Excited baryons from Bayesian priors and overlap fermions

Abstract

Using the constrained-fitting method based on Bayesian priors, we extract the masses of the two lowest states of octet and decuplet baryons with both parities. The calculation is done on quenched 163 × 28 lattices of a = 0.2 fm using an improved gauge action and overlap fermions, with the pion mass as low as 180 MeV. The rich structure of the excited baryon spectrum, as documented by the particle data group [1], provides a fertile ground for exploring the nature of quark-quark interactions. One outstanding example is the ordering of the lowestlying states which has the order of positive and negative-parity excitations inverted between N , ∆ and Λ channels. Conventional quark models have difficulty explaining the ordering in a consistent manner. There are two contrasting views. One is from the constituent quark model [2,3] which has the interaction dominated by onegluon-change type, i.e., color-spin λ c

Structure and flow of the nucleon eigenstates in lattice QCD

“…(15). However access to the excited state masses requires additional effort due to the presence of these energy states at the subleading of the exponential.…”

“…For example, the Roper resonance has been described as a hybrid baryon with explicitly excited gluon field configurations [5,6], or as a breathing mode of the ground state [7] or as a five quark (meson-baryon) state [8]. Significant resources have been devoted in the past from the lattice QCD perspective to find the elusive low-lying Roper state, in both quenched [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] and in full [26][27][28][29][30] QCD.…”

Nucleon excited state wave functions from lattice QCD

“…Robust methods have been developed that allow the isolation and study of the states associated with these resonances in lattice QCD [2,[10][11][12][13][14][15][16][17][18][19][20]. In this study, we apply the variational method [21,22] to extract the ground state and first three P 11 excited states of the proton associated with the Roper [3] and other higher energy P 11 states.…”

Isolating excited states of the nucleon in lattice QCD

“…[8] using Wilson fermions and an operator product expansion spectral ansatz. Since then several attempts have been made to address these issues in the lattice framework [9][10][11][12][13][14][15][16], but in many cases no potential identification of the Roper state has been made [9][10][11][12][13]. Recently however, in the analysis of [14,15,17], a lowlying Roper state has been observed by using advanced fitting techniques [18,19] based on Bayesian priors.…”