Investigation of the deuteron spin structure at short nucleon-nucleon distances in the reaction of polarized-deuteron fr
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EMENTARY PARTICLES AND FIELDS Experiment
Investigation of the Deuteron Spin Structure at Short Nucleon–Nucleon Distances in the Reaction of Polarized-Deuteron Fragmentation to Cumulative Pions L. S. Azhgirey† , S. V. Afanasiev, Yu. T. Borzounov, L. B. Golovanov, L. S. Zolin* , V. I. Ivanov, A. Yu. Isupov** , V. P. Ladygin, A. G. Litvinenko, A. I. Malakhov, V. N. Penev, V. F. Peresedov, Yu. K. Pilipenko, S. G. Reznikov, P. A. Rukoyatkin, and A. N. Khrenov Joint Institute for Nuclear Research, Dubna, Moscow oblast, 141980 Russia Received October 12, 2010
Abstract—Experimental results on the vector (Ay ) and tensor (Ayy ) analyzing powers in the fragmentation of 5- and 9-GeV/c polarized deuterons to high-momentum pions in the kinematical region corresponding to pion production on a strongly correlated nucleon pair (cumulative meson production) are presented. The angular and momentum dependences of Ayy are not described by calculations performed in the impulse approximation by using standard deuteron wave functions. An explanation for our data should be sought on the basis of models that treat the deuteron at short distances (deuteron-core region) as a multiquark state—for example, a 6q cluster, whose high orbital angular momentum (D wave) leads to the observed π)X on the pion transverse momentum. strong dependence of the reaction tensor analyzing power A(d, DOI: 10.1134/S1063778811070027
1. INTRODUCTION
Blokhintsev put forth the flucton hypothesis long before the discovery of the quark structure of hadrons.
Investigation of the deuteron-core structure with allowance for spin degrees of freedom provides a key to obtaining deeper insight into the structure of nuclear forces at short distances. This is one of the intricate problems in strong-interaction physics— without solving this problem, it is impossible to explain the properties of nuclear matter as such and special features of the nuclear structure that manifest themselves in the form of collective effects under conditions where a group of nucleons forms a cluster of strongly correlated particles. Evidence in support of the presence of such clusters in nuclei was obtained in 1957 at the synchrocyclotron of the Joint Institute for Nuclear Research (JINR, Dubna) in experiments devoted to studying the direct knockout of deuterons from nuclei undergoing quasielastic interaction with incident protons, the energy transfer to a nucleon pair being two orders of magnitude higher than the nucleon binding energy in the deuteron [1]. In order to explain the results of those experiments, D.I. Blokhintsev [2] proposed the model of fluctons, which are fluctuations of the nuclear-matter density.
A key role of analyzing the structure of the deuteron core as a proton–neutron flucton in exploring the flucton component in nuclei was highlighted [3–5] in implementing experiments devoted to studying cumulative reactions and initiated after the formulation of A.M. Baldin’s hypothesis of the cumulative effect in the fragmentation of relativistic nuclei [6].
†
Deceased. E-mail: zolin@sunh
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