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New data on polarization (asymmetry) in  + p Backward angles, 1.94 & 2.07 GeV/c

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New data on polarization (asymmetry) in  + p Backward angles, 1.94 & 2.07 GeV/c

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  1. Asymmetry Measurementsin the Elastic Pion-Proton Scattering at 1.94 and 2.07 GeV/c. I.G. Alekseev, P.E. Budkovsky, V.P. Kanavets, L.I. Koroleva, B.V. Morozov, V.M. Nesterov, V.V. Ryltsov, D.N. Svirida, A.D. Sulimov, V.V. Zhurkin.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, S.P. Kruglov, 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. Preface • New data on polarization (asymmetry) in +p • Backward angles, 1.94 & 2.07 GeV/c • The latest experiment in the series of the polarization parameter measurements by ITEP-PNPI collaboration in the last decade (A at 1.00, 1.43 and 1.62 GeV/c, P at 1.43, 1.78 and 2.07 GeV/c) • Available momentum range (0.8-2.1) GeV/c •  65 % of light quark resonances in 3 clusters • MAIN GOAL: • Data for the UNAMBIGUOUS RECONSTRUCTION of the elastic pscattering amplitudes by PWA • PHYSICS INTEREST to the LIGHT BARYON SPECTROSCOPY is enhanced by the observation of : • resonance clusters with masses 1.7 and 1.9 GeV/c2 • resonances with negative parity in 1.9 GeV/c2 peak • parity doublets in these clusters • missing resonances near 2 GeV/c2 which do not fit well the constituent quark model

  3. Background • Light baryon resonances in the latest PDG are based mainlyon PWA’s KH80 and CMB80, both performed more than two decades ago. • More recent analyses by VPI/GWU group did not revealed 4 of 13 resonances in clusters • Latest data on polarization in p and spin rotation parameters do not confirm KH80 and CMB80 in the backward scattering region Experiment PRESENT MEASUREMENTS: +p, cm=(148-176)o, P=1.94 and 2.07 GeV/c • No or very poor experimental information up to now • Main difficulty: extremely small cross section in the explored domain • Significant background • Its careful subtraction and systematic error estimate

  4. Experimental Setup MAIN ELEMENTS: • Vertically polarized proton target PT • 4 sets of wire chambers for tracking • Trigger scintillation counters • Aerogel Cherenkov counter for +tagging Beam Arm Proton Arm Aerogel Counter Pion Arm I Pion Arm II TARGET: • Cylinder 30mm, h=30mm, propanediole C3H8O2, free proton density 10 % • Magnetic field 2.5 T • 3He evaporation type cryostat at 0.5 K • Dynamic nuclear orientation • Polarization (70-80) %, measurement accuracy 2 % • Sign reverse once per day

  5. Data Processing 1 MAIN DIFFICULTY: • Very low cross section ELASTIC EVENT SELECTION: • Coplanarity and kinematic correlation  ,  – deviations from the elastic kinematics • Additional background suppression by momentum analysis  factor 2 in S/B ratio NORMALIZATION: • Using “unpolarized” event counts 1.94 GeV/c 2.07 GeV/c Measurement region

  6. Data Processing 2 BACKGROUND SUBTRACTION: • 2-dim cubic polynomial fit for the background SYSTEMATIC ERROR ESTIMATES: • Various cuts on the locus region

  7. Results: Asymmetry P at 1.94 GeV/c in +p • Best correspondence to KH80 and the oldest VPI/GWU analysis • Data suggests even deeper minimum at 165o • Significant deviation from CMB80 and latest VPI/GWU solution

  8. Results: Asymmetry P at 2.07 GeV/c in +p • Best resemblance to CMB80 • Angular dependence looks contradictory to all other analyses • Obvious contradiction to the latest VPI/GWU solution • No disagreement with existing data

  9. Conclusion • GWU group significantly improved their analysis in the recent years • New polarization parameter data require NEW GLOBAL TYPE PWA • We extremely welcome the recent efforts of the Helsinki group on resurrection of KH80 analysis Acknowledgements • Our thanks to Professor G.Hoehler for very interesting and fruitful discussion • We are grateful to the ITEP accelerator team for providing us with the excellent beam conditions and to ITEP cryogenic laboratory for supply with liquid helium and nitrogen. • This work was partially supported by the Russian Fund for Basic Research grant 02-02-16111 and Russian State Scientific Program "Fundamental Nuclear Physics". • GREAT THANKS to the organizers of this interesting conference ! ! !

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