[en] There is a strong experimental and theoretical interest in determining the structure of hypernuclei and the effect of strangeness in strongly interacting many-body systems. Recently, we presented the first calculations of hypernuclei in the p shell from first principles. However, these calculations showed either slow convergence with respect to model-space size or, when the hyperon-nucleon potential is transformed via the Similarity Renormalization Group, strong induced three-body terms. By including these induced hyperon-nucleon-nucleon (YNN) terms explicitly, we get precise binding and excitation energies. We present first results for p-shell hypernuclei and discuss the origin of the YNN terms, which are mainly driven by the evolution of the Λ-Σ conversion terms. We find that they are tightly connected to the hyperon puzzle, a long-standing issue where the appearance of hyperons in models of neutron star matter lowers the predicted maximum neutron star mass below the bound set by the heaviest observed objects.

[en] Tremendous progress is being made on the experimental study of hypernuclei, especially on the spectroscopy of p-shell hypernuclei. Their theoretical description, however, is limited to phenomenological models or very light (i.e. s-shell) systems. We present the first ab-initio calculations of p-shell hypernuclei using chiral Hamiltonians including hyperon-nucleon and two- plus three-nucleon interactions, which to date constitute the most consistent starting-point to solving the hypernuclear many-body problem. The many-body calculations are performed in the framework of the importance-truncated no-core shell model using leading-order (LO) chiral hyperon-nucleon and chiral two- plus three-body nucleon-nucleon interactions at N³LO and N²LO, respectively. To improve convergence with respect to model space size, the interactions are evolved consistently using a similarity renormalization group transformation. We show absolute energies and spectra for selected single-lambda-hypernuclei up to the _ΛLi isotope chain.

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[en] The no-core shell model (NCSM) and valence-space shell model (SM) are successful tools for the description of the nuclear spectroscopy. Both methods are computationally demanding and are limited by the model-space dimensions. To extend the NCSM and SM to larger model spaces, we apply an importance-truncation (IT) scheme based on a perturbative importance measure reducing the model spaces to the relevant basis states for the description of one or a few target eigenstates. This IT scheme necessitates an extrapolation to vanishing importance measure. Since the dependence of the energies on the importance measure can be highly non-linear, the extrapolation can give rise to large uncertainties. We present a more sophisticated extrapolation technique based on the energy variance, which vanishes in the limit of the full model space. We demonstrate the efficiency of the IT-NCSM and IT-SM with energy-variance extrapolation for ground-state and excitation energies of p-shell nuclei (IT-NCSM) and pf-shell nuclei (IT-SM) by comparing the results to both, full and importance-truncated NCSM and SM calculations with the conventional threshold extrapolation.

[en] Tremendous progress is being made on the experimental study of hypernuclei, especially on the spectroscopy of p-shell hypernuclei. Their theoretical description, however, is limited to phenomenological models or to very light (i.e. s-shell) systems. We present ab initio calculations of p-shell hypernuclei using chiral Hamiltonians including leading-order (LO) hyperon-nucleon as well as two- and three-nucleon interactions at N³LO and N²LO, respectively. To improve convergence with respect to model space size, the Hamiltonians are evolved using a Similarity Renormalization Group (SRG) transformation. The many-body calculations are carried out in the framework of the importance-truncated no-core shell model. We present the first ab initio results for the spectroscopy of _Λ⁷Li, _Λ⁹Be and _Λ¹³C obtained using chiral and phenomenological hyperon-nucleon interactions. We also discuss the role of SRG-induced hyperon-nucleon-nucleon (YNN) terms which hint at the impact of chiral YNN interactions.

[en] We explore the systematics of ground-state and excitation energies in singly-strange hypernuclei throughout the helium and lithium isotopic chains — from ${}_{\mathrm{\Lambda }}{}^5\mathrm{He}$ to ${}_{\mathrm{\Lambda }}{}^{11}\mathrm{He}$ and from ${}_{\mathrm{\Lambda }}{}^7\mathrm{Li}$ to ${}_{\mathrm{\Lambda }}{}^{12}\mathrm{Li}$ — in the ab initio no-core shell model with importance truncation. All calculations are based on two- and three-baryon interaction from chiral effective field theory and we employ a similarity renormalization group transformation consistently up to the three-baryon level to improve the model-space convergence. While the absolute energies of hypernuclear states show a systematic variation with the regulator cutoff of the hyperon–nucleon interaction, the resulting neutron separation energies are very stable and in good agreement with available data for both nucleonic parents and their daughter hypernuclei. We provide predictions for the neutron separation energies and the spectra of neutron-rich hypernuclei that have not yet been observed experimentally. Furthermore, we find that the neutron drip lines in the helium and lithium isotopic chains are not changed by the addition of a hyperon.

[en] Particle identification (PID) is an important task for many experimental techniques. A well-known approach for PID in many detection systems is based on pulse shape analysis (PSA), i.e. identification based on the difference in the pulse shape produced by different particle species. In most methods specific features of the detector signals are analyzed employing profound knowledge of the involved pulse shapes and the need of precise adjustments for individual detectors. A new approach to achieve PID based on PSA uses clustering algorithms without making any assumptions on the shape of detector pulses and is thus applicable to many detector types. The method is also self-tuning, i.e. no adjustment to a specific detector is necessary. In this talk a method is presented that uses the fuzzy c-means clustering algorithm and has already been applied to liquid scintillators for γ-n discrimination. The same method can be used without modifications to perform γ-p discrimination for CsI(Tl) scintillator signals and in particular produces identical results for different individual detectors.

[en] The decay time of CsI(Tl) scintillating material consists of more than a single exponential component. The ratio between the intensity of these components varies as a function of the ionizing power of the absorbed particles, such as gamma-rays or protons, and the temperature. This property can therefore be used for particle discrimination and for temperature monitoring, using pulse shape analysis. An unsupervised method that uses fuzzy clustering algorithms for particle identification based on pulse shape analysis is presented. The method is applied to discriminate between photon- and proton-induced signals in CsI(Tl) scintillator detectors. The first results of a method that uses pulse shape analysis for correcting the temperature-dependent gain effect of the detector are also presented. The method aims at conserving a good energy resolution in a temperature varying environment without the need to measure the temperature of the detector externally.