Progress in Particle and Nuclear Physics最新文献

One of the many physical questions that have emerged from studies of heavy-ion collisions at RHIC and the LHC concerns the validity of hydrodynamic modelling at the very early stages, when the Quark–Gluon Plasma system produced is still far from isotropy. In this article we review the idea of far-from-equilibrium hydrodynamic attractors as a way to understand how the complexity of initial states of nuclear matter is reduced so that a hydrodynamic description can be effective.

One of characteristic phenomena for nuclei beyond the proton dripline is the simultaneous emission of two protons (2p). The current status of our knowledge of this most recently observed and the least known decay mode is presented. First, different approaches to theoretical description of this process, ranging from effective approximations to advanced three-body models are overviewed. Then, after a brief survey of main experimental methods to produce 2p-emitting nuclei and techniques to study their decays, experimental findings in this research field are presented and discussed. This review covers decays of short-lived resonances and excited states of unbound nuclei as well as longer-lived, ground-state radioactive decays. In addition, more exotic decays like three- and four-proton emission are addressed. Finally, related few-body topics, like two-neutron and four-neutron radioactivity, and the problem of the tetraneutron are shortly discussed.

Phase transitions in a non-perturbative regime can be studied by ab initio Lattice Field Theory methods. The status and future research directions for LFT investigations of Quantum Chromo-Dynamics under extreme conditions are reviewed, including properties of hadrons and of the hypothesized QCD axion as inferred from QCD topology in different phases. We discuss phase transitions in strong interactions in an extended parameter space, and the possibility of model building for Dark Matter and Electro-Weak Symmetry Breaking. Methodological challenges are addressed as well, including new developments in Artificial Intelligence geared towards the identification of different phases and transitions.

Extensive experimental and theoretical explorations over the last decades showed that the nucleon (proton/neutron) is not just a simple system of 3 quarks bound by gluons, but a complex system of valence and sea quarks as well as gluons (summarized as partons) which are all interacting with each other and moving relative to each other, following the rules of quantum chromo dynamics (QCD). To understand how the properties of these colored building blocks are related to the basic properties of the nucleon like its mass, its spin or its charge, a full understanding of the relevant effective degrees of freedom and of the effective interactions at large distances is required. In the classical picture of parton dynamics in high energy interactions the description is often simplified into two cases. On the one side the classical form factors, providing a 2D picture of the transverse position distribution and on the other side, the one-dimensional picture of a fast moving nucleon as a collection of co-linearly moving quarks and gluons, described in terms of the longitudinal momentum fraction in parton distribution functions. However, recent experimental and theoretical advances during the last two decades showed, that such a simple picture is not adequate for a full description, especially if transverse spin dependent observables are involved. It turned out, that the intrinsic transverse motion of partons and also the correlation between momentum and position information have to be considered, requiring a full 3-dimensional understanding of the nucleon structure. This review will give an overview on the main experimental data for 3D nucleon structure studies, available from lepton and hadron scattering and its interpretation in terms of generalized parton distributions (GPDs) and transverse momentum dependent parton distributions (TMDs). Recent global fits of both types of distribution functions based on experimental data and their physics content will be presented and discussed on the way to a full 3D imaging of the nucleon. Furthermore, an overview of current and future trends and new perspectives in the field will be provided.

As a free, intensive, rarely interactive, and well directional messenger, solar neutrinos have been driving both solar physics and neutrino physics developments for more than half a century. Since more extensive and advanced neutrino experiments are under construction, being planned or proposed, we are striving toward an era of precise and comprehensive measurement of solar neutrinos in the next decades. In this article, we review recent theoretical and experimental progress achieved in solar neutrino physics. We present not only an introduction to neutrinos from the standard solar model and the standard flavor evolution, but also a compilation of a variety of new physics that could affect and hence be probed by solar neutrinos. After reviewing the latest techniques and issues involved in the measurement of solar neutrino spectra and background reduction, we provide our anticipation on the physics gains from the new generation of neutrino experiments.

Primordial black holes are under intense scrutiny since the detection of gravitational waves from mergers of Solar-mass black holes in 2015. More recently, the development of numerical tools and the precision observational data have rekindled the effort to constrain the black hole abundance in the lower mass range, that is $M<10^{23}$g. In particular, primordial black holes of asteroid mass $M\sim 10^{17}$–$10^{23}$g may represent 100% of dark matter. While the microlensing and stellar disruption constraints on their abundance are weaker than originally proposed, Hawking radiation of these black holes seems to be the primary method for detecting or constraining such black holes. Hawking radiation constraints on primordial black holes date back to the first papers by Hawking. Black holes evaporating in the early universe may have generated the baryon asymmetry, modified Big Bang nucleosynthesis, distorted the cosmic microwave background and/or produced cosmological backgrounds of stable particles such as photons and neutrinos. At the end of their lifetime, exploding primordial black holes would produce high energy cosmic rays that would provide invaluable access to the physics at energies up to the Planck scale. In this review, we describe the main principles of Hawking radiation, which lie at the intersection of general relativity, quantum mechanics and statistical physics/thermodynamics. We then present an up-to-date status of the different constraints on primordial black holes that rely on the evaporation phenomenon, and give, where relevant, prospects for future work. In particular, we also discuss non-standard black holes and the emission of Beyond the Standard Model degrees of freedom.

In this work, we review the experimental and theoretical developments of bottomonia production in proton+proton and heavy-ion collisions. The bottomonia production process is proving to be one of the most robust processes to investigate the fundamental aspects of Quantum Chromodynamics at both low and high temperatures. The LHC experiments in the last decade have produced large statistics of bottomonia states in wide kinematic ranges in various collision systems. The bottomonia have three ${\rm Y}$ S-states which are reconstructed in dilepton invariant mass channel with high mass resolution by LHC detectors and P-states are measured via their decay to S-states. We start with the details of measurements in proton+proton collisions and their understanding in terms of various effective theoretical models. Here we cover both the Tevatron and LHC measurements with $\sqrt{s}$ spanning from 1.8 TeV to 13 TeV. The bottomonia states have particularly been very good probes to understand strongly interacting matter produced in heavy-ion collisions. The Pb+Pb collisions have been performed at $\sqrt{s_{NN}}$ = 2.76 TeV and 5.02 TeV at LHC. This led to the detailed study of the modification of bottomonia yields as a function of various observables and collision energy. At the same time, the improved results of bottomonia production became available from RHIC experiments which have proven to be useful for a quantitative comparison. A systematic study of bottomonia production in p+p, p+Pb and Pb+Pb has been very useful to understand the medium effects in these collision systems. We review some of the (if not all the) models of bottomonia evolution due to various processes in a large dynamically evolving medium and discuss these in comparison with the measurements.