Isospin Violation in X(3872): Explanation From a New Tetraquark Model

TL;DR

This paper proposes a new tetraquark model for X(3872) that explains isospin violation in its decay, aligning with recent experimental data and suggesting specific tests for the model.

Contribution

A novel tetraquark isoscalar X(3872) model that accounts for isospin violation only in decay, consistent with recent B decay data.

Findings

X(3872) is an isoscalar resonance produced with conserved isospin.

Isospin violation occurs only in electromagnetic decay channels.

The narrow decay width is due to limited phase space for certain decay modes.

Abstract

New data for X(3872) production in B decays provide a separation between X production and decay, sharpen several experimental puzzles and impose serious constraints on all models. Both charged and neutral B decays produce a narrow neutral resonant state that decays to both J/\psi \rho and J/\psi \omega, while no charged resonances in the same multiplet are found. This suggests that the X is an isoscalar resonance whose production conserves isospin, while isospin is violated only in the decay by an electromagnetic interaction allowing the isospin-forbidden J/\psi \rho decay. A tetraquark isoscalar X model is proposed which agrees with all present data, conserves isospin in its production and breaks isospin only in an electromagnetic X(3872) --> J/\psi \rho^o decay. The narrow X decay width results from the tiny phase space available for the J/\psi \omega decay and enables competition with the electromagnetic isospin-forbidden J/\psi \rho decay which has much larger phase space. Experimental tests are proposed for this isospin production invariance.