INVESTIGATION OF POLARIZATION PHENOMENA IN PROTON-NUCLEUS SCATTERING AT 1 GEV.

Study of interaction of the 1 GeV protons with atomic nuclei using a high resolution magnetic spectrometer is an essential part of the physical program at the PNPI synchrocyclotron. A typical momentum resolution Δ p/p of about 10^-3 is needed for reliable separation of the elastic scatterring and the scattering with excitation of the nucleus target. The high resolution was achieved due to an original method of reducing energy spread of the proton beam extracted from the synchrocyclotron and a high performance of the magnetic spectrometer [1] which detects the scattered protons. The nuclear matter distributions were investigated in proton elastic scattering experiments at 1 GeV . The data obtained were analyzed using Glauber multiple-scattering model. The polarization [2],[3] of the scattered protons was measured for the first time in the kinematics domain where the Glauber model was applicable. Later, the deuteron wave function at small distances was studied in (p,2p) quasi-elastic scattering. Here the polarization measurements allow for effective control of the reaction mechanism. A new series of (p,2p) experiments was started in the year 1993. A (new) low momentum arm of the magnetic spectrometer was put into operation together with two proportional chamber polarimeters installed in each spectrometer arm. Two final protons were detected in coincidence at non-symmetric scattering angles θ₁=18-25 deg. and θ₂=53.2 deg. Overall resolution on separation energy E_s varied from 2 to 3 MeV. The polarizations of both scattered protons were measured. At first, a phenomenon of effective polarization of a nucleon in a nucleus [2] was studied, using this apparatus. Various theoretical considerations predict a partial restoration of chiral symmetry in nuclear matter. This effect may be observed through modification of the nucleon mass in nuclear medium resulting in modification of the NN-scattering amplitude. The spin-orbital part of the NN-amplitude, and measured polarizations, are most sensitive to the nucleon mass modification. The present (p,2p) experiments are aimed at study of this phenomenon. The experiments are performed jointly with physicists from Research Center for Nuclear Physics, Osaka, Japan. A reduction of the measured polarization in the (p,2p) reaction with the S-shell protons of nuclei ⁶Li (1S), ¹²C (1S), ⁴⁰Ca (2S) in comparison with that in the free elastic proton-proton scattering was observed. It was shown that this reduction could not be explained by conventional rescattering and absorption in the nuclear matter. A strong correlation between the value of the polarization reduction and the effective mean nuclear density was established [4]. On the other hand, the experiment with a liquid helium (⁴He) target [5] showed that, if nuclear matter is strongly heterogeneous, the scale of nuclear medium influence is determined rather by the mean binding energy of the S-shell protons than by the effective nuclear density of the nucleus. In March 2005, in the experiment with ¹⁶O (water ice target) [6] the general relativistic approach for description of nucleon-nucleus interaction was checked. An answer to the question whether the nuclear density or the binding energy of a nucleon on a nuclear shell is the right parameter to describe the NN-amplitude modification might be obtained in a (p,2p) scattering experiments on protons knocked out of a nucleus from a very deep shell, like, e.g., (1S) shell of the ⁴⁰Ca. The corresponding experiment was performed in the year 2006. The data obtained in this experiment are presently analyzed.

[1]. O.V.Miklukho, N.P.Aleshin, S.L.Belostotski, O.G.Grebenyuk, O.Ya.Fedorov, A.A.Izotov, A.Yu.Kisselev, Yu.G.Narishkin, V.V.Nelyubin, A.N.Prokofiev, D.A.Prokofiev, Yu.A.Scheglov, A.V.Shvedchikov, V.V.Vikhrov, A.A.Zhgun, A.A.Zhdanov
Polarization in the Quasielastic Scattering of 1 GeV Protons on Light Nuclei. Physics of Atomic Nuclei, Vol.63, No.5, 2000, pp. 824-833.

[2]. O.V.Miklukho, N.P.Aleshin, S.L.Belostotski, Yu.V.Elkin, O.G.Grebenyuk, O.Ya.Fedorov, A.A.Izotov, A.A.Jgoun, A.Yu.Kisselev, M.P.Levchenko, Yu.G.Narishkin, V.V.Nelyubin, A.N.Prokofiev, D.A.Prokofiev, Yu.A.Scheglov, A.V.Shvedchikov, V.V.Vikhrov, and A.A.Zhdanov
Polarization in quasi-elastic (p,2p) reaction on 7Li nucleus in complete kinematics at 1 GeV , Nucl.Phys.A683, 2001, 145-156.

[3]. O.V.Miklukho, V.A.Andreev, M.N.Andronenko, G.M.Amalsky, S.L.Belostotski, O.A.Domchenkov, O.Ya.Fedorov, O.G.Grebenyuk, A.A.Izotov, A.A.Jgoun, A.Yu.Kisselev, M.A.Kopytin, Yu.G.Naryshkin, A.N.Prokofiev, D.A.Prokofiev, Yu.M.Sanjiev, A.V.Shvedchikov, V.V.Sulimov, S.I.Trush, V.V.Vikhrov, and A.A.Zhdanov (Petersburg Nuclear Physics Institute RAS, 188350 Gatchina) T.Noro, K.Hatanaka, J.Kamiya, Y.Kitamura, E.Obayashi, H.Sakaguchi, H.Takeda, T.Wakasa, Y.Yasuda, and H.Yoshida (Research Center for Nuclear Physics, Osaka 567-0047, Japan)
Study of nuclear medium effects on polarization in (p,2p) scattering at 1 GeV, Czech.J.Phys. Vol.52 (Suppl.C), 2002, 293-300.

[4]. V.A. Andreev 1), M.N. Andronenko 1), G.M. Amalsky 1), S.L. Belostotski 1), O.A. Domchenkov 1), O.Ya. Fedorov 1), K. Hatanaka 2), A.A. Izotov 1), A.A. Jgoun 1), J. Kamiya 2), A.Yu. Kisselev 1), M.A. Kopytin 1), O.V. Miklukho 1), Yu.G. Naryshkin 1), T. Noro 3), E. Obayashi 2), A.N. Prokofiev 1), D.A. Prokofiev 1), H. Sakaguchi 4), V.V. Sulimov 1), A.V. Shvedchikov 1), H. Takeda 4), S.I. Trush 1), V.V. Vikhrov 1), T. Wakasa 2), Y. Yasuda 4), H.P. Yoshida 2), and A.A. Zhdanov 1).
1)- Petersburg Nuclear Physics Institute, Gatchina 188300, Russia 2)- Research Center for Nuclear Physics, Osaka University, Ibaraki 567-0047, Japan 3)- Department of Physics, Kyushu University, Fukuoka 812-8581, Japan 4)- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
Polarizations for proton knockout reactions from s1/2-orbits at 1 GeV , Phys.Rev., v. C69, 2004, p.024604

[5]. O.V.Miklukho, G.M.Amalsky, V.A.Andreev, S.L.Belostski, Yu.V.Elkin, O.Ya.Fedorov, K.Hatanaka, A.A.Izotov, A.Yu.Kisselev, L.M.Kochenda, A.I.Kovalev, M.P.Levchenko, T.Noro, A.N.Prokofiev, D.A.Prokofiev, H.Sakaguchi, A.V. Shvedchikov, V.A.Trautman, V.A.Trofimov, S.I.Trush, D.O.Veretennikov, A.A.Zdanov
Polarization in Quasielastic (p,2p) Scattering from 4He Nucleus at 1 GeV , Physics of Atomic Nucleus, Vol.69, No.3, 2006, pp.474-481.

[6]. O. Miklukho, S. Belostotski, K. Hatanaka, A. Kisselev, T. Noro, H. Sakaguchi
Study of medium effect on properties of pp interaction at 1 GeV, in: Main Results of Scientific Investigations in PNPI RAS in 2005-2006 , to be published.