Nucleon resonance studies in π + π - electroproduction off protons at high photon virtualities

1. Nucleon resonance studies in π+ π- electroproduction off protons at high photon virtualities E. Isupov, EMIN-2009

2. Plan of the talk • Major objectives for N* studies in Nelectroproduction at high Q2 • Recent CLAS data on the π+ π- p electroproduction • Evaluation of vNN* electrocouplings • Preliminary data at high Q2 • Conclusions and outlook

3. Primary objectives in the studies of N* structure in 2 electroproduction • Our experimental program seeks to determine • N-N* transition helicity amplitudes (electrocouplings) at photon virtualities 0.2< Q2<5.0 GeV2for almost all excited proton states from analyzing double-pion electroproduction. • provide input for advanced coupled-channel approach developing by EBAC. • This comprehensive information on Q2 evolution of the N-N* electrocouplings will allow us to: • determine the active degrees of freedom in N* structure at various distances; • study the nonperturbative strong interactions which are responsible for • the ground and excited nucleon state formation, • and how they emerge from QCD.

4. How N* electrocouplings can be accessed • Isolate the resonant part of production amplitudes by fitting the measured observables within the framework of reaction models, which are rigorously tested against data. • N* electrocouplings can then be determined from resonant amplitudes under minimal model assumptions.   e’ γv γv e * p N*,△ + v N N’ N’ N N p A3/2, A1/2, S1/2 GM, GE, GC Non-resonant amplitudes. 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, 065201 (2007);B.Julia-Diaz, et al., arXiv:0904.1918[nucl-th]

5. P11(1440) electrocouplings from the CLAS data on N/N electroproduction Npreliminary N Light front models: I. Aznauryan S. Capstick hybrid P11(1440)‏ • Good agreement between the electrocouplings obtained from the N and N channels: Reliable measure of the electrocouplings. • The electrocouplings for Q2 > 2.0 GeV2are consistent with P11(1440) structure as a 3-quark radial excitation of the nucleon. • Zero crossing for the A1/2amplitude has been observed for the first time, indicating the importance of light-front dynamics.

6. High lying resonance electrocouplings from N CLAS data analysis NCLAS preliminary Δ(1700)D33 Nworld N(1720)P13 NCLAS Q2=0

7. CLAS

8. Event Selection • Electron ID • Calorimeter cuts • Cherenkov cut • Fiducial cuts • Zvertex cut • Momentum corrections • Zvertex corrections

9. EC sampling fraction before and after electron ID cuts

10. Charged hadrons ID • Beta vs Momentum cuts • Fiducial cuts • Momentum corrections for positive pion • Energy loss corrections for proton • Zvertex corrections • Zvertex cut

11. Delta beta vs Momentum for charged hadrons

12. Missing Mass of negative pion

13. 3-body final state kinematics variables 3-body final state kinematics variables: M+- , Mp+ are invariant masses of the +- and p+ systems respectively; d- =d(cos-)d- is solid angle for emitted -; p+ is the angle between two planes on the plot.

14. Cross-section extraction 7-fold differential cross-section L – luminosity, N – number of events inside multidimensional cell, eff-efficiency determined from monte-carlo simulation. Then we obtain virtual photon cross-section

15. Preliminary differential cross-sections at W=1.934 GeV Preliminary

16. Cross-sections at higher Q2 Fully integrated 2 cross section Q2=0.95 GeV2 Q2=2.2 GeV2 preliminary

17. Cross-sections at higher Q2 Fully integrated 2 cross section preliminary Q2=2.7 GeV2 Q2=3.3 GeV2 Q2=3.9 GeV2 Q2=4.6 GeV2

18. JLAB-MSU isobar model (JM) for N electroproduction. Isobar channels included: 3-body processes: -++ • All well established N*s with decays and 3/2+(1720) candidate, seen in CLAS 2 data. • Reggeized Born terms with effective FSI & ISI treatment . • Extra contact term. p • 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. 18

19. continued 3-body processes: Isobar channels included: (-)‏ • +D013(1520), +F015(1685), -P++33(1640) isobar channels; observed for the first time in the CLAS data at W > 1.5 GeV. (P++33(1640))‏ (+)‏ F015(1685)‏ Direct 2 production V. Mokeev, V .Burkert, J. Phys. 69, 012019 (2007); V. Mokeev et al., arXiv:0809:4158[hep-ph]

20. Description of the CLAS N differential cross sections within the framework of JM model +F015(1685)‏ full JM calc. +0 p -++ 2 direct +D013(1520)‏

21. Resonant & non-resonant parts of N cross sections as determined from the CLAS data fit within the framework of JM model resonant part non-resonant part full cross sections

22. Conclusions and outlook • For the first time differential cross-sections of double pion electroproduction were extracted in 2.0<Q2<5.0 GeV2 • It makes possible to use phenomenological model JM in order to establish all essential mechanisms, contributing to double pion electroproduction at this still unexplored kinematic area • In near term prospect we expect to evaluate electrocouplings for prominent resonances in 2.0<Q2<5.0 GeV2 region.