Bound state nature of the exotic Zb states

The assumption that the newly observed charged bottomonia states Z(b)(10610) and Z(b)(10650) are of molecular nature is confronted with the measured invariant-mass distributions for the transitions of the Y(5S) to the final states h(b)pi(+)pi(-) and h(b)(2P)pi(+)pi(-). It is shown that the assumption that the Z(b)(10610) and Z(b)(10650) are B (B) over bar* + c.c. and B*(B) over bar* bound states, respectively, with very small binding energies is consistent with the data. The calculation is based on a power counting for bottom meson loops, which is explicitly given up to two-loop in the framework of a nonrelativistic effective-field theory. We also show that if the Z(b) states are of molecular nature, then the data should not be analyzed by using a Breit-Wigner parametrization.