Results from the analysis of the CLAS data on double charge pion electroproduction. presented by V.I.Mokeev.
Results from the analysis of the CLAS data on double charge pion electroproduction.
presented by V.I.Mokeev
The studies of N* electrocouplings at various Q2 elucidate relevant degrees of freedom in their structure and allow us to understand quark interactions, which are responsible for baryon formation from fundamental constituents.
Promising way to study non-Abelian origin of strong interactions in non-perturbative domain, predictedin lattice simulations for quark binding in baryons.
gluon self coupling in
Lattice QCD calculation of gluon flux distribution in a system of 3 heavy quarks.
Non-resonant amplitudes and N* hadronic couplings in various meson electroproduction channels are entirely different, while N* electrocouplings are expected to be the same.
p, h, pp,..
A3/2, A1/2, S1/2
Gm, Ge, Gc
Credible evaluation of N* electrocouplings should be achieved in successful description of all available observables in various electroproduction channels combined with common resonance electrocouplings.
CLAS data on meson electroproduction
at Q2<4.0 GeV2
Exclusive channels in pN
scattering responsible for
FSI in meson electroproduction
1p/2p channels are strongly coupled by FSI.
1p/2p channels are major contributors.
Simplest measurements with unpolarized e- beam and p target, no use of polarization observables in the final state offer 9 independent single differential cross-sections in each (W,Q2) bin.
All these cross-sections are available from CLAS for the first time.
Contributing mechanisms may be established from theirs manifestations in variety of observables JM approach.
Quasi-2-body mechanisms included:
Quasi-2-body mechanisms included:
Direct 2p production in JM05.
V.Mokeev, V.Burkert, et al., Proc. of NSTAR2005 Workshop p. 47
Direct 2p production mechanisms, established from analysis of the CLAS data: M.Ripani, V.Burkert, et.al., Phys.Rev. Lett. 91, 022002 (2003).
CLAS data fit under various assumptions on direct 2p production mechanisms:
3-body phase space
the contributions from
direct 2p mechanisms,
described on previous
CLAS data M.Ripani, V.D.Burkert, et. al.
Reasonable description of invariant mass and p- angular distributions was achieved in entire kinematics area covered by CLAS data.
Fit of single differential cross-sections from recent CLAS 2p data (1.3<W<1.6 GeV, 0.25<Q2<0.6 GeV2) within the framework of JM05 model.
Reasonable description of 4 differential cross-sections, studied previously, was achieved.
Failure in description of p+ and
p angular distributions is related to the shortcomings in treatment of direct 2p production (dashed magenta lines).
All significant mechanisms, contributing to ep→p-p+p channel at W<1.6 GeV and Q2<0.6 GeV2 were established from the CLAS data analysis.
Reasonable description of
ai-angular distributions with model parameters fitted to 6 other diff. cross-sections offers compelling evidence for reliability of JM06 model.
preliminary CLAS data
N* electrocouplings and parameters for non-resonant mechanisms were varied. The c2/d.p. were estimated from comparison between measured and calculated differential cross-sections.
c2/d.p. for selected in fit cross-sections:
the contributions from all isobar channels
CLAS data fit
The data on isobar channel contributions are available for N* studies in the coupled channel analysis, under development at EBAC.
from analysis of 1p CLAS data
from analysis of CLAS 2p data
within the framework of JM06
combined analysis of 1p/2p CLAS data
Ground p state
light cone (LC)
3q core +meson -baryon cloud +??
EBAC is developing coupled channel approach to disentangle meson-baryon dressing and “bare” quark core contributions to N* electrocouplings.
The contribution from quark core increases with Q2. Data on N* electrocouplings at high Q2 are needed to study quark interactions in baryons .
After 12 GeV Upgrade CLAS12 will be only facility foreseen worldwide, capable to study electrocouplings for full spectrum of N*’s at Q2 from 5.0 to 10 GeV2.
3q core +meson –baryon cloud +??
Fully integrated 2p cross section at Q2 from 4.5 to 5.2 GeV2
Evidence for substantial N* contributions