Search results for "Nuclear and High Energy Physic"
showing 10 items of 8253 documents
Weak decay ofΛc+for the study ofΛ(1405)andΛ(1670)
2015
We study the ${\mathrm{\ensuremath{\Lambda}}}_{c}$ decay process to ${\ensuremath{\pi}}^{+}$ and the meson-baryon final state for the analysis of $\mathrm{\ensuremath{\Lambda}}$ resonances. Considering the Cabibbo-Kobayashi-Maskawa matrix, color suppression, diquark correlation, and the kinematical condition, we show that the final meson-baryon state should be in a pure $I=0$ combination, when the meson-baryon invariant mass is small. Because the $I=1$ contamination usually makes it difficult to analyze $\mathrm{\ensuremath{\Lambda}}$ resonances directly from experiments, the ${\mathrm{\ensuremath{\Lambda}}}_{c}$ decay is an ideal process to study $\mathrm{\ensuremath{\Lambda}}$ resonances.…
Study ofJ/ψ→pp¯andJ/ψ→nn¯
2012
The decays J/psi -> p (p) over bar and J/psi -> n (n) over bar have been investigated with a sample of 225.2 x 10(6) J/psi events collected with the BESIII detector at the BEPCII e(+)e(-) collider. The branching fractions are determined to be B(J/psi -> p (p) over bar) = (2.112 +/- 0.004 +/- 0.031 x 10(-3) and B(J/psi -> n (n) over bar) =(2.07 +/- 0.01 +/- 0.17) x 10(-3). Distributions of the angle theta between the proton or antineutron and the beam direction are well described by the form 1 + alpha cos(2)theta, and we find alpha = 0.595 +/- 0.012 +/- 0.015 for J/psi -> p (p) over bar and alpha = 0.50 +/- 0.04 +/- 0.21 for J/psi -> n (n) over bar. Our branching- fraction results suggest a …
Measurement of the production fraction times branching fractionf(b→Λb)·B(Λb→J/ψΛ)
2011
The \Lambda_b(udb) baryon is observed in the decay \Lambda_b --> J/\psi \Lambda using 6.1 fb^{-1} of p\bar{p} collisions collected with the D0 detector at \sqrt{s}=1.96 TeV. The production fraction multiplied by the branching fraction for this decay relative to that for the decay B^0 --> J/\psi K^0_s is measured to be 0.345 \pm 0.034 (stat.) \pm 0.033 (syst.) \pm 0.003 (PDG). Using the world average value of f(b --> B^0)B(B^0 --> J/\psi K^0_s) = (1.74 \pm 0.08) \times 10^{-5}, we obtain f(b --> \Lambda_b)B(\Lambda_{b} --> J/\psi \Lambda) = (6.01 \pm 0.60 (stat.) \pm 0.58 (syst.) \pm 0.28 (PDG)) \times 10^{-5}. This measurement represents an improvement in precision by about a factor of thre…
Infinite momentum frame calculation of semileptonic heavyΛb→Λctransitions including HQET improvements
1997
We calculate the transition form factors that occur in heavy {Lambda}-type baryon semileptonic decays such as, e.g., in {Lambda}{sub b}{r_arrow}{Lambda}{sub c}{sup +}+l{sup {minus}}+{bar {nu}}{sub l}. We use Bauer-Stech-Wirbel-type infinite momentum frame wave functions for the heavy {Lambda}-type baryons which we assume to consist of a heavy quark and a light spin-isospin zero diquark system. The form factors at q{sup 2}=0 are calculated from the overlap integrals of the initial and final {Lambda}-type baryon states. To leading order in the heavy mass scale the structure of the form factors agrees with the HQET predictions including the normalization at zero recoil. The leading order {omeg…
Λb and Λc baryon decays at finite values of heavy quark masses
2000
Semileptonic decays of Lambda_b and Lambda_c baryons are studied within the Relativistic Three-Quark Model using finite heavy quark mass values. Employing the same parameters as have been used previously for the description of exclusive decays of heavy baryons in the heavy quark limit we calculate the six form factors of the process and the corresponding decay rates. Our calculation shows that the ``finite mass'' corrections are important in heavy-to-light transitions and are not negligible in heavy-to-heavy transitions.
Including theΔ(1232)resonance in baryon chiral perturbation theory
2005
Baryon chiral perturbation theory with explicit $\ensuremath{\Delta}(1232)$ degrees of freedom is considered. The most general interactions of pions, nucleons, and \ensuremath{\Delta} consistent with all underlying symmetries as well as with the constraint structure of higher-spin fields are constructed. By use of the extended on-mass-shell renormalization scheme, a manifestly Lorentz-invariant effective-field theory with a systematic power counting is obtained. As applications, we discuss the mass of the nucleon, the pion-nucleon \ensuremath{\sigma} term, and the pole of the \ensuremath{\Delta} propagator.
In-flight calibration of the ROSAT HRI ultraviolet sensitivity
2000
Comparing measured and estimated count rates of a few selected sample stars, we confirm the validity and provide the in-flight calibration of the ROSAT HRI UV/visible effective area model in Zombeck et al. The count rate estimates for Betelgeuse derived with this model are in agreement with the measured HRI upper limit. This result is also confirmed in an erratum by Berghöfer et al. aimed at revising their previous calculation, which was overestimated by more than 2 orders of magnitude. Adopting this ROSAT HRI UV/visible effective area model and measured UV/visible spectra of a set of sample stars covering the range of Teff 3000-40,000 K, we have built the calibration curves to estimate UV/…
Cosmic Dark Radiation and Neutrinos
2013
New measurements of the cosmic microwave background (CMB) by the Planck mission have greatly increased our knowledge about the universe. Dark radiation, a weakly interacting component of radiation, is one of the important ingredients in our cosmological model which is testable by Planck and other observational probes. At the moment, the possible existence of dark radiation is an unsolved question. For instance, the discrepancy between the value of the Hubble constant, H-0, inferred from the Planck data and local measurements of H-0 can to some extent be alleviated by enlarging the minimal ACDM model to include additional relativistic degrees of freedom. From a fundamental physics point of v…
Effect of three-body forces on response functions in infinite neutron matter
2015
International audience; We study the impact of three-body forces on the response functions of cold neutron matter. These response functions are determined in the random phase approximation (RPA) from a residual interaction expressed in terms of Landau parameters. Special attention is paid to the non-central part, including all terms allowed by the relevant symmetries. Using Landau parameters derived from realistic nuclear two- and three-body forces grounded in chiral effective field theory, we find that the three-body term has a strong impact on the excited states of the system and in the static and long-wavelength limit of the response functions for which a new exact formula is established.
A neutron source for IGISOL-JYFLTRAP : Design and characterisation
2017
A white neutron source based on the Be(p, nx) reaction for fission studies at the IGISOL-JYFLTRAP facility has been designed and tested. 30MeV protons impinge on a 5mm thick water-cooled beryllium disc. The source was designed to produce at least 1012 fast neutrons/s on a secondary fission target, in order to reach competitive production rates of fission products far from the valley of stability. The Monte Carlo codes MCNPX and FLUKA were used in the design phase to simulate the neutron energy spectra. Two experiments to characterise the neutron field were performed: the first was carried out at The Svedberg Laboratory in Uppsala (SE), using an Extended-Range Bonner Sphere Spectrometer and …