1. Dima Svirida (ITEP) Asymmetry Measurements in 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.ru Yu.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. Zolin Joint Institute for Nuclear Research, Dubna, Moscow district, 141980, Russia.

2. Dima Svirida (ITEP)  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  p scattering 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/c 2 resonances with negative parity in 1.9 GeV/c 2 peak parity doublets in these clusters missing resonances near 2 GeV/c 2 which do not fit well the constituent quark model Preface

3. Dima Svirida (ITEP)  Light baryon resonances in the latest PDG are based mainly on 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 Background 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. Dima Svirida (ITEP) Experimental Setup MAIN ELEMENTS:  Vertically polarized proton target PT  4 sets of wire chambers for tracking  Trigger scintillation counters  Aerogel Cherenkov counter for  + tagging TARGET:  Cylinder  30mm, h=30mm, propanediole C 3 H 8 O 2, free proton density  10 %  Magnetic field 2.5 T  3 He evaporation type cryostat at 0.5 K  Dynamic nuclear orientation  Polarization (70-80) %, measurement accuracy 2 %  Sign reverse once per day Beam Arm Proton Arm Pion Arm IPion Arm II Aerogel Counter

5. Dima Svirida (ITEP) 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. Dima Svirida (ITEP) Data Processing 2 BACKGROUND SUBTRACTION:  2-dim cubic polynomial fit for the background SYSTEMATIC ERROR ESTIMATES:  Various cuts on the locus region

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

8. Dima Svirida (ITEP)  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 Results: Asymmetry P at 2.07 GeV/c in  + p

9. Dima Svirida (ITEP)  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 Conclusion 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 ! ! !