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

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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 : [email protected] 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.
slide2
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

slide3
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
slide4
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
slide5
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

slide6
Data Processing 2

BACKGROUND SUBTRACTION:

  • 2-dim cubic polynomial fit for the background

SYSTEMATIC ERROR ESTIMATES:

  • Various cuts on the locus region
slide7
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
slide8
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
slide9
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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