Central exclusive production of scalar \chi_c meson at the Tevatron, RHIC and LHC energies

We calculate several differential distributions for exclusive double diffractive $\chi_c(0^{++})$ production in proton-antiproton collisions at the Tevatron and in proton-proton collisions at RHIC and LHC in terms of unintegrated gluon distributions (UGDFs) within the $k_t$-factorisation approach. The uncertainties of the Khoze-Martin-Ryskin approach are discussed in detail. The $g^* g^* \to \chi_c(0^{++})$ transition vertex is calculated as a function of gluon virtualities applying the standard pNRQCD technique. The off-shell effects are discussed and quantified. They lead to a reduction of the cross section by a factor 2--5, depending on the position in the phase space and UGDFs. Different models of UGDFs are used and the results are shown and discussed. The cross section for diffractive component depends strongly on UGDFs. We calculate also the differential distributions for the $\gamma^* \gamma^* \to \chi_c(0^{++})$ fusion mechanism. The integrated cross section for photon-photon fusion is much smaller than that of diffractive origin. The two components have very different dependence on momentum transfers $t_1, t_2$ in the nucleon lines as well as azimuthal-angle correlations between both outgoing nucleons.Comment: 34 pages, 23 figures, 2 table

Natural Nuclear Reactor Oklo and Variation of Fundamental Constants Part 1: Computation of Neutronics of Fresh Core

Using modern methods of reactor physics we have performed full-scale calculations of the natural reactor Oklo. For reliability we have used recent version of two Monte Carlo codes: Russian code MCU REA and world wide known code MCNP (USA). Both codes produce similar results. We have constructed a computer model of the reactor Oklo zone RZ2 which takes into account all details of design and composition. The calculations were performed for three fresh cores with different uranium contents. Multiplication factors, reactivities and neutron fluxes were calculated. We have estimated also the temperature and void effects for the fresh core. As would be expected, we have found for the fresh core a significant difference between reactor and Maxwell spectra, which was used before for averaging cross sections in the Oklo reactor. The averaged cross section of Sm-149 and its dependence on the shift of resonance position (due to variation of fundamental constants) are significantly different from previous results. Contrary to results of some previous papers we find no evidence for the change of the fine structure constant in the past and obtain new, most accurate limits on its variation with time: -4 10^{-17}year^{-1} < d alpha/dt/alpha < 3 10^{-17} year^{-1} A further improvement in the accuracy of the limits can be achieved by taking account of the core burnup. These calculations are in progress.Comment: 25 pages, 14 figures, 12 tables, minor corrections, typos correcte

Current state and prospects of grain logistics development in Ukraine

Considering the lack of elevator capacities and the imbalance in the distribution of commodity flows due to the occupation and blocking of seaports, other modes of transport are currently unable to provide the required volumes of grain for export, and the safety of the harvest is under threat. Therefore, the issue of logistics development in war conditions is urgent, which determines the relevance of the study. The purpose of the study is to analyse the pre-war and current state of the grain logistics system and to identify efficient ways of its development during the war and after its end. The study is based on the following methods: dialectical, historical, monographic, abstract-logical, systematic and classification, analytical forecasting, statistical, economic, economic-mathematical, and graphical. Investigated the length of roads in Ukraine and forecasted the reduction of roads due to military operations. The analysis of exportimport logistics was performed, and the advantages of maritime transport were determined, the share of which in exports was 99.5%, and in imports, the majority of transportation was by rail (44.9%). The state of elevator capacities was explored, the lack of which in 2021 amounted to 18.3 million tons (17.4%), the volume of their losses due to hostilities in 2022 was determined – 12.6 million tons (22.2%), the impact of the war on the growth of prices for grain storage services was analysed. A critical analysis of the infrastructure projects of the National Council for the Restoration of Ukraine from the Consequences of the War is performed and identified their disadvantages. The proposed measures to improve logistics will allow for reducing the lack of elevator capacities, increasing grain exports, accelerating the movement of products across the border and reducing logistics costs. The results of the research can be used by public authorities in the establishment of programs for the development of agrarian logistics, business structures – for the development of infrastructure projects and improvement of logistics systems of enterprises, scientists – for further investigation of grain logistics problems and determining the prospects for its developmen

Would unitarity slow down the rise of F2(x,Q2)F_2(x,Q^2) at x→0x\to 0?

On the grounds of the $U$--matrix form of $s$--channel unitarization, we consider constraints unitarity provides for the total cross--section of the virtual photon--induced reactions and discuss the preasymptotic nature of hadron and photon scatterings at $\sqrt{s}\leq 0.5$ TeV.Comment: 8 pages, LaTeX, no figure