Measurement of the analyzing power of high-transverse-momentum charged hadrons in proton-nucleus collisions at an energy
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EMENTARY PARTICLES AND FIELDS Experiment
Measurement of the Analyzing Power of High-Transverse-Momentum Charged Hadrons in Proton–Nucleus Collisions at an Energy of 40 GeV V. V. Abramov, A. A. Volkov, P. I. Goncharov, A. Yu. Kalinin, A. V. Korablev, Yu. P. Korneev, A. V. Kostritsky, A. N. Krinitsyn, V. I. Kryshkin, A. A. Markov, V. V. Talov, L. K. Turchanovich, and A. V. Khmelnikov Institute for High Energy Physics, Protvino, Moscow oblast, 142284 Russia Received September 26, 2006; in final form, February 12, 2007
Abstract—The transverse single-spin asymmetry was measured for charged hadrons (π ± , K ± , p, p¯) produced in proton–nucleus collisions. The measurements were performed at the FODS-2 spectrometer by using a polarized proton beam that was accelerated to an energy of 40 GeV at the accelerator of the Institute for High Energy Physics (IHEP, Protvino) and which was made to hit carbon and copper nuclear targets. The data in question were obtained in the range of c.m. angles between 73◦ and 94◦ near the central region (−0.01 < xF < 0.27, 0.7 < pT < 3.6 GeV/с). The single-spin asymmetry for π + and K + mesons is significant at high values of pT and moderately small positive values of xF . The analyzing power for other hadrons (π − , K − , p, p¯) is compatible with zero in the pT range studied here. The dependence of the analyzing power on the mass number of the target nucleus is insignificant. PACS numbers: 13.85.Ni, 13.88.+e, 13.87.Fh, 13.75.Gs, 13.85.Hd, 12.38.-t, 12.38.Qk DOI: 10.1134/S1063778807100109
1. INTRODUCTION Large transverse single-spin asymmetries (or the analyzing power) observed in inclusive reactions induced in high-energy hadron collisions [1–5] have not received an unambiguous and generally accepted explanation [6]. Possibly, the origin of single-spin effects is associated with quark interaction at long distances (confinement) and the phenomenon of chiral-symmetry breaking in quantum chromodynamics (QCD). Of great interest in this respect is the instanton model [7, 8], which takes into account quark interaction with the gluon condensate. As a result, quarks develop an effective dynamical mass and a significant anomalous chromomagnetic moment, with the result that there may arise the dependence of single-spin effects on kinematical variables and on the quark flavor. In order to reveal these dependences, it is necessary to measure the single-spin asymmetry for various reactions over a broad range of kinematical variables. The measurements in question were performed by using a polarized proton beam of energy 40 GeV. The present article reports on a continuation of the series of studies performed with the FODS-2 spectrometer over two runs of 2003 in three kinematical regions corresponding to the angles of 90, 160, and 230 mrad between the arm axis and the beam-axis direction in
the laboratory frame [9]. In this article, we present only data for the nominal arm angle of 160 mrad, which corresponds to angles of π ± -meson production in the range between 73◦ and 94◦ in the reference frame comoving with th
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