Nucleon Resonance Electrocouplings from the CLAS Meson Electroproduction Data. Page: 4 of 6
This article is part of the collection entitled: Office of Scientific & Technical Information Technical Reports and was provided to UNT Digital Library by the UNT Libraries Government Documents Department.
Extracted Text
The following text was automatically extracted from the image on this page using optical character recognition software:
with very different background demonstrate that the reaction models described above
provided reliable evaluation of these fundamental quantities. It makes possible to de-
termine electrocouplings of all resonances that decay preferentially to the either Nn or
Nrr final states analyzing independently the Nn or n+g--p electroproduction channels,
respectively. The studies of Nn exclusive channels are the primary source of informa-
tion on electrocouplings of the N* states with masses less than 1.6 GeV [4]. The studies
of +--p electroproduction off protons allowed us to check the results from NKi data
analyses for the resonances that have substantial decays to both Nxi and Nxiur channels.
Furthermore, they are of particular importance for the evaluation of high lying resonance
electrocouplings, since most N*'s with masses above 1.6 GeV decay preferentially with
two pion emission.
Preliminary results on electrocouplings of S31(1620), S11(1650), F15(1685),
D33(1700) and P13(1720) states were obtained from the CLAS +--p electroproduc-
tion data [8]. Electrocouplings of the D33(1700) state determined from NEi (previously
available world data [23]) and x+--p (the CLAS results) electroproduction channels
are shown in Fig. 3. The CLAS results improved considerably our knowledge of the
D33(1700) electrocouplings. They provided accurate data on the Q2-evolution of the
transverse electrocouplings and first information on the longitudinal electrocouplings of
all above mentioned excited proton states.
Analyses of the Nn and +--p electroproduction channels provided access to elec-
trocouplings of all prominent excited proton states. .
Analysis of the CLAS results on P1 (1440) electrocouplings revealed major features
of this state structure that remained a mystery for decades. Two light-front quark mod-
els [18, 19] and conceptually different the covariant valence quark-spectator diquark
model [20] provided good description of P1 (1440) electrocouplings at Q2 > 1.5 GeV2.
In these models, the P11(1440) structure is described as first radial excitation of three
constituent quarks in the ground state. The CLAS results showed that at Q2 > 1.5 GeV2
the P1 (1440) structure is determined mostly by a core of three constituent quarks. How-
ever, at Q2 < 1.0 GeV2 quark models fail to describe theA1/2 electrocouplings. This is an
indication for additional contributions beyond those from a quark core. A general unitar-
ity condition requires the contributions to yvNN* electrocouplings from meson-baryon
dressing when the N* state is excited through a sequence of the following processes:
a) non-resonant meson-baryon production by virtual photon and b) resonance forma-
tion in subsequent meson-baryon scattering [21]. The absolute values of meson-baryon
dressing amplitudes determined from the data on Nn photo-, electro- and hadroproduc-
tion [22] are shown in Fig 1. They are maximal at small photon virtualities and may, in
part, be responsible for the differences between quark model expectations and the CLAS
results on P11(1440) electrocouplings.
Electrocouplings of the D13(1520) state, shown in Fig. 2, are well described at Q2 >
2.0 GeV2 within the framework of quark model [24], assuming the contributions from
three constituent quarks in the first orbital excitation with L=1. This model underesti-
mates the A3/2 electrocoupling at Q2 < 1.5 GeV2. At these photon virtualities absolute
values of meson-baryon dressing contributions to this electrocoupling are maximal [22].
Differences between the CLAS results on D13(1520) electrocouplings and expectations
of quark model [24] may be related to the meson-baryon cloud.
We concluded that the structure of excited proton states with masses less than 1.6
Upcoming Pages
Here’s what’s next.
Search Inside
This article can be searched. Note: Results may vary based on the legibility of text within the document.
Tools / Downloads
Get a copy of this page or view the extracted text.
Citing and Sharing
Basic information for referencing this web page. We also provide extended guidance on usage rights, references, copying or embedding.
Reference the current page of this Article.
Inna Aznauryan, Volker Burkert, Viktor Mokeev. Nucleon Resonance Electrocouplings from the CLAS Meson Electroproduction Data., article, April 1, 2012; Newport News, Virginia. (https://digital.library.unt.edu/ark:/67531/metadc831181/m1/4/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.