Anomalous signals due to cosmic rays observed by the bar gravitational wave detector NAUTILUS

Cosmic ray showers interacting with the resonant mass gravitational wave antenna NAUTILUS, cooled down to 0.1 K, have been detected. The experimental results show large signals at a rate much greater than expected. Since August 2000 NAUTILUS has been running at T = 1.1 K (non-superconductor aluminium). There is evidence at the 3 standard deviation level that the rate of the large signals is dependent on the bar temperature. The rate is compatible with zero at a bar temperature of 1.1 K.