Nucleus Collisions Research Articles

Segregation and Collisions in Galactic Nuclei: Rates of Destructive Events Near a Supermassive Black Hole

The centers of galaxies host a supermassive black hole (SMBH) surrounded by a dense stellar cluster. The cluster is expected to develop mass segregation, in which gravitational scatterings among the stars cause heavier objects to sink closer to the central black hole, while lighter objects will tend to be overconcentrated in the outer regions. This work focuses on the implications of mass segregation on the different channels for violent destruction of stars in the cluster: tidal disruptions, gravitational-wave-driven inspirals and high-velocity destructive collisions between stars. All such events occur close to the central black hole, where the heavier objects congregate. The analysis is based on a simplified Monte Carlo simulation, which evolves a two-mass population in a cluster surrounding a Milky Way–like SMBH. The simulation is based on the single-mass scheme used by Sari & Fragione and Balberg & Yassur, which has been extended to allow for the dynamical friction effects typical of unequal-mass populations. The effects of mass segregation on the rates of the different destruction channels are analyzed self-consistently in the overall evolution of the cluster. Also considered are stars which are injected into the cluster after being disrupted from a binary system by the SMBH. Such stars are captured in the inner regions of the cluster, and so their orbital evolution, as well as their destruction rate, are therefore influenced by heavy objects that might be abundant in the vicinity of the SMBH.

Multinucleon Transfer Studies of the 70Zn (15 MeV/nucleon) + 64Ni System with Focus on Excitation Energy Distributions

Existing high-resolution experimental data collected with the MAGNEX spectrometer were analyzed to investigate peripheral collisions of medium-mass nuclei from the reaction 70Zn (15 MeV/nucleon) + 64Ni. The main focus of this work was to correlate the observed ejectiles with the excitation energy of their progenitors. Experimental excitation energy distributions were generated and compared with the Deep-Inelastic Transfer (DIT) model. This revealed a dominance of direct reaction mechanisms located at low excitation energies and more complex mechanisms at higher energies. Future efforts include further detailed studies of the excitation energy distributions to elucidate the multinucleon transfer mechanisms and to comprehend the resolution limits achievable with medium-mass nuclei such as 70Zn.

Small-x structure of oxygen and neon isotopes as seen by the Large Hadron Collider

Results on collisions of 16O nuclei performed at the Relativistic Heavy Ion Collider (RHIC) have been presented for the first time at Quark Matter 2023 by the STAR collaboration. 16O+16O collisions are also expected to take place in the near future at the Large Hadron Collider (LHC) at much higher beam energies. We explore the potential of beam-energy-dependent studies for this system to probe small-x dynamics and QCD evolution. We perform 3 + 1D IP-Glasma simulations to predict the rapidity dependence of the initial geometry of light-ion collisions, focusing on 16O+16O and 20Ne+20Ne collisions at √SNN = 70 GeV and 7 TeV. The choice of 20Ne is motivated by its strongly elongated geometry, which may respond differently to the effect of the highenergy evolution compared to the more spherical 16O. We find that smearing induced by soft gluon production at high energy causes mild variations in the initial-state eccentricities as a function of the collision energy. These effects could be resolved in future experiments and deserve further investigation.

Experimental search for the QCD critical endpoint

The phase diagram of strong interaction has been a subject of intense theoretical and experimental research. One of the big questions in this regard is whether a critical endpoint is associated with the phase transition of strongly interacting matter. There have been rapid theoretical developments to answer this question. On the experimental side, a tremendous effort is put forward to hunt for the critical point in collisions of atomic nuclei. This article gives an experimental overview of some of the key results for critical point searches, mainly focusing on net-proton number fluctuations in nuclear collisions.

Coherent J/ψ photoproduction and polarization in peripheral Pb−Pb collisions

Photonuclear reactions are induced by the strong electromagnetic field generated by ultrarelativistic heavy-ion collisions. These processes have been extensively studied in ultraperipheral collisions, where the impact parameter is larger than twice the nuclear radius. In recent years, the observation of coherent J/ψ photoproduction at very low transverse momentum has been claimed in nucleus−nucleus (A−A) collisions with nuclear overlap, based on the measurement of an excess in the J/ψ yield with respect to hadroproduction expectations. Such quarkonium measurements can help to constrain the nuclear gluon distribution at low Bjorken-x and high energy. The photoproduced quarkonium is expected to preserve the polarization of the incoming photon due to the s-channel helicity conservation. In this contribution, we report on the new preliminary measurements of the y-differential cross section and the first polarization analysis of coherently photoproduced J/ψ in peripheral Pb−Pb collisions with the ALICE detector at forward rapidity in the dimuon decay channel. Comparison with models will be shown when available.

Optimization of asymmetry of Pb-Pb nucleus collision based on Glauber model simulation

Currently, researchers wanted to optimize the radiation by selecting certain asymmetry to produce high-energy particles in QGP collision. Our research utilized the Glauber-Monto-Carlo Model to simulate the collision and tried to find the domain of different independent variables to maximize the asymmetry of the cross-section. We have conducted relevant analysis and research on the principles of this model and generated relevant images using ROOT. The result shows that at the number level of 106, for the number of bins equals 10, we have (0.4, 0.5) for eccentricity in the second harmonic, (0.9, 1.0) for eccentricity in the third harmonic, (2.51, 3.14) for azimuthal angle difference, and (125, 166) for the number of participants, and, for number of bins equal to 20, (0.45, 0.50) for eccentricity in second harmonic, (0.95, 1.0) for eccentricity in the third harmonic, (2.82, 3.14) for azimuthal angle difference, and (146, 166) for the number of participants.

Unconventional Synthesis of Hierarchically Twinned Copper as Efficient Electrocatalyst for Nitrate-Ammonia Conversion.

Twin boundary (TB) engineering provides exciting opportunities to tune the performance levels of metal-based electrocatalysts. However, the controllable construction of TB greatly relies on surfactants, blocking active sites, and electron transfer by surfactants. Here, a surfactant-free and facile strategy is proposed for synthesizing copper (Cu) nanocatalysts with dense hierarchical TB networks (HTBs) by the rapid thermal reductions in metastable CuO nanosheets in H2 . As revealed by in situ transmission electron microscopy, the formation of HTBs is associated with the fragmentation of nanosheets in different directions to generate abundant crystal nuclei and subsequently unconventional crystal growth through the collision and coalescence of nuclei. Impressively, the HTBs endow Cu with excellent electrocatalytic performance for direct nitrate-ammonia conversion, superior to that of Cu with a single-oriented TB and without TB. It is discovered that the HTBs induce the formation of compressive strains, thereby creating a synergistic effect of TBs and strains to efficiently tune the binding energies of Cu with nitrogen intermediates (i.e., NO2 *) and thus promote the tandem reaction process of NO3 - -to-NO2 - and subsequent NO2 - -to-NH3 electrocatalysis. This work demonstrates the crucial role of HTBs for boosting electrocatalysis via the synergistic effect of TBs and strains.

Universality of Nucleon–Nucleon Correlations in Nuclei and Cumulative Pion Production

The structure of nuclear matter at short internucleon distances is one of the poorly studied aspects of nuclear physics. At distances of the order of the nucleon radius, nuclear matter is represented by the pairs of correlated nucleons with relative momenta exceeding the Fermi momenta that emerge for a short time. Such structures, whose local density is comparable to the density of neutron stars, arise from fluctuations in the average nuclear density. One of the important characteristics of nucleon–nucleon correlations is their universality implying the independence of their properties from the nuclear mass number. Therefore, the peculiarities of these objects of nuclear structure reflect the properties of nuclear matter rather than specific nuclei. Information about the short-distance physics is extracted from the analysis of processes with high energy–momentum transfers. Until now, the property of universality has been observed in electron–nucleus collisions only for the breakup of nucleon pairs. In this paper we analyze the data on the cumulative production of pions by protons on a set of nuclear targets and for the first time have established the existence of universality of two-nucleon correlations in the production of π+ and π– mesons. We have obtained evidence for the involvement of three-nucleon correlations in the production of pions beyond the kinematics of their production in interactions with two-nucleon objects.

Geometry of relativistic nuclei collision and hurst correlation curves

Geometry of relativistic nuclei collision and hurst correlation curves

The relationship between and eccentricities based on Glauber model

This report aims to determine the probability range of the number of collisions under the optimum collision condition. The optimum condition was obtained by determining the average values of the given variables in the Glauber Model. Graphs of against eccentricity 1, 2, and 3 (Ecc1, 2, and 3) were plotted respectively according to the data generated from the Glauber Model Simulation in CERN ROOT. Then, the optimum average value was plotted as a vertical line on the graph to determine the range of . The probability ratio of an optimum collision versus maximum probability in an event was concluded to fall in a certain range of 0.30 0.07, and this range is verified to be a stable range that could be used for prediction of optimum collision numbers in future nuclei collision experiment. This probability ratio can be used to predict the optimum collision with only provided.

Impact of gold ion irradiation on the initial alteration rate of the International Simple Glass

This study addresses the impact of 7 MeV Au irradiation on the initial alteration rate of International Simple Glass (ISG), considered as a reference for nuclear glasses. This irradiation scenario simulates the effect of nuclear collisions of the recoil nuclei of α decays. In order to study the very first moments of glass alteration, non-irradiated and Au-ion irradiated ISG glass monoliths were altered in pure water at 90 °C, pH 9 and with a ratio of glass surface area to solution volume of 0.01 cm−1. Glass alteration was monitored by measuring the releases of the glass elements in solution by UV–visible spectrophotometry and Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES). Under these alteration conditions, the releases of the elements in solution are congruent. The initial alteration rate was found to be (2.0 ± 0.8) times higher for the irradiated glass monoliths than for non-irradiated samples.

A novel method for calculating Bose–Einstein correlation functions with Coulomb final-state interaction

Measurements of Bose–Einstein correlations played a crucial role in the discovery and the subsequent detailed exploration of the Quark-Gluon-Plasma (QGP) created in high-energy collisions of heavy nuclei. Such measurements gave rise to femtoscopy, a flourishing sub-field of high-energy physics, and there are important new directions to explore and discoveries to be made in the near future. One of these important current topics is the precise investigation of the shape of the correlation functions utilizing Lévy-stable sources. In this paper, we utilize Lebesgue’s dominated convergence theorem and Fubini’s theorem to present a novel method of calculating the shape of the two-particle correlation functions, including the Coulomb final-state interaction. This method relies on an exact calculation of a large part of the necessary integrals of the Coulomb wave function and can be utilized to calculate the correlation function for any source function with an easily accessible Fourier transform. In this way, it is eminently applicable to Lévy-stable source functions. In this particular case, we find that the new method is more robust and allows the investigation of a wider parameter range than the previously utilized techniques. We present an easily applicable software package that is ready to use in experimental studies.

COLLISIONS OF COMET NUCLEI WITH METEOROID SWARIES AND THEIR CONSEQUENCES

The article considers the collisions of nuclei of selected comets with known meteor showers. It was revealed that as a result of the collision, the nuclei of comets showed significant activity of the nucleus. For some comets, the sublimation velocity increased and as a result, dust jets were observed. Some comets collided with one or two meteor showers, as a result of their collision with comets C/1743 X1, C/1796 P1, C/1823 Y1, C/1844 Y1, C/1858 L1, C/1877 G1, C/1995 O1 and 109P/1862 O1 formed synchron bands in the second and third types of cometary tail. As a result of the collision, some comets formed an anomalous tail, the successive bombardment of meteoroids led to a large destruction of the surface of the nucleus and fragmentation (C/1823 Y1, C/1888 R1, C/1892 E1, D/1894 F1, C/1932 M1, C/1954 O1, C/1969 T1, C/1995 O1, C/2004 Q2, 6P/1976, 7P/1869 G1, 10P/1930, 19P/1918, 26P/1927 F1, 96P/1986 J1, 109P/1862 O1 and 213P /2011). According to observational data, it has been established that each meteor shower contains large bodies that reach several meters in size. It was the collisions of large bodies from meteor showers that led to the destruction of some of the studied comets. After the formation of an anomalous tail and the destruction of the comet's nucleus, large dust particles and fragments of the rocky nucleus always remain along the orbit, which later form new meteoroid swarms.

Nuclear viscosity estimated by dynamics of neck formation in the early stage of nuclear collision

The very early stage of the coalescence of two nuclei is studied and used to estimate the nuclear viscosity. The time evolution of the neck region has been simulated by the unified Langevin equation method, which is used in the analysis of heavy-ion collisions from the approaching stage to the fusion-fission stage. It is found that the transition from viscous to inertial coalescence that appeared in the neck growth of macroscopic drops can also be seen in the present simulation in nucleus–nucleus collisions. The dynamics of neck growth is analyzed in terms of the hydrodynamical formula and the viscosity coefficient of nuclear matter is estimated using the analogy of macroscopic drops.

Double charmed meson in pp and pA collisions production at the LHC within the dipole approach in momentum representation

A study of double charmed meson production in proton–proton and proton–nucleus collisions at the LHC energies is performed. Based on the color dipole formalism developed in the transverse momentum representation and the double parton scattering mechanism, predictions are made for the transverse momentum differential cross section for different pairs of D-mesons. The theoretical results consider the center-of-mass energy and forward rapidities associated to the measurements by the LHCb Collaboration. The results considering different unintegrated gluon distributions are presented and compared to data and predictions for proton–nucleus collisions are provided.

Advanced silicon tracking detector developments for the future Electron-Ion Collider

The proposed Electron-Ion Collider (EIC) will operate high-luminosity high-energy electron+proton and electron+nucleus collisions at the collision energies from 20 GeV to 141 GeV to solve several fundamental questions in the high energy and nuclear physics fields. Its instantaneous luminosity can reach 1033−34cm−2s−1 and the bunching crossing rate is around 10 ns. The EIC project has received CD1 approval from the US DOE in 2021 and moves toward the machine design and preparation for construction. To realize various particle measurements with high precision at the future EIC, a low material-budget and high-granularity silicon vertex and tracking detector with fine spatial and momentum resolutions and nearly 4π solid angle coverage is desired. The Monolithic Active Pixel Sensor (MAPS) and AC Coupled Low Gain Avalanche Diode (AC-LGAD) technologies stand out of several advanced technology options for the EIC silicon vertex and tracking detector subsystems. The MAPS technology has advanced features of low material budget, low power consumption, good radiation resistance and fine spatial resolution. The AC-LGAD technology can achieve fast timing resolution. Latest studies and progress of the EIC silicon vertex and tracking detector conceptual design, performance validations in simulation and ongoing MAPS and AC-LGAD R&D will be shown. Schedule and plan of the EIC project detector development will be discussed as well.

Ultra-Peripheral Collisions physics with ATLAS

Exclusive production of dilepton pairs, γγ → ℓℓ, ℓ = e, μ, τ, is studied using data from ultraperipheral collisions (UPC) of lead nuclei at TeV recorded by the ATLAS detector [1] at the LHC. The process of interest proceeds via photon-photon interactions in the strong electromagnetic fields of relativistic lead nuclei. In the case of the dielectron production, within experimental uncertainties the measured integrated cross section is in good agreement with the QED predictions from the Monte Carlo programs STARlight and SuperChic, confirming the broad features of the initial photon fluxes. The differential cross section shows systematic differences from these predictions which are more pronounced at high absolute rapidity, |yee | and scattering angle, |cosθ*|. In the dimuon production case, the measured cross sections at large absolute rapidity |yμμ | is found to be about 10-20% larger in data than in the calculations, suggesting the presence of larger fluxes of photons in the initial state. The γγ → ττ process is observed in the UPCs with a significance exceeding 5 standard deviations. This observation can be turned into a constraint on the τ-lepton anomalous magnetic moment. Measurement of light-by-light scattering data are also performed during the LHC Run 2. The diphoton invariant mass distribution is used to set limits on the production of axion-like particles. This result provides the most stringent limits to date on axion-like particle production for masses in the range 6-100 GeV.

Excitation Function of Freeze-Out Parameters in Symmetric Nucleus–Nucleus and Proton–Proton Collisions at the Same Collision Energy

We analyze the transverse momentum (pT) spectra of π+, π−, K+, K−, p, p¯, Λ, Λ¯, Ξ, Ξ¯, Ω−, Ω¯+ or Ω−+Ω¯+ in different centrality intervals in gold–gold (Au–Au) and lead–lead (Pb–Pb) symmetric collisions at 200 GeV and 2.76 TeV, respectively, by Tsallis–Pareto-type function. Proton–proton collisions at the same centre of mass energies are also analyzed for these particles to compare the results obtained from these systems. The present work extracts the effective temperature T, non-extensivity parameter (q), the mean transverse momentum spectra (⟨pT⟩), the multiplicity parameter (N0), kinetic freeze-out temperature (T0) and transverse flow velocity (βT). We reported a plateau structure of pT, T, T0, βT, pT and q in central collisions. Beyond the plateau region, the excitation function of all the above parameters decreases towards the periphery, except q, which has a reverse trend. The multiplicity parameter is also extracted, which is found to be decreasing towards the periphery from the central collisions. In addition, we observed that the excitation function of pp collisions is nearly the same to that of the most peripheral symmetric nucleus–nucleus collisions at the same colliding energy. Throughout the analyses, the same multiplicity parameters for particles and their antiparticles have been reported, which show the symmetric production of particles and their antiparticles.

Exclusive dielectron production in ultraperipheral Pb+Pb collisions at sqrt{s_{textrm{NN}}} = 5.02 TeV with ATLAS

Exclusive production of dielectron pairs, γγ → e+e−, is studied using {mathcal{L}}_{textrm{int}} = 1.72 nb−1 of data from ultraperipheral collisions of lead nuclei at sqrt{s_{textrm{NN}}} = 5.02 TeV recorded by the ATLAS detector at the LHC. The process of interest proceeds via photon–photon interactions in the strong electromagnetic fields of relativistic lead nuclei. Dielectron production is measured in the fiducial region defined by following requirements: electron transverse momentum {p}_{textrm{T}}^e > 2.5 GeV, absolute electron pseudorapidity |ηe| < 2.5, dielectron invariant mass mee> 5 GeV, and dielectron transverse momentum {p}_{textrm{T}}^{ee} < 2 GeV. Differential cross-sections are measured as a function of mee, average {p}_{textrm{T}}^e , absolute dielectron rapidity |yee|, and scattering angle in the dielectron rest frame, |cos θ*|, in the inclusive sample, and also with a requirement of no activity in the forward direction. The total integrated fiducial cross-section is measured to be 215pm 1{left(textrm{stat}.right)}_{-20}^{+23}left(textrm{syst}.right)pm 4left(textrm{lumi}.right) μb. Within experimental uncertainties the measured integrated cross-section is in good agreement with the QED predictions from the Monte Carlo programs Starlight and SuperChic, confirming the broad features of the initial photon fluxes. The differential cross-sections show systematic differences from these predictions which are more pronounced at high |yee| and |cos θ*| values.

Spontaneous vacuum decay in low-energy collisions of heavy nuclei beyond the monopole approximation

The problem of spontaneous vacuum decay in low-energy collisions of heavy nuclei is considered beyond the scope of the monopole approximation. The time-dependent Dirac equation is solved in a rotating coordinate system with $z$-axis directed along the internuclear line and the origin placed at the center of mass. The probabilities of electron-positron pair creation and the positron energy spectra are calculated in the approximation neglecting the rotational coupling. The two-center potential is expanded over spherical harmonics and the convergence with respect to the number of terms in this expansion is studied. The results show that taking into account the two-center potential instead of its spherically symmetric part preserves all the signatures of the transition to the supercritical regime that have been found in the framework of the monopole approximation and even enhances some of them.