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ISSN - 15507998, Physical Review D - Particles, Fields, Gravitation and Cosmology, 2012, vol. 86, p. -

First study of η c(1S), η(1760) and X(1835) production via η ′π +π - final states in two-photon collisions

Zhang C. C., Aihara H., Asner D. M., Aushev T., Bakich A. M., Ban Y., Belous K., Bischofberger M., Browder T. E., Chen A., Cheon B. G., Chilikin K., Chistov R., Choi Y., Dalseno J., Danilov M., Eidelman S., Feindt M., Gaur V., Gabyshev N., Goh Y. M., Han Y. L., Hayashii H., Horii Y., Hou W. S., Hyun H. J., Iijima T., Inami K., Ishikawa A., Iwabuchi M., Julius T., Kiesling C., Kim H. O., Kim M. J., Kim Y. J., Ko B. R., Kodyš P., Korpar S., Krokovny P., Kuzmin A., Li J., Libby J., Liu Y., Liu Z. Q., Louvot R., Matvienko D., McOnie S., Mizuk R., Nakano E., Nakao M., Nakazawa H., Natkaniec Z., Nishida S., Ohshima T., Okuno S., Olsen S. L., Pakhlov P., Pakhlova G., Park H., Park H. K., Pestotnik R., Petrič M., Piilonen L. E., Röhrken M., Ryu S., Sahoo H., Sakai Y., Santel D., Sanuki T., Schneider O., Schwanda C., Sevior M. E., Shapkin M., Shebalin V., Shen C. P., Shibata T. A., Shiu J. G., Shwartz B., Smerkol P., Sohn Y. S., Solovieva E., Stanič S., Starič M., Sumihama M., Sumiyoshi T., Tikhomirov I., Uchida M., Uehara S., Uglov T., Unno Y., Uno S., Varner G., Vinokurova A., Vorobyev V., Wang P.

The invariant mass spectrum of the η ′π +π - final state produced in two-photon collisions is obtained using a 673fb -1 data sample collected in the vicinity of the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e +e - collider. We observe a clear signal of the η c(1S) and measure its mass and width to be M(η c(1S))=(2982.7±1.8(stat)±2.2(syst)±0.3(model)) MeV/c2 and Γ(η c(1S))=(37.8-5.3+5.8(stat)±2.8(syst) ±1.4(model))MeV/c2. The third error is an uncertainty due to possible interference between the η c(1S) and a nonresonant component. We also report the first evidence for η(1760) decay to η ′π +π -; we find two solutions for its parameters, depending on the inclusion or not of the X(1835), whose existence is of marginal significance in our data. From a fit to the mass spectrum using coherent X(1835) and η(1760) resonant amplitudes, we set a 90% confidence level upper limit on the product Γ γγB(η ′π +π -) for the X(1835). © 2012 American Physical Society.