High Energy Physics Seminars

Rigidity dependence studies of cosmic ray solar diurnal anisotropy at GRAPES-3

by Dr. Meeran Zuberi (DHEP TIFR Mumbai)

Monday, December 26, 2022 from to (Asia/Kolkata)
at AG-66
The diurnal variations of the galactic cosmic rays (GCR) measured by ground-based detectors represent an anisotropic flow of GCR at 1 AU, also known as solar diurnal anisotropy (SDA). The GRAPES-3 muon telescope (G3MT) has been recording high statistics of muons at a rate of about 50,000 per second for the past two decades, allowing us to probe the tiny variations in the muon flux caused by solar phenomena. We have examined 22 years (2000–2021) of G3MT data using the Fourier series technique to obtain the daily SDA amplitude and phase. We observe a strong relationship between yearly averages of SDA amplitude and interplanetary magnetic fields (IMF) measured by the NASA satellites located at the first Lagrangian point. A cross-correlation study of the daily SDA amplitude and the IMF reveals the IMF’s instantaneous role in this phenomenon. Furthermore, the directional capability of the G3MT is exploited to study this phenomenon at various median rigidity bins. The measured SDA amplitude and phase show a strong rigidity dependence. We find that the phase has a dominant 22-year variation controlled by the drift effect due to solar polar magnetic field reversal, regardless of their rigidity. However, the higher rigidity bin phase variation shows an additional component of the 11 years controlled by the diffusion effect due to the change in the strength of the IMF associated with the 11-year sunspot cycle. The details of this work will be discussed during the talk.