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Avraham Gal

Publications and source records attributed to Avraham Gal.

At least 19 recordsLinked to original sources
arXiv2026

Remarks on MAMI's recent determination of $B_Λ({_Λ^3}{\rm H})$

A recent report on ${^7{\rm Li}}(e,e'K^+)$ electroproduction runs by the A1 collaboration at the Mainz Microtron (MAMI) assigns a sharp pion-momentum line at $p_{π^-}\approx 113.8\pm 0.1$ MeV/c to ${_Λ^3}{\rm H}\toπ^-+{^3{\rm He}}$ weak decay, resulting in exceptionally large ${_Λ^3}{\rm H}$ binding-energy $B_Λ({_Λ^3}{\rm H})=0.523\pm 0.013\pm 0.075$ MeV. Here I discuss an alternative interpretation of the observed sharp line in terms of ${_Λ^7}{\rm He}_{\rm g.s.}\toπ^-+{^7{\rm Li}}(E_{\rm x}=478$ keV) weak decay and its implications for $B_Λ({_Λ^7}{\rm He})$.

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arXiv2026

In Memoriam: Igal Talmi (1925-2026)

A brief obituary of Igal Talmi (1925-2026) focusing on his scientific heritage. Published in Nuclear Physics News 36 (2026) 39-40.

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arXiv2026

Hypernuclear constraints on $ΛN$ and $ΛNN$ interactions

Recent work on using density dependent $Λ$-nuclear optical potentials in calculations of $Λ$-hypernuclear binding energies is reviewed. It is found that all known $Λ$ binding energies in the mass range $16 \leq A \leq 208$ are well fitted in terms of two interaction parameters: one, attractive, for the spin-averaged $ΛN$ interaction and another one, repulsive, for the $ΛNN$ interaction. The $ΛN$ interaction term by itself overbinds $Λ$ hypernuclei, in quantitative agreement with recent findings obtained in EFT and Femtoscopy studies. The strength of the $ΛNN$ interaction term is compatible with values required to resolve the hyperon puzzle.

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arXiv2026

Tribute to Tullio Bressani, Bogdan Povh and Toshimitsu Yamazaki

In this HYP2025 talk I pay tribute to Tullio Bressani (1940-2024), Bogdan Povh (1932-2024) and Toshimitsu Yamazaki (1934-2025), all of whom made lasting contributions to shaping up Strangeness Nuclear Physics. Yoshinori Akaishi's (1941-2025) record is also noted.

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arXiv2025

Tribute to Toshimitsu Yamazaki (1934-2025): Quest for Exotic Hadronic Matter

In this talk I pay tribute to Toshimitsu Yamazaki who died earlier this year. Yamazaki's leading contributions to Hadronic Physics, in particular to Strangeness Nuclear Physics in Japan and elsewhere, are well known. Two of the five Recurring Themes of his research, as listed in the Japan Academy site, are highlighted here: (i) Discovery of deeply bound pionic-atom states, and (ii) Search for kaonic nuclei -- Kaonic Proton Matter (KPM). I conclude by reviewing briefly my own recent work, confirming Farrar's conjecture that a deeply bound $H$ dibaryon is not ruled out by the weak-decay observation of $ΛΛ$ hypernuclei. However, the relatively long lifetime of such a deeply bound $H$ is much too short to qualify it for a Dark-Matter candidate.

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arXiv2024

$ΛNN$ input to neutron stars from hypernuclear data

This work is a sequel to our two 2023 publications [PLB 837 137669, NPA 1039 122725] where fitting 14 1$s_Λ$ and 1$p_Λ$ single-particle binding energies in hypernuclei across the periodic table led to a well-defined $Λ$-nucleus optical potential. The potential consists of a Pauli modified linear-density ($ΛN$) and a quadratic-density ($ΛNN$) terms. The present work reports on extending the above analysis to 21 $Λ$ single-particle data points input by including 1$d_Λ$ and 1$f_Λ$ states in medium-weight and heavy hypernuclei. The upgraded results for the $ΛN$ and $ΛNN$ potential depths at nuclear-matter density $ρ_0=0.17$~fm$^{-3}$, $D^{(2)}_Λ=-37.5\mp 0.7$~MeV and $D^{(3)}_Λ=+9.8\pm 1.2$~MeV together with the total depth $D_Λ=-27.7\pm 0.5$~MeV, agree within errors with the earlier results. The $Λ$ hypernuclear overbinding associated with the $ΛN$-induced potential depth $D^{(2)}_Λ$ agrees quantitatively with a recent combined analysis of low-energy $Λp$ scattering data and correlation functions [PLB 850 (2024) 138550]. These results, particularly the size of the repulsive $D^{(3)}_Λ$, provide an essential input towards resolving the 'hyperon puzzle' in the core of neutron stars. We also show that a key property of our $ΛNN$-induced potential term, i.e. a need to suppress the quadratic-density $ΛNN$ term involving an excess neutron and a $N=Z$ core nucleon, can be tested in the forthcoming JLab E12-15-008 experiment.

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arXiv2024

Hypernuclear constraints on the existence and lifetime of a deeply bound $H$ dibaryon

We study to what extent the unique observation of $ΛΛ$ hypernuclei by their weak decay into known $Λ$ hypernuclei, with lifetimes of order 10$^{-10}$ s, rules out the existence of a deeply bound doubly-strange (${\cal S}$=$-$2) $H$ dibaryon. Treating ${_{ΛΛ}^{~~6}}{\rm He}$ (the Nagara emulsion event) in a realistic $Λ-Λ-{^4}$He three-body model, we find that the ${_{ΛΛ}^{~~6}}{\rm He}\to H + {^4{\rm He}}$ strong-interaction lifetime increases beyond 10$^{-10}$ s for $m_H < m_Λ+m_n$, about 176 MeV below the $ΛΛ$ threshold, so that such a deeply bound $H$ is not in conflict with hypernuclear data. Constrained by $Λ$ hypernuclear $Δ{\cal S}$=1 nonmesonic weak-interaction decay rates, we follow EFT methods to evaluate the $Δ{\cal S}$=2 $H\to nn$ weak-decay lifetime of $H$ in the mass range $2m_n \lesssim m_H < m_Λ+m_n$. The resulting $H$ lifetime is of order 10$^5$ s, many orders of magnitude shorter than required to qualify for a dark-matter candidate.

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arXiv2024

Deciphering $Ξ^-$ capture events in light emulsion nuclei

We recently showed that all five KEK and J-PARC uniquely assigned two-body $Ξ^-$+${^A}$Z$\to{_Λ^{A'}}$Z'+${_Λ^{A''}}$Z'' capture events in CNO light emulsion nuclei are consistent with Coulomb-assisted $1p_{Ξ^-}$ nuclear states in a $Ξ$-nuclear potential of nuclear-matter depth $V_Ξ\gtrsim 20$ MeV [1]. Here we argue that the recently reported $^{14}$N capture events named KINKA and IRRAWADDY are more likely $1p_{Ξ^0}$--$^{14}$C nuclear states [2] than $1s_{Ξ^-}$--$^{14}$N states, the latter assignment implying considerably smaller values of $V_Ξ$.

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arXiv2023

$ΛNN$ content of $Λ$-nucleus potential

A minimally constructed $Λ$-nucleus density-dependent optical potential is used to calculate binding energies of observed $1s_Λ$, $1p_Λ$ states across the periodic table, leading to a repulsive $ΛNN$ contribution $D_Λ^{(3)}\approx 14$ MeV to the phenomenological $Λ$-nucleus potential depth $D_Λ\approx -30$ MeV. This value is significant in connection with the so-called 'hyperon puzzle'.

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arXiv2022

$Ξ$-nuclear constraints from $Ξ^-$ emulsion capture events

All five KEK and J-PARC two-body $Ξ^-$+$^A$Z $\to$ $^{A'}_Λ$Z'+$^{A''}_Λ$Z'' capture events in light emulsion nuclei, including KISO and IBUKI in $^{14}$N, are consistent with Coulomb-assisted $1p_{Ξ^-}$ nuclear states. The underlying $Ξ$-nuclear potential is strongly attractive, with nuclear-matter depth $V_Ξ$ larger than 20 MeV. The recent $^{14}$N capture events KINKA and IRRAWADDY assigned by J-PARC E07 to $1s_{Ξ^-}$ nuclear states, and implying considerably shallower $V_Ξ$, have also another interpretation as $1p_{Ξ^0}$ nuclear states.

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arXiv2022

Recent progress on few-body hypernuclei

Few-body $Λ$ hypernuclei provide valuable information towards understanding strange matter. Recent experimental progress by the STAR Collaboration at the RHIC facility and by the ALICE Collaboration at the LHC has been matched by theoretical progress reviewed here: (i) lifetimes of the hypertriton $_Λ^3$H, $_Λ^3$n if particle-stable, $_Λ^4$H and $_Λ^4$He and their charge symmetry breaking, and (ii) the onset of $ΛΛ$ hypernuclear binding.

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arXiv2020

Extracting $σ_{πN}$ from pionic atoms

We discuss a recent extraction of the $πN$ $σ$ term $σ_{πN}$ from a large-scale fit of pionic-atom strong-interaction data across the periodic table. The value thus derived, $σ_{πN}^{\rm FG}=57\pm 7$ MeV, is directly connected via the Gell-Mann--Oakes--Renner expression to the medium-renormalized $πN$ isovector scattering amplitude near threshold. It compares well with the value derived recently by the Bern-Bonn-Jülich group, $σ_{πN}^{\rm RS}=58\pm 5$ MeV, using the Roy-Steiner equations to control the extrapolation of the vanishingly small near threshold $πN$ isoscalar scattering amplitude to zero pion mass.

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arXiv2020

From $\bar{K}N$ Interactions to $\bar{K}$-Nuclear Quasi-Bound States

We review the current status of our study of $K^-$-nuclear interactions and $K^-$-nuclear quasi-bound states. The adopted $K^-$-nuclear optical potential consists of two parts -- the single-nucleon one constructed microscopically from chirally motivated $\bar{K}N$ amplitudes, and a phenomenological multi-nucleon one constrained in fits to kaonic atoms data. The inclusion of multi-nucleon absorption in our calculations of $K^{-}$ quasi-bound states in many-body systems leads to huge widths, considerably exceeding the binding energies. If this feature is confirmed the observation of such states is unlikely. Finally, a development of a new microscopical model for in-medium $K^-NN$ absorption is discussed as well.

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arXiv2019

The d*(2380) and its family of pion assisted dibaryons

The status of $NΔ$ and $ΔΔ$ dibaryons introduced by Dyson and Xuong in 1964 is briefly reviewed with focus on the d*(2380), tentatively assigned as a $ΔΔ$ dibaryon resonance. It is argued that the apparently small value of width, $Γ_{d^\ast}$$\approx$70 MeV, favors hadronic structure for the d*(2380) dibaryon rather than a six-quark structure.

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arXiv2019

Recent progress on hypernuclei

Some of last year's progress made in hypernuclear physics is reviewed as follows: (i) resolving the $_Λ^5$He overbinding problem in single-$Λ$ hypernuclei [1]; (ii) arguing that the onset of binding double-$Λ$ hypernuclei is most likely at $A$=5, with the neutral systems $_{ΛΛ}^{\,\,3}$n and $_{ΛΛ}^{\,\,4}$n unbound by a large margin [2]; and (iii) revising the calculated value of the loosely bound $_Λ^3$H lifetime to a level of $\sim$20% shorter than the free $Λ$ lifetime [3], given recent claims from relativistic heavy ion experiments that $τ(_Λ^3$H) is shorter than $τ_Λ$ by as much as $\approx$(30$\pm$8)%. Also discussed briefly in this context is the lifetime expected for the questionable $_Λ^3$n hypernucleus.

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arXiv2019

Towards resolving the $_Λ^3$H lifetime puzzle

Recent $_Λ^3$H lifetime measurements in relativistic heavy ion collision experiments have yielded values shorter by (30$\pm$8)% than the free $Λ$ lifetime $τ_Λ$, thereby questioning the naive expectation that $τ({_Λ^3}{\rm H})\approxτ_Λ$ for a weakly bound $Λ$ hyperon. Here we apply the closure approximation introduced by Dalitz and coworkers to evaluate the $_Λ^3$H lifetime, using $_Λ^3$H wavefunctions generated by solving three-body Faddeev equations. Our result, disregarding pion final-state interaction (FSI), is $τ({_Λ^3}{\rm H})$=(0.90$\pm$0.01)$τ_Λ$. In contrast to previous works, pion FSI is found attractive, reducing further $τ({_Λ^3}{\rm H})$ to $τ({_Λ^3}{\rm H})$=(0.81$\pm$0.02)$τ_Λ$. We also evaluate for the first time $τ({_Λ^3}{\rm n})$, finding it considerably longer than $τ_Λ$, contrary to the shorter lifetime values suggested by the GSI HypHI experiment for this controversial hypernucleus.

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arXiv2019

Old and New in Strangeness Nuclear Physics

Several persistent problems in strangeness nuclear physics are discussed in this opening talk at HYP2018, Portsmouth-Norfolk VA, June 2018: (i) the $^3_Λ$H and $^3_Λ$n (if existing) lifetimes; (ii) charge symmetry breaking in $Λ$ hypernuclei; (iii) the overbinding of $^5_Λ$He which might be related to the hyperon puzzle in neutron stars; and (iv) does $Λ^\ast$(1405) survive in strange hadronic matter?

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