3,958 research outputs found

    Preface

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    Theoretical status of Bs-mixing and lifetimes of heavy hadrons

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    We review the theoretical status of the lifetime ratios τB+/τBd, τBs/τBd, τΛb/τBd and τBc and of the mixing quantities ΔMs, ΔΓs and ϕs. ΔMs and ΔΓs suffer from large uncertainties due to the badly known decay constants, while the ratio ΔΓs/ΔMs can be determined with almost no non-perturbative uncertainties, therefore it can be used perfectly to find possible new physics contributions in the mixing parameters. We suggest a very clear method of visualizing the bounds on new physics and demonstrate this by combining the latest experimental numbers on the mixing quantities quantities with theory – one already gets some hints for new physics contributions, but more precise experimental numbers are needed to draw some definite conclusions. We conclude with a ranking list of all the discussed quantities according to their current theoretical uncertainties and point out possible improvements

    Intermolecular rovibrational bound states of H2O–H2 dimer from a multiconfiguration time dependent Hartree approach

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    We compute the rovibrational eigenstates of the H2O–H2 Van der Waals complex using the accurate rigid-rotor potential energy surface of Valiron et al. (2008) with the MultiConfiguration Time Dependent Hartree (MCTDH) method. The J=0–2 rovibrational bound states calculations are done with the Block Improved Relaxation procedure of MCTDH and the subsequent assignment of the states is achieved by inspection of the wavefunctions’ properties. The results of this work are found to be in close agreement with previous time independent calculations reported for this complex and therefore supports the use of the MCTDH approach for the rovibrational spectroscopic study of such weakly bound complexes

    A new ab initio potential energy surface for the collisional excitation of N2H(+) by H2

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    10 pags.; 14 figs.© 2015 AIP Publishing LLC. We compute a new potential energy surface (PES) for the study of the inelastic collisions between N2H+ and H2 molecules. A preliminary study of the reactivity of N2H+ with H2 shows that neglecting reactive channels in collisional excitation studies is certainly valid at low temperatures. The four dimensional (4D) N2H+–H2 PES is obtained from electronic structure calculations using the coupled cluster with single, double, and perturbative triple excitation level of theory. The atoms are described by the augmented correlation consistent triple zeta basis set. Both molecules were treated as rigid rotors. The potential energy surface exhibits a well depth of ≃2530 cm−1. Considering this very deep well, it appears that converged scattering calculations that take into account the rotational structure of both N2H+ and H2 should be very difficult to carry out. To overcome this difficulty, the “adiabatic-hindered-rotor” treatment, which allows para-H2(j = 0) to be treated as if it were spherical, was used in order to reduce the scattering calculations to a 2D problem. The validity of this approach is checked and we find that cross sections and rate coefficients computed from the adiabatic reduced surface are in very good agreement with the full 4D calculationsThis research was supported by the CNRS national program “Physique et Chimie du Milieu Interstellaire.” F.L. and Y.K. also thank the Agence Nationale de la Recherche (ANR-HYDRIDES), contract No. ANR-12-BS05-0011-01. We acknowledge Laurent Pagani for stimulating this work.Peer Reviewe

    A novel background reduction strategy for high level triggers and processing in gamma-ray Cherenkov detectors

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    Gamma ray astronomy is now at the leading edge for studies related both to fundamental physics and astrophysics. The sensitivity of gamma detectors is limited by the huge amount of background, constituted by hadronic cosmic rays (typically two to three orders of magnitude more than the signal) and by the accidental background in the detectors. By using the information on the temporal evolution of the Cherenkov light, the background can be reduced. We will present here the results obtained within the MAGIC experiment using a new technique for the reduction of the background. Particle showers produced by gamma rays show a different temporal distribution with respect to showers produced by hadrons; the background due to accidental counts shows no dependence on time. Such novel strategy can increase the sensitivity of present instruments.Comment: 4 pages, 3 figures, Proc. of the 9th Int. Syposium "Frontiers of Fundamental and Computational Physics" (FFP9), (AIP, Melville, New York, 2008, in press

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    H2, HD, and D2 in the small cage of structure II clathrate hydrate: vibrational frequency shifts from fully coupled quantum six-dimensional calculations of the vibration-translation-rotation eigenstates

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    We report the first fully coupled quantum six-dimensional (6D) bound-state calculations of the vibration-translation-rotation eigenstates of a flexible H2, HD, and D2 molecule confined inside the small cage of the structure II clathrate hydrate embedded in larger hydrate domains with up to 76 H2O molecules, treated as rigid. Our calculations use a pairwise-additive 6D intermolecular potential energy surface for H2 in the hydrate domain, based on an ab initio 6D H2–H2O pair potential for flexible H2 and rigid H2O. They extend to the first excited (v = 1) vibrational state of H2, along with two isotopologues, providing a direct computation of vibrational frequency shifts. We show that obtaining a converged v = 1 vibrational state of the caged molecule does not require converging the very large number of intermolecular translation-rotation states belonging to the v = 0 manifold up to the energy of the intramolecular stretch fundamental (≈4100 cm−1 for H2). Only a relatively modest-size basis for the intermolecular degrees of freedom is needed to accurately describe the vibrational averaging over the delocalized wave function of the quantum ground state of the system. For the caged H2, our computed fundamental translational excitations, rotational j = 0 → 1 transitions, and frequency shifts of the stretch fundamental are in excellent agreement with recent quantum 5D (rigid H2) results [A. Powers et al., J. Chem. Phys. 148, 144304 (2018)]. Our computed frequency shift of −43 cm−1 for H2 is only 14% away from the experimental value at 20 K

    Design and construction of new central and forward muon counters for CDF II

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    New scintillation counters have been designed and constructed for the CDF upgrade in order to complete the muon coverage of the central CDF detector, and to extend this coverage to larger pseudorapidity. A novel light collection technique using wavelength shifting fibers, together with high quality polystyrene-based scintillator resulted in compact counters with good and stable light collection efficiency over lengths extending up to 320 cm. Their design and construction is described and results of their initial performance are reported.Comment: 20 pages, 15 figure
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