Recent developments in phenomenological analysis of the CLAS data on 2$pi$ electroproduction are presented. The contributions from isobar channels and $P_{11}(1440)$, $D_{13}(1520)$ electrocouplings at $Q^{2}$ from 0.25 to 0.6 GeV$^2$ were determined from the analysis of comprehensive data on differential and fully integrated 2$pi$ cross sections. Experiment Numbers: E94-005 Group: Hall B
Exclusive $pi^+pi^-p$ photo- and electroproduction data from CLAS have considerably extended the information on the spectrum and structure of nucleon resonances. The data from the $pi^+pi^-p$ and $Npi$ channels have provided results on the electrocouplings of most resonances in the mass region up to 1.8 GeV and at photon virtualities up to 5.0 GeV$^2$. The recent CLAS data on $pi^+pi^-p$ photoproduction have improved knowledge on the photocouplings of nucleon resonances in the mass range of 1.6 GeV $<$ $M_{N^*}$ $<$ 2.0 GeV and on their decays to the $pi Delta$ and $rho p$ final hadron states. For the first time, the electrocouplings of the $N(1440)1/2^+$ and $N(1520)3/2^-$ excited states have become available from $pi^+pi^-p$ data at 2.0 GeV$^2$ $<$ $Q^2$ $<$ 5.0 GeV$^2$. Analyses of the combined $pi^+pi^-p$ photo- and electroproduction data have revealed evidence for the candidate-state $N(1720)3/2^+$. The new results on the nucleon resonance spectrum, electroexcitation amplitudes from analysis of the CLAS $pi^+pi^-p$ photo- and electroproduction data, and their impact on the exploration of strong QCD are presented.
First comprehensive data on the evolution of nucleon resonance photocouplings with photon virtuality Q^2 are presented for excited proton states in the mass range from 1.4 to 2.0 GeV. N^* photocouplings were determined in phenomenological analysis of CLAS data on 2 pi photo and electroproduction within the framework of the JLAB-MSU phenomenological model.
We report on the first measurement of cross sections for exclusive deeply virtual pion electroproduction off the proton, $e p to e^prime n pi^+$, above the resonance region at backward pion center-of-mass angles. The $varphi^*_{pi}$-dependent cross sections were measured, from which we extracted three combinations of structure functions of the proton. Our results are compatible with calculations based on nucleon-to-pion transition distribution amplitudes (TDAs) and shed new light on nucleon structure.
The transition gamma_{v}pN^* amplitudes (electrocouplings) for prominent excited nucleon states obtained in a wide area of photon virtualities offer valuable information for the exploration of the N^* structure at different distances and allow us to access the complex dynamics of non-perturbative strong interaction. The current status in the studies of gamma_{v}pN^* electrocouplings from the data on exclusive meson electroproduction off protons measured with the CLAS detector at Jefferson Lab is presented. The impact of these results on exploration of the N^* structure is discussed.
We discuss the recent data of exclusive $pi^0$ (and $pi^+$) electroproduction on the proton obtained by the CLAS collaboration at Jefferson Lab. It is observed that the cross sections, which have been decomposed in $sigma_T +epsilonsigma_L$, $sigma_{TT}$ and $sigma_{LT}$ structure functions, are dominated by transverse amplitude contributions. The data can be interpreted in the Generalized Parton Distribution formalism provided that one includes helicity-flip transversity GPDs.