We demonstrate a novel method to search for physics beyond the standard model by determining the $\beta -\nu$ angular correlation from the recoil-ion energy distribution after $\beta$ decay of ions stored in a Penning trap. This recoil-ion energy distribution is measured with a retardation spectrometer. The unique combination of the spectrometer with a Penning trap provides a number of advantages, e.g., a high recoil-ion count rate and low sensitivity to the initial position and velocity distribution of the ions and completely different sources of systematic errors compared to other state-of-the-art experiments. Results of a first measurement with the isotope ${}^{35}\mathrm{Ar}$ are presented. Although currently at limited precision, we show that a statistical precision of about 0.5% is achievable with this unique method, thereby opening up the possibility of contributing to state-of-the-art searches for exotic currents in weak interactions.

The integral cross section of the ${}^{12}\mathrm{C}(n,p){}^{12}\mathrm{B}$ reaction has been determined for the first time in the neutron energy range from threshold to several GeV at the n_TOF facility at CERN. The measurement relies on the activation technique with the $\beta$ decay of ${}^{12}\mathrm{B}$ measured over a period of four half-lives within the same neutron bunch in which the reaction occurs. The results indicate that model predictions, used in a variety of applications, are mostly inadequate. The value of the integral cross section reported here can be used as a benchmark for verifying or tuning model calculations.

According to the Hugenholtz-Van Hove theorem, the nuclear symmetry energy $S\left(\rho \right)$ and its slope $L\left(\rho \right)$ at arbitrary densities can be decomposed in terms of the density and momentum dependence of the single-nucleon potentials in isospin-asymmetric nuclear matter. We quantify the correlations between several well-known isovector observables and $L\left(\rho \right)$ to locate the density range in which each isovector observable is most sensitive to the density dependence of the $S\left(\rho \right)$. We then study the correlation coefficients between those isovector observables and all the components of the $L\left(\rho \right)$. The neutron skin thickness of ${}^{208}\mathrm{Pb}$ is found to be strongly correlated with the $L\left(\rho \right)$ at a subsaturation density of $\rho =0.59{\rho }_0$ through the density dependence of the first-order symmetry potential. Neutron star radii are found to be strongly correlated with the $L\left(\rho \right)$ over a wide range of suprasaturation densities mainly through both the density and momentum dependence of the first-order symmetry potential. Finally, we find that although the crust-core transition pressure has a complex correlation with the $L\left(\rho \right)$, it is strongly correlated with the momentum derivative of the first-order symmetry potential and the density dependence of the second-order symmetry potential.

Based on the longitudinal Garvey-Kelson relation and its odd-even features recently discerned, we construct simple relations of $\alpha$-decay energies (denoted by $Q$) for four neighboring nuclei. These relations are found to yield very small deviations from available experimental data. We apply these new relations to both description of experimental $\alpha$-decay energies and prediction of the unknown $Q$ values of heavy nuclei.

We present the details of calculations we previously performed for the large $j$ behavior of certain $3j$ and $9j$ symbols.

We study excited-state properties of neutron-rich calcium isotopes based on chiral two- and three-nucleon interactions. We first discuss the details of our many-body framework, investigate convergence properties, and for two-nucleon interactions benchmark against coupled-cluster calculations. We then focus on the spectroscopy of ${}^{47-56}\mathrm{Ca}$, finding that with both 3N forces and an extended $pf{g}_{9/2}$ valence space, we obtain a good level of agreement with experiment. We also study electromagnetic transitions and find that experimental data are well described by our calculations. In addition, we provide predictions for unexplored properties of neutron-rich calcium isotopes.

The nuclear symmetry energy coefficients of finite nuclei are extracted by using the differences between the masses of isobaric nuclei. Based on the masses of more than 2400 nuclei with $A=10$–270, we investigate the model dependence in the extraction of the symmetry energy coefficient. We find that the extraction of the symmetry energy coefficients is strongly correlated with the forms of the Coulomb energy and the mass dependence of the symmetry energy coefficient adopted. The values of the extracted symmetry energy coefficients increase by about 2 MeV for heavy nuclei when the Coulomb correction term is involved. The values of the bulk symmetry energy coefficient $S_0$ and the surface-to-volume ratio $\kappa$ are simultaneously investigated based on the extracted symmetry energy coefficients.

Nucleon exchange mechanism is investigated in deep-inelastic symmetric heavy-ion collisions in the basis of the stochastic mean-field approach. By extending the previous work to off-central collisions, an analytical expression is deduced for the diffusion coefficient of the nucleon exchange mechanism. Numerical calculations are carried out for ${}^{40}\mathrm{Ca}+{}^{40}\mathrm{Ca}$ and ${}^{90}\mathrm{Zr}+{}^{90}\mathrm{Zr}$ systems and the results are compared with the phenomenological nucleon exchange model. Also, calculations are compared with the available experimental results of deep-inelastic collisions between calcium nuclei.

In this paper we study the azimuthal correlations of heavy quarks in $\mathrm{Pb}+\mathrm{Pb}$ collisions with $\sqrt{s}=2.76$ TeV at the Large Hadron Collider. Due to the interaction with the medium, heavy quarks and antiquarks are deflected from their original direction and the initial correlation of the pair is broadened. We investigate this effect for different transverse momentum classes. Low-momentum heavy-quark pairs lose their leading-order back-to-back initial correlation, while a significant residual correlation survives at large momenta. Due to the larger acquired average deflection from their original directions the azimuthal correlations of heavy-quark pairs are broadened more efficiently in a purely collisional energy loss mechanism compared to that including radiative corrections. This discriminatory feature survives when next-to-leading-order production processes are included.

The jet fragmentation function of inclusive jets with transverse momentum $p_{\mathrm{T}}$ above $100\text{GeV}/c$ in PbPb collisions has been measured using reconstructed charged particles with $p_{\mathrm{T}}$ above $1\text{GeV}/c$ in a cone of radius 0.3 around the jet axis. A data sample of PbPb collisions collected in 2011 at a nucleon-nucleon center-of-mass energy of $\sqrt{s_{{}_{\mathit{NN}}}}=2.76\text{TeV}$ corresponding to an integrated luminosity of $150\mu {\mathrm{b}}^{-1}$ is used. The results for PbPb collisions as a function of collision centrality and jet transverse momentum are compared to reference distributions based on $\mathit{pp}$ data collected at the same center-of-mass energy in 2013, with an integrated luminosity of $5.3{\text{pb}}^{-\text{1}}$. A centrality-dependent modification of the fragmentation function is found. For the most central collisions, a significant enhancement is observed in the PbPb/$\mathit{pp}$ fragmentation function ratio for charged particles with $p_{\mathrm{T}}$ less than $3\text{GeV}/c$. This enhancement is observed for all jet $p_{\mathrm{T}}$ bins studied.

Recently, the Weinberg compositeness condition of a bound state was generalized to account for resonant states and higher partial waves. We apply this extension to the case of the $\Lambda \left(1520\right)$ resonance and quantify the weight of the meson-baryon components in contrast to other possible genuine building blocks. This resonance was theoretically obtained from a coupled channels analysis using the $s$-wave $\pi {\Sigma }^{*}$ and $K{\Xi }^{*}$ and the $d$-wave $\overline{K}N$ and $\pi \Sigma$ channels, applying the techniques of the chiral unitary approach. We obtain the result that this resonance is essentially dynamically generated from these meson-baryon channels, leaving room for only $15\%$ weight of other kinds of components in its wave function.

We present and discuss numerical predictions for the neutron density distribution of ${}^{208}\mathrm{Pb}$ using various nonrelativistic and relativistic mean-field models for the nuclear structure. Our results are compared with the very recent pion photoproduction data from Mainz. The parity-violating asymmetry parameter for elastic electron scattering at the kinematics of the PREX experiment at JLab and the neutron skin thickness are compared with the available data. We consider also the dependence between the neutron skin and the parameters of the expansion of the symmetry energy.

We show that in asymmetric heavy-ion collisions, especially off-central $\mathrm{Cu} + \mathrm{Au}$ collisions, a sizable strength of electric field directed from Au nucleus to Cu nucleus is generated in the overlapping region, because of the difference in the number of electric charges between the two nuclei. This electric field would induce an electric current in the matter created after the collision, which results in a dipole deformation of the charge distribution. The directed flow parameters $v_1^{\pm }$ of charged particles turn out to be sensitive to the charge dipole and provide us with information about electric conductivity of the quark gluon plasma.

The neutron decay of an unbound resonance in ${}^{12}\mathrm{Be}$ has been measured at $1243\pm 21$ keV decay energy with a width of $634\pm 60$ keV. This state was populated with a one-proton removal reaction from a 71 MeV/u ${}^{13}\mathrm{B}$ beam incident upon a beryllium target. The invariant mass reconstruction of the resonance was achieved by measuring the daughter fragment in coincidence with neutrons. Despite being above the $2n$ separation energy, the state decays predominantly by the emission of one neutron to ${}^{11}\mathrm{Be}$, setting an upper limit on the branching ratio for the two-neutron decay channel to ${}^{10}\mathrm{Be}$ of less than 5%. From the characteristics of the population and decay of the resonance, it is concluded that this state cannot correspond to the previously observed state at $4580\pm 5$ keV.

Using fusion-evaporation reactions, a gas-filled recoil separator, and recoil-electron and recoil-electron-$\alpha$ tagging techniques, a new isomeric ${\frac{1}{2}}^{+}$ state [$T_{1/2}=45\left(3\right)\mathrm{ms}$] in ${}^{201}\mathrm{At}$ is identified, and an earlier reported corresponding state [$T_{1/2}=273\left(9\right)\mathrm{ms}$] in ${}^{199}\mathrm{At}$ is confirmed. The ${\frac{1}{2}}^{+}$ state is suggested to originate from an intruder $\pi {\left(s_{1/2}\right)}^{-1}$ configuration. In addition, nuclear structure of states below and above this ${\frac{1}{2}}^{+}$ state are studied in both nuclei. The isomer decays through a cascade of an $E3$ transition followed by a mixed $M1/E2$ transition to the ${\frac{9}{2}}^{-}$ ground state, and it is interpreted to be fed from nearly spherical ${\frac{3}{2}}^{+}$ and ${\frac{5}{2}}^{+}$ states originating from $\pi {\left(d_{3/2}\right)}^{-1}$ and $\pi {\left(d_{5/2}\right)}^{-1}$ configurations, respectively.

We calculate the nuclear matrix elements (NMEs) for neutrinoless double-beta decays of $pf$-shell nuclei using the shell model (SM) and energy density functional (EDF) methods. The systematic study of the decays of $\mathrm{Ca}\to \mathrm{Ti}$, $\mathrm{Ti}\to \mathrm{Cr}$ and $\mathrm{Cr}\to \mathrm{Fe}$ isotopes allows for a detailed comparison between the two nuclear structure many-body approaches. We observe that while the dominant Gamow-Teller part of the NME differs roughly by a factor of 2 between SM and EDF, when we restrict the calculations to spherical EDF states and seniority-zero SM configurations, the NMEs obtained by both methods are strikingly similar. This points out the important role of nuclear structure correlations for neutrinoless double-beta decay NMEs. We identify correlations associated with high-seniority components in the initial and final states of the decay as one of the reasons for the discrepancies between SM and EDF results. We also explore exact projection to good isospin, and conclude that it strongly reduces the Fermi contribution of the NMEs, but it has only a moderate effect in the Gamow-Teller part. This work opens up the door for NME benchmarks between different theoretical approaches, and constitutes a step forward towards more reliable estimations of the NMEs.

The ${\mu }^{-}+{}^2\mathrm{H}\to {\nu }_{\mu }+n+n$, ${\mu }^{-}+{}^3\mathrm{He}\to {\nu }_{\mu }+{}^3\mathrm{H}$, ${\mu }^{-}+{}^3\mathrm{He}\to {\nu }_{\mu }+n+d$, and ${\mu }^{-}+{}^3\mathrm{He}\to {\nu }_{\mu }+n+n+p$ capture reactions are studied with various realistic potentials under full inclusion of final-state interactions. Our results for the two- and three-body break-up of ${}^3\mathrm{He}$ are calculated with a variety of nucleon-nucleon potentials, among which is the AV18 potential, augmented by the Urbana IX three-nucleon potential. Most of our results are based on the single-nucleon weak-current operator. As a first step, we tested our calculation in the case of the ${\mu }^{-}+{}^2\mathrm{H}\to {\nu }_{\mu }+n+n$ and ${\mu }^{-}+{}^3\mathrm{He}\to {\nu }_{\mu }+{}^3\mathrm{H}$ reactions, for which theoretical predictions obtained in a comparable framework are available. Additionally, we have been able to obtain for the first time a realistic estimate for the total rates of the muon capture reactions on ${}^3\mathrm{He}$ in the break-up channels: 544 ${\mathrm{s}}^{-1}$ and 154 ${\mathrm{s}}^{-1}$ for the $n+d$ and $n+n+p$ channels, respectively. Our results are compared with the most recent experimental data, finding a rough agreement for the total capture rates, but failing to reproduce the differential capture rates.

The ternary breakup mechanism of ${}^{238}\mathrm{U}+{}^{197}\mathrm{Au}$ at $15A$ MeV has been investigated by a hybrid model that combines the improved quantum molecular dynamics (ImQMD) model together with a statistical code gemini++. The results are in good agreement with the experimental data and indicate that in peripheral reactions, ternary breakup in this reaction results from quasi-U statistical fission while for central and semicentral collisions it can be understood by a two-step mechanism: deep-inelastic collision (DIC) followed by a sequential binary breakup of one of the DIC products. In the process of DIC, there is a large mass transfer from Au to U to form transuranium. Due to the low fission barrier, such transuranium nuclei will decay into stable light nuclei through various fission modes. An event-by-event analysis shows that the second breakup mainly occurs in the deexcitation process and most of the ternary breakup events are from semicentral and peripheral collisions that correspond to deep inelastic and quasi-elastic reactions, respectively.

A new measurement of the rare, doubly radiative decay $\eta \to {\pi }^0\gamma \gamma$ was conducted with the Crystal Ball and TAPS multiphoton spectrometers together with the photon tagging facility at the Mainz Microtron MAMI. New data on the dependence of the partial decay width, $\Gamma (\eta \to {\pi }^0\gamma \gamma )$, on the two-photon invariant-mass squared, $m^2\left(\gamma \gamma \right)$, as well as a new, more precise value for the decay width, $\Gamma (\eta \to {\pi }^0\gamma \gamma )=(0.33\pm 0.{03}_{\mathrm{tot}})$ eV, are based on analysis of $1.2\times {10}^3\eta \to {\pi }^0\gamma \gamma$ decays from a total of $6\times {10}^7\eta$ mesons produced in the $\gamma p\to \eta p$ reaction. The present results for $d\Gamma (\eta \to {\pi }^0\gamma \gamma )/d{m}^2\left(\gamma \gamma \right)$ are in good agreement with previous measurements and recent theoretical calculations for this dependence.