More Like this

1. Low-lying baryon resonances from lattice QCD

   Bulava, J; Cid-Mora, B; Hanlon, A; Hoerz, B; Mohler, D; Morningstar, C; Moscoso, J; Nicholson, A; Romero-Lopez, F; Skinner, S; et al (June 2024, IL NUOVO CIMENTO C)

   Recent results studying the masses and widths of low-lying baryon resonances in lattice QCD are presented. The S-wave Nπ scattering lengths for both total isospins I = 1/2 and I = 3/2 are inferred from the finite-volume spectrum below the inelastic threshold together with the I = 3/2 P-wave containing the ∆(1232) resonance. A lattice QCD computation employing a combined basis of three-quark and meson-baryon interpolating operators with definite momentum to determine the coupled channel Σπ-NK scattering amplitude in the Λ(1405) region is also presented. Our results support the picture of a two-pole structure suggested by theoretical approaches based on SU(3) chiral symmetry and unitarity. 

   more » « less
2. Two-Pole Nature of the Lambda(1405) Resonance from Lattice QCD

   https://doi.org/10.1103/PhysRevLett.132.051901  

   Bulava, John; Cid-Mora, Bárbara; Hanlon, Andrew D.; Hörz, Ben; Mohler, Daniel; Morningstar, Colin; Moscoso, Joseph; Nicholson, Amy; Romero-López, Fernando; Skinner, Sarah; et al (January 2024, Physical Review Letters)

   This Letter presents the first lattice QCD computation of the coupled channel πΣ−¯KN scattering amplitudes at energies near 1405 MeV. These amplitudes contain the resonance Λ(1405) with strangeness S=−1 and isospin, spin, and parity quantum numbers I(JP)=0(1/2−). However, whether there is a single resonance or two nearby resonance poles in this region is controversial theoretically and experimentally. Using single-baryon and meson-baryon operators to extract the finite-volume stationary-state energies to obtain the scattering amplitudes at slightly unphysical quark masses corresponding to mπ≈200  MeV and mK≈487  MeV, this study finds the amplitudes exhibit a virtual bound state below the πΣ threshold in addition to the established resonance pole just below the ¯KN threshold. Several parametrizations of the two-channel K matrix are employed to fit the lattice QCD results, all of which support the two-pole picture suggested by SU(3) chiral symmetry and unitarity. 

   more » « less
3. I=3/2 Nπ scattering and the ∆(1232) resonance on $$N_f=2+1$$ CLS ensembles using the stochastic LapH method

   https://doi.org/10.22323/1.363.0039  

   Andersen, Christian Walther; Bulava, John; Hörz, Ben; Morningstar, Colin (January 2020, Proceedings of Science)

   Calculations of the elastic I=3/2 nucleon-pion scattering phase shifts on two lattice QCD ensembles with mπ=200MeV and 280MeV are presented. The ensembles both employ Nf=2+1 Wilson clover fermions. We determine the Δ(1232) resonance parameters from a finite volume scattering analysis. In one study the single partial wave simplification is employed to compute the p-wave amplitude while in the other we treat the partial wave mixing between s- and p-wave contributions. Fitting our data to a Breit-Wigner resonance model we find mΔ/mπ=7.13(9) and 4.75(5) on the two ensembles respectively, showing that for a lighter quark mass the resonance mass moves from near the Nπ threshold to near the Nππ threshold, in agreement with experiment. 

   more » « less
4. Progress on Meson-Baryon Scattering

   https://doi.org/10.22323/1.396.0170  

   C. Morningstar; J. Bulava; A. Hanlon; B. Hörz; D. Mohler; A. Nicholson; S. Skinner; A. Walker-Loud (January 2021, 38th International Symposium on Lattice Field Theory, LATTICE2021 26th-30th July, 2021)

   Progress in computing various meson-baryon scattering amplitudes is presented on a single en- semble from the Coordinated Lattice Simulations (CLS) consortium with m π = 200 MeV and Nf = 2 + 1 dynamical fermions. The finite-volume Lüscher approach is employed to determine the lowest few partial waves from ground- and excited-state energies computed from correla- tion matrices rotated in a single pivot using a generalized eigenvector solution. This analysis requires evaluating matrices of correlation functions between single- and two-hadron interpolat- ing operators which are projected onto definite spatial momenta and finite-volume irreducible representations. The stochastic LapH method is used to estimate all needed quark propagators. Preliminary results are presented for I = 1/2, 3/2 N π amplitudes including the ∆(1232) resonance and the I = 0 S-wave amplitude with unit strangeness relevant for the Λ(1405). 

   more » « less
5. Lattice QCD study of $\pi \mathrm{\Sigma }-\overline{K}N$ scattering and the $\mathrm{\Lambda }\left(1405\right)$ resonance

   https://doi.org/10.1103/PhysRevD.109.014511  

   Bulava, John; Cid-Mora, Bárbara; Hanlon, Andrew D.; Hörz, Ben; Mohler, Daniel; Morningstar, Colin; Moscoso, Joseph; Nicholson, Amy; Romero-López, Fernando; Skinner, Sarah; et al (January 2024, Physical Review D)

   A lattice QCD computation of the coupled channel πΣ–¯KN scattering amplitudes in the Λ(1405) region is detailed. Results are obtained using a single ensemble of gauge field configurations with Nf=2+1 dynamical quark flavors and mπ≈200  MeV and mK≈487  MeV. Hermitian correlation matrices using both single baryon and meson-baryon interpolating operators for a variety of different total momenta and irreducible representations are used. Several parametrizations of the two-channel scattering K-matrix are utilized to obtain the scattering amplitudes from the finite-volume spectrum. The amplitudes, continued to the complex energy plane, exhibit a virtual bound state below the πΣ threshold and a resonance pole just below the ¯KN threshold. 

   more » « less