1. First measurement of a long-lived $\pi^+ \pi^-$ atom lifetime
- Author
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Adeva, B., Afanasyev, L., Anania, A., Aogaki, S., Benelli, A., Brekhovskikh, V., Cechak, T., Chiba, M., Chliapnikov, P. V., 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, G. F., Vidal, A. Romero, Ryazantsev, A., Rykalin, V., Saborido, J., Schacher, J., Sidorov, A., Smolik, J., Takeutchi, F., Trojek, T., Trusov, S., Vrba, T., Yazkov, V., Yoshimura, Y., Zrelov, P., Adeva, B., Afanasyev, L., Anania, A., Aogaki, S., Benelli, A., Brekhovskikh, V., Cechak, T., Chiba, M., Chliapnikov, P. V., 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, G. F., Vidal, A. Romero, Ryazantsev, A., Rykalin, V., Saborido, J., Schacher, J., Sidorov, A., Smolik, J., Takeutchi, F., Trojek, T., Trusov, S., 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 hydrogen-like $\pi^+\pi^-$ atoms, produced by protons hitting a beryllium target. A part of these atoms crossed the gap of 96~mm and got broken up in the 2.1~\textmu{}m thick platinum foil. Analysing the observed number of atomic pairs, $n_A^L= \left.436^{+157}_{-61}\right|_\mathrm{tot}$, the lifetime of the 2$p$ state is found to be ${\tau_{2p}=(\left.0.45^{+1.08}_{-0.30}\right|_\mathrm{tot}) \cdot10^{-11}}$s, not contradicting the corresponding QED $2p$ state lifetime ${\tau_{2p}^\mathrm{QED}=1.17 \cdot 10^{-11}}$s. This lifetime value is three orders of magnitude larger than our previously measured value of the $\pi^+\pi^-$ atom ground state lifetime $\tau=(\left.3.15^{+0.28}_{-0.26}\right|_\mathrm{tot})\cdot 10^{-15}$s. Further studies of long-lived $\pi^+\pi^-$ atoms will allow to measure energy differences between $p$ and $s$ atomic states and so to determine $\pi\pi$ scattering lengths with the aim to check QCD predictions., Comment: 7 pages, 8 figures
- Published
- 2018
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