Search for invisible decays of sub-GeV dark photons in missing-energy events at the CERN SPS

We report on a direct search for sub-GeV dark photons (A') which might be produced in the reaction e^- Z \to e^- Z A' via kinetic mixing with photons by 100 GeV electrons incident on an active target in the NA64 experiment at the CERN SPS. The A's would decay invisibly into dark matter particles resulting in events with large missing energy. No evidence for such decays was found with 2.75\cdot 10^{9} electrons on target. We set new limits on the \gamma-A' mixing strength and exclude the invisible A' with a mass < 100 MeV as an explanation of the muon g_\mu-2 anomaly.Comment: 6 pages, 3 figures; Typos corrected, references adde

Spherical Bondi accretion onto a magnetic dipole

Quasi-spherical supersonic (Bondi-type) accretion to a star with a dipole magnetic field is investigated using resistive magnetohydrodynamic simulations. A systematic study is made of accretion to a non-rotating star, while sample results for a rotating star are also presented. A new stationary subsonic accretion flow is found with a steady rate of accretion to the magnetized star smaller than the Bondi accretion rate. Dependences of the accretion rate and the flow pattern on the magnetic momentum of the star and the magnetic diffusivity are presented. For slow star's rotation the accretion flow is similar to that in non-rotating case, but in the case of fast rotation the structure of the subsonic accretion flow is fundamentally different and includes a region of ``propeller'' outflow. The methods and results described here are of general interest and can be applied to systems where matter accretes with low angular momentum.Comment: 15 pages, 15 figures, used emulapj.st

The CMS Micro-strip Gas Chamber Project: Development of a high resolution tracking detector for harsh radiation environments

Thirty-two large area Micro-Strip Gas Chambers were tested in a high intensity, 350~MeV pion beam at PSI to prove that we had reached a Milestone for the Compact Muon Solenoid (CMS) experiment. The particle rate was approximately 6 kHz/mm2, distributed over the whole active area of the detectors, and this rate was maintained for a total integrated time of 493 hours. All of the chambers were operated with signal-to-noise values at or above that corresponding to 98 % hit detection efficiency at CMS; the average S/N was 31. No indications of any gain instabilities or ageing effects were observed. In the official 3-week Milestone period, three strips from a total of 16384 were damaged, a result which is twenty times lower than the minimal requirement for CMS. The spark rate of the detectors was very low and decreased with time to an average of one spark per chamber per day. The cathode voltages of 24 of the chambers were increased over a one week period to investigate the behaviour of the detectors at higher gains; the maximum S/N value was 2.4 times that at the normal working point. No significant increase in spark rate or strip loss rate was detected and the chambers operated stably. The detector efficiencies and imaging capabilities were also investigated. The MSGC design features and the assembly and test methodologies that enabled us to achieve these results are reported

Pseudo-Schwarzschild description of transonic spherical accretion onto compact objects

A number of `modified' Newtonian potentials of various forms are available in the literature which accurately approximate some general relativistic effects important for studying accretion discs around a Schwarzschild black hole. Such potentials may be called `pseudo-Schwarzschild' potentials because they nicely mimic the space-time around a non-rotating/slowly rotating compact object. In this paper, we examine the validity of the application of some of these potentials to study the spherically symmetric, transonic, hydrodynamic accretion onto a Schwarzschild black hole. By comparing the values of various dynamical and thermodynamic accretion parameters obtained for flows using these potentials with full general relativistic calculations, we have shown that though the potentials discussed in this paper were originally proposed to mimic the relativistic effects manifested in disc accretion, it is quite reasonable to use most of the potentials in studying various dynamical as well as thermodynamic quantities for spherical accretion to compromise between the ease of handling of a Newtonian description of gravity and the realistic situations described by complicated general relativistic calculations. Also we have shown that depending on the chosen regions of parameter space spanned by specific energy ${\cal E}$ and adiabatic index $\gamma$ of the flow, one potential may have more importance than another and we could identify which potential is the best approximation for full general relativistic flow in Scwarzschild space-time for particular values of ${\cal E}$ and $\gamma$.Comment: 15 one-column pages. 6 black and white post-script figures. Published in A&

СИНТЕЗ ТА АНТИБАКТЕРІАЛЬНІ ВЛАСТИВОСТІ 4-АМІНОФЕНІЛСУЛЬФОНАМІДУ, ІММОБІЛІЗОВАНОГО НА ПОЛІМЕРНОМУ НОСІЇ

The aim of the study. Today the immobilization of drugs to the polymeric carriers is increasingly important, due to the requirements to reduce the toxicity and prolongation of action of drugs. It is known the immobilization of the Sulfonamides on the Stiromali, methacrylate polymer matrices, wherein the pharmacologically active sulfanilamide easily remove from the polymer upon the application, by the acid hydrolysis. At the same time it is noted that immobilized sulfonamides derived from aminomethylated Styrene-divinylbenzene copolymer, although hydrolytic stability, maintain the antibacterial properties. In order to expand the examples of covalent immobilization of sulfonamides we synthesized 4-aminophenylsulfonamide on pellet and brous forms of styrene and divinylbenzene with SO2 as a bridging group.Materials and Methods. As a raw materials, we used the pellet macroporous sulfonated Styrene-divinylbenzene copolymer and copolymers Polypropylene and Styrene. Sulfochlorination of these copolymers the polymeric sulfonyl chlorides were obtained. This compounds were used in the reaction with 4-aminophenilsulfonamidom. Antibacterial properties of the material were studied by determining the growth inhibition zones of test E. coli K12 microorganism in a nutrient medium.Results and Discussion. The structure of synthesized immobilized 4-aminophenylsulfonamide proven by IR spectroscopy. It is shown that such materials exhibit a relatively pronounced antibacterial properties test culture of microorganisms E. coli K-12, in spite of their resistance to hydrolysis. Сonclusions. It is suggested that the hydrolysis of the materials takes place at a specic enzymatic catalysis in the medium with the release of 4-aminophenylsulfonamide.Мета роботи. У сучасних умовах іммобілізація лікарських засобів на полімерних носіях набуває все більшого значення, що пов’язане з вимогами до зменшення токсичності та пролонгації дії препаратів. Відома іммобілізація сульфаніламідних препаратів на стиромалі, метакрилатних полімерних матрицях, де фармакологічно активний сульфаніламід легко вивільняється з полімеру при застосуванні, в результаті кислотного гідролізу. Разом з тим спостерігається, що іммобілізовані сульфаніламіди, отримані на основі амінометильованого співполімеру стиролу з дивінілбензолом, незважаючи на стійкість до гідролізу, зберігають антибактеріальні властивості. З метою розширення прикладів ковалентної іммобілізації сульфаніламідів нами синтезовані 4-амінофенілсульфонаміди на гранульній і волокнистій формах співполімерів стиролу з дивінілбензолом через місткову групу SO2.Матеріали і методи. Як вихідну сировину використано макропористий гранульний співполімер стиролу з дивінілбензолом і сульфовані волокнисті форми прищепленого до поліпропіленової нитки співполімеру стиролу з дивінілбензолом. Сульфохлоруванням цих співполімерів отримано полімерні сульфохлориди, які використовували в реакції з 4-амінофенілсульфонамідом. Антибактеріальні властивості матеріалу досліджені за визначенням зон пригнічення росту тест-мікроорганізмів E.coli К-12 на поживному середовищі.Результати й обговорення. Будову синтезованих іммобілізованих 4-амінофенілсульфонамідів доведено методом ІЧ спектроскопії. Показано, що такі матеріали проявляють виражені антибактеріальні властивості щодо тест-культури мікроорганізмів E. coli К-12, незважаючи на їхню стійкість до гідролізу.Висновки. Зроблено припущення, що гідроліз матеріалів перебігає при специфічному ферментативному каталізі на поживному середовищі виділенням 4-амінофенілсульфонаміду

Production properties of K*(892) vector mesons and their spin alignment as measured in the NOMAD experiment

First measurements of K*(892) mesons production properties and their spin alignment in nu_mu charged current (CC) and neutral current (NC) interactions are presented. The analysis of the full data sample of the NOMAD experiment is performed in different kinematic regions. For K*+ and K*- mesons produced in nu_mu CC interactions and decaying into K0 pi+/- we have found the following yields per event: (2.6 +/- 0.2 (stat.) +/- 0.2 (syst.))% and (1.6 +/- 0.1 (stat.) +/- 0.1 (syst.))% respectively, while for the K*+ and K*- mesons produced in nu NC interactions the corresponding yields per event are: (2.5 +/- 0.3 (stat.) +/- 0.3 (syst.))% and (1.0 +/- 0.3 (stat.) +/- 0.2 (syst.))%. The results obtained for the rho00 parameter, 0.40 +/- 0.06 (stat) +/- 0.03 (syst) and 0.28 +/- 0.07 (stat) +/- 0.03 (syst) for K*+ and K*- produced in nu_mu CC interactions, are compared to theoretical predictions tuned on LEP measurements in e+e- annihilation at the Z0 pole. For K*+ mesons produced in nu NC interactions the measured rho00 parameter is 0.66 +/- 0.10 (stat) +/- 0.05 (syst).Comment: 20 p

Search for Axionlike and Scalar Particles with the NA64 Experiment

We carried out a model-independent search for light scalar (s) and pseudoscalar axionlike (a) particles that couple to two photons by using the high-energy CERN SPS H4 electron beam. The new particles, if they exist, could be produced through the Primakoff effect in interactions of hard bremsstrahlung photons generated by 100 GeV electrons in the NA64 active dump with virtual photons provided by the nuclei of the dump. The a(s) would penetrate the downstream HCAL module, serving as shielding, and would be observed either through their $a(s)\to\gamma \gamma$ decay in the rest of the HCAL detector or as events with large missing energy if the a(s) decays downstream of the HCAL. This method allows for the probing the a(s) parameter space, including those from generic axion models, inaccessible to previous experiments. No evidence of such processes has been found from the analysis of the data corresponding to $2.84\times10^{11}$ electrons on target allowing to set new limits on the $a(s)\gamma\gamma$-coupling strength for a(s) masses below 55 MeV.Comment: This publication is dedicated to the memory of our colleague Danila Tlisov. 7 pages, 5 figures, revised version accepted for publication in Phys. Rev. Let