Photoproduction of K^{+}K^{-} Pairs in Ultraperipheral Collisions

Area of Science:

• Nuclear Physics
• Particle Physics
• High-Energy Physics

Background:

• K+K- pairs are produced in photonuclear collisions via phi(1020) decays or direct production.
• Measuring K+K- photoproduction probes interactions between photons, kaons, and nuclear targets.
• Previous kaon-proton scattering studies occurred at lower energies than probed here.

Purpose of the Study:

• To present the first measurement of coherent K+K- pair photoproduction on lead ions in ultraperipheral collisions.
• To investigate direct K+K- production.
• To analyze the K+K- mass spectrum and cross section at high center-of-mass energies.

Main Methods:

• Utilized the ALICE detector for ultraperipheral collisions of lead ions.
• Measured coherent photoproduction of K+K- pairs at low transverse momentum.
• Analyzed the K+K- mass spectrum using a cocktail fit including phi(1020) decays and direct production.

Main Results:

• Observed significant K+K- production at low transverse momentum, consistent with coherent photoproduction on lead targets.
• Measured a coherent photoproduction cross section of dσ/dy = 3.37 ± 0.61(stat) ± 0.15(syst) mb in the 1.1-1.4 GeV/c^2 mass range.
• The measured cross section is larger than expected from phi(1020) photoproduction alone, indicating substantial direct K+K- production.

Conclusions:

• The study provides the first evidence of direct K+K- photoproduction on heavy nuclei at high energies.
• The results offer insights into the couplings of photons to charged kaons and nuclear targets.
• The findings necessitate further theoretical and experimental investigations into direct K+K- photoproduction mechanisms.