Philip L Cole Idaho State University April 17, 2012

Motivation L 2I 2J L N* J.J.Dudek and R.G.Edwards, Hybrid Baryons in QCD arXiv: [hep-ph] (January 10, 2012)

Photo & Electroproduction Difficulties (New Opportunities) – Access to N* structure – Non-perturbative strong interactions responsible for formation of N*s – A lot of resonances could be present in a relatively narrow energy region – Nonresonance background is almost equally as complicated Experiments – Jefferson Lab (USA) – MAMI (Germany) – ELSA (Germany) – ESRF (France) – SPring-8 (Japan) – BES (China) ¶ ¶ A unique way of studying the baryon spectrum and N* hadronic decays is via BES: J/ψ  N*,…

CLAS and JLab

Studying N*s gives insight into structure Indeed in the words of the theorist, Craig Roberts: “there is no greater challenge in the Standard Model, and few in physics, than learning to understand the truly non-perturbative long-range behavior of the strong interaction.”

Electromagnetic Excitation of N*s Both parts of the program are being pursued in various meson photo and electroproduction channels, e.g. Nπ, pη, pπ + π -, KΛ, KΣ, pω, pρ 0 using cross sections and polarization observables. Global analysis of ALL meson photo- and electroproduction channels – within the framework of an advanced coupled-channel approach developed by EBAC (Excited Baryon Analysis Center – JLab).

Physics Goals for CLAS6

First electroproduction data: channels:  + n,  0 p, and  p P 33 (1232)P 11 (1440)D 13 (1520) S 11 (1535) Q 2 evolution information on the  v NN* electrocouplings for the states: P 33 (1232), P 11 (1440), D 13 (1520), and S 11 (1535) for Q 2 < 5.0 GeV. I.G. Aznauryan et al., (CLAS Collaboration) Phys. Rev. C80, (2009). P 11 (1440), D 13 (1520), S 31 (1620), P 13 (1720), and D 33 (1780) We recently published the preliminary (first) results on the electrocouplings of the states P 11 (1440), D 13 (1520), S 31 (1620), P 13 (1720), and D 33 (1780) at Q 2 < 0.6 GeV 2 in N  electro- production from protons V.I. Mokeev, I.G. Aznauryan, V.D. Burkert, arXiv: [nucl-ex] + I.G. Aznauryan, V.D. Burkert, V.I. Mokeev, arXiv: [nucl-ex] Announcement of Firsts from CLAS

Observables Range [GeV 2 ] Number of data points dσ/dΩ(π 0 ) dσ/dΩ(π + ) A e (π 0 ), A t (π 0 ) A e (π + ), A t (π + ) A et (π 0 ) Number of data points >116000, W<1.7 GeV, 0.15<Q 2 <6.0 GeV 2, almost complete coverage of the final state phase space.

Why N  /N  electroproduction channels are important CLAS data on meson electro- production at Q 2 < 4.0 GeV 2 N  /N  channels are the two major contributors in N* excitation region; these two channels combined are sensitive to almost all excited proton states; they are strongly coupled by  N→  N final state interaction; may substantially affect exclusive channels having smaller cross sections, such as  p,K , and K . Therefore knowledge on  electroproduction mechanisms is key for the entire N* Program Therefore knowledge on  electroproduction mechanisms is key for the entire N* Program

How N* electrocouplings can be accessed How N* electrocouplings can be accessed vv N  p   p  e e’ γvγv N N’N’ N*,△ A 3/2, A 1/2, S 1/2 G M, G E, G C  Consistent results on N* electrocouplings obtained in analyses of various meson channels (e.g. πN, ηp, ππN) with entirely different non-resonant amplitudes will show that they are determined reliably Advanced coupled-channel analysis methods are being developing at EBAC: B.Julia-Diaz, T-S.H.Lee et al., PRC76, (2007);T.Sato and T-S.H.Lee arXiv: [nucl-th] Isolate the resonant part of production amplitudes by fitting the measured observables within the framework of reaction models, which are rigorously tested against data. These N* electrocouplings can then be determined from resonant amplitudes under minimal model assumptions. N γvγv  N’N’ + Non-resonant amplitudes.

Any contributing mechanism has considerably different shapes of cross sections in various observables defined by the particular behavior of their amplitudes. A successful description of all observables allows us to check and to establish the dynamics of all essential contributing mechanisms. Full JM calc  -   ++  + D 13 (1520)  + F 15 (1685) pp 2  direct G.V.Fedotov et al., PRC 79 (2009), M.Ripani et al., PRL 91 (2003),

Hadron Structure with Electromagnetic Probes resolution of probe low high ,.. Allows to address central question: What are the relevant degrees-of-freedom at varying distance scale? q e.m. probe LQCD/DSE quark mass (GeV)     3-q core pQCD 3-q core+ MB cloud

Within the relativistic Quark Model framework [ B.Julia-Diaz et al., PRC 69, (2004 )], the bare-core contribution is reasonably described by the three-quark component of the wavefunction One third of G * M at low Q 2 is due to contributions from meson–baryon (MB) dressing: Data from exclusive π 0 production bare quark core Q 2 =5GeV 2 Effects of Meson-Baryon Dressing

The P 11 (1440) electrocouplings from the CLAS data Quark models: I. Aznauryan LC S. Capstick LC Relativistic covariant approach by G.Ramalho/F.Gross. EBAC-DCC MB dressing (absolute values). A 1/2 S 1/2     p 2010     p 2011 NN

A 1/2 S 1/2 A 3/2 M.Giannini/E.Santopinto hCQM MB dressing abs val. (EBAC) The data on A 1/2 electrocoupling at Q 2 >2.0 GeV 2 for the first time offer almost direct access to quark core. They are of particular interest for the models of N* structure based on QCD.

CLAS12 JLab Upgrade to 12 GeV Luminosity > cm -2 s -1 General Parton Distributions Transverse parton distributions Longitudinal Spin Structure N* Transition Form Factors Heavy Baryon Spectroscopy Hadron Formation in Nuclei Solenoid, ToF, Central Tracker Forward Tracker, Calorimeter, Particle ID

explore the interactions between the dressed quarks, which are responsible for the formation for both ground and excited nucleon states. probe the mechanisms of light current quark dressing, which is responsible for >97% of nucleon mass. Approaches for theoretical analysis of N* electrocouplings: LQCD, DSE, Ads/CFT relativistic quark models. See details in the 62-page White Paper of EmNN* JLAB Workshop, October 13-15, 2008: Aznauryan et al., arXiv: [nucl-th] Need to multiply by 3p 2 to get the Q 2 per quark Q 2 = 12 GeV 2 Independent QCD Analyses Line Fit: DSE Points: LQCD

Projections for N* Transitions For the foreseeable future, CLAS12 will be the only facility worldwide, which will be able to access the N* electrocouplings in the Q 2 regime of 5 GeV 2 to 10 GeV 2, where the quark degrees of freedom are expected to dominate. Our experimental proposal “Nucleon Resonance Studies with CLAS12” was approved by PAC34 for the full 60-day beamtime request. CLAS published CLAS PRL subm. CLAS12 projected CLAS published CLAS preliminay CLAS12 projected CLAS12

21 Nucleon Resonance Studies with CLAS12

22 V.M. Braun 8, I. Cloët 9, R. Edwards 5, M.M. Giannini 4,7, B. Julia-Diaz 2, H. Kamano 2, T.-S.H. Lee 1,2, A. Lenz 8, H.W. Lin 5, A. Matsuyama 2, M.V. Polyakov 6, C.D. Roberts 1, E. Santopinto 4,7, T. Sato 2, G. Schierholz 8, N. Suzuki 2, Q. Zhao 3, and B.-S. Zou 3 JLab PAC 34, January 26-30, 2009 Argonne National Laboratory (IL,USA) 1, Excited Baryon Analysis Center (VA,USA) 2, Institute of High Energy Physics (China) 3, Istituto Nazionale di Fisica Nucleare (Italy) 4, Jefferson Lab (VA, USA) 5, Ruhr University of Bochum (Germany) 6, University of Genova (Italy) 7, University of Regensburg (Germany) 8, and University of Washington (WA, USA ) 9 Open invitation. List is open to any and all who wish to participate !

The results from our experiment will be used by EBAC and the Theory Support Group for our proposal to provide access to the dynamics of non-perturbative strong interactions among dressed quarks and their emergence from QCD and the subsequent formation into baryon resonances; information on how the constituent quark mass arises from a cloud of low-momentum gluons, which constitute the dressing to the current quarks. [ This process of dynamical chiral symmetry breaking accounts for over 97% of the nucleon mass] [ This process of dynamical chiral symmetry breaking accounts for over 97% of the nucleon mass] enhanced capabilities for exploring the behavior of the universal QCD  -function in the infrared regime.

Thank you

BACKUP SLIDES

Dyson-Schwinger Equation (DSE) Approach DSE provides an avenue to relate N* electrocouplings at high Q 2 to QCD and to test the theory’s capability to describe the N* formation based on QCD. DSE approaches provide a link between dressed quark propagators, form factors, and scattering amplitudes and QCD. N* electrocouplings can be determined by applying Bethe-Salpeter /Fadeev equations to 3 dressed quarks while the properties and interactions are derived from QCD. By the time of the upgrade DSE electrocouplings of several excited nucleon states will be available as part of the commitment of the Argonne NL and the University of Washington.

P 11 (1440) electrocouplings from the CLAS data on N  /N  electroproduction N  NN Light front models: I. Aznauryan S. Capstick hybrid P 11 (1440) [Q 3 g]

Current Status of Lattice QCD LQCD calculations of the  (1232)P 33 and N(1440)P 11 transitions have been carried out with large  -masses. By the time of the upgrade LQCD calculations of N* electrocouplings will be extended to Q 2 = 10 GeV 2 near the physical  -mass as part of the commitment of the JLAB LQCD and EBAC groups in support of this proposal.  (1232)P 33 N(1440)P 11

JLAB-MSU meson-baryon model (JM) for N* electrocoupling extraction from the    - p electroproduction data 3-body processes: Isobar channels included: All well established N*s with   decays and 3/2 + (1720) candidate. Reggeized Born terms with effective FSI and ISI treatment (absorptive approximation). Extra  contact term. All well established N*s with  p decays and 3/2 + (1720) candidate. Diffractive ansatz for non-resonant part and  -line shrinkage in N* region.  -  ++ pp Unitarized Breit-Wigner anstaz for resonant amplitudes. V. I. Mokeev, V.D. Burkert, T.-S.H. Lee et al., Phys. Rev. C80, (2009)

JLAB-MSU meson-baryon model (JM) for N* electrocoupling extraction from the    - p electroproduction data 3-body processes: Isobar channels included:  + D 0 13 (1520),  + F 0 15 (1685),  - P (1640) isobar channels observed for the first time in the CLAS data at W > 1.5 GeV. F 0 15(1685) (P ++ 33(1640)) (-)(-) (+)(+) Evidence for  + D 0 13 (1520) isobar channel in the CLAS  +  - p data full JM results with  + D 0 13 (1520) implemented full JM results without  + D 0 13 (1520) and adjusted direct 2  production  + D 0 13 (1520) contribution W=1.74 GeV Q 2 =0.65 GeV 2 M  + p, GeV

N* parameters of the JM model and their relationships to the observables Regular Breit-Wigner (BW) ansatz as the start point : amplitudes are related to the partial N* decay widths to the  or  p final states of definite helicity  f f dec is the kinematical factor, which depends on resonance spin, mass and abs. CM 3-momenta values of the stable final hadron averaged over the line of unstable final hadron at the running W (p) and at W=M N* (p N* ).  f and  f are the CM final stable hadron ermission angles. Definition of  v NN* electrocouplings :  is N* electromagnetic decay width, q  N* is abs. photon CM 3-momentum value at W=M N*. The relationships between N* electroproduction amplitudes T em and  v NN* electrocouplings A 1/2, A 3/2, S 1/2 are obtained imposing the requirement: fully integrated resonant cross section should be described by the relativistic Breit-Wigner formula in a case of single contributing resonance. Exact expressions for the factors f em and f dec can be found in: M.Ripani et al., Nucl. Phys. A673, 220 (2000). The A 1/2, A 3/2, S 1/2  v NN* electrocouplings and  f N* partial decay widths are determined at resonant point W=M N*.

Electromagnetic Excitation of N*s vv N  p   p  e e’ γvγv N N’N’ N*,△ A 3/2, A 1/2, S 1/2 M l+/-, E l+/-, S l+/-  Measure the electromagnetic excitations of low-lying baryon states (<2 GeV) and their transition form factors over the range Q 2 = 0.1 – 7 GeV 2 and measure the electro- and photo-production of final states with one and two pseudo-scalar mesons. DOE Milestone 2012

error bars include systematic uncertainties M.Giannini/ E.Santopinto hyper-centric CQM D 13 (1520) electrocouplings from the CLAS data on N  /N  electroproduction electrocouplings as determined from the N  & N  channels are in good agreement overall but the apparent discrepancies for the A 3/2 amplitude at Q 2 < 0.4 GeV 2 will be further investigated in a combined N  /N  analysis hypercentric Consituent Quark Model calculations reasonably describe electrocouplings at Q 2 >2.5 GeV 2, suggesting that the 3-quark component is the primary contribution to the structure of this state at high Q 2.

Meson-baryon dressing / Quark core contributions in the A 1/2 electrocouplings of the P 11 (1440) & D 13 (1520) states. Estimates from EBAC for the MB dressing: B.Julia- Diaz et al., PRC 76, 5201 (2007). P 11 (1440)D 13 (1520) Light Front quark model by I.Aznauryan hypercentric - quark model by M.Giannini MB dressing effects have substantial contribution to low lying N* electrouplings at Q 2 <1.0 GeV 2 and gradually decrease with Q 2 ; Contribution from dressed quarks increases with Q 2 and are expected to be dominant at Q 2 >5.0 GeV 2.

Roper resonance in LQCD CLAS data Includes the quark loops in the sea, which are critical in order to reproduce the CLAS data at Q 2 <1.0 GeV 2 M π = 390, 450, 875 MeV L box =3.0, 2.5, 2.5 f H.W. Lin and S.D. Cohen, arXiv: A 1/2, S 1/2 => F 1 *, F 2 *