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NSTAR 2007 WORKSHOP ON THE PHYSICS OF EXCITED NUCLEONS 5 – 8 SEP. 2007 BONN, GERMANY BARYON RESONANCE EXPERIMENTS AT COSY. Wolfgang Schroeder Physikalisches Institut, University of Erlangen-Nuremberg, Germany. Content. CONTENT. • Motivation • Accelerator

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NSTAR 2007 WORKSHOP ON THE PHYSICS OF EXCITED NUCLEONS 5 – 8 SEP. 2007 BONN, GERMANY


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    1. NSTAR 2007 WORKSHOP ON THE PHYSICS OF EXCITED NUCLEONS 5 – 8 SEP. 2007 BONN, GERMANY BARYON RESONANCE EXPERIMENTS AT COSY Wolfgang Schroeder Physikalisches Institut, University of Erlangen-Nuremberg, Germany

    2. Content CONTENT • Motivation • Accelerator • Experiments at COSY (ANKE, TOF) • Results • Summary • Outlook (ANKE,TOF,WASA) W. Schroeder, BARYON RESONANCE EXPERIMENTS AT COSY 5. Sep. 2007

    3. Motivation W. Schroeder, BARYON RESONANCE EXPERIMENTS AT COSY 5. Sep. 2007 MOTIVATION Main goal of COSY physics: Better understanding of structure and dynamics of hadrons: Coherent approach combining theory and experiment required One class of observables: Properties of baryon resonances

    4. COSY W. Schroeder, BARYON RESONANCE EXPERIMENTS AT COSY 5. Sep. 2007 COSY @ FZ Jülich Circumference: 184m Polarized protons & deuterons Phase space cooling: electron and stochastic Max. beam momentum: 3.7 GeV/c

    5. COSY W. Schroeder, BARYON RESONANCE EXPERIMENTS AT COSY 5. Sep. 2007 COSY @ FZ Jülich ANKE Circumference: 184m Polarized protons & deuterons Phase space cooling: electron and stochastic Max. beam momentum: 3.7 GeV/c TOF

    6. Experiments W. Schroeder, BARYON RESONANCE EXPERIMENTS AT COSY 5. Sep. 2007 ANKE - EXPERIMENT

    7. Experiments W. Schroeder, BARYON RESONANCE EXPERIMENTS AT COSY 5. Sep. 2007 ANKE - EXPERIMENT magnetic spectrometer at internal target position of COSY

    8. Experiments W. Schroeder, BARYON RESONANCE EXPERIMENTS AT COSY 5. Sep. 2007 TOF - EXPERIMENT

    9. Experiments W. Schroeder, BARYON RESONANCE EXPERIMENTS AT COSY 5. Sep. 2007 TOF - EXPERIMENT large angle (non magnetic) spectrometer with modular vacuum vessel

    10. Experiments W. Schroeder, BARYON RESONANCE EXPERIMENTS AT COSY 5. Sep. 2007 TOF - EXPERIMENT start detector system

    11. Experiments W. Schroeder, BARYON RESONANCE EXPERIMENTS AT COSY 5. Sep. 2007 Comparison ANKE • higher beam momentum: Y* up to 1540 MeV/c2 •high resolution • charged particle id TOF • threshold region: only few partial waves, no Y* •high acceptance • overdetermined kinematics

    12. Results W. Schroeder, BARYON RESONANCE EXPERIMENTS AT COSY 5. Sep. 2007 RESULTS I. Excited Hyperons II. Pentaquark III. N* Decays to KY

    13. Results I W. Schroeder, BARYON RESONANCE EXPERIMENTS AT COSY 5. Sep. 2007 Evidence for Y0(1480) • two final states: Y0*π+X-and π-X+ • three-particle coincidences (pK +π ±)

    14. Results I W. Schroeder, BARYON RESONANCE EXPERIMENTS AT COSY 5. Sep. 2007 Evidence for Y0(1480) MM(pK+ p+), MeV/c2 MM(pK+), MeV/c2

    15. Results I W. Schroeder, BARYON RESONANCE EXPERIMENTS AT COSY 5. Sep. 2007 Evidence for Y0(1480) Select: MM(pK+p+) =1197 MeV/c2 MM(pK+ p+), MeV/c2 MM(pK+), MeV/c2

    16. Results I W. Schroeder, BARYON RESONANCE EXPERIMENTS AT COSY 5. Sep. 2007 Evidence for Y0(1480) Select: MM(pK+p+) =1197 MeV/c2 MM(pK+ p+), MeV/c2 Projection onto MM(pK+) – axis: MM(pK+), MeV/c2 MM(pK+), MeV/c2

    17. Results I W. Schroeder, BARYON RESONANCE EXPERIMENTS AT COSY 5. Sep. 2007 Evidence for Y0(1480) Comparison of Monte Carlo simulations and experimental data Phys. Rev. Lett. 96 (2006) 012002 Add in MC: Y0*: M=1480 MeV/c2, Γ=60 MeV/c2 Entries / 10 MeV/c2 experiment - simulation without Y0(1480) MM(pK+), MeV/c2

    18. Results I W. Schroeder, BARYON RESONANCE EXPERIMENTS AT COSY 5. Sep. 2007 Evidence for Y0(1480) Same parameters of additional Y0(1480) for both decay channels Phys. Rev. Lett. 96 (2006) 012002 p+X- p-X+ Entries / 10 MeV/c2 Entries / 10 MeV/c2 MM(pK+), MeV/c2 MM(pK+), MeV/c2

    19. Results I L(1405) S0(1385) p0 p0 S0(1193) g L(1116) p- p(938) W. Schroeder, BARYON RESONANCE EXPERIMENTS AT COSY 5. Sep. 2007 L(1405)/S0(1385) Decay to L(1116) viap0 Decay to L(1116) viap0g

    20. Results I W. Schroeder, BARYON RESONANCE EXPERIMENTS AT COSY 5. Sep. 2007 Shape of L(1405) measured through its S0p0 decay • four-particle coincidences (pK + pp-) • Invariant mass of (p,p-) m(L)

    21. Results I W. Schroeder, BARYON RESONANCE EXPERIMENTS AT COSY 5. Sep. 2007 L(1405)/ S0(1385) Inv. M(p,p-), MeV/c2 MM(p,K+), MeV/c2 MM(pK+pp-), MeV/c2 MM(pK+pp-), MeV/c2 tag S0(1385) tag L(1405)

    22. Results I W. Schroeder, BARYON RESONANCE EXPERIMENTS AT COSY 5. Sep. 2007 S0(1385) Peak at (1385 ± 10) MeV/c2 Width ~ 50 MeV/c2 Entries / 10 MeV/c2 arXiv: 0705.1039 MM(p,K+), MeV/c2 Shaded: MC all, Solid grey: resonant contribution, solid blue: non-resonant phase space

    23. Results I W. Schroeder, BARYON RESONANCE EXPERIMENTS AT COSY 5. Sep. 2007 L(1405)/ S0(1385) Inv. M(p,p-), MeV/c2 MM(p,K+), MeV/c2 MM(pK+pp-), MeV/c2 MM(pK+pp-), MeV/c2 tag S0(1385) tag L(1405)

    24. Results I W. Schroeder, BARYON RESONANCE EXPERIMENTS AT COSY 5. Sep. 2007 Background subtracted line shape of L(1405) Entries / 10 MeV/c2 fitted non-resonant MC Background subtracted lineshape of L(1405) decaying into S0p0 (arXiv: 0705.1039) Comparison: Dotted line: p-p → K0(Sp)0 D.W. Thomas, et al. , Nucl. Phys. B56 (1973) 15 Solid line: K-p → p+p-S+p- R.J. Hemingway, Nucl. Phys. B253 (1984) 742 MM(p,K+), MeV/c2

    25. Results I W. Schroeder, BARYON RESONANCE EXPERIMENTS AT COSY 5. Sep. 2007 Line shape of L(1405) Line shape of the L(1405) is not represented satisfactorily by a Breit Wigner resonance Entries / 10 MeV/c2 MM(p,K+), MeV/c2 Open question about the nature of the L(1405): - p-wave q3 baryon - K-p molecular state - two overlapping states - pentaquark L.S. Geng, E. Oset, arXiv: 0707.3343

    26. ResultsII W. Schroeder, BARYON RESONANCE EXPERIMENTS AT COSY 5. Sep. 2007 Negative results for pentaquark TOF: Three independent analyses of the reaction Tagging S+ S(pK0) = +1 TOF covers the full phase space

    27. ResultsII W. Schroeder, BARYON RESONANCE EXPERIMENTS AT COSY 5. Sep. 2007 Negative results for pentaquark within statistical errors: no signal in the region of interest ds/dm, mb/(GeV/c2) Phys. Lett. B649 (2007) 351 Invariant mass pK0, GeV/c2

    28. Results II W. Schroeder, BARYON RESONANCE EXPERIMENTS AT COSY 5. Sep. 2007 Negative results for pentaquark Bands: 95% confidence level stot(pp S+Q+) < 0.15 mb Phys. Lett. B649 (2007) 351 stot,X, mb mass of resonance, GeV/c2

    29. Results II W. Schroeder, BARYON RESONANCE EXPERIMENTS AT COSY 5. Sep. 2007 Negative results for pentaquark ANKE: Investigation of the reaction: At 95% confidence level: stot(pp Q+p+L)< 0.058 mb atpbeam = 3.65 GeV/c J. Phys. G 34 (2007) 627 Maximum permissible Q+ signal

    30. ResultsIII W. Schroeder, BARYON RESONANCE EXPERIMENTS AT COSY 5. Sep. 2007 N* decays to KY Little is known on N* decaying into strange channels No information on N* → KL for L >1 No information on N* → KS at all TOF: Investigation of N* resonances in the mass region of 1.6 – 1.9 GeV/c2

    31. ResultsIII Meson Exchange Model pL final state interaction + W. Schroeder, BARYON RESONANCE EXPERIMENTS AT COSY 5. Sep. 2007 Total cross section of pp  K+Lp TOF Excitation function is not decisive!

    32. ResultsIII W. Schroeder, BARYON RESONANCE EXPERIMENTS AT COSY 5. Sep. 2007 TOF: pp  K+Lp: Dalitz plot analysis Data 2.95 GeV/c Data 2.95 GeV/c

    33. Results III W. Schroeder, BARYON RESONANCE EXPERIMENTS AT COSY 5. Sep. 2007 Data 2.95 GeV/c RESULTS pp  K+Lp: Dalitz plot analysis Data 2.95 GeV/c Model parametrisation of Sibirtsev Eur. Phys. J. A27 (2006) 269, private communication Full Model only resonances only FSI + =

    34. ResultsIII C1650 C1710 + C1720 p [GeV/c] W. Schroeder, BARYON RESONANCE EXPERIMENTS AT COSY 5. Sep. 2007 pp  K+Lp: Dalitz plot analysis Strong contribution of N*-Resonances in the reaction pp  pK+L: I [A.U.] In good agreement with calculation of Shyam Phys. Rev C60 (1999) 055213

    35. ResultsIII W. Schroeder, BARYON RESONANCE EXPERIMENTS AT COSY 5. Sep. 2007 TOF: pp  K+Lp: Dalitz plot analysis At the moment: No discrimination between N*(1710) and N*(1720) N*(1710) P11 N*(1720) P13 I(JP) = 1/2(1/2+) I(JP) = 1/2(3/2+) Goal: Separation using polarized beam Comparison with other approach Partial wave analysis (E.Klempt et al.)

    36. ResultsIII W. Schroeder, BARYON RESONANCE EXPERIMENTS AT COSY 5. Sep. 2007 pp  K+Lp: Partial wave analysis arXiv:hep-ph/0703216, private communication Phys.Lett B632 (2006) 27 entries 1.Solution (red) 2. Solution (blue) Initial. pp interaction 3P2, 3P0,1S0Initial. pp interaction 3P2, 3P1,1S0 Ambiguous result

    37. Results III W. Schroeder, BARYON RESONANCE EXPERIMENTS AT COSY 5. Sep. 2007 pp  K+Lp: Partial wave analysis Dependence of beam asymmetry arXiv:hep-ph/0703216 private communication beam asymmetry Very different behavior of the two solutions! Discrimination between solutions possible!

    38. Summary W. Schroeder, BARYON RESONANCE EXPERIMENTS AT COSY 5. Sep. 2007 SUMMARY (Excited Hyperons) Y0* observed in pp collisions in two final states: Y0*π+X -and Y0*  π-X+ Entries / 10 MeV/c2 Y0* mass: (1480 ± 15 ) MeV/c2 Y0* width: (60 ± 15 ) MeV/c2 Phys. Rev. Lett. 96 (2006) 012002 MM(p,K+), MeV/c2 Lineshape of L(1405) from S0p0 decay first time in proton induced reactions arXiv:0705.1039 Entries / 10 MeV/c2 MM(p,K+), MeV/c2

    39. Summary W. Schroeder, BARYON RESONANCE EXPERIMENTS AT COSY 5. Sep. 2007 SUMMARY (Pentaquark) ds/dm, mb/(GeV/c2) stot(pp  S+Q+)< 0.15 mb Phys. Lett. B649 (2007) 351 Inv. mass pK0, GeV/c2 stot(pp  Q+p+L)< 0.058 mb J. Phys. G 34 (2007) 627

    40. Summary W. Schroeder, BARYON RESONANCE EXPERIMENTS AT COSY 5. Sep. 2007 SUMMARY (N*) Contribution of N*-Resonances in the reaction pp  pK+L: Partial wave analysis: Isospin amplitudes from polarization observables beam asymmetry

    41. Outlook W. Schroeder, BARYON RESONANCE EXPERIMENTS AT COSY 5. Sep. 2007 OUTLOOK I Upcoming Program for TOF: Measurements with pol. beam Straw tube tracker Measurements with LD2 target N*->KL/KS pL scattering length ANKE: nL scattering length

    42. Outlook W. Schroeder, BARYON RESONANCE EXPERIMENTS AT COSY 5. Sep. 2007 OUTLOOK II Studies of excited hyperons with WASA at COSY WASA allows the measurement of neutral particles and g WASA at COSY is now in operation!

    43. Additional Additional

    44. Results I W. Schroeder, BARYON RESONANCE EXPERIMENTS AT COSY 5. Sep. 2007 Line shape of L(1405) L.S. Geng, E. Oset, arXiv: 0707.3343 Line shape reproduce by: K exchange mechanism (high energy pole) p- (r-) exchange mechanism broadening the distributen

    45. ResultsII W. Schroeder, BARYON RESONANCE EXPERIMENTS AT COSY 5. Sep. 2007 Negative results for pentaquark χ2 of fit Calculation of upper limits for Q+ cross section 95% CL assumed cross section for Q+ in mb ds/dm, mb/(GeV/c2) Fit: 3rd order polynomial + varying amount of Q+ resonance Invariant mass pK0, GeV/c2

    46. Results RESULTS: pp  K+Lp: Dalitz plot analysis Data 2.95 GeV/c

    47. Results RESULTS: pp  K+Lp: Dalitz plot analysis Data 2.95 GeV/c Model calculation of Sibirtsev

    48. Results RESULTS: pp  K+Lp: Dalitz plot analysis Data 2.95 GeV/c Model calculation of Sibirtsev only FSI

    49. Results RESULTS: pp  K+Lp: Dalitz plot analysis Data 2.95 GeV/c Model calculation of Sibirtsev included resonances: N*(1650) N*(1710) N*(1720)

    50. Results RESULTS: pp  K+Lp: Dalitz plot analysis Data 2.95 GeV/c Model calculation of Sibirtsev only resonances only FSI +