Reviews in Physics最新文献

The advent of radioactive ion beam facilities and new detector technologies have opened up new possibilities to investigate the radioactive decays of highly unstable nuclei, in particular the proton emission, α decay and heavy cluster decays from neutron-deficient (or proton-rich) nuclei around the proton drip line. It turns out that these decay measurements can serve as a unique probe for studying the structure of the nuclei involved. On the theoretical side, the development in nuclear many-body theories and supercomputing facilities have also made it possible to simulate the nuclear clusterization and decays from a microscopic and consistent perspective. In this article we would like to review the current status of these structure and decay studies in heavy nuclei, regarding both experimental and theoretical opportunities. We then discuss in detail the recent progress in our understanding of the nuclear α formation probabilities in heavy nuclei and their indication on the underlying nuclear structure.

Phosphor-free InGaN/GaN multiple quantum well (MQW) white light-emitting diodes (LEDs) have the advantages of simpler device process and potentially higher efficiency, and have attracted much attention in recent years. A host of technologies are emerging for implementing such white-light LEDs. Among them, the key issue is the color tuning of different emission wavelengths from InGaN/GaN MQWs with different indium (In) content. However, owing to the limited growth technology for long-wavelength InGaN/GaN MQWs with high In content, it is very attractive to study selective area epitaxy (SAE) of InGaN/GaN MQWs on GaN microstructures with non- or semipolar microfacets combined with (0001) c-plane. In this paper, we briefly review the previous developments of InGaN/GaN MQW based phosphor-free white light LEDs, then the particular technology for the growth of InGaN/GaN MQWs on the regrown GaN microfacets using SAE has been introduced, and related mechanisms for the formation of different non- or semipolar GaN microfacets fabricated by various mask patterns are discussed in detail. Furthermore, sophisticated approaches made use of the InGaN/GaN MQWs on GaN microfacets to fabricated phosphor-free white light LEDs with polychromatic emissions are reviewed.

The first collisions of lead nuclei, delivered by the CERN Large Hadron Collider (LHC) at the end of 2010, at a centre-of-mass energy per nucleon pair $\sqrt{s_{\mathrm{NN}}}=$ 2.76 TeV, marked the beginning of a new era in ultra-relativistic heavy-ion physics. Following the Run 1 period, LHC also successfully delivered Pb–Pb collisions at the collision energy $\sqrt{s_{\mathrm{NN}}}=$ 5.02 TeV at the end of 2015. The study of the properties of the produced hot and dense strongly-interacting matter at these unprecedented energies is experimentally pursued by all four big LHC experiments, ALICE, ATLAS, CMS, and LHCb. This review presents selected experimental results from heavy-ion collisions delivered during the first three years of the LHC operation focusing on the bulk matter properties and the dynamical evolution of the created system. It also presents the first results from Run 2 heavy-ion data at the highest energy, as well as from the studies of the reference pp and p–Pb systems, which are an integral part of the heavy-ion programme.

Neutrino physics is nowadays receiving more and more attention as a possible source of information for the long-standing investigation of new physics beyond the Standard Model. The rather recent measurement of the third mixing angle θ₁₃ in the standard mixing oscillation scenario encourages the pursuit of what is still missing: the size of any leptonic CP violation, absolute neutrino masses and the characteristic nature of the neutrino. Several projects are currently running and they are providing impressive results. In this review, the phenomenology of neutrino oscillations that results from the last two decades of investigations is reviewed, with emphasis on our current knowledge and on what lesson can be taken from the past. We then present a critical discussion of current studies on the mass ordering and what might be expected from future results. Our conclusion is that decisions determining the next generation of experiments and investigations have to be strictly based on the findings of the current generation of experiment. In this sense it would be wise to wait a few years before taking decisions on the future projects. In the meantime, since no direct path forward is evident for the future projects, the community must be committed to their careful evaluation.

This paper is an experimental review of the study of processes with a single top quark at the LHC. The pioneering times are over, and this is now a sector of “precision physics” at colliders. Angular distributions of the decay products of singly-produced top quarks are unique tests of the electroweak interaction. Searches for rare final states of the form $t+X$ (where $X=\gamma ,Z,H$) are very sensitive to new physics, and will enter with Run II in a very interesting zone of the parameter space of some theories. The relative sign of the Yukawa coupling of the top quark with respect to the Higgs coupling to gauge bosons will be conclusively measured very soon in the tHq final state.

After the LHC Run 1, the standard model (SM) of particle physics has been completed. Yet, despite its successes, the SM has shortcomings vis-à-vis cosmological and other observations. At the same time, while the LHC restarts for Run 2 at 13 TeV, there is presently a lack of direct evidence for new physics phenomena at the accelerator energy frontier. From this state of affairs arises the need for a consistent theoretical framework in which deviations from the SM predictions can be calculated and compared to precision measurements. Such a framework should be able to comprehensively make use of all measurements in all sectors of particle physics, including LHC Higgs measurements, past electroweak precision data, electric dipole moment, $g-2,$ penguins and flavor physics, neutrino scattering, deep inelastic scattering, low-energy $e^{+}{e}^{-}$ scattering, mass measurements, and any search for physics beyond the SM. By simultaneously describing all existing measurements, this framework then becomes an intermediate step, pointing us toward the next SM, and hopefully revealing the underlying symmetries. We review the role that the standard model effective field theory (SMEFT) could play in this context, as a consistent, complete, and calculable generalization of the SM in the absence of light new physics. We discuss the relationship of the SMEFT with the existing kappa-framework for Higgs boson couplings characterization and the use of pseudo-observables, that insulate experimental results from refinements due to ever-improving calculations. The LHC context, as well as that of previous and future accelerators and experiments, is also addressed.

This article briefly reviews the current status and near-term prospects of experimental searches for neutrinoless double-beta decay. After discussing the motivation and history of neutrinoless double-beta decay, we will focus on the status of current experiments and the factors limiting their sensitivity. We will then discuss the prospects and requirements for proposed experiments that will probe the inverted neutrino mass hierarchy.

The first collisions of lead nuclei, delivered by the CERN Large Hadron Collider (LHC) at the end of 2010, at a centre-of-mass energy per nucleon pair $\sqrt{s_{\mathrm{NN}}}=$ 2.76 TeV, marked the beginning of a new era in ultra-relativistic heavy-ion physics. The study of the properties of the produced hot and dense strongly-interacting matter at these unprecedented energies is currently experimentally pursued by all four big LHC experiments, ALICE, ATLAS, CMS, and LHCb. The more than a factor 10 increase of collision energy at LHC, relative to the previously achieved maximal energy at other collider facilities, results in an increase of production rates of hard probes. This review presents selected experimental results focusing on observables probing hard processes in heavy-ion collisions delivered during the first three years of the LHC operation. It also presents the first results from Run 2 heavy-ion data at the highest energy, as well as from the studies of the reference pp and p–Pb systems, which are an integral part of the heavy-ion programme.

The top quark is the heaviest elementary particle known and its mass (m_top) is a fundamental parameter of the Standard Model (SM). The m_top value affects theory predictions of particle production cross-sections required for exploring Higgs-boson properties and searching for New Physics (NP). Its precise determination is essential for testing the overall consistency of the SM, to constrain NP models, through precision electroweak fits, and has an extraordinary impact on the Higgs sector, and on the SM extrapolation to high-energies. The methodologies, the results, and the main theoretical and experimental challenges related to the m_top measurements and combinations at the Large Hadron Collider (LHC) and at the Tevatron are reviewed and discussed. Finally, the prospects for the improvement of the m_top precision during the upcoming LHC runs are briefly outlined.