V.I.Mokeev Hadron2011, June 13 –17, 2011, Munich

Nucleon resonance electrocouplings from CLAS data on pion electroproduction

V.I. Mokeev, I.G. Aznauryan, V.D. BurkertJefferson Lab

Hadron2011 Conference at University of Munich June 13-17 2011

V.I.Mokeev Hadron2011, June 13 –17, 2011, Munich

Primary objectives in the studies of gvNN* electrocouplings with CLAS

Current experimental program with 6.0 GeV electron beam:

• seeks to determine gvNN* transition helicity amplitudes (electrocouplings) at photon virtualities 0.2<Q2<5.0 GeV2 for most excited proton states from analyzing several meson electroproduction channels combined;

• employs advanced coupled channel approach under development at EBAC and worldwide..

Proposal on the future studies of N* electrocouplings at 5.0<Q2<12 GeV2 with CLAS12 detector was approved by PAC.

The information on Q2 evolution of the gvNN* electrocouplings will allow us to

• determine the active degrees of freedom in N* structure versus distance scale;

• study the non-perturbative strong interactions which are responsible for the ground and excited nucleon state formation;

• explore how N*’s emerge from QCD.

V.I.Mokeev Hadron2011, June 13 –17, 2011, Munich

N* parameters from analyses of exclusive electroproduction channels

γv

N N’

N*,△

A3/2, A1/2, S1/2

GM, GE, GC

, , p hpp,..

N

, , ,..p h pp

N’+*

• Separation of resonant and non-resonant contributions represents most challenging part, and can be achieved within the framework of reaction models.

• N* ‘s can couple to various exclusive channels with entirely different non-resonant amplitudes, while their electrocouplings should remain the same.

• Consistent results from the analyses of major meson electroproduction channels Np and p+p-p show that model uncertainties in extracted N* electrocouplings are under control.

Resonant amplitudes Non-resonant amplitudes

V.I.Mokeev Hadron2011, June 13 –17, 2011, Munich

Summary of the CLAS data on Np electroproduction off protons

Observablesarea, GeV2

Number of data points

dσ/dΩ(π0) 0.16-1.45

3.0-6.0398309000

dσ/dΩ(π+) 0.25-0.60

1.7-4.32558830 849

Ae(π0) , At(π0) 0.25-0.65 3981

Ae(π+) , At(π+) 0.40-0651.7 - 3.5

17303 535

Aet(π0) 0.25-0.61 1521

2Q

Number of data points >116000, W<1.7 GeV, 0.15<Q2<6.0 GeV2 , almost complete coverage of the final state phase space.

Low Q2 results:I. Aznauryan et al., PRC 71, 015201 (2005); PRC 72, 045201 (2005).

High Q2 results on Roper: I. Aznauryan et al., PRC 78, 045209 (2008).

Final analysis:I.G.Aznauryan,V.D.Burkert, et al.(CLAS Collaboration), PRC 80. 055203 (2009).

All data sets can be found in:http://clasweb.jlab.org/physicsdb/

V.I.Mokeev Hadron2011, June 13 –17, 2011, Munich

Unitary Isobar Model (UIM) for Np electroproduction

•Final-state pN rescatteringin K-matirix approximation.

I. Aznauryan, Phys. Rev. C67, 015209 (2003) p+

• Based on MAID modelD.Drechsel et al.,NP, A645,145 (1999).

• All well established N*’s with M<1.8 GeV, Breit-Wigner amplitudes.

• Non-resonant Born terms:pole/reggeized meson

t-channel exchange; s- and u-nucleon terms.

p

p p

pp

p

N

N

N

N

N, ,w r p

V.I.Mokeev Hadron2011, June 13 –17, 2011, Munich

Fixed-t Dispersion Relations for invariant Ball amplitudes

Dispersion relations for 6*3 invariant Ball amplitudes:

17 Unsubtracted Dispersion Relations

(i=1,2,4,5,6)

γ*p→Nπ

The Ball amplitudes Bi (±,0)

are invariant functions in the transition current:

uIu PN 5

defined mostly by N*’s1 Subtracted Dispersion

Relation

(i=3)

')''

1(Im

π

P)

us

1)((

)]t,(s,[ReRe)0,,(

)0,(2

N

,0),(

i2

N

2s)(v,

i

2,0)(

i

,0)(

i

mηη

mQR

QBB

dss ssssthr

iiB

')'

1

'

1(Im

π

P

),(t

)(eg-)

u

1

s

1)(()t,(s,Re

)(

3

2

2

2

2

N

2

N

2(v)

3

2(-)

3mmm

QRQB

dss ssss

t

thrB

QfQF

sub

V.I.Mokeev Hadron2011, June 13 –17, 2011, Munich

Fits to gp→p+n differential cross sections and structure functions

DR

UIMDR w/o P11

DR

UIMQ2=2.44 GeV2

Q2=2.05 GeV2

L=0 Legendre moments from various structure functions

ds/

dWp

V.I.Mokeev Hadron2011, June 13 –17, 2011, Munich

The CLAS data on p+p-p differential cross sections and description within the JM model

full JM calc.

p-D++

p+D0

2p direct

rp

p+D013(1520)

p+F015(1685)

G.V.Fedotov et al, PRC 79 (2009), 015204 M.Ripani et al, PRL 91 (2003), 022002

V.I.Mokeev User Group Meeting June 18 2008 9

JLAB-MSU meson-baryon model (JM) for p+p-p electroproduction

3-body processes:

Isobar channels included:

• All well established N*s with pD decays and 3/2+(1720) candidate.

• Reggeized Born terms with effective FSI and ISI treatment (absorptive approximation).

• Extra pD contact term.

• All well established N*s with rp decays and 3/2+(1720) candidate.

• Diffractive ansatz for non-resonant part and r-line shrinkage in N* region.

p-D++

r0p

V.I. Mokeev , V.D. Burkert, T.-S.H. Lee et al., Phys. Rev. C80, 045212 (2009)

V.I.Mokeev Hadron2011, June 13 –17, 2011, Munich

JLAB-MSU meson-baryon model (JM) for p+p-p electroproduction

3-body processes: Isobar channels included:

• p+D013(1520), p+F0

15(1685), p-P++33(1640)

isobar channels observed for the first time in the CLAS data at W > 1.5 GeV.

F015(1685)

(P++33(1640))

(p-)

(p+)

Unitarized Breit-Wigner Anstaz for resonant amplitudesI.J.R.Aitchison, Nuclear Physics , A189 (1972), 417

Off-diagonal transitions incorporated into JM:

S11(1535) ↔ S11(1650)D13(1520) ↔ D13(1700)3/2+(1720) ↔ P13(1700)

WMMMS NNi

N i 2

**

2

*

1 )( Inverse of JM unitarized N* propagator:

N*a N*a

diagonal

N*a N*b

off-diagonal

V.I.Mokeev Hadron2011, June 13 –17, 2011, Munich

Direct 2p production required by unitarity:

Most relevantat W<1.60 GeV.

Negligible atW>1.70 GeV

JLAB-MSU meson-baryon model (JM) for p+p-p electroproduction

• Lorentz invariant contractionof the initial and the finalparticle spin-tensors• exponential propagators fortwo unspecified exchanges

Magnitudes and relative phases fit to the data

phases=0

W=1.51 GeVQ2=0.65 GeV2

phases fit to the data

W=1.51 GeVQ2=0.65 GeV2

V.I.Mokeev Hadron2011, June 13 –17, 2011, Munich

N pp CLAS preliminary.

N p CLAS

Good agreement between the electrocouplings obtained from the Np and Npp channels. N* electrocouplings are measurable and model independent quantities.

I. Aznauryan,V. Burkert, et al., PRC 80,055203 (2009).

A1/2S1/2

A3/2

F15(1685)

A3/2

P11(1440) P11(1440)

D13(1520)

N p world

V. Burkert, et al., PRC 67,035204 (2003).

N p Q2=0, PDG.

N p Q2=0, CLAS

M. Dugger, et al., PRC 79,065206 (2009).

gvNN* electrocouplings from the CLAS data on Np/Npp electroproduction

V.I.Mokeev Hadron2011, June 13 –17, 2011, Munich

High lying resonance electrocouplings from gp→ p+p-p

Δ(1700)D33

A1/2

A3/2 S1/2

Studies of p+p-p electroproduction offer best opportunity for extraction of electrocouplings for N* states with masses above 1.6 GeV. Most of them decay preferably to Npp final states.

Electrocouplings of S31(1620), S11(1650), F35(1685), D33(1700) ,and P13(1720) states were obtained for the first time from the p+p-p electroproduction data.

N pp CLAS preliminary.

N p world

V.D.Burkert, et al., PRC 67,035204 (2003).

N p Q2=0, PDG.

N p Q2=0, CLAS

M.Dugger, et al., PRC 79,065206 (2009).

All CLAS results on N* electrocouplings can be found in: www.jlab.org/~mokeev/resonance_electrocouplings/

V.I.Mokeev Hadron2011, June 13 –17, 2011, Munich

Mystery of P11(1440) structure is solved

Quark models:I. Aznauryan LC

S. Capstick LCRelativistic covariant approach byG.Ramalho /F.Gross .

The electrocouplings are consistent with P11(1440) structure as a combined contribution of: a) internal quark core as a first radial excitation of three dressed quarks in the ground proton state, and b) external meson-baryon dressing.

EBAC-DCC MB dressing (absolute values).

A1/2

S1/2

Meson-baryon dressing amplitudes:

V.I.Mokeev Hadron2011, June 13 –17, 2011, Munich

Lattice QCD

Computedfrom CLASresults onP11(1440)electrocouplings

F2

F1

F1

F2

p

p

n

n

V.I.Mokeev Hadron2011, June 13 –17, 2011, Munich

Approaching physical pion mass, and accounting for quark loops in the sea, LQCD is making progress toward evaluation of N* electrocouplings from first QCD principles.

Experimental data.

V.I.Mokeev Hadron2011, June 13 –17, 2011, Munich

S11 (1535) electrocouplings and their interpretation

Analysis of pη channel assumes S1/2=0Branching ratios: βNπ = βNη = 0.45

QCD-based LQCD & LCSR calculations (black solid lines) by Regensburg Univ. Group reproduces data trend at Q2>2.0 GeV2

Successful description of S11(1535) electrocouplings based on OCD!

CLAS pηCLAS nπ+

LC SR

LCQM

A1/2 (Q2) from Nπ and pη are consistent First extraction of S1/2(Q2) amplitude

CLAS pηCLAS nπ+

HallC pη

V.I.Mokeev Hadron2011, June 13 –17, 2011, Munich

Resonance Transitions at 12 GeV

CLAS12 projected

Experiment E12-09-003 will extend access to transition FF for many prominent states

in the range up to Q2=12GeV2.

quar

k m

ass

(GeV

)

Electromagnetic form factors are sensitive to the dynamical dressed

quark mass.

In this experiment we will probe the transition from “dressed quarks” to current pQCD quarks for the first time.

accessibleat 6 GeV

accessibleat 12 GeV

V.I.Mokeev Hadron2011, June 13 –17, 2011, Munich

• The measurements with CLAS in N* excitation region extended considerably data on Np electroproduction cross sections, polarization asymmetries with full coverage of the final state phase space. Nine independent differential and fully integrated p+p-p electroproduction cross section were obtained for the first time.

• Good description of the data on N p and p+p-p electroproduction was achieved, allowing us to separate resonant and non-resonant contributions, needed for the evaluation of N* electrocouplings.

• For the first time consistent results on electrocouplings of several N* states were obtained in independent analyses of dominant Np and p+p-p electroproduction channels with completely different non-resonant contributions, offering an evidence for reliable electrocoupling extraction.

• Preliminary results on electrocouplings of high lying S31(1620), S11(1650), F15(1685), D33(1700), and P13(1720) states have become available from p+p-p electroproduction for the first time

Conclusions and Outlook

V.I.Mokeev Hadron2011, June 13 –17, 2011, Munich

• Analyses of the CLAS data on N* electrocouplings within the framework of different quark models and the EBAC-DCC coupled channel approach showed that the structure of resonances with masses < 1.6 GeV is determined by internal quark core and external meson-baryon cloud.

• Lattice QCD, Dyson-Schwinger equations of QCD are making progress toward evaluation of N* electrocouplings from first principles of QCD. Analyses of experimental data on N* electrocouplings within the framework of these approaches offer a promising avenue to explore how excited proton states emerge from QCD.

• The future studies of N* electrocouplings at Q2>5.0 GeV2 with CLAS12 will allow us for the first time to access quark degrees of freedom almost directly, and to explore how dynamical dressed quark masses, structure and their interactions, that are responsible for N* formation in confinement regime, come from QCD.

N* electrocoupling studies are of particular importance in order to understand how diverse world of hadron matter is created by fundamental QCD interactions.

Conclusions and Outlook

V.I.Mokeev Hadron2011, June 13 –17, 2011, Munich

Back-up

V.I.Mokeev Hadron2011, June 13 –17, 2011, Munich

Comparison between the CLAS and MAID results

P11(1440)

A1/2

S1/2

MAID07 MAID08

V.I.Mokeev Hadron2011, June 13 –17, 2011, Munich

Comparison between the CLAS and MAID results

D13(1520)

A1/2

S1/2

MAID07 MAID08

A3/2

V.I.Mokeev Hadron2011, June 13 –17, 2011, Munich

Resonant and non-resonant parts of p+p-p cross sections as determined from the CLAS data fit within the framework of JM model

full cross sections resonant part non-resonant part

V.I.Mokeev Hadron2011, June 13 –17, 2011, Munich

N* decay parameters to Npp final states from the CLAS p+p-p electroproduction data

Parameters CLAS p+p-p electro production data

PDG

G total, MeV 126±7 100-125

pD BF, % 24-33 15-25

rp BF, % 7-16 15-25

Parameters` CLAS p+p-p electro production data

PDG

G total, MeV 136±8 125-175

pD BF, % 5-11 <1

rp BF, % 3.6-13.7 <4

N pp decays of D13(1520) are close to those reported in the PDG.

For S11(1535) they are greater than the PDG values with almost equal pD and rp BF’s.

D13(1520)

S11(1535) Note: uncertainties for G tot were obtained by varying Npp decay widths only.