Physics of Particles and Nuclei最新文献

Abstract

In addition to (Lambda ) hyperons, new data on (Sigma ) hyperons production are compared to different Monte-Carlo models and contribute to understand hadron production mechanisms. The first measurements of the transverse momentum (({{p}_{{text{T}}}})) spectra of ({{Sigma }^{0}}) and ({{overline Sigma }^{0}}) hyperons in pp collisions at (sqrt s = 7) TeV at the LHC are presented. The ({{Sigma }^{0}})(({{overline Sigma }^{0}})) is reconstructed via its electromagnetic decay channel (Lambda (overline Lambda ) + gamma ), while the (Lambda )((overline Lambda )) baryon is detected via its decay into (p + {{pi }^{ - }}) ((bar {p}) + ({{pi }^{ + }})). The low-energy photon is measured via conversion into ({{e}^{ + }}{{e}^{ - }}) pairs in the detector material and in PHOS calorimeter by exploiting the unique capability of the ALICE detector. The complementary results on the first detection of ({{Sigma }^{ + }}) and ({{overline Sigma }^{ - }}) hyperon at the LHC with ALICE are shown in pp collisions at (sqrt s = 13) TeV. The ({{Sigma }^{ + }})(({{overline Sigma }^{ - }})) is reconstructed via its weak decay into p((bar {p}) + {{pi }^{0}}) with the challenging detection of low-energy photons from ({{pi }^{0}}) decay. Also, the first reconstruction of ({{overline Sigma }^{ pm }} to bar {n} + {{pi }^{ pm }}) decays and ({{overline Sigma }^{ pm }}) transverse momenta spectra in pp and p-Pb collisions are presented. Antineutron is identified and reconstructed with PHOS by unique signature of the annihilation process.

Abstract

Silicon pixel photomultipliers (SiPM) are widely used in various fields of scientific experimental equipment. As a rule, the use of SiPM in physical experiments at accelerators assumes the presence of a radiation background in the area where the detection equipment is located. Radiation defects created in the space charge region (SCR) of pixels lead to an increase in thermal generation current, which is a source of noise. The main and practical issues for any experiment are lifetime and degradation rate of the main parameters and SiPM operating modes that reduce the negative effects from the radiation damage accumulation over time. This paper attempts to practically answer some of these questions.

Abstract

One of the primary observables that is sensitive to the transport characteristics of the strongly interacting matter created in relativistic heavy-ion collisions is the elliptic flow ({{v}_{2}}) of the produced particles. The relative elliptical flow fluctuations are of great interest because they can be used as a probe of the initial conditions using the ratio of cumulants ({{{{v}_{2}}{ 4} } mathord{left/ {vphantom {{{{v}_{2}}{ 4} } {{{v}_{2}}{ 2} }}} right. kern-0em} {{{v}_{2}}{ 2} }}). In this work, we study the centrality dependence of elliptic flow fluctuations using the state-of-the-art models of heavy-ion collisions spanning the range (sqrt {{{s}_{{NN}}}} ) = 5–11 GeV.

To explain why nuclei exist and to represent some aspects of their internal organization, it is important to understand in what form time exists in the Nature itself. To this end, we restore the fundamental notions of electric and magnetic fields in the framework of the general relativity theory and derive the general covariant Maxwell equations for these fields. This makes it possible to define natural time and recognizes that there are two different natural times. We connect the existence of dual natural time with the existence of nuclei.

Collisions of relativistic nuclei provide a unique opportunity to study the phase diagram of strongly interacting matter. New data on the yields, spectra, and lifetimes of hyperons and hypernuclei will allow many aspects of the dynamics of nucleus–nucleus collisions to be revealed due to their dependence on the nature of phase transformations and the equation of state in the medium, as well as on the type of hyperon–nucleon potentials at high densities. The study of the production of strange particles will play a significant role in the physics program of the MPD experiment at the NICA accelerator complex, therefore, studying the detector characteristics for the reconstruction of hyperons and hypernuclei is an important task at the current stage of the project implementation.

A review on the gluon transverse momentum dependent distribution (TMD) and its application to the analysis of the (ep) DIS at the HERA energies, hard and soft (pp) processes at LHC energies and mid-rapidity is presented.

One of the key tasks of the PHENIX experiment is studying the properties of the quark–gluon plasma (QGP). An efficient method for studying the properties of the QGP is measuring the azimuthal anisotropy of particle production in ultrarelativistic collisions of heavy ions. The azimuthal anisotropy is characterized by the coefficients of the Fourier transform of the function of particle distribution over the azimuthal angle. The measurement of the second coefficient of the Fourier transform (({{v}_{2}})), which is called the elliptic flow, makes it possible to investigate the collective behavior of nuclear matter and, thus, to study the QGP properties. In this study, a review of the recent results of measurement of hadron elliptic flows as a function of the transverse momentum and centrality of nuclei collisions in the PHENIX experiment is presented. The data of measured values of ({{v}_{2}}) for neutral and charged hadrons in the Cu + Au and Au + Au collisions at energy (sqrt {{{s}_{{NN}}}} ) = 200 GeV are presented.

Preliminary results on determination of the microscopic Hubble constant for pions and nucleons in Au + Au collisions at (sqrt {{{s}_{{NN}}}} = 7.8) GeV for a range of times and (b = 7.5) fm are presented and discussed. The data are simulated within PHSD model. A typically used method based on the fit of the velocity profile is considered in detail. Also a new method for determination of the Hubble parameter is proposed. It consists in the analysis of the statistical distribution of the divergence of the velocity field and getting the Hubble parameter as a position of a particular peak of the distribution. A comparison of the methods is done.

The results of an analysis of the invariant mass spectra of photon pairs produced in (d)Cu interactions at a momentum of 3.83 GeV/c per nucleon, are presented. Signals in the form of enhanced structures at invariant masses of about 17 and 38 MeV/c² are observed. The results of testing of the observed signals, including the results of the Monte Carlo simulation are presented. The test results support the conclusion that the observed signals are the consequence of detection of the particles with masses of about 17 and 38 MeV/c² decaying into a pair of photons.

In the variational method, we study the energy levels of pionic helium ((pi -e-{text{He}})) and kaonic helium ((K - e - {text{He}})) with an electron in the ground state and a meson in the excited state with the principal and orbital quantum numbers n ~ l + 1 ~ 20. Variational wave functions are taken in the Gaussian form. Matrix elements of the basic Hamiltonian and corrections to vacuum polarization and relativism are calculated analytically in a closed form. We calculate some bound state energies and transition frequencies, which can be studied experimentally.