Observation of double radiative capture on pionic hydrogen

Area of Science:

• Nuclear Physics
• Particle Physics
• Quantum Electrodynamics

Background:

• Pionic hydrogen is a fundamental system for studying pion-nucleon interactions.
• Radiative capture processes provide insights into fundamental symmetries and interactions.
• Previous studies focused on single radiative capture, leaving double radiative capture less explored.

Purpose of the Study:

• To report the first experimental observation of double radiative capture in pionic hydrogen.
• To measure the branching ratio and angle-energy distributions for this process.
• To compare experimental results with theoretical predictions for pion annihilation mechanisms.

Main Methods:

• Experiments were conducted at the TRIUMF cyclotron.
• The RMC spectrometer was utilized to detect gamma-ray coincidences.
• Measurements involved observing gamma rays following negative pion (pi-) stops in liquid hydrogen.

Main Results:

• The branching ratio for double radiative capture was measured to be [3.05+/-0.27(stat)+/-0.31(syst)]x10(-5).
• Angle-energy distributions were analyzed.
• The results align with theoretical predictions.

Conclusions:

• The first observation of double radiative capture on pionic hydrogen is confirmed.
• Experimental data supports the theoretical model predicting a dominant pipi-->gammagamma annihilation mechanism.