Observation of π^{-}K^{+} and π^{+}K^{-} Atoms

Area of Science:

• Particle Physics
• Hadron Spectroscopy
• Quantum Chromodynamics

Background:

• The existence of hydrogenlike πK atoms, composed of pi and K mesons, has been a long-standing prediction in particle physics.
• Experimental evidence for these exotic atoms has been challenging to obtain due to their short lifetimes and production mechanisms.

Purpose of the Study:

• To provide the first statistically significant observation of the strange dimesonic πK atom.
• To confirm the existence of this exotic hadronic bound state experimentally.

Main Methods:

• Utilizing the upgraded DIRAC experiment at CERN's Super Proton Synchrotron (SPS).
• Producing πK atoms via the interaction of 24 GeV/c protons with platinum and nickel targets.
• Identifying πK atoms by detecting characteristic πK pairs resulting from their breakup (ionization) in the target material.
• Analyzing pairs with small relative momenta (Q) in their center-of-mass system.

Main Results:

• Observed 349±62 atomic πK pairs, indicative of πK atom breakup.
• Achieved a statistical significance of 5.6 standard deviations for the observed signal.
• This represents the first statistically significant evidence for the strange dimesonic πK atom.

Conclusions:

• The study presents the first definitive experimental evidence for the existence of the strange dimesonic πK atom.
• This observation validates theoretical predictions and opens new avenues for studying hadronic matter.
• The DIRAC experiment's upgraded capabilities were crucial for this significant discovery.