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We have developed a learning unit based on the Standard Model of particle physics, featuring novel typographic illustrations of elementary particles and particle systems. Since the unit includes antiparticles and systems of antiparticles, a visualization of anticolor charge was required. We propose an alternative to the commonly used complementary-color method, whereby antiparticles and antiparticle systems are identified through the use of stripes instead of a change in color. We presented our proposal to high school students and physics teachers, who evaluated it to be a more helpful way of distinguishing between color charge and anticolor charge.

The top quark is the heaviest elementary particle known. It has been proposed many times that new physics beyond the current theory of elementary particles may reveal itself in top quark interactions. The charge asymmetry in the pair production of a fermion and its antiparticle has been known for many decades. Early measurements of such asymmetry in top quark pair production showed a disagreement with the prediction by more than 3 standard deviations. Many years of an effort on both experimental and theoretical side have allowed to understand the top quark pair charge asymmetry better and to bring back the agreement between the measurements and the theory. In this article, these efforts are reviewed together with the discussion about a potential future of such measurements.

We discuss a covariant relativistic Boltzmann equation which describes the evolution of a system of particles in spacetime evolving with a universal invariant parameter &tau, The observed time t of Einstein and Maxwell, in the presence of interaction, is not necessarily a monotonic function of &tau, If t ( &tau, ) increases with &tau, the worldline may be associated with a normal particle, but if it is decreasing in &tau, it is observed in the laboratory as an antiparticle. This paper discusses the implications for entropy evolution in this relativistic framework. It is shown that if an ensemble of particles and antiparticles, converge in a region of pair annihilation, the entropy of the antiparticle beam may decreaase in time.

A study of positron capture in a two-(pressure) stage buffer gas accumulation apparatus is presented for a variety of species, including some molecules which are known to be either efficient for positron trapping, or are frequently used to cool the particles when held in these devices. Absolute accumulation efficiencies are reported for all species. A detailed optimisation procedure, which has identified the main processes responsible for positron capture and loss in the trap, has been deployed to explore accumulation efficiency as the gas pressure and the electrostatic well depth in the trap are systematically varied. Accumulation exploiting energy loss via molecular vibrational transitions has been observed for the first time for a number of gases, though at much lower efficiency than achieved using electronic excitation processes.

We study the out-of-equilibrium properties of 1+1 dimensional quantum electrodynamics (QED), discretized via the staggered-fermion Schwinger model with an Abelian Zn gauge group. We look at two relevant phenomena: first, we analyze the stability of the Dirac vacuum with respect to particle/antiparticle pair production, both spontaneous and induced by an external electric field; then, we examine the string breaking mechanism. We observe a strong effect of confinement, which acts by suppressing both spontaneous pair production and string breaking into quark/antiquark pairs, indicating that the system dynamics displays a number of out-of-equilibrium features.

The observation of sub-GeV antideuteron in the cosmic ray flux could be a very strong signature of dark matter (DM) annihilation in our galaxy. The predicted antideuteron flux resulting from secondary interactions of primary cosmic rays with the Inter-Stellar medium is expected to be very low and in particular is kinematically suppressed at low energy (sub-GeV). Well motivated theories beyond the Standard Model contain viable dark matter candidates, which could lead to a significant enhancement of the antideuteron flux due to annihilation or decay of dark matter particles. This flux contribution is believed to be relatively large at low energies, where the secondary background is suppressed, which leads to an high interest in the development of new detection techniques for low energy antideuteron. Current search of antideuteron in cosmic rays are based on the well established technique of magnetic spectrometry (BESS-Polar II and AMS-02 experiments). With the aim to explore kinetic energy regions below 0.2 GeV/n, i.e. below the lower threshold of current and past magnetic spectrometers, some new detection techniques, involving stopping antideuterons captured to form exotic atoms, have been developed. The GAPS experiment, based on the detection of characteristics X-rays, and the ADHD concept, based on the metastable states in Helium target, will be described. In particular the performances of an high pressure (200 bar) Helium scintillator prototype, capable of fast timing and good spatial and energy resolution will be shown. As a result of the preliminary test phase of this prototype in the INFN-TIFPA laboratory, the perspectives of this detection technique for antiproton rejection and its sensitivity to the Dark Matter search in the antideuteron annihilation channel will be described.

Theories beyond the Standard Model predict dark matter candidates that could provide a significant enhancement of the antideuteron and antiproton flux, in particular at low energies. The General Antiparticle Spectrometer (GAPS) experiment is the first antimatter search experiment designed specifically for low-energy cosmic ray antideuterons and antiprotons. GAPS identifies antideuterons and antiprotons using a technique based on exotic atoms. This novel detection technique allows GAPS to have unprecedented sensitivity in the low energy range ( 0.25 GeV/n) for antiprotons and antideuterons. The apparatus consists of 10 planes of lithium-drifted Si (Si(Li)) detectors, surrounded on all sides by a plastic scintillator time-of-flight. GAPS is designed to carry out its science program using long-duration balloon flights in Antarctica and is currently scheduled by NASA for its first flight in late 2020. This presentation will describe the design, status, and discovery potential of the GAPS scientific program.

Positrons (i.e., antielectrons) find use in a wide variety of applications, and antiprotons are required for the formation and study of antihydrogen. Available sources of these antiparticles are relatively weak. To optimize their use, most applications require that the antiparticles be accumulated into carefully prepared plasmas. We present an overview of the techniques that have been developed to efficiently accumulate low energy antiparticles and create, in particular, tailored antiparticle plasmas. Techniques are also described to create tailored antiparticle beams. Many of these techniques are based on methods first developed by the nonneutral plasma community using electron plasmas for increased data rate. They have enabled the creation and trapping of antihydrogen, have been critical to studies of positron and positronium interactions with matter, including advanced techniques to characterize materials and material surfaces, and have led to the creation and study of the positronium molecule. Rather than attempting to be comprehensive, we focus on techniques that have proven most useful, applications where there has been significant, recent progress, and areas that hold promise for future advances. Examples of the latter include the ever more precise comparisons of the properties of antihydrogen and hydrogen, tests of gravity using antihydrogen and positronium atoms, and efforts to create and study phases of the many-electron, many-positron system.

We extract the valence part of the nucleón Boer-Mulder (BM) function from the new COMPASS data on the unpolarized cosϕh and cos2ϕh asymmetries in SIDIS on deuteron for producing the hadron h and its antiparticle h ¯ at azimuthal angle ϕh . Our results, obtained with only standard assumption of factorization of the xB (zh ) and transverse momentum dependences, differ significantly from the presently published data on the BM function, obtained using a model assumption of proportionality to the better known Sivers function. This suggests that the published results on the BM function should be reconsidered.

The chiral Majorana fermion, is a massless fermionic particle being its own antiparticle, which was predicted to live in (1+1)D (i.e. one-dimensional space plus one-dimensional time) or (9+1)D. In condensed matter physics, one-dimensional (1D) chiral Majorana fermion can be viewed as the 1/2 of the chiral Dirac fermion, which could arise as the quasiparticle edge state of a two-dimensional (2D) topological state of matter. The appearance of an odd number of 1D chiral Majorana fermions on the edge implies that there exist the non-Abelian defects in the bulk. The chiral Majorana fermion edge state can be used to realize the non-Abelian quantum gate operations on electron states. Starting with the topological states in 2D, we illustrate the general and intimate relation between chiral topological superconductor and quantum anomalous Hall insulator, which leads to the theoretical prediction of the chiral Majorana fermion from the quantum anomalous Hall plateau transition in proximity to a conventional s-wave superconductor. We show that the propagation of chiral Majorana fermions leads to the same unitary transformation as that in the braiding of Majorana zero modes, and may be used for the topological quantum computation.

The stronger than expected 21-cm absorption was observed by EDGES recently, and another anomaly of $$^8$$ Be transitions would be signatures of new interactions. These two issues may be related to each other, e.g., pseudoscalar A mediated fermionic millicharged dark matter (DM) and the 21-cm absorption could be induced by photon mediated scattering between MeV millicharged DM and hydrogen. This will be explored in this paper. For fermionic millicharged DM $$\bar{\chi } \chi $$ with masses in a range of $$2 m_A< 2 m_{\chi } < 3 m_A$$ , the p-wave annihilation $$\bar{\chi } \chi \rightarrow A A$$ would be dominant during DM freeze-out. The s-wave annihilation $$\bar{\chi } \chi $$ $$\rightarrow A, \gamma $$ $$\rightarrow e^+ e^-$$ is tolerant by constraints from CMB and the 21-cm absorption. The millicharged DM can evade constraints from direct detection experiments. The process of $$K^+ \rightarrow \pi ^+ \pi ^0$$ with the invisible decay $$\pi ^0 \rightarrow \bar{\chi } \chi $$ could be employed to search for the millicharged DM, and future high intensity $$K^+$$ sources, such as NA62, will do the job.

We summarize our recent 1.5 parts per billion measurement of the antiproton magnetic moment using the multi Penning-trap system of the BASE collaboration. The result was achieved by combining the detection of individual spin-transitions of a single antiproton with a novel two-particle spectroscopy technique, which dramatically improved the data sampling rate. This measurement contributes to improve the test of the fundamental charge, parity, time reversal (CPT) invariance in the baryon sector by a factor of 350 compared to our last measurement, and by a factor of 3000 compared to the best competing measurement. We review the measurement technique and discuss the improved limits on CPT-violating physics imposed by this measurement.

In this paper, we investigate the behavior of the quantum coherence for bipartite fermionic systems in noninertial frames beyond the single-mode approximation. It is shown a redistribution of coherence between particle and antiparticle modes, and the behavior in terms of coherence for fermionic systems is convergent in the infinite acceleration limit. We demonstrate that the physical accessible coherence is not always destroyed with the increase in acceleration, which is different from the features of entanglement in the accelerated frame. Besides, we obtain a quantitative relationship about the redistribution of coherence via the $$l_1$$ -norm measure. It is worth mentioning that a rotation operation can change the coherence values, since the amount of coherence is related to the selection of reference basis.

The energy dependence of light (anti)nuclei and (anti)hypertriton production are investigated in central Au-Au collisions from AGS up to LHC energies at midrapidity, using the parton and hadron cascade model (PACIAE) together with the dynamically constrained phase-space coalescence model(DCPC). We find that the yields, yield ratios of the antiparticles to their corresponding particles, the coalescence parameters $B_A$ and the strangeness population factor $s_3$ of light (anti)nuclei and (anti)hypertriton all show strong dependences on the energy. Furthermore, we analyze and discuss the strangeness population factor $s_3$ and the coalescence parameters $B_A$ , and find a transition point near 20 GeV. These results thus suggest, in relativistic heavy-ion collisions, the potential usefulness of the $s_3$ and $B_A$ of light nuclei production as an indirect probe of the transition point related to the QCD critical phenomena. The results from PACIAE+DCPC model are well consistent with experimental data within the error margin.

In direct accordance to the overall relevant experimental demonstrations, we represent the charged pion π- as a heavy electron h - in precessional-orbital (P-O) motion at essentially the light speed c about υ ¯ e -orbit of a normal at quantised angle π − θ1/2 = − arccos ( 1 / 3 ) to the z axis. h - is the level N = 1 oscillation of charge −e and its electromagnetic radiation originally generated in the weak potential field of another particle. The P-O kinetic energy current and two additional opposite ones created upon π- decay represent confined neutrinos υ ¯ e , υ ¯ μ , υ μ . The muon µ- is a xy-projected h - in two superposing P-O motions along υ ¯ e − , υ μ - orbits of normals at angles π − θ1/2, θ1/2 to z. The µ- (rest) mass is a geometric projection of the reduced π- mass, M μ = ( M π − M υ μ ) cos θ 1 / 2 = 105.86 MeV . The µ- mass is fundamentally predetermined by the mixed two states ml = −1, +1 of level n = 2 of a double heavy positronium in the CM frame produced in a relativistic e -, e + collision, and is ab initio predicted to be M μ − = ( 3 4 2 α + 1 ) M e = 105.549 MeV , where α = e 2 / 4 π ∈ 0 ℏ c . The un-projected n = 2 level gives the bound π- mass containing a friction term O η , M π + O η = ( 2 α + 1 ) M e = 140.525 MeV . Their antiparticles π+, µ+ and the tauons τ∓ can be similarly represented. The remaining unstable elementary particles can be constructed as composites of two or more single charged ones in certain spatial quantised P-O motions.

International audience; The vector potential quantization procedure extended to a single free of cavity photon state issues to the zero-energy electromagnetic field ground state (EFGS), a quantum vacuum component, overcoming the vacuum energy singularity in quantum electrodynamics. We show that the EFGS oscillations generate photons and that the elementary electron/positron charge is expressed precisely by the EFGS quantized amplitude. We also show that the gravitational constant is equally expressed through the same EFGS quantized amplitude putting in evidence the electromagnetic nature of gravity and introducing the quantum vacuum influence in the cosmological equations. Fluctuations of the EFGS give birth to low energy transient photons as well as to particles/antiparticles which might be respectively at the origin of the dark energy and dark matter in the universe.

Background Breakthrough resolutions in current biopolymer engineering rely on reliable diagnostics of atomic-deficient spaces over the finest sub-nanometer length scales. One such diagnostic is positron annihilation lifetime spectroscopy, which probes space-time continuum relationships for the interaction between electrons and their antiparticle (positrons) in structural entities like free-volume defects, vacancies, vacancy-like clusters, interfacial voids and pores, etc. Objectives This paper is intended to highlight the possibilities of positron annihilation lifetime spectroscopy as an informative instrumentation tool to parameterize free-volume evolution in light-cured dimethacrylate dental restorative composites exemplified by Charisma® (Heraeus Kulzer GmbH, Hanau, Germany) and Dipol® (Oksomat-AN Ltd, Kyiv, Ukraine). Material and methods The subjects of the study were the commercially available dimethacrylate-type dental restorative composites Charisma® and Dipol®. The analysis used a fast-fast coincidence system of 230 ps resolution based on 2 photomultiplier tubes coupled to BaF2 scintillator detectors and ORTEC® (ORTEC, Oak Ridge, USA) electronics to register lifetime spectra in normal-measurement statistics evolving ~1 million coincidences. Results The annihilation process in both composites is identified as mixed positron-Ps (positronium) trapping, where ortho-Ps decaying is caused entirely by free-volume holes in the polymer matrix, and the 2nd component is defined mainly by interfacial free-volume holes between filler nanoparticles and the surrounding polymer. The most appropriate model-independent estimation of photopolymerization volumetric shrinkage in dental restorative composites can be done using averaged positron annihilation lifetime. Partiallyconstrained x4-term analysis of lifetime spectra is less efficient, giving greater scatter of variance with an additional artifact of fixed shortest lifetime allowing unresolved mixing in the 2nd component. A meaningful phenomenological description of transformations in Ps and positron-trapping sites under light curing, which occurs more efficiently in Charisma® than in Dipol® nanocomposites, can be developed at the basis of a semi-empirical model exploring a x3-x2-coupling decomposition algorithm. Conclusions A deep understanding of void-evolution processes in dimethacrylate dental composites employing positron annihilation lifetime spectroscopy makes it possible to diagnose, characterize and engineer novel biomaterials for advanced use in medical practice.

We study the electromagnetic coupling of a neutrino that propagates in a two-stream electron background medium. Specifically, we calculate the electromagnetic vertex function for a medium that consists of a \emph{normal} electron background plus another electron \emph{stream} background that is moving with a velocity four-vector $v^\mu$ relative to the normal background. The results can be used as the basis for studying the neutrino electromagnetic properties and various processes in such a medium. As an application, we calculate the neutrino dispersion relation in the presence of an external magnetic field ($\vec B$), focused in the case in which $B$ is inhomogeneous, keeping only the terms of the lowest order in $1/m^2_W$ and linear in the $B$ and its gradient. We show that the dispersion relation contains additional anisotropic terms involving the derivatives of $\vec B$, such as the gradient of $\hat k\cdot(\vec v\times\vec B)$, which involve the stream background velocity, and a term of the form $\hat k\cdot(\nabla\times \vec B)$ that can be present in the absence of the stream background, in addition to a term of the form $\hat k\cdot\vec v$ and the well known term $\hat k\cdot\vec B$ that arises in the constant $\vec B$ case. The derivative-dependent terms are even under a $CP$ transformation. As a result, in contrast to the latter two just mentioned, they depend on the sum of the particle and antiparticle densities and therefore can be non-zero in a $CP$-symmetric medium in which the particle and antiparticle densities are equal., Comment: Title changes, 39 pages, 2 figures

The time evolution of a finite fermion system towards statistical equilibrium is investigated using analytical solutions of a nonlinear partial differential equation that had been derived earlier from the Boltzmann collision term. The solutions of this fermionic diffusion equation are rederived in closed form, evaluated exactly for simplified initial conditions, and applied to hadron systems at low energies in the MeV-range, as well as to quark systems at relativistic energies in the TeV-range where antiparticle production is abundant. Conservation laws for particle number including created antiparticles, and for the energy are discussed., 31 pages, 7 figures

High-energy physicists are limited to studying a single vacuum and its excitations, the particles of the standard model. For condensed-matter physicists, every new phase of matter brings a new “‘vacuum.” Remarkably, the low-energy excitations of these new vacua can be very different from the individual electrons, protons, and neutrons that constitute the material. The materials multiverse contains universes where the particle-like excitations carry only a fraction of the elementary electronic charge ( 1 ), are magnetic monopoles ( 2 ), or are their own antiparticles ( 3 ). None of these properties have ever been observed in the particles found in free space. Often, emergent gauge fields accompany these “fractionalized” particles ( 2 , 4 , 5 ), just as electromagnetic gauge fields accompany charged particles. On page 1101 of this issue, Hassan et al. ( 6 ) provide a glimpse of the emergent behaviors of a putative new phase of matter, the dipole liquid. What particles live in this universe, and what new physics is found in this and neighboring parts of the multiverse?

In this paper, we show how to carry out a relatively more realistic and complete reconstruction of supernova neutrino spectra in the future large liquid-scintillator detectors, by implementing the method of singular value decomposition with a proper regularization. For a core-collapse supernova at a distance of $10~{\rm kpc}$ in the Milky Way, its $\overline{\nu}^{}_e$ spectrum can be precisely determined from the inverse beta-decay process $\overline{\nu}^{}_e + p \to e^+ + n$, for which a $20~{\rm kiloton}$ liquid-scintillator detector with the resolution similar to the Jiangmen Underground Neutrino Observatory (JUNO) may register more than 5000 events. We have to rely predominantly on the elastic neutrino-electron scattering $\nu + e^- \to \nu + e^-$ and the elastic neutrino-proton scattering $\nu + p \to \nu + p$ for the spectra of $\nu^{}_e$ and $\nu^{}_x$, where $\nu$ denotes collectively neutrinos and antineutrinos of all three flavors and $\nu^{}_x$ for $\nu^{}_\mu$ and $\nu^{}_\tau$ as well as their antiparticles. To demonstrate the validity of our approach, we also attempt to reconstruct the neutrino spectra by using the time-integrated neutrino data from the latest numerical simulations of delayed neutrino-driven supernova explosions., Comment: 26 pages, 6 figures, more discussions, final version in PRD

Four experiments have demonstrated new levels of sensitivity to neutrinoless double-beta decay, a process whose existence would prove that neutrinos are their own antiparticles.

Insights from spectroscopic experiments led to the development of quantum mechanics as the common theoretical framework for describing the physical and chemical properties of atoms, molecules and materials. Later, a full quantum description of charged particles, electromagnetic radiation and special relativity was developed, leading to quantum electrodynamics (QED). This is, to our current understanding, the most complete theory describing photon–matter interactions in correlated many–body systems. In the low-energy regime, simplified models of QED have been developed to describe and analyse spectra over a wide spatiotemporal range as well as physical systems. In this Review, we highlight the interrelations and limitations of such theoretical models, thereby showing that they arise from low-energy simplifications of the full QED formalism, in which antiparticles and the internal structure of the nuclei are neglected. Taking molecular systems as an example, we discuss how the breakdown of some simplifications of low-energy QED challenges our conventional understanding of light–matter interactions. In addition to high-precision atomic measurements and simulations of particle physics problems in solid-state systems, new theoretical features that account for collective QED effects in complex interacting many-particle systems could become a material-based route to further advance our current understanding of light–matter interactions. Quantum electrodynamics (QED) is the most complete theoretical framework to date to complement experimental spectroscopies in chemistry. Owing to its complexity, several approximations are needed in order to be able to apply QED in practice. This Review highlights how the breakdown of some of these approximations challenges our understanding of light–matter interactions and discusses how new theoretical developments can help to overcome these approximations.

We discuss a generalization of the Pauli-Gursey transformation, which is motivated by the Autonne-Takagi factorization, to an arbitrary $n$ number of generations of neutrinos using $U(2n)$ that defines general canonical transformations and diagonalizes symmetric complex Majorana mass matrices in special cases. The Pauli-Gursey transformation mixes particles and antiparticles and thus changes the definition of the vacuum and C. We define C, P and CP symmetries at each Pauli frame specified by a generalized Pauli-Gursey transformation. The Majorana neutrinos in the C and P violating seesaw model are then naturally defined by a suitable choice of the Pauli frame, where only Dirac-type fermions appear with well-defined C, P and CP, and thus the C symmetry for Majorana neutrinos agrees with the C symmetry for Dirac-type fermions. This fully symmetric setting corresponds to the idea of Majorana neutrinos as Bogoliubov quasi-particles. In contrast, the conventional direct construction of Majorana neutrinos in the seesaw model, where CP is well-defined but C and P are violated, encounters the mismatch of C symmetry for Majorana neutrinos and C symmetry for chiral fermions; this mismatch is recognized as the inevitable appearance of the singlet (trivial) representation of C symmetry for chiral fermions., Comment: 15 pages. Slightly expanded with some explanatory paragraphs added. This version is going to appear in Phys.Lett. B

In this study, exergetic, environmental and economic (3E) analyses have been performed in order to provide sustainability indicators from resource extraction to the final product of stationary power Molten Carbonate Fuel Cells (MCFC) systems (500 kW). Two environmental life cycle impact assessment methods have been selected: the ReCiPe 2016 hierarchical midpoint and endpoint, and the Cumulative Exergy Extraction from the Natural Environment (CEENE). The levelized cost of electricity (LCOE) under technology cost and performance parameters was calculated to analyze the system from the economic point of view. The global warming potential (GWP) is estimated to be 0.549 kg CO2-eq/kWh while acidification (5.06e−4 kg SO2-eq/kWh), eutrophication (9.81e−4 kg P-eq. freshwater/kWh), ozone layer depletion (4.11e−6 kg CFC-11-eq/kWh) and human toxicity (1.07 kg 1,4-DB-eq/kWh). Aggregated CEENE was estimated to be about 8.55 MJex/kWh. Results show that majority of impacts are dominated by fuel supply, while some others are dominated by manufacturing of system. GWP is the only impact category dominated by system operation. Due to potentially high electrical efficiency, MCFC energy systems can lead to lower CEENE and improvements of global warming, fossil fuel and resource scarcity, and photochemical oxidant formation potential with respect to other conventional energy conversion systems. Advances in longer lifetimes of the MCFC stack can help trigger innovation in manufacturing processes and will lead to less resource use of electricity, metal, and minerals, thus less resource scarcity and toxicity related burdens. The baseline LCOE is calculated 0.1265 €/kWh being comparable with the Italian grid (0.15–0.16 €/kWh). The costing results indicate that the unit decreasing the system capital cost could potentially reduce the LCOE by around 25%. Advancing the use of life-cycle thinking in MCFC industry with site-specific data raise systems credibility and enables clarifying the trade-offs between the sustainability pillars, thus designing more sustainable products. © 2018 Elsevier Ltd

We use the concept of quantum entanglement to analyze the Schwinger effect on an entangled state of a qubit and a bosonic mode coupled with the electric field. As a consequence of the Schwinger production of particle-antiparticle pairs, the electric field decreases both the correlation and the entanglement between the qubit and the particle mode. This work exposes a profound difference between bosons and fermions. In the bosonic case, entanglement between the qubit and the antiparticle mode cannot be caused by the Schwinger effect on the preexisting entanglement between the qubit and the particle mode, but correlation can., Comment: 15 pages

A positron is an antiparticle of an electron that can be formed in diverse methods: natural or artificial β-decay process, fission and fusion reactions, and a pair production of electron-positron occurred in the reactor and the high energy accelerator centers. Usually a long-lifetime radio isotope is customized for the construction of a slow positron beam lines in many laboratories. The typical intensity of this beam depends upon the strength of the positron source, moderator efficiency, and guiding, pulsing, focusing and detecting systems. This article will review a few positron beam lines and their potential applications in research, especially in the Positronium Bose-Einstein Condensation.

Abstract We describe a multi-step “rotating wall” compression of a mixed cold antiproton–electron non-neutral plasma in a 4.46 T Penning–Malmberg trap developed in the context of the AEḡIS experiment at CERN. Such traps are routinely used for the preparation of cold antiprotons suitable for antihydrogen production. A tenfold antiproton radius compression has been achieved, with a minimum antiproton radius of only 0.17 mm. We describe the experimental conditions necessary to perform such a compression: minimizing the tails of the electron density distribution is paramount to ensure that the antiproton density distribution follows that of the electrons. Such electron density tails are remnants of rotating wall compression and in many cases can remain unnoticed. We observe that the compression dynamics for a pure electron plasma behaves the same way as that of a mixed antiproton and electron plasma. Thanks to this optimized compression method and the high single shot antiproton catching efficiency, we observe for the first time cold and dense non-neutral antiproton plasmas with particle densities n ≥ 1013 m−3, which pave the way for an efficient pulsed antihydrogen production in AEḡIS. Graphical abstract

Experiments aiming to directly detect dark matter (DM) particles have yet to make robust detections, thus underscoring the need for complementary approaches such as searches for new particles at colliders, and indirect DM searches in cosmic-ray spectra. Low energy (< 0.25 GeV/n) cosmic-ray antiparticles such as antideuterons are strong candidates for probing DM models, as the yield of these particles from DM processes can exceed the astrophysical background by more than two orders of magnitude. The General Antiparticle Spectrometer (GAPS), a balloon borne cosmic-ray detector, will perform an ultra-low background measurement of the cosmic antideuteron flux in the regime < 0.25 GeV/n, which will constrain a wide range of DM models. GAPS will also detect approximately 1000 antiprotons in an unexplored energy range throughout one long duration balloon (LDB) flight, which will constrain < 10 GeV DM models and validate the GAPS detection technique. Unlike magnetic spectrometers, GAPS relies on the formation of an exotic atom within the tracker in order to identify antiparticles. The GAPS tracker consists of ten layers of lithium-drifted silicon detectors which record dE/dx deposits from primary and nuclear annihilation product tracks, as well as measure the energy of the exotic atom deexcitation X-rays. A two-layer, plastic scintillator time of flight (TOF) system surrounds the tracker and measures the particle velocity, dE/dx deposits, and provides a fast trigger to the tracker. The nuclear annihilation product multiplicity, deexcitation X-ray energies, TOF, and stopping depth are all used together to discern between antiparticle species. This presentation provided an overview of the GAPS experiment, an update on the construction of the tracker and TOF systems, and a summary of the expected performance of GAPS in light of the upcoming LDB flight from McMurdo Station, Antarctica in 2020., 4 pages, 3 figures, The 39th International Conference on High Energy Physics (ICHEP2018), Seoul, Korea

This chapter introduces the primary Cosmic Rays (CRs). Primary CRs are high-energy and stable particles originating in astrophysical environments. They are protons, fully ionized atomic nuclei and electrons. Part of the primary radiation can interact in (or close to) the acceleration regions producing other high-energy charged and neutral secondary particles. Antiparticles (mainly positrons and antiprotons) are also present in the cosmic radiation, but in most cases, they are originated during the propagation of primary protons and electrons. All the particles produced far from the acceleration regions during the propagation of primary CRs, or produced on their arrival in the Earth’s atmosphere, are denoted as secondary CRs. Particle detectors play a fundamental role in the history of CRs. As described, the intensity of this ionizing radiation is modulated by the solar activity. Below a few tens of GeV, the primary CR flux arriving on Earth also depends on the magnetic latitude, as it is affected by the geomagnetic field. The theoretical models on the origin of CRs rely on many astrophysical parameters and experimental observations about nature, energy density, confinement time, and chemical composition of CRs as a function of their energy.

The $p$-wave superfluid $^3$He is a textbook example of topological superfluids. Among its multiple superfluid phases, the B phase ($^3$He-B) is known as a topological state protected by time-reversal symmetry. One of the important topological features of $^3$He-B is the formation of bound states at its surface. Notably, such surface Andreev bound states are predicted to be Majorana fermions, i.e., their antiparticles are identical to their particles. Because of the well-elucidated bulk properties of the superfluid $^3$He owing to its cleanliness, $^3$He-B provides an ideal platform to pursue Majorana fermions in condensed matter systems. In this article, we review recent investigations of surface Andreev bound states by the mobility of ions trapped below a free surface of $^3$He-B.The free surface is an ideal surface providing a specular boundary condition; The surface Andreev bound states formed there are expected to be Majorana fermions with a well-defined energy spectrum. We show that the temperature and depth dependences of the experimentally obtained mobility of negative ions [H. Ikegami {\it et al.,} {\it J. Phys. Soc. Jpn.} {\bf 82} 124607 (2013)] are {\it quantitatively} reproduced by a theoretical study that includes scattering of the surface Andreev bound states [Y. Tsutsumi, {\it Phys. Rev. Lett.} {\bf 118} 145301 (2017)].This quantitative agreement unambiguously demonstrates the experimental detection of surface Andreev bound states.We also discuss the future prospects of the Majorana physics in $^3$He-B., Comment: 16 pages, 4 figures

Neutrinoless double beta decay, if observed, would be proof that the neutrino is its own antiparticle, would be evidence for total lepton number violation, and could allow a measurement of the absolute neutrino mass. Tracking calorimeter experiments have particular strengths, including the ability to search for this decay amongst several different isotopes hosted in source foils. Full event reconstruction provides powerful background rejection capability, and, in the event of a discovery, topological measurements are a powerful handle to determine the nature of the lepton number violating process. I will present the latest results from the NEMO-3 experiment together with the current status and future prospects for its successor: SuperNEMO.

The transverse momentum spectra of $\pi^{-}$, $\pi^{+}$, $K^{-}$, $K^{+}$, $\bar{p}$, and $p$ produced in Au+Au collisions at center-of-mass energy $\sqrt{s_{NN}}=7.7$, 11.5, 19.6, 27, 39, 62.4, 130, and $200$ GeV are analyzed in the framework of a multisource thermal model. The experimental data measured at midrapidity by the STAR Collaboration are fitted by the (two-component) standard distribution. The effective temperature of emission source increases obviously with the increase of the particle mass and the collision energy. At different collision energies, the chemical potentials of up, down, and strange quarks are obtained from the antiparticle to particle yield ratios in given transverse momentum ranges available in experiments. With the increase of logarithmic collision energy, the chemical potentials of light flavor quarks decrease exponentially., Comment: 9 pages, 2 figures. Advances in High Energy Physics, accepted

The Jagiellonian Positron Emission Tomograph (J-PET) is a novel device being developed at Jagiellonian University in Krakow, Poland based on organic scintillators. J-PET is an axially symmetric (M. Mohammed) has been affiliated to affiliation 6. Please check if correct, otherwise, provide the correct affiliation.and high acceptance scanner that can be used as a multi-purpose detector system. It is well suited to pursue tests of discrete symmetries in decays of positronium in addition to medical imaging. J-PET enables the measurement of both momenta and the polarization vectors of annihilation photons. The latter is a unique feature of the J-PET detector which allows the study of time reversal symmetry violation operator which can be constructed solely from the annihilation photons momenta before and after the scattering in the detector.

We collect the yields of charged pions ( &pi, &minus, and &pi, + ), charged kaons ( K &minus, and K + ), anti-protons ( p &macr, ), and protons (p) produced in mid-rapidity interval (in most cases) in central gold&ndash, gold (Au&ndash, Au), central lead&ndash, lead (Pb&ndash, Pb), and inelastic or non-single-diffractive proton&ndash, proton ( p p ) collisions at different collision energies. The chemical potentials of light particles and quarks are extracted from the yield ratios, &pi, / &pi, + , K &minus, / K + , and p &macr, / p , of antiparticles to particles over an energy range from a few GeV to above 10 TeV. At a few GeV (&sim, 4 GeV), the chemical potentials show, and the yield ratios do not show, different trends comparing with those at other energies, although the limiting values of the chemical potentials and the yield ratios at very high energy are 0 and 1, respectively.

We study the production of charged particles (${K}^{+}$, ${K}^{\ensuremath{-}}$, $p$, and $\overline{p}$) in proton-proton ($pp$) collisions at $\sqrt{s}=0.9\phantom{\rule{4pt}{0ex}}\mathrm{TeV}$ within the paciae model whose parameters we fix by comparing the yield of charged particles with experimental data from ALICE. We analyze the production of ${K}^{\ensuremath{-}}p$ and ${K}^{+}\overline{p}$ bound states with the paciae+dcpc model. Results of our work indicate that in $pp$ collisions at $\sqrt{s}=0.9\phantom{\rule{4pt}{0ex}}\mathrm{TeV}$ the $\mathrm{\ensuremath{\Lambda}}(1405)$ and its antiparticle may be produced at almost the same rate if the $\mathrm{\ensuremath{\Lambda}}(1405)$ is a ${K}^{\ensuremath{-}}p$ bound state formed during the hadron rescattering period. The combined yield of ${K}^{\ensuremath{-}}p$ and ${K}^{+}\overline{p}$ bound states is found to be of the order of ${10}^{\ensuremath{-}3}$, but the experimental results indicate that the combined yield of $\mathrm{\ensuremath{\Lambda}}(1405)+\overline{\mathrm{\ensuremath{\Lambda}}}(1405)$ is of the order of ${10}^{\ensuremath{-}2}$ if $\mathrm{\ensuremath{\Lambda}}(1405)$ is a standard three-quark baryon. Since there are no experimental data available on this observable at present, our work may provide a guide for future experiments.

Antimatter nuclei in cosmic rays (CR) represent a promising discovery channel for the indirect search of dark matter. We present astrophysical background calculations of CR antideuteron ($\overline{d}$) and antihelium ($\overline{He}$). These particles are produced by high-energy collisions of CR protons and nuclei with the gas nuclei of the interstellar medium. In our calculations, we also consider production and shock acceleration of antinuclei in the shells of supernova remnants (SNRs). The total flux of $\overline{d}$ and $\overline{He}$ particles is constrained using new AMS measurements on the boron/carbon (B/C) and antiproton/proton ($\bar{p}/p$) ratios. The two ratios leads to different antiparticle fluxes in the high-energy regime $E\gtrsim$ 10 GeV/n where, in particular, $\bar{p}/p$-driven calculations leads to a significantly larger antiparticle flux in comparison to predictions from conventional B/C-driven constraints. On the other hand, both approaches provide consistent results in the sub-GeV/n energy window, which is where dark matter induced signal may exceed the astrophysical background. In this region, the total antinuclei flux, from interaction in the insterstellar gas and inside SNRs, is tightly bounded by the data. Shock-acceleration of antiparticles in SNRs has a minor influence in the astrophysical background for dark matter searches., Proceedings of the EPS Conference on High Energy Physics EPS-HEP 2017, Venice

The Alpha Magnetic Spectrometer (AMS) is a new generation high-energy physics experiment installed on the International Space Station in May 2011 and operating continuously since then. Using an unprecedently large collection of particles and antiparticles detected in space, AMS is performing precision measurements of cosmic ray energy spectra and composition. In this paper, we discuss the physics of solar modulation in Galactic cosmic rays that can be investigated with AMS my means of dedicated measurements on the time-dependence of cosmic-ray proton, helium, electron and positron fluxes., Proceedings of the 18th Lomonosov Conference - 2017, Moscow, Russia

In order to test CPT symmetry between antihydrogen and its counterpart hydrogen, the ASACUSA collaboration plans to perform high precision microwave spectroscopy of ground-state hyperfine splitting of antihydrogen atom in-flight. We have developed an apparatus (“cusp trap”) which consists of a superconducting anti-Helmholtz coil and multiple ring electrodes. For the preparation of slow antiprotons and positrons, Penning- Malmberg type traps were utilized. The spectrometer line was positioned downstream of the cusp trap. At the end of the beamline, an antihydrogen beam detector was located, which comprises an inorganic Bismuth Germanium Oxide (BGO) single-crystal scintillator housed in a vacuum duct and surrounding plastic scintillators. A significant fraction of antihydrogen atoms flowing out the cusp trap were detected.

One of the main tasks of the NICA/MPD physics program is a study of strangeness production in nuclear collisions. In this paper the MPD detector performance for measurements of Λ, Ξ− and Ω− hyperons and their antiparticles \(\bar \Lambda\), \(\bar \Xi ^ +\) and \(\bar \Omega ^ +\) in central Au+Au collisions at NICA energies is presented.

The influence of neutrinoless electron to positron conversion on cooling of strongly magnetized iron white dwarfs is studied. It is shown that they can be good candidates for soft gamma-ray repeaters and anomalous X-ray pulsars., Comment: published version, 32 pages, 6 tables, 1 figure

On the basis of a previously developed macroscopic theory of statistical systems with an interparticle scalar interaction, numerical models of the cosmological evolution of a two-component Boltzmann system of scalar charged particles have been constructed and analyzed in the case of symmetry between particles and antiparticles. The main features of this class of cosmological models have been identified, in particular, the possibility of quite rapid transitions to different regimes of cosmological expansion has been demonstrated.

Electron-acoustic shock waves (EASWs) in an unmagnetized electron-positron-ion plasma system (consisting of a cold mobile viscous electron fluid, hot electrons and positrons following the q-nonextensive distribution, and immobile positive ions) are studied analytically. The Burgers equation is derived by using the well-known reductive perturbation method. The basic features (viz. polarity, amplitude, width, phase speed, etc.) of EASWs are briefly addressed. The basic features of EASWs are found to be significantly modified by the effects of nonextensivity of the hot electrons and positrons, the relative number density and temperature ratios, and the kinematic viscosity of the cold electrons. The present investigation can be useful in understanding the fundamental characteristics of EASWs in various space plasmas.

Ettore Majorana (1906-1938) disappeared while traveling by ship from Palermo to Naples in 1938. His fate has never been fully resolved and several articles have been written that explore the mystery itself. His demise intrigues us still today because of his seminal work, published the previous year, that established symmetric solutions to the Dirac equation that describe a fermionic particle that is its own anti-particle. This work has long had a significant impact in neutrino physics, where this fundamental question regarding the particle remains unanswered. But the formalism he developed has found many uses as there are now a number of candidate spin-1/2 neutral particles that may be truly neutral with no quantum number to distinguish them from their anti-particles. If such particles exist, they will influence many areas of nuclear and particle physics. Most notably the process of neutrinoless double beta decay can only exist if neutrinos are massive Majorana particles. Hence, many efforts to search for this process are underway. Majorana's influence doesn't stop with particle physics, however, even though that was his original consideration. The equations he derived also arise in solid state physics where they describe electronic states in materials with superconducting order. Of special interest here is the class of solutions of the Majorana equation in one and two spatial dimensions at exactly zero energy. These Majorana zero modes are endowed with some remarkable physical properties that may lead to advances in quantum computing and, in fact, there is evidence that they have been experimentally observed. This review first summarizes the basics of Majorana's theory and its implications. It then provides an overview of the rich experimental programs trying to find a fermion that is its own anti-particle in nuclear, particle, and solid state physics., Comment: Invited review for Reviews of Modern Physics; v2: shortened and reorganized version to appear in RMP, 28 pages 12 figures. This version emphasizes the distinction between the generic Majorana fermions in particle physics and Majorana zero modes discussed in condensed matter physics

We revisit the decaying wino dark matter scenario in the light of the updated positron fraction, electron and positron fluxes in cosmic ray recently reported by the AMS-02 collaboration. We show the AMS-02 results favor the mass of the wino dark matter at around a few TeV, which is consistent with the prediction on the wino mass in the pure gravity mediation model., Comment: 10 pages, 1 figure

The Dirac equation, which was derived by combining, in a consistent manner, the relativistic invariance condition with the quantum probability principle, has shown its fecundity by explaining the half-integer spin of fermions and predicting antiparticles, the former resulting from a wave beat between a particle and its antiparticle. In our previous papers, it was conjectured that the spinning motion of the electron was that of a massless charge at light speed, this internal motion being responsible for the rest mass measured in external motions and interactions. Implications of this concept on such basic properties as time, mass, electric charge, and magnetic moment were considered. The present paper is a recollection of these ideas aimed at a general understanding of quantum matter.