The double spin asymmetry in the (-->)e(-->)p --> e(prime)pi(+)n reaction has been measured for the first time in the resonance region for four-momentum transfer Q2 = 0.35-1.5 GeV(2). Data were taken ...at Jefferson Lab with the CLAS detector using a 2.6 GeV polarized electron beam incident on a polarized solid NH3 target. Comparison with predictions of phenomenological models shows strong sensitivity to resonance contributions. Helicity-1/2 transitions are found to be dominant in the second and third resonance regions. The measured asymmetry is consistent with a faster rise with Q(2) of the helicity asymmetry A1 for the F(15)(1680) resonance than expected from the analysis of the unpolarized data.
We report on the first measurement of exclusive {xi}{sup -}(1321) hyperon photoproduction in {gamma}p{yields}K{sup +}K{sup +}{xi}{sup -} for 3.2<E{sub {gamma}}<3.9 GeV. The final state is identified ...by the missing mass in p({gamma},K{sup +}K{sup +})X measured with the CLAS detector at Jefferson Laboratory. We have detected a significant number of the ground state {xi}{sup -}(1321)(1/2){sup +} and have estimated the total cross section for its production. We also have strong evidence for the first excited state {xi}{sup -}(1530)(3/2){sup +}. Photoproduction provides a copious source of {xi}'s. We discuss the possibilities of a search for the recently proposed {xi}{sub 5}{sup -} and {xi}{sub 5}{sup +} pentaquarks.
The Heavy Photon Search experiment took its first data in a 2015 engineering run using a 1.056 GeV, 50 nA electron beam provided by CEBAF at the Thomas Jefferson National Accelerator Facility, ...searching for a prompt, electroproduced dark photon with a mass between 19 and 81 MeV/c2. A search for a resonance in the e+e− invariant mass distribution, using 1.7 days (1170 nb−1) of data, showed no evidence of dark photon decays above the large QED background, confirming earlier searches and demonstrating the full functionality of the experiment. Upper limits on the square of the coupling of the dark photon to the standard model photon are set at the level of 6×10−6. Future runs with higher luminosity will explore new territory.
A new electromagnetic calorimeter consisting of 140 lead tungstate (PbWO4) scintillating crystals was constructed for the PrimEx-η experiment at Jefferson lab. The calorimeter was integrated into the ...data acquisition and trigger systems of the GlueX detector and used in the experiment to reconstruct Compton scattering events. The experiment started collecting data in the spring of 2019 and acquired about 30% of the required statistics. The calorimeter is a prototype for two PbWO4-based detectors: the Neutral Particle Spectrometer (NPS) and the lead tungstate insert of the Forward CALorimeter (FCAL) of the GlueX detector. The article presents the design and performance of the Compton calorimeter and gives a brief overview of the FCAL and NPS projects.
The reaction {sup 2}H(e,e{sup '}p)n has been studied with full kinematic coverage for photon virtuality 1.75<Q{sup 2}<5.5 GeV{sup 2}. Comparisons of experimental data with theory indicate that for ...very low values of neutron recoil momentum (p{sub n}<100 MeV/c) the neutron is primarily a spectator and the reaction can be described by the plane-wave impulse approximation. For 100<p{sub n}<750 MeV/c, proton-neutron rescattering dominates the cross section, while {delta} production followed by the N{delta}{yields}NN transition is the primary contribution at higher momenta.
We have measured the 3He(e,e'pp)n reaction at 2.2 GeV over a wide kinematic range. The kinetic energy distribution for "fast" nucleons (p>250 MeV/c) peaks where two nucleons each have 20% or less, ...and the third nucleon has most of the transferred energy. These fast pp and pn pairs are back to back with little momentum along the three-momentum transfer, indicating that they are spectators. Calculations by Sargsian and by Laget also indicate that we have measured distorted two-nucleon momentum distributions by striking one nucleon and detecting the spectator correlated pair.
PDF
