Self-Consistent Data Analysis of the Proton Structure Function g1 and Extraction of its Moments

The reanalysis of all available world data on the longitudinal asymmetry A|| is presented. The proton structure function g1 was extracted within a unique framework of data inputs and assumptions. These data allowed for a reliable evaluation of moments of the structure function g1 in the Q2 range from 0.2 up to 30 GeV2. The Q2 evolution of the moments was studied in QCD by means of Operator Product Expansion (OPE).Comment: Proceeding of 3rd International Symposium on the Gerasimov-Drell-Hearn Sum Rule and its extensions, Old Dominion University, Norfolk, Virginia June 2-5, 200

Higher twist analysis of the proton g_1 structure function

We perform a global analysis of all available spin-dependent proton structure function data, covering a large range of Q^2, 1 < Q^2 < 30 GeV^2, and calculate the lowest moment of the g_1 structure function as a function of Q^2. From the Q^2 dependence of the lowest moment we extract matrix elements of twist-4 operators, and determine the color electric and magnetic polarizabilities of the proton to be \chi_E = 0.026 +- 0.015 (stat) + 0.021/-0.024 (sys) and \chi_B = -0.013 -+ 0.007 (stat) - 0.010/+0.012 (sys), respectively.Comment: 6 pages, 2 figures, to appear in Phys. Lett.

Data analysis techniques, differential cross sections, and spin density matrix elements for the reaction gamma p -\u3e phi p

High-statistics measurements of differential cross sections and spin density matrix elements for the reaction gamma p -\u3e phi p have been made using the CLAS detector at Jefferson Lab. We cover center-of-mass energies (v s) from 1.97 to 2.84 GeV, 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 f natural lineshape and effects of the detector resolution, that are found to be comparable in magnitude. We study both the charged-(phi -\u3e K+ K-) and neutral( phi -\u3e(KsKL0)-K-0) K (K) over bar 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 f mass resolution. Our final results are reported in 10- and mostly 30-MeV-wide root s bins for the charged-and the neutral-modes, respectively. Possible effects from K+Lambda* channels with pK (K) over bar 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

First measurement of the polarization observable E in the (p)over-right-arrow((gamma)over-right-arrow, pi(+))n reaction up to 2.25 GeV

First results from the longitudinally polarized frozen-spin target (FROST) program are reported. The double-polarization observable E, for the reaction (p) over right arrow((gamma) over right arrow, pi( + ))n, has been measured using a circularly polarized tagged-photon beam, with energies from 0.35 to 2.37 GeV. The final-state pions were detected with the CEBAF Large Acceptance Spectrometer in Hall B at the Thomas Jefferson National Accelerator Facility. These polarization data agree fairly well with previous partial-wave analyses at low photon energies. Over much of the covered energy range, however, significant deviations are observed, particularly in the high-energy region where high-L multipoles contribute. The data have been included in new multipole analyses resulting in updated nucleon resonance parameters. We report updated fits from the Bonn-Gatchina, Jfilich-Bonn, and SAID groups. (C) 2015 The Authors. Published by Elsevier B.V

Photoproduction of Lambda and Sigma(0) hyperons using linearly polarized photons

Background: Measurements of polarization observables for the reactions (gamma) over right arrowp -\u3e K+ Lambda and (gamma) over right arrowp -\u3e K+ Sigma(0) have been performed. This is part of a program of measurements designed to study the spectrum of baryon resonances in particular, and nonperturbative QCD in general. Purpose: The accurate measurement of several polarization observables provides tight constraints for phenomenological fits, which allow the study of strangeness in nucleon and nuclear systems. Beam-recoil observables for the (gamma) over right arrowp -\u3e K+ Sigma(0) reaction have not been reported before now. Method: Themeasurements were carried out using linearly polarized photon beams incident on a liquid hydrogen target, and the CLAS detector at the Thomas Jefferson National Accelerator Facility. The energy range of the results is 1.71 \u3c W \u3c 2.19 GeV, with an angular range -0.75 \u3c cos theta(K)* \u3c +0.85. Results: The observables extracted for both reactions are beam asymmetry Sigma, target asymmetry T, and the beam-recoil double polarization observables O-x and O-z. Conclusions: Comparison with theoretical fits indicates that, in the regions where no previous data existed, the new data contain significant new information, and strengthen the evidence for the set of resonances used in the latest Bonn-Gatchina fit

Search for baryon-number and lepton-number violating decays of Lambda hyperons using the CLAS detector at Jefferson Laboratory

We present a search for ten baryon number violating decay modes of. 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 - \u3e ml) and conserve either the sum or the difference of baryon and lepton number (B +/- L). The tenth decay mode (Lambda - \u3e (p) over bar 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) x 10(-7) at the 90% confidence level

Strangeness Suppression of q(q)over-bar Creation Observed in Exclusive Reactions

We measured the ratios of electroproduction cross sections from a proton target for three exclusive meson-baryon final states: AK(+), p pi(0), and n pi(+), with the CLAS detector at Jefferson Lab. Using a simplemodel of quark hadronization, we extract q (q) over bar creation probabilities for the first time in exclusive two-body production, in which only a single q (q) over bar pair is created. We observe a sizable suppression of strange quark-antiquark pairs compared to nonstrange pairs, similar to that seen in high-energy production

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The retention of phosphorus in surface waters through co-precipitation of phosphate with Fe-oxyhydroxides during exfiltration of anaerobic Fe(II) rich groundwater is not well understood. We developed an experimental field set-up to study Fe(II) oxidation and P immobilization along the flow-path from groundwater into surface water in an agricultural experimental catchment of a small lowland river. We physically separated tube drain effluent from groundwater discharge before it entered a ditch in an agricultural field. Through continuous discharge measurements and weekly water quality sampling of groundwater, tube drain water, exfiltrated groundwater, and surface water, we investigated Fe(II) oxidation kinetics and P immobilization processes. The oxidation rate inferred from our field measurements closely agreed with the general rate law for abiotic oxidation of Fe(II) by O₂. Seasonal changes in climatic conditions affected the Fe(II) oxidation process. Lower pH and lower temperatures in winter (compared to summer) resulted in low Fe oxidation rates. After exfiltration to the surface water, it took a couple of days to more than a week before complete oxidation of Fe(II) is reached. In summer time, Fe oxidation rates were much higher. The Fe concentrations in the exfiltrated groundwater were low, indicating that dissolved Fe(II) is completely oxidized prior to inflow into a ditch. While the Fe oxidation rates reduce drastically from summer to winter, P concentrations remained high in the groundwater and an order of magnitude lower in the surface water throughout the year. This study shows very fast immobilization of dissolved P during the initial stage of the Fe(II) oxidation process which results in P-depleted water before Fe(II) is completely depleted. This cannot be explained by surface complexation of phosphate to freshly formed Fe-oxyhydroxides but indicates the formation of Fe(III)-phosphate precipitates. The formation of Fe(III)-phosphates at redox gradients seems an important geochemical mechanism in the transformation of dissolved phosphate to structural phosphate and, therefore, a major control on the P retention in natural waters that drain anaerobic aquifers