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The velocity gain of neutral particles (atoms, molecules, etc) from laser acceleration is always small. A possible scheme to obtain a high speed neutral particle beam is multistage acceleration. However, according to previous theoretical and experimental studies, generally, lateral acceleration is larger than longitudinal acceleration. These transverse velocities destroy the expected quality of the longitudinally transmitted neutral particle beam. In order to realize multistage accelerations of neutral particle, it is necessary to restrain the beam divergence caused by lateral acceleration. How to optimize and utilize these laterally accelerated neutral particles is worthy of in-depth study. In this paper, we use a multi-mode combined laser pulse and a flattened Gaussian laser pulse to accelerate the neutral atoms. The transverse divergence of the beam is well controlled while the longitudinal acceleration is retained, which provides the possibility for improving the beam quality of neutral particles as well as the corresponding multistage acceleration.

We consider collisional Penrose process for charged, rotating black holes together with a simple model of pair creation, in which two oppositely charged particles are produced in a collision of two neutral particles. We highlight that significant energy extraction is possible without assuming fine-tuning or extremality as long as the escaping particles are sufficiently charged.

The application of a neutral particle analyzer (NPA) diagnostic at the Globus-M/M2 spherical tokamaks is discussed. Physical principles of the diagnostic are reviewed. Two general approaches—active and passive measurements—are described. Examples of NPA application for the ion temperature and isotope composition measurements are presented. NPA-aided studies of the energetic ions in the MHD-free discharges, as well as in the experiments with sawtooth oscillations and toroidal Alfvén eigenmodes, are considered.

A precise understanding of hadronic interactions is essential to interpreting the mass composition of ultra-high energy cosmic rays from the results of air shower experiments. The Large Hadron Collier forward (LHCf) experiment aims to measure forward neutral particles for validation of hadronic interaction models adopted in air shower simulations. We already published the production cross sections of forward photons and neutrons for proton-proton collisions at √s=13 TeV. Recently, we showed a preliminary result of the energy spectrum of forward η mesons for proton-proton collisions at √s=13 TeV. Moreover, in September 2022, we had another data-taking for proton-proton collisions at √s=13.6 TeV. In data taking, we planned to obtain a number of π 0 and η candidates ten times larger for precise measurements and to perform the joint operation with ATLAS Roman pots and zero-degree calorimeters. Thanks to the joint operation with the ATLAS Roman pots, we can measure diffractive mass and neutral particles from diffractive dissociation simultaneously. Furthermore, energy resolution for neutrons is expected to be improved from 40% to 20% by combining the LHCf and the ATLAS zero-degree calorimeters. In this work, we report the status and prospects of the LHCf experiment.

A bstract Pileup involves the contamination of the energy distribution arising from the primary collision of interest (leading vertex) by radiation from soft collisions (pileup). We develop a new technique for removing this contamination using machine learning and convolutional neural networks. The network takes as input the energy distribution of charged leading vertex particles, charged pileup particles, and all neutral particles and outputs the energy distribution of particles coming from leading vertex alone. The PUMML algorithm performs remarkably well at eliminating pileup distortion on a wide range of simple and complex jet observables. We test the robustness of the algorithm in a number of ways and discuss how the network can be trained directly on data.

Core-ion temperature measurements are based on resolving the energy components and the analysis of fast neutrals coming out of the magnetic confinement of plasma. ADITYA-tokamak (R/a = 75 cm/25 cm) uses Neutral Particle Analyzer (NPA) based charge exchange diagnostic system for measurement of the core ion-temperature in the range of 100–300 eV of Aditya plasma. Several ohmic plasma discharges are investigated for the Aditya tokamak, which provides an estimate of core ion-temperature (T i0 ) evaluation with time and its comparison with the core electron-temperature (T e0 ). The analysis shows the ratio of T i0 /T e0 is typically in the rage of 30%–40%. Attempts have been made to estimate the neutral hydrogen (n H °) density in the core regime and its evolution with time using a simple approach. The core neutral densities estimated in the order of 10 8 –10 9  cm −3 for ohmic discharges in ADITYA-tokamak. Effect of the ion cyclotron radio frequency heating (ICRH) on the experimental charge-exchange spectrum is also observed, which shows a typical increase of the perpendicular ion temperature (T i⊥ ) by ~ 50 eV.

Quantum atomic and molecular gases are flexible systems for studies of fundamental many-body physics. They have traditionally been produced in harmonic electromagnetic traps and thus had inhomogeneous densities, but recent advances in light shaping for optical trapping of neutral particles have led to the development of flat-bottomed optical box traps, allowing the creation of homogeneous samples. Box trapping simplifies the interpretation of experimental results, provides more direct connections with theory and, in some cases, allows qualitatively new, hitherto impossible experiments. It has now been achieved for both Bose and Fermi atomic gases in various dimensionalities, and also for gases of heteronuclear molecules. Here we review these developments and the consequent breakthroughs in the study of both equilibrium and non-equilibrium phenomena such as superfluidity, turbulence and the dynamics of phase transitions.Optical box traps create a potential landscape for quantum gases that is close to the homogeneous theoretical ideal. This Review of box trapping methods highlights the breakthroughs in experimental many-body physics that have followed their development.

We investigate the dynamics of neutral timelike particles around a hairy black hole in Horndeski’s theory, which is characterized by a coupling parameter with the dimension of length. With deriving the particles’ relativistic periastron precessions, a preliminary bound on the hairy black hole is obtained by using the result of the S2 star’s precession with GRAVITY. It is tighter than the previous result constrained by the shadow size from EHT observations of M87* by about 3–4 orders of magnitude. We also analyse the particles’ periodic motions around the hole in the strong gravitational field. It clearly shows that small variations in the coupling parameter can make the neutral particles’ motions back and forth from the quasi-periodic orbits to the periodic orbits or no bound orbit. Our present work might provide hints for distinguishing the hairy black hole in Horndeski’s theory from the classical hole by using the particles’ dynamics in the strong gravitational field.

Several models of physics beyond the Standard Model predict the existence of dark photons, light neutral particles decaying into collimated leptons or light hadrons. This paper presents a search for long-lived dark photons produced from the decay of a Higgs boson or a heavy scalar boson and decaying into displaced collimated Standard Model fermions. The search uses data corresponding to an integrated luminosity of 36.1 fb - 1 collected in proton–proton collisions at s = 13   Te recorded in 2015–2016 with the ATLAS detector at the Large Hadron Collider. The observed number of events is consistent with the expected background, and limits on the production cross section times branching fraction as a function of the proper decay length of the dark photon are reported. A cross section times branching fraction above 4 pb is excluded for a Higgs boson decaying into two dark photons for dark-photon decay lengths between 1.5 mm and 307 mm.

We answer several questions of the referees and readers that arose after publication of the commented article [1]. Moreover, we see that it is impossible to consider correct relativistic quantum mechanics without negative energies, tachyons, and without appropriate forms of discrete symmetries.