Measurement of neutral-meson masses in meson-nucleus interactions at a momentum of 7 GeV/ c at the Hyperon-M setup
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EMENTARY PARTICLES AND FIELDS Experiment
Measurement of Neutral-Meson Masses in Meson–Nucleus Interactions at a Momentum of 7 GeV/cc at the Hyperon-M Setup M. Yu. Bogolyubsky1), S. V. Evdokimov1), V. I. Izucheev1) , D. I. Patalakha1), B. V. Polishchuk1), S. A. Sadovsky1), A. S. Soloviev1), M. V. Stolpovsky1), Yu. V. Kharlov1)* , N. A. Kuzmin2) , V. P. Obudovsky2), Yu. P. Petukhov2), and S. Ya. Sychkov2) Received March 25, 2013
Abstract—The π 0 , η, K 0 , ω, and f2 (1270) masses were measured at the HYPERON-M setup in meson– nucleus interactions at a momentum of 7 GeV/c by using six nuclear targets: Be, C, Al, Cu, Sn, and Pb. The experiment in question proved to be insensitive to the expected effects of a modification to the omega-meson mass in nuclear matter. As for the f2 (1270) meson, its mass and width values averaged over all experimental data, mf2 = 1275.8 ± 1.0(stat.) ± 0.4(syst.) MeV/c2 and Γf2 = 190.3 ± 1.9(stat.) ± 1.8(syst.) MeV/c2 , agree well with the world-average values. At the same time, our experimental data do not rule out the possible effect of an in-medium modification to the f2 (1270)-meson mass for heavy nuclei at a level better than 0.4%. DOI: 10.1134/S1063778813110045
INTRODUCTION The problem of the origin of hadron masses is one of the key problems in quantum chromodynamics (QCD). The chiral quark condensate ¯ q q in the QCD vacuum is nonzero because of dynamical chiralsymmetry breaking, and this in turn determines the dynamical mass of quarks in hadrons [1]. However, the effect of hot or dense (or both hot and dense) nuclear matter leads to a change in the quark condensate. According to QCD lattice calculations at zero baryochemical potential, μ ≈ 0, and a high medium temperature T [2], the quark condensate decreases fast above the temperature of T = 200 MeV. A decrease in the quark condensate is also predicted under conditions of cold nuclear matter [1, 3]. The possible change in the chiral condensate is studied experimentally both under conditions of hot matter in ultrarelativistic heavy-ion collisions and in cold and dense matter by using hadron–nucleus collisions [1]. The objective of the present study was to explore experimentally the properties of neutral mesons in cold nuclear matter. For this purpose, we have performed a series of measurements of the masses of π 0 , η, K 0 , ω, and f2 (1270) mesons produced in meson– nucleus interactions on various nuclear targets. The 1)
Institute for High Energy Physics, pl. Nauki 1, Protvino, Moscow oblast, 142281 Russia. 2) Joint Institute for Nuclear Research, Dubna, Moscow oblast, 141980 Russia. * E-mail: [email protected]
respective experiments consisted in measuring the masses of short-lived ω and f2 (1270) mesons, which, after their production and formation within a target nucleus, undergo decay within the same nucleus because of their short lifetime. In the same experiments, one can also perform reference measurements of the masses of comparatively long-lived neutral mesons (π 0 , η, and K 0 ), which, irrespective of where their product
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