About estimations of a one-photon background in neutrino-oscillation experiments at low neutrino energies
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ELEMENTARY PARTICLES AND FIELDS Theory
About Estimations of a One-Photon Background in Neutrino-Oscillation Experiments at Low Neutrino Energies* V. P. Efrosinin Institute for Nuclear Research, Russian Academy of Sciences, pr. Shestidesyatiletiya Oktyabrya 7a, Moscow, 117321 Russia Received July 31, 2006; in final form, February 14, 2007
Abstract—The possible sources of one-photon radiation as a background for the quasi-elastic reaction νµ + n → µ− + p are considered. They are relevant in experiments on determination of oscillation parameters at low neutrino energies (Eν ∼ 1 GeV). The estimation for the cross section of the reaction νµ + n → µ− + p + γ is given at Eνlab = 0.7 GeV as 0.65% of the corresponding cross section of quasielastic reaction. The mechanisms of quasi-elastic reaction are also considered at low neutrino energies on a quark level. PACS numbers: 13.15.-f DOI: 10.1134/S1063778807110129
The current accelerator experiments on νµ −νe neutrino oscillation deal with neutrino beams at low energies (Eν ∼ 1 GeV). To shed light on the neutrino-oscillation parameters, rather precise knowledge of the neutrino–nucleon interactions in this energy region is required. Since Cherenkov detectors employed in these experiments poorly distinguish an electron from a photon, it is extremely important to study the possible background from other reactions with one or two photons to the main quasi-elastic reaction of a neutrino on a nucleon: (1) νµ + n → µ− + p.
for the cross sections of the one-photon reactions, σ(νµ p → νµ pγ)/σ(νµ n → µ− pγ). The following contribution of reaction (3) is substantially less than the contribution of the reaction νµ + n → µ− + p + γ.
(5)
The calculation of the cross section of reaction (5) is the first goal of the present study. The two-photon background in our case is determined by the reaction νµ + n → µ − + p + π 0 .
(6)
In this work, we give estimations of the cross sections of the processes that are of interest to us at neutrino energy in the laboratory system Eνlab = 0.7 GeV. The processes with neutral currents (2) νµ + p → νµ + p, νµ + n → νµ + n
The experimental cross section of reaction (6) at Eνlab = 0.7 GeV is σ 0.07 × 10−38 cm2 [1]. The pair of photons from π 0 decay is successfully identified by data processing of experiments except for the restricted kinematic configurations. Reaction (6) together with the reaction
are not interesting in experimental analysis of neutrino oscillations. However, the reaction (3) νµ + p → νµ + p + γ
νµ + n → µ − + n + π +
can contribute to the one-photon background. At the same time, the ratio of the cross sections at the given neutrino energy is known from experiments [1]: σ(νµ p → νµ p)/σ(νµ n → µ− p) ∼ 0.1. The Q2
(4)
interval over which this ratio was measured is 0.3−1.0 GeV2 . Approximately the same ratio is valid ∗
The text was submitted by the authors in English.
(7)
can also contribute to the one-photon background. The experimental cross section of reaction (7) is approximately the same as that of reaction (6), and at Eνlab
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