Light Baryon Spectroscopy

Abstract

This review treats the advances in Light Baryon Spectroscopy of the last two decades, which were mainly obtained by measuring meson-production reactions at photon facilities all over the world. We provide a consistent compendium of experimental results, as well as a review of the theoretical methods of amplitude analysis used to analyze the data. The most significant datasets are presented in detail and are listed in combination with a full set of the relevant references. In addition, a brief summary of spin-formalisms, which are ubiquitous in Light Baryon Spectroscopy, as well as a review on complete experiments, are provided. The synthesis of the reviewed knowledge is presented in a full interpretation of the new results on the Light Baryon Spectrum.

Theory introduction to baryon spectroscopy

“…There is a wide spectrum of nonrelativistic and relativistic quark models, see e.g. [1,4,5,[12][13][14] for reviews, including quark models based on one-gluon exchange [11,15,16], Goldstone-boson exchange [17,18], diquark models [19][20][21], string models [22], large-N c models [23,24], hypercentral quark models [25,26], light-front and holographic models [27], and models based on Bethe-Salpeter equations [28,29].…”

“…Excited N and ∆ baryons have traditionally been extracted from N π scattering, but if they did not strongly couple to N π it would be hard to see their peaks in experimental cross sections. New photoproduction experiments and improved partial-wave analyses have indeed added several new states to the PDG [5], but the spectrum as of today (Fig. 1) is still quite sparse compared to what the quark model predicts.…”

“…O denotes the symmetry of the orbital part and SF the spin-flavor multiplets. The J P quantum numbers in bold color can be identified with well-established (two-, three-, four-star) states [4,5], whereas those in gray do not have good experimental candidates.…”

“…Because such approaches start from hadronic Lagrangians, the internal hadrons in the loop diagrams are in principle offshell, and one may distinguish 'bare' vs. 'dressed' states to quantify the effect of meson-baryon interactions. Multichannel amplitude analyses have been instrumental in the experimental extraction of the baryon spectrum, see [5,38,39] and references therein.…”

“…Light baryon spectroscopy has undergone much experimental progress in recent years [1][2][3][4][5]. Its theoretical description remains, however, challenging for several reasons.…”