[en] We present here the results of the first search for the associated production of the Higgs boson with a tt-bar pair, using the events where the Higgs boson decays to two photons in CMS. In order to maximize acceptance and sensitivity to such a small signal, we device two different sets of event selection criteria, optimized for leptonic and all-hadronic tt-bar decays. In the absence of a significant excess over the background-only predictions, we proceed to set an observed (expected) 95% confidence level upper limit on tt-bar_H production cross section times BR(H → γγ) of 5.4 (5.3) times the Standard model value using 19.6 fb^-1 of 8 TeV pp collisions. (authors)

[en] The observation of a boson compatible with the Standard Model (SM) Higgs particle is the starting point for the complete understanding of the electroweak symmetry-breaking mechanism. More specifically, the exact determination of the Higgs couplings to bosons and fermions is crucial to establish if the properties of this particle are compatible with the theoretical predictions. In order to achieve a good sensitivity in couplings measurements it is important to consider those production modes where the Higgs boson is produced in association with W/Z bosons or quarks. The characteristic topology of these events allows to perform an exclusive analysis, crucial for accurate measurements of couplings.

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[en] This paper describes the first application of 3D density reconstruction from a limited number of background oriented schlieren (BOS) images in a large research-type low speed wind tunnel. The tested flow is an ad hoc co-flowing hot jet generated at the wingtip of a simplified airfoil. Ray deviation maps captured by 12 synchronized cameras are combined to reconstruct the three dimensional density field of the jet, in the line of the direct 3D BOS technique described in Nicolas et al (2016 Exp. Fluids 57 1–21). A comparison with thermocouple sampling shows consistent results and highlights the efficiency of this new method for thermal measurement of a low speed convective flow. Finally, we underline the new possibilities for fluid dynamic characterization offered by combining stereo particle image velocimetry and 3D BOS measurements. (paper)

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[en] A prototype for a sampling calorimeter made out of cerium fluoride crystals interleaved with tungsten plates, and read out by wavelength-shifting fibres, has been exposed to beams of electrons with energies between 20 and 150 GeV, produced by the CERN Super Proton Synchrotron accelerator complex. The performance of the prototype is presented and compared to that of a GEANT4 simulation of the apparatus. Particular emphasis is given to the response uniformity across the channel front face, and to the prototype's energy resolution.

[en] The CMS electromagnetic calorimeter (ECAL) comprises 75848 scintillating lead tungstate crystals. 61200 crystals are contained in the ECAL Barrel section and are read out by avalanche photodiode (APD) with internal gain of about 50. This gain is achieved with a high voltage (HV) of about 400 Volts. The gain stability requirement implies a supply voltage stable to within 0.01%. We describe our experience with the installed Barrel HV power supply system, which has been used for data taking since 2008.