Physics of Particles and Nuclei最新文献

Abstract

To measure the characteristics of quark and gluon jets in hadron–hadron collisions, two samples of jets are used. Given the large statistics of jets at the LHC, the two-sample method requires taking into account the following corrections: (1) use of measured fractions of quark and gluon jets instead of the model ones, (2) amendment for the contribution of jets with an unidentified type, (3) taking into account the dependence of the distributions of quark and gluon jets on the conditions for jet sample selections. The paper presents an improved two-sample method that takes into account these corrections.

Abstract

Measuring the spectra of light hadrons is one of the priority tasks of the MPD experiment at NICA. The assessment of the efficiency of recording differential transverse momentum spectra of production of identified hadrons in the MPD detector, which are produced in collisions of bismuth nuclei at an energy of (sqrt {{{s}_{{NN}}}} = 9.2) GeV, is presented.

Abstract

We investigate the finite-temperature structure of ghost and gluon propagators within an approach based on the rainbow truncated Dyson–Schwinger equations in the Landau gauge. The method early used for modeling quark, ghost and gluon propagators in vacuum is extended to finite temperatures. In Euclidean space, within the Matsubara imaginary time formalism the Dyson–Schwinger equation splits into a system of coupled equations for transversal and longitudinal propagatators. This system is considered within the rainbow approximation generalized to finite temperatures and solved numerically. The solutions to the ghost and gluon propagators are obtained as functions of temperature (T), Matsubara frequency ({{Omega }_{n}}) and three-momentum squared ({{k}^{2}}). It is found that in the vicinity of a certain value of the temperature ({{T}_{0}} sim 150) MeV the longitudinal gluon propagator increases quite fastly, whereas the transversal propagator does not exhibit any irregularity. This is in qualitative agreement with the results obtained within the QCD lattice calculations in this temperature interval.

Abstract

The usual Minkowski vacuum in an accelerated frame of reference is known to look like a “thermal bath” of particles. This effect is well known and called the Unruh effect, and is an analog of Hawking radiation in space with zero curvature. Thus, the Minkowski vacuum looks like a heated medium from the point of view of an accelerated observer, and the natural goal is to study the properties of such a medium in more detail. We show that if the Minkwoski vacuum is cooled, and we achieve a temperature below the Unruh temperature, then a phase transition occurs associated with the “fall beyond the horizon” of the lower Matsubara modes. This transition has many remarkable features, for example, for massless particles it is “polynomial,” and is also associated with the breaking of conformal symmetry.

Abstract

Analysis of new experimental data obtained by the TOTEM and ATLAS Collaborations at the LHC together with old data obtained at the SPS and Tevatron colliders at small momentum transfer in the framework of the high energy generalized structure (HEGS) model allows one to determine the dependence of different parts of the hadron elastic scattering amplitude on the mandelstam kinematic variables the (s) and (t).

Abstract

Modeling the deficiency of mature neurons allows one to predict the development of hippocampus-dependent cognitive impairment in response to irradiation with heavy particles. We use a mathematical model of adult neurogenesis that we developed to calculate the effect of heavy particles on the numbers of mature neurons. To reproduce an experimental data, the model was modified to consider the death of neural stem cells in response to irradiation. As a result, the survival rate of dividing progenitor cells, immature neurons and, for the first time, mature neurons after irradiation with ¹²C, ²⁸Si, and ⁵⁶Fe particles was calculated.

Abstract

Some results of data analysis of hadron production in (p + p) and (A + A) collisions obtained in the framework of (z)-scaling are discussed. A possible signature of phase transition in the matter created in central ({text{Au}} + {text{Au}}) collisions in the scaling regime is observed. The concept of the (z)-scaling is based on the principles of self-similarity, locality and fractality of particle interactions at a constituent level. The self-similarity variable (z) and the scaling function (psi (z)) are expressed via the experimentally measurable quantities and some model parameters characterizing the structure of colliding objects, fragmentation process and specific heat of the produced medium. The irregularities of fractal entropy and specific heat parameter ({{c}_{{{text{AuAu}}}}}) observed in (K_{S}^{0})-meson production in ({text{Au}} + {text{Au}}) collisions at RHIC are considered as an indication of phase transition in nuclear matter.

Abstract

This work examines some properties of the formation of electron beams for modern SR sources and colliders. Trends in this area are described. Characteristic parameters of such sources for developed and designing accelerator facilities are discussed. Latest developments at the Budker Institute of Nuclear Physics, Siberian Branch, Russian Academy of Sciences, in the field of electron guns are described, as well as plans for the development of electron sources at the institute for possible future SR sources and colliders are given.

In the framework of the model with string fusion and the formation of string clusters, the correlations between multiplicities in two separated rapidity windows in pp collisions at LHC energies were studied and the results obtained were compared with data from the ALICE collaboration at CERN. The simulation is conducted within the framework of a Monte Carlo implementation of the color quark–gluon string model. String fusion effects are considered by implementing a finite lattice in the plane of the impact parameter. The dependence of the correlation coefficient between multiplicities in two rapidity observation windows on the distance between these windows is calculated for four values of their width and three values of initial energy. It is shown that the model with string clusters describes the major features of the behavior of the correlation coefficient: its increase with increasing initial energy, decrease with increasing rapidity distance between observation windows, and nonlinear dependence on the width of the rapidity window.

Femtoscopy is a primary tool for measuring the spatiotemporal characteristics of small and short-lived systems created in particle or nuclear collisions with an accuracy of 1 fm. The possibility of such measurements is due to the effects of quantum statistics and final state interactions which create the momentum correlations of two or more particles at small relative momenta in their center-of-mass system. We report on the calculations of like-sign koan femtoscopic correlations produced in Au + Au at the BES-I region from RHIC using the Ultrarelativistic Quantum Molecular Dynamics Model (UrQMD). We discuss the 3D pion and kaon radii as a function of the transverse momentum of the particles and the centrality of the collision.