Hadron Spectroscopy at CLAS and the Evolution of Strong Degrees of Freedom

Gothe, R. W.

doi:10.1016/j.nuclphysbps.2009.01.019

Title: Hadron Spectroscopy at CLAS and the Evolution of Strong Degrees of Freedom

Conference · Sun Feb 01 00:00:00 EST 2009

DOI:https://doi.org/10.1016/j.nuclphysbps.2009.01.019· OSTI ID:2001051

Gothe, R. W.

Understanding the strong force constitutes one of the biggest challenges in fundamental science that we can and have to tackle now as the needed experimental and theoretical tools become available. Perturbative Quantum ChromoDynamics (pQCD) at small distances, which is governed by quark and gluon fields, and Chiral Perturbation Theory (ChPT) at larger distances, which is governed by pion fields, are both already experimentally validated. However, strong fields at intermediate distances, where they generate about 98% of the total mass of nucleons and therefore of all normal matter, are not understood on similarly firm grounds. Electron scattering in particular serves as an ideal tool to investigate this intermediate region by measuring the resonance transition form factors of three-quark systems with varying momentum transfer and spatial resolution of the probe. The status of the research program at Jefferson Lab to study baryon transition form factors and the evolution of the underlying effective degrees of freedom, or the origin of mass, will be exemplified by recent results in single and double-pion production obtained with CLAS by the Hall B collaborations. These results demonstrate that the separation of resonance and background contributions and therefore the extraction of the electro-coupling amplitudes of resonances become easier and cleaner at higher four-momentum transfers (Q2). Furthermore, the double-pion in comparison to the single-pion channel shows a higher sensitivity to energetically higher lying resonances and a distinctly different dependence on the contributing background amplitudes. The combined analysis of the single- and double-pion data thus reduces model dependent uncertainties significantly, which allows us to extract the resonant electro-coupling amplitudes in an unprecedented quality.

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Research Organization:: Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)

Sponsoring Organization:: USDOE Office of Science (SC), Nuclear Physics (NP)

DOE Contract Number:: AC05-06OR23177

OSTI ID:: 2001051

Report Number(s):: JLAB-PHY-08-912; DOE/OR/23177-0657

Resource Relation:: Journal Volume: 187; Conference: 8th international Conference on Hyperon, Charm, and Beauty Hadrons, Columbia, SC, June 22, 2008, Nuclear Physics B - Proceedings Supplements

Country of Publication:: United States

Language:: English

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