We present a search for ten baryon-number violating decay modes of $Lambda$ hyperons using the CLAS detector at Jefferson Laboratory. Nine of these decay modes result in a single meson and single lepton in the final state ($Lambda rightarrow m ell$)
and conserve either the sum or the difference of baryon and lepton number ($B pm L$). The tenth decay mode ($Lambda rightarrow bar{p}pi^+$) represents a difference in baryon number of two units and no difference in lepton number. We observe no significant signal and set upper limits on the branching fractions of these reactions in the range $(4-200)times 10^{-7}$ at the $90%$ confidence level.
High-statistics measurements of differential cross sections and spin density matrix elements for the reaction $gamma p to phi p$ have been made using the CLAS detector at Jefferson Lab. We cover center-of-mass energies ($sqrt{s}$) from 1.97 to 2.84 G
eV, with an extensive coverage in the $phi$ production angle. The high statistics of the data sample made it necessary to carefully account for the interplay between the $phi$ natural lineshape and effects of the detector resolution, that are found to be comparable in magnitude. We study both the charged- ($phi to K^+ K^-$) and neutral- ($phi to K^0_S K^0_L$) $Koverline{K}$ decay modes of the $phi$. Further, for the charged mode, we differentiate between the cases where the final $K^-$ track is directly detected or its momentum reconstructed as the total missing momentum in the event. The two charged-mode topologies and the neutral-mode have different resolutions and are calibrated against each other. Extensive usage is made of kinematic fitting to improve the reconstructed $phi$ mass resolution. Our final results are reported in 10- and mostly 30-MeV-wide $sqrt{s}$ bins for the charged- and the neutral-mode, respectively. Possible effects from $K^+ Lambda^ast$ channels with $p Koverline{K}$ final-states are discussed. These present results constitute the most precise and extensive $phi$ photoproduction measurements to date and in conjunction with the $omega$ photoproduction results recently published by CLAS, will greatly improve our understanding of low energy vector meson photoproduction.
We present measurements of the differential cross section and Lambda recoil polarization for the gamma p to K+ Lambda reaction made using the CLAS detector at Jefferson Lab. These measurements cover the center-of-mass energy range from 1.62 to 2.84 G
eV and a wide range of center-of-mass K+ production angles. Independent analyses were performed using the K+ p pi- and K+ p (missing pi -) final-state topologies; results from these analyses were found to exhibit good agreement. These differential cross section measurements show excellent agreement with previous CLAS and LEPS results and offer increased precision and a 300 MeV increase in energy coverage. The recoil polarization data agree well with previous results and offer a large increase in precision and a 500 MeV extension in energy range. The increased center-of-mass energy range that these data represent will allow for independent study of non-resonant K+ Lambda photoproduction mechanisms at all production angles.
A common situation in experimental physics is to have a signal which can not be separated from a non-interfering background through the use of any cut. In this paper, we describe a procedure for determining, on an event-by-event basis, a quality fact
or ($Q$-factor) that a given event originated from the signal distribution. This procedure generalizes the side-band subtraction method to higher dimensions without requiring the data to be divided into bins. The $Q$-factors can then be used as event weights in subsequent analysis procedures, allowing one to more directly access the true spectrum of the signal.
