arXiv subjects

D. Gazda

Publications and source records attributed to D. Gazda.

11 recordsLinked to original sources

arXiv2023

Hypertriton lifetime

Over the last decade, conflicting values of the hypertriton ${}_{\Lambda}^3\mathrm{H}$ lifetime $\tau({}_{\Lambda}^3\mathrm{H})$ were extracted from relativistic heavy-ion (RHI) collision experiments, ranging from values compatible with the free-$\Lambda$ lifetime $\tau_\Lambda$-as expected naively for a very weakly bound $\Lambda$ in ${}_{\Lambda}^3\mathrm{H}$-to lifetimes as short as $\tau({}_{\Lambda}^3\mathrm{H}) \approx (0.4-0.7)\,\tau_\Lambda$. In a recent work [Phys. Lett. B 811, 135916 (2020)] we studied this ${}_{\Lambda}^3\mathrm{H}$ lifetime puzzle theoretically using realistic three-body ${}_{\Lambda}^3\mathrm{H}$ and ${}^3\mathrm{He}$ wave functions computed within the ab initio no-core shell model approach with interactions derived from chiral effective field theory. In particular, $\tau({}_{\Lambda}^3\mathrm{H})$ was found to be strongly correlated with the $\Lambda$ separation energy $B_\Lambda$ in ${}_{\Lambda}^3\mathrm{H}$, the value of which is rather poorly known experimentally and, in addition, is known to suffer from sizable theoretical uncertainties inherent in the employed nuclear and hypernuclear interaction models. In the present work we find that these uncertainties propagate into $\tau({}_{\Lambda}^3\mathrm{H})$, and thus limit considerably the theoretical precision of its computed value. Although none of the conflicting RHI measured $\tau({}_{\Lambda}^3\mathrm{H})$ values can be excluded, but rather can be attributed to a poor knowledge of $B_\Lambda$, we note the good agreement between the lifetime value $\tau({}_{\Lambda}^3\mathrm{H})=238(27)$ ps computed at the lowest value $B_\Lambda=66$ keV reached by us and the very recent ALICE measured lifetime value $\tau^{\mathrm{ALICE}}({}_{\Lambda}^3\mathrm{H})=253(11)(6)$ ps associated with the ALICE measured $B_\Lambda$ value $B^{\mathrm{ALICE}}_\Lambda=102(63)(67)$ keV [Phys. Rev. Lett. 131, 102302 (2023)].

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arXiv2022

Lifetime of the hypertriton

Conflicting values of the hypertriton lifetime $\tau({}_\Lambda^3\mathrm{H})$ were derived in relativistic heavy ion (RHI) collision experiments over the last decade. A very recent ALICE Collaboration measurement is the only experiment where the reported $\tau({}_\Lambda^3\mathrm{H})$ comes sufficiently close to the free-$\Lambda$ lifetime $\tau_\Lambda$,as expected naively for a very weakly bound $\Lambda$ in ${}_\Lambda^3\mathrm{H}$. We revisited theoretically this ${}_\Lambda^3\mathrm{H}$ lifetime puzzle, using ${}_\Lambda^3\mathrm{H}$ and ${}^3\mathrm{He}$ wave functions computed within the abinitio no-core shell model employing interactions derived from chiral effective field theory to calculate the two-body decay rate $\Gamma({}_\Lambda^3\mathrm{H}\to{}^3\mathrm{He}+\pi^-)$. We found significant but opposing contributions arising from $\Sigma NN$ admixtures in ${}_\Lambda^3\mathrm{H}$ and from $\pi^- -{}^3\mathrm{He}$ final-state interaction. To derive $\tau({}_\Lambda^3\mathrm{H})$, we evaluated the inclusive $\pi^-$ decay rate $\Gamma_{\pi^-}({}_\Lambda^3\mathrm{H})$ by using the measured branching ratio $\Gamma({}_\Lambda^3\mathrm{H}\to{}^3\mathrm{He}+\pi^-)/\Gamma_{\pi^-}({}_\Lambda^3\mathrm{H})$ and added the $\pi^0$ contributions through the $\Delta I = \frac{1}{2}$ rule. The resulting $\tau({}_\Lambda^3\mathrm{H})$ varies strongly with the rather poorly known $\Lambda$ separation energy $E_{\mathrm{sep}}({}_\Lambda^3\mathrm{H})$ and it is thus possible to associate each one of the distinct RHI $\tau({}_\Lambda^3\mathrm{H})$ measurements with its own underlying value of $E_{\mathrm{sep}}({}_\Lambda^3\mathrm{H})$.

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arXiv2022

Nuclear physics uncertainties in light hypernuclei

The energy levels of light hypernuclei are experimentally accessible observables that contain valuable information about the interaction between hyperons and nucleons. In this work we study strangeness $S = -1$ systems $^{3,4}_\Lambda$H and $^{4,5}_\Lambda$He using the ab initio no-core shell model (NCSM) with realistic interactions obtained from chiral effective field theory ($\chi$EFT). In particular, we quantify the finite precision of theoretical predictions that can be attributed to nuclear physics uncertainties. We study both the convergence of the solution of the many-body problem (method uncertainty) and the regulator- and calibration data-dependence of the nuclear $\chi$EFT Hamiltonian (model uncertainty). For the former, we implement infrared correction formulas and extrapolate finite-space NCSM results to infinite model space. We then use Bayesian parameter estimation to quantify the resulting method uncertainties. For the latter, we employ a family of 42 realistic Hamiltonians and measure the standard deviation of predictions while keeping the leading-order hyperon-nucleon interaction fixed. Following this procedure we find that model uncertainties of ground-state $\Lambda$ separation energies amount to $\sim 20(100)$ keV in $^3_\Lambda$H($^4_\Lambda$H,He) and $\sim 400$ keV in $^5_\Lambda$He. Method uncertainties are comparable in magnitude for the $^4_\Lambda$H,He $1^+$ excited states and $^5_\Lambda$He, which are computed in limited model spaces, but otherwise much smaller. This knowledge of expected theoretical precision is crucial for the use of binding energies of light hypernuclei to infer the elusive hyperon-nucleon interaction.

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arXiv2020

Revisiting the hypertriton lifetime puzzle

Conflicting values of the hypertriton ($_{\Lambda}^{3}$H) lifetime were extracted in recent relativistic heavy-ion collision experiments. The ALICE Collaboration's reported $_{\Lambda}^{3}$H lifetime $\tau(_{\Lambda}^{3}$H) is compatible within measurement uncertainties with the free $\Lambda$ lifetime $\tau_{\Lambda}$, as naively expected for a loosely bound $\Lambda$ hyperon in $_{\Lambda}^{3}$H, whereas STAR's reported range of $\tau(_{\Lambda}^{3}$H) values is considerably shorter: $\tau_{\rm STAR}(_{\Lambda}^{3}$H)$\sim$(0.4-0.7)$\tau_{\Lambda}$. This $_{\Lambda}^{3}$H lifetime puzzle is revisited theoretically using $_{\Lambda}^{3}$H three-body wavefunctions generated in a chiral effective field theory approach to calculate the decay rate $\Gamma(_{\Lambda}^{3}$H$\,\to ^3$He$\,+\pi^-$). Significant but opposing contributions arise from $\Sigma NN$ admixtures in $_{\Lambda}^{3}$H and from $\pi^-$-$^3$He final-state interaction. Evaluating the inclusive $\pi^-$ decay rate $\Gamma_{\pi^-}(_{\Lambda}^{3}$H) via a branching ratio $\Gamma(_{\Lambda}^{3}$H$\,\to ^{3}$He+$\pi^-)/\Gamma_{\pi^-}(_{\Lambda}^{3}$H) determined in helium bubble-chamber experiments, and adding $\Gamma_{\pi^0}(_{\Lambda}^{3}$H) through the $\Delta I=\frac{1}{2}$ rule, we derive $\tau(_{\Lambda}^{3}$H) assuming several different values of the $\Lambda$ separation energy $B_{\Lambda}(_{\Lambda}^{3}$H). It is concluded that each of ALICE and STAR reported $\tau(_{\Lambda}^{3}$H) intervals implies its own constraint on $B_{\Lambda}(_{\Lambda}^{3}$H): $B_{\Lambda}\lesssim 0.1$ MeV for ALICE, $B_{\Lambda}\gtrsim 0.2$ MeV for STAR.

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arXiv2013

No-Core Shell Model for Nuclear Systems with Strangeness

We report on a novel ab initio approach for nuclear few- and many-body systems with strangeness. Recently, we developed a relevant no-core shell model technique which we successfully applied in first calculations of lightest $Λ$ hypernuclei. The use of a translationally invariant finite harmonic oscillator basis allows us to employ large model spaces, compared to traditional shell model calculations, and use realistic nucleon-nucleon and nucleon-hyperon interactions (such as those derived from EFT). We discuss formal aspects of the methodology, show first demonstrative results for ${}_Λ^3$H, ${}_Λ^4$H and ${}^4_Λ$He, and give outlook.

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arXiv2012

Calculations of $K^-$ nuclear quasi-bound states based on chiral meson-baryon amplitudes

In-medium ${\bar K}N$ scattering amplitudes developed within a new chirally motivated coupled-channel model due to Cieply and Smejkal that fits the recent SIDDHARTA kaonic hydrogen 1s level shift and width are used to construct $K^-$ nuclear potentials for calculations of $K^-$ nuclear quasi-bound states. The strong energy and density dependence of scattering amplitudes at and near threshold leads to $K^-$ potential depths $-Re V_K \approx 80 -120$ MeV. Self-consistent calculations of all $K^-$ nuclear quasi-bound states, including excited states, are reported. Model dependence, polarization effects, the role of p-wave interactions, and two-nucleon $K^-NN\rightarrow YN$ absorption modes are discussed. The $K^-$ absorption widths $Γ_K$ are comparable or even larger than the corresponding binding energies $B_K$ for all $K^-$ nuclear quasi-bound states, exceeding considerably the level spacing. This discourages search for $K^-$ nuclear quasi-bound states in any but lightest nuclear systems.

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arXiv2011

K^- nuclear potentials from in-medium chirally motivated models

A self consistent scheme for constructing K^- nuclear optical potentials from subthreshold in-medium Kbar-N s-wave scattering amplitudes is presented and applied to analysis of kaonic atoms data and to calculations of K^- quasibound nuclear states. The amplitudes are taken from a chirally motivated meson-baryon coupled-channel model, both at the Tomozawa-Weinberg leading order and at the next to leading order. Typical kaonic atoms potentials are characterized by a real part -Re V(K^-;chiral)=(85+/-5) MeV at nuclear matter density, in contrast to half this depth obtained in some derivations based on in-medium Kbar-N threshold amplitudes. The moderate agreement with data is much improved by adding complex rho- and rho^2-dependent phenomenological terms, found to be dominated by rho^2 contributions that could represent Kbar-NN -> YN absorption and dispersion, outside the scope of meson-baryon chiral models. Depths of the real potentials are then near 180 MeV. The effects of p-wave interactions are studied and found secondary to those of the dominant s-wave contributions. The in-medium dynamics of the coupled-channel model is discussed and systematic studies of K^- quasibound nuclear states are presented.

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arXiv2011

Chirally motivated K^- nuclear potentials

In-medium subthreshold KbarN scattering amplitudes calculated within a chirally motivated meson-baryon coupled-channel model are used self consistently to confront K^- atom data across the periodic table. Substantially deeper K^- nuclear potentials are obtained compared to the shallow potentials derived in some approaches from threshold amplitudes, with Re V_{chiral} = -(85+/-5) MeV at nuclear matter density. When KbarNN contributions are incorporated phenomenologically, a very deep K^- nuclear potential results, Re V_{chiral+phen.} = -(180+/-5) MeV, in agreement with density dependent potentials obtained in purely phenomenological fits to the data. Self consistent dynamical calculations of K^- nuclear quasibound states are reported and discussed.

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arXiv2009

Multi-$\bar{K}$ hypernuclei

Relativistic mean field calculations of multi-$\bar{K}$ hypernuclei are performed by adding $K^-$ mesons to particle-stable configurations of nucleons, $Λ$ and $Ξ$ hyperons. For a given hypernuclear core, the calculated $\bar{K}$ separation energy $B_{\bar{K}}$ saturates with the number of $\bar{K}$ mesons for more than roughly 10 mesons, with $B_{\bar{K}}$ bounded from above by 200 MeV. The associated baryonic densities saturate at values 2-3 times nuclear-matter density within a small region where the $\bar{K}$-meson densities peak, similarly to what was found for multi-$\bar{K}$ nuclei. The calculations demonstrate that particle-stable multistrange $\{N,Λ,Ξ\}$ configurations are stable against strong-interaction conversions $Λ\to N \bar{K}$ and $Ξ\to N \bar{K} \bar{K}$, confirming and strengthening the conclusion that kaon condensation is unlikely to occur in strong-interaction self-bound strange hadronic matter.

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arXiv2008

Multi-$\bar{K}$ nuclei and kaon condensation

We extend previous relativistic mean-field (RMF) calculations of multi-$\bar K$ nuclei, using vector boson fields with SU(3) PPV coupling constants and scalar boson fields constrained phenomenologically. For a given core nucleus, the resulting $\bar K$ separation energy $B_{\bar K}$, as well as the associated nuclear and $\bar K$-meson densities, saturate with the number $κ$ of $\bar K$ mesons for $κ> κ_{\rm sat} \sim 10$. Saturation appears robust against a wide range of variations, including the RMF nuclear model used and the type of boson fields mediating the strong interactions. Because $B_{\bar K}$ generally does not exceed 200 MeV, it is argued that multi-$\bar K$ nuclei do not compete with multihyperonic nuclei in providing the ground state of strange hadronic configurations and that kaon condensation is unlikely to occur in strong-interaction self-bound strange hadronic matter. Last, we explore possibly self-bound strange systems made of neutrons and ${\bar K}^0$ mesons, or protons and $K^-$ mesons, and study their properties.

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arXiv2008

Dynamics of \bar{K} and multi-\bar{K} nuclei

We report on self-consistent calculations of single-K^- nuclear states and multi-Kbar nuclear states in 12C, 16O, 40Ca and 208Pb within the relativistic mean-field (RMF) approach. Gradient terms motivated by the p-wave resonance Sigma(1385) are found to play a secondary role for single-K^- nuclear systems where the mean-field concept is acceptable. Significant contributions from the Kbar N -> pi Lambda conversion mode, and from the nonmesonic Kbar NN -> YN conversion modes which are assumed to follow a rho^2 density dependence, are evaluated for the deep binding-energy range of over 100 MeV where the decay channel Kbar N -> pi Sigma is closed. Altogether we obtain K^- total decay widths of 50-100 MeV for binding energies exceeding 100 MeV in single-K^- nuclei. Multi-Kbar nuclear calculations indicate that the binding energy per Kbar meson saturates upon increasing the number of Kbar mesons embedded in the nuclear medium. The nuclear and Kbar densities increase only moderately and are close to saturation, with no indication of any kaon-condensation precursor.

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