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.
The primary motivation of the GlueX experiment is to search for and ultimately study the pattern of gluonic excitations in the meson spectrum produced in $gamma p$ collisions. Recent lattice QCD calculations predict a rich spectrum of hybrid mesons t
hat have both exotic and non-exotic $J^{PC}$, corresponding to $qbar{q}$ states ($q=u,$ $d,$ or $s$) coupled with a gluonic field. A thorough study of the hybrid spectrum, including the identification of the isovector triplet, with charges 0 and $pm1$, and both isoscalar members, $|sbar{s} >$ and $|ubar{u} > + |dbar{d} >$, for each predicted hybrid combination of $J^{PC}$, may only be achieved by conducting a systematic amplitude analysis of many different hadronic final states. Detailed studies of the performance of the gx detector have indicated that identification of particular final states with kaons is possible using the baseline detector configuration. The efficiency of kaon detection coupled with the relatively lower production cross section for particles containing hidden strangeness will require a high intensity run in order for analyses of such states to be feasible. We propose to collect a total of 200 days of physics analysis data at an average intensity of $5times 10^7$ tagged photons on target per second. This data sample will provide an order of magnitude statistical improvement over the initial GlueX running, which will allow us to begin a program of studying mesons and baryons containing strange quarks. In addition, the increased intensity will permit us to study reactions that may have been statistically limited in the initial phases of GlueX. Overall, this will lead to a significant increase in the potential for gx to make key experimental advances in our knowledge of hybrid mesons and excited $Xi$ baryons.
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.
High-statistics differential cross sections for the reactions gamma p -> p eta and gamma p -> p eta-prime have been measured using the CLAS at Jefferson Lab for center-of-mass energies from near threshold up to 2.84 GeV. The eta-prime results are the
most precise to date and provide the largest energy and angular coverage. The eta measurements extend the energy range of the worlds large-angle results by approximately 300 MeV. These new data, in particular the eta-prime measurements, are likely to help constrain the analyses being performed to search for new baryon resonance states.
