Azimuthal correlations of projectile and target fragments in collisions between gold nuclei of energy 10.6 GeV per nucle
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EMENTARY PARTICLES AND FIELDS Experiment
Azimuthal Correlations of Projectile and Target Fragments in Collisions between Gold Nuclei of Energy 10.6 GeV per Nucleon and Emulsion Nuclei U. U. Abdurakhmanov, K. G. Gulamov, S. I. Zhokhova, V. V. Lugovoi* , V. Sh. Navotny** , and V. M. Chudakov Institute for Physics and Technology, Fizika–Solntse Research and Production Association, Uzbek Academy of Sciences, ul. G. Mavlyanova 2b, Tashkent, 700084 Republic of Uzbekistan Received October 31, 2006; in final form, August 14, 2007
Abstract—Intra- and intergroup azimuthal correlations of projectile and target fragments are found in collisions between gold and emulsion nuclei. The statistical significance of these correlations is high. The methodological distortions associated with the measurement errors are investigated in detail and are taken into account. PACS numbers: 25.70.Pq, 25.75.+r, 24.85.+p DOI: 10.1134/S1063778808030125
Ten stacks of NIKFI BR-2 nuclear photoemulsion, which contain 30 plates each, were irradiated with gold nuclei accelerated to an energy of 10.6 GeV per nucleon at the BNL/AGS accelerator. The sensitivity of the emulsion was not lower than 30 grains per 100 µm for particles producing a minimum ionization. Scanning along a track revealed 1057 inelastic interactions. For charged secondaries, we measured angles θ with respect to the projectile-momentum direction and azimuthal angles ϕ in the xz plane orthogonal to the projectile momentum. The angles ϕ were measured from the x axis, which is parallel to the emulsion plane (0 ≤ ϕ < 2π). Particles producing an ionization of I > 1.4I0 , where I0 is the ionization along the tracks of relativistic singly charged particles, were classified as strongly ionizing particles. Our experiment was described in detail elsewhere [1–3]. In each event, the set of charged secondaries was broken down into three groups: that of target fragments (group 1), that of projectile fragments (group 2), and that of other particles (group 3). Group 1 included strongly ionizing particles, with the exception of projectile fragments; if their total number was less than ten, it was increased to ten by incorporating relativistic singly charged particles characterized by maximum angles θ. Group 2 included strongly ionizing particles characterized by very small angles θ and relativistic singly charged particles characterized by angles of θ < 1◦ , but, if their total number was less * **
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than ten, it was increased to ten by adding relativistic singly charged particles for which minimum angles θ were in excess of 1◦ . We investigated only 736 events in which the number of other particles was not less than ten. In order to investigate azimuthal correlations of projectile (target) fragments, we employed the quantities β1 and β2 described in [4]: ⎡ 2 n cos(kϕi ) (1) βk = ⎣ i=1
+
n
2 sin(kϕi )
⎤ − n⎦ n(n − 1),
k = 1, 2.
i=1
Here, n is the number of particles in a group in one event and ϕi is the azimuthal angle of the ith particl
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