New results from the studies of theN(1440)1/2+, N(1520)3/2

Abstract

The transition helicity amplitudes from the proton ground state to the N (1440)1/2 + , N (1520)3/2 − , and ∆(1620)1/2 − resonances (γvpN * electrocouplings) were determined from the analysis of nine independent one-fold differential π + π − p electroproduction cross sections off a proton target, taken with CLAS at photon virtualities 0.5 GeV 2 < Q 2 < 1.5 GeV 2 . The phenomenological reaction model employed for separation of the resonant and non-resonant contributions to this exclusive channel was further developed. The N (1440)1/2 + , N (1520)3/2 − , and ∆(1620)1/2 − electrocouplings were obtained from the resonant amplitudes of charged double-pion electroproduction off the proton in the aforementioned area of photon virtualities for the first time. Consistent results on γvpN * electrocouplings available from independent analyses of several W -intervals with different non-resonant contributions offer clear evidence for the reliable extraction of these fundamental quantities. These studies also improved the knowledge on hadronic branching ratios for the N (1440)1/2 + , N (1520)3/2 − , and ∆(1620)1/2 − decays to the π∆ and ρN final states. These new results provide a substantial impact on the QCD-based approaches that describe the N * structure and demonstrate the capability to explore fundamental ingredients of the non-perturbative strong interaction that are behind the excited nucleon state formation.

Measurements of ep→e′π+π−p′ cross sections with CLAS at 1.40Isupov1, Burkert2, Carman3 et al. 2017Phys. Rev. CSelf Cite410440View full textAdd to dashboardCite

“…Furthermore, the structure of excited nucleons represents a complex interplay between the inner core of three dressed quarks and the external meson-baryon cloud [1,[4][5][6] their relative contributions evolving with photon virtuality Q 2 . Therefore, measurements of γ v pN * electrocouplings as a function of Q 2 allow for a detailed charting of the spatial structure of nucleon resonances in terms of their quark cores and higher Fock states.…”

“…Nucleon resonance electrocouplings have been obtained from the exclusive channels: π + n and π 0 p at Q 2 < 5.0 GeV 2 in the mass range up to 1.7 GeV, ηp at Q 2 < 4.0 GeV 2 in the mass range up to 1.6 GeV, and π + π − p at Q 2 < 1.5 GeV 2 in the mass range up to 1.8 GeV [1,4,8,[15][16][17][18][19]. The studies of the N(1440) 1 [15].…”

“…Many excited nucleon states with masses above 1.6 GeV decay preferentially to the ππN final states, making exclusive π + π − p electroproduction off protons a major source of information on these electrocouplings. First accurate results on the electrocouplings of the (1620)1/2 − , which couples strongly to ππN, have been published from the analysis of CLAS data on π + π − p electroproduction [4]. Preliminary results on electrocouplings of two other resonances, the (1700)3/2 − and the N(1720)3/2 + , show dominance of ππN decays and were obtained from the π + π − p data [17].…”

“…An extension of the measured π + π − p electroproduction cross sections towards higher photon virtualities is critical for the extraction of resonance electrocouplings at the distance scale where the transition to the dominance of dressed quark degrees of freedom in the N * structure is expected [1,2]. These data will provide input for reaction models aimed at determining γ v pN * electrocouplings for the N * resonances in the mass range above 1.6 GeV [4,16,23]. These data will also provide necessary input for global multichannel analyses of the exclusive meson photo-, electro-, and hadroproduction channels [6,21,[24][25][26].…”

Electroproduction of lightest nucleon resonances up to Q*2=12 GeV*2 in quark models at light front

“…Specifically new insights have been obtained in π and 2π electroproduction off the proton with the polarized electron beam at JLab (CLAS/CLAS12 Collaborations, see, e.g., recent overviews [1,2]). In the context of projected extensive studies of baryons with J P = 1/2 ± , 3/2 ± , 5/2 ± , etc., there is an interest in calculation of electrocouplings of baryons at large Q 2 .…”