Observation of the strange sea in the proton via inclusive phi-meson production in neutral current deep inelastic scattering at HERA Dahkki Chekanov, S, Krakauer, D, Magill, S, Musgrave, V, Repond, J, Yoshida, R, Mattingly, M, Antonioli, P, Bari, G, Basile, M, Bellagamba, L, Boscherini, D, Bruni, A, Bruni, G, Romeo, G, Cifarelli, L, Cindolo, F, Contin, A, Corradi, M, De Pasquale, S, Giusti, P, Iacobucci, G, Margotti, A, Nania, R, Palmonari, F