[en] The (π^-,K degree) reaction, which complements the (π⁺,K⁺) reaction, offers another means to study Λ-hypernulei at PILAC. The physics motivation for measuring the (π^-,K degree) reaction is discussed. The feasibility or detecting K degree at PILAC using the LAMPF Neutral Meson Spectrometer and a simple dipole spectrometer is studied with Monte-Carlo simulations. We conclude that the (π^-,K degree) reaction can be well pursued at PILAC. 18 refs., 5 figs., 3 tabs

[en] We consider backgrounds to the detection of the two-body hadronic decay modes of neutral B mesons and baryons. The largest background is due to the correlated production of pairs of high-p/sub T/ hadrons in the target, but this can be adequately rejected provided the experimental apparatus has sufficient resolution in mass and decay vertex. Another possible source of background arises from the production and decay of charmed and strange particles. Since these particles can travel considerable distances before decaying, they can give rise to backgrounds which may not be rejectable by means of vertex cut. We have simulated several backgrounds from charm, and we find them to be small compared to the expected level of signal. 8 refs., 1 fig., 2 tabs

[en] High precision data of lepton angular distributions in inclusive Z boson production, reported by the CMS and ATLAS Collaborations, showed pronounced transverse momentum (qT) dependencies of the A₀ and A₂ coefficients. Violation of the Lam-Tung relation, A₀=A₂, was also found. An intuitive understanding of these results can be obtained from a geometric approach. We predict that A₀ and A₂ for Z plus single gluon-jet events are very different from that of Z plus single quark-jet events, allowing a new experimental tool for checking various algorithms which attempt to discriminate quark jets from gluon jets. We also predict that the Lam-Tung relation would be more severely violated for the Z plus multiple-jet data that what has been observed so far for inclusive Z production data. These predictions can be readily tested using existing LHC data.

[en] The recent progress on our understanding of the flavor structure of the nucleon sea is reviewed. The large flavor asymmetry between the up and down sea quark distributions is now well established. This asymmetry strongly suggests the importance of the mesonic degree of freedom in the description of the nucleon sea. Implications of the meson clouds on other aspects of nucleon parton distributions and possible future measurements for testing various theoretical models are also discussed.

[en] Primordial neutrinos decoupled in the early Universe predominantly in helicity eigenstates. As the neutrinos propagate through the Universe, cosmic and galactic magnetic and gravitational fields can flip their helicities. Spin rotation of Dirac neutrinos by magnetic fields can be significant if they have magnetic moments well beyond Standard Model estimates, e.g., as was suggested for solar neutrinos by the XENON1T experiment. Majorana neutrinos would not undergo such rotation. The helicity flip probability is sensitive not only to the magnetic moment of the neutrino but also to the properties of galactic and cosmic fields, and thus can potentially probe astrophysical magnetic fields. As we indicate, even a moment several orders of magnitude smaller than that discussed by XENON1T could lead to significant helicity changes of Dirac neutrinos as they propagate to detectors on Earth. We determine the effects of gravitational inhomogeneities on primordial neutrinos helicities as well. (author)

[en] Primordial neutrinos provide information on the Universe at a very early stage, roughly one second after the big bang. Their detection would have a major impact on our knowledge in cosmology and neutrino physics. The most promising experimental technique for detecting these extremely low energy primordial neutrinos involves their capture on a radioactive tritium target. The capture rate depends on certain yet unknown neutrino properties, including their masses and their Dirac or Majorana nature. We show that the capture rate also depends on the helicity of primordial neutrinos, which evolves as neutrinos propagate through the cosmic gravitational and magnetic fields. We predict the dependence of the capture rate on various properties of primordial neutrinos. (author)

[en] At high center of mass energies, hadroproduction of heavy quarks can be expressed in terms of the same color dipole cross section as low Bjorken-x deep inelastic scattering. We show analytically that, at leading order, the dipole formulation is equivalent to the gluon-gluon fusion mechanism of the conventional parton model. In phenomenological application, we employ a parametrization of the dipole cross section which also includes higher order and saturation effects, thereby going beyond the parton model. Numerical calculations in the dipole approach agree well with experimental data on open charm production over a wide range of energy. The dipole approach and the next to leading order parton model yield similar values for open charm production, but for open bottom production, the dipole approach tends to predict somewhat higher cross sections than the parton model

[en] Neutrinos produced by nuclear reactors have played a major role in advancing our knowledge of the properties of neutrinos. The first direct detection of the neutrino, confirming its existence, was performed using reactor neutrinos. More recent experiments utilizing reactor neutrinos have also found clear evidence for neutrino oscillation, providing unique input for the determination of neutrino mass and mixing. Ongoing and future reactor neutrino experiments will explore other important issues, including the neutrino mass hierarchy and the search for sterile neutrinos and other new physics beyond the standard model. In this article, we review the recent progress in physics using reactor neutrinos and the opportunities they offer for future discoveries. (review)

[en] The existence of the five-quark Fock states for the intrinsic charm quark in the nucleons was suggested some time ago, but conclusive evidence is still lacking. We generalize the previous theoretical approach to the light-quark sector and study possible experimental signatures for such five-quark states. In particular, we compare the d-u and u+d-s-s data with the calculations based on the five-quark Fock states. The qualitative agreement between the data and the calculations is interpreted as evidence for the existence of the intrinsic light-quark sea in the nucleons. The probabilities for the |uuduu> and |uuddd> Fock states are also extracted.

[en] We have generalized the approach of Brodsky et al. for the intrinsic charm quark distribution in the nucleons to the light-quark sector involving intrinsic u-bar, d-bar, s and s-bar sea quarks. We compare the calculations with the existing d-bar-u-bar, s+s-bar, and u-bar+d-bar-s-s-bar data. The good agreement between the theory and the data allows the extraction of the probabilities for the |uuduu-bar >, |uuddd-bar >, and |uudss-bar > five-quark Fock states in the proton. We also calculate the x-dependence of the intrinsic charm after taking into consideration the QCD evolution of the intrinsic quark distribution.