Factorization in the Production and Decay of the X(3872)

The production and decay of the X(3872) are analyzed under the assumption that the X is a weakly-bound molecule of the charm mesons D^0 \bar D^{*0} and D^{*0} \bar D^0. The decays imply that the large D^0 \bar D^{*0} scattering length has an imaginary part. An effective field theory for particles with a large complex scattering length is used to derive factorization formulas for production rates and decay rates of X. If a partial width is calculated in a model with a particular value of the binding energy, the factorization formula can be used to extrapolate to other values of the binding energy and to take into account the width of the X. The factorization formulas relate the rates for production of X to those for production of D^0 \bar D^{*0} and D^{*0} \bar D^0 near threshold. They also imply that the line shape of X differs significantly from that of a Breit-Wigner resonance.Comment: 23 pages, 8 figures, revtex4, typos correcte

Pion Interactions in the X(3872)

We consider pion interactions in an effective field theory of the narrow resonance X(3872), assuming it is a weakly bound molecule of the charm mesons D^{0} \bar D^{*0} and D^{*0} \bar D^{0}. Since the hyperfine splitting of the D^{0} and D^{*0} is only 7 MeV greater than the neutral pion mass, pions can be produced near threshold and are non-relativistic. We show that pion exchange can be treated in perturbation theory and calculate the next-to-leading-order correction to the partial decay width \Gamma[X \to D^0 \bar D^{0} \pi^0].Comment: 26 pages, 11 figures, revtex4, to appear in Phys. Rev.

Production of the X(3872) in B Meson Decay by the Coalescence of Charm Mesons

If the recently-discovered charmonium state X(3872) is a loosely-bound S-wave molecule of the charm mesons \bar D^0 D^{*0} or \bar D^{*0} D^0, it can be produced in B meson decay by the coalescence of charm mesons. If this coalescence mechanism dominates, the ratio of the differential rate for B^+ \to \bar D^0 D^{*0} K^+ near the \bar D^0 D^{*0} threshold and the rate for B^+ \to X K^+ is a function of the \bar D^0 D^{*0} invariant mass and hadron masses only. The identification of the X(3872) as a \bar D^0 D^{*0}/\bar D^{*0} D^0 molecule can be confirmed by observing an enhancement in the \bar D^0 D^{*0} invariant mass distribution near the threshold. An estimate of the branching fraction for B^+ \to X K^+ is consistent with observations if X has quantum numbers J^{PC} = 1^{++} and if J/\psi \pi^+ \pi^- is one of its major decay modes.Comment: 4 pages, 3 figures, revtex

Simple test for high Jc and low Rs superconducting thin films

A simple method, fishing high-Tc superconductor thin films out of liquid nitrogen bath by a permanent magnet (field > Hc1) due to the effect of high flux pinning, has been suggested to identify films having high critical current density (Jc > 106 A/cm2 at 77 K) and thus a low microwave surface resistance (Rs). We have demonstrated that a Nd-Fe-B magnet, having a maximum field of ~ 0.5 T, could fish out Tl-1223 superconducting thin films on LSAT substrate with a thickness of ~ 5000 Angstrong having Jc > 1 MA/cm2 (at 77 K) whereas it could not fish out other films with Jc < 0.1 MA/cm2 at 77 K. The fished out films exhibit Rs values 237 - 245 ((at 77 K and 10 GHz, which is lower than that (Rs = 317 (() of the best YBCO film at the same temperature and frequency. On the other hand, the non-fishable films show very high Rs values. This method is a very simple tool to test for high Jc and good microwave properties of superconducting films of large area which otherwise require a special and expensive tool.Comment: 5 pages including 2 figures, to be published as Rapid Commun. in Supercond. Sci. Techno