N* Production in N* Production in αα-p and p-p -p and p-p ScatteringScattering

(Study of t(Study of the Breathing Mode of the he Breathing Mode of the Nucleon)Nucleon)

Investigation of the Investigation of the ScalarScalar StructureStructure of of baryons (related to strong baryons (related to strong

non-valence quark excitations)non-valence quark excitations)

H.P. Morsch, MENU2004

Comparison with operator sum rules:

• Cross section covers maximum monopole strength

• Extraction of the baryon compressibility, KB ~1.3 GeV

First evidence for the breathing mode of the nucleon from α-p scatteringat SATURNE (Phys.Rev.Lett. 69,1336 (1992)

Strong L=0 excitation in the region of the P11(1440)

ProjectileΔ excitation

Points to be discussed:Points to be discussed:

1. Theoretical studies of a low lying P11 resonance

2. Results of α-p experiment 3. What are the properties of the Roper resonance?

Roper resonance contains 2 structures: 1. Radial mode 2. Second order Δ excitation

4. New analysis of p-p scattering at beam momenta 5-30 GeV/c

5. What can we learn about the baryon structure from this excitation? Comparison with the longitudinal e-p amplitude S1/2

6. Summary

1.Theoretical studies of a low lying1.Theoretical studies of a low lying PP1111 resonance resonance

• Constituent quark model: • Gluon exchange • Pion exchange • Relativistic quark model• Bag model • Skyrmion model• Algebraic models • Hybrid structure• P11 generated by strong σ-N

interaction• Lattice QCD calculations

1s2s transition

mass of P11 high

mass of P11 lower

mass of P11 right (adjusted)(oscillation of the bag)

P11 is the lowest N* excitation(flat top) Jπ=1/2+ is lowest statenot confirmed by new e-p data

P11 contains valence quark contribution!

2. Saturne experiment 2. Saturne experiment αα-p scattering-p scattering

22 ||)0( oii

ni YrELSn

Observation of a strong monopole excitation in the P11(1440) region

Analysis in terms of operator sum rules

S1=energy weighted sumS-1= energy inversely weighted sumH.P.Morsch, Z.Phys. A350, 61 (1994)

Results of DWBA calculations:P11 excitation covers the full sum S1

Transition density not compatible with valence quark picture!H.P.Morsch et al., Phys.Rev. C67, 064001 (2003)

3. What are the properties of the Roper 3. What are the properties of the Roper resonance?resonance?

Shape of the resonance in a-p different from pi-N:

mo~1440 MeV, Γ~300-360 MeV in π-N

mo~1390 MeV, Γ~190 MeV in α-p

T-matrix description of α-p and π-N scatteringH.P.Morsch and P.Zupranski, Phys.Rev.C61,024002 (99)

Two resonance picture consistentwith γ-p2πo p (radial mode not

excited)

new helicity amplitudesfrom Mainz!

4.New analysis of p-p scattering at beam momenta 4.New analysis of p-p scattering at beam momenta 5-30 GeV/c5-30 GeV/c

Contibuting resonancesΔ33 (1232)

D13 (1520), F15 (1680),strong res. at 1400 MeV

Strongest resonance at1400 MeV, width 200 MeV

No other resonance seen (high selectivity)

What are position and width of the strong resonance?What are position and width of the strong resonance?

Resonance parameters:mo =1400±10 MeV Γ = 200 ± 20 MeV

Position and widthconsistent with Saturneresonance observed in

α-p scattering

What is the evidence for P11 ?What are the decay modes?

change of mo change of width

What is the evidence for PWhat is the evidence for P1111??

Information from the t-dependence of the p-p differential cross section

Resonance at 1400 MeV is strongly peaked at small momentum transfer –tCharacteristic for L=0 excitation !

P11 resonance

Calculation of the differential cross sectionsCalculation of the differential cross sectionsin DWBA using an effective interaction describedin DWBA using an effective interaction describedby multi-gluon exchange (adjusted to fit elastic by multi-gluon exchange (adjusted to fit elastic p-p p-p scattering)Cross section covers the full energy weighted sum rule, consistent with α-p!

What are the decay modes of the PWhat are the decay modes of the P11 11 resonance resonance

at 1400 MeV ?at 1400 MeV ?Information from exclusive experiments:

2 prong events: p-p p N* with N* p πo and n π+

Large yields observed for D13 (1520) and F15(1680)consistent with π-N (elast. width 60% and 70%, resp.)

4 prong events: p-p p N* with N* p π+ π-

Strong peak above 2π threshold

Description of the π+ π- invariant mass spectrum consistent with the inclusive p-p p N* spectra:

Strong contribution from the P11 resonance at 1400 MeVEstimated 2π branching B2π= 75±20%

5. What can we learn about the baryon structure 5. What can we learn about the baryon structure from excitation of the Pfrom excitation of the P1111(1400)?(1400)?

Sensitivity of the calculated differential cross sections to the nucleon transition density

Quantitative description of the data requires a surface peaked transition

density ρtr(r)(consistent with the results from α-p)

Transition density not consistent with pure valence quark excitation

(constituent quark model)

How can we understand the surface peaked transition density?

How can we understand the observed transition density?How can we understand the observed transition density?

1. Excitation of valence quarks

2. Strong sea quark contribution

Sea quark contribution much stronger (~factor 4) than that

of the valence quarks!

The „breathing“ of the sea quark contribution indicates its existence

also in the g.s. density

What do we learn from the longitudinal electron scatteringamplitude S1/2? (data from JLab)

Comparison with the longitudinal e-p amplitude SComparison with the longitudinal e-p amplitude S1/2 1/2 for the for the

Roper resonance excitationRoper resonance excitationC.Smith, NSTAR2004, I.G.Aznauryan, V.D.Burkert, et al., nucl-th/0407021, L.Tiator, Eur.J.Phys.16 (2004)

Transition density for the description of S1/2

requires: 1. valence quark excitation 2. sea quark component

Direct relation of the nucleon transition densityto the amplitude S1/2

Difference between (p,p‘) and (e,e‘):(p,p‘) samples the matter densities(e,e‘) samples the charge densities

For a better determination of the charge transition density more precise data onS1/2 (at different q2) needed!

Multi-gluon potential and compressibilityMulti-gluon potential and compressibility

From operator sum rules baryon compressibility KB deduced.

From the description of the (p,p‘) cross sections of scalar excitations a scalar multi-gluon potential VN(r)is derived!From this the compressibility KN

is defined:

0|

)(2

22

rrN

N dr

rdr VK

Obtained compressibility consistent with sum rule estimate! Scalar modes can be interpreted as vibrations of the multi-gluon field

6. Summary6. Summary1. Evidence for the compression mode from α-p (Saturne resonance)

2. Properties of the Roper resonance P11(1440)

3. Analysis of p-p scattering at beam momenta 5-30 GeV/c

4. Transition density derived from (p,p‘) indicates strong sea-quark effects

5. From multi-gluon potential compressibility KN (consistent with that from operater sum rules) scalar modes

interpreted as vibrations of the multi-gluon potential

Full energy weighted sum rule observed Extraction of baryon compressibility KB~1.3 GeV

Two structures: 1. breathing mode 2. second order Δ excitation(consistent with γ-induced reactions)

Strongest resonance P11 at 1400 MeV (mass, width and sum rule strength consistent with α-p)Decay of P11(1400) dominant into 2π-N channel

similar effect observed in the charge transition density derived from the longitudinal electron scattering amplitude S1/2