Moscow University Physics Bulletin最新文献

A search is reported for near-threshold resonances decaying to (textrm{J}/psitextrm{J}/psi), using the 13 TeV proton–proton collision data collected by the CMS experiment. Two structures are observed at masses of about 6550 and 6930 MeV with local significance exceeding 5 standard deviations. The second one is consistent with the X(6900) previously reported by the LHCb experiment. Evidence for a third structure is found at about 7300 MeV with a local significance of 4 standard deviations. Models employing interference between these states were tested and can provide a better description of the spectrum between the resonances.

ALICE-3 is the future experiment based on the novel silicon technologies which is designed as a very compact, very precise and very fast spectrometer with a wide rapidity coverage. The detector is designed to work with high luminosities not reachable for the current ALICE experiment. Considerable increase in collected statistics coupled with improvement in precision of measurements and available acceptance will give opportunity for the areas of studies not covered by physics program of the ALICE collaboration before or highly improve and differentiate results obtained before. One of such areas of studies is precise, differential analysis of open charm production in wide transverse and rapidity ranges in different colliding systems at maximum LHC energies. In this contribution we present results of feasibility studies for reconstruction of neutral D-mesons (ground and excited states) in decay channels with photons in the final state in pp, p-Pb, and Pb-Pb collisions at LHC energies using the apparatus of the future ALICE-3 experiment. We discuss possible advantages of the usage of electromagnetic calorimeter for high transverse momentum measurements, estimate signal to background ratios within the approach and estimate the required statistics needed for precise measurements at the highest reachable transverse momentum.

The MPD (Multipurpose Detector) experiment is being conducted at the Joint Institute for Nuclear Research in Dubna. This is an international project aimed at studying the properties of extremely hot and dense baryonic matter, which is formed during collisions of heavy ions, which are accelerated to high energies by the NICA accelerator complex. MPD includes various detector systems: time-of-flight (TOF) detector, time-projection camera (TPC), electromagnetic calorimeter (ECal), and others. TOF and TPC are involved in the identification of charged hadrons, and ECal—electrons and photons.

The COHERENT collaboration measures coherent elastic neutrino-nucleus scattering (CEvNS) at Spallation Neutron Source (SNS) in Oak Ridge National Laboratory (ORNL) and explores related physics opportunities. In this paper we provide a status update of ongoing CEvNS efforts including the liquid argon, high-purity germanium and NaI[Tl] detectors, and share the plans of next-generation CEvNS experiments at SNS. We describe the effort aiming to measure neutrino inelastic interactions with ({}^{16})O, ({}^{40})Ar, ({}^{127})I, ({}^{textrm{nat}})Pb, and ({}^{232})Th nuclei. We also provide a status update of the SNS neutrino flux measurement with a heavy water Cherenkov detector and present the COHERENT reach of accelerator-produced dark matter and sterile neutrino searches. Furthermore, we briefly describe ORNL plans of the SNS beampower upgrade and construction of the Second Target Station.

Using the model of nucleon-flucton interaction, the yields of pions and protons are estimated in the new cumulative region of central rapidities and high transverse momenta, accessible for experimental study in dd collisions at the NICA SPD. It is shown that in this new region the yield of pions increases compared to protons, while in the region of fragmentation of a nucleus the yield of cumulative protons is dominant. The effect is explained by different mechanisms of their formation in the cumulative region—the coherent coalescence (recombination) of three flucton quarks to form a proton and the fragmentation of one flucton quark into a pion.

The physics of neutrino oscillations has developed rapidly over the past few decades. Although there are still unmeasured parameters that determine this process. Measuring these parameters is the main goal of current and future projects in this area of particle physics. This review will discuss current neutrino accelerator experiments measuring three flavor neutrino oscillations (NOvA and T2K), and also briefly describe the prospects for future experiments (DUNE and Hyper-Kamiokande) and possible projects currently being considered.

We review the status of neutrino mass constraints obtained from cosmological observations, with a particular focus on the results derived considering Cosmic Microwave Background (CMB) data by various experiments (Planck, ACT, and SPT), Baryon Acoustic Oscillation (BAO) determinations and other late-universe probes. We discuss the role played by priors and parameterizations in the Bayesian analyses, both at the time of determining neutrino masses or their ordering, and compare cosmological bounds with terrestrial constraints on both quantities.

The BESIII detector on the BEPCII collider collected the world’s largest dataset at the peaks of (J/psi), (psi(3686)) and (psi(3770)). The use of polarization and entanglement states in multidimensional angular distribution analysis can provide new probe to the production and decay characteristics of hyperon anti hyperon pairs. In a recent series of studies, significant transverse polarization in hyperon decay has been observed in (J/psi), (psi(3686)) decaying into the (Lambdabar{Lambda}), (Sigma^{+}bar{Sigma}^{-}), (Xi^{0}bar{Xi}^{0}), and (Xi^{-}bar{Xi}^{+}) final states. The weak decay parameters of hyperons and antihyperons are also independently determined for the first time. The most accurate testing for direct (CP) violation has been achieved.

Properties of fractal entropy (S_{delta,epsilon}) reflecting fractality as general feature of (K_{S}^{0})-meson production in Au + Au collisions in the (z)-scaling approach is studied. The entropy is expressed via the momentum fractions of the colliding nuclei and the momentum fractions of the secondary objects produced in constituent interactions. The structure of colliding nuclei and fragmentation processes is described by fractal dimensions. The principle of maximum entropy with the assumption of fractal self-similarity of hadron structure and fragmentation processes determines the underlying constituent subprocess and leads to the conservation of new quantity, named fractal cumulativity. Statistical properties of the fractal entropy, quantization of fractal dimensions, and their symmetry relations are discussed.

Recent results on the central exclusive diffractive production of dihadrons are presented in the framework of the Regge-eikonal model.