126075755
The study of gamma/phi_3-sensitive hadronic decays at LHCb
39676478
High rate packets transmission on ethernet LAN using commodity hardware
We report on measurements performed to test the reliability of high rate data transmission over copper Gigabit Ethernet for the LHCb online system. High reliability of such transmissions will be crucial for the functioning of the software trigger layers of the LHCb experiment, at the CERN's LHC accelerator. The technological challenge in the system implementation consists of handling the expected high data throughput of event fragments using, to a large extent, commodity equipment. We report on performance evaluations (throughput, error rates and frame drop) of the main components involved in data transmission: the Ethernet cable, the PCI bus and the operating system (the latest kernel versions of Linux). Three different platforms have been used.
62765062
LHCb experience with LFC replication
Database replication is a key topic in the framework of the LHC Computing Grid to allow processing of data in a distributed environment. In particular, the LHCb computing model relies on the LHC File Catalog, i.e. a database which stores information about files spread across the GRID, their logical names and the physical locations of all the replicas. The LHCb computing model requires the LFC to be replicated at Tier-1s. The LCG 3D project deals with the database replication issue and provides a replication service based on Oracle Streams technology. This paper describes the deployment of the LHC File Catalog replication to the INFN National Center for Telematics and Informatics (CNAF) and to other LHCb Tier-1 sites. We performed stress tests designed to evaluate any delay in the propagation of the streams and the scalability of the system. The tests show the robustness of the replica implementation with performance going much beyond the LHCb requirements.
117771341
A search for time-integrated CP violation in $D^{0} \rightarrow h^{-}h^{+}$ decays
The LHCb Collaboration has recently observed evidence of CP violation in neutral D meson decays. CP violation in the charm sector is generically expected to be very small in the Standard Model, but can be enhanced in many models of new physics. In this document we will present the results of a search for time-integrated \CP violation in $D^0 \rightarrow h^- h^+$ with $(h=K,\pi)$ decays, performed with around 0.6 fb$^{-1}$ of data collected by LHCb in 2011. The difference in CP asymmetry between $D^0 \rightarrow K^- K^+$ and $D^0 \rightarrow \pi^- \pi^+$, $\Delta A_{CP} = A_{CP}(K^- K^+) - A_{CP}(\pi^- \pi^+)$ is measured to be $\Delta A_{CP} = [-0.82 \pm 0.21 (stat.) \pm 0.11 (syst.)]%$ . This differs from the hypothesis of CP conservation by 3.5 sigma.
118666057
Tensor force effects and high-momentum components in the nuclear symmetry energy
We analyze microscopic many-body calculations of the nuclear symmetry energy and its density dependence. The calculations are performed in the framework of the Brueckner-Hartree-Fock and the self-consistent Green’s functions methods. Within Brueckner-Hartree-Fock, the Hellmann-Feynman theorem gives access to the kinetic energy contribution as well as the contributions of the different components of the nucleon-nucleon interaction. The tensor component gives the largest contribution to the symmetry energy. The decomposition of the symmetry energy in a kinetic part and a potential energy part provides physical insight on the correlated nature of the system, indicating that neutron matter is less correlated than symmetric nuclear matter. Within the self-consistent Green’s function approach, we compute the momentum distributions and we identify the effects of the high momentum components in the symmetry energy. The results are obtained for the realistic interaction Argonne V18 potential, supplemented by the Urbana IX three-body force in the Brueckner-Hartree-Fock calculations.
116891509
Status and Future Perspectives on the Measurement of the Unitarity Triangle Angle α
A summary on the status of the measurements of the Unitarity Triangle angle α using the decays B → ππ, B → ρπ and B → ρρ and on the future perspectives at the Large Hadron Collider experiment LHCb is presented. The UTfit collaboration, combining the BABAR measurements from B → ρπ and B → ρρ, give as Standard Model solution the value α = (106 ± 8)°. The LHCb Collaboration has estimated the sensitivity on α from the B0 → ρπ decay obtaining a relative error σαα ⩽ 0.1, in one nominal year of data taking.
118709020
Symmetric nuclear matter with chiral three-nucleon forces in the self-consistent Green's functions approach
We present calculations for symmetric nuclear matter using chiral nuclear interactions within the self-consistent Green's functions approach in the ladder approximation. Three-body forces are included via effective one-body and two-body interactions, computed from an uncorrelated average over a third particle. We discuss the effect of the three-body forces on the total energy, computed with an extended Galitskii-Migdal-Koltun sum-rule, as well as on single-particle properties. Saturation properties are substantially improved when three-body forces are included, but there is still some underlying dependence on the similarity renormalization group evolution scale.
14762623
Correlated density-dependent chiral forces for infinite-matter calculations within the Green's function approach
The properties of symmetric nuclear and pure neutron matter are investigated within an extended self-consistent Green's function method that includes the effects of three-body forces. We use the ladder approximation for the study of infinite nuclear matter and incorporate the three-body interaction by means of a density-dependent two-body force. This force is obtained via a correlated average over the third particle, with an in-medium propagator consistent with the many-body calculation we perform. We analyze different prescriptions in the construction of the average and conclude that correlations provide small modifications at the level of the density-dependent force. Microscopic as well as bulk properties are studied, focusing on the changes introduced by the density dependent two-body force. The total energy of the system is obtained by means of a modified Galitskii-Migdal-Koltun sum rule. Our results validate previously used uncorrelated averages and extend the availability of chirally motivated forces to a larger density regime.
120314857
Latent heat of nuclear matter
We study the latent heat of the liquid-gas phase transition in symmetric nuclear matter using self-consistent mean-field calculations with a few Skyrme forces. The temperature dependence of the latent heat is rather independent of the mean-field parametrization and it can be characterized by a few parameters. At low temperatures, the latent heat tends to the saturation energy. Near the critical point, the latent heat goes to zero with a well-determined mean-field critical exponent. A maximum value of the latent heat in the range l similar to 25-30 MeV is found at intermediate temperatures, which might have experimental relevance. All these features can be explained from very basic principles.
17099587
Self-consistent Green's functions formalism with three-body interactions
We extend the self-consistent Green's functions formalism to take into account three-body interactions. We analyze the perturbative expansion in terms of Feynman diagrams and define effective one- and two-body interactions, which allows for a substantial reduction of the number of diagrams. The procedure can be taken as a generalization of the normal ordering of the Hamiltonian to fully correlated density matrices. We give examples up to third order in perturbation theory. To define nonperturbative approximations, we extend the equation of motion method in the presence of three-body interactions. We propose schemes that can provide nonperturbative resummation of three-body interactions. We also discuss two different extensions of the Koltun sum rule to compute the ground state of a many-body system.
118749543
Shear viscosity of $\beta$-stable nuclear matter
Viscosity plays a critical role in determining the stability of rotating neutron stars. We report the results of a calculation of the shear viscosity of $\beta$~-~stable matter, carried out using an effective interaction based on a state-of-the-art nucleon-nucleon potential and the formalism of correlated basis functions. Within our approach the equation of state, determining the proton fraction, and the nucleon-nucleon scattering probability are consistently obtained from the same dynamical model. The results show that, while the neutron contribution to the viscosity is always dominant, above nuclear saturation density the electron contribution becomes appreciable.