Improved measurement of the 'head-tail' effect in nuclear recoils

We present new results with a prototype detector that is being developed by the DMTPC collaboration for the measurement of the direction tag ('head-tail') of dark matter wind. We use neutrons from a 252Cf source to create low-momentum nuclear recoils in elastic scattering with the residual gas nuclei. The recoil track is imaged in low-pressure time-projection chamber with optical readout. We measure the ionization rate along the recoil trajectory, which allows us to determine the direction tag of the incoming neutrons.