1 / 15

N* Production in α -p and p-p Scattering (Study of t he Breathing Mode of the Nucleon)

N* Production in α -p and p-p Scattering (Study of t he Breathing Mode of the Nucleon). Investigation of the Scalar Structure of baryons (related to strong non-valence quark excitations). H.P. Morsch, MENU2004. First evidence for the breathing mode of the nucleon from α -p scattering

nash
Download Presentation

N* Production in α -p and p-p Scattering (Study of t he Breathing Mode of the Nucleon)

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. N* Production in α-p and p-p Scattering(Study of the Breathing Mode of the Nucleon) Investigation of the ScalarStructure of baryons (related to strong non-valence quark excitations) H.P. Morsch, MENU2004

  2. First evidence for the breathing mode of the nucleon from α-p scattering at SATURNE (Phys.Rev.Lett. 69,1336 (1992) Comparison with operator sum rules: • Cross section covers maximum monopole strength • Extraction of the baryon compressibility, KB ~1.3 GeV Strong L=0 excitation in the region of the P11(1440) Projectile Δ excitation

  3. Points to be discussed: • Theoretical studies of a low lying P11 resonance • Results of α-p experiment • What are the properties of the Roper resonance? Roper resonancecontains 2 structures: 1. Radial mode 2. Second order Δ excitation • New analysis of p-p scattering at beam momenta 5-30 GeV/c • What can we learn about the baryon structure from this excitation? Comparison with the longitudinal e-p amplitude S1/2 • Summary

  4. 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 1s2s 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 state not confirmed by new e-p data P11 contains valence quark contribution! 1.Theoretical studies of a low lyingP11 resonance

  5. 2. Saturne experiment α-p scattering Observation of a strong monopole excitation in the P11(1440) region Analysis in terms of operator sum rules S1=energy weighted sum S-1= energy inversely weighted sum H.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)

  6. 3. What are the properties of the Roper 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 scattering H.P.Morsch and P.Zupranski, Phys.Rev.C61,024002 (99) Two resonance picture consistent with γ-p2πo p (radial mode not excited) new helicity amplitudes from Mainz!

  7. 4.New analysis of p-p scattering at beam momenta 5-30 GeV/c Contibuting resonances Δ33 (1232) D13 (1520), F15 (1680), strong res. at 1400 MeV No other resonance seen (high selectivity) Strongest resonance at 1400 MeV, width 200 MeV

  8. What are position and width of the strong resonance? Resonance parameters: mo =1400±10 MeV Γ = 200 ± 20 MeV Position and width consistent with Saturne resonance observed in α-p scattering What is the evidence for P11 ? What are the decay modes? change of mo change of width

  9. What is the evidence for P11? Information from the t-dependence of the p-p differential cross section Resonance at 1400 MeV is strongly peaked at small momentum transfer –t Characteristic for L=0 excitation !  P11 resonance Calculation of the differential cross sections in DWBA using an effective interaction described by multi-gluon exchange (adjusted to fit elastic p-p scattering) Cross section covers the full energy weighted sum rule, consistent with α-p!

  10. What are the decay modes of the P11 resonance 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 MeV Estimated 2π branching B2π= 75±20%

  11. 5. What can we learn about the baryon structure from excitation of the P11(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?

  12. 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 scattering amplitude S1/2? (data from JLab)

  13. Comparison with the longitudinal e-p amplitude S1/2 for the Roper resonance excitation C.Smith, NSTAR2004, I.G.Aznauryan, V.D.Burkert, et al., nucl-th/0407021, L.Tiator, Eur.J.Phys.16 (2004) Difference between (p,p‘) and (e,e‘): (p,p‘) samples the matter densities (e,e‘) samples the charge densities Direct relation of the nucleon transition density to the amplitude S1/2 Transition density for the description of S1/2 requires: 1. valence quark excitation 2. sea quark component For a better determination of the charge transition density more precise data on S1/2 (at different q2) needed!

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

  15. 6. Summary Full energy weighted sum rule observed  Extraction of baryon compressibility KB~1.3 GeV • Evidence for the compression mode from α-p (Saturne resonance) • Properties of the Roper resonance P11(1440) • Analysis of p-p scattering at beam momenta 5-30 GeV/c • Transition density derived from (p,p‘) indicates strong sea-quark effects • From multi-gluon potential  compressibility KN (consistent with that from operater sum rules)  scalar modes interpreted as vibrations of the multi-gluon potential 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

More Related