Two of the most basic goals of nuclear physics are to understand the mechanisms responsible for the formation of hadrons and explain their structure in terms of the gluons and quarks of quantum chromodynamics (QCD). In this connection, measurements of the nucleon excitation (N*) spectrum and exploration of N* structure through the study of resonance electroexcitation amplitudes (γvNN* electrocoupling parameters) on a broad domain of photon virtualities present unique opportunities for elucidating these crucial aspects of nonperturbative strong-interaction dynamics.
Pushing the idea of an electron microscope to higher and higher energies allows us to investigate nucleons and their excitations with higher and higher resolution via electron scattering experiments carried out at the Thomas Jefferson National Accelerator Facility (TJNAF) in Virginia. The contact persons of this nucleon excitation program, Ralf Gothe (USC) and Viktor Mokeev (JLab), have forged a close collaboration of theorists and experimentalists that has already started to reveal some of the remaining secrets of the strong interaction that binds quarks into nucleons and nucleons into nuclei. Among these secrets are: what is the origin of more than 98% of the mass that surrounds us, up to which distance scale are mesons contributing to the formation of baryons, and how does nature confine colored quarks.
Carrying out the next generation of experiments at Jefferson Lab that might allow us to finally understand the strong interaction, Ralf Gothe and his group are building a large-scale time-of-flight detector here at USC with unprecedented time resolution that will ensure proper particle identification in all CLAS (CEBAF Large Acceptance Spectrometer) experiments after the TJNAF upgrade to 12 GeV.
Selected Lectrures, Talks, and Proceedings
Impact of the γvNN* Electrocoupling Parameters at High Photon Virtualities and Preliminary Cross Sections off the Neutron, Presentation and Proceedings, ECT* Workshop on Nucleon Resonances, Trento, Italy (2015).
Nucleon Resonances - their Structure - and Non-Perturbative QCD, 5th Workshop on Non-Perturbative Aspects of Field Theories, Morelia, Mexico, (2015).
Nucleon Resonances and their Structure, 6th Workshop of the APS Topical Group on Hadronic Physics, Baltimore, MD (2015).
Exclusive Electroexcitation of Baryon Resonances with CLAS and CLAS12, Quark Confinement and the Hadron Spectrum XI, St. Petersburg, Russia, (2014).
Transition Form Factors: A unique Opportunity to Connect Non-Perturbative Strong Interaction to QCD, Presentation and Proceedings, NSTAR 2013, Peniscola, Valencia Community, Spain (2013).
Experimental Probes into the Essence of Matter, ANL Colloquium, Argonne National Lab, Argonne, IL (2013).
Hadronspectroscopy, Presentation at the Users Group Workshop and Annual Meeting, Jefferson Lab, Newport News, VA (2012).
Transition Form Factors: A Unique Window into the Baryon Structure, Many Manifestations of Non-Perturbative QCD, Caraguatatuba, Sao Paulo, Brazil (2012).
Challenges of the N* Program, Presentation and Proceedings, NSTAR 2011, Jefferson Lab, Newport News, VA (2011).
CLAS12 Forward Time-of-Flight at USC: A Status Report, CLAS Collaboration Meeting, Jefferson Lab, Newport News, VA (2010).
Lectures on the Nucleon Resonance Structure at Large Q2, Part 1 and Part 2, 25th Annual Hampton University Graduate Studies Program, Jefferson Lab, Newport News, VA (2010).
CLAS12 Forward Time-of-Flight at USC: A Comprehensive Update and Presentations, FToF12 Technical System Review, Jefferson Lab, Newport News, VA (2009).
Roadmap to the CLAS12 Physics Program, Presentation at the Users Group Workshop and Annual Meeting, Jefferson Lab, Newport News, VA (2009).
Nucleon Resonance Studies after the 12 GeV Upgrade at JLab, Presentation at APS Topical Group on Hadronic Physics, GHP 2009, Denver, CO (2009).
Nucleon Transition Form Factors at JLab: Status and Outlook, Presentation and Proceedings, NSTAR 2009, Beijing, China (2009).
Nucleon Resonance Studies with CLAS12, Presentation at 34th JLab Program Advisory Committee, Jefferson Lab, Newport News, VA (2009).Hadron Spectroscopy at CLAS and the Evolution of Strong Degrees of Freedom, Nuclear Physics B (Proc. Suppl.) 187 (2009) 130-135, Proceedings of the 8th International Conference on Beauty, Charm and Hyperons in Hadronic Interactions.
N* Transition Form Factors at JLab: The Evolution of Baryonic Degrees of Freedom, Presentation at Exclusive Reactions at High Momentum Transfers, Jefferson Lab, Newport News, VA (2007).
Nucleon Transition Form Factors and New Perspectives, Proceedings of APS Topical Group on Hadronic Physics Meeting, Nashville, TN (2007).
ToF12 Progress Report, Presentation of Tests Results and Ongoing Work for the 12-GeV-Upgrade of the Time-of-Flight Detectors at JLab, Jefferson Lab, Newport News, VA (2007).
Selected Approved Proposals and Support
A Search for Hybrid Baryons in Hall B with CLAS12, Research Proposal PR12-16-010, Jefferson Lab, Newport News, VA (2016).
Nucleon Resonance Structure Studies via Exclusive KY Electroproduction at 6.6 GeV and 8.8 GeV, Research Proposal PR12-16-010A, Jefferson Lab, Newport News, VA (2016).
Exclusive N*→KY Studies with CLAS12, Research Proposal for E12-06-108A, Jefferson Lab, Newport News, VA (2014).
Nucleon Resonance Studies with CLAS12, Update of the Research Proposal for E12-09-003, Jefferson Lab, Newport News, VA (2010).
Nucleon Resonance Studies with CLAS12, Research Proposal for E12-09-003 for the Upgraded CLAS12 Detector at JLab, Jefferson Lab, Newport News, VA (2009).
Theory Support for the Excited Baryon Program at the JLab 12 GeV Upgrade, in Support of the "Nucleon Resonance Studies with CLAS12" Proposal (2009).
Search for Exotic Cascades with CLAS, Proposal and Ongoing Research, Jefferson Lab, Newport News, VA (2004).
"Studies of Excited Nucleons in Exclusive Electroproduction" Write-Up and "Experimental Overview on Baryon Spectroscopy: Current and Future" Presentation leading to the "QCD and Hadron Physics" White Paper, Contributions to the NSAC Long Range Plan, and finally to the 2015 NSAC Long Range Plan itself (2014-15).
Studies of Nucleon Resonance Structure in Exclusive Meson Electroproduction, Chief-Editor, Review Article (2013).
Excited Baryon Program at JLab, A Contribution to the NSAC Long Range Plan (2007).
Studium des elektroinduzierten N→Δ-Überganges, Habilitationsschrift zur Erlangung der venia legendi der Rheinischen Friedrich-Wilhelms-Universität zu Bonn (1998).
Recent publications since 2006
Recent invited talks since 2006