Title: 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
1Asymmetry 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_at_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. Zolin Joint
Institute for Nuclear Research, Dubna, Moscow
district, 141980, Russia.
2Preface
- 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
3Background
- Light baryon resonances in the latest PDG are
based mainlyon PWAs 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, P1.94 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
4Experimental 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, h30mm, 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
5Data 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
6Data Processing 2
- BACKGROUND SUBTRACTION
- 2-dim cubic polynomial fit for the background
- SYSTEMATIC ERROR ESTIMATES
- Various cuts on the locus region
7Results 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
8Results 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
9Conclusion
- 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 ! ! !