# Discerning the two $K_1(1270)$ poles in $D^0\to \pi^+ V P$ decay

## TL;DR

This paper investigates the two-pole structure of the $K_1(1270)$ resonance within the $D^0 o ext{pi}^+ VP$ decay, proposing experimental channels to observe the distinct poles based on their different couplings.

## Contribution

It introduces a theoretical analysis of how the two-pole nature of $K_1(1270)$ can be observed in $D^0$ decays through invariant mass distributions of specific $VP$ channels.

## Key findings

- Different $VP$ channels are sensitive to each pole of $K_1(1270)$.
- Final $ar K^* ext{pi}$ and $
ho ar K$ channels can reveal the two-pole structure.
- The study suggests experimental reactions to identify the double-pole nature.

## Abstract

Within the chiral unitary approach, the axial-vector resonance $K_1(1270)$ has been predicted to manifest a two-pole nature. The lowest pole has a mass of 1195 Mev and a width of 246 Mev and couples mostly to $K^*\pi$, and the highest pole has a mass of 1284 Mev and a width of 146 Mev and couples mostly to $\rho K$. We analyze theoretically how this double-pole structure can show up in the $D^0\to \pi^+ VP$ decays by looking at the vector-pseudoscalar ($VP$) invariant mass distribution for different $VP$ channels, exploiting the fact that each pole couples differently to different $VP$ pairs. We find that the final $\bar K^*\pi$ and $\rho \bar K$ channels are sensible to the different poles of the $K_1(1270)$ resonance and hence are suitable reactions to analyze experimentally the double pole nature of this resonance.