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arXiv · 1501.05732

Observation of a new narrow axial-vector meson $a_1(1420)$

C. Adolph·R. Akhunzyanov·M. G. Alexeev·G. D. Alexeev·A. Amoroso·V. Andrieux·V. Anosov·A. Austregesilo·C. Azevedo·B. Badelek·F. Balestra·J. Barth·R. Beck·Y. Bedfer·J. Bernhard·K. Bicker·E. R. Bielert·R. Birsa·J. Bisplinghoff·M. Bodlak·M. Boer·P. Bordalo·F. Bradamante·C. Braun·A. Bressan·M. Buechele·E. Burtin·W. -C. Chang·M. Chiosso·I. Choi·S. U. Chung·A. Cicuttin·M. L. Crespo·Q. Curiel·S. Dalla Torre·S. S. Dasgupta·S. Dasgupta·O. Yu. Denisov·L. Dhara·S. V. Donskov·N. Doshita·W Duennweber·V. Duic·M. Dziewiecki·A. Efremov·P. D. Eversheim·W. Eyrich·M. Faessler·A. Ferrero·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·I. Gnesi·M. Gorzellik·S. Grabmueller·A. Grasso·M. Grosse-Perdekamp·B. Grube·T. Grussenmeyer·A. Guskov·F. Haas·D. Hahne·D. von Harrach·R. Hashimoto·F. H. Heinsius·F. Herrmann·F. Hinterberger·N. Horikawa·N. d'Hose·C. -Yu Hsieh·S. Huber·S. Ishimoto·A. Ivanov·Yu. Ivanshin·T. Iwata·R. Jahn·V. Jary·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
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Abstract

The COMPASS collaboration at CERN has measured diffractive dissociation of 190 GeV/$c$ pions into the $\pi^-\pi^-\pi^+$ final state using a stationary hydrogen target. A partial-wave analysis (PWA) was performed in bins of $3\pi$ mass and four-momentum transfer using the isobar model and the so far largest PWA model consisting of 88 waves. A narrow $J^{PC} = 1^{++}$ signal is observed in the $f_0(980)\,\pi$ channel. We present a resonance-model study of a subset of the spin-density matrix selecting $3\pi$ states with $J^{PC} = 2^{++}$ and $4^{++}$ decaying into $\rho(770)\,\pi$ and with $J^{PC} = 1^{++}$ decaying into $f_0(980)\,\pi$. We identify a new $a_1$ meson with mass $(1414^{+15}_{-13})$ MeV/$c^2$ and width $(153^{+8}_{-23})$ MeV/$c^2$. Within the final states investigated in our analysis, we observe the new $a_1(1420)$ decaying only into $f_0(980)\,\pi$, suggesting its exotic nature.

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C. Adolph, R. Akhunzyanov, M. G. Alexeev, G. D. Alexeev, A. Amoroso, V. Andrieux, V. Anosov, A. Austregesilo, C. Azevedo, B. Badelek, F. Balestra, J. Barth, R. Beck, Y. Bedfer, J. Bernhard, K. Bicker, E. R. Bielert, R. Birsa, J. Bisplinghoff, M. Bodlak, M. Boer, P. Bordalo, F. Bradamante, C. Braun, A. Bressan, M. Buechele, E. Burtin, W. -C. Chang, M. Chiosso, I. Choi, S. U. Chung, A. Cicuttin, M. L. Crespo, Q. Curiel, S. Dalla Torre, S. S. Dasgupta, S. Dasgupta, O. Yu. Denisov, L. Dhara, S. V. Donskov, N. Doshita, W Duennweber, V. Duic, M. Dziewiecki, A. Efremov, P. D. Eversheim, W. Eyrich, M. Faessler, A. Ferrero, 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, I. Gnesi, M. Gorzellik, S. Grabmueller, A. Grasso, M. Grosse-Perdekamp, B. Grube, T. Grussenmeyer, A. Guskov, F. Haas, D. Hahne, D. von Harrach, R. Hashimoto, F. H. Heinsius, F. Herrmann, F. Hinterberger, N. Horikawa, N. d'Hose, C. -Yu Hsieh, S. Huber, S. Ishimoto, A. Ivanov, Yu. Ivanshin, T. Iwata, R. Jahn, V. Jary, 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. 2015-01-23. Observation of a new narrow axial-vector meson $a_1(1420)$. https://doi.org/10.1103/physrevlett.115.082001

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