1. 2014 JLAB User Group Meeting
New results on the spectrum and structure of high-lying N*-states from exclusive pion electroproduction with the CLAS
V.I. Mokeev
Jefferson Lab
2014 JLAB User Group Meeting

2. Studies of Nucleon Resonances in Exclusive Meson Electroproduction
Our experimental program seeks to determine
gvNN* electrocouplings at photon virtualities up to 5.0 GeV2 for most of the excited proton states through analyzing major meson electro-production channels independently and in global multi-channel analyses.
Absolutely needed part of efforts with the goal to explore dynamics of strong interaction in non-perturbative regime and its emergence from QCD.
Unique source of information on the mechanisms which are responsible for the formation of N*-states with different quantum numbers from quarks and gluons.
See details in the review papers:
I.G. Aznauryan, V.D. Burkert, Prog. Part. Nucl. Phys. 67, 1 (2012).
I.G. Aznauryan et al., Int. J. Mod. Phys. E22, (2013).
A. Bashir et al., Comm. Theor. Phys. 58, 79 (2012).
J. Dudek ``Hadron Resonances from QCD”, talk at Hall-B/JPAC Meeting:
userweb.jlab.org/~mokeev/HALLB_PAC_meetings/September18/ .

3. Dynamical Constituents of the Ground and Excited Nucleons
Emergence of dressed dynamical quarks:
quark/gluon confinement
D.Q.
N/N* states as the bound systems
of dressed dynamical quarks:
D.Q.
D.Q.
D.Q.
more than 98% of dressed quark (N/N*) masses as well as their dynamical structure are generated non-perturtbatively through dynamical chiral symmetry breaking (DCSB). The Higgs mechanism accounts for less than 2% of the nucleon and N* mass.
the momentum dependence of the dressed quark mass reflects the transition from quark/gluon confinement to asymptotic freedom.

4. Mapping Dressed Quark Mass Function
I.C.Cloet, C.D.Roberts, A.W.Thomas,
Phys. Rev. Lett. 111, (2013).
Similar studies for the D(1232)3/2+ and
N(1440)1/2+ electrocouplings are in progress.
data on elastic form factors at Q2>5.0 GeV2 are sensitive to momentum dependence of quark mass function.
mass function should be the same for dressed quarks in the ground and excited nucleon states.
consistent results on dressed quark mass function determined from the data on elastic form factors and transition gvNN* electrocouplings are critical for reliable extraction of this quantity.
mpGE/GM (Q2)
in DSEQCD .
Mapping dressed quark mass function addresses the most challenging problems of hadron physics:
how >98% of hadron masses are generated non-prturbatively?
how quark-gluon confinement in baryons emerges from QCD?

5. Non-resonant amplitudes
Definition of gvNN* electrocouplings and basics for their extraction from the data on exclusive meson electroproduction off nucleons
Resonant amplitudes
Non-resonant amplitudes e’
p, h, pp,..
p, h, pp,.. γv e *
N*,△ + N N’ N’ N
A1/2(Q2), A3/2(Q2), S1/2(Q2) or
G1(Q2), G2(Q2), G3(Q2)
GM(Q2), GE(Q2), GC(Q2)
N*’s photo-/electrocouplings gvNN* are defined
at W=MN* through the N* electromagnetic
decay width Gg :
See details in:
I.G.Aznauryan and
V.D.Burkert, Progr. Part. Nucl. Phys. 67, 1 (2012).
Separation of resonant/non-resonant contributions within the framework of reaction models; Breit Wigner ansatz for parameterization of resonant amplitudes; fit of resonance electroexcitation and hadronic parameters to the data.
Consistent results on gvNN* electrocouplings from different meson electroproduction channels and different analysis approaches demonstrated reliable extraction of N* parameters.

6. Summary of the CLAS Data on Exclusive Meson Electroproduction off Protons in N* Excitation Region
Hadronic final state
Covered
W-range, GeV
Covered Q2-range, GeV2 C
Measured observables
p+n
ds/dW
ds/dW, Ab
p0p
ds/dW, Ab,At,Abt hp
K+L
thresh-2.6
K+S0 P’
p+p-p
Nine 1-fold differential cross sections
ds/dW-CM angular
distributions
Ab,At,Abt-longitudinal
beam, target, and
beam-target asym-
metries
P’ –recoil polarization
of strange baryon
Almost full coverage
of the final hadron
phase space in
pN, p+p-p, hp, and KY electroproduction
The data are available in the CLAS Physics
Data Base:

7. N* Electroexcitation in Exclusive Meson Electroproduction off Protons
Hadronic decays of prominent N*s at W<1.8 GeV
CLAS data on yields of meson
electroproduction at Q2<4 GeV2
State
Bran. Fract. to Np.
Bran. Fract. to Nh
Bran.Fract. Nππ
Δ(1232)P33
0.995
N(1440)P11
N(1520)D13
N(1535)S11
0.48±0.03
0.46±0.02
D(1620)S31
N(1650)S11
N(1685)F15
Δ(1700)D33
N(1720)P13
> 0.7
Np/Npp channels are major and complementary sources of information on gvNN* electrocouplings of most resonances with masses up to 1.8 GeV

8. Data driven JLAB-MSU meson-baryon model (JM)
Approaches for Extraction of gvNN* Electrocouplings from the CLAS Exclusive Meson Electroproduction Data
Analyses of different pion electroproduction channels independently:
p+n and p0p channels:
Unitary Isobar Model (UIM) and Fixed-t Dispersion Relations (DR)
I.G.Aznauryan, Phys. Rev. C67, (2003).
I.G.Aznauryan et al., CLAS Coll., Phys Rev. C80, (2009).
p+p-p channel:
Data driven JLAB-MSU meson-baryon model (JM)
V.I.Mokeev, V.D.Burkert et al., Phys. Rev. C80, (2009).
V.I.Mokeev et al., CLAS Coll., Phys. Rev. C86, (2012).
Global coupled-channel analyses of the CLAS/world data of pN, gr,vN → pN, hN, ppN, KL, KS exclusive channels:
T.-S. H. Lee , AIP Conf. Proc. 1560, 413 (2013).
H. Kamano et al., Phys. Rev. C88, (2013).

9. Fits to gp→p+n Differential Cross Sections and Structure FunctionsDR
UIM DR
UIM
DR w/o P11
Q2=2.44 GeV2
Q2=2.05 GeV2
ds/dWp
Legendre moments Dl (l=0,1,2) from various structure functions

10. 1.40<W<2.30 GeV; 0.5<Q2<1.5 GeV2
The CLAS Data on p+p-p Differential Cross Sections and their Fit within the Framework of Meson-Baryon Model JM
M.Ripani et al., PRL 91 (2003),
1.40<W<2.30 GeV; 0.5<Q2<1.5 GeV2
full JM calc.
p+D0
resonant contribution rp
p-D++
non-resonant contribution
p+N0 (1520) D13

11. gvNN* Electrocouplings of Low-Lying Resonances
CLAS data:
S1/2
N(1440)1/2+ Np
2009
p+p-p
2012
p+p-p
prelim.
A1/2
N(1440)1/2+
A3/2
N(1520)3/2-
Consistent values of low-lying resonance electrocouplings determined in independent analyses of Np and p+p-p exclusive channels strongly support:
reliable electrocoupling extraction;
capabilities of the reaction models to obtain resonance electrocouplings in independent analyses of Np and p+p-p electroproduction channels.

12. meson-baryon dressing
The N*-Structure from QCD-Based and Phenomenological Analyses of N→D Magnetic Form Factor
The mechanisms of the
meson-baryon dressing
(beyond the scope of DSEQCD, can be estimated in coupled channel approaches)
G*M (Jones-Scardon)
Q2/mr2
Quark core contribution from DSEQCD:
J.Segovia, et al., Phys Rev. C88 3, (2013).
combined contributions from outer
meson-baryon cloud and inner quark
core to measured form factor.
promising potential of DSEQCD in
describing bare quark contribution
starting from QCD and accessing
dressed quark mass function and
dressed quark-gluon vertex.
Contact interaction. Non-perturbative mass generation:
contact interaction.
contact interaction & quark
anomalous magn. moment.
projection for quark running mass.
bare G*M inferred from exp. data within Argonne-Osaka c.c. approach.

13. Interplay between Quark Core and Meson-Baryon Cloud in the N* Structure
Q2 GeV2
E. Santopinto and M. M. Giannini,
PRC 86, (2012).
B. Juliá-Díaz, T.-S.H. Lee, et al.,
PR C 77, (2008).
MB dressing abs. values
(Argonne-Osaka ).
Almost direct access to:
quark core from the data on N(1520)3/2- state electrocouplings at Q2>2.0 GeV2,
prospect to map-out dressed quark mass function;
meson-baryon cloud from the data on N(1675)5/2- state electrocouplings.
LQCD is making promising progress towards evaluation of gvNN* electrocouplings (see
J.Dudek talk at Hall-B/JPAC Meeting:
userweb.jlab.org/~mokeev/HALLB_PAC_meetings/September18/

14. Structure at W~1.7 GeV in exclusive p+p-p electroproduction
Analysis within the framework of JM03’ of only five one-fold differential cross sections
M.Ripani et al, CLAS Coll,
Phys. Rev. Lett. 91, (2003).
no new 3/2+ (1720) state , N(1720)3/2+ conventional
state decays preferentialy to rp
employing 3/2+(1720) candidate or no 3/2+(1720),
while N(1720)3/2+ decays preferentialy to pD.
Two equally sucssessful ways for the data description:
different than in PDG02’ N(1720)3/2+ Npp hadronic decay widths:
Gtot, MeV
BF(pD) %
BF(rp)
N(1720)3/2+
CLAS, con-
ventional
114±19
63±12
19±9
PDG 02’
<20
70-85
new 3/2+(1720) state, while Npp hadronic decays
of N(1720)3/2+ remain consistent with PDG02’
Gtot, MeV
BF(pD) %
BF(rp)
3/2+(1720)
candidate
88±17
41±13
17±10.
N1720)3/2+
conventional.
161±31
<20
60-100
W, GeV

15. Recent analysis of the ep→ p+p-p CLAS data at W~1.7 GeV
The CLAS data fit within the JM14-model at 1.66<W<1.76 GeV and Q2=0.65, 0.95, 1.30 GeV2
conventional N*-states with pD, rp couplings fit to the data
3/2+(1720) candidate state is included to the fit
2.85<c2/d.p.<3.03
2.56<c2/d.p.<2.80
Data on qp-, qp+ , qp angular distributions revealed the contribution from resonance(s) wiith Jp=3/2+.
Single state with Jp=3/2+ should have major pD (>60%) and minor rp (<15%) decays to be consistent with
lagre pD and small rp channel contributions as seen in the data on p+p and p+p- mass distributions, respectively.

16. Signature of 3/2+(1720) candidate state
Accounting for the contribution of only conventional N(1720)3/2+ resonance with hadronic decays to the
pD and rp final states listed in the previous slide does not allow us to describe the data on a(p+p)(p-p’)
angular distributions.
W=1.69 Gev Q2=0.65 GeV2
W=1.71 Gev Q2=0.95 GeV2
W=1.69 Gev Q2=1.30 GeV2
No 3/2+(1720)
candidate
state
The contri-
bution from
3/2+(1720)
candidate
state
Successful data description requires two N*-states with Jp=3/2+ of close masses, one of which decays mostly (>45%) to the pD with minor decays (<10%) to the rp final states (new 3/2+(1720)), the other (conventional N(1720)3/2+) has comparable decay probabilities to the pD and rp final states (>30%).

17. Parameters of 3/2+(1720) new state inferred from the CLAS data
provides better description of a(p+p)(p-p’)
angular distributions at 1.66<W<1.76 GeV;
describes the data in all measured Q2-bins with
the same hadronic parameters, seen both in p-D++ and
p+D0 channels;
however, results in just modest overall improvement
in description of all nine 1-fold differential cross sections.
Analyses of p+p-p photo- and electroproduction data in wider area of Q2 complemented by the data of KY channels are needed. .
Hadronic parameters of 3/2+(1720)
Mass, GeV
1.72±0.015
Gtot, MeV
118.6±6.3
BF (pD), %
47-64
BF (rp), %

18. Electrocouplings of high lying N*-states from the CLAS ep→p+p-p data
Determined assuming the contribution from of 3/2+(1720) new state
D(1620)3/2-
S1/2
D(1700)3/2-
A1/2
N(1720)3/2+
A3/2
Independent data fit in different W-intervals:
green: 1.46<W<1.56 GeV
magenta: 1.56<W<1.66 GeV
red: 1.61<W<1.71 GeV
blue: 1.66<W<1.76 GeV
black: 1.71<W<1.81 GeV
consistent electrocoupling values offer
sound evidence for their reliable extraction.
p+p-p electroproduction channel provided first preliminary results on D(1620)1/2-, N(1650)1/2-, N(1680)5/2+, D(1700)3/2- , and N(1720)3/2+ electrocouplings of a good accuracy.
Prospect: evaluation of high-mass N* electrocouplings
from independent analyses of KY channels.
D.S.Carman et al., CLAS Collaboration, “Exclusive
N*→KY Studies with CLAS12”, Proposal for PAC42.

19. Future studies of the p+p-p channel
p+p-p Photoproduction, CLAS Preliminary
New p+p-p Electroproduction, CLAS Preliminary
s, mbn
Exploratory fit
within the
framework of
the JM14’ model
R.W.Gothe,
G.V.Fedotov,
USC
E.N.Golovach,
MSU
W, GeV
Search for the 3/2+(1720) in photoproduction data:
JM14’ model (fit of differential cross section)
Bonn-Gatchina approach (event based
likelihood analysis), U.Thoma, A.Sarantsev, et al.
E.L. Isupov,
MSU/Univ. of Ohio
Relative contributions from resonance structures
increase with Q2 and W. Structure at W~1.7 GeV
is pronounced in all Q2-bins.
Extraction of gvNN* electrocouplings of most N*‘s
in mass range up to 2.0 GeV from p+p-p electropro-
duction data within the framework of JM-model at
0.4< Q2< 5.0 GeV2.

20. Conclusions and Outlook
High quality meson electroproduction data from the CLAS allowed us to determine
electrocouplings of most well established resonances in mass range up to 1.8 GeV
from independent analyses of p+n, p0p and p+p-p electroproduction channels.
Consistent electrocoupling values for the transitions to N(1440)1/2+ and N(1520)3/2-
states obtained in independent analyses of Np/Npp exclusive channels demonstrated
capabilities of the developed reaction models for reliable extraction of N*-parameters in
independent analyses of Np and p+p-p electroproduction data.
Preliminary results on electrocouplings of N(1650)1/2-, N(1675)5/2-, N(1680)5/2+
resonances were obtained from analysis of the CLAS p+n data at 1.5<Q2<5.0 GeV2 and
for D(1620)1/2-, N(1650)1/2-, N(1680)5/2+, D(1700)3/2-, and N(1720)3/2+ resonances from p+p-p
electroproduction data at 0.5<Q2<1.5 GeV2 for the first time.
The CLAS p+p-p electroproduction data at W~1.7 GeV can be better described
implementing new baryon state 3/2+(1720). Electrocouplings and hadronic decay parameters
of candidate 3/2+(1720) state were determined from the data fit.
Physics analyses of the CLAS results on resonance electrocouplings revealed the struc-
ture of N*-states at Q2<5.0 GeV2 as complex interplay between meson-baryon and quark
degrees of freedom. The studies of different N*-states are essential in order to disentangle
different components in the N* structure getting access to the non-perturbative strong
interaction mechanisms which is responsible for N* formation from quarks and gluons.

21. Conclusions and Outlook
The CLAS data on electrocouplings of most excited proton states with masses up to 1.8 GeV offer a unique opportunity for theory to explore particular manifestations of non-perturbative strong interaction in the structure of N*-states of different quantum numbers, as well as their emergence from QCD.
Future studies of p+p-p and KY photo/electroproduction data will allow us to search for new baryon states and to obtain electrocouplings of all pronounced N* states at photon virtualities Q2<5.0 GeV2.
N*- studies with the CLAS12 detector is the only foreseen worldwide program allowing us to obtain N*-electrocouplings at highest photon virtualities ever achieved in exclusive processes: 5<Q2<12 GeV2. Almost direct access to quark degrees of freedom is expected at these distances and offers a unique opportunity to explore non-perturbative strong interaction of dressed quarks which is responsible for the N* formation, addressing the most challenging open questions: how the dominant part of hadron masses is generated and how quark-gluon confinement in baryons emerges from QCD.

22. Back -up

23. p+p-p Electroproduction Amplitudes in the JM Modelg p- g
p-/+
D++/0 (1232)P33, N0 (1520)D13,
D++ (1600)P33, N0(1680)F15 p+ = p p p p’
The data-driven reaction
model for extraction of
gvNN* electrocouplings
and pD, rp decay widths
from fitting all available
observables of gvp ->p+p-p
exclusive reaction. p’ g p-
p-, p+, … g r p+
p+, p-, … + +
Last diagram 1&2) meson meson 3) meson baryon exchange bubbles, more generally 2q and 3q exchange. p p’ p
p’,p’, …
V.I.Mokeev, V.D. Burkert, et al., (CLAS Collaboration) Phys. Rev. C86, (2012).
V.I.Mokeev, V.D. Burkert , et al., Phys. Rev. C80, (2009).
V.I.Mokeev, NSTAR 2013 Workshop Peniscola, Spain, May 27-30, 2013

24. Signals from N* states in the CLAS KY electroproduction data
D.Carman, private communication
Q2=1.8 GeV2
Q2=2.6 GeV2
Q2=3.45 GeV2
3/2 - 5/2-
(1950) KL
the structures in W-dependencies of Cl –moments at the same W-values in all Q2-bins are consistent with the contributions from resonances of spin-parities listed in the plots
1/2 +3/2+
(1850)
1/2+3/2+
(2000) KS
reaction model(s) are needed
for extraction of N* parameters
from KY electroproduction KS
3/2-5/2-
(2050)
W GeV

25. Quark Core vs Meson-Baryon Cloud in the Structure of P11(1440)
First evaluation of the quark core contribution
to the P11(1440) electrocouplings starting from QCD Lagrangian within Dyson-Schwinger Equations of QCD:
D.J.Wilson, et al, Phys. Rev. C85, (2012).
Poincare-covariant, symmetry preserving DSEQCD evaluation.
Account for quark mass/structure formation in dressing of bare quark by gluon cloud.
Simplified contact interaction generates momentum independent quark mass.
A1/2
Consistent results on the quark core contribution from:
DSEQCD.
global meson photo-, electro-, and
hadroproduction data analysis
within EBAC/ Argonne-Osaka approach.
Measured dressed electrocouplings are substantially different from the estimated quark core contribution. Different data analyses suggest sizable meson-baryon cloud at Q2<5.0 GeV2 which gradually decreases with Q2 .

26. Why resonances of different quantum numbers should be studied
Npp CLAS
preliminary
N* hadr. coupl.
are varied
fixed D33 (1700) hadr. couplings
Np Q2=0,
CLAS
Δ(1700)D33
Np world
BF(Npp): 80-90%
A1/2
V.D.Burkert,
et al., PRC
67,
(2003).
M.Dugger,
et al., PRC 79,065206
(2009).
computed from N(1520)3/2-, (1535)1/2- electrocouplings assuming single quark current and SU(6) spin-flavor symmetry (I.G. Aznauryan and V.D. Burkert, Progr. Nucl. Part. Phys. 67, 1 (2012)).
Measured electrocouplings are different with respect to the expected
A3/2
gvNN* electrocouplings of different resonances provide
complementary information on manifestation of non-per-
turbative strong interaction in the structure of excited
states of different quantum numbers.
gvNN* electrocouplings of all promenent N*-states
should be studied.

27. Impact of the Recent LQCD studies of N* Spectrum and Structure on
the N* Program with CLAS/CLAS12
J.J.Dudek, R.G.Edwards, Phys. Rev. D85, (2012).
each N* state with MN* <1.8 GeV
has partner in computed LQCD
spectrum, but level ordering is
not always consistent to the data
wave functions of the low-lying
N* states dominate by 1-2 SU(6)
configurations, while the wave
function of high lying N*’s may
contain many SU(6) configurations
presence of hybrid-N*s with
dominant contribution of hybrid
components at MN*>1.9 GeV marked by
Should be verified by experiment !
New direction in N* studies proposed in V.D.Burkert, arXiv: [nucl-ex]:
Search for hybrid N*-states looking for:
overpopulation of SU(6)-multiplet;
particular behavior of gvNN* electrocouplings, which reflects presence of the hybrid
component.

28. Transition N-P11(1440) form factors in LQCD
Includes the quark loops in the sea , which are
critical in order to reproduce the CLAS data at Q2<1.0 GeV2
A1/2, S1/2 => F1*, F2*
Mπ = 390, 450, 875 MeV
L box =3.0, 2.5, 2.5 f
H.W. Lin and S.D. Cohen, arXiv:
CLAS data
Exploratory LQCD results provide reasonable description of the CLAS data from the QCD
Lagrangian.
Prospects for LQCD evaluation with improved projection operators, approaching physical mp in the box of appropriate size.
V.I.Mokeev DNP Fall Meeting, October 23-26, Newport News, VA, USA

29. Evidence for chiral symmetry breaking from Q2-evolution of the ground state and S11(1535) parity partner form factors
In chiral symmetry limit:
-F1, F1*
M,m are S11(1535) and proton masses, k= 1.79
F1*, F2* p→S11(1535) form factors from
the CLAS data
F2, F2*
parameterization of elastic Dirac F1 and
Pauli F2 form factors
Evaluation of F1* and F2* starting
from QCD within the framework of
Light Cone Sum Rule & LQCD.
V.Braun et al., Phys. Rev. Lett., 103,
(2009) .
Update: LCSR at NLO is in progress
J.Rohrwild, priv. com.

30. Summary of the CLAS data on KY electroproduction off protons
Observables
Channel
Coverage over Q2, GeV2
Coverage over W, GeV
References
Px,y,z
KL,KS0
[1] Ae KL
[2]
ds/dW
[3]
[4]
1. D.S. Carman et al.,(CLAS Collaboration), Phys. Rev. C79, (2009).
2. R. Nasseripour et al., (CLAS Collaboration), Phys. Rev. C77, (2008).
3. P. Ambrozewicz et al., (CLAS Collaboration), Phys. Rev. C75, (2007).
4. D.S. Carman et al., (CLAS Collaboration), Phys. Rev. Lett. 90, (2003).
More than 85% of meson electroproduction data worldwide were obtained
in experiments with the CLAS detector and available in the CLAS Physics
Data Base:

31. CLAS12 Central Detector Forward Detector
CLAS12 supports a broad program in hadronic physics.
Plans to study excited baryons and mesons:
Search for hybrid mesons and baryons
Spectroscopy of Ξ* , Ω-
N* Transition form
factors at high Q2.
Forward
Detector

32. Resonance Transitions with the CLAS12
12 GeV experiment E will extend access to electrocouplings for all prominent N* states in the range up to Q2=12GeV2.
Resonance electrocouplings in regime of quark core dominance can be related to the running quark masses and their dynamical structure.
P11(1440) A1/2
Light front quark model:
I.G.Aznauryan, V.D. Burkert,
PRC85, (2012).
accessible
at 6 GeV
LQCD
DSE
quark mass (GeV)
accessible
at 12 GeV
DSEQCD :
contact inte-
raction;
realistic QCD
interaction.
CLAS12 projected
Probe the transition from confinement to pQCD regimes, allowing us to explore how confinement in baryons emerge from QCD and how >98 % of baryon masses are generated non-perturbatively via dynamical chiral symmetry breaking.