Measurement of the Dipion Mass Spectrum in X(3872) -> J/Psi Pi+ Pi- Decays

TL;DR

This study measures the dipion mass spectrum in X(3872) decays to determine its quantum numbers, finding evidence favoring a C=+1 assignment consistent with a J/Psi Rho decay hypothesis.

Contribution

The paper provides the first detailed dipion mass spectrum measurement in X(3872) decays, constraining its quantum numbers and supporting the J/Psi Rho decay mode over other hypotheses.

Findings

Data favors J/Psi Rho decay hypothesis

Supports C=+1 quantum number assignment for X(3872)

Models with Rho-Omega interference fit the data well

Abstract

We measure the dipion mass spectrum in X(3872)--> J/Psi Pi+ Pi- decays using 360 pb-1 of pbar-p collisions at 1.96 TeV collected with the CDF II detector. The spectrum is fit with predictions for odd C-parity (3S1, 1P1, and 3DJ) charmonia decaying to J/Psi Pi+ Pi-, as well as even C-parity states in which the pions are from Rho0 decay. The latter case also encompasses exotic interpretations, such as a D0-D*0Bar molecule. Only the 3S1 and J/Psi Rho hypotheses are compatible with our data. Since 3S1 is untenable on other grounds, decay via J/Psi Rho is favored, which implies C=+1 for the X(3872). Models for different J/Psi-Rho angular momenta L are considered. Flexibility in the models, especially the introduction of Rho-Omega interference, enable good descriptions of our data for both L=0 and 1.