Laser spectroscopy of pionic helium atoms

Area of Science:

• Atomic Physics
• Particle Physics
• Quantum Optics

Background:

• Charged pions (π⁻) are the lightest mesons, crucial for understanding fundamental forces.
• Mesonic atoms, where electrons are replaced by mesons, offer high-precision measurements.
• Previous attempts at laser spectroscopy of mesonic atoms were hindered by short lifetimes and low atom yields.

Purpose of the Study:

• To achieve laser spectroscopy on a novel, long-lived mesonic atom: metastable pionic helium (π⁴He⁺).
• To enable precise determination of meson properties and explore potential exotic forces.
• To establish a new experimental platform for meson studies using quantum optics techniques.

Main Methods:

• Synthesis of metastable pionic helium (π⁴He⁺) in a superfluid helium target.
• Laser excitation of the π⁻-occupied orbital transition (n, l) = (17, 16) → (17, 15) at 183,760 GHz.
• Detection of nuclear fission fragments (neutrons, protons, deuterons) following laser-induced resonance.

Main Results:

• Successfully synthesized and detected laser-induced resonance in metastable pionic helium (π⁴He⁺).
• Demonstrated the unique atomic structure of π⁴He⁺, free from hyperfine interactions.
• Confirmed the nanosecond-scale lifetime of π⁴He⁺, enabling laser spectroscopy.

Conclusions:

• This work overcomes previous limitations in mesonic atom spectroscopy.
• It establishes a new experimental paradigm for studying mesons using quantum optics.
• The findings pave the way for precise measurements of pion properties and constraints on new physics.