S-wave pi-K scattering length from lattice QCD

TL;DR

This study calculates the S-wave pi-K scattering lengths for isospin channels 1/2 and 3/2 using lattice QCD, providing results consistent with experimental signs and exploring quark-mass dependence and chiral theory limitations.

Contribution

First lattice QCD calculation of pi-K scattering lengths for both isospin channels with detailed analysis and comparison to experimental signs.

Findings

Signs of scattering lengths agree with experiment: attraction in I=1/2, repulsion in I=3/2

Quark-mass dependence of scattering lengths analyzed

Discussion on limitations of chiral perturbation theory

Abstract

The $S$-wave $\pi K$ scattering lengths are calculated for both the isospin 1/2 and 3/2 channels in the lattice QCD by using the finite size formula. We perform the calculation with $N_f=2+1$ gauge configurations generated on $32^3 \times 64$ lattice using the Iwasaki gauge action and nonperturbatively $O(a)$-improved Wilson action at $1/a = 2.17$ GeV. The quark masses correspond to $m_\pi = 0.30 - 0.70$ GeV. For $I=1/2$, to separate the contamination from excited states, we construct a $2 \times 2$ matrix of the time correlation function and diagonalize it. Here, we adopt the two kinds of operators, $\bar{s}u$ and $\pi K$. It is found that the signs of the scattering lengths are in agreement with experiment, namely attraction in $I=1/2$ and repulsion in $I=3/2$. We investigate the quark-mass dependence of the scattering lengths and also discuss the limitation of chiral perturbation theory.