ISSN 1063-7788, Physics of Atomic Nuclei, 2009, Vol. 72, No. 9, pp. 1501–1512. c  Pleiades Publishing, Ltd., 2009. Original Russian Text c  K.S. Kuzmin, V.A. Naumov, 2009, published in Yadernaya Fizika, 2009, Vol. 72, No. 9, pp. 1555–1566. ELEMENTARY PARTICLES AND FIELDS Theory Axial Mass in Quasielastic Antineutrino–Nucleon Scattering Accompanied by Strange-Hyperon Production K. S. Kuzmin 1)* and V. A. Naumov ** Joint Institute for Nuclear Research, Dubna, Moscow oblast, 141980 Russia Received December 29, 2008; in final form, March 23, 2009 Abstract—Reactions of quasielastic Λ-, Σ − -, and Σ 0 -hyperon production in antineutrino–nucleon inter- actions are studied. An axial-mass (M A ) value that agrees with a fit to all accelerator data on exclusive and inclusive νN and νN reactions was extracted from a global statistical analysis of experimental data on differential and total cross sections for ∆Y =0 and 1 quasielastic reactions of neutrino and antineutrino scattering on various nuclear targets. PACS numbers: 13.15.+g, 13.40.Gp, 25.30.Pt, 25.80.Pw DOI: 10.1134/S1063778809090105 1. INTRODUCTION A reliable description of νN and νN interactions is necessary for processing and interpreting the results of present-day and planned experiments employing beams of accelerator and atmospheric (anti)neutrinos to study neutrino oscillations, quantum decoherence, neutrino stability, and nonstandard neutrino–matter interactions, as well as the results of experiments devoted to searches for exotic processes (such as proton decay and n n transitions in nuclei), in which case the interactions of neutrinos (predominantly of atmospheric origin) with a detector medium are an experimentally uncontrollable source of background events. Since, at the present time, there is no universal model for calculating cross sections for neutrino in- teractions with nucleons and nuclei that is applicable over a broad region of energies, the use of an inco- herent superposition of basic contributions describing elastic and quasieleastic neutrino scattering (the lat- ter being accompanied by nucleon charge exchange conserving hypercharge Y or by light-hyperon pro- duction involving a change of unity in Y ), the neutrino production of single pions (which involves baryon res- onances in the intermediate state), and deep-inelastic scattering (described within the quark-parton model, where the quark distributions are extracted from data on the scattering of high-energy charged leptons and neutrinos) is a traditional approach to solving the 1) Institute of Theoretical and Experimental Physics, Bol’shaya Cheremushkinskaya ul. 25, Moscow, 117218 Russia. * E-mail: kkuzmin@theor.jinr.ru ** E-mail: vnaumov@theor.jinr.ru problem in question. Corrections caused by reactions of resonance neutrino production of several pions, single kaons, and eta mesons, as well as reactions of coherent neutrino scattering on nuclei, are taken sometimes into account along with dominant contri- butions. In the present study, we explore the contribu- tion (a nondominant but a significant one) to the total νN cross section from quasielastic Λ-, Σ − - , and Σ 0 -hyperon production allowed by the ∆Y = ±1, ∆I =1/2, and ∆Y =∆Q selection rules (where I is the isospin and Q is the electric charge). The cross sections for these processes are suppressed in relation to those for ordinary quasielastic ν  p →  + n ( = e, µ, τ ) scattering by a factor of sin 2 θ C ≈ 0.05 (where θ C is the Cabibbo angle) and have been poorly studied experimentally for this reason. At the present time, it is therefore impossible to test the validity of alternative models for transition form factors appear- ing in the ∆Y =1 weak hadron current by directly using data on νN cross sections. The axial-vector form factor and the pseudoscalar form factor, which is related to it, introduce the largest uncertainty. The pseudoscalar contribution to the ν e,µ n and ν e,µ p cross sections is very small and cannot be measured at the present time for this reason. However, it is of impor- tance for calculating quasielastic ν τ n and ν τ p cross sections, for which there are no experimental data, but which are required for studying ν µ ↔ ν τ neutrino os- cillations in experiments such as ICARUS/ICANOE and OPERA (see, for example, [1]), which are able to identify events featuring a tau lepton in the final state. In the dipole approximation, the axial-vector form factor is determined by the constants D and F , which 1501