On the accuracy of DFT exchange-correlation functionals for H bonds in small water clusters II: The water hexamer and van der Waals interactions

Second order Moeller-Plesset perturbation theory (MP2) at the complete basis set (CBS) limit and diffusion quantum Monte Carlo (DMC) are used to examine several low energy isomers of the water hexamer. Both approaches predict the so-called "prism" to be the lowest energy isomer, followed by "cage", "book", and "cyclic" isomers. The energies of the four isomers are very similar, all being within 10-15 meV/H2O. This reference data is then used to evaluate the performance of several density-functional theory (DFT) exchange-correlation (xc) functionals. A subset of the xc functionals tested for smaller water clusters [I: Santra et al., J. Chem. Phys. 127, 184104 (2007)] has been considered. Whilst certain functionals do a reasonable job at predicting the absolute dissociation energies of the various isomers (coming within 10-20 meV/H2O), none predict the correct energetic ordering of the four isomers, nor does any predict the correct low total energy isomer. All xc functionals tested either predict the book or cyclic isomers to have the largest dissociation energies. A many-body decomposition of the total interaction energies within the hexamers leads to the conclusion that the failure lies in the poor description of van der Waals (dispersion) forces in the xc functionals considered. It is shown that the addition of an empirical pairwise (attractive) C6/R6 correction to certain functionals allows for an improved energetic ordering of the hexamers. The relevance of these results to density-functional simulations of liquid water is also briefly discussed.Comment: 15 pages including 4 figures; related publications can be found at http://www.fhi-berlin.mpg.de/th/th.htm

Refining specifications in adaptive testing of nondeterministic finite state machines

This paper addresses testing of nondeterministic FSMs. An implementation FSM is allowed to be less nondeterministic than its specification, so the reduction relation between machines is the conformance relation. Execution of a given test needs to be adaptive to avoid application of unneeded input sequences, since the test can have different inputs depending on output produced by the implementation under test in response to previous input. To further reduce testing efforts during test execution, the paper suggests performing refinement of the specification FSM by removing traces absent in the implementation, which has already passed some subtest of a given complete (sound and exhaustive) test. The test execution process can be terminated as soon as the executed so far subtest is complete for the current refined version of the specification. The sufficient conditions formulated in the paper can be used for this purpose

Observation of excited Ωc0\Omega_c^0 baryons in Ωb−→Ξc+K−π−\Omega_b^- \to \Xi_c^+ K^-\pi^-decays

International audienceThe first observation of the Ωb-→Ξc+K-π- decay is reported using p p collision data at center of mass energies of 7, 8, and 13 TeV collected by the LHCb experiment, corresponding to an integrated luminosity of 9  fb-1. Four excited Ωc0 baryons are observed in the Ξc+ K- mass projection of the Ωb-→Ξc+K-π- decays with the significance of each exceeding five standard deviations. They coincide with the states previously observed in prompt pp and e+e- production. Relative production rates, masses, and natural widths of the states are measured, and a test of spin hypotheses is performed. Moreover, the branching ratio of Ωb-→Ξc+K-π- is measured relative to the Ωb-→Ωc0π- decay mode and a precise measurement of the Ωb- mass of 6044.3±1.2±1.1-0.22+0.19  MeV is obtained

Observation of excited Ωc0\Omega_c^0 baryons in Ωb−→Ξc+K−π−\Omega_b^- \to \Xi_c^+ K^-\pi^-decays

The first observation of the $Ω_b^- → Ξ_c^+ K^- π^-$ decay is reported using p p collision data at center of mass energies of 7, 8, and 13 TeV collected by the LHCb experiment, corresponding to an integrated luminosity of 9 fb$^{-1}$. Four excited $Ω_c^0$ baryons are observed in the $Ξ_c^+ K^-$ mass projection of the $Ω_b^-→ Ξ_c^+ K^- π^-$ decays with the significance of each exceeding five standard deviations. They coincide with the states previously observed in prompt pp and $e^+ e^-$ production. Relative production rates, masses, and natural widths of the states are measured, and a test of spin hypotheses is performed. Moreover, the branching ratio of $Ω_b^- → Ξ_c^+ K^- π^-$ is measured relative to the $Ω_b^- → Ω_c^0 π^-$ decay mode and a precise measurement of the $Ω_b^-$ mass of $6044.3±1.2±1.1_{-0.22}^{+0.19}$ MeV is obtained

Observation of the Mass Difference Between Neutral Charm-Meson Eigenstates

A measurement of mixing and CP violation in neutral charm mesons is performed using data reconstructed in proton-proton collisions collected by the LHCb experiment from 2016 to 2018, corresponding to an integrated luminosity of 5.4 fb$^{-1}$. A total of 30.6 million $D^0 → K_S^0 π^+ π^-$ decays are analyzed using a method optimized for the measurement of the mass difference between neutral charm-meson eigenstates. Allowing for CP violation in mixing and in the interference between mixing and decay, the mass and decay-width differences are measured to be $x_{CP}$=[3.97±0.46(stat)±0.29(syst)]×10$^{-3}$ and $y_{CP}$=[4.59±1.20(stat)±0.85(syst)]×10$^{-3}$, respectively. The CP-violating parameters are measured as $Δx$=[-0.27±0.18(stat)±0.01(syst)]×10$^{-3}$ and $Δy$=[0.20±0.36(stat)±0.13(syst)]×10$^{-3}$. This is the first observation of a nonzero mass difference in the $D^0$ meson system, with a significance exceeding seven standard deviations. The data are consistent with CP symmetry and improve existing constraints on the associated parameters

Observation of the Mass Difference Between Neutral Charm-Meson Eigenstates

International audienceA measurement of mixing and CP violation in neutral charm mesons is performed using data reconstructed in proton-proton collisions collected by the LHCb experiment from 2016 to 2018, corresponding to an integrated luminosity of 5.4  fb-1. A total of 30.6 million D0→KS0π+π- decays are analyzed using a method optimized for the measurement of the mass difference between neutral charm-meson eigenstates. Allowing for CP violation in mixing and in the interference between mixing and decay, the mass and decay-width differences are measured to be xCP=[3.97±0.46(stat)±0.29(syst)]×10-3 and yCP=[4.59±1.20(stat)±0.85(syst)]×10-3, respectively. The CP-violating parameters are measured as Δx=[-0.27±0.18(stat)±0.01(syst)]×10-3 and Δy=[0.20±0.36(stat)±0.13(syst)]×10-3. This is the first observation of a nonzero mass difference in the D0 meson system, with a significance exceeding seven standard deviations. The data are consistent with CP symmetry and improve existing constraints on the associated parameters