Table of contents

The recent measurement of two solar mass pulsars has initiated an intense discussion on its impact on our understanding of the high-density matter in the cores of neutron stars. A task force meeting was held from 7–10 October 2013 at the Frankfurt Institute for Advanced Studies to address the presence of quark matter in these massive stars. During this meeting, the recent observational astrophysical data and heavy-ion data was reviewed. The possibility of pure quark stars, hybrid stars and the nature of the QCD phase transition were discussed and their observational signals delineated.

Electromagnetic reactions on light nuclei are fundamental to advance our understanding of nuclear structure and dynamics. The perturbative nature of the electromagnetic probes allows to clearly connect measured cross sections with the calculated structure properties of nuclear targets. We present an overview on recent theoretical ab initio calculations of electron-scattering and photonuclear reactions involving light nuclei. We encompass both the conventional approach and the novel theoretical framework provided by chiral effective field theories. Because both strong and electromagnetic interactions are involved in the processes under study, comparison with available experimental data provides stringent constraints on both many-body nuclear Hamiltonians and electromagnetic currents. We discuss what we have learned from studies on electromagnetic observables of light nuclei, starting from the deuteron and reaching up to nuclear systems with mass number A = 16.

Fluid dynamical models preceded the first heavy ion accelerator experiments, and led to the main trend of this research since then. In recent years fluid dynamical processes became a dominant direction of research in high energy heavy ion reactions. The Quark–Gluon plasma formed in these reactions has low viscosity, which leads to significant fluctuations and turbulent instabilities. One has to study and separate these two effects, but this is not done yet in a systematic way. Here we present a few selected points of the early developments, the most interesting collective flow instabilities, their origins, their possible ways of detection and separation form random fluctuations arising from different origins, among these the most studied is the randomness of the initial configuration in the transverse plane.

I review recent measurements of a large set of flow observables associated with event-shape fluctuations and collective expansion in heavy ion collisions. First, these flow observables are classified and experiment methods are introduced. The experimental results for each type of observables are then presented and compared to theoretical calculations. A coherent picture of initial condition and collective flow based on linear and nonlinear hydrodynamic responses is derived, which qualitatively describe most experimental results. I discuss new types of fluctuation measurements that can further our understanding of the event-shape fluctuations and collective expansion dynamics.

In this contribution we discuss in detail the most widespread formalisms employed to derive relativistic dissipative fluid dynamics from the Boltzmann equation: Chapman–Enskog expansion and Israel–Stewart theory. We further point out the drawbacks of each theory and explain possible ways to circumvent them. Recent developments in the derivation of fluid dynamics from the Boltzmann equation are also discussed.

This contribution to the focus issue covers anisotropic flow in hybrid approaches. The historical development of hybrid approaches and their impact on the interpretation of flow measurements is reviewed. The major ingredients of a hybrid approach and the transition criteria between transport and hydrodynamics are discussed. The results for anisotropic flow in (event-by-event) hybrid approaches are presented. Some hybrid approaches rely on hadronic transport for the late stages for the reaction (so called afterburner) and others employ transport approaches for the early non-equilibrium evolution. In addition, there are 'full' hybrid calculations where a fluid evolution is dynamically embedded in a transport simulation. After demonstrating the success of hybrid approaches at high Relativistic Heavy Ion Collider and Large Hadron Collider energies, existing hybrid caluclations for collective flow observables at lower beam energies are discussed and remaining challenges outlined.

The charmonium transverse momentum distribution is more sensitive to the nature of the hot quantum chromodynamic matter created in high energy nuclear collisions compared with the yield. Taking a detailed transport approach for charmonium motion together with a hydrodynamic description for the medium evolution, the cancellation between the two hot nuclear matter effects, the dissociation and the regeneration, controls the charmonium transverse momentum distribution. In particular, the second moment of the distribution can be used to differentiate between the hot mediums produced at SPS, RHIC and LHC energies.

The collective expansion of matter created in collisions of heavy-ions, ranging from collision energies of tens of MeV to a few TeV per nucleon pair, proved to be one of the best probes to study the detailed properties of these unknown states of matter. Collective expansion originates from the initial pressure gradients in the created hot and dense matter. These pressure gradients transform the initial spatial deformations and inhomogeneities of the created matter into momentum anisotropies of the final state particle production, which we call anisotropic flow. These momentum anisotropies are experimentally characterized by so-called flow harmonics. In this paper I review ALICE measurements of the flow harmonics at the CERN Large Hadron Collider and discuss some of the open questions.

We consider the possibility of detecting relic anti-neutrinos by their resonant absorption in a nucleus, which is capable of undergoing electron capture. Ongoing and future developments in Penning Trap Mass Spectrometry and Cryogenic Micro-Calorimetry may bring this possibility closer to reality.

The relative immunity of muons to synchrotron radiation suggests that they might be used in place of electrons as probes in fundamental high-energy physics experiments. Muons are commonly produced indirectly through pion decay by interaction of a charged particle beam with a target. However, the large angle and energy dispersion of the initial beams as well as the short muon lifetime limits many potential applications. Here, we describe a fast method for manipulating the longitudinal and transverse phase-space of a divergent pion–muon beam to enable efficient capture and downstream transport with minimum losses. We also discuss the design of a handling system for the removal of unwanted secondary particles from the target region and thus reduce activation of the machine. The compact muon source we describe can be used for fundamental physics research in neutrino experiments.

Applying Discretized Light Cone Quantization, we perform the first calculation of the spectrum of true muonium, the ${{\mu }^{+}}{{\mu }^{-}}$ atom, as modified by the inclusion of an $|e\bar{e}\rangle$ Fock component. The shift in the mass eigenvalue is found to be largest for triplet states. If m_e is taken to be a substantial fraction of ${{m}_{\mu }}$, the integrated probability of the electronic component of the ${{1}^{3}}{{S}_{1}}$ state is found to be as large as $O({{10}^{-2}})$. Initial studies of the Lamb shift for the atom are performed. Directions for making the simulations fully realistic are discussed.

Considering the constraints from the flavor physics, precision electroweak measurements, Higgs data and dark matter detections, we scan over the parameter space of the minimal supersymmetric Standard Model (MSSM) and calculate the cross section of the ${{{\rm e}}^{+}}{{{\rm e}}^{-}}\to {\rm h}\gamma$ process in the allowed parameter space. We find that, since the loop-induced ${\rm h}\gamma \gamma$ and ${\rm hZ}\gamma$ gauge couplings can simultaneously contribute to the process ${{{\rm e}}^{+}}{{{\rm e}}^{-}}\to {\rm h}\gamma$, the cross section can be sizably enhanced by a light stau, maximally 1.47 (1.38) times larger than the Standard Model prediction at $\sqrt{s}=240\ (350)$ GeV. So with high luminosity, measurements on the ${{{\rm e}}^{+}}{{{\rm e}}^{-}}\to {\rm h}\gamma$ process may be used to test for the anomalous ${\rm h}\gamma \gamma$ and ${\rm hZ}\gamma$ gauge couplings in the MSSM at a Higgs factory.

We use an effective field-theoretical model to describe a QCD-type phase transition in the early universe. It is assumed that the formation of a new phase proceeds via supercooling and thermal activation. A subsequent rolling-down process is characterized by a microscopic time scale of a few ${\rm fm}/{\rm C}$. An iterative scheme is formulated where the Hubble parameter is determined self-consistently with the order parameter dynamics. A possibility of a 'mini-inflation' scenario is discussed critically. On the macroscopic scale (μs) the delayed phase transition is described dynamically by solving the Friedman equations. The evolution through the mixed phase after supercooling/reheating is considered and the entropy generated in this process is estimated.

We investigate the chaoticity parameter λ in two-pion interferometry in an expanding boson gas model. The degree of Bose–Einstein condensation of identical pions, density distributions, and Hanbury–Brown–Twiss (HBT) correlation functions are calculated for expanding gas within the mean-field description with a harmonic oscillator potential. The results indicate that a source with thousands of identical pions may exhibit a degree of Bose–Einstein condensation at the temperatures encountered during the hadronic phase in relativistic heavy-ion collisions. This finite condensation may decrease the chaoticity parameter λ in two-pion interferometry measurements at low pion-pair momenta, but influence only slightly the λ value at high pion-pair momentum.

Deformed quasiparticle random phase approximation with realistic nucleon–nucleon interactions is employed to investigate β-decay half-lives and β-delayed neutron emission probabilities of neutron-rich Kr and Sr isotopes. The residual particle–particle and particle-hole interactions are obtained in terms of the Brückner G-matrix with the charge-dependent Bonn nucleon–nucleon force. Both allowed Gamow–Teller and first-forbidden transitions are taken into account. The available experimental half-lives are well reproduced with a factor of about three. Predictions on β-decay properties are made for more neutron-rich isotopes, which could be useful for future experiments.

Berkelium isotopes have been produced in ¹¹B-induced reaction on ²³⁸U. The EC decay of ²⁴⁴Bk → ²⁴⁴Cm has been studied by carrying out the single and coincidence measurements of the γ-rays emitted during the de-excitation of the ²⁴⁴Cm levels. Radiochemical separations have been carried out to minimize the contribution from the fission products and target. The new half-life of ²⁴⁴Bk is obtained as 5.02 ± 0.03 h, which is close to the theoretically calculated value. The relative intensities of the decay γ-rays have been re-evaluated. Based on the coincidence measurements, a tentative partial level scheme for ²⁴⁴Bk → ²⁴⁴Cm decay has been proposed.

Superheavy nuclei produced until now are decaying mainly by α emission and spontaneous fission. Calculated α decay half-lives are in agreement with experimental data to within one order of magnitude. The discrepancy between theory and experiment can be as high as ten orders of magnitude for spontaneous fission. We analyze a way to improve the accuracy by using the action integral based on cranking inertia and a potential barrier computed by the macroscopic-microscopic method with a two-center shell model. Illustrations are given for ²⁸²Cn which has a measured fission half-life.

Nuclear fusion cross-sections considerably higher than corresponding theoretical predictions are observed in low-energy experiments with metal matrix targets and accelerated deuteron beams. The cross-section increment is significantly higher for liquid than for solid targets. We propose that the same two-body correlation entropy used in evaluating the metal melting entropy explains the large liquid–solid difference of the effective screening potential that parameterizes the cross-section increment. This approach is applied to the specific case of the $^{6}{\rm Li}{{({\rm d},\alpha )}^{4}}{\rm He}$ reaction, whose measured screening potential liquid–solid difference is $(235\pm 63)$ eV. Cross sections in the two metals with the highest two-body correlation entropy (In and Hg) have not yet been measured: increments of the cross sections in liquid relative to the ones in solid metals are estimated with the same procedure.

Using a multi-phase transport (AMPT) model, we investigate the effect of partonic cascade on two-pion HBT parameters of the core–halo source in relativistic heavy-ion collisions. The evolution time as a function of the partonic cross section for Au+Au central collisions at $\sqrt{{{s}_{NN}}}=200$ GeV shows that the evolution time of the pion emission source is decreased with an increasing partonic cross section, and the drop is due to the evolution time of the core. The partonic cascade with a larger cross section leads to a shorter lifetime of the source.

We show analytically that in the cumulative particles production off nuclei multiple interactions leads to a glory-like backward-focusing effect. Employing the small phase space method, we arrived at a characteristic angular dependence of the production cross section ${\rm d}\sigma \sim 1/\sqrt{\pi -\theta }$ near the strictly backward direction. This effect takes place for any number $n\geqslant 3$ of interactions of rescattered particles, either elastic or inelastic (with resonance excitations in intermediate states), when the final particle is produced near the corresponding kinematical boundary. In the final angles interval, including the value $\theta =\pi$, the angular dependence of the cumulative production cross section can have a crater-like (or funnel-like) form. Such a behaviour of the cross section near the backward direction is in qualitative agreement with some of the available data. Explanation of this effect and the angular dependence of the cross section near $\theta \sim \pi$ are presented for the first time

Observations with the Cherenkov telescopes are in principle limited to clear sky conditions due to significant absorption of Cherenkov light by clouds. If the cloud level is high enough or the atmospheric transmission of the cloud is high, then high energy showers (with TeV energies) can still produce enough Cherenkov photons allowing detection by telescopes with large sizes and cameras with large field of view (FOV). In this paper, we study the possibility of observations of showers, induced by high-energy particles in the atmosphere, in the presence of clouds that are completely or partially opaque for Cherenkov radiation. We show how the image parameters of the Cherenkov light distribution on the telescope camera are influenced for different opacity and altitude of the cloud. By applying the Monte Carlo simulations, we calculate the scaled LENGTH and WIDTH parameters with the purpose to separate γ-ray and proton initiated showers in real data. We show, that the high level of the night sky background effects the selection efficiency of the γ-ray initiated showers. However, application of the higher image-cleaning level significantly improves expected quality factors. The estimated γ-ray selection efficiency for the detector with the camera field of view (FOV) limited to 8$^{{}^\circ }$ is slightly better than for the camera with an unlimited FOV, although the number of identified γ-ray events is lower. We conclude that large Cherenkov telescopes with large FOV cameras can be used for observations of very high energy γ-rays in the presence of clouds. Consequently, the amount of useful data can be significantly enlarged.