Parity-violating Asymmetry Parameter Research Articles

Measurement of the {Lambda}_b^0 \u2192 J/\u03c8\u039b angular distribution and the {Lambda}_b^0 polarisation in pp collisions

This paper presents an analysis of the {Lambda}_b^0 → J/ψΛ angular distribution and the transverse production polarisation of {Lambda}_b^0 baryons in proton-proton collisions at centre-of-mass energies of 7, 8 and 13 TeV. The measurements are performed using data corresponding to an integrated luminosity of 4.9 fb−1, collected with the LHCb experiment. The polarisation is determined in a fiducial region of {Lambda}_b^0 transverse momentum and pseudorapidity of 1 < pT< 20 GeV/c and 2 < η < 5, respectively. The data are consistent with {Lambda}_b^0 baryons being produced unpolarised in this region. The parity-violating asymmetry parameter of the Λ → pπ− decay is also determined from the data and its value is found to be consistent with a recent measurement by the BES III collaboration.

Measurement of the Λb polarization and angular parameters in Λb→J/ψΛ decays from pp collisions at s=7 and 8 TeV

An analysis of the decay $\Lambda_b \to J/\psi(\to\mu^+\mu^-)\Lambda(\to p \pi^-)$ decay is performed to measure the $\Lambda_b$ polarization and three angular parameters in data from pp collisions at $\sqrt{s} =$ 7 and 8 TeV, collected by the CMS experiment at the LHC. The $\Lambda_b$ polarization is measured to be 0.00 $\pm$ 0.06 (stat) $\pm$ 0.06 (syst) and the parity-violating asymmetry parameter is determined to be 0.14 $\pm$ 0.14 (stat) $\pm$ 0.10 (syst). The measurements are compared to various theoretical predictions, including those from perturbative quantum chromodynamics.

B-hadrons spectroscopy and decay properties with the ATLAS experiment

The parity violating asymmetry parameter αb in Λb→ΛJ/ψ decay was measured using the ATLAS detector in proton–proton collisions at the Large Hadron Collider at s=7 TeV, using data collected in the 2011 run. Furthermore, a search for excited states of the Bc± meson was performed using 4.9 fb−1 of 7 TeV and 19.2 fb−1 of 8 TeV proton–proton collision data. A new state was observed through its hadronic transition to the ground state, with an invariant mass of 6842 ± 7 ± 4 MeV, consistent with predictions for the Bc±(2S) meson.

Neutron density distribution and neutron skin thickness ofPb208

We present and discuss numerical predictions for the neutron density distribution of $^{208}\mathrm{Pb}$ using various nonrelativistic and relativistic mean-field models for the nuclear structure. Our results are compared with the very recent pion photoproduction data from Mainz. The parity-violating asymmetry parameter for elastic electron scattering at the kinematics of the PREX experiment at JLab and the neutron skin thickness are compared with the available data. We consider also the dependence between the neutron skin and the parameters of the expansion of the symmetry energy.

Elastic and quasi-elastic electron scattering off isotopic and isotonic chains

We present theoretical predictions for electron scattering on Z = 20 isotopic and N = 20 isotonic chain. The calculations are done within the framework of the distorted-wave Born approximation for elastic scattering and the plane-wave Born approximation for the QE one. The proton and neutron density distributions are evaluated adopting a relativistic Dirac- Hartree model. We present results for the elastic and quasi-elastic cross sections and for the parity-violating asymmetry and investigate the evolution of nuclear properties as a function of the neutron and proton number. We also present a comparison with the parity-violating asymmetry parameter obtained by the PREX Collaboration on 208Pb.

Elastic and quasi-elastic electron scattering on theN=14, 20, and 28 isotonic chains

We present theoretical predictions for electron scattering on the N = 14, 20, and 28 isotonic chains from proton-deficient to proton-rich nuclei. The calculations are performed within the framework of the distorted-wave Born approximation and the proton and neutron density distributions are evaluated adopting a Relativistic Hartree-Bogoliubov (RHB) approach with a density dependent meson-exchange interaction. We present results for the elastic and quasi-elastic cross sections and for the parity-violating asymmetry parameter. Owing to the correlations between the evolution of the electric charge form factors along each chain with the underlying proton shell structure of the isotones, elastic electron scattering experiments on isotones can provide useful informations about the occupation and filling of the single-particle levels of protons.

Elastic and quasi-elastic electron scattering off nuclei with neutron excess

We present theoretical predictions for electron scattering on oxygen and calcium isotopic chains. The calculations are done within the framework of the distorted-wave Born approximation and the proton and neutron density distributions are evaluated adopting a relativistic Dirac-Hartree model. We present results for the elastic and quasi-elastic cross sections and for the parity-violating asymmetry. As a first step, the results of the models are tested in comparison with some of the data available for elastic and quasi-elastic scattering on 16O and 40Ca nuclei. Then, the evolution of some nuclear properties is investigated as a function of the neutron number. We also present a comparison with the parity-violating asymmetry parameter obtained by the PREX Collaboration on 208Pb and give a prediction for the future experiment CREX on 48Ca.

Measurements of the [formula omitted] decay amplitudes and the [formula omitted] polarisation in pp collisions at [formula omitted

An angular analysis of Λb0→J/ψΛ decays is performed using a data sample corresponding to 1.0 fb−1 collected in pp collisions at s=7 TeV with the LHCb detector at the LHC. A parity violating asymmetry parameter characterising the Λb0→J/ψΛ decay of 0.05±0.17±0.07 and a Λb0 transverse production polarisation of 0.06±0.07±0.02 are measured, where the first uncertainty is statistical and the second systematic.

Parity Violating Electron Scattering in the Relativistic Eikonal Approximation

The parity violating electron scattering is investigated in the relativistic Eikonal approximation. The parity violating asymmetry parameters for many isotopes are calculated. In calculations the proton and neutron densities are obtained from the relativistic mean-field theory. We take Ni isotopes as examples to analyse the behaviour of the parity violating asymmetry parameters. The results show that the parity violating asymmetry parameter is sensitive to the difference between the proton and neutron densities. The amplitude of the parity violating asymmetry parameter increases with the distance between the minima of proton and neutron form factors. Our results are useful for future parity violating electron scattering experiments. By comparing our results with experimental data one can test the validity of the relativistic mean-field theory in calculating the neutron densities of nuclei.

Hadronic decay structure and ν τ helicity in τ − → π − π −π +ν τ with the OPAL Detector at LEP

The hadronic structure of τ − → π − π − π + ν τ events observed with the OPAL detector at LEP during 1992–1994 has been measured. A model dependent as well as a model independent approach have been used. Deficiencies of the two theoretical models considered become visible with the available data sample. A non-resonant contribution seems to be required in the model description. Interference terms of axial-vector and non-axial-vector contributions have been measured for the first time in a model independent approach. No evidence for non-axial-vector contributions has been found. Finally, the parity violating asymmetry parameter γ VA has been measured model independently to be 1.29 ± 0.26 ± 0.11 and, for comparison, it has also been measured in a model dependent way.

Measurement of the hadronic decay current in τ−→π− − + v τ

The decay τ−→π−−+vτ has been studied using data collected with the OPAL detector at LEP during 1992 and 1993. The hadronic structure functions for this decay are measured model independently assuming G-parity invariance and neglecting scalar currents. Simultaneously the parity violating asymmetry parameter is determined to be\(\gamma VA = 1.08 _{ - 0.41 - 0.25}^{ + 0.46 + 0.14} \), consistent with the Standard Model prediction of γVA=1 for left-handed tau neutrinos. Models of Kuhn and Santamaria and of Isgur et al. are used to fit distributions of the invariant 3π mass as well as 2π mass projections of the Dalitz plot. The model dependent mass and width of thea1 resonance are measured to be\(m_{a_1 } = 1.266 \pm 0.014_{ - 0.002}^{ + 0.012} \) GeV and\(\Gamma _{a_1 } = 0.610 \pm 0.049_{ - 0.019}^{ + 0.053} \) GeV for the Kuhn and Santamaria model and\(m_{a_1 } = 1.202 \pm 0.009_{ - 0.001}^{ + 0.009} \) GeV and\(\Gamma _{a_1 } = 0.422 \pm 0.023_{ - 0.004}^{ + 0.033} \) GeV for the Isgur et al. model. The model dependent values obtained for the parity violating asymmetry parameter are γVA=0.87±0.27−0.06+0.05 for the Kuhn and Santamaria model and γVA=1.10±0.31−0.14+0.13 for the Isgur et al. model. Within the Isgur et al. model the ratio of theS-andD-wave amplitudes is measured to beD/S=−0.09±0.03±0.01.

Analysis of some observable effects of weak neutral currents coupled to charged leptons

We have analyzed the parity-violating effects in the processes $e+\overline{e}\ensuremath{\rightarrow}{k}_{1}+{k}_{2}+X$, ${k}_{1}+{k}_{2}\ensuremath{\rightarrow}e+\overline{e}+X$, and $e+{k}_{1}\ensuremath{\rightarrow}e+{k}_{2}+X$, where $e$, $\overline{e}$ are the electron, positron states, ${k}_{1}$ ${k}_{2}$ are the hadron states, and $X$ is the inclusive hadron state, due to the possible coupling of weak neutral currents to charged leptons. We estimate that for gauge theories of the weak interaction, the parity-violating asymmetry parameter for the distribution in $e+\overline{e}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}+{\ensuremath{\pi}}^{\ensuremath{-}}+{\ensuremath{\pi}}^{0}$ may be of the order of 5% in the resonance region of the ${A}_{1}$ meson and experimentally observable.