Speaker: Leonid Nemenonv The π-π atom lifetime and π-π scattering lengths have been measured in the experiment DIRAC at CERN. The results, published in 2011, have been obtained by investigating more than 21000 π pairs from ionizing π-π atoms (atomic pairs). In 2010 the DIRAC collaboration has finished data taking to observe K+π- and K-π+ atoms and to measure their lifetime and K-π scattering lengths. Simultaneously, DIRAC has collected additional 21000 π-π atomic pairs, which are used at present for calibration. This data allows also to estimate the K+K- atom yield. The experimental results on K-π and π-π atoms will be presented. In 2012 the data taking of a further π-π atom study, the observation of long-lived π-π atoms, has been completed. Such an observation opens the possibility to measure the Lamb shift of the π-π atom and to extract another combination of π-π scattering lengths. Moreover, the Lamb shift and the resulting π-π scattering length measurement can be done, in principal, with a precision significantly better compared with existing experimental methods. On the theoretical side, lattice calculations will, in near future, improve the π-π scattering length accuracy. Therefore, the proposed Lamb shift measurement is the unique possibility, to check "Low Energy QCD". The methods to measure the Lamb shift and the dedicated DIRAC experiment will be presented. All the experimental studies of π-π and K-π atoms have been performed at the CERN PS, using the 24 GeV/c proton beam. Furthermore, it will be pointed out that the yield of K-π atoms (ππ atoms) will increase by about 30 (17) times for 450 GeV/c protons (CERN SPS) and dedicated angles, what allows a much more precise investigation of the K-π atom and the π-π atom Lamb shift. |
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