleon (Y tau) and trinucleon-trinucleon (tau tau) interactions are derived by folding G-matrices of YN and NN interactions with trinucleon density distributions. It is found that the binding energy of Lambda_He^7 is 4.04 MeV below the Lambda+t+t threshold without Lambda-Sigma coupling and the binding energy is increased to 4.46 MeV when the coupling effect is included. This state is 7.85 MeV above the He^6+Lambda threshold and it may have a chance to be observed as a Feshbach resonance in Li^7 (e,e'K^+)Lambda_He^7 experiment done at Jefferson Lab.

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arXiv2008

Kaonic Nuclear Systems KbarN and KbarNN as Decaying States

The formation spectra of model KbarN and KbarNN systems formed by (K-, n) reactions are investigated in order to obtain a theoretical basis for a proper interpretation of experimental data concerning kaonic nuclear quasi-bound states. It has been clarified that the experimentally observable kaonic nuclear state K-pp should be regarded as the decaying state introduced by Kapur-Peierls, which is different from the pole state solution of the Faddeev equation.

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arXiv2005

Full-coupled channel approach to S=-2 s-shell hypernuclear systems

We describe full-coupled-channel ab initio calculations among the octet baryons for S=-2 s-shell hypernuclei,_{LambdaLambda}^4H,_{LambdaLambda}^5H and_{LambdaLambda}^6He. The wave function includes Lambda Lambda, Lambda Sigma, N Xi, and Sigma Sigma channels. Minnesota NN, D2^\prime YN and Nijmegen model D simulated YY interactions are used. This is the first attempt to explore the few-body problem of the full-coupled channel scheme for A=4-6, S=-2 multistrangeness hypernuclear systems. Bound state solutions of the Lambda Lambda hypernuclei,_{LambdaLambda}^4H,_{LambdaLambda}^5H and _{LambdaLambda}^6He, are obtained.

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arXiv2005

Strange tribaryons as Kbar-mediated dense nuclear systems

We discuss the implications of recently discovered strange tribaryons in 4He(stopped-K-, p)S0 (3115) and 4He(stopped-K, n) S1 (3140) within the framework of deeply bound kbar states formed on shrunk nuclear cores. S1 (3140) corresponds to T=0 ppnK-, whereas S0 (3115) to T=1 pnnK-, which is an isobaric analog state of pppK-, predicted previously. The observed binding energies can be accounted for by including the relativistic effect and by invoking a medium-enhanced kbar-N interaction by 15%. We propose various experimental methods to further study these and related bound systems.

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arXiv2004

Full-Coupled Channel Approach to Doubly Strange $s$-Shell Hypernuclei

We describe {\it ab initio} calculations of doubly strange, $S=-2$, $s$-shell hypernuclei ($^4_{ΛΛ}$H, $^5_{ΛΛ}$H, $^5_{ΛΛ}$He and $^6_{ΛΛ}$He) as a first attempt to explore the few-body problem of the {\it full}-coupled channel scheme for these systems. The wave function includes $ΛΛ$, $ΛΣ$, $NΞ$ and $ΣΣ$ channels. Minnesota $NN$, D2$^\prime$ $YN$, and simulated $YY$ potentials based on the Nijmegen hard-core model, are used. Bound state solutions of these systems are obtained. We find that a set of phenomenological $B_8B_8$ interactions among the octet baryons in $S=0, -1$ and -2 sectors, which is consistent with all of the available experimental binding energies of $S=0, -1$ and -2 $s$-shell (hyper-)nuclei, can predict a particle stable bound state of $^4_{ΛΛ}$H. For $^5_{ΛΛ}$H and $^5_{ΛΛ}$He, $ΛN-ΣN$ and $ΞN-ΛΣ$ potentials enhance the net $ΛΛ-NΞ$ coupling, and a large $Ξ$ probability is obtained even for a weaker $ΛΛ-NΞ$ potential.

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arXiv2003

New effective nuclear forces with a finite-range three-body term and their application to AMD+GCM calculations

We propose new effective inter-nucleon forces with a finite-range three-body operator. The proposed forces are suitable for describing the nuclear structure properties over a wide mass number region, including the saturation point of nuclear matter. The forces are applied to microscopic calculations of $Z=N$ ($A\le 40$) nuclei and O isotopes with a method of antisymmetrized molecular dynamics. We present the characteristics of the forces and discuss the importance of the finite-range three-body term.

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arXiv2003

Brueckner Rearrangement Effects in $^5_Λ$He and $^6_{ΛΛ}$He

Rearrangement effects in light hypernuclei are investigated in the framework of the Brueckner theory. We can estimate without detailed numerical calculations that the energy of the $α$-core is reduced by more than 2.5 MeV when the $Λ$ adheres to $^4$He to form $^5_Λ$He. Similar assessment of rearrangement contributions is essential to deduce the strength of $ΛΛ$ interaction from experimentally observed $ΔB_{ΛΛ}$. The recently observed experimental value of $\sim$ 1 MeV for the $ΔB_{ΛΛ}$ of \hll suggests that the matrix element of $<ΛΛ|v|ΛΛ>$ in \hll is around -2 MeV.

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arXiv2003

Stochastic Variational Search for $^{4}_{ΛΛ}$H

A four-body calculation of the $pnΛΛ$ bound state, $^{\ 4}_{ΛΛ}$H, is performed using the stochastic variational method and phenomenological potentials. The $NN$, $ΛN$, and $ΛΛ$ potentials are taken from a recent Letter by Filikhin and Gal, PRL{\bf 89}, 172502 (2002). Although their Faddeev-Yakubovsky calculation found no bound-state solution over a wide range of $ΛΛ$ interaction strengths, the present variational calculation gives a bound-state energy, which is clearly lower than the $_Λ^3{H}+Λ$ threshold, even for a weak $ΛΛ$ interaction strength deduced from a recent experimental $B_{ΛΛ}(^{6}_{ΛΛ}{He})$ value. The binding energies obtained are close to, and slightly larger than, the values obtained from the three-body $dΛΛ$ model in the Letter.

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arXiv2002

Lambda Lambda-XiN Coupling Effects in Light Hypernuclei

The significance of $ΛΛ$-$Ξ$N coupling in double-$Λ$ hypernuclei has been studied. The Pauli suppression effect due to this coupling in $^6_{ΛΛ}$He has been found to be 0.43 MeV for the coupling strength of the NSC97e potential. This indicates that the free-space $ΛΛ$ interaction is stronger by about $5^{\circ}$ phase shift than that deduced from the empirical data of $^6_{ΛΛ}$He without including the Pauli suppression effect. In $^5_{ΛΛ}$He and $^5_{ΛΛ}$H, an attractive term arising from $ΛΛ$-$Ξ$N conversion is enhanced by the formation of an alpha particle in intermediate $Ξ$ states. According to this enhancement, we have found that the $ΛΛ$ binding energy ($ΔB_{ΛΛ}$) of $^5_{ΛΛ}$He is about 0.27 MeV larger than that of $^6_{ΛΛ}$He for the NSC97e coupling strength. This finding deviates from a general picture that the heavier is the core nucleus, the larger is $ΔB_{ΛΛ}$.

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arXiv2002

Ab initio approach to s-shell hypernuclei 3H_Lambda, 4H_Lambda, 4He_Lambda and 5He_Lambda with a Lambda N-Sigma N interaction

Variational calculations for s-shell hypernuclei are performed by explicitly including $Σ$ degrees of freedom. Four sets of YN interactions (SC97d(S), SC97e(S), SC97f(S) and SC89(S)) are used. The bound-state solution of $_Λ^5$He is obtained and a large energy expectation value of the tensor $ΛN-ΣN$ transition part is found. The internal energy of the $^4$He subsystem is strongly affected by the presence of a $Λ$ particle with the strong tensor $ΛN-ΣN$ transition potential.

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arXiv2002

High-density K nuclear systems with isovector deformation

Using a phenomenological KN potential which reproduces $Λ$(1405) as an I=0 bound state of KN, we investigated deeply bound kaonic nuclei, ppnK$^-$ and $^8$BeK$^-$, with the method of Antisymmetrized Molecular Dynamics. Our calculations show that strongly bound kaonic nuclear systems with unusual exotic structures are formed around the K$^-$, which attracts the surrounding nucleons to an extremely high-density assembly and induces a proton-neutron separation, ``isovector deformation''.

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arXiv1999

Can We Extract Lambda-Lambda Interaction from Two-Particle Momentum Correlation ?

We analyze the invariant mass spectrum of Lambda-Lambda in $^{12}C(K^-,K^+ Lambda Lambda)$ reaction at P(K^+)=1.65 GeV/c by using a combined framework of IntraNuclear Cascade (INC) model and the correlation function technique. The observed enhancement at low-invariant masses can be well reproduced with attractive Lambda-Lambda interactions with the scattering length either in the range a = -6 \sim -4 fm (no bound state) or a = 7 \sim 12 fm (with bound state). We also discuss Lambda-Lambda correlation functions in central relativistic heavy-ion collisions as a possible way to eliminate this discrete ambiguity.

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