The sigma-meson production in excited Upsilon decay processes: constraint from chiral symmetry

In the recent letter [T. Komada, M. Ishida, S. Ishida, Phys. Lett. B 508 (2 001) 31], hereafter referred to as I, we have shown that the pi pi mass spe ctra in various excited Y decay processes are phenomenologically well repro duced by a coherent sum of a Breit-Wigner amplitude and of the direct 2 pi -production amplitude. On the other hand, the pi pi -production amplitude w as widely believed to be suppressed generally near the threshold, because o f the derivative coupling property of Nambu-Goldstone pi meson. In this Let ter we show that the "threshold-suppression" does not hold in the process w ith large energy release, in conformity with the steep increase from the pi pi threshold observed in the transition Y(3S --> IS), and that the method of I is consistent with chiral symmetry. Furthermore, applying an effective amplitude explicitly consistent with chiral symmetry, we reanalyze the typ ical pi pi -spectra. (C) 2001 Elsevier Science B.V. All rights reserved.