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

Beam Asymmetry Σ for the Photoproduction of η and ή Mesons at Eγ = 8.8GeV

We report on the measurement of the beam asymmetry Σ for the reactions →γp→pη and →γp→pη′ from the GlueX experiment using an 8.2–8.8-GeV linearly polarized tagged photon beam incident on a liquid hydrogen target in Hall D at Jefferson Laboratory. These measurements are made as a function of momentum transfer −t with significantly higher statistical precision than our earlier η measurements and are the first measurements of η′ in this energy range. We compare the results to theoretical predictions based on t-channel quasiparticle exchange. We also compare the ratio of Ση to Ση′ to these models as this ratio is predicted to be sensitive to the amount of s¯s exchange in the production. We find that photoproduction of both η and η′ is dominated by natural parity exchange with little dependence on −t

First Results from The GlueX Experiment

The GlueX experiment at Jefferson Lab ran with its first commissioning beam in late 2014 and the spring of 2015. Data were collected on both plastic and liquid hydrogen targets, and much of the detector has been commissioned. All of the detector systems are now performing at or near design specifications and events are being fully reconstructed, including exclusive production of $\pi^{0}$, $\eta$ and $\omega$ mesons. Linearly-polarized photons were successfully produced through coherent bremsstrahlung and polarization transfer to the $\rho$ has been observed.Comment: 8 pages, 6 figures, Invited contribution to the Hadron 2015 Conference, Newport News VA, September 201

Beam asymmetry Σ for the photoproduction of η and η′ mesons at Eγ = 8.8GeV

We report on the measurement of the beam asymmetry Σ for the reactions → γ p → p η and → γ p → p η ′ from the GlueX experiment using an 8.2–8.8-GeV linearly polarized tagged photon beam incident on a liquid hydrogen target in Hall D at Jefferson Laboratory. These measurements are made as a function of momentum transfer − t with significantly higher statistical precision than our earlier η measurements and are the first measurements of η ′ in this energy range. We compare the results to theoretical predictions based on t -channel quasiparticle exchange. We also compare the ratio of Σ η to Σ η ′ to these models as this ratio is predicted to be sensitive to the amount of s ¯ s exchange in the production. We find that photoproduction of both η and η ′ is dominated by natural parity exchange with little dependence on − t

First Measurement of Near-Threshold J /ψ Exclusive Photoproduction off the Proton

We report on the measurement of the γp→J/ψp cross section from Eγ=11.8 GeV down to the threshold at 8.2 GeV using a tagged photon beam with the GlueX experiment. We find that the total cross section falls toward the threshold less steeply than expected from two-gluon exchange models. The differential cross section dσ/dt has an exponential slope of 1.67±0.39 GeV-2 at 10.7 GeV average energy. The LHCb pentaquark candidates Pc+ can be produced in the s channel of this reaction. We see no evidence for them and set model-dependent upper limits on their branching fractions B(Pc+→J/ψp) and cross sections σ(γp→Pc+)×B(Pc+→J/ψp)

Measurement of the photon beam asymmetry in γ⃗p→K+Σ0 at Eγ = 8.5 GeV

We report measurements of the photon beam asymmetry Σ for the reaction γ⃗p→K+Σ0 (1193) using the GlueX spectrometer in Hall D at Jefferson Lab. Data were collected by using a linearly polarized photon beam in the energy range of 8.2–8.8 GeV incident on a liquid hydrogen target. The beam asymmetry Σ was measured as a function of the Mandelstam variable t , and a single value of Σ was extracted for events produced in the u channel. These are the first exclusive measurements of the photon beam asymmetry Σ for the reaction in this energy range. For the t channel, the measured beam asymmetry is close to unity over the t range studied, − t = ( 0.1 – 1.4 ) ( GeV / c ) 2 , with an average value of Σ = 1.00 ± 0.05 . This agrees with theoretical models that describe the reaction via the natural-parity exchange of the K ∗ (892) Regge trajectory. A value of Σ = 0.41 ± 0.09 is obtained for the u channel integrated up to − u = 2.0 ( GeV / c ) 2

Measurement of beam asymmetry for π- Δ++ photoproduction on the proton at Eγ=8.5 GeV

We report a measurement of the π- photoproduction beam asymmetry for the reaction γp→π-Δ++ using data from the GlueX experiment in the photon beam energy range 8.2-8.8 GeV. The asymmetry ς is measured as a function of four-momentum transfer t to the Δ++ and compared to phenomenological models. We find that ς varies as a function of t: negative at smaller values and positive at higher values of |t|. The reaction can be described theoretically by t-channel particle exchange requiring pseudoscalar, vector, and tensor intermediaries. In particular, this reaction requires charge exchange, allowing us to probe pion exchange and the significance of higher-order corrections to one-pion exchange at low momentum transfer. Constraining production mechanisms of conventional mesons may aid in the search for and study of unconventional mesons. This is the first measurement of the process at this energy. © 2021 American Physical Society