Neutral weak currents in pion electroproduction on the nucleon

Parity violating asymmetry in inclusive scattering of longitudinally polarized electrons by unpolarized protons with $\pi^0$ or $\pi^+$ meson production, is calculated as a function of the momentum transfer squared $Q^2$ and the total energy $W$ of the $\pi N$-system. This asymmetry, which is induced by the interference of the one-photon exchange amplitude with the parity-odd part of the $Z^0$-exchange amplitude, is calculated for the $\gamma^*(Z^*)+p\to N+\pi$ processes ($\gamma^*$ is a virtual photon and $Z^*$ a virtual Z-boson) considering the $\Delta$-contribution in the $s-$channel, the standard Born contributions and vector meson ($\rho$ and $\omega$) exchanges in the $t-$channel. Taking into account the known isotopic properties of the hadron electromagnetic and neutral currents, we show that the P-odd term is the sum of two contributions. The main term is model independent and it can be calculated exactly in terms of fundamental constants. It is found to be linear in $Q^2$. The second term is a relatively small correction which is determined by the isoscalar component of the electromagnetic current. Near threshold and in the $\Delta$-region, this isoscalar part is much smaller (in absolute value) than the isovector one: its contribution to the asymmetry depend on the polarization state (longitudinal or transverse) of the virtual photon.Comment: 30 pages 9 figure

The African intellectuals’ project

Soon after taking the position of editor of IJARS at the beginning of 2019, I was contacted by the dean of Unisa’s College of Graduate Studies (CGS), Prof. Lindiwe Zungu, who informed me that the university’s principal and vice-chancellor, Prof. Mandla Makhanya, had decided to revive his project, the African Intellectuals’ Project (AIP). I was asked to coordinate this project, through which Makhanya sought to invite scholars, academics, and intellectuals, both on and outside of the African continent, to deliver presentations reflecting on the ills afflicting Africa and, at the same time, to offer possible solutions. In pursuing the AIP, Prof. Makhanya was carrying on a perennial tradition

Studies of new Higgs boson interactions through nonresonant HH production in the b¯bγγ fnal state in pp collisions at √s = 13 TeV with the ATLAS detector

A search for nonresonant Higgs boson pair production in the b ¯bγγ fnal state is performed using 140 fb−1 of proton-proton collisions at a centre-of-mass energy of 13 TeV recorded by the ATLAS detector at the CERN Large Hadron Collider. This analysis supersedes and expands upon the previous nonresonant ATLAS results in this fnal state based on the same data sample. The analysis strategy is optimised to probe anomalous values not only of the Higgs (H) boson self-coupling modifer κλ but also of the quartic HHV V (V = W, Z) coupling modifer κ2V . No signifcant excess above the expected background from Standard Model processes is observed. An observed upper limit µHH < 4.0 is set at 95% confdence level on the Higgs boson pair production cross-section normalised to its Standard Model prediction. The 95% confdence intervals for the coupling modifers are −1.4 < κλ < 6.9 and −0.5 < κ2V < 2.7, assuming all other Higgs boson couplings except the one under study are fxed to the Standard Model predictions. The results are interpreted in the Standard Model efective feld theory and Higgs efective feld theory frameworks in terms of constraints on the couplings of anomalous Higgs boson (self-)interactions

Search for non-resonant Higgs boson pair production in the 2b+2l+ETmiss final state in pp collisions at s = 13 TeV with the ATLAS detector

A search for non-resonant Higgs boson pair (HH) production is presented, in which one of the Higgs bosons decays to a b-quark pair (bb ̄) and the other decays to WW*, ZZ*, or τ+τ−, with in each case a final state with l+l−+ neutrinos (l = e, μ). The analysis targets separately the gluon-gluon fusion and vector boson fusion production modes. Data recorded by the ATLAS detector in proton-proton collisions at a centre-of-mass energy of 13 TeV at the Large Hadron Collider, corresponding to an integrated luminosity of 140 fb−1, are used in this analysis. Events are selected to have exactly two b-tagged jets and two leptons with opposite electric charge and missing transverse momentum in the final state. These events are classified using multivariate analysis algorithms to separate the HH events from other Standard Model processes. No evidence of the signal is found. The observed (expected) upper limit on the cross-section for non-resonant Higgs boson pair production is determined to be 9.7 (16.2) times the Standard Model prediction at 95% confidence level. The Higgs boson self-interaction coupling parameter κλ and the quadrilinear coupling parameter κ2V are each separately constrained by this analysis to be within the ranges [−6.2, 13.3] and [−0.17, 2.4], respectively, at 95% confidence level, when all other parameters are fixed

Measurement of the H → γ γ and H → ZZ∗ → 4 cross-sections in pp collisions at √s = 13.6 TeV with the ATLAS detector

The inclusive Higgs boson production cross section is measured in the di-photon and the Z Z∗ → 4 decay channels using 31.4 and 29.0 fb−1 of pp collision data respectively, collected with the ATLAS detector at a centre of-mass energy of √s = 13.6 TeV. To reduce the model dependence, the measurement in each channel is restricted to a particle-level phase space that closely matches the chan nel’s detector-level kinematic selection, and it is corrected for detector effects. These measured fiducial cross-sections are σfid,γ γ = 76+14 −13 fb, and σfid,4 = 2.80 ± 0.74 fb, in agreement with the corresponding Standard Model predic tions of 67.6±3.7 fb and 3.67±0.19 fb. Assuming Standard Model acceptances and branching fractions for the two chan nels, the fiducial measurements are extrapolated to the full phase space yielding total cross-sections of σ (pp → H) = 67+12 −11 pb and 46±12 pb at 13.6 TeV from the di-photon and Z Z∗ → 4 measurements respectively. The two measure ments are combined into a total cross-section measurement of σ (pp → H) = 58.2±8.7 pb, to be compared with the Stan dard Model prediction of σ (pp → H)SM = 59.9 ± 2.6 p

Electron and photon energy calibration with the ATLAS detector using LHC Run 2 data

This paper presents the electron and photon energy calibration obtained with the ATLAS detector using 140 fb−1 of LHC proton-proton collision data recorded at root(s) = 13 TeV between 2015 and 2018. Methods for the measurement of electron and photon energies are outlined, along with the current knowledge of the passive material in front of the ATLAS electromagnetic calorimeter. The energy calibration steps are discussed in detail, with emphasis on the improvements introduced in this paper. The absolute energy scale is set using a large sample of Z-boson decays into electron-positron pairs, and its residual dependence on the electron energy is used for the first time to further constrain systematic uncertainties. The achieved calibration uncertainties are typically 0.05% for electrons from resonant Z-boson decays, 0.4% at ET tilde 10 GeV, and 0.3% at ET tilde 1 TeV; for photons at ET tilde 60 GeV, they are 0.2% on average. This is more than twice as precise as the previous calibration. The new energy calibration is validated using J/psi -> ee and radiative Z-boson decays