Moscow University Physics Bulletin最新文献

We study the contribution of hadronic scattering of light-by-light to the fine and hyperfine structure of muonic atoms which is connected with scalar meson exchange.

The article presents the results of modeling the heavy-ion collisions of xenon and lead systems in the Monte Carlo generator HYDJET++. The relations of the azimuthal distributions of charged particles in Xe–Xe and Pb–Pb collisions are given. The simulation results are compared with the CMS experiment. In addition, predictions are given for the azimuthal distributions of charged particles in relativistic collisions of oxygen nuclei.

The (K^{+}topi^{+}pi^{0}pi^{0}gamma) decay is observed by the OKA collaboration. The branching ratio is measured to be (left(3.3pm 0.8(textrm{stat.})right)times 10^{-6}). The branching ratio and (gamma) energy spectrum are consistent with ChPT prediction.

Based on 4.5 fb({}^{-1}) (e^{+}e^{-}) data taken at the center-of-mass energies (sqrt{s}=4.6{-}4.7) GeV with the BESIII detector, we improve measurement the absolute branching fraction and report the form factor measurement in (Lambda_{c}^{+}toLambda e^{+}nu_{e}), and observed the (Lambda_{c}^{+}to pK^{-}e^{+}nu_{e}). The inclusive decay (Lambda_{c}to Xe^{+}nu_{e}) is also improved measurement. Moreover, we report the first amplitude analysis of (Lambda_{c}toLambdapi^{+}pi^{0}) and the observe the Cabibbo-suppressed decay (Lambda_{c}^{+}to npi^{+}).

The non-Abelian nature of quantum chromodynamics predicts the existence of exotic states, such as glueballs, hybrids, and multiquarks states. The experimental confirmation of these states would provide fundamental information about QCD in the confinement regime and would be a direct test of the QCD theory. The radiative decays of charmonium are glue-rich processes and are considered to be excellent probes for the production of gluonic matter and light hadron structures. The BESIII experiment, which is in operation at the BEPCII electron-positron collider in Beijing since 2009, has collected world leading high statistic data samples in the charmonium region, this offers unique possibilities to study exotic QCD states in the charmonium sector.

Studying the properties of deconfined state of partonic matter, or so-called quark-gluon plasma (QGP), can be performed using different observables, such as azimuthal anisotropy of emitted hadrons in heavy-ion collisions. To quantify observed azimuthal anisotropy in momentum space the elliptic flow ((v_{2})) is used. Since the spatial azimuthal anisotropy arises in the early stages after the collision of nuclei, where the QGP phase can dominate, the elliptic flow is considered a sensitive tool to study the collective behavior in QGP. To study the development of the elliptic flow, measurements of (v_{2}) values can be made for different particle’s species and collision geometries. The measurement of (v_{2}) for (pi^{0}) mesons is particularly interesting in this regard since their production is measurable up to high values of transverse momentum ((p_{T}>5) GeV/c). The talk will present new results for (pi^{0}) elliptic flow in Cu (+) Au collisions as a function of (pi^{0}) transverse momentum for different centralities. This set of results provides an additional opportunity to identify the dominant mechanisms in the development of (pi^{0}) elliptic flow over a wide range of transverse momentum in Cu (+) Au collisions.

Results of study of the (K^{+}rightarrowpi^{0}e^{+}nugamma) decay at OKA setup are presented. More than 150K candidates for this decay have been selected. The branching ratios, normalized to that of (K_{e3}) decay are calculated for different cuts on (E^{*}_{gamma}) and (Theta^{*}_{egamma}). In particular, the branching ratio for (E^{*}_{gamma}>30) MeV and (Theta^{*}_{egamma}>20^{circ}) is measured (textrm{R}=frac{Br(K^{+}rightarrowpi^{0}e^{+}nu_{e}gamma)}{Br(K^{+}rightarrowpi^{0}e^{+}nu_{e})}=(0.610pm 0.007(textrm{stat.})pm 0.011(textrm{syst.}))times 10^{-2}), which is in a good agreement with ChPT (O(p^{6})) calculations.

Recent results on the B hadron decays from the CMS experiment at the LHC are reported. The observation of the ({{textrm{B}}^{0}}to{psitextrm{(2S)}}{{textrm{K}}^{0}_{textrm{S}}}{{{pi}^{+}{pi}^{-}}}) and ({{textrm{B}}^{0}_{textrm{s}}}to{psitextrm{(2S)}}{{textrm{K}}^{0}_{textrm{S}}}) decays is presented together with the first observation of the (etatomu^{+}mu^{-}mu^{+}mu^{-}) decay and the first observation of the ({Lambda^{0}_{textrm{b}}}to{textrm{J}/psi}{Xi^{-}}{{textrm{K}}^{+}}) decay. The results are based on data sample collected in pp collisions at 13 TeV.

SATURNE is the Sarov tritium neutrino experiment that aims at the first observation of coherent elastic neutrino–atom scattering and the search for neutrino electromagnetic properties. A marked feature of the experiment is the use of a high-intensity tritium source of electron antineutrinos with a total tritium mass of at least 1 kg (10 MCi). Three detectors are being developed for the goals of the experiment. A 1-m({}^{3}) liquid He-4 detector operating at a temperature between 40 and 60 mK is designed both to register coherent elastic neutrino–atom scattering and to search for the neutrino magnetic moment at a level of (mu_{nu}sim 10^{-13},mu_{textrm{B}}), which is about an order of magnitude better than the world-leading upper limits on the (mu_{nu}) value. A 4-kg Si crystal detector operating at a temperature in the range of 10–50 mK and a 14-kg SrI({}_{2})(Eu) scintillation detector operating at a temperature between (-60) and (-40) ({}^{circ})C are purposed for testing the (mu_{nu}) value on the order of (sim 10^{-12},mu_{textrm{B}}), which is competitive with or even better than the world-leading upper limits.

The soft and hard QCD processes are analyzed by the CMS experiment using samples of proton-proton collisions collected by the LHC at sqrts (=) 7, 8, and 13 TeV. Measurements of jet production rates, jet properties, particle multiplicity, particle momentum spectra, and correlations are presented. The results are compared to predictions of theoretical models at leading- and next-to-leading orders of QCD. The data in combination with HERA and ATLAS results are used to measure the strong coupling constant and for PDF constraints.