1. First Measurement of a Long-Lived π^{+}π^{-} Atom Lifetime.
- Author
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Adeva B, Afanasyev L, Anania A, Aogaki S, Benelli A, Brekhovskikh V, Cechak T, Chiba M, Chliapnikov PV, Doskarova P, Drijard D, Dudarev A, Dumitriu D, Fluerasu D, Gorin A, Gorchakov O, Gritsay K, Guaraldo C, Gugiu M, Hansroul M, Hons Z, Horikawa S, Iwashita Y, Karpukhin V, Kluson J, Kobayashi M, Kruglov V, Kruglova L, Kulikov A, Kulish E, Lamberto A, Lanaro A, Lednicky R, Mariñas C, Martincik J, Nemenov L, Nikitin M, Okada K, Olchevskii V, Ovsiannikov V, Pentia M, Penzo A, Plo M, Prusa P, Rappazzo GF, Romero Vidal A, Ryazantsev A, Rykalin V, Saborido J, Schacher J, Sidorov A, Smolik J, Takeutchi F, Trojek T, Trusov S, Urban T, Vrba T, Yazkov V, Yoshimura Y, and Zrelov P
- Abstract
The adapted DIRAC experiment at the CERN PS accelerator observed for the first time long-lived hydrogenlike π^{+}π^{-} atoms, produced by protons hitting a beryllium target. A part of these atoms crossed the gap of 96 mm between the target and a 2.1 μm thick platinum foil, in which most of them dissociated. Analyzing the observed number of atomic pairs, n_{A}^{L}=436_{-61}^{+157}|_{tot}, the lifetime of the 2p state is found to be τ_{2p}=(0.45_{-0.30}^{+1.08}|_{tot})×10^{-11} s, not contradicting the corresponding QED 2p state lifetime τ_{2p}^{QED}=1.17×10^{-11} s. This lifetime value is three orders of magnitude larger than our previously measured value of the π^{+}π^{-} atom ground state lifetime τ=(3.15_{-0.26}^{+0.28}|_{tot})×10^{-15} s. Further studies of long-lived π^{+}π^{-} atoms will allow us to measure energy differences between p and s atomic states and so to discriminate between the isoscalar and isotensor ππ scattering lengths with the aim to check QCD predictions.
- Published
- 2019
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