Vertex locator (VELO) is a silicon microstrip detector situated around the interaction point in the large Hadron Collider beauty (LHCb) spectrometer at the Large Hadron Collider. The LHCb experiment ...is dedicated to studying charge conjugation and parity symmetry violation in the heavy flavor sector and rare decays of B mesons. The precise reconstruction of both the primary and secondary vertices, obtained by the VELO, is crucial in the selection of signal events containing b and c quarks and lifetime measurements. VELO consists of two retractable parts that operate at 8 mm from the interaction region. Its proximity to proton beams makes the LHCb VELO a place for studying radiation damage effects in silicon detectors in proton-proton and heavy-ion collisions. The latest results from radiation damage studies and their impact on the operation of the LHCb VELO after the first data-taking period (Run I) and the ongoing Run II are presented in this paper. The main macroscopic parameters, influenced by particle fluence, are described along with selected methods of their monitoring. All the results show that VELO sustains the impact of high fluence of radiation, and its performance will not change significantly until the end of Run II.
Abstract
The standard model of particle physics currently provides our best description of fundamental particles and their interactions. The theory predicts that the different charged leptons, the ...electron, muon and tau, have identical electroweak interaction strengths. Previous measurements have shown that a wide range of particle decays are consistent with this principle of lepton universality. This article presents evidence for the breaking of lepton universality in beauty-quark decays, with a significance of 3.1 standard deviations, based on proton–proton collision data collected with the LHCb detector at CERN’s Large Hadron Collider. The measurements are of processes in which a beauty meson transforms into a strange meson with the emission of either an electron and a positron, or a muon and an antimuon. If confirmed by future measurements, this violation of lepton universality would imply physics beyond the standard model, such as a new fundamental interaction between quarks and leptons.
We present a new measurement of the positive muon magnetic anomaly, a_{μ}≡(g_{μ}-2)/2, from the Fermilab Muon g-2 Experiment using data collected in 2019 and 2020. We have analyzed more than 4 times ...the number of positrons from muon decay than in our previous result from 2018 data. The systematic error is reduced by more than a factor of 2 due to better running conditions, a more stable beam, and improved knowledge of the magnetic field weighted by the muon distribution, ωover ˜_{p}^{'}, and of the anomalous precession frequency corrected for beam dynamics effects, ω_{a}. From the ratio ω_{a}/ωover ˜_{p}^{'}, together with precisely determined external parameters, we determine a_{μ}=116 592 057(25)×10^{-11} (0.21 ppm). Combining this result with our previous result from the 2018 data, we obtain a_{μ}(FNAL)=116 592 055(24)×10^{-11} (0.20 ppm). The new experimental world average is a_{μ}(exp)=116 592 059(22)×10^{-11} (0.19 ppm), which represents a factor of 2 improvement in precision.
PDF
