studies of n* structure from the clas meson electroproduction data

M. Ripani, MENU 2013, Rome, September 30 – October 4, 2013

Studies of N* Structure from the CLAS Meson Electroproduction Data

N,N* quark core

MENU 2013 Conference

M. Ripani,INFN Genova


Studies of the N*-Structure 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.

This information is needed to study the evolution of relevant degrees of freedom in N* structure with distance and to access the non-perturbative strong interaction which generates N* states as bound systems of quarks and gluons

(see I. G. Aznauryan et al., Int. J. Mod. Phys. E22, 133015 (2013)).

The non-perturbative strong interaction represents the most important part of the Standard Model that we have yet to explore.

It is the only fundamental sector where relevant degrees of freedom accessible in the measurements can be very different with respect to those entered in the basic QCD Lagrangian.


Extraction of gvNN* electrocouplings from the data on exclusivemeson electroproduction off protons

γv

N N’

N*,△

• A1/2(Q2), A3/2(Q2), S1/2(Q2)or

• G1(Q2), G2(Q2), G3(Q2) or• GM(Q2), GE(Q2), GC(Q2)

p, h, pp,..

N

p, h, pp,..

N’+*

• 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 demonstrate reliable extraction of N* parameters.

Resonant amplitudes Non-resonant amplitudes

2

2/3

2

2/1*

2

)12(

2AAMJ

MqNr

Nr

pg

g

N*’s photo-/electrocouplings gvNN* are definedat W=MN* through the N* electromagneticdecay width g :

See details in:I.G.Aznauryan andV.D.Burkert, Progr. Part. Nucl. Phys. 67, 1 (2012).

e

e’

V.I.Mokeev User Group Meeting June 18 2008

CEBAF Large Acceptance Spectrometer

Liquid D2 (H2)target +g start counter; e minitorus

Drift chambersargon/CO2 gas, 35,000 cells

Electromagnetic calorimetersLead/scintillator, 1296 PMTs

Torus magnet6 superconducting coils

Gas Cherenkov counterse/pi separation, 216 PMTs

Time-of-flight countersplastic scintillators, 684 PMTs

Large angle calorimetersLead/scintillator, 512 PMTs

The unique combination of the CEBAF continuous electron beam and the CLAS detector makes Hall-B@JLAB the only facility operational worldwide, that is capable of measuring unpolarized cross sections and polarization asymmetries of most exclusive meson electroproduction channels with substantial contributions at W<3.0 GeV and Q2<5.0 GeV2.

V.I.Mokeev, NSTAR 2013 Workshop Peniscola, Spain, May 27-30, 2013


Summary of the CLAS Data on Exclusive Meson Electroproduction off Protons in N* Excitation Region

Hadronic final state

CoveredW-range, GeV

Covered Q2-range, GeV2

C

Measured observables

p+n 1.1-1.401.1-1.551.1-1.7

0.15-0.40 0.3-0.6 1.7-4.2

ds/dW ds/dW ds/dW, Ab

p0p 1.1-1.401.1-1.71.1-1.7

0.15-0.40 0.4-0.7 0.75-6.0

ds/dW ds/dW, Ab,At,Abt

ds/dW

hp 1.5-2.0 0.2-4.0 ds/dW

K+L 1.65-2.351.65-2.35

0.65-2.55 1.4-2.6

ds/dW P’

K+S0 1.7-2.11.8-2.51.7-2.6

0.5-2.55 1.5-3.50 1.8-3.50

ds/dW P’ ds/dW

p+p-p 1.3-1.61.4-2.1

0.2-0.6 0.5-1.5

Nine 1-fold differential cross sections

• ds/dW-CM angulardistributions• Ab,At,Abt-longitudinalbeam, target, and beam-target asym-metries• P’ –recoil polarization of strange baryon

The data are available in the CLAS Physics Data Base:

http://depni.sinp.msu.ru/cgi-bin/jlab/db.cgi

Almost full coverageof the final hadron phase space in pN, p+p-p, hp, and KY electroproduction


CLAS data on yields of meson electroproduction at Q2<4 GeV2

N* Electroexcitation in Exclusive Meson Electroproduction off Protons

State Bran. Fract. to Np.

Bran. Fract. to Nh

Bran.Fract. Nππ

Δ(1232)P33 0.995

N(1440)P11 0.55-0.75 0.3-0.4

N(1520)D13 0.55-0.65 0.4-0.5

N(1535)S11 0.48±0.03 0.46±0.02

D(1620)S31 0.20-0.30 0.70-0.80

N(1650)S11 0.60-0.95 0.03-0.11 0.1-0.2

N(1685)F15 0.65-0.70 0.30-0.40

Δ(1700)D33 0.1-0.2 0.8-0.9

N(1720)P13 0.1-0.2 > 0.7

Hadronic decays of prominent N*s at W<1.8 GeV.


• Analyses of different meson electroproduction channels independently: p+n and p0p channels: Unitary Isobar Model (UIM) and Fixed-t Dispersion Relations (DR) I.G.Aznauryan, Phys. Rev. C67, 015209 (2003). I.G.Aznauryan et al., CLAS Coll., Phys Rev. C80, 055203 (2009). hp channel: Extension of UIM and DR I.G.Aznauryan, Phys. Rev. C68, 065204 (2003). Data fit at W<1.6 GeV, assuming S11(1535) dominance H.Denizli et al., CLAS Coll., Phys.Rev. C76, 015204 (2007). p+p-p channel: Data driven JLAB-MSU meson-baryon model (JM) V.I.Mokeev, V.D.Burkert et al., Phys. Rev. C80, 045212 (2009). V.I.Mokeev et al., CLAS Coll., Phys. Rev. C86, 035203 (2012). Global coupled-channel analyses of the CLAS/world data of pN, gvN → pN, hN, ppN, KL,

KS exclusive channels: N. Suzuki, T. Sato, T.-S.H. Lee, Phys.Rev. C82 (2010) 045206

H. Kamano, T.-S. H. Lee, AIP Conf.Proc. 1432 (2012) 74-79

Approaches for Extraction of gvNN* Electrocouplings from the CLAS Exclusive Meson Electroproduction Data


Fits to gVp→pn Differential Cross Sections and Structure Functions

DR

UIMDR w/o P11

DRUIMQ2=2.44 GeV2

Q2=2.05 GeV2

Legendre moments Dl (l=0,1,2) from various structure functions

ds/dW

p


The CLAS Data on pp-p Differential Cross Sections and their Fitwithin the Framework of Meson-Baryon Reaction Model JM

full JM calc.p-D++

p+D0

2p directrpp+D0

13(1520)

p+F015(1680)

G.V.Fedotov et al, PRC 79 (2009), 0152041.30<W<1.56 GeV; 0.2<Q2<0.6 GeV2

M.Ripani et al, PRL 91 (2003), 0220021.40<W<2.30 GeV; 0.5<Q2<1.5 GeV2

V.I.Mokeev User Group Meeting June 18 2008 10

JM Model Analysis of the p+p-p ElectroproductionMajor objectives: extraction of gvNN* electrocouplings and pD, rp decay widths.

• V.I.Mokeev, V.D. Burkert, et al., (CLAS Collaboration) Phys. Rev. C86, 035203 (2012).

• V.I.Mokeev, V.D. Burkert , et al., Phys. Rev. C80, 045212 (2009).

p-

p

p p’

gD/0 (1232)P33, N0 (1520)D13, D (1600)P33, N0(1680)F15

p-/

p’

p

g

gg

pp

p

p’,p’, …

p’

p-

p

p-, p, …

p, p-, …

=

+ +

• six meson-baryonchannels and directp+p-p production.

• N* contribute to pDand rp channels only.

• unitarized Breit-Wigneransatz for resonantamplitudes.

r

V.I.Mokeev, NSTAR 2013 Workshop Peniscola, Spain, May 27-30, 2013


Developed based on approach: I.J.R.Aitchison, Nuclear Physics , A189 (1972), 417.

Off-diagonal transitions incorporated into the full resonant amplitudes of the JM model:

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

ii WMMMS NNi

N i 2**

2*

1 )( -- - Inverse of the JM unitarized N* propagator:N* N*

diagonal

N* N*

off-diagonal

Unitarized Breit-Wigner ansatz for resonant amplitudes

Full resonant amplitude of unitarized Breit-Wigner ansatz is consistent with restrictions imposed by a general unitarity condition, as well as with the resonant Argonne-Osaka ansatz in on-shell approximation.


NΔ Transition Form Factors

bare quark core

CLASHall A Hall

CMAMIBates

Meson-Baryoncloud

T. Sato and T-S. H. Lee, PRC 63, 055201 (2001).

No evidences for pQCD onset at Q2<7 GeV2

Successful description was achieved taking into account meson-baryon dressing and quark core

Quadrupole RatiosMagnetic Dipole Form Factor

The mechanisms of themeson-baryon dressing

pQCD: REM → 1.0

pQCD: ~1/Q5

pQCD: RSM → const

Quark core was well described by the relativistic QM: B.Julia-Diaz et al., PRC 69, 035212 (2004).


Quark vs Meson-Baryon Degrees of Freedom in N→D Form Factors

GeVGeV

qp

mmmDgdressed

q

bare

q

G

IR

368.0007.0

4)( 2

2

- p

Q2/mr2

Quark core contribution from DSEQCD:J.Segovia, et al., arXiv:1305.0292[nucl-th].

Contact interaction. Non-perturbative mass generation:

contact interaction. contact interaction & quarkanomalous magn. moment. projection for quark running mass. bare G*M inferred from exp. data within Argonne-Osaka c.c. approach.

G* M

(Jon

es-S

cadr

on)

G1 and G2 N→D f.f. from LF quark model:I.G.Aznauryan, V.D.Burkert, Phys. Rev. C85,055202 (2012).

quark core.

meson-baryon cloud from Argonne-Osaka approach.dressed G1 and G2 f.f.

For the first time this quark model accounts for momentum dependence of dressed quark mass.


The P11(1440) Structure from the CLAS Electrocoupling Data

Light Front quark models:

I.G.Aznauryan,

• The physics analyses of these results revealed the P11(1440) structure as a combined contribution of: a) quark core as a first radial excitation of the nucleon 3-quark ground state and b) meson-baryon dressing.

Meson-Baryon dressing: (absolute values)

A1/2

S1/2pp-p prelim.

pp-p 2012

Np2009

B,Julia-Diaz et al., PRC 77, 045205 (2008).

PRC 76, 025212 (2007).

S.Capstick and B.D.Keister, PRD51, 3598 (1995).

CLAS data:

• Consistent values of P11(1440) electrocouplingsdetermined in independent analyses of Np and p+p-p exclusive channels strongly support reliable electrocoupling extraction.


Quark Core vs Meson-Baryon Cloud in the Structure of P11(1440)

Consistent results on the quark core contribution from:

A1/2

• 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.

GeVGeV

GeV

qp

mm

m

mDg

dressed

q

bare

q

GIR

G

IR

368.0007.0

8.093.04

4)( 2

2

-

p

p

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 .

First evaluation of the quark core contribution to the P11(1440) electrocouplings starting from QCD Lagrangian within Dyson-Schwinger Equations of QCD:

global meson photo-, electro-, and hadroproduction data analysis within EBAC/ Argonne-Osaka approach.

D.J.Wilson, et al, Phys. Rev. C85, 025205 (2012).

DSEQCD.


gvNN* Electrocouplings of D13(1520) and S11(1535) Resonances

D13(1520)A1/2

D13(1520)A3/2

S11(1535)A1/2

M.Giannini,E.Santopinto, PRC 86, 065202 (2012).S.Capstick, B..D.Keister , PRD51, 3598 (1995).

MB dressing abs. values (EBAC/Argonne-Osaka)

• a good agreement between the results from Np, Nh and p+p-p exclusive channels.• access to the lowest orbital excitation of 3-q system and DCSB manifestation through comparison of the ground and S11(1535) state structure (chiral partners).• contributions from inner quark core and external meson-baryon cloud, which depends substantially on the resonance quantum numbers.

hp CLAS, Hall-C


High lying resonance electrocouplings from the pp-p CLAS data analysisΔ(1700)D33

A1/2

pp-p electroproduction channel provided first preliminary results on S31(1620), S11(1650), F15(1685), D33(1700) , and P13(1720) electrocouplings with good accuracy.

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

Np Q2=0, CLASM.Dugger, et al., PRC 79,065206 (2009).

A3/2

Npp CLASpreliminary

computed from the data on D13(1520) andS11(1535) electrocouplings within the framework of SQTM approach:I.G. Aznauryan and V.D. Burkert, Progr.Nucl. Part. Phys. 67, 1 (2012).

Single quark electromagnetic current and SU(6) spin-flavor symmetry play an important role in the structure and electroexcitation of D13(1520), S11(1535), and D33(1700) states.

BF(Npp): 80-90%


High lying resonance electrocouplings from the pp-p CLAS data analysis

N (1685)F15 A1/2

A3/2

MAID analysis of Np electroproductionL.Tiator et al., Eur. Phys. J. Spec. Top.198, 141 (2011).

The results from pp-p channel confirmed the previousMAID analysis of Np electroproduction

Hypercentral constituent quark model by M.M.Giannini, E.Santopinto, PRC 86, 065202 (2012).

Difference between the experimental results and QM expectations is likely related to meson-baryon cloudcontributions.

Evaluations of meson-baryon cloud contributions to electrocouplings of high mass resonances are needed.

Bethe-Salpeter Bonn model byM.Ronninger, B.Ch.Metsch, EPJA49, 8 (2013).

BF(Np): 65-70%BF(Npp): 30-40%


High lying resonance electrocouplings from the pp-p CLAS data analysis

A1/2D(1620)S31

S1/2

Hypercentral constituent quark model by M.Giannini,E.Santopinto, PRC 86, 065202 (2012).Bethe-Salpeter Bonn model byM.Ronninger, B.Ch.Metsch, EPJA49, 8 (2013).

• Only known N*-state with dominant longitudinalelectroexcitation at Q2>0.5 GeV2 .

• This feature is well reproduced within the framework of hypercentral quark model.

• Data on electrocouplings of most excited proton states in mass range up to 1.8 GeV demonstrated distinctive differences in the structure of resonances of different quantum numbers.

• The studies of the ground and all prominent excited state structure combined are needed in order to explore the mechanisms of the ground and N*-state formation from quarks and gluons.


• High quality meson electroproduction data from the CLAS detector allowed us to determine electrocouplings of P33(1232), P11(1440), D13(1520), and S11(1535) resonances from analyses of Np and Nh channels at Q2<5.0 GeV2 and Q2 <4.0 GeV2 , respectively, as well as from the p+p-p electroproduction at Q2<1.5 GeV2. Consistent values of gvNN* electrocouplings from independent analyses of Np/Npp and Np/Nh channels confirmed reliable extraction of these fundamental quantities.

• Preliminary results on electrocouplings of S31(1620), S11(1650), F15(1680), D33(1700), and P13(1720) resonances were obtained from analysis of p+p-p electroproduction at 0.5<Q2

<1.5 GeV2 for the first time.

• Analyses of the results on gvNN* electrocouplings revealed the N*-structure as internal core of three constituent quarks surrounded by external meson-baryon cloud. Resonances of different quantum numbers provided complementary information on the N* structure. The data on electrocouplings of all prominent N*-states are needed.

• Electrocouplings of most N*-states in mass range up to 2.0 GeV will be determined in few years from independent analyses of Np and Npp electroproduction at photon virtualities up to 5.0 GeV2.

Conclusions and Outlook


Conclusions and outlook • The dedicated experiment on N* studies with the CLAS12 detector at the

largest photon virtualities ever achieved 5.0<Q2<12 GeV2 is scheduled for the first year of running after completion of the Jefferson Lab 12 GeV Upgrade Project.

• The N* program with the CLAS12 detector opens up the prospects to elucidate the emergence of >98 % of nucleon and N* masses from QCD.


Back up


Forward Detector

CLAS12

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.

Central Detector


Resonance Transitions with the CLAS1212 GeV experiment E12-09-003 will extend access to electrocouplings for all prominent N* states in the range up to Q2=12GeV2.

quar

k m

ass

(GeV

)

Resonance electrocouplings in regime of quark core dominance can be related to the running quark masses and their dynamical structure.

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.

accessibleat 6 GeV

accessibleat 12 GeV

LQCDDSE

CLAS12 projected

Light front quark model:I.G.Aznauryan, V.D. Burkert,PRC85, 055202 (2012).

DSEQCD :contact inte-raction;realistic QCDinteraction.

P11(1440) A1/2


Studies of Nucleon Resonance Structure in Exclusive Meson Electroproduction

• I. G. Aznauryan, A. Bashir, V. Braun, S.J. Brodsky, V.D. Burkert, L. Chang, Ch. Chen, B. El-Bennich, I.C. Cloët, P.L. Cole, R.G. Edwards, G.V. Fedotov, M.M. Giannini, R.W. Gothe, F. Gross, Huey-Wen Lin, P. Kroll, T.-S.H. Lee, W. Melnitchouk, V.I. Mokeev, M.T. Peña, G. Ramalho, C.D. Roberts, E. Santopinto, G F. de Teramond, K. Tsushima, D.J. Wilson

27 authors – 99 pages

• Will be published in Int. J. Mod. Phys. E22, 1330015 (2013).

http://arxiv.org/abs/1212.4891


Evidence for new N* states and couplings

StateN((mass)JP

PDG 2010 PDG 2012 KΛ KΣ Nγ

N(1710)1/2+ ***(not seen in

GW analysis)

*** *** ** ***

N(1880)1/2+ ** ** * **

N(1895)1/2- ** ** * ***

N(1900)3/2+ ** *** *** ** ***

N(1875)3/2- *** *** ** ***

N(2150)3/2- ** ** **

N(2000)5/2+ * *** ** * **

N(2060)5/2- *** ** ***

Bonn-Gatchina Analysis – A.V. Anisovich et al., EPJ A48, 15 (2012)Strong impact from the CLAS KY photoproduction data on the signala from new states

New states still need to be confirmed


Why studies of ground and excited nucleon states combined are needed?

Di-quarkJp

Ground state

P11

½+(1440) S11

½-(1535) S11

½-(1650)0+ 77%

1+ 23% 100%

0- 51% 43%

1- 49% 57%

• N* states of different quantum numbers offer complementary information on mechanisms of baryon generation from quarks and gluons.

• N* electrocouplings allow us to explore strong regime of QCD at

larger transverse distances with larger s than the ground state form factors.

Di-quark content of ground and N* states from DSEQCD with vector x vector interaction, C.D.Roberts et al.,AIP Conf. Proc. 1432, 309 (2012).

N* spectrum and structure from LQCD, J.J.Dudek, R.G.Edwards, Phys. Rev. D85, 054016 (2012).


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, 054016 (2012).• each N* state with MN* <1.8 GeVhas partner in computed LQCD spectrum, but level ordering isnot 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

New direction in N* studies proposed in V.D.Burkert, arXiv:1203.2373 [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.

Should be verified by experiment !


The Approaches for Extraction of gvNN* Electrocouplings from Np Exclusive Electroproduction off Protons

I. G.Aznauryan, Phys. Rev. C67, 015209 (2003), I.G.Aznauryan, V. D.Burkert, et al. (CLAS Collaboration), PRC 80. 055203 (2009). p+

p

p p

pp

p

N

N

N

N

Nw,r,p

Unitary Isobar Model (UIM)The Model based on fixed-t Dispersion Relations (DR)

• the real parts of 18 invariant Np electroproduction amplitudes are computed from their imaginary parts employing model independent fixed-t dispersion relations.

• the imaginary parts of the Np electroproduction amplitudes at W>1.3 GeV are dominated by resonant parts and were computed from N* parameters fit to the data.


Resonant /non-resonant contributions from the fit of p+p-p electroproduction cross sections within the JM model

W=1.51 GeV, Q2=0.38 GeV2 W=1.51 GeV, Q2=0.43 GeV2

full cross sectionswithin the JM model

resonant part non-resonant part

Reliable isolation of the resonant cross sections is achieved


Transition N-P11(1440) form factors in LQCD

CLAS data

Includes the quark loops in the sea , which arecritical in order to reproduce the CLAS data at Q2<1.0 GeV2

Mπ = 390, 450, 875 MeVL box =3.0, 2.5, 2.5 f

• Exploratory LQCD results provide reasonable description of the CLAS data from the QCDLagrangian.

• Prospects for LQCD evaluation with improved projection operators, approaching physical mp in the box of appropriate size.

H.W. Lin and S.D. Cohen, arXiv:1108.2528

A1/2, S1/2 => F1*, F2

*


gvNN* Electrocouplings: A Unique Window into the Quark StructureMeson-Baryon Dressing

absolute meson-baryon cloud amplitudes (EBAC)

quark core contributions (constituent quark models)

D13(1520)

Data on gvNN* electrocouplings from E12-09-003 experiment (Q2 > 5 GeV2) will afford for the first time direct access to the non-perturbative strong interaction among dressed quarks, their emergence from QCD, and the subsequent N* formation.

CLAS: Np and Np/Npp combined

P11(1440)


Anticipated N* Electrocouplings from data on Np & Npp electroproduction

Open circles represent projections and all other markers the available results with the 6-GeV electron beam

Examples of published and projected results obtained within 60d for three prominent excited proton states from analyses of Np and Npp electroproduction channels. Similar results are expected for many other resonances at higher masses, e.g. S11(1650), F15(1685), D33(1700), P13(1720), …

This experiment will – for the foreseeable future – be the only experiment that can provide data on gvNN* electrocouplings for almost all well established excited proton states at the highest photon virtualities ever achieved in N* studies up to Q2 of 12 GeV2.

S11(1535)D13(1520)P11(1440)

CLAS CLAS

CLASHall C

studies of n* structure from the clas meson electroproduction data

Documents

proton studies of n

reliable extraction

resonant contributions

extraction of gvnn

mokeev user group meeting

s photoelectrocouplings

clas detector

electro production