Measurement of the Solar Magnetic Field effect on cosmic rays using the Sun shadow observed by the ARGO-YBJ experiment
The cosmic rays originating outside the solar system are blocked by the Sun and form a shadow in the sky map, whose shape is affected by the magnetic field between the Sun and the Earth. Therefore the Sun shadow can be used as a probe of the magnetic field and its intensity variations. In this work, we report on the observation of the rigidity dependent variation of the Sun shadow signal in the rigidity range 0.4-200 TV, using the ARGO-YBJ data collected in the years from 2008 to 2012, when the solar activity varied from the minimum to the maximum. The Moon shadow is also investigated and used to remove the geomagnetic effect on the Sun shadow. According to our measurement, the solar magnetic field significantly affects the flux of cosmic rays with energy lower than 100 TV, that appear to be strongly correlated with the solar activity, while at higher rigidity the solar influence is less evident. We also discuss the possibility to study the different magnetic field components around the Sun.