The mixing of $D_{s1}(2460)$ and $D_{s1}(2536)$

TL;DR

This paper investigates the mixing mechanism of the axial-vector mesons $D_{s1}(2460)$ and $D_{s1}(2536)$ using intermediate hadron loops, constructing a unitarity-respecting propagator matrix to extract their masses, widths, and mixing angles.

Contribution

It introduces a novel two-state mixing model incorporating hadron loop effects and complex mixing matrices, providing new insights into the mixing angles and mass shifts of these mesons.

Findings

Identified two poles corresponding to the mesons with specific masses and widths.

Determined large mixing angles for both states, influenced by complex matrix elements.

Constrained mixing angles using recent BaBar experimental data.

Abstract

The mixing mechanism of axial-vectors $D_{s1}(2460)$ and $D_{s1}(2536)$ is studied via intermediate hadron loops, e.g. $D^* K$, to which both states have strong couplings. By constructing the two-state mixing propagator matrix that respects the unitarity constraint and calculating the vertex coupling form factors in a chiral quark model, we can extract the masses, widths and mixing angles of the physical states. Two poles can be identified in the propagator matrix. One is at $\sqrt{s}=2454.5 \ \textrm{MeV}$ corresponding to $D_{s1}(2460)$ and the other at $\sqrt{s}=(2544.9-1.0i) \ \textrm{MeV}$ corresponding to $D_{s1}(2536)$. For $D_{s1}(2460)$, a large mixing angle $\theta=47.5^\circ$ between ${}^3P_1$ and ${}^1P_1$ is obtained. It is driven by the real part of the mixing matrix element and corresponds to $\theta'=12.3^\circ$ between the $j=1/2$ and $j=3/2$ state mixing in the heavy quark limit. For $D_{s1}(2536)$, a mixing angle $\theta=39.7^\circ$ which corresponds to $\theta'=4.4^\circ$ in the heavy quark limit is found. An additional phase angle $\phi=-6.9^\circ \sim 6.9^\circ$ is needed at the pole mass of $D_{s1}(2536)$ since the mixing matrix elements are complex numbers. Both the real and imaginary part are found important for the large mixing angle. We show that the new experimental data from BaBar provide a strong constraint on the mixing angle at the mass of $D_{s1}(2536)$, from which two values can be extracted, i.e. $\theta_1=32.1^\circ$ or $\theta_2=38.4^\circ$. Our study agrees well with the latter one. Detailed analysis of the mass shift procedure due to the coupled channel effects is also presented.