Measurement of radiative widths of $a_2(1320)$ and $π_2(1670)$
C. Adolph, R. Akhunzyanov, M. G. Alekseev, G. D. Alexeev, A. Amoroso, V. Andrieux, V. Anosov, A. Austregesilo, B. Badelek, F. Balestra, J. Barth, G. Baum, R. Be… 展开作者
C. Adolph, R. Akhunzyanov, M. G. Alekseev, G. D. Alexeev, A. Amoroso, V. Andrieux, V. Anosov, A. Austregesilo, B. Badelek, F. Balestra, J. Barth, G. Baum, R. Beck, Y. Bedfer, A. Berlin, J. Bernhard, K. Bicker, J. Bieling, R. Birsa, J. Bisplinghoff, M. Bodlak, M. Boer, P. Bordalo, F. Bradamante, C. Braun, A. Bressan, M. Buechele, E. Burtin, L. Capozza, M. Chiosso, S. U. Chung, A. Cicuttin, M. L. Crespo, Q. Curiel, S. Dalla Torre, S. S. Dasgupta, S. Dasgupta, O. Yu. Denisov, S. V. Donskov, N. Doshita, V. Duic, W. Duennweber, M. Dziewiecki, A. Efremov, C. Elia, P. D. Eversheim, W. Eyrich, M. Faessler, A. Ferrero, A. Filin, M. Finger, M. Finger~jr., H. Fischer, C. Franco, N. du~Fresne~von~Hohenesche, J. M. Friedrich, V. Frolov, F. Gautheron, O. P. Gavrichtchouk, S. Gerassimov, R. Geyer, I. Gnesi, B. Gobbo, S. Goertz, M. Gorzellik, S. Grabmueller, A. Grasso, B. Grube, A. Guskov, T. Guthoerl, F. Haas, D. von Harrach, D. Hahne, R. Hashimoto, F. H. Heinsius, F. Herrmann, F. Hinterberger, Ch. Hoeppner, N. Horikawa, N. d'Hose, S. Huber, S. Ishimoto, A. Ivanov, Yu. Ivanshin, T. Iwata, R. Jahn, V. Jary, P. Jasinski, P. Joerg, R. Joosten, E. Kabuss, B. Ketzer, G. V. Khaustov, Yu. A. Khokhlov, Yu. Kisselev, F. Klein, K. Klimaszewski, J. H. Koivuniemi, V. N. Kolosov, K. Kondo, K. Koenigsmann, I. Konorov, V. F. Konstantinov, A. M. Kotzinian, O. Kouznetsov, Z. Kral, M. Kraemer, Z. V. Kroumchtein, N. Kuchinski, F. Kunne, K. Kurek, R. P. Kurjata, A. A. Lednev, A. Lehmann, S. Levorato, J. Lichtenstadt, A. Maggiora, A. Magnon, N. Makke, G. K. Mallot, C. Marchand, A. Martin, J. Marzec, J. Matousek, H. Matsuda, T. Matsuda, G. Meshcheryakov, W. Meyer, T. Michigami, Yu. V. Mikhailov, Y. Miyachi, A. Nagaytsev, T. Nagel, F. Nerling, S. Neubert, D. Neyret, V. I. Nikolaenko, J. Novy, W. -D. Nowak, A. S. Nunes, I. Orlov, A. G. Olshevsky, M. Ostrick, R. Panknin, D. Panzieri, B. Parsamyan, S. Paul, M. Pesek, S. Platchkov, J. Pochodzalla, V. A. Polyakov, J. Pretz, M. Quaresma, C. Quintans, S. Ramos, G. Reicherz, E. Rocco, A. Rychter, N. S. Rossiyskaya, D. I. Ryabchikov, V. D. Samoylenko, A. Sandacz, S. Sarkar, I. A. Savin, G. Sbrizzai, P. Schiavon, C. Schill, T. Schlueter, A. Schmidt, K. Schmidt, H. Schmieden, K. Schoenning, S. Schopferer, M. Schott, O. Yu. Shevchenko, L. Silva, L. Sinha, S. Sirtl, M. Slunecka, S. Sosio, F. Sozzi, A. Srnka, L. Steiger, M. Stolarski, M. Sulc, R. Sulej, H. Suzuki, A. Szabelski, T. Szameitat, P. Sznajder, S. Takekawa, J. ter~Wolbeek, S. Tessaro, F. Tessarotto, F. Thibaud, S. Uhl, I. Uman, M. Vandenbroucke, M. Virius, J. Vondra, L. Wang, T. Weisrock, M. Wilfert, R. Windmolders, H. Wollny, K. Zaremba, M. Zavertyaev, E. Zemlyanichkina, M. Ziembicki.
The COMPASS Collaboration at CERN has investigated the reaction $π^- γ\rightarrow π^-π^-π^+$ embedded in the Primakoff reaction of $190~\textrm{GeV}$ pions scattering in the Coulomb field of a lead target, $π^- \text{Pb} \rightarrow π^-π^-π^+ \text{Pb}$. Exchange of quasi-real photons is selected by isolating the sharp Coulomb peak observed at momentum transfer below $0.001~(\text{GeV}/c)^2$. Using a partial-wave analysis the amplitudes and relative phases of the $a_2(1320)$ and $π_2(1670)$ mesons have been extracted, and the Coulomb and the diffractive contributions have been disentangled. Measuring absolute production cross sections we have determined the radiative width of the $a_2(1320)$ to be $Γ_0(a_2(1320) \rightarrow πγ) = (358 \pm 6_{\textrm{stat}} \pm 42_{\textrm{syst}})~\textrm{keV}$. As the first measurement, $Γ_0(π_2(1670) \rightarrow πγ) = (181 \pm 11_{\textrm{stat}} \pm 27_{\textrm{syst}})~\textrm{keV} \cdot (\textrm{BR}^{\textrm{PDG}}_{f_2 π}/\textrm{BR}_{f_2 π})$ is obtained for the radiative width of the $π_2(1670)$, where in this analysis the branching ratio $\textrm{BR}^{\textrm{PDG}}_{f_2 π}=0.56$ has been used. We compare these values to previous measurements and theoretical predictions.
