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Atoms, consisting of π+π-, K+π- or K-π+, as a tool to check precise "Low Energy QCD" predictions

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.
Monica Tecchio,
May 2, 2013, 12:56 PM