Measurement of the dipion mass spectrum in X(3872)→J/ψπ+π- decays

Abstract

We measure the dipion mass spectrum in X(3872)→J/ψπ+π- decays using 360pb-1 of p̄p collisions at s=1.96TeV collected with the CDFÂ II detector. The spectrum is fit with predictions for odd C-parity (S13, P11, and DJ3) charmonia decaying to J/ψπ+π-, as well as even C-parity states in which the pions are from ρ0 decay. The latter case also encompasses exotic interpretations, such as a D0D̄*0 molecule. Only the S13 and J/ψρ hypotheses are compatible with our data. Since S13 is untenable on other grounds, decay via J/ψρ is favored, which implies C=+1 for the X(3872). Models for different J/ψ-ρ angular momenta L are considered. Flexibility in the models, especially the introduction of ρ-ω interference, enables good descriptions of our data for both L=0 and 1. © 2006 The American Physical Society