Search for Photoproduction of Axionlike Particles at GlueX

We present a search for axionlike particles, a, produced in photon-proton collisions at a center-of-mass energy of approximately 4 GeV, focusing on the scenario where the a-gluon coupling is dominant. The search uses a → γγ and a → π+π−π0 decays, and a data sample corresponding to an integrated luminosity of 168  pb−1 collected with the GlueX detector. The search for a → γγ decays is performed in the mass range of 180 \u3c ma \u3c480  MeV, while the search for a → π+π−π0 decays explores the 600 \u3c ma \u3c 720  MeV region. No evidence for a signal is found, and 90% confidence-level exclusion limits are placed on the a-gluon coupling strength. These constraints are the most stringent to date over much of the mass ranges considered

Measurement of Spin Density Matrix Elements in Λ(1520) Photoproduction at 8.2-8.8 GeV

We report on the measurement of spin density matrix elements of the Λ(1520) in the photoproduction reaction γp→Λ(1520)K+, via its subsequent decay to K−p. The measurement was performed as part of the GlueX experimental program in Hall D at Jefferson Laboratory using a linearly polarized photon beam with Eγ = 8.2 GeV–8.8 GeV. These are the first such measurements in this photon energy range. Results are presented in bins of momentum transfer squared, − (t − t0). We compare the results with a Reggeon exchange model and determine that natural exchange amplitudes are dominant in Λ(1520) photoproduction

Measurement of Deeply Virtual Compton Scattering Off \u3csup\u3e4\u3c/sup\u3eHe with the CEBAF Large Acceptance Spectrometer at Jefferson Lab

We report on the measurement of the beam spin asymmetry in the deeply virtual Compton scattering off 4He using the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab using a 6 GeV longitudinally polarized electron beam incident on a pressurized 4He gaseous target. We detail the method used to ensure the exclusivity of the measured reactions, in particular the upgrade of CLAS with a radial time projection chamber to detect the low-energy recoiling 4He nuclei and an inner calorimeter to extend the photon detection acceptance at forward angles. Our results confirm the theoretically predicted enhancement of the coherent (e4He→e′4Heγ′) beam spin asymmetries compared to those observed on the free proton, while the incoherent (e4He→ e′p′γ′X′) asymmetries exhibit a 30% suppression. From the coherent data, we were able to extract, in a model-independent way, the real and imaginary parts of the only 4He Compton form factor, HA, leading the way toward 3D imaging of the partonic structure of nuclei

Characteristics of Yerevan High Transparency Scintillators

Optical transmission, light output and time characteristics are given for long scintillator strips fabricated at the Yerevan Physics Institute using the extrusion method. It is shown that at 45% relative (to anthracene) light output, good transmission (2.5/2.9 m attenuation length with photomultiplier direct readout and 3/3.5 m attenuation length fiber readout) and time characteristics (average decay time 2.8 nsec) were obtained