Physics of Particles and Nuclei Letters最新文献

We present the results of [1], where good agreement was obtained between calculations within the framework of analytic QCD and experimental data on polarized Bjorken sum rule. The heavy quark contributions are taken into account.

In this paper, an approach to the analysis of hydraulic characteristics for the cooling and thermal stabilization systems of subdetectors in the MPD setup is described, including mathematical modeling and bench tests. Distributed and discrete models are used to simulate the cooling fluid flow. For bench tests, an automated test bench representing a software–hardware complex with vacuum and circulation pumps and liquid pressure, liquid flow rate, and temperature sensors has been developed. The test bench design may be transformed in compliance with formulated test problems. It has been experimentally established that, at a nominal cooling fluid flow rate of 0.006 kg/s, the pressure drop on one cooling pipeline of ADC64ECal modules is ≈0.12 atm. Numerical calculation and experimental measurement results for the pressure drop agree with each other with a deviation less than 2%. The transition to the leakless mode (absolute pressure, 0.4–0.0 atm) does not change the pressure–flow rate characteristic of the ECal panel when compared to the regime of flow at a superatmospheric pressure. The proposed approach is applicable to a broad spectrum of problems on the characterization and commissioning of the thermal stabilization and cooling system of the ТРС detector and other MPD setup detectors.

The IBR-4 pulsed reactor with a power of 4 MW and a pulse repetition frequency of 10 1/s is considered as a pulsed neutron source to replace the IBR-2M reactor, which will be decommissioned by the end of the 2030s. The IBR-4 design is based on the MBIR reactor implementing the principles of continuity of succesful solutions used in the IBR-2 and IBR-2M reactors. The IBR-4 core ensures the nuclear safety of the reactor and minimizes low-frequency fluctuations in pulse energy. The IBR-4 design is a development of the basic design of the core with the addition of beryllium reflectors and small-volume water moderators. The IBR-4 reactor makes it possible to obtain thermal neutron flux densities on the surface of the water moderator for the extracted neutron beams at a level of 1.2 × 10¹⁴ n/(cm² s), and, in the region close to the surface of the moderator, 3.0 × 10¹⁴ n/(cm² s). Thus, IBR-4 is a powerful pulsed source of thermal neutrons.

In this paper, we consider the lepton and photon invariant mass distribution in the Z boson decay into two leptons and photon. The measurements were performed with the ATLAS detector and have best accuracy today, the systematic uncertainty does not exceed 0.6%. Quantitative comparison of the measurement results with the predictions of modern event generators implementing the calculation of the Standard Model for this process was performed. The discovered deviations from the predictions of the generators are interpreted using the effective interaction of the Z boson with two leptons and photon. The addition of the effective interaction contribution turned out to be significant at the confidence level of ( > ,5sigma ) for PowHeg + PHOTOS and ( > ,4.7sigma ) for Sherpa 2.2. The charge asymmetry for this process was calculated at different values of the Weinberg angle sine. The asymmetry reaches a maximum and minimum at sine values of about 0.2 and 0.7, respectively. Numerically, the asymmetry is 0.03 at maximum and –0.03 at minimum, which does not allow one to explain the experimental value of the asymmetry of (0.088 pm 0.022) at lepton and photon invariant mass equal to the W boson mass.

We present the preliminary measurement of the two-photon η-meson production cross section: ({{e}^{ + }}{{e}^{ - }} to {{e}^{ + }}{{e}^{ - }}eta (550)). The measurements were carried out by the SND detector at the VEPP-2000 collider in the energy range from 1 to 2 GeV, the integral luminosity of the order of 0.5 fb^–1 was used. The η-meson was detected at the six-photon final state, without scattered electrons registration. From the cross section of this process, we extract the two-photon η-meson width. The experimental results obtained can be used to calculate the hadronic contribution to the light by light scattering and to interpret the results of the muon anomalous magnetic moment measurement’s and to calculate the electromagnetic interaction constant at Z boson mass scale.

There is a deep link between gravity and thermodynamics; in a precise way gravity can be derived from entanglement entropy in conformal field theories. However, this depends crucially on properties of horizons, and asymptotic symmetries of phase space. To explore how this relation behaves under dynamical processes, we consider covariant gravitational phase space enhanced with bulk conformal symmetry. As is well known, the Noether–Wald entropy has an explicit form in terms of the Abbott–Deser–Tekin conserved surface charges of gauge theories. We find a new vector contribution to the Abbott–Deser–Tekin charges that arises for conformal symmetries. In applying this to the causal diamond, we derive a general relation for surface gravity, based on the conformal invariance of horizons, that allows us to find slices where the zeroth law holds, as well as the degree to which a first law arises on the phase space.

This work is devoted to studying the potential of machine learning techniques in relativistic nuclear physics for distinguishing between various physical theories and, consequently, gaining a deeper comprehension of the underlying physical processes in ultra-relativistic nuclear collisions. Recent findings on the modeling of p + p and A + A interactions within the framework of the color string fusion model suggest that it is feasible to describe the experimentally observed event-by-event azimuthal asymmetry in a unified manner across various colliding systems. Such a description has become possible by considering two mechanisms of string interaction: (1) changes in the magnitude of the colour field in the region of string overlap in the transverse collision plane (2) Lorentz boosts applied to particles emerging as a result of string motion due to their mutual attraction. We demonstrate that it is feasible to train machine learning algorithms using ({{p}_{{text{T}}}})–(phi ) distributions from event-by-event data to distinguish between the proposed sources of collective behaviour.

We re-use some original ideas of de Broglie, Schrödiger, Dirac and Feynman to revise the ensemble interpretation of wave function in quantum mechanics. To this end we introduce coherence (auto-concordance) of ensembles of quantum trajectories in the space-time. The coherence condition accounts phases proportional to classical action, which are in foundation of the Feynman path integral technique. Therefore, our interpretation is entirely based on well-known and tested concepts and methods of wave mechanics. Similarly to other ensemble interpretations our approach allows us to avoid all problems and paradoxes related to wave function collapse during a measurement process. Another consequence is that no quantum computation or quantum cryptography method will ever work if it assumes that a particular q-bit represents the entire wave function.

The influence of short-range rapidity correlations on the fluctuation of the number of charged particles in a given rapidity interval of observation is investigated. It is shown that for pp collisions at LHC energies, the fluctuations of the particle number from a given string cluster are, due to the presence of short-range correlations between particles, significantly larger than the Poisson ones. The value of the scaled and robust variance of the multiplicity for pp collisions is calculated at three initial energies: 0.9, 2.76, and 7 TeV, both with and without taking into account the processes of string fusion and formation of string clusters. A comparison with experimental data is performed and it is shown that the results obtained taking into account the formation of string clusters agree well with the experimental values, in contrast to the case where string fusion processes are not taken into account.

Scalar diquark model of proton improved by parton intrinsic transverse momentum in hadrons is able to describe the strong scaling violation in proton production large transverse momentum ({{p}_{ bot }}) within perturbative QCD in a wide energy range: (sqrt s = 11.5,,{text{GeV}}) at U70 (NRC KI—IHEP, Protvino), (sqrt s = 23.4,,{text{GeV}}) at Tevatron (FNAL, Chicago), and (sqrt s = 62,,{text{GeV}}) at ISR (CERN, Geneva) is presented. Estimates for the production of tetraquark exotic states formed by scalar diquarks in the SPD experiment at the forthcoming NICA collider (JINR, Dubna) have been obtained.