Event excess in the MiniBooNE search for ¯νμ→¯νe oscillations

The MiniBooNE experiment at Fermilab reports results from a search for ˉν_{μ}→ˉν_{e} oscillations, using a data sample corresponding to 5.66×102? protons on target. An excess of 20.9±14.0 events is observed in the energy range 475相似文献   

Thrombin allostery

Thrombin is a Na(+)-activated, allosteric serine protease that plays multiple functional roles in blood pathophysiology. Binding of Na(+) is the major driving force behind the procoagulant, prothrombotic and signaling functions of the enzyme. This review summarizes our current understanding of the molecular basis of thrombin allostery with special emphasis on the kinetic aspects of Na(+) activation. The molecular mechanism of thrombin allostery is a remarkable example of long-range communication that offers a paradigm for many other biological systems.     

Reactions within fluorobenzene-ammonia heterocluster ions: experiment and theory

Reactions occurring within gas phase fluorobenenze-ammonia heterocluster cations (FC(6)H(5)-(NH(3))(n=1-4)) have been studied through the use of a triple quadrupole mass spectrometer as well as employing density functional theory (DFT). Collision induced dissociation (CID) experiments were conducted in which mass selected cluster ions are accelerated into a cell containing argon gas and the resulting products then subsequently mass analyzed. Two dominate reaction channels are observed. The first is simple evaporative loss of neutral ammonia from the cluster ion. The second involves a substitution reaction occurring within the cluster ion to form the aniline cation, C(6)H(5)NH(2)(+), where the reactivity was found to vary as a function of cluster size. DFT calculations have been performed to both help analyze the structure and the reactivity of these cluster ions. Pronounced differences in activation energies were found that provide an explanation for the observed variation of reactivity as a function of cluster size. An ad hoc model based upon the Arrhenius equation was developed to fit both the experimental collision energy dependence of the reaction and the observed lowering of the reaction barrier to aniline formation as a function of cluster size.     

Electron impact ionization efficiency curves of van der Waals clusters

The study of van der Waals clusters is an area of growing interest and is being widely studied for a number of reasons. The measurement of the ionization efficiency (IE) curves have yielded a wealth of information by enabling ionization and appearance energies of ions to be determined which are essential for the calculation of thermochemical data. In the case of van der Waals clusters, the measurement ofIE curves enables one to determine the qualitative trends in the ionization potentials as a function of cluster size. In additionIE curves have also offered valuable insight into ionization related processes occurring in clusters. This paper will cover some of the more recent studies of Penning ionization, exciton induced decay and Coulomb explosion in van der Waals clusters through the use of electron impactIE curves.     

A partial-wave analysis of the neutral 3π system produced in the reaction π−p → (π+π−π0) n at 12 and 15 GeV/c

Data on the charge-exchange reaction π^?p → (π⁺π^?π⁰)n have been taken at beam momenta of 12 and 15 GeV/c, using the CERN Omega Multiparticle Spectrometer. A partial-wave analysis has been made of the (3π)⁰ system. We observe both natural and unnatural spin-parity production. The natural parity states can be identified with established resonances. In addition a natural spin-parity enhancement is observed at a mass of about 2 GeV/c² with J^P = 4⁺ preferred. We have called this effect the A₂¹ (2030). The unnatural spin-parity production found is consistent with reggeized Deck model predictions. No unambiguous A₁ or A₃ production is observed.     

Production of A20and ω1 (1675) in the reaction π−p → π+π−π0n at 12 and 15 GeV/c

Data on the reaction π^?p → π⁺π^?π⁰ have been taken at 12 and 15 GeV/c with the CERN Omega multiparticle spectrometer. In a 3-pion partial-wave analysis strong production of $\text{A}{}_2{}^0\text{(1310)}\text{and}\text{ω}{}^1\text{(1675)}$ is observed. Total and differential cross sections are determined and density matrix elements presented as a function of t in the t- and s-channel frames. The energy dependence of A₂⁰ production is studied, and a comparison of $\text{ω(780),}\text{A}{}_2{}^0\text{(1310)}\text{and}\text{ω}{}^1\text{(1675)}$ production is made.     

Beta-alpha correlation in the decay of 20Na

We have measured the β-α angular correlation in the allowed positron decay of ²⁰Na to the 7.42 MeV state of ²⁰Ne. The correlation is of the form $\text{1 +}\text{a}\text{cos}\text{θ +}\text{p}\text{cos}{}^2\text{θ}$. We find $\text{p}\text{= ?0.003 ± 0.005}$ in reasonable agreement with expectations based on the conserved vector current theory.