Moscow University Physics Bulletin最新文献

In this talk recent new results from CMS on the search for New Physics effects in heavy flavor decays are presented. Particularly, lepton flavor unification violation was searched for by measuring (R(K)) and (R(J/psi)) ratios. Also, lepton flavor violating decay (taurightarrow 3mu) was searched for and upper limit on its branching fraction was extracted. The discussed results were obtained with the RUN II data of pp collisions at (sqrt{s}=13) TeV.

The (K^{+}topi^{0}mu^{+}nugamma) ((K_{mu 3gamma})) decay is measured with OKA detector at the RF-separated 17.7 GeV/c momentum kaon beam from the U-70 synchrotron. The data obtained corresponds to the value of (2.62times 10^{10}) ‘‘live’’ kaons passing to the decay volume. About 1000 (K_{mu 3gamma}) events are extracted. The ratio of (textrm{Br}(K_{mu 3gamma})/textrm{Br}(K_{mu 3})) is measured. The T-odd correlation ({xi}_{pimugamma}), which is the mixed product of the momenta of (mu^{+},pi^{0}), and (gamma) in the kaon rest frame, is measured. The asymmetry of the distribution in (xi) is characterized by the ratio (A_{xi}=(N_{+}-N_{-})/(N_{+}+N_{-})), where (N_{+}) ((N_{-})) is the number of events with positive (negative) (xi). The values of (A_{xi}) is obtained. Our results are preliminary, with systematic errors being estimated.

Spectroscopy of the fully heavy tetraquarks with open charm and/or bottom is studied within the relativistic quark model, based on the quasipotential approach and QCD. A special emphasize is given to the asymmetric in flavor compositions. A tetraquark is considered as a bound state of a diquark and an antidiquark which are treated as a spatially extended colored objects and interact as a whole. Relativistic effects are consistently taken into account. It is found, that a significant mixing between the asymmetric in flavor states of tetraquarks occurs for the same total momentum-parity ((J^{P})), but different full spins of the tetraquark ((S)) within the same excitation. We confront the calculated masses of such tetraquarks with the fall-apart decay thresholds into a pair of heavy mesons. Such comparison allows us to select states that could be observed as narrow resonances.

Joint analysis of the results of the Neutrino-4 experiment and the data of the GALLEX, SAGE and BEST experiments confirms the parameters of neutrino oscillations declared by the Neutrino-4 experiment ((Delta m_{14}^{2}=7.3text{ eV}^{2}) and (sin^{2}2theta_{14}approx 0.36)) and increases the confidence level to (5.8sigma). Such a sterile neutrino thermalizes in cosmic plasma, contributes 5(%) to the energy density of the Universe, and can explain (15{-}20%) of dark matter. It is discussed that the extension of the neutrino model by introducing two more heavy sterile neutrinos in accordance with the number of types of active neutrinos but with very small mixing angles to avoid thermalization will make it possible to explain the large-scale structure of the Universe and bring the contribution of sterile neutrinos to the dark matter of the Universe to the level of 27(%). This approach to the problem of dark matter means that dark matter can be explained in terms of an extended Standard Model with right-handed neutrinos.

Recent CMS results on conventional spectroscopy and production of heavy flavour in (pp) collisions at (sqrt{s}=13) TeV states are reported. The observations and properties of new excited beauty baryons are discussed, as well as precision measurements of cross section ratios.

This paper, based on an invited talk at the 21th Lomonosov Conference of Elementary Particle Physics, discuss the sensitivity of future (e^{+}e^{-}) colliders to probe the Higgs sector and its relations to a New Physics at a TeV scale.

The most recent measurements on inclusive production of W and Z bosons obtained with CMS in proton–proton collision are reviewed. Results include total cross sections as well as decay properties of W and Z bosons. Recent differential results on Drell–Yan dilepton productions in a wide range of invariant masses will be also discussed.

We report on the current state of implementation of the Sarov tritium neutrino experiment at the National Center for Physics and Mathematics. The experiment will involve a high-intensity tritium neutrino source and three different detection systems sensitive to very low energy depositions. As an outcome, it is expected to observe for the first time coherent elastic neutrino-atom scattering and achieve a record-high sensitivity to the neutrino magnetic moment.

In the paper we show preliminary results of the ({e^{+}e^{-}totext{K}^{0}_{text{S}}text{K}^{0}_{text{L}}}) cross section measurements in the center-of-mass energy range from 1.05 to 2.0 GeV. The analysis is based on data collected with the CMD-3 detector at VEPP-2000 collider corresponding to the integrated luminosity of 233 pb({}^{-1}). We have developed the selection procedure of the signal process and calculated the detection efficiency and radiative corrections. The cross section is measured with the highest statistical precision in comparison to the previous experiments.

The paper presents initial steps to distinguish the contribution of anomalous operators in Wtb vertex from the Standard Model for final state processes tWb using a deep neural network. A scenario with vector left- and right-handed operators at the Wtb vertex is considered as an example and as a most difficult for the separation. The deep neural network was trained on preselected kinematic variables that exhibit different behavior for the Standard Model cases and the presence of a right vector operator at the Wtb vertex. The presented results can be interpreted in the context of further prospects for searching for anomalous operators in Wtb vertex for the processes of single- and double-resonant production of top quarks with the final state tWb.