Enhancing Experiment Central Service Reliability: from delivery to security and virtualization

The four LHC experiments rely on experiment specific services running on machines mainly located at CERN. Some of these services have been rated by the experiments as very critical: any loss or degradation of performance has a major impact on the experiment's production and analysis activities. It is therefore important to provide a reliable and robust operational environment. In this work we describe the strategy based on service deployment, security and virtualization adopted to enhance the reliability of ATLAS and CMS central services

Discriminating the heavy jet production mechanisms in associated Z + heavy flavor events at the LHC

We reconsider the associated Z boson and charm or beauty jet production at the LHC by paying special attention to the formation dynamics of heavy jets. Two different approaches are studied: first one, where heavy quarks are produced in the hard scattering subprocesses, implemented in the Monte-Carlo generator pegasus, and another method, where the hard scattering is calculated at NLO with MadGraph5_aMC@NLO and TMD parton shower is included (implemented in the Monte-Carlo generator Cascade3). We compare the predictions obtained in both schemes with latest experimental data for associated $Z + b$ production cross sections and the relative production rate $\sigma (Z + c)/\sigma (Z + b)$ collected by the ATLAS and CMS Collaborations at $\sqrt{s} = 13$ TeV. We introduce two kinematic observables (denoted as $z_b$ and $p_T^\mathrm{rel}$) which can be used to discriminate between the heavy jet production mechanisms. Using these variables we trace the shape of the simulated b-jet events and recommend that these observables be taken into consideration in the forthcoming experimental analyses

Discriminating the heavy jet production mechanisms in associated Z + heavy flavor events at the LHC

We reconsider the associated Z boson and charm or beauty jet production at the LHC by paying special attention to the formation dynamics of heavy jets. Two different approaches are studied: first one, where heavy quarks are produced in the hard scattering subprocesses, implemented in the Monte-Carlo generator pegasus, and another method, where the hard scattering is calculated at NLO with MadGraph5_aMC@NLO and TMD parton shower is included (implemented in the Monte-Carlo generator Cascade3). We compare the predictions obtained in both schemes with latest experimental data for associated $Z + b$ production cross sections and the relative production rate $\sigma (Z + c)/\sigma (Z + b)$ collected by the ATLAS and CMS Collaborations at $\sqrt{s} = 13$ TeV. We introduce two kinematic observables (denoted as $z_b$ and $p_T^\mathrm{rel}$) which can be used to discriminate between the heavy jet production mechanisms. Using these variables we trace the shape of the simulated b-jet events and recommend that these observables be taken into consideration in the forthcoming experimental analyses

High-pressure synthesis of cubic ZnO and its solid solutions with MgO doped with Li, Na, and K

The possibility of doping ZnO in its metastable rock salt structure with Li, Na, and K intended to act as acceptor dopants was investigated. For the first time, MgxZn1−xO alloys and pure ZnO with a rock salt structure doped with Li, Na, and K metals was obtained by high-pressure synthesis from pure oxides with the addition of carbonates or acetates of the corresponding metals as dopant sources. Successful stabilization of the metastable rock salt structure and phase purity were confirmed by X-ray diffraction. Transmission electron microscopy was used to study the particle size of nanocrystalline precursors, while the presence of Li, Na, and K metals in rock salt ZnO was detected by electron energy-loss spectroscopy and X-ray photoelectron spectroscopy in MgxZn1−xO alloys. Electron paramagnetic resonance measurements revealed the acceptor behavior of Li, Na, and K dopants based on the influence of the latter on native defects and natural impurities in ZnO-MgO alloys. In addition, diffuse reflectance spectroscopy was used to derive band gaps of quenched rock salt ZnO and its alloys with MgO

Doping nature of group V elements in ZnO single crystals grown from melts at high pressure

International audienceZnO single crystals doped with group-V elements have been grown from melt at high pressure. Dopants were introduced in several forms such as Sb2O3, P, As, Sb and Zn3X2 (X = P, As, Sb) in the high-pressure cell. Systematic studies of morphology were performed using optical microscopy and scanning electron microscopy. Crystal structure and lattice parameters were studied using X-ray diffraction and X-ray crystallography. Crystals exhibited distinct changes of size, shape and color compared to undoped ZnO melt-grown single crystals due to the dopants influence. X-ray photoelectron spectroscopy was used to determine valence states of group-V elements when incorporated in ZnO lattice. Photoluminescence, Raman spectroscopy and electron paramagnetic resonance spectroscopy were employed to investigate the nature of defects formed as the result of doping. Formation of VZn and VZn-complexes was confirmed and their concentrations were measured. Estimates of the number of VZn per one dopant atom showed that the ratio is noticeably higher than the one suggested for the shallow complex As(P, Sb)Zn-2VZn commonly regarded as responsible for acceptor properties in ZnO

Doping nature of group V elements in ZnO single crystals grown from melts at high pressure

ZnO single crystals doped with group-V elements have been grown from melt at high pressure. Dopants were introduced in several forms such as Sb2O3, P, As, Sb and Zn3X2 (X = P, As, Sb) in the high-pressure cell. Systematic studies of morphology were performed using optical microscopy and scanning electron microscopy. Crystal structure and lattice parameters were studied using X-ray diffraction and X-ray crystallography. Crystals exhibited distinct changes of size, shape and color compared to undoped ZnO melt-grown single crystals due to the dopants influence. X-ray photoelectron spectroscopy was used to determine valence states of group-V elements when incorporated in ZnO lattice. Photoluminescence, Raman spectroscopy and electron paramagnetic resonance spectroscopy were employed to investigate the nature of defects formed as the result of doping. Formation of VZn and VZn-complexes was confirmed and their concentrations were measured. Estimates of the number of VZn per one dopant atom showed that the ratio is noticeably higher than the one suggested for the shallow complex As(P, Sb)Zn-2VZn commonly regarded as responsible for acceptor properties in ZnO