First Measurement of a Long-Lived π^{+}π^{-} Atom Lifetime.

Area of Science:

• Particle Physics
• Atomic Physics

Background:

• The study of exotic atoms provides insights into fundamental interactions.
• Pionium (π⁺π⁻ atoms) are short-lived, making their study challenging.

Purpose of the Study:

• To observe and measure the lifetime of long-lived hydrogenlike pionium (π⁺π⁻ atoms).
• To test predictions from Quantum Electrodynamics (QED) and Quantum Chromodynamics (QCD).

Main Methods:

• Utilized the adapted DIRAC experiment at the CERN PS accelerator.
• Protons impacted a beryllium target, producing pionium atoms.
• Analyzed the dissociation of pionium atoms after traversing a platinum foil.

Main Results:

• Observed long-lived hydrogenlike pionium atoms for the first time.
• Measured the lifetime of the 2p state as τ₂p=(0.45⁻⁰.³⁰⁺¹·⁰⁸)×10⁻¹¹ s.
• This lifetime is three orders of magnitude longer than the ground state lifetime.

Conclusions:

• The measured 2p state lifetime is consistent with QED predictions.
• Further studies will enable discrimination between isoscalar and isotensor ππ scattering lengths.
• This research aims to check QCD predictions regarding pion interactions.