The tensor analysing power component T21 of the exclusive π - -

meson photoproduction on deuteron in the resonance region.

V.N.Stibunov1, L.M. Barkov2, V.F.Dmitriev2, B.A. Lazarenko2, A.Yu. Loginov1, S.I. Mishnev2, D.M. Nikolenko2, A.V. Osipov1, I.A.

Rachek2, R. Sh. Sadykov2, Yu.V. Shestakov2, A.A. Sidorov1, D.K. Toporkov2 and S.A. Zevakov2.

1 Nuclear Physics Institute of Tomsk Polytechnical University, Tomsk, Russia2 Budker Institute of Nuclear Physics, Novosibirsk, Russia

SPIN’2008

V.N. Stibunov, NPI TPU, Tomsk. SPIN'2008, UVA

Introduction

We present the experimental and calculated data about the tensor analysing power component T21 of the dpp- reaction in the photon energy range (280-900) MeV.The experimental results were obtained on the internal polarized deuterium target of the Novosibirsk electron storage ring VEPP-3. The experimental setup registrated two protons in coincidence for the proton energy interval (55 -220) MeV and for proton angle interval (45o – 90o). We have measured the tensor target asymmetries of the reaction dpp- in the experiment where kinematics are completely defined. The goal of this experiment consists in getting of a better knowledge of the properties of the NN, NN and ∆N systems.

V.N. Stibunov, NPI TPU, Tomsk. SPIN'2008, UVA 3

VEPP-3 storage ring

• Orbit length: 74,4 m

• Electron energy: 0,35 – 2 GeV

• Electron current: up to 150 mA

• Beam life time: 8000 sec

V.N. Stibunov, NPI TPU, Tomsk. SPIN'2008, UVA 4

General view of the target system at VEPP-3 storage ring

• SC – storage cell• CP – cryopump• HM – holding field magnet• IP – ion pump• GP – getter pump• QM – quadrupole magnet• ABS – atomic beam source• BRP – Breit-Rabi polarimeter• QMA – quadrupole magnet

analyser

V.N. Stibunov, NPI TPU, Tomsk. SPIN'2008, UVA 5

Target storage cell

• The cell was coated with drifilm to inhibit atom depolarization during collisions with the cell walls.

• The polarized beam from the ABS is injected into an open-ended, T-shaped storage cell with elliptical cross section 1324mm

• Cooling the cell with liquid nitrogen further increased the density, to achieve an estimated target thickness of 81013 at/cm2

• The direction of the polarization axis was fixed by a megnetic holding field H, varied along the storage cell within the interval 88 — 95 mT

V.N. Stibunov, NPI TPU, Tomsk. SPIN'2008, UVA 6

Cryogenic atomic beam source for polarized deuterium target

• S1 S5 – superconducting sextupoles;• MFT/SFT – medium/strong field transition;• The flux of deuteron polarized atoms – 8,21016 at/sec;• Tensor polarization, Pzz 98%;

• Vector polarization, Pz = 0;

V.N. Stibunov, NPI TPU, Tomsk. SPIN'2008, UVA 7

Schematic overview of the particle detection system

• Total electron beam current integral collected: 566 kC

V.N. Stibunov, NPI TPU, Tomsk. SPIN'2008, UVA 8

Low-Q polarimeter at VEPP-3

V.N. Stibunov, NPI TPU, Tomsk. SPIN'2008, UVA 9

Cross section

V.N. Stibunov, NPI TPU, Tomsk. SPIN'2008, UVA 10

Tensor target asymmetry

V.N. Stibunov, NPI TPU, Tomsk. SPIN'2008, UVA 11

Selection of dpp- events

• the proton vertexes 7mm from beam line• (E, E) analysis in hadron telescopes• complanar events ( 12o)

V.N. Stibunov, NPI TPU, Tomsk. SPIN'2008, UVA 12

Calculation of the polarization observables and differential cross section

V.N. Stibunov, NPI TPU, Tomsk. SPIN'2008, UVA 13

Results on T21

measurement

total amplitude plane wave approximation experiment

V.N. Stibunov, NPI TPU, Tomsk. SPIN'2008, UVA 14

Results on T21

measurement

total amplitude plane wave approximationexperiment

V.N. Stibunov, NPI TPU, Tomsk. SPIN'2008, UVA

Summary1. The T21 -component of the tensor analysing power of the reaction dpp- has

been obtained at the photon energy range (280 - 900) MeV.

2. Dependences of the T21-component from a photon energy, from the momenta, angles of the emitted particles and from effective masses of the pp, p, pp - systems have been obtained.

3. Theoretical calculations with taking into account N and NN rescattering give only qualitative consent with the experimental results.

4. Difference (more than 3) of the theoretical and experimental results are exists both in broad interval of the change variables, and in narrow interval, comparable to accuracy of the measurement.

5. Our Collaboration conducts preparation of the new experiments for the pion photoproduction research on the tensor polarized deuterons:

• in the other kinematical regions;• by the tagged photons; • the two-spin experiments.

We work with variants of theoretical calculations which include excitation of thedibarion resonances in the pion photoproduction on the tensor polarized deuterons