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We report on a measurement of Spin Density Matrix Elements (SDMEs) in hard exclusive ρ 0 meson muoproduction at COMPASS using 160 GeV/ c polarised μ + and μ - beams impinging on a liquid hydrogen target. The measurement covers the kinematic range 5.0 GeV/ c 2 < W < 17.0 GeV/ c 2 , 1.0 (GeV/ c ) 2 < Q 2 < 10.0 (GeV/ c ) 2 and 0.01 (GeV/ c ) 2 < p T 2 < 0.5 (GeV/ c ) 2 . Here, W denotes the mass of the final hadronic system, Q 2 the virtuality of the exchanged photon, and p T the transverse momentum of the ρ 0 meson with respect to the virtual-photon direction. The measured non-zero SDMEs for the transitions of transversely polarised virtual photons to longitudinally polarised vector mesons ( γ T ∗ → V L ) indicate a violation of s -channel helicity conservation. Additionally, we observe a dominant contribution of natural-parity-exchange transitions and a very small contribution of unnatural-parity-exchange transitions, which is compatible with zero within experimental uncertainties. The results provide important input for modelling Generalised Parton Distributions (GPDs). In particular, they may allow one to evaluate in a model-dependent way the role of parton helicity-flip GPDs in exclusive ρ 0 production.

Recent theoretical and experimental studies highlight the possibility of new fundamental particle physics beyond the Standard Model that can be probed by sub-eV energy experiments. The OSQAR photon regeneration experiment looks for “Light Shining through a Wall” from the quantum oscillation of optical photons into “Weakly Interacting Sub-eV Particles”, like axion or axion-like particles (ALPs), in a 9 T transverse magnetic field over the unprecedented length of 2 × 14.3  m. No excess of events has been detected over the background. The di-photon couplings of possible new light scalar and pseudo-scalar particles can be constrained in the massless limit to be less than 8.0 × 10 - 8  GeV - 1 . These results are very close to the most stringent laboratory constraints obtained for the coupling of ALPs to two photons. Plans for further improving the sensitivity of the OSQAR experiment are presented.

This paper presents the current data acquisition system (DAQ) of the COMPASS experiment at CERN and discusses development of a new DAQ. The aim of the new DAQ is to substitute software event building by structure composed of special FPGA cards that will do the event building. The software part of the new DAQ is robust multinode system with high emphasis on reliability. It is based on state machines and implemented in C++ with usage of the QT framework, the DIM library, and the IPBus technology. A prototype of the system has been developed and tested. The new DAQ software fulfills given requirements.

This paper briefly introduces the data acquisition system of the COMPASS experiment and is mainly focused on the part that is responsible for the monitoring of the nodes in the whole newly developed data acquisition system of this experiment. The COMPASS is a high energy particle experiment with a fixed target located at the SPS of the CERN laboratory in Geneva, Switzerland. The hardware of the data acquisition system has been upgraded to use FPGA cards that are responsible for data multiplexing and event building. The software counterpart of the system includes several processes deployed in heterogenous network environment. There are two processes, namely Message Logger and Message Browser, taking care of monitoring. These tools handle messages generated by nodes in the system. While Message Logger collects and saves messages to the database, the Message Browser serves as a graphical interface over the database containing these messages. For better performance, certain database optimizations have been used. Lastly, results of performance tests are presented.

The glass samples from glass-forming area of the ZnO-Al2O3-SiO2 phase diagram were prepared by standard melt-quenching method at 1400–1600 °C temperature range for 10–12 h. The subsequent annealing with a heating ramp of 5 °C/min to 850 °C yielded glass-ceramics nature of samples. X-ray diffraction measurements identified the presence of amorphous phase for as-prepared samples and two crystalline phases, including monoclinic Zn2SiO4, and rhombohedral Zn2SiO4 (willemite), after annealing. The scintillation and luminescence properties of prepared glass and annealed glass-ceramics were investigated by using the time-resolved luminescence spectroscopy. The restoration of the intense UV emission peaking at around 360 nm under the X-ray excitation (40 kV), overcoming the standard Bi4Ge3O12 scintillator intensity by more than 160%, was discovered after annealing while as-prepared glass samples exhibited negligible luminescence response to the X-ray exposure. The corresponding scintillation decay with leading component in sub-nanosecond scale was detected for annealed samples. The bandgap of willemite was estimated from the photoluminescence excitation spectra to be at 5.85 eV, photoluminescence emission shows the band in UV region with corresponding photoluminescence decay times spanning from units to tens of nanosecond. The impact of annealing conditions on the material´s structural and optical properties is discussed in detail.

This contribution focuses on the deployment and first results of the new data acquisition system (DAQ) of the COMPASS experiment at CERN laboratory. The COMPASS experiment is a fixed target experiment with maximum rate of 1.5 GB s. The DAQ utilizing FPGA-based event builder is designed to be able to readout data at maximum rate of the experiment. The DAQ is developed under name RCCARS (run control, configuration, and readout system). The RCCARS has been deployed for the pilot run starting from the September 2014 and further developed for long run in 2015. In the paper, we present performance and stability results of the new DAQ architecture; we compare it with the original system in more details.

Hydrothermally grown zinc molybdate oxide (ZMO) nanocrystals were prepared for their interesting scintillation properties at room temperature. Here we report on the comparison of two time resolved photoluminescence (PL) decay measurements of ZMO: one using time correlated single photon counting (TCSPC) based on short pulse excitation and the second based on the frequency resolved phase delay between sinusoidal excitation and emission. Both methods allow PL decay to be measured with a time resolution about 1 ns. While the time resolution of the TCSPC was limited by the excitation pulse width (slightly below 1 ns), the time resolution of the phase shift method was limited by the maximum operating frequency of the conventional UV LED (3 MHz). The phase method offers a low-cost alternative to TCSPC measurements of ZnO nanorods.

The InGaN multiple quantum wells (MQW) samples with the undoped and Si doped GaN barriers were grown by Metal Organic Vapour Phase Epitaxy (MOVPE). By comparing defects-related emission bands in the undoped GaN and InGaN layers, one may conclude that the band is complex in the InGaN layer, composed of at least two contributions peaking at 2.17 and 2.39 eV, respectively. In and Si affect the intensity of the defects-related band – the larger the In and/or Si concentration the stronger the band. The detailed investigation of the observed phenomena was conducted, and the observed peculiarities were explained.

We report on a measurement of Spin Density Matrix Elements (SDMEs) in hard exclusive ω meson muoproduction on the proton at COMPASS using 160 GeV/c polarised μ+ and μ- beams impinging on a liquid hydrogen target. The measurement covers the range 5.0 GeV/c2

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