A Simple Explanation for the X(3872) Mass Shift Observed for Decay to D^{*0} {D^0}bar

TL;DR

The paper explains the observed 3 MeV mass shift of X(3872) in D*0 D0bar decay as a consequence of final state angular momentum effects near threshold, suggesting a spin-parity of 2-.

Contribution

It provides a simple threshold effect explanation for the mass shift and proposes spin-parity 2- for X(3872), based on decay width and angular momentum considerations.

Findings

Mass shift of ~3 MeV explained by angular momentum effects.

Spin-parity 2- is favored for X(3872).

Experimental resolution slightly increases the observed mass shift.

Abstract

We propose a simple explanation for the increase of approximately 3 MeV/c^2 in the mass value of the X(3872) obtained from D^{*0} {D^0}bar decay relative to that obtained from decay to J/psi pi+ pi-. If the total width of the X(3872) is 2-3 MeV, the peak position in the D^{*0} {D^0}bar invariant mass distribution is sensitive to the final state orbital angular momentum because of the proximity of the X(3872) to D^{*0} {D^0}bar threshold. We show that for total width 3 MeV and one unit of orbital angular momentum, a mass shift ~3 MeV/c^2 is obtained; experimental mass resolution should slightly increase this value. A consequence is that spin-parity 2^- is favored for the X(3872).