Philip L ColeIdaho State University

April 17, 2012

MotivationMotivationL2I 2J

LN*

J.J.Dudek and R.G.Edwards, Hybrid Baryons in QCDarXiv:1201.2349[hep-ph] (January 10, 2012)

Photo & ElectroproductionPhoto & Electroproduction

• Difficulties (New Opportunities)– Access to N* structure – Non-perturbative strong interactions

responsible for formation of N*s– A lot of resonances could be present

in a relatively narrow energy region– Nonresonance background is almost

equally as complicated

• Experiments– Jefferson Lab (USA)– MAMI (Germany)– ELSA (Germany)– ESRF (France)

– SPring-8 (Japan)– BES (China) ¶

¶ A unique way of studying the baryon spectrum and N* hadronic decays is via BES: J/ψ N*,…

/q e e

p

/e

CLAS and JLabCLAS and JLab

Studying N*s gives insight into structureStudying N*s gives insight into structure

Indeed in the words of the theorist, Craig Roberts: “there is no greater challenge in the Standard Model, and few in physics, than learning to

understand the truly non-perturbative long-range behavior of the strong interaction.”

Electromagnetic Excitation of N*sElectromagnetic Excitation of N*s

• Both parts of the program are being pursued in various meson photo and electroproduction channels, e.g. Nπ, pη, pπ+π-, KΛ, KΣ, pω, pρ0 using cross sections and polarization observables.

• Global analysis of ALL meson photo- and electroproduction channels – within the framework of an advanced coupled-channel approach developed by EBAC (Excited Baryon Analysis Center – JLab).

Physics Goals for CLAS6Physics Goals for CLAS6

• First electroproduction data: • channels: +n, 0p, and p • Q2 evolution information on the vNN* electrocouplings for the states: PP3333(1232)(1232), PP1111(1440)(1440), DD1313(1520)(1520), and

SS1111(1535) (1535) for Q2 < 5.0 GeV. I.G. Aznauryan et al., (CLAS Collaboration) Phys. Rev. C80, 055203 (2009).

• We recently published the preliminary (first) results on the electrocouplings of the states PP1111(1440), D(1440), D1313(1520), S(1520), S3131(1620), (1620),

PP1313(1720), (1720), andand D D3333(1780) (1780) at Q2 < 0.6 GeV2 in N electro-production from protons V.I. Mokeev, I.G. Aznauryan, V.D. Burkert, arXiv:1109.1294 [nucl-ex] + I.G. Aznauryan, V.D. Burkert, V.I. Mokeev, arXiv:1108.1125 [nucl-ex]

Announcement of Firsts from CLASAnnouncement of Firsts from CLAS

ObservablesRange [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.

Why NWhy N/N/N electroproduction channels are electroproduction channels are importantimportant

CLAS data on meson electro-production at Q2 < 4.0 GeV2• N/N channels are the two major

contributors in N* excitation region;

• these two channels combined are sensitive to almost all excited proton states;

• they are strongly coupled by N→N final state interaction;

• may substantially affect exclusive channels having smaller cross sections, such as p,K, and K.

Therefore knowledge on Therefore knowledge on electroproduction electroproduction mechanisms is key for mechanisms is key for the entire N* Programthe entire N* Program

How N* electrocouplings can be accessedHow N* electrocouplings can be accessed

v Np

p

e

e’

γv

N N’

N*,△

A3/2, A1/2, S1/2

GM, GE, GC

Consistent results on N* electrocouplings obtained in analyses of various meson channels (e.g. πN, ηp, ππN) with entirely different non-resonant amplitudes will show that they are determined reliably

Advanced coupled-channel analysis methods are being developing at EBAC: B.Julia-Diaz, T-S.H.Lee et al., PRC76, 065201 (2007);T.Sato and T-S.H.Lee arXiv:0902.353[nucl-th]

• Isolate the resonant part of production amplitudes by fitting the measured observables within the framework of reaction models, which are rigorously tested against data.

• These N* electrocouplings can then be determined from resonant amplitudes under minimal model assumptions.

N

γv

N’+Non-resonant amplitudes.

• Any contributing mechanism has considerably different shapes of cross sections in various observables defined by the particular behavior of their amplitudes. • A successful description of all observables allows us to check and to establish the dynamics of all essential contributing mechanisms.

Full JM calc

-

+ +D13(1520) +F15(1685)

p2 direct

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

Hadron Structure with Hadron Structure with Electromagnetic ProbesElectromagnetic Probes

resolution of probe

low

high

,.. Allows to address central question:What are the relevant degrees-of-freedom at varying distance scale?

q

e.m. probe

LQCD/DSEqu

ark

mas

s (G

eV)

3-q core

pQCD

3-q core+MB cloud

Within the relativistic Quark Model framework [B.Julia-Diaz et al., PRC 69, 035212 (2004)], the bare-core contribution is reasonably described by the three-quark component of the wavefunction

One third of G*M at low Q2 is

due to contributions from meson–baryon (MB) dressing:

GD = 1(1+Q2/0.71)2

Data from exclusive π0 production

bare quark core

Q2=5GeV2

Effects of Meson-Baryon DressingEffects of Meson-Baryon Dressing

The P11(1440) electrocouplings from the CLAS data

Quark models:I. Aznauryan LC

S. Capstick LC

Relativistic covariant approach byG.Ramalho/F.Gross .

EBAC-DCC MB dressing (absolute values).

A1/2

S1/2

p 2010

p 2011

N

A1/2 S1/2

A3/2

M.Giannini/E.SantopintohCQM

MB dressing abs val. (EBAC)

The data on A1/2 electrocoupling at Q2>2.0 GeV2 for the first time offer almost direct access to quark core. They are of particular interest for the models of N* structure based on QCD .

CLAS12CLAS12 JLab Upgrade to 12 GeV

Luminosity > 1035cm-2s-1

• General Parton Distributions• Transverse parton distributions• Longitudinal Spin Structure • N* Transition Form Factors• Heavy Baryon Spectroscopy • Hadron Formation in Nuclei

Solenoid, ToF,Central Tracker

Forward Tracker,Calorimeter, Particle ID

• explore the interactions between the dressed quarks, which are responsible for the formation for both ground and excited nucleon states.

• probe the mechanisms of light current quark dressing, which is responsible for >97% of nucleon mass.

Approaches for theoretical analysis of N* electrocouplings: LQCD, DSE, Ads/CFT relativistic quark models. See details in the 62-page White Paper of EmNN* JLAB Workshop, October 13-15, 2008:http://www.jlab.org/~mokeev/white_paper/Aznauryan et al., arXiv:0907.1901[nucl-th]

Need to multiply by 3p2 to get the Q2 per quark

Q2 = 12 GeV2

Independent QCD Analyses Independent QCD Analyses Line Fit: DSE Points: LQCDLine Fit: DSE Points: LQCD

Projections for N* Transitions

For the foreseeable future, CLAS12 will be the only facility worldwide, which will be able to access the N* electrocouplings in the Q2 regime of 5 GeV2 to 10 GeV2, where the quark degrees of freedom are expected to dominate. Our experimental proposal “Nucleon Resonance Studies with CLAS12” was approved by PAC34 for the full 60-day beamtime request. http://www.physics.sc.edu/~gothe/research/pub/nstar12-12-08.pdf.

CLAS published

CLAS PRL subm.

CLAS12 projected

CLAS published

CLAS preliminay

CLAS12 projected

CLAS12CLAS12

20

Nucleon Resonance Studies with Nucleon Resonance Studies with

CLAS12CLAS12

21

V.M. Braun8, I. Cloët9, R. Edwards5, M.M. Giannini4,7, B. Julia-Diaz2, H. Kamano2,

T.-S.H. Lee1,2, A. Lenz8, H.W. Lin5, A. Matsuyama2, M.V. Polyakov6, C.D. Roberts1,

E. Santopinto4,7, T. Sato2, G. Schierholz8, N. Suzuki2, Q. Zhao3, and B.-S. Zou3

JLab PAC 34, January 26-30, 2009

Argonne National Laboratory (IL,USA)1,Excited Baryon Analysis Center (VA,USA)2,Institute of High Energy Physics (China)3,

Istituto Nazionale di Fisica Nucleare (Italy)4,Jefferson Lab (VA, USA)5,

Ruhr University of Bochum (Germany)6,University of Genova (Italy)7,

University of Regensburg (Germany)8,and University of Washington (WA, USA)9

Open invitation. List is open to any and all who wish to participate!

The results from our experiment will be The results from our experiment will be used by EBAC and the Theory Support used by EBAC and the Theory Support Group for our proposal to provideGroup for our proposal to provide

• access to the dynamics of non-perturbative strong interactions among dressed quarks and their emergence from QCD and the subsequent formation into baryon resonances;

• information on how the constituent quark mass arises from a cloud of low-momentum gluons, which constitute the dressing to the current quarks.

[[This process of dynamical chiral symmetry This process of dynamical chiral symmetry breaking accounts for over 97% of the breaking accounts for over 97% of the nucleon mass]nucleon mass]

• enhanced capabilities for exploring the behavior of the universal QCD -function in the infrared regime.

Thank you

BACKUP SLIDES

Dyson-Schwinger Equation (DSE) ApproachDyson-Schwinger Equation (DSE) ApproachDSE provides an avenue to relate N* electrocouplings at high Q2 to QCD and to test the theory’s capability to describe the N* formation based on QCD.

DSE approaches provide a link between dressed quark propagators, form factors, and scattering amplitudes and QCD.

N* electrocouplings can be determined by applying Bethe-Salpeter /Fadeev equations to 3 dressed quarks while the properties and interactions are derived from QCD.

By the time of the upgrade DSE electrocouplings of several excited nucleon states will be available as part of the commitment of the Argonne NL and the University of Washington.

PP1111(1440) electrocouplings from (1440) electrocouplings from the CLAS data on Nthe CLAS data on N/N/N

electroproductionelectroproductionNN

Light front models:

I. Aznauryan

S. Capstick

hybrid P11(1440) [Q3g]

Current Status of Lattice QCDCurrent Status of Lattice QCD

LQCD calculations of the (1232)P33 and N(1440)P11 transitions have been carried out with large -masses. By the time of the upgrade LQCD calculations of N* electrocouplings will be extended to Q2 = 10 GeV2 near the physical -mass as part of the commitment of the JLAB LQCD and EBAC groups in support of this proposal.

(1232)P33 N(1440)P11

JLAB-MSU meson-baryon model (JM) for N* electrocoupling extraction from the -p electroproduction data

3-body processes:

Isobar channels included:

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

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

• Extra contact term.

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

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

-++

p

Unitarized Breit-Wigner anstaz for resonant amplitudes.

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

JLAB-MSU meson-baryon model (JM) for N* electrocoupling extraction from the -p electroproduction data

3-body processes: Isobar channels included:

• +D013(1520), +F0

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

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

F015(1685)

(P++33(1640))

(-)

(+)

Evidence for +D013(1520) isobar channel in the CLAS +-p data

full JM results with +D0

13(1520) implemented

full JM results without +D0

13(1520) and adjusted direct 2 production

+D013(1520) contribution

W=1.74 GeV Q2=0.65 GeV2

M+p, GeV

N* parameters of the JM model and their relationships to the observablesRegular Breit-Wigner (BW) ansatz as the start point :

*

**

22

*

**

)(NNNN

pemNNdecf

res

MWMTT

TWi

amplitudes are related to the partial N* decay widths to the or p final states of definite helicityf

*Ndecf T

f

fNN

fN

pMJfT

edTTN

NNdecNdecf

i

fNdecfNdecf

p

J

),,(

))(cos(

*

**,*

0

*

0

***

*

fdec is the kinematical factor, which depends onresonance spin, mass and abs. CM 3-momenta values of the stable final hadron averaged over the line of unstable final hadron at the running W (p) and at W=MN* (pN*). f and f are the CM final stable hadron ermission angles.

Definition of vNN* electrocouplings :

2

2/3

2

2/1**

2

)12(

2* AAMJ

Mq

NN

nucN

is N* electromagnetic decay width, qN* is abs. photon CM 3-momentum value at W=MN* .

The relationships between N* electroproduction amplitudes Tem and vNN* electrocouplings A1/2, A3/2, S1/2

are obtained imposing the requirement: fully integrated resonant cross section should be described by the relativistic Breit-Wigner formula in a case of single contributing resonance.

Exact expressions for the factors fem and fdec can be found in: M.Ripani et al., Nucl. Phys. A673, 220 (2000).

)(),(

)(***

2

2/3

2

2/12

2/12{*),,( QAQA

QSqqMfT NNempemN

The A1/2, A3/2, S1/2 vNN* electrocouplings and f N* partial decay widths are determined at resonant point W=MN*.

Electromagnetic Excitation of N*s Electromagnetic Excitation of N*s

v N

p

p

e

e’

γv

N N’

N*,△

A3/2, A1/2, S1/2

Ml+/-, El+/-, Sl+/-

Measure the electromagnetic excitations of low-lying baryon states (<2 GeV) and their transition form factors over the range Q2 = 0.1 – 7 GeV2 and measure the electro- and photo-production of final states with one and two pseudo-scalar mesons.

DOE Milestone 2012

error bars include systematic uncertainties

M.Giannini/E.Santopintohyper-centricCQM

DD1313(1520) electrocouplings from the CLAS data (1520) electrocouplings from the CLAS data on Non N/N/N electroproduction electroproduction

• electrocouplings as determined from the N & N channels are in good agreement overall

• but the apparent discrepancies for the A3/2 amplitude at Q2 < 0.4 GeV2 will be further investigated in a combined N/N analysis

• hypercentric Consituent Quark Model calculations reasonably describe electrocouplings at Q2>2.5 GeV2, suggesting that the 3-quark component is the primary contribution to the structure of this state at high Q2.

Meson-baryon dressing / Quark core contributions in the Meson-baryon dressing / Quark core contributions in the AA1/2 1/2 electrocouplings of the electrocouplings of the PP1111(1440) & D(1440) & D1313(1520) states.(1520) states.

Estimates from EBAC for the MB dressing: B.Julia-Diaz et al., PRC 76, 5201 (2007).

P11(1440) D13(1520)

Light Front quark model by I.Aznauryan

hypercentric -quark model by M.Giannini

Roper resonance in LQCD

CLAS data

Includes the quark loops in the sea, which are critical 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 H.W. Lin and S.D. Cohen, arXiv:1108.2528

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

*