Search for ν_μ →ν_e oscillations with the OPERA experiment in the CNGS beam

A first result of the search for ν_μ →ν_e oscillations in the OPERA experiment, located at the Gran Sasso Underground Laboratory, is presented. The experiment looked for the appearance of ν_e in the CNGS neutrino beam using the data collected in 2008 and 2009. Data are compatible with the non-oscillation hypothesis in the three-flavour mixing model. A further analysis of the same data constrains the non-standard oscillation parameters θ_new and Δm²_new. For large Δm²_new values (> 0.1 eV²) , the OPERA 90% C.L. upper limit on sin² (2θ_new) based on a Bayesian statistical method reaches the value 7.2 x10⁻³.