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  1. Asymmetry Measurementsin the Elastic Pion-Proton Scattering in the Resonance Energy Range. I.G. Alekseev, P.E. Budkovsky, V.P. Kanavets, L.I. Koroleva, B.V. Morozov, V.M. Nesterov, V.V. Ryltsov, A.D. Sulimov, D.N. Svirida.Institute for Theoretical and Experimental Physics, B. Cheremushkinskaya 25, Moscow, 117218, Russia.Tel: 7(095)129-96-29, Fax: 7(095)883-96-01, E-mail : Vadim.Kanavets@itep.ruYu.A. Beloglazov, E.A. Filimonov, A.I. Kovalev, D.V. Novinsky, V.A. Shchedrov, V.V. Sumachev, V.Yu. Trautman. Petersburg Nuclear Physics Institute, Gatchina, Leningrad district, 188350, Russia.N.A. Bazhanov, E.I. Bunyatova, L.S. ZolinJoint Institute for Nuclear Research, Dubna, Moscow district, 141980, Russia.

  2. Background • Light baryon resonances in the latest PDG are based mainly on N PWA’s KH80 and CMB80, both performed nearly 30 years ago. • More recent analyses by GWU/VPI group did not revealed 4 of 13 resonances • Recent data by ITEP-PNPI on the spin rotation parameters A and R in  p do not confirm KH80 and CMB80 in the backward scattering region, while the agreement with GWU is far from perfect either • No experimental data on the normal polarization P in the backward angular domain due to extremely low cross section  large PWA discrepancies Experiment • MAIN GOAL: • Data for the UNAMBIGUOUS RECONSTRUCTION of the elastic pscattering amplitudes by PWA to resolve problems in LIGHT BARYON SPECTROSCOPY • PRESENT SERIES OF MEASUREMENTS: • New data on the normal polarization (asymmetry) P in  p and  +p • Backward angles (150170)o c.m., several momentum points, where the PWA disagreement is most pronouncing: 0.80, 1.78, 1.94 and 2.07 GeV/c • Available beam momentum range (0.8-2.1) GeV/c ideal for resonance spectroscopy: 65 % of light quark resonances in 3 clusters

  3. Experimental Setup MAIN ELEMENTS: • Vertically polarized proton target PT • 3 sets of XY wire chambers for tracking • Additional set for larger pion acceptance • Trigger scintillation counters C1-C12 • TOF or Aerogel Cherenkov counter for +tagging Beam Arm PT p  Proton Arm Aerogel Counter Pion Arm I Pion Arm II TARGET: • Cylinder 30mm, h=30mm, propanediole C3H8O2, free proton density 10 % • Pair of superconducting Helmholtz coils, magnetic field 2.35 T • 3He evaporation type cryostat at 0.5 K • Polarization (70-80) % by DNO, measurement accuracy ≈2 % • Sign reverse once per day

  4. Experimental Conditions and Data Processing MAIN DIFFICULTY: • Low cross section < 0.1mb/sr ELASTIC EVENT SELECTION: • Coplanarity and kinematic angular correlation  ,  – deviations from the elastic kinematics NORMALIZATION: • Using “unpolarized” event counts – quasi-elastic 2-particle events in the vicinity of the elastic peak, but not under it Measurement region

  5. Data Processing 2 BACKGROUND SUBTRACTION: • 2-dim 12-parameter polynomial fit for the background + error matrix SYSTEMATIC ERROR ESTIMATES: • Various cuts on the elastic locus region Bg/S = 0.1– 0.2 Bg/S  0.8    

  6. Results: Asymmetry P at 1.78 GeV/c in – p ERRORS include: • Elastic event numbers • Background error matrix • Intensity and efficiency normalization uncertainty • Overall scale error due to target polarization uncertainty is 3% and is NOT included FEATURES: • “Calibration” run • Best correspondence to CMB80, >3 from KH80 • Agreement with the older data in two leftmost points • Saturated minimum @153o  close to PWA branching point • Sharp step @167o high L wave present

  7. Asymmetry P at 2.07 GeV/c in –p FEATURES: • Data are not followed by any of the PWA solutions • The closest are SM95 and CMB80, others don’t even resemble data behavior • Agreement with earlier ITEP results • Narrow local minimum @157o, twice confirmed,  high L wave present

  8. Asymmetry P at 0.80 GeV/c in +p FEATURES: • Data are best described by the latestSP06 of GWU • SM95–much lower values,CMB80 – no sharp peak • Obvious contradiction to MARTIN(75) , excluded from latest GWU PWAs

  9. Asymmetry P at 1.94 GeV/c in +p FEATURES: • Deeper minimum than that from the closest KH80 • Behavioral disagreement toCMB80 • Significant deviation from SP06

  10. Asymmetry P at 2.07 GeV/c in +p FEATURES: • Extremely low cross section  poor quality of the data, high background levels 1 • Most resemble CMB80 • Qualitatively different from all others, though don’t 3 contradict to KH80 and SM95

  11. Conclusion • “Classic” PWAs are far from good agreement with the new data • Behavioral disagreement of CMB80 and KH80 may indicate wrong choice of the solution branches, and thus wrong extraction of resonance properties • GWU group significantly improved their analysis in the recent years, yet it looks unstable in the energy domain above 1.8 GeV/c • ITEP-PNPI team believes that their new data notably improves the database for partial wave analyses and becomes a significant step towards reliable light baryon spectrum Acknowledgements • We are grateful to the ITEP accelerator team for providing us with the excellent beam conditions • This work was partially supported by the Russian Fund for Basic Research grants 02-02-16121 and 04-02-16335, Russian State Corporation on the Atomic Energy ‘Rosatom’ and Russian State Scientific Program "Fundamental Nuclear Physics". GREAT THANKS to the organizers of DSPIN-09 ! ! !

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