Near-threshold diffractive psi-meson photoproduction from the proton

Area of Science:

• Nuclear Physics
• Particle Physics
• High-Energy Physics

Background:

• The study focuses on the photoproduction of phi mesons, which are vector mesons, on proton targets.
• Understanding these interactions is crucial for probing the structure of hadrons and the nature of fundamental forces.

Purpose of the Study:

• To investigate the photoproduction of phi mesons on protons using linearly polarized photons.
• To analyze the differential cross sections and angular distributions in the low-energy region (threshold to 2.37 GeV).
• To determine the underlying mechanisms, particularly the role of helicity conservation and parity processes.

Main Methods:

• Experiments were conducted using linearly polarized photons.
• Measurements focused on forward angles and the energy range from the reaction threshold up to 2.37 GeV.
• Differential cross sections and angular distributions were analyzed.

Main Results:

• The differential cross sections at t = -|t|min exhibited a local maximum around 2.0 GeV, deviating from a smooth increase.
• Angular distribution analysis indicated that phi meson photoproduction is predominantly governed by helicity-conserving processes.
• The observed local maximum is unlikely to be attributed to unnatural-parity processes.

Conclusions:

• The photoproduction of phi mesons on protons shows a significant energy dependence with a notable peak.
• Helicity conservation appears to be the dominant mechanism in this low-energy regime.
• Unnatural-parity processes are not the primary cause of the observed resonance-like structure.