baryon form factors

BARYON FORM FACTORS• TWO GAMMA EXCHANGE RESOLVED THE DISCREPANCY

BETWEEN THE DATA OBTAINED BY ROSENBLUTH SEPARATION AND POLARIZATION TRANSFER FOR GE(p)

• QUALITY DATA ON N(1440), N(1535) and some higher N* TRANSITION FORM FACTORS

• CONSISTENT RESULTS FOR THE STRANGENESS FORM FACTORS OF THE PROTON FROM SAMPLE, HAPPEX, A4 AND G0. CHALLENGE FOR THEORY

• CLEAR INDICATIONS FOR LONG RANGE ”PION CLOUD” IN ALL NUCLEON FORM FACTORS

• PRECISION DATA ON GE(n)

• NEW PRECISION DATA FOR gP (p)

• FORM FACTORS --- DVCS --- PARTON DISTRIBUTIONS

NEXT FEW YEARS

• NEW DATA ON THE FORM FACTORS IN THETIME LIKE REGION OF Q2

• GLUON POLARIZATION

• TRANSVERSITY … COMPASS-II, FAIR

THEORIST’S FORM FACTORS

• CALCULATE FROM CURRENT MATRIX ELEMENTS

– GE(Q2) = (1+τ)1/2 <1/2, Q/2| I0 | 1/2, -Q/2>– GM(Q2)= (1+1/τ)1/2 <1/2, Q/2 | Ix | 1/2, -Q/2>– τ = Q2/4 M2)

• ELECTRIC FORM FACTORS IN THE BREIT FRAME

– GE(Q2) = ∫ d3R eiQ·R ρ(R),– GM(Q2) =∫ d3R eiQ·R (1/2) <j, j| r × j(R) |j, j>

– in the Breit frame, where Q0 = 0

• GOVERNING SINGULARITIES IN TIME-LIKE REGION

EXPERIMENTALISTS FORM FACTORS:SPACE-LIKE Q2

• DIFFERENTIAL CROSS SECTION

• dσ/dΩ = σM{ (GE2+τGM

2) /(1+τ)+2τ GM2 tan2 θ/2}

– One-photon exchange approximation– forward-backward Rosenbluth separation

• SPIN POLARIZATION TRANSFER

• GE/GM = - ( Pt / Pl ) {(E + E’)/2 M} tan θ/2

– no forward-backward separation, but instrumental challenge

EXPERIMENTALISTS FORM FACTORS:TIME-LIKE Q2

M. Mirazita et al. 2005

AXIAL FORM FACTOR RELATION TO PION

DECAYLO ChPT (PCAC)

B. Juliá-Díaz et al., PRC 70

EXOTIC FORM FACTORS

• THE STRANGENESS FORM FACTORSCONTRIBUTION FROM SS- PAIRS

• THE ANAPOLE FORM FACTORAXIAL PART IN ELECTROMAGNETIC CURRENT

J = … (GF/Mp2) FA(Q2)(Q2-Q Q )

arises from PV quark interactions

• TRANSVERSITY<P|q

-(0) q(0)|P> » q[P S –P S]

I.A.Qattan et al, PRL 94, 142301 (2005)

GEp/GM

p EXPERIMENT

TWO PHOTON EXCHANGE

P. Guichon & M. Vanderhaeghen PRL 91, 142303 (2003)

Need only a 6% correction in the dependent term in the differential cross section from TPE to resolve the discrepancy

= 1/1+2(1+) tan2 (/2)

HADRONIC CALCULATIONBlunden et al, PRL 91, 142304 (2003)

nucl/th&0506039

nucl-th/0506039

THE (1232) CONTRIBUTIONIS SMALL !

S. Kondratyuk et al, nucl-th/0506026

PARTONIC CALCULATIONA.V.Afanasev et al, PRD 72,013008 (2005)

Ratio of e- to e+

scattering decisive!

Exp’t planned atNovosibirsk

GE ON THE LATTICE

ISOVECTOR FORM FACTORC. Alexandrou (2005)

PRELIMINARY

GM ON THE LATTICE

ISOVECTOR FORM FACTORC. Alexandrou (2005)

PRELIMINARY

LONG RANGE STRUCTURE IN THE NUCLEON FORM FACTORS

J. Friedrich & Th. Walcher, EPJA A17, 607 (2003)

THE PION CLOUD

THE PION CLOUD

J.Friedrich & Th. Walcher, EPJA A17, 607 (2003)

POINCARÉ COVARIANT QUARK MODELS

GENERATORS OF POINCARÉ TRANSFORMATIONS:

H, P, J, K K: boosts

CHOICE OF KINEMATIC SUBGROUP:

INSTANT FORM KINEMATICS: P, J, K{H} O(3)

LIGHT FRONT KINEMATICS: P, K, J{H} O(1,2)

POINT FORM KINEMATICS: J, K, P{H} SO(1,3)

SU(6) quark model for instant, point and frontform kinematics: fitted wave functions

B. Julia-Diaz, D.O.R & F. CoesterPRC 69, 035212 (2004)

BARYON PHENOMENOLOGY WITH DIFFERENT KINEMATICS

B. Juliá-Díaz, F. Coester & DOR, PRC C69 (2004) 035212

SU(6) spin-isospin wave functions x (1 + P2/4 b2)-a

hyperspherical momentum P = ((4/3)(p12+p2

2+p32))1/2

GE(n) & Foldy term

Consistent quark model demands covarianttreatment of the boosts

1-2% mixed symmetry S-stateSufficient to fix the qqq quark model

rn2

exp= -0.1161 ± 0.0022 fm2,rn

2 Foldy= -0.126 fm2

solid: instant, dotted: point dashed: front

S’: 2% instant,point,1% front

GROUND STATE WAVE FUNCTION ANDCONFINING POTENTIAL

Point form quark model form factorsR.F.Wagenbrunn et al, hep-ph/0509047

Very small matter radius r2 = 0.1 fm2

AXIAL & INDUCED PSEUDOSCALAR FORM FACTORS

J = {GA(Q2) 5 – i (Q/2 M) GP (Q2) 5 }a

gP(Q2) = (m/ 2 M) GP(Q2)

MUON CAPTURE : Q2 = - m2

PROBLEM & RESOLUTION

• ChPT: gP = 8.3 § 0.2

N. Kaiser, PRC 67, 027002 (2003)

• TRIUMF RMC:gP = 12.2 § 1.1

D. H. Wright, PRC 57, 373 (1998)

• New result on ortho-para transition in μ- molecular H: factor 2.7

gP = 10.6 § 1.1

J.H.D. Clarke et al nucl-ex/0509025(+ Triumf RMC)

- Introduces problems with earlier data …

Quark model results for GA and GP

MA=1.077§ 0.039 GeV/c2

A.Liesenfeldet al,

PL B 468, 20 (1999)

1232) ! N

qqq quark model underestimates the

transtion form factor by » 30 %

Pion cloud and/or sea-quarks

Sato-Uno-Lee PRC 67, 065201 (2003)

– N - COUPLED CHANNEL CALCULATION

Coupled channel \pi-N-\Delta model

T. Sato and T.-S. H. LeeNucl-th/0404025

HADRONIC COUPLED CHANNELS -N- MODEL

I.Aznauryuan,ANL talk 2005

Bates,CLAS,PDG

NΔ TRANSITION FORM FACTOR ACCORDING TO QCD LATTICE CALCULATION

C. Alexandrou et al, PRL 94, 020601 (2005)

C. Alexandrou et al.,hep-lat/0509140

Effective field theory NV. Pascalutsa and M. Vanderhaeghen,

hep-ph/0508060


PRD C71, 015201 (2005)

N(1440) HELICITY AMPLITUDES

N(1535) HELICITY AMPLITUDESI.G.Aznauryan (CLAS), PRD C71, 015201 (2005)

γ, Z0

STRANGENESS FORM FACTORS

E. J. Beise et al, Prog. Part. Phys. 54, 289 (2005)

D. Armstrong & K.Carter, CERN Courier 45, 8 (2005)GO: PRL 95, 092001 (2005), A4: Prog.Part.Nucl.Phys. 55, 320 (2005)

SAMPLE: PLB 583, 79 (2004), HAPPEX: PRC 69, 065501 (2004)

BUT μs = GMs(0) SHOULD BE NEGATIVE !

ASYMMETRIC LONG RANGE FLUCTUATION … PSEUDOSCALAR MESON LOOP

P↑

+e

-e/3 (strange quark)

K+

Λ, Σ0

< K+ 0 |T| p> » <| ¢ q| >

POSITIVE MAGNETIC MOMENT CONTRIBUTION ?

NO ... MULTIPLY BY – 3 (< s- |γμ| s>

NEGATIVE GMs !

D.Beck andR.D.McKeown,Ann Rev Nucl

Part Sci51, 189 (2001)

• K,K* loops in the ”chiral” quark model

μs = - 0.046 nm

L. Hannelius & DOR, PRC 62, 045204 (2000)

• QCD Lattice calculation with chiral extrapolation

μs = - 0.046 ± 0.019 nm

D.B.Leinweber & al, PRL 94, 212001 (2005)

” tremendous challenge for future experiments”

SPIN DEPENDENT HYPERFINE INTERACTIONLOWERS ANTISYMMETRIC SPIN STATES

<S=0 | 1¢2 |S=0> = -3

<S=1 | 1¢2 |S=1> =+1

COLOR MAGNETIC HF INTERACTION:

V= (2 / 9 m2) s 1 ¢ 2 (r)

FLAVOR-SPIN INTERACTION ...fits the exp’t spectrum

V = C ij Fi¢F

j i ¢ j , C » 30

NUCLEON: <N| i¢j|N> = -2

<| i¢j i¢ j|N> = +10

The is in the S-state, Not KΛ like!

B.S.Zou & DOR, PRL 95, 072001 (2005)

GM(p) FOR TIME LIKE Q2Fenice/ADONE

E835/FNAL

M. Mirazita et al, INFN preprint (2005)


GM(p) FOR TIME LIKE Q2

GM (n) FOR TIME LIKE Q2


F. Iachello & Q. Wan, PRC 69, 055204 (2004)

GM(n) Vector meson pole + scalar meson pole

phenomenology

SUMMARY

• TWO PHOTON EXCHANGE AFFECTS ROSENBLUTH

SEPARATION OF GE , GM

• ALL FORM FACTORS INDICATE ”PION CLOUD”

STRUCTURE IN BARYONS• QCD LATTICE CALCULATIONS APPROACH

EMPIRICAL NUCLEON FORM FACTORS• REALISTIC ChPT EXTRAPOLATION TO SMALL QUARK

MASS ESSENTIAL• THE COMPONENT IN THE PROTON IS NOT A

KΛ FLUCTUATION

baryon form factors

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