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Nucleon Excited States

Nucleon Excited States. Ralf W. Gothe University of South Carolina Mini-Workshop on Nucleon Excited States PAC25 January 17, 2004 Introduction N D transition “Missing” Resonances, Strange Resonances and Two Pion Production Pentaquark States Outlook. Physics Goals.

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Nucleon Excited States

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  1. Nucleon Excited States Ralf W. Gothe University of South Carolina Mini-Workshop on Nucleon Excited States PAC25 January 17, 2004 Introduction N D transition “Missing” Resonances, Strange Resonances and Two Pion Production Pentaquark States Outlook

  2. Physics Goals • Understand QCD in the full strong coupling regime • transition form factors • mass spectrum, quantum numbers of nucleon excited states • relevant degrees-of-freedom • wave function and interaction of the constituents

  3. CLAS Coverage for ep e’X at 4 GeV 5.0 4.0 3.0 2.0 1.0 CLAS 0 1.0 1.5 2.0 2.5

  4. CLAS Coverage for ep e’pX at 4 GeV 2.0 missing states 1.5 1.0 CLAS 1.5 0. 1.0 0.5

  5. Electromagnetic Probe • helicity amplitudes are sensitive to the difference in wave functions of N and N* • can separate electric and magnetic parts of the transition amplitude • is linearly polarized • varying Q2 allows to change the spatial resolution and enhances different multipoles • sensitive to missing resonance states

  6. N D(1232) Transition Form Factors SU(6): E1+=S1+=0

  7. Cross Section Decomposition example: e p e’ p po

  8. g*p ppo– Response Functions CLAS

  9. Multipole Analysis forg*p ppo CLAS Q2 = 0.9 GeV2 |M1+|2 Re(E1+M1+*) |M1+|2 Re(S1+M1+*)

  10. Multipole RatiosREM, RSMbefore 1999 Sign? Q2 dependence? • Data could not determine sign or Q2 dependence

  11. Multipole RatiosREM, RSMin 2002 Sign? < 0 ! Q2 dependence ! Slope < 0 • No trend towards • pQCD behavior is • observed for Q2 up • to 4 GeV2.

  12. N D(1232) Transition Form Factors • Preliminary results from ELSA and Hall A using different techniques confirm CLAS data.

  13. N D(1232) Transition Form Factors Need data at low Q2 • Lattice QCD indicates that the pion cloud makes E1+ /M1+ more negative at small Q2. • Data at low Q2 needed to study effects of the pion cloud.

  14. Preliminary Multipole RatiosREM, RSM • Dynamical models and full LQCD calculations indicate the importance of the pion cloud at low Q2 consistent with the trend of data. • Full LQCD results indicate a small oblate deformation of the D(1232). • Data at high Q2 needed to study the transition to pQCD. preliminary

  15. Very Preliminary Multipole RatiosREM ,RSM preliminary • New trend towards pQCD behavior may or may not show up. • Experiment E-01-002 in Hall C will reach Q²~8 GeV² and after the energy upgrade REM and RSM can be measured up to Q²~12 GeV².

  16. N D Transition and Background Terms • systematic uncertainties in extraction of E1+/M1+ from ep e’p po around 0.5% • differences in treatment of background terms (models not constrained) • will become more severe for higher Q2 (D dropping faster) • more experimental information on hand (polarization and isospin) • single-spin asymmetry sTL’ for e p e’p (po) ande p e’p+ (n) • polarization transfer in e p e’p (po) • differential cross sections for e p e’p+n (D less important) CLAS Hall A CLAS

  17. Polarized Beam Observables CLAS sLT’response function for e p e p po sLT’ = 0 if only a single diagram contributes (sensitive to the interference between D and background)

  18. Polarization Measurement in e p e’ p (po) Hall A mb/sr Q2 = 1 GeV2 W = 1.232 GeV Results sensitive to non-resonant contributions SAID MAID Parametrisations of available data

  19. p+ Electroproduction CLAS

  20. Electromagnetic Probe • helicity amplitudes are sensitive to the difference in wave functions of N and N* • can separate electric and magnetic parts of the transition amplitude • is linearly polarized • varying Q2 allows to change the spatial resolution and enhances different multipoles • sensitive to missing resonance states

  21. Quark Model Classification of N* D13(1895) Mart and Bennhold “Missing” P13(1870) Capstick and Roberts D13(1520) S11(1535) ? D(1232) Roper P11(1440) + q³g + q³qq + N-Meson + …

  22. “Missing” Resonances? Problem: symmetric CQM predicts many more states than observed (in pN scattering) Possible solutions: 1. di-quark model old but always young fewer degrees-of-freedom open question: mechanism for q2 formation? 2. not all states have been found • possible reason: decouple from pN-channel • model calculations: missing states couple to • Npp (Dp, Nr), Nw, KY 3. chiral symmetry approach new all baryonic and mesonic excitations beyond the groundstate octets and decuplet are generated by coupled channel dynamics (not only L(1405), L(1520), S11(1535) or f0(980)) gcoupling not suppressed electromagnetic excitation is ideal

  23. Resonances in Hyperon Production? CLAS g*p K+Y forward hemisphere backward hemisphere preliminary N* ?

  24. LPhotoproduction off the Proton Bump at 1.9 GeV D13(1895) ? CLAS Dominant resonances S11(1650) P11(1710) P13(1720) Carnegie Mellon

  25. Resonances ing*p pp+p- CLAS Analysis performed by Genova-Moscow collaboration Step #1: Q² 0.65 GeV² 0.95 GeV² use the best information presently available GNpp : PDG GNg:expt. Data or SQTM 1.30 GeV² extra strength

  26. Attempts to fit observed extra strength CLAS Step #2: • vary parameters of the photocouplings • vary parameters of known P13, P11, D13 • introduce new P13 New P13(1720) consistent with predictied missing P13 , but at lower mass.

  27. Attempts to fit observed extra strength CLAS Step #2: • vary parameters of the photocouplings • vary parameters of known P13, P11, D13 • introduce new P13 W(GeV)

  28. PWA ingp pp+p- CLAS W=2240 MeV

  29. Resonances ingp pp+p- CLAS

  30. Resonances ingp pp+p- CLAS F15(1680) P13(1720) preliminary

  31. JLab:Q+- Exclusive Process I CLAS gd K-K+p(n) Q+ • Mass1.542±0.005 GeV/c² • < 21 MeV/c² Significance 5.2±0.6s

  32. JLab:Q+- Exclusive Process II p+ g K* K- K0 K+ Q+ p n CLAS gp p+K-K+(n) Events Q+ K* M(K-p+)

  33. JLab:Q+- Exclusive Process III g p+ p- K- N* K+ p Q+ n CLAS gp p+K-K+(n) Q+ combined analysis II & III • Mass1.555±0.010 GeV/c² • < 26 MeV/c² Significance 7.8±1.0s cut

  34. JLab:Q+- Exclusive Process III g p+ p- K- N* K+ p Q+ n CLAS gp p+K-K+(n) N* ? Mass ~ 2.440GeV/c²

  35. Outlook: Observation of ExoticX−− combined analyis NA49 X0 X(1530) M=1.862± 0.002 GeV/c² G< 18 MeV/c² CERN SPS hep-ex/0310014

  36. Outlook: Observation of ExoticX−− Diakonov et al. Hep-ph/9703373 Diakonov, Petrov hep-ph/0310212 Jaffee, Wilczek hep-ph/0307341 Jaffee, Wilczek hep-ph/0312369 R.A. Arndt et al. nucl-th/0312126 X0 X(1530) PAC 25 at JLab M=1.862± 0.002 GeV/c² CERN SPS hep-ex/0310014

  37. Hadron multiplets K p K N S X W─ Q+ Mesons qq Baryons qqq Baryons built from meson-baryon, or qqqqq …

  38. New Tools: Exploit Weak Decays in Direct Reconstruction X −−→ p− X− L→ p− p X −→ p− L Electron beam gn→K+K+X5−− • X− ct = 4.9 cm • ct = 7.9 cm Negatives bend outwards <gb> ~ 1.5

  39. New Tools: Frozen Spin Target for CLAS Technical problem: build polarized target for tagged photon beam - minimum obstruction of CLAS solid angle - low distortion of particle trajectories in magnetic field Solution: - frozen spin target - temperature 50mK - magnetic field 5kG Bonn target at Mainz GDH experiment 5 Tesla polarizing magnet Status: - design in progress at JLab - procurement started for polarizing magnet CLAS JLab design

  40. New Tools: Bound Nucleon Structure (BoNuS) Physics issue: tag process off a neutron bound in deuterium by detecting the spectator proton in coincidence with the scattered e’ CLAS coils Technical problem: spectator protons have • - low momentum and low range • - isotropic angular distribution (no correlation) • - high rate pair spectrometer • Solution: • - high pressure gas target • - surrounded by radial drift chamber • - GasElectronMultiplier gap

  41. New Tools: BoNuS Detector • Radial Time Projection Chamber (RTPC) Goal: detect spectator protons with momenta as low as 70 MeV/c • Cylindrical prototype with GEM readout being developed by Howard Fenker • Flat GEM prototype has been built and is being tested

  42. New Cherenkov detector optimized for low Q2 kinematics New Tools: Gas Cherenkov Counter • Needed for E-03-106 (GDH Integral at very low Q2), M. Ripani, et al. PMTs + Winston cones multilayer m-metal + iron shield Mirrors

  43. New Tools: DVCS in N* Physics ep e’gN* e’ g (p, h, w, …) g* e CLAS (preliminary) hard process x+x x-x Bjorken regime GPDs N* p 2-particle correlations function • t, x dependence of N* transition • map out transition-GPDs N*’s D • decouple g virtuality from momentum transfer to the nucleon • study nucleon dynamics at the parton level Mnp+ (GeV)

  44. New Tools: Setup for DVCS CLAS s.c. solenoid PbWO4 Electromagnetic calorimeter Physics Goal measure x, t, Q2 - dependence of ep e’p gin a wide kinematics range to constrain GPD models. Technical Problem • need to detect all final state particles to identify process • double luminosity to 2x1034 cm-2 s-1 Technical solution • add forward calorimeter (436 lead PbWO4 crystals) • readout via avalanche photodiodes (APD) • super conducting 5 Tesla solenoid Moller shield

  45. Final state selects the quark flavors u, d, s • => probes the GPD structure complementary • to DVCS • Filter for spin-(in)dependent GPDs Deeply Virtual Meson Production

  46. DVCS Experiment Superconducting solenoid: needed for shielding Moller electrons PbWO4 e.m. calorimeter needed for photon detection Solenoid under construction at SACLAY cryostat coil windings calorimeter

  47. DVCS - 100 Crystal Prototype for Test Run Connexion board APD / Preamplifier Back frame Support frame Mother board + preamplifier Optical fiber system mounted on the front frame Alignement system + / - 5 mm Connectors Fixing plate on the CLAS support Ph. Rosier, Orsay

  48. DVCS Experiment • PbWO4 crystal calorimeter • 440 tapered crystals, APDs, on site (ITEP, JLab) • Mechanical structure in final design stage (Orsay) • Preamps - designs being evaluated (ITEP, Orsay) • 5 x 5 crystal prototype built and being tested

  49. PrimEx Experiment PbWO4 crystal channel Electron beam test results

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