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Decay width of light quark hybrid meson from the lattice

C. McNeile, C. Michael

TL;DR

This study uses $N_f=2$ lattice QCD to investigate the spectrum and decays of the light-quark spin-exotic hybrid meson with $J^{PC}=1^{-+}$. By validating S-wave decay extraction on the benchmark $b_1 \to \omega \pi$, the authors then determine the mass and decay amplitudes of the hybrid using stochastic volume sources and non-local hybrid operators. They report a hybrid mass of about $2.2(2)\,$GeV and, for the decays to $\pi b_1$ and $\pi f_1$, effective couplings leading to partial widths of roughly $400(120)\,$MeV and $90(60)\,$MeV, respectively, implying a sizable total width. The results indicate significant mixing with open two-body channels in dynamical fermion simulations, highlighting systematic uncertainties but providing quantitative predictions (notably dominant $\pi b_1$ decay) to guide experimental investigations.

Abstract

Lattice QCD with $N_f=2$ flavours of sea quark is used to explore the spectrum and decay of a $J^{PC}=1^{-+}$ spin-exotic hybrid meson. We test lattice determination of S-wave decay amplitudes at threshold using $b_1 \to πω$ where agreement with data is found. We find a hybrid meson state at 2.2(2) GeV with a partial width to $πb_1$ of 400(120) MeV and to $πf_1$ of 90(60) MeV.

Decay width of light quark hybrid meson from the lattice

TL;DR

This study uses lattice QCD to investigate the spectrum and decays of the light-quark spin-exotic hybrid meson with . By validating S-wave decay extraction on the benchmark , the authors then determine the mass and decay amplitudes of the hybrid using stochastic volume sources and non-local hybrid operators. They report a hybrid mass of about GeV and, for the decays to and , effective couplings leading to partial widths of roughly MeV and MeV, respectively, implying a sizable total width. The results indicate significant mixing with open two-body channels in dynamical fermion simulations, highlighting systematic uncertainties but providing quantitative predictions (notably dominant decay) to guide experimental investigations.

Abstract

Lattice QCD with flavours of sea quark is used to explore the spectrum and decay of a spin-exotic hybrid meson. We test lattice determination of S-wave decay amplitudes at threshold using where agreement with data is found. We find a hybrid meson state at 2.2(2) GeV with a partial width to of 400(120) MeV and to of 90(60) MeV.

Paper Structure

This paper contains 9 sections, 4 equations, 4 figures, 3 tables.

Table of Contents

  1. Introduction
  2. Lattice methods
  3. Stochastic method
  4. Lattice configurations and two point correlators
  5. Transition $b_1 \to \omega \pi$
  6. Hybrid meson decay
  7. Discussion
  8. Conclusions
  9. Acknowledgements

Figures (4)

  • Figure 1: Effective mass (from $t:(t-a)$) of the $J^{PC}=1^{-+}$ hybrid meson in lattice units from a $2\times 3$ matrix of correlators for U355. The fit described in the text is illustrated.
  • Figure 2: Normalised ratio $R(t)$ of transition $b_1 \to \pi \omega$ at time $t$ in lattice units (a factor of $(12/16)^{3/2}$ has been included for the U395 12 data set). The continuous (dotted) straight lines represent fits to the expected behaviour for U355 (C410) and their slopes ($xa$) are related to the effective coupling constant $\overline{g}$ as described in the text.
  • Figure 3: Effective coupling of transition $b_1 \to \pi \omega$ evaluated from the slope in fig. 2 at time $t/r_0=1$ for different lattices with different pion masses (in units of $r_0 \approx 0.5$ fm). The strange quark mass corresponds to $(m(\pi)r_0)^2 \approx 3.4$.
  • Figure 4: Normalised ratio of $\hat{\rho} \to b_1 \pi$ and $\hat{\rho} \to f_1 \pi$. The operator used for $\hat{\rho}$ is either U-bends of size 2 or 3 (H2 or H3) or the same combined with fuzzing (FH2 or FH3). The $\pi$ and axial meson are always fuzzed. The straight lines represent the trend of the data: the slope ($xa$) is the quantity required.