Pionic Hydrogen
collaboration © 2007

Webmaster: D.Gotta

Design: M.Nekipelov


Pionic Hydrogen

Measurement of the strong interaction width and shift of the ground state

"QCD Lamb shift"

Physics interest:

  • Precise determination of the pion-nucleon scattering lengths.
  • Extraction of the pion-nucleon coupling constant
    and the pion-nucleon σ-term.
  • The pionic deuterium level shift reveals isospin breaking effects by constraining the scattering lengths as obtained from pionic hydrogen.
  • The pionic deuterium ground state width is dominated by true absorption and directly related to pion production strength α at threshold.


  • To measure the strong interaction width Γ and shift ε of the ground state of pionic hydrogen with high precision better than 1% for the shift and about 2% for the width.


  • Use the PSI cyclotron trap to produce pionic atoms in a controlled environment.
  • Use crystal spectrometers and CCD detectors to measure precisely the X-ray energies and line shapes.
  • Perform measurements at different hydrogen densities.
  • Perform measurements for different transitions.
  • Perform measurements of muonic hydrogen to quantify the Doppler broadening of X-ray lines from Coulomb explosion.
  • Correlate cascade theory to the Doppler broadening corrections.

Atomic cascade in pionic hydrogen:


Preliminary results

ε1s /meV Γ1s / meV α / μb
πH 823 ± 19 --- 2006

Final results

πH + 7086 ± 10 --- 2014
πD - 2356 ± 31 1171 +23/-49 251 +5/-11 2010


Related experiments:

  • Precise determination of the charged pion mass.
  • Fluorescence X-rays.