Photoproduction ofφmesons from the proton: Polarization observables and strangeness in the nucleon

Abstract

The polarization observables in φ meson photoproduction is studied to probe the strangeness content of the nucleon. In addition to the dominant diffractive production and the one-pion-exchange process, we take into account the direct knockout mechanism that arises from the possible hidden strangeness content of the nucleon. We find that some double polarization observables are very sensitive to the strangeness content of the proton because of the different spin structures of the amplitudes associated with different mechanisms. This suggests that such measurements could be very useful in probing the strangeness content in the proton. The orbitally excited quark-cluster configurations in the proton are included in the calculation and found to have little effect. PACS number(s): 13.88.+e, 24.70.+s, 25.20.Lj, 13.60.Le

Hard exclusive photoproduction ofΦmesons

“…The corresponding predictions of both approaches are again comparable around θ cm = 90 • . A (somewhat smaller) negative beam asymmetry has also been found in another model which is based on pomeron exchange, pion exchange, and a direct knockout production from the strange-quark sea in the proton [39]. It would be interesting to see experimentally, whether polarization observables like the target asymmetry T y , the recoil polarization P y ′ , or the vector-meson polarization V y ′ , which vanish in leading-order perturbative QCD, are still sizable at momentum transfers of a few GeV.…”

Dynamical coupled channels calculation of pion and omega meson production

“…[35]) require the analytic continuation of the T matrix amplitudes to the physical pole position; this work is in preparation. The prediction for the PBA [44] in γp → ωp…”

Double-spin asymmetries in the cross section of $\rho^0$ and $\phi$ production at intermediate energies

“…It implies sensitivity of the asymmetry to the strangeness content of the nucleon through interference of ss knockout with the diffractive VMD amplitude. In kinematic conditions ( W = 4.2 GeV, Q 2 ≃ 0) similar to those of HERMES, and assuming the strangeness probability for the proton is P ss = 0.01, the predicted asymmetry [27] at −t ′ =0 ranges between -0.05 and +0.03, while for −t ′ =0.5 GeV 2 the range is -0.06 to +0.15, depending on the unknown relative phase of the amplitudes. The experimental result is compatible with zero strangeness content, but favours a negative phase δ ss if the strangeness is non-zero as assumed.…”