Dima Svirida, ITEP

Asymmetry Measurements in the Elastic Pion-Proton Scattering

in the Resonance Energy Range. I.G. Alekseev, P.E. Budkovsky, V.P. Kanavets, L.I. Koroleva, B.V. Morozov,

V.M. Nesterov, V.V. Ryltsov, A.D. Sulimov, D.N. Svirida.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, 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.

Dima Svirida, ITEP

MAIN GOAL: Data for the UNAMBIGUOUS RECONSTRUCTION of the elastic p scattering amplitudes by PWA to resolve problems in LIGHT BARYON SPECTROSCOPYPRESENT SERIES OF MEASUREMENTS: New data on the normal polarization (asymmetry) P in p and +p Backward angles (150170)o c.m., several momentum points, where the PWA disagreement is most pronouncing: 0.80, 1.78, 1.94 and 2.07 GeV/c Available beam momentum range (0.8-2.1) GeV/c ideal for resonance spectroscopy: 65 % of light quark resonances in 3 clusters

Experiment

Background Light baryon resonances in the latest PDG are based mainly on N PWA’s

KH80 and CMB80, both performed nearly 30 years ago. More recent analyses by GWU/VPI group did not revealed 4 of 13 resonances Recent data by ITEP-PNPI on the spin rotation parameters A and R in p do not

confirm KH80 and CMB80 in the backward scattering region, while the agreement with GWU is far from perfect either

No experimental data on the normal polarization P in the backward angular domain due to extremely low cross section large PWA discrepancies

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Experimental Setup MAIN ELEMENTS: Vertically polarized proton target PT 3 sets of XY wire chambers for tracking Additional set for larger pion acceptance Trigger scintillation counters C1-C12 TOF or Aerogel Cherenkov counter for + tagging TARGET: Cylinder 30mm, h=30mm, propanediole C3H8O2, free proton density 10 % Pair of superconducting Helmholtz coils, magnetic field 2.35 T 3He evaporation type cryostat at 0.5 K Polarization (70-80) % by DNO, measurement accuracy ≈2 % Sign reverse once per day

Beam Arm

Proton Arm

Pion Arm I Pion Arm II

Aerogel Counter

p

PT

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Experimental Conditions and Data Processing

MAIN DIFFICULTY: Low cross section < 0.1mb/sr

ELASTIC EVENT SELECTION: Coplanarity and kinematic angular correlation , – deviations from the elastic kinematicsNORMALIZATION: Using “unpolarized” event counts – quasi-elastic 2-particle events in the vicinity of the elastic peak, but not under it

Measurement region

p, GeV/c dd NEL <Bg/S>

p 1.78 0.02-0.10 3252 0.45p 2.07 0.03-0.05 2047 0.43+p 0.80 0.03-0.17 3128 0.19+p 1.94 0.05-0.07 1066 1.01+p 2.07 0.02-0.03 701 1.56

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Data Processing 2BACKGROUND SUBTRACTION: 2-dim 12-parameter polynomial fit for the background + error matrixSYSTEMATIC ERROR ESTIMATES: Various cuts on the elastic locus region

Bg/S = 0.1– 0.2 Bg/S 0.8

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FEATURES: “Calibration” run Best correspondence to CMB80,

>3 from KH80 Agreement with the older data

in two leftmost points Saturated minimum @153o

close to PWA branching point Sharp step @167o high L

wave present

Results: Asymmetry P at 1.78 GeV/c in – p

ERRORS include: Elastic event numbers Background error matrix Intensity and efficiency

normalization uncertainty Overall scale error due to target

polarization uncertainty is 3% and is NOT included

Dima Svirida, ITEP

FEATURES: Data are not followed by

any of the PWA solutions The closest are SM95 and

CMB80, others don’t even resemble data behavior

Agreement with earlier ITEP results

Narrow local minimum @157o, twice confirmed, high L wave present

Asymmetry P at 2.07 GeV/c in – p

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Asymmetry P at 0.80 GeV/c in + p

FEATURES: Data are best described by

the latest SP06 of GWU SM95 – much lower values,

 CMB80 – no sharp peak Obvious contradiction to

MARTIN(75) , excluded from latest GWU PWAs

Dima Svirida, ITEP

Asymmetry P at 1.94 GeV/c in + p

FEATURES: Deeper minimum than that

from the closest KH80 Behavioral disagreement to

 CMB80 Significant deviation from

SP06

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Asymmetry P at 2.07 GeV/c in + p

FEATURES: Extremely low cross section

poor quality of the data, high background levels 1

Most resemble CMB80 Qualitatively different from

all others, though don’t 3 contradict to KH80 and SM95

Dima Svirida, ITEP

“Classic” PWAs are far from good agreement with the new data Behavioral disagreement of CMB80 and KH80 may indicate wrong choice of the solution branches, and thus wrong extraction of resonance properties GWU group significantly improved their analysis in the recent years, yet it looks unstable in the energy domain above 1.8 GeV/c ITEP-PNPI team believes that their new data notably improves the database for partial wave analyses and becomes a significant step towards reliable light baryon spectrum

Conclusion

Acknowledgements We are grateful to the ITEP accelerator team for providing us with the excellent beam conditions This work was partially supported by the Russian Fund for Basic Research grants 02-02-16121 and 04-02-16335, Russian State Corporation on the Atomic Energy ‘Rosatom’ and Russian State Scientific Program "Fundamental Nuclear Physics".

GREAT THANKS to the organizers of DSPIN-09 ! ! !