Using experimental data recorded in a low temperature helium jet, we have studied the statistics of velocity increments: upsilon(r)(x) = upsilon(x+r)-upsilon(x) conditioned on a "rate of energy transfer" anzatz, e(r):P(upsilon(r)/e(r)) For a fixed value of e(r), the histograms of upsilon(r) are found Gaussian at all scale, i.e. there is no intermittency at fixed e(r). Intermittency is caused by the fluctuations of the latter quantity. If P(upsilon(r)/e(r)) is Gaussian, it is characterized uniquely by its variance sigma(2) = [upsilon(r)(2)\e(r)] - [upsilon(r)/e(r)](2) and mean upsilon(0) = [upsilon(r)\e(r)]. We show that sigma is related to e(r) by a power law, valid at any scale, and that upsilon(0) is close to logarithmic in e(r) in the inertial range. With these two relationships, the statistics of upsilon(r) at fixed e(r) are completely determined by e(r). Therefore, the relevant quantity to describe intermittency is the transfer rate of energy, acting as a driving process for the velocity fluctuations.