The magnetic field dependence of the quantum critical fluctuations close to the antiferromagnetic transition in CeCu5.9Au0.1 is investigated directly by neutron scattering at TAS7 in Riso in a horizontal magnet. The butterfly-shaped critical wave vector region in the a*c*-plane persists up to H = 1.8 T (Hparallel toc) and the magnetic spectrum can be represented by the same function used for 0 T, including the unusual exponent alpha = 0.75. The field only changes the dynamics like an effective temperature T-eff = (T-2 + (muH/k(B))(2))(0.5) with a moment mu = 1.3mu(beta). This result is entirely consistent with and complements the 0 T neutron scattering and the uniform magnetization data, which are successfully described by E/T and H/T scaling properties, respectively, establishing the unusual non-Fermi-liquid behavior in this heavy fermion compound. (C) 2002 Elsevier Science B.V. All rights reserved.