Experimental estimation of the lifetime of atoms formed by π+ and π− mesons

Inquiry for the π+-π− bound state conversion into two π0's as being due to the Weinberg π-π interaction

“…Our result proves do not contradict the up to now estimation τ = 2.9 +∞ −2.1 ·10 −15 sec set out in Ref. [17]. It might be instructive to recall the results of τ calculation obtained in the previous investigations, surveyed in Section 2, appear to be some smaller as compare to our one.…”

First πK atom lifetime and πK scattering length measurements

“…6 presents the π + K − Coulomb peak at Q L = 0 and a second weaker peak from Λ decays at Q L = 30 MeV/c. 5 The final analysis sample contains only events which fulfil the following criteria: …”

“…The relative yield of atoms to Coulomb pairs [22] is given by the ratio of (4) to (5). The total number N A of produced π K atoms is determined by the model-independent relation (6) where N C (q ≤ q 0 ) is the number of Coulomb pairs with relative momenta q ≤ q 0 and k(q 0 ) a known function of q 0 .…”

“…Pion-pion interaction at low energy is the simplest hadron-hadron process. The observation of dimesonic π + π − atoms (pionium) has been reported in [5] and a measurement of their lifetime in [6].…”

Observation of πK-atoms with DIRAC-II

“…The mean life of the atoms can then be calculated from the number of observed low-momentum pairs. This method was first proposed in 1985 [8] and was successfully applied to π + π − -atoms (measurement of A 2π ) in Serpukhov on the U-70 synchrotron internal proton beam [3,9], and with DIRAC-I at the CERN-PS on beam line T8 [3]. Data from DIRAC-I lead to a mean life τ 2π = (2.91± 0.49 0.62 ) fs for π + π − -atoms [3].…”