N* Transition Form Factors at JLab

1Ralf W. Gothe N* Transition Form Factors Exclusive Reactions 2007

N* Transition Form Factors at JLab:The Evolution of Baryonic Degrees of Freedom

Ralf W. GotheUniversity of South Carolina

Exclusive Reactions at High Momentum TransfersMay 21-24, 2007

Jefferson Lab, Newport News, VA

IntroductionN ∆, N Roper, and other N N* Transitions1π and 2π Production


Physics Goals

Understand QCD in the full strong coupling regimetransition form factors to nucleon excited states

allow us to studyrelevant degrees-of-freedomwave function and interaction of the constituents

?! ?

! ?

?

!!

pπ

Models Quarks and Gluons as Quasiparticles

ChPTNucleon and

Mesons

pQCDq, g, qq

< 0.1fm 0.1 – 1.0 fm > 1.0 fm<


CLAS for Inclusive ep e’X at 4 GeVCLAS

Resonances cannot be uniquely separated in inclusive scattering


CLAS for Exclusive ep e’pX at 4 GeV

1.50. 0.5 1.0

1.0

1.5

2.0

mis

sing

stat

es

CLAS


Lattice QCD indicates a small oblate deformationof the ∆(1232) and that the pion cloud makes E1+ /M1+more negative at small Q2.

Data at low Q2 needed to study effects of the pioncloud.

Need data atlow Q2

N ∆(1232) Transition Form Factors

γv Nλγp=1/2

λγp=3/2


C. Alexandrou et al., PRL, 94, 021601 (2005)

REM (%)

RSM (%)

Quenched LQCD describes REM within error bars, but shows discrepancies with RSM at low Q2 . Pion cloud effects?

Low-Q2 Mutipole Ratios for REM, RSM

Need data atlow Q2


Low-Q2 Mutipole Ratios for REM, RSM

C. Alexandrou et al., PRL, 94, 021601 (2005)

preliminary

Quenched LQCD describes REM within error bars, but shows discrepancies with RSM at low Q2 . Pion cloud effects?

Significant discrepancy between CLAS and Bates/MAMI results for RSM.

C. Smith


S11 Q3A1/2

F15 Q5A3/2P11 Q3A1/2D13 Q5A3/2

F15 Q3A1/2

D13 Q3A1/2

Constituent Counting Rule

A1/2 α 1/Q3

A3/2 α 1/Q5

GM α 1/Q4*

(GeV

)


New trend towards pQCD behavior does not show up.

CLAS12 can measure REM and RSMup to Q²~12 GeV².

N → ∆ Multipole Ratios REM , RSM

0 2 4 6

-5

0

(%)

EM

R

DMT

Sato-Lee

Maid 2003

0 2 4 6

-30

-20

-10

0

(%)

SM

R

DMTSato-Lee

Maid 2003

Ji

]2/c2 [GeV2Q

REM +1

M. Ungaro

0 2 4 60.2

0.4

0.6

0.8

1

]2/c2 [GeV2Q

D /

3G* M

G

DMTSato-Lee (Bare)Sato-Lee (Dressed)BraunMaid 2003GPD

GM 1/Q4*


π electro-production (UIM, DR)

PDG estimation

π, 2π combined analysis


PDG estimation

π, 2π combined analysisK. Park (Data) I. Aznauryan (UIM)

preliminary

Roper Electro-Coupling Amplitudes A1/2, S1/2

nr |q3>

|q3+g>

LF |q3>

|q3+qq>

LF |q3>

nr |q3>

nr |q3>|q3+qq>

|q3+g> LF |q3>

nr |q3>

|q3+g>

LF |q3>

|q3+qq>

nr |q3>

nr |q3>|q3+qq>

|q3+g>

-80

-60

-40

-20

0

20

40

60

0 1 2 3 4

Q2 (GeV2)

A1/

2(10

-3G

eV-1

/2)

-30

-20

-10

0

10

20

30

40

50

0 1 2 3 4

Q2 (GeV2)S 1/

2(10

-3G

eV-1

/2)

-80

-60

-40

-20

0

20

40

60

0 1 2 3 4

Q2 (GeV2)

A1/

2(10

-3G

eV-1

/2)

-30

-20

-10

0

10

20

30

40

50

0 1 2 3 4

Q2 (GeV2)S 1/

2(10

-3G

eV-1

/2)


preliminary

0

20

40

60

80

100

0 1 2 3 4

Q2 (GeV2)

A1/

2(10

-3G

eV-1

/2)

-60

-50

-40

-30

-20

-10

0

10

20

30

0 1 2 3 4

Q2 (GeV2)S 1/

2(10

-3G

eV-1

/2)

S11(1535) Electro-Coupling Amplitudes A1/2, S1/2


PDG estimation

S11, D13 combined analysis (SQTM)K. Park (Data) I. Aznauryan (UIM)

η production (UIM, DR)

nr |q3>

LF |q3>

LF |q3>nr |q3>

nr |q3>LF |q3>

LF |q3>

nr |q3>


Energy-Dependence of π+ Multipoles for P11, S11

imaginary partreal part

Q2 = 0 GeV2

The study of some baryon resonances becomes easier at higher Q2.

Q2 = 2.05 GeV2

preliminary

I. Aznauryan (UIM)


Legendre Moments of Structure FunctionsQ2=2.05GeV2

M1- = 0

M1- = 0

I. Aznauryan UIM fit

The dominating final state multipole amplitude M1- of the P11(1440) resonance is at high Q2 are much more prominent than at small Q2.

K. Park

preliminary

CLAS


πΝ invariant mass / MC phase space

BES/BEPC, Phys. Rev. Lett. 97 (2006)

/J p nψ π −→ /J p nψ π +→BES Bing-Song Zou

and

Ν∗(1440): Μ = 1358 m 17 Γ = 179 m 56

Ν∗(2050): Μ = 2068 +15−40

Γ = 165 m 42


Fermion Helicity Conservation

Helicity Conservationλ=λ´ for q M>>

Quark mass extrapolated to the chiral limit, where q is the momentum variable of the tree-level quark propagator using the Asquat action.

Bowman et al.(LQCD)

(GeV

)


preliminary

-100

-80

-60

-40

-20

0

20

0 1 2 3 4

A1/

2(10

-3G

eV-1

/2)

-25

0

25

50

75

100

125

150

175

200

0 1 2 3 4

A3/

2(10

-3G

eV-1

/2)

-60

-40

-20

0

20

40

0 1 2 3 4

Q2 (GeV2)

S 1/2(

10-3

GeV

-1/2

)

-1

-0.75

-0.5

-0.25

0

0.25

0.5

0.75

1

0 1 2 3 4

Q2 (GeV2)

Ahe

l

D13(1520) Helicity AsymmetryAhel = A1/2

2 – A3/22

A1/22 + A3/2

2

A1/2

A3/2


Nucleon Resonances in 2π Electroproduction

p(e,e’)X

p(e,e’p)π0

p(e,e’π+)n

p(e,e’pπ+)π−

2π channel is sensitiveto N*’s heavier than1.4 GeV

Provides complementaryinformation to the 1πchannel

Many higher lying N*’sdecay preferably to ππNfinal states

Q2 < 4.0GeV2 Trigger

W in GeV


W=1.86 GeV, Q2=0.95 GeV**2

0

10

20

30

40

50

60

1 1.2 1.4 1.6 1.80

10

20

30

40

50

60

0.25 0.5 0.75 1

0

10

20

30

40

50

1 1.2 1.4 1.6 1.80

2

4

6

8

10

12

14

0 50 100 150 200

direct 2π production

Full calculationsγp→π-∆++

γp→π+∆0

γp→ρpγp→π-∆++(1600)

γp→π+F015(1685)

γp→π+D13(1520)

Combined fit of various single differential cross sections allowed to establish all significant mechanisms

Isobar Model JM05

Contributing Mechanisms to γ(∗)p → pπ+π-

JM05


CLAS photo-production

W(GeV)

Background

Resonances

Full calculation

no 3/2+

N* contributions are much smaller than non-resonant mechanisms

0

5

10

15

20

25

30

1.4 1.5 1.6 1.7 1.8 1.9 2 2.1

electro-production

W(GeV)

M. Ripani

3/2+(1720)P?3(1720)

Full JM05 calculation with and without a new 3/2+(1720) state

Resonances in γ(∗)p → pπ+π-


W=1.7 GeV, Q2=0 GeV**2

P13(1720) branching fraction for ρpextracted by a the fit within the JM05 model (without 3/2+(1720))

Preliminary real (M. Bellis) and published (M. Ripani) virtual photon data, combined fit needs both the candidate 3/2+(1720) and the P13(1720) state

Q2 0.00 GeV2 0.65 GeV2

BF(ρp) 63%±25% 20%±10%

Discrepancy

Combined Analysis of γ(∗)p → pπ+π-

Fit without 3/2+(1720), only variation of electromagnetic and π∆ ρP hadronic couplings and masses of P13(1720), P33(1600)

Fit with 3/2+(1720)

preliminary


Resonances

CLAS

Background

Full JM05

no 3/2+

3/2+(1720)P?3(1720)

Resonances and Background in γ(∗)p → pπ+π−

0102030405060708090

1.4 1.6 1.8 20

5

10

15

20

25

30

35

1.4 1.6 1.8 2

0

5

10

15

20

25

30

1.4 1.6 1.8 202468

101214161820

1.4 1.6 1.8 2

electro-productionphoto-production

JM05


Combined 1π-2π Analysis of CLAS Data

PDG at Q2=0

Previous world data

2π analysis

1π-2π combined at ////Q2=0.65 GeV2

Many more examples:////P11(1440), D13(1520), S31(1650), ////S11(1650), F15(1685), D13(1700),////…

EBAC at JLab:////Full coupled channel analysis

D33(1700) D33(1700)

P13(1720) P13(1720)

Q2 GeV2

(A2 1/

2 +S2 1/

2 )(1

/2) *1

000

GeV

−1/2

Q2 GeV2A

3/2*

1000

GeV

−1/2

Q2 GeV2

(A2 1/

2 +S2 1/

2 )(1

/2) *1

000

GeV

−1/2

Q2 GeV2

A3/

2*10

00 G

eV−1/2

0255075

100125150175200225

0 0.5 1 1.5

-40

-20

0

20

40

60

80

100

120

0 0.5 1 1.5

0102030405060708090

100

0 0.5 1 1.5-120

-100

-80

-60

-40

-20

0

20

0 0.5 1 1.5

preliminary

JM05


Combined 1π-2π Analysis of CLAS Data

PDG at Q2=0

2π analysis

1π-2π combined at Q2=0.65 GeV2

Previous world data


0

1

2

3

-1 -0.5 0 0.5 1

dσ(γ

* p→πo p)

/dΩ

(µb

/sr) φ=15o

0

1

2

3

4

-1 -0.5 0 0.5 1

φ=45o

0

2

4

6

-1 -0.5 0 0.5 1

φ=75o

0

2

4

6

-1 -0.5 0 0.5 1

φ=105o

0

2

4

6

-1 -0.5 0 0.5 1

φ=135o

cos θc.m.

0

2

4

6

-1 -0.5 0 0.5 1

φ=165o

cos θc.m.

0

0.5

1

1.5

2

-1 -0.5 0 0.5 1

dσ(γ

* p→πo p)

/dΩ

(µb

/sr) φ=15o

0

0.5

1

1.5

2

-1 -0.5 0 0.5 1

φ=45o

0

1

2

3

-1 -0.5 0 0.5 1

φ=75o

0

1

2

3

-1 -0.5 0 0.5 1

φ=105o

0

1

2

3

4

-1 -0.5 0 0.5 1

φ=135o

cos θc.m.

0

0.5

1

1.5

2

-1 -0.5 0 0.5 1

φ=165o

cos θc.m.

γvp → π0p

1π Data Description by N* Electro-Couplings of the Combined Analysis

W=1.52 GeV Q2=0.65 GeV2 W=1.68 GeV Q2=0.65 GeV2 JM05CLAS


W=1.54 GeV Q2=0.65 GeV2 W=1.66 GeV Q2=0.65 GeV2

The successful description of all 1π and 2π observables measured with CLAS at Q2=0.65 GeV2 demonstrates the credibility of the N* background separation.

2π Data Description by N* Electro-Couplings of the Combined Analysis

JM05CLAS


prelim

inary

Roper Electro-Coupling Amplitudes A1/2, S1/2

PDG at Q2=0

1π analysis (UIM)

1π-2π combined at////Q2=0.65 GeV2

Newest 2π analysis ////at low Q2 (JM 06)

CLAS


Inclusive Structure Function in the Resonance Region

Event Generators

Genova-EG: Dipole Form Factor

SI-DIS: Deep Inelastic Scattering

3. R R

2. R R

P. Stoler, PRPLCM 226, 3 (1993) 103-171


W (GeV

)Q 2

(GeV 2)

Num

ber

of e

vent

s

1.7

1.725

1.75

1.775

1.8

1.825

1.85

1.875

1.9

5

5.5

6

6.5

7

7.5

8

0

10000

20000

30000

40000

50000

60000

Kinematical Coverage of CLAS1260 days

L= 1035 cm-2 sec-1, ∆W = 0.025 GeV, ∆Q2 = 0.5 GeV2

Genova-EG (e’,pπ+π−) detected


Conclusion: Do Exclusive Electron Scattering

-150-125-100

-75-50-25

0255075

0 1 2 3 4Q2 (GeV2)

A1/

2 (1

0-3G

eV-1

/2)

P11(1440) -60

-40

-20

0

20

40

60

80

0 1 2 3 4Q2 (GeV2)

S 1/2

(10-3

GeV

-1/2

)P11(1440)

Q2 = 2.05 GeV2

0 2 4 6

-5

0

(%)

EM

R

DMT

Sato-Lee

Maid 2003

0 2 4 6

-30

-20

-10

0

(%)

SM

R

DMTSato-Lee

Maid 2003

Ji

]2/c2 [GeV2Q

0 2 4 60.2

0.4

0.6

0.8

1

]2/c2 [GeV2QD

/ 3G

* MG

DMTSato-Lee (Bare)Sato-Lee (Dressed)BraunMaid 2003GPD

-100

-80

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-40

-20

0

20

0 1 2 3 4

A1/

2(10

-3G

eV-1

/2)

-25

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125

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200

0 1 2 3 4

A3/

2(10

-3G

eV-1

/2)

-60

-40

-20

0

20

40

0 1 2 3 4

Q2 (GeV2)

S 1/2(

10-3

GeV

-1/2

)

-1

-0.75

-0.5

-0.25

0

0.25

0.5

0.75

1

0 1 2 3 4

Q2 (GeV2)

Ahe

l

D13(1520)

D13(1520)

... to

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N* Transition Form Factors at JLab