Helium identification with LHCb

The identification of helium nuclei at LHCb is achieved using a method based on measurements of ionisation losses in the silicon sensors and timing measurements in the Outer Tracker drift tubes. The background from photon conversions is reduced using the RICH detectors and an isolation requirement. The method is developed using pp collision data at √(s) = 13 TeV recorded by the LHCb experiment in the years 2016 to 2018, corresponding to an integrated luminosity of 5.5 fb-1. A total of around 105 helium and antihelium candidates are identified with negligible background contamination. The helium identification efficiency is estimated to be approximately 50% with a corresponding background rejection rate of up to O(10^12). These results demonstrate the feasibility of a rich programme of measurements of QCD and astrophysics interest involving light nuclei

Curvature-bias corrections using a pseudomass method

Momentum measurements for very high momentum charged particles, such as muons from electroweak vector boson decays, are particularly susceptible to charge-dependent curvature biases that arise from misalignments of tracking detectors. Low momentum charged particles used in alignment procedures have limited sensitivity to coherent displacements of such detectors, and therefore are unable to fully constrain these misalignments to the precision necessary for studies of electroweak physics. Additional approaches are therefore required to understand and correct for these effects. In this paper the curvature biases present at the LHCb detector are studied using the pseudomass method in proton-proton collision data recorded at centre of mass energy √(s)=13 TeV during 2016, 2017 and 2018. The biases are determined using Z→μ + μ - decays in intervals defined by the data-taking period, magnet polarity and muon direction. Correcting for these biases, which are typically at the 10-4 GeV-1 level, improves the Z→μ + μ - mass resolution by roughly 18% and eliminates several pathological trends in the kinematic-dependence of the mean dimuon invariant mass

Momentum scale calibration of the LHCb spectrometer

For accurate determination of particle masses accurate knowledge of the momentum scale of the detectors is crucial. The procedure used to calibrate the momentum scale of the LHCb spectrometer is described and illustrated using the performance obtained with an integrated luminosity of 1.6 fb-1 collected during 2016 in pp running. The procedure uses large samples of J/ψ → μ + μ - and B+ → J/ψ K + decays and leads to a relative accuracy of 3 × 10-4 on the momentum scale

Electric field activated hydrogen dissociative adsorption to nitrogen-doped graphene

博士(工学)法政大学 (Hosei University

Early Pleistocene integration of the Yellow River II: Evidence from the Plio-Pleistocene sedimentary record of the Fenwei Basin

The Yellow River is the 2nd longest river in China and the 6th longest river in the world. However, the timing and mechanism of its integration remains debated. During the establishment of its present geometry, the Yellow River captured and deeply incised into a series of local drainage basins along its Upper and Middle Reaches. The termination of basin filling, therefore, can be linked to the development of the Yellow River. The Sanmen paleolake, a Plio-Pleistocene endorheic mega-lake situated in the Fenwei Basin, was the last catchment basin captured by the Yellow River before it emptied into the sea. The final termination of the lacustrine deposition in the Fenwei Basin can therefore indicate the integration of the Yellow River. Here, we present the results of a detailed magnetostratigraphic and magnetic susceptibility study of a lacustrine-loess section from the southeastern part of the Fenwei Basin (Sanmenxia Subbasin), and aim to (1) explore the sedimentary evolution of the Sanmen paleolake and refine the age of the Sanmen Formation in this area, and (2) investigate the precise timing of the integration of the Yellow River. Our results show that the Sanmenxia Subbasin was occupied by a salty lake between 2.7 and 2.2 Ma, then it gradually changed to an alternation of shallow lake and floodplain environments between 2.2 and 1.6 Ma, and it finally irreversible dried up at ∼1.6 Ma and was subsequently covered by loess-paleosol sequences. The drying up of the Sanmen paleolake at ∼1.6 Ma indicated the establishment of the connection between the Middle and Lower Reaches of the Yellow River