Definitive evidence of cosmic γ-ray flux reduction during solar eclipse totality: Observations from the 22 July 2009 eclipse in India

Over the past quarter century, many attempts have been made to observe an expected inverted Gaussian decrease in the low-energy $\gamma$-ray flux during total solar eclipses, coinciding with the point of totality. However, these studies have produced varied results. Here, we present an experimental setup optimized for cosmic $\gamma$-ray collection while minimizing terrestrial interference. Using four large-volume NaI(Tl) scintillation detectors, we collected $\gamma$-ray flux data during the total solar eclipse of 22 July 2009 from two geographically distinct locations in India: Indore and Siliguri. The detectors were elevated above the ground to further reduce signal contamination by terrestrial $\gamma$-rays, enabling the measurement of flux before, during, and after the eclipse visible from these sites. Despite the careful setup, varying levels of radon daughters in the rain during the eclipse period complicated the spectral analysis. To address this, we developed a RooFit-based method that combines exponential and Gaussian functions to generate unified energy spectra, accounting for temporal variations and the effects of rain. Furthermore, we developed a novel method to isolate the true background from rain-induced interference, revealing a $\sim$6% reduction in $\gamma$-ray flux during totality at both sites. With improvements in the experimental setup, modelling, and innovative data analysis, this study establishes a foundational approach for future total solar eclipse experiments.