Atmospheric Temperature Effect in Secondary Cosmic Rays Observed With a 2 m(2)Ground-Based tRPC Detector

A high time resolution 2 m(2)tracking detector, based on timing Resistive Plate Chamber (tRPC) cells, has been installed at the Faculty of Physics of the University of Santiago de Compostela (Spain) in order to improve our understanding of the cosmic rays arriving at the Earth's surface. Following a short commissioning of the detector, a study of the atmospheric temperature effect of the secondary cosmic ray component was carried out. To take into account this effect, temperature coefficients,W-T(h), were obtained from cosmic ray data using a method based on Principal Component Analysis (PCA). The results obtained show good agreement with the theoretical expectation. The method successfully removes the correlation present between the different atmospheric layers, which would be dominant otherwise. We briefly describe the initial calibration and pressure correction procedures, essential to isolate the temperature effect. Overall, the measured cosmic ray rate displays the expected anticorrelation with the effective atmospheric temperature, through the coefficient alpha(T) = -0.279 +/- 0.051%/K. Rates follow the seasonal variations, and unusual short-term events are clearly identified too.