# ICHEP2018 SEOUL

Jul 4 – 11, 2018
COEX, SEOUL
Asia/Seoul timezone

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

Jul 6, 2018, 6:00 PM
15m
101 (COEX, Seoul)

### 101

#### COEX, Seoul

Parallel Strong Interactions and Hadron Physics

### Speaker

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

### Description

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

 abstract-DIRAC-2.docx abstract-DIRAC-2.pdf ICHEP2018-DIRAC-Afanasyev.pdf ICHEP2018-DIRAC-Afanasyev.pdf ICHEP2018-DIRAC-Afanasyev.pptx