a new & theoretical/experimental collaborative effort on baryon resonance extraction * philip...

Philip Cole NSTAR 2009 北京中国 April 19-22, 2009 Idaho State University

A newA new& &

theoretical/experimental theoretical/experimental collaborative effort collaborative effort

on baryon resonance extractionon baryon resonance extraction**

Philip ColeIdaho State UniversityApril 22, 2009.

**through a proposed NSF PIRE through a proposed NSF PIRE projectproject

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**through an overarching funding mechanismthrough an overarching funding mechanism


Issues (1)

They have very different contributions They have very different contributions to the production backgroundto the production background. • electron-positron collider electron-positron collider • electron beam onto fixed targetelectron beam onto fixed target

They separately have unique N* They separately have unique N* signaturessignatures • BES: J/BES: J/ BN* BN* BBM (e.g. BBM (e.g. NNNNππ, NN, NNηη) ) • CLAS:CLAS: N* N* BM/BMM (e.g. N BM/BMM (e.g. Nππ/N/Nππππ))

BES and CLAS datasets

── ──── ──

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Issues (2)

BES at BEPC has collected high statistics data on J/ψ production. Its decay into baryon-antibaryon channels offers a unique and complementary way of probing nucleon resonances (N*).

CLAS at JLab has access to N* form factors at high Q2, which is advantageous for the study of structure of nucleon resonances,

The low-background BES results will be able to provide guidance guidance for the search for less-dominantfor the search for less-dominant excited states at JLab.

Several N* states have been seen at BES in the mass region of 2 GeV. M. Ablikim et al., (BES Collaboration), Phys. Rev. Lett. 97, 062001 (2006).

With the precision electron and photon beams afforded by JLab, not only would the existence of these new N* states be existence of these new N* states be confirmedconfirmed, but it would further allow for their properties to be their properties to be precisely mapped outprecisely mapped out at various distances or Q at various distances or Q22.

BES tells where to dig and CLAS has the steam shovelBES tells where to dig and CLAS has the steam shovel

Coordination of efforts between BES and CLAS is timelyCoordination of efforts between BES and CLAS is timely3


And the time has come; the talks have started…

August 1-4, 2006: China-U.S. Symposium on Medium Energy Physics in Beijing. China. (Chinese Academy of Sciences)

January 25-26, 2007: Workshop on Partial Wave Analysis and Dalitz Plot Analysis. IHEP. Beijing, China

http://bes.ihep.ac.cn/conference/PWA/PWA%20workshop.htm

October 13-15, 2008: JLab Workshop: “Electromagnetic N-N* Transition Form Factors,” (Organized by: V. Burkert, B. Julia-Diaz, R. Gothe, T.S. H. Lee, and V. Mokeev) http://conferences.jlab.org/EmNN/program.html

which generated the whitepaper: JLAB-PHY-09-993, “Theory Support for the Excited Baryon Program at the JLab 12 GeV Upgrade,” Dec, 2008, 60 pp. See: https://www.jlab.org/~mokeev/white_paper/

(Editors: V. Burkert, T.-S. H. Lee, & V. Mokeev).

April 19-22, 2009 NSTAR 2009 (This Conference)

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http://bes.ihep.ac.cn/conference/PWA/PWA%20workshop.htm

http://conferences.jlab.org/EmNN/program.html

https://www.jlab.org/~mokeev/white_paper/


OUTLINE Introduction (Issues) BES CLAS Theoretical Advances

Partial-Wave Analysis (BES) Coupled-Channel Approach (EBAC) MAID SAID Bonn/Gatchina

CLAS12 approved experimental proposal PIRE pre-proposal Path Forward.

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BES and BES and BEPCBEPC

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Baryon spectroscopy from J/ decays at BES/BEPC

**,*,*,/ NBMBJ

New mechanism for baryon production & an ideal isospin filter

BingSong Zou MENU 07 7


2. N* resonances observed in N N

+ c.c.npπJ/ψ



Off-shell nucleon contribution

N*(1440)

N*(1520)N*(1535)

N*(1650)N*(1675)N*(1680)

?

npπJ/ψ



The new N*(2065) peak in N mass spectrum

J/n N*(2065) with L=0 (small excess energy)

limits its JP to be 3/2+ or 1/2+ (spin filter)

221540- MeV/c 4014165 ,MeV/c 3 2068 M

PWA with event-based Maximum-Likelihood method

Both 3/2+ and 1/2+ are there.

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Multiple Meson Final States

Q: What about BN* BBMM (+ c.c.)?

A: BES III can sample this phase space for charged and neutral final-state particles. (cf. Yifang Wang’s talk on 19 April 2009)

Complementary features to CLASComplementary features to CLAS

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── ──


See: Physics at BES III. IHEP-Report-BES-III-2008-001-v2Editors: Kuang-Ta Chao and Yifang Wang. (Yellow (Yellow Book)Book)arXiv:0809.1869v1 [hep-ex] 10 Sep 2008

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• 3,000,000 (p) • 650,000 (p•4,500 (p

With 500 Million J/With 500 Million J/ expected in April-June run 5x10 expected in April-June run 5x1088 x B.R. x B.R.

• 1,200,000 (p)• 500,000 (p0)• 450,000 (K

Multiply the above numbers by 20 for 10Multiply the above numbers by 20 for 101010 events! events!

http://arxiv.org/abs/0809.1869v1


CLAS data on meson electroproduction at Q2 < 4.0 GeV2

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

• 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

/q e e

p

/e

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/q e e

p

/e

CLAS and JLabCLAS and JLab

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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

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Electromagnetic Excitation of N*s

The experimental N* Program has two major components:

1) Transition form factors of known resonances to study their internal structure and the interactions among constituents, which are responsible for resonance formation.

2) Spectroscopy of excited baryon states, search for new states. 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.

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Philip Cole NSTAR 2009 北京中国 April 19-22, 2009 Idaho State University 17

How 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:See: B.Julia-Diaz, et al., arXiv:0904,1918v1 [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.

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Primary objectives in our studies of N* structure with CLAS

Our experimental program seeks to determine

• N-N* transition helicity amplitudes (electrocouplings) • their evolution with photon virtualities for Q2 < 5.0 GeV2 for almost all

excited proton states by analyzing single- and double-meson electroproduction channels combined,

• employ advanced coupled-channel approach developing by EBAC.

This comprehensive information on Q2 evolution of the N-N* electrocouplings will allow us to:

• determine the active degrees of freedom in N* structure at various distances;

• study the nonperturbative strong interactions which are responsible for the ground and excited nucleon state formation, and how they emerge from QCD.

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P11(1440) electrocouplings from the CLAS data on N/N electroproduction

NN

Light front models:

I. Aznauryan

S. Capstick

hybrid P11(1440) [Q3g]

• Good agreement between the electrocouplings obtained from the N and N channels: Reliable measure of the electrocouplings.

• The electrocouplings for Q2 > 2.0 GeV2 are consistent with P11(1440)

structure as a 3-quark radial excitation.

• Zero crossing for the A1/2 amplitude has been observed for the first time, indicating an importance of light-front dynamics. 19


Resonance Analysis Tools

Amplitude & multipole analysis (GWU-SAID, MAID)

Phenomenological analysis procedures have been developed, e.g. unitary isobar models (UIM), dispersion relations (DR), that separate non-resonant and resonant amplitudes in single channels.

PWA from BES/IHEP – BingSong Zou, Jian-Xiong Wang

Dynamical coupled channel approaches for single and double pion analysis are being developed within the Excited Baryon Analysis Center (EBAC) effort. They are most important in the extraction of transition form factors for higher mass baryon states.

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Nucleon resonances are broad and Nucleon resonances are broad and overlappingoverlapping careful analyses of angular careful analyses of angular distributions for differential distributions for differential cross sections and polarization cross sections and polarization observables are neededobservables are needed


Coupled-channels picture of resonance excitation (EBAC)

T=

T T T T T T T

T T T T T T T

T T T T T T T

T T T T T T T

T T T T T T T

T T T T T T T

T T T T T T T

The same N* resonance must be found in different reaction channels in a consistent way!

N N

N N* N KΛ KΣ

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EBAC strategy (summary)

ElectromagneticN-N* form factors

QQCCDD

Lattice QCDHadron Models

Dynamical Coupled-Channels Analysis @ EBAC

Reaction Data

Bruno Juliá Díaz

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Meson-baryon dressing vs Quark core contribution in NΔ Transition Form Factor – GM. EBAC analysis.

Within the framework of relativistic QM [B. Julia-Diaz et al., PRC 69, 035212 (2004)], the bare-core contribution is very well described by the three-quark component of the wf.

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 core

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Conclusions (so far on CLAS stuff) The CLAS Collaboration has developed phenomenogical The CLAS Collaboration has developed phenomenogical

approaches with the goal of determining N* approaches with the goal of determining N* electrocouplings from combined fits of measured electrocouplings from combined fits of measured observables in both the Nobservables in both the N & N & N electroproduction electroproduction data.data.

A good description of the CLAS data on NA good description of the CLAS data on N electroproduction and differential cross sections inelectroproduction and differential cross sections inp p channel has been achieved, affording us to access the channel has been achieved, affording us to access the resonant parts of amplitudes, which are directly related resonant parts of amplitudes, which are directly related to N* electrocouplings.to N* electrocouplings.

The consistent results extracted from these two channels The consistent results extracted from these two channels strongly indicate a reliable electrocoupling measurement. strongly indicate a reliable electrocoupling measurement.

Comparison of the data on N* electrocouplings with quark Comparison of the data on N* electrocouplings with quark model expectations in coordination with EBAC model expectations in coordination with EBAC evaluations for MB cloud show that for Qevaluations for MB cloud show that for Q22<1.0 GeV<1.0 GeV22 both both the MB cloud and quark core play an important role in the MB cloud and quark core play an important role in the N* structure. the N* structure.

Contribution from the MB cloud decreases with QContribution from the MB cloud decreases with Q22, but , but can be still sizable at Qcan be still sizable at Q22<5.0 GeV<5.0 GeV22, while at Q, while at Q22>5.0 GeV>5.0 GeV22 quark degrees of freedom are expected to dominatequark degrees of freedom are expected to dominate. 24


Highest priorityHighest priority recommendation in the recommendation in the DOE/NSF DOE/NSF Nuclear Science Advisory Committee (NSAC) Nuclear Science Advisory Committee (NSAC) Long-Long-Range PlanRange Plan, , 174 pages, Dec. 2007174 pages, Dec. 2007.

http://www.sc.doe.gov/np/nsac/docs/Nuclear-Science.High-Res.pdf Recommendation IRecommendation I:: We recommend completion We recommend completion

of the 12 GeV CEBAF Upgrade at Jefferson of the 12 GeV CEBAF Upgrade at Jefferson Lab. The Upgrade will enable new insights into Lab. The Upgrade will enable new insights into

the structure of the nucleon, the transition between the hadronic and

quark/gluon description of nuclei, and the nature of confinement.

JLab’s Future

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http://www.sc.doe.gov/np/nsac/docs/Nuclear-Science.High-Res.pdf


Hadron Structure with e.m. 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

26


Physics objectives in the N* studies with CLAS12

• 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, relativistic quark models. See details in the White Paper of EmNN* JLAB Workshop, October 13-15, 2008:http://www.jlab.org/~mokeev/white_paper/

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

Q2 = 12 GeV2

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

CLAS12

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29

CLAS12 Detector

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Nucleon Resonance Studies with

CLAS12 D. Arndt4, H. Avakian6, I. Aznauryan11, A. Biselli3, W.J. Briscoe4, V. Burkert6,

V.V. Chesnokov7, P.L. Cole5, D.S. Dale5, C. Djalali10, L. Elouadrhiri6, G.V. Fedotov7, T.A. Forest5, E.N. Golovach7, R.W. Gothe*10, Y. Ilieva10, B.S. Ishkhanov7, E.L. Isupov7, K. Joo9, T.-S.H. Lee1,2, V. Mokeev*6, M. Paris4, K. Park10, N.V. Shvedunov7, G. Stancari5, M. Stancari5, S. Stepanyan6, P. Stoler8, I. Strakovsky4, S. Strauch10, D. Tedeschi10, M. Ungaro9, R. Workman4,

and the CLAS Collaboration

JLab PAC 34, January 26-30, 2009Approved for 60 days beamtime

Argonne National Laboratory (IL,USA)1, Excited Baryon Analysis Center (VA,USA)2,Fairfield University (CT, USA)3, George Washington University (DC, USA)4,

Idaho State University (ID, USA)5, Jefferson Lab (VA, USA)6,Moscow State University (Russia)7, Rensselaer Polytechnic Institute (NY, USA)8,University of Connecticut (CT, USA)9, University of South Carolina (SC, USA)10,

and Yerevan Physics Institute (Armenia) 11

SpokespersonContact Person* 30


Theory Support

Group V.M. Braun8, I. Cloët9, R. Edwards5, M.M. Giannini4,7, B. Juliá-Díaz2, 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. Open invitation. List is open to any and all who wish to participateList is open to any and all who wish to participate!!

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NeedNeed to find the best way to theoretically extract the most pertinent observables from this huge database.

NeedNeed a coordinated and dedicated effort between theorists and experimentalists to develop new and efficient analysis tools.

NeedNeed complementary techniques for extracting these observables for extracting baryon resonances from BES and Jlab.

NeedNeed an infusion of young talent to maintain the N* “lifeblood.”

NeedNeed a partnership among experimentalists centered at CLAS and at BES and theorists working in BES and based in China and theorists working with the Excited Baryon Analysis Center at JLab.

There is a huge amount of high-quality data streaming in from

CLAS CLAS and BESBES

JJ// BN* BN* BBM(M) in BBM(M) in BESBES is complementary to N* is complementary to N* BM/BMM (e.g, NBM/BMM (e.g, Nππ//NNππππ)) in in CLASCLAS

Coordination of efforts between Coordination of efforts between BESBES and and CLASCLAS is timely is timely

── ──

And this collaborative work can lead to significant discovery potentialAnd this collaborative work can lead to significant discovery potential 32


Partnership for International Research and Education (PIRE)

We are seeking NSF PIRE support for a new U.S./China collaboration

formed of experimentalists, theorists, and phenomenologists.

11 institutions in the U.S. and in the PRC with 18 PIs/senior personnel/ foreign collaborators for analyzing this torrent of data from CLAS and BES

Many talented theorists: China: Partial-Wave Analysis of excited baryons at the Institute for High Energy

Physics in Beijing and at the Beijing Electron Positron Collider. USA: Coupled-Channel Approach at Excited Baryon Analysis Center at JLab

Many talented experimentalists

We submitted a pre-proposal on Feb. 16, 2009 for $3M for this five-year program. We will hear word on invite-to-proposal stage by late May or early June.

~650 pre-proposals → ~75 invited → ~15 funded

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List of Participants – PIRE: Nucleon Resonance Studies (Pre-Proposal)

PI/CoPIs: Philip L. Cole (PI and Program ManagerPI and Program Manager, Associate Professor of Physics)

Department of Physics, Idaho State University, Pocatello, ID 83209 Ralf W. Gothe (First CoPI and Deputy Program ManagerFirst CoPI and Deputy Program Manager, Professor of Physics)

Steffen Strauch (CoPI, Associate Professor of Physics) Department of Physics and Astronomy, University of South Carolina, Columbia, SC 29208 Kyungseon Joo (CoPI, Associate Professor of Physics) Department of Physics, University of Connecticut, Storrs, CT 06269

Senior Personnel: Volker D. Burkert (Hall B Leader) Latifa Elouadrhiri (Assistant Project Manager for the 12 GeV Upgrade – Hall B) Victor I. Mokeev (Hall B Staff Scientist II)

Thomas Jefferson National Accelerator Facility, Physics Division, Newport News, VA 23606 Tsung-Shung Harry Lee (Senior Physicist and Director of Excited Baryon Analysis Center – JLab)

Physics Division. Argonne National Laboratory. Argonne, IL 60439 Debra M. Easterly1 (Director of Research Development & Compliance, NSF ADVANCE Grant Project Director for ISU) Angela V. Petit2 (Assistant Professor of English)

1Office of Research, 2Department of English, Idaho State University, Pocatello, ID 83209 Kevin Kelley1 (Professor of Physics) Scott Galer2 (Associate Professor of Chinese and Chair of Foreign Languages and Literatures)

1Department of Physics, 2Department of Foreign Languages and Literatures, Brigham Young University – Idaho, Rexburg, ID 83460

Foreign Collaborators: Qiang Zhao (Chief Chinese LiaisonChief Chinese Liaison, Professor of Physics and Group Leader of the Theory Division) Bing-Song Zou (Deputy Chinese LiaisonDeputy Chinese Liaison, Professor of Physics and Director of the Theory Division) Theory Division, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, P.R. China Cong-Feng Qiao (Executive Dean and Professor of Physics)

College of Physical Sciences, Graduate School of the Chinese Academy of Sciences Beijing 100049, P.R. China Xue-Qian Li (Professor of Physics)

Physics Department, Nankai University, Tianjin 300071, P.R. China Bi-Tao Hu (Vice Dean and Professor of Physics)

The School of Nuclear Science and Technology, Lanzhou University, Lanzhou 730000, P.R. China Inna Aznauryan (Leading Staff Scientist)

Yerevan Physics Institute – Yerevan State University, Yerevan, Armenia, 375036

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Letter of Recommendation from Prof. T.D. Lee*

* Nobel Prize in 1957, parity violation in the weak decay.

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Message to take home.

36

Why N*s are importantWhy N*s are important. (quoted from Nathan Isgur1,2)

•The first is that nucleons are the stuff of which our world is made.•My second reason is that they are the simplest system in which the quintessentially nonabelian character of QCD is manifest.

•The third reason is that history has taught us that, while relatively simple, baryons are sufficiently complex to reveal physics hidden from us in the mesons”

1Workshop on Excited Nucleons and Hadronic Structure (2000).2Baryon Spectroscopy, E. Klempt and J.-M. Richard, arXiv:0901.2055v1[hep-ph]1 4 Jan 2009

We need to spread the word to lay and expert audiences alike that excited baryon research is indeed exciting and crucial to science.


Questions to the N* Community:

1. How best to coordinate efforts between JLab and IHEP?2. How best to coordinate efforts between BES and CLAS? 3. How best to open and fund unique opportunities for

• students,students,• postdoctoral researchers,postdoctoral researchers,• senior experimentalists, andsenior experimentalists, and• senior theoristssenior theorists.

on collaborating between CLAS and BES on N* Physics?

How to proceed – in a transformational way – so as to tackle the fundamental issue of what generates mass in the proton, say?

37


Path Forward

We need overarching funding so thatWe need overarching funding so that Experimentalists from BES and CLAS can collaborate,Experimentalists from BES and CLAS can collaborate, Theorists from EBAC and IHEP can collaborate, andTheorists from EBAC and IHEP can collaborate, and Open opportunities for young bright physicists on both Open opportunities for young bright physicists on both

sides of the Pacific to work on this problem.sides of the Pacific to work on this problem.

A grant from the Partnership for International Research and Education (PIRE) from the Office of International Science and Engineering of the National Science Foundation would offer this transformational opportunity.

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We need to understand how strong interactions evolve from pQCD to the quark confinement regime in baryons. This can only be done by understanding N* structure.


Thanks to

BingSong Zou (IHEP and BES) Victor Mokeev (JLab)

for providing me their slides

39


Extra Slides

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1. Experimental observables – Starting point for PWA

P1, M1

P2, M2

k1, m1

k2, m2

kn, mn

Experimental distribution probability:

Wexp(k1, … , kn) ~ |M(k1, … , kn )|2 (k1, … , kn ) dn(k1, … , kn )

amplitude efficiency phase space

various projections

BingSong Zou PWA at BES Workshop 07

41


2. PWA framework

R1 R2

= + + ……

M(k1, … , kn ) = C1AR1 (k1, … , kn ) + C2AR2 (k1, … , kn ) + …

Wth(k1, … , kn ; C1 ,C2 , … )

PWA: fitting experimental data to get C1 ,C2 , …

Old fashion : 2-fit to various projections

Modern technique: event-based, multi-dimensional Maximum Likelihood

fit to Wexp(k1, … , kn) CERNLIB programs : FUMILI, MINUIT


42


Some references :W.Rarita, J.Schwinger, Phys. Rev. 60, 61 (1941)

E.Behtends, C.Fronsdal, Phys. Rev. 106, 345 (1957)S.U.Chung, PRD48, 1225 (1993); PRD57, 431 (1998)

B.S.Zou, D.V.Bugg, Eur. Phys. J. A16, 537 (2003) for mesonsB.S.Zou, F.Hussian, PRC67, 015204 (2003) for baryons

Basic ingredients : (1)spin wave-function for single particle(2)orbital wave-function for two-particle

system(3) g,

(4) Breit-Wigner propagator, form factor


43

3. Construction of PWA covariant tensor amplitudes


The first experiment “seeing” N*(1440) in N mass spectrum

BESII MeVPDG06 M = MeV



High-lying resonance electrocouplings from N CLAS data analysis

D33(1700) P13(1720)

NCLAS Nworld Nworld Q2=0• Analysis of the CLAS data provides first-time information on the electrocouplings for

N*s that decay primarily to the N final states• The A1/2 electrocoupling of P13(1720) decreases rapidly with Q2. • At Q2>0.9 GeV2 |A3/2| > |A1/2|. Search for Q2 regime where the helicity conserving A1/2

amplitude of P13(1720) dominates and is important question for N* studies at high Q2 45


Meson-baryon dressing / Quark core contributions in the A1/2 electrocouplings of the P11(1440) & D13(1520) states.

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

P11(1440) D13(1520)

Light Front quark model by I.Aznauryan

hypercentric -quark model by M.Giannini

46


1. Fixing hadronic parameters

2. Good model to describe N reactions at Q2 = 0.

What is needed for extracting electromagnetic N-N* form factors?

Pure hadronic process; Determined fromN N, N, N

Pure hadronic process; Determined fromN N, N, N

Before analyzing eN e’ N, e’ N, … , we need

Determined fromN N, N, NDetermined fromN N, N, N

Critical for the model construction

Starting point to explore Q2 > 0 region

Bruno Juliá Díaz47


Coupled Channel Analysis (EBAC)

Pion-nucleon and two-pion-nucleon contributions to the non-resonant T matrix.

T.-S. Harry Lee

48


List of the questions relating to the List of the questions relating to the motivation of N* studies using an 11-motivation of N* studies using an 11-GeV electron beam for probing photon GeV electron beam for probing photon

virtualities from 5.0 to 10 GeVvirtualities from 5.0 to 10 GeV22..

1. How will our proposed N* transition helicity amplitude proposed N* transition helicity amplitude data in the Qdata in the Q22 region of 5.0 to 10 GeV region of 5.0 to 10 GeV22 impact your impact your theoretical approachtheoretical approach and, in general, how will this data extend our overall understanding of strong interactions responsible in the formation of N*s?

A set 7 Questions was sent to all theorists who attended the Workshop 49


Need for Theoretical Support

Small exclusive channel cross sections, channel couplings due to unitary constraints can lead to strong distortions of amplitudes.

Requires a complete and thorough coupled-channel analysis which includes all major channels with all attendant observables.

The Excited Baryon Analysis Center (EBAC) was established in 2006 at JLab to provide theoretical support for the excited baryons experimental program.

PWA efforts at BES

50


To justify this claim of being able to access quark-core degrees of freedom at high photon virtualities, we ask you to make estimates of the Q2-behavior of the two components, i.e.

a) constituent quark core b) meson-baryon dressing of N-N* photon vertices,

which contribute to the AA1/21/2, AA3/23/2, SS1/2 1/2 N-N* transition amplitudes: for the N* states: PP3333(1232), P(1232), P1111(1440), D(1440), D1313(1520), S(1520), S1111(1535), F(1535), F1515(1685), P(1685), P1313(1720), D(1720), D3333(1700)(1700)

in the region 5.0 < Q5.0 < Q2 2 < 10 GeV< 10 GeV22.

v N

p

p

2. We anticipate that by studying N* behavior at photon photon virtualities ranging from 5.0 to 10 GeVvirtualities ranging from 5.0 to 10 GeV22, it will give us access to resonance structure at distances, where the expected contributions from meson-baryon dressing meson-baryon dressing to the N-N* vertices to the N-N* vertices are presumably small.are presumably small. *Hence this probe will allow for probe will allow for effectively delineating the constituent quark-core effectively delineating the constituent quark-core configurations from other competing processesconfigurations from other competing processes.

γv

N

N*,△

AA3/23/2, A, A1/21/2, S, S1/21/2

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

e

e’

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3. How will the data on N-N* transition helicity amplitudes, How will the data on N-N* transition helicity amplitudes, obtained at 5.0 < Qobtained at 5.0 < Q2 2 < 10 GeV< 10 GeV22, extend our knowledge on the , extend our knowledge on the binding potential and effective interactions responsible for 3-binding potential and effective interactions responsible for 3-quark configuration mixing quark configuration mixing (i.e. OGE, OPE, instanton,…) within constituent quark models?

How will such data on N* electrocouplings at high Q2 help us in getting access to light-cone wave functions of excited proton states and the associated currents?

What can we learn about the evolution constituent quark form factors?

What are the prospects of relating the constituent quark, covariant and Dyson-Schwinger models to the underlying QCD and, in turn, how will this data on N* electrocouplings at high Q2 be useful in establishing these relations?

4. Is it possible or likely that data on N* electrocouplings at high Q2 will afford us access to excited flux tubes as a possible active degree of freedom in the N* structure? And could this be used to study flux tube self-interactions?

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5. How does the rapid riserapid rise of the dressed-quark running massdressed-quark running mass impact the N-N* transition helicity amplitudes, as revealed from both

• the studies of the dressed-quark propagator within the framework of Dyson-Schwinger equations

• and from lattice calculations?

How then may this running mass phenomenon be established in the studies of N* electrocouplings at high Q2?

6. What are the prospects of having lattice calculations

which relate the underlying QCD data in N-N* helicity transition amplitudes at Q2 up to 10 GeV2?

And would such N* electrocoupling data be of significant benefit in making lattice calculations within this high Q2 regime, where the expected contributions from meson-baryon dressing of N-N* photon vertices become negligible?

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Summary-I (from Workshop N-N*)

Transition form factors for PP3333(1232), P(1232), P1111(1440), D(1440), D1313(1520), & S(1520), & S1111(1535). (1535). measured over large Q2 range. no sign of approaching asymptotic QCD limit --> need for 12 GeV upgrade pion dressing of vertex needed to describe form factors.

Roper P11(1440) transition form factor determined for the first time. zero-crossing of magnetic form factor behaves like a Q3 radial excitation at short distances Q2 <0.7 GeV2 determined from the 1π and 2π exclusive channels, as well as

from a combined analysis of both these channels, are in a good agreement (also in agreement with MAID – Tiator)

Able to extract reliable results on N* electrocouplings from meson electroproduction data. the P P1111(1440) and D(1440) and D1313(1520)(1520). 1π and 2π channels have completely different

nonresonant mechanisms AND ARE IN AGREEMENT! description of all observables in both these channels with common N*

electrocouplings good testing ground for efficacy of 2π: JM06, 1π: JLab/GWU-SAID/MAID reaction models.

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Summary II (from Workshop N-N*)

Exists good prospect to relate QCD and Q2 evolution of N*s within the framework of Dyson-Schwinger & Bethe-Salpeter approaches and Lattice QCD (with caveat of more powerful computers) as determined through Light Cone wavefunctions.

Healthy progress in Constituent Quark Models

Can extract reliable information on N* electrocouplings from combined fit of

multiple polarization observables in Nπ, Nππ, pη, and KY in electro- and photoproduction needed to resolve ambiguities in baryon resonance analysis.

EBAC essential to support the baryon resonance program with coupled channel calculations

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a new & theoretical/experimental collaborative effort on baryon resonance extraction * philip...

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