17 research outputs found
A Direct Measurement of Hard Two-Photon Exchange with Electrons and Positrons at CLAS12
One of the most surprising discoveries made at Jefferson Lab has been the
discrepancy in the determinations of the proton's form factor ratio between unpolarized cross section measurements and the
polarization transfer technique. Over two decades later, the discrepancy not
only persists but has been confirmed at higher momentum transfers now
accessible in the 12-GeV era. The leading hypothesis for the cause of this
discrepancy, a non-negligible contribution from hard two-photon exchange, has
neither been conclusively proven or disproven. This state of uncertainty not
only clouds our knowledge of one-dimensional nucleon structure but also poses a
major concern for our field's efforts to map out the three-dimensional nuclear
structure. A better understanding of multi-photon exchange over a wide phase
space is needed. We propose making comprehensive measurements of two-photon
exchange over a wide range in momentum transfer and scattering angle using the
CLAS12 detector. Specifically, we will measure the ratio of positron-proton to
electron-proton elastic scattering cross sections, using the proposed positron
beam upgrade for CEBAF. The experiment will use 2.2, 4.4, and 6.6 GeV lepton
beams incident on the standard CLAS12 unpolarized hydrogen target. Data will be
collected by the CLAS12 detector in its standard configuration, except for a
modified trigger to allow the recording of events with beam leptons scattered
into the CLAS12 central detector. The sign of the beam charge, as well as the
polarity of the CLAS12 solenoid and toroid, will be reversed several times in
order to suppress systematics associated with local detector efficiency and
time-dependent detector performance. The proposed high-precision determination
of two-photon effects will be...Comment: Experimental Proposal E12+23-008 submitted to Jefferson Lab PAC 51,
34 pages, 18 figure
Search for axion-like particles through nuclear Primakoff production using the GlueX detector
We report on the results of the first search for the production of axion-like
particles (ALP) via Primakoff production on nuclear targets using the GlueX
detector. This search uses an integrated luminosity of 100
pbnucleon on a C target, and explores the mass region of 200
< < 450 MeV via the decay . This mass range is
between the and masses, which enables the use of the measured
production rate to obtain absolute bounds on the ALP production with
reduced sensitivity to experimental luminosity and detection efficiency. We
find no evidence for an ALP, consistent with previous searches in the quoted
mass range, and present limits on the coupling on the scale of (1 TeV). We
further find that the ALP production limit we obtain is hindered by the peaking
structure of the non-target-related dominant background in GlueX, which we
treat by using data on He to estimate and subtract these backgrounds. We
comment on how this search can be improved in a future higher-statistics
dedicated measurement
Measurement of the helicity asymmetry E for the γ→ p→ → pπ reaction in the resonance region: The CLAS Collaboration
The double-spin-polarization observable E for γ→ p→ → pπ has been measured with the CEBAF Large Acceptance Spectrometer (CLAS) at photon beam energies Eγ from 0.367 to 2.173GeV (corresponding to center-of-mass energies from 1.240 to 2.200GeV) for pion center-of-mass angles, cosθπ0c.m. , between - 0.86 and 0.82. These new CLAS measurements cover a broader energy range and have smaller uncertainties compared to previous CBELSA data and provide an important independent check on systematics. These measurements are compared to predictions as well as new global fits from The George Washington University, Mainz, and Bonn-Gatchina groups. Their inclusion in multipole analyses will allow us to refine our understanding of the single-pion production contribution to the Gerasimov-Drell-Hearn sum rule and improve the determination of resonance properties, which will be presented in a future publication
ENERGY AND ENVIRONMENTAL ROLL CALL VOTING IN THE U.S. CONGRESS IN 1975 AND 1979
This article argues that the energy and environmental policy areas in Congress are no longer considered components of the government management dimension. The two policy areas have separated from the government management dimension constructed by Clausen and are now distinct and autonomous Congressional policy areas. The models of roll call voting for energy and environment issues are very different. Energy is tied more closely to technical considerations while environmental issues are more emotional and more closely tied to quality of life concerns. Copyright 1984 by The Policy Studies Organization.