Jul 4 – 11, 2018
Asia/Seoul timezone

Experimental Investigation of π+π− and K+K− atoms

Jul 6, 2018, 6:00 PM
101 (COEX, Seoul)


COEX, Seoul

Parallel Strong Interactions and Hadron Physics Strong Interactions and Hadron Physics


Leonid Afanasyev (Joint Institute for Nuclear Research (RU))


The DIRAC experiment at the CERN PS accelerator observed for the first time the long-lived hydrogenlike π+π− atoms. Atoms were produced by PS proton beam on the Be target. Part of the atoms in the long-lived states crossed the gap of 96 mm and then broken in the Platinum foil of 2.1 µm. producing π+π− pairs(atomic pairs). From the analysis of the $n_A^L = 436_{-61}^{+157}$ observed atomic pairs the lifetime of 2p state was evaluated to $\tau_{2P} = 0.22_{-0.18}^{+1.55} \times 10^{-11}$ s. This value of the long-lived atom lifetime is on the three order of magnitude more than our measured value of the atom ground state lifetime $\tau_{1S} = 3.15_{-0.26}^{+0.28} \times 10^{-15}$ s and do not contradicts to the QED value $\tau_{2P} = 1.17 \times 10^{-11}$ s. Further study of long-lived π+π− atoms will allow to measure the energy differences between p and s atomic states, to determine ππ scattering lengths and check the precise QCD predictions for these parameters.

On the same setup there were identified more than 7000 K+K- pairs with effective mass less than 2MK + 5Mev. In the distributions of K+K– pairs there is a strong signature of the Coulomb enhancement: the pairs number is increasing with the decreasing of the relative momentum in the pair c.m.s. The observed number of K+K– pairs with small relative momentum allows us to evaluate for the first time the number of K+K– atoms produced simultaneously with this pairs.

Primary author

Leonid Afanasyev (Joint Institute for Nuclear Research (RU))

Presentation materials