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.

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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/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

Preface

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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

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

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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 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

Beam Arm

Proton Arm

Pion Arm I Pion Arm II

Aerogel Counter

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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

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Data Processing 2

BACKGROUND SUBTRACTION:

2-dim cubic polynomial fit for the background

SYSTEMATIC ERROR ESTIMATES:

Various cuts on the locus region

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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

Results: Asymmetry P at 1.94 GeV/c in +p

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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

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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 ! ! !