First Measurement of CNO solar neutrinos with Borexino

by Dr Xuefeng Ding (Princeton University)

Thursday 23 Jul 2020, 15:00 → 16:00 US/Eastern

Borexino recently announced the first measurement of solar neutrinos from the CNO cycle process. The carbon-nitrogen-oxygen (CNO) cycle is one of two known sets of fusion reactions by which stars convert hydrogen to helium. It is thought to be more important in stars more massive than 1.3 solar mass or in late stages. Proposed as early as the 1930s by H. Bethe, it remains hypothetical until this work.
Located at the Laboratori Nazionali del Gran Sasso (LNGS) in Italy, Borexino is a liquid scintillator detector that detects solar neutrinos by their elastic scattering on electrons. Most of the natural radioactive isotope backgrounds were removed during the purification campaign. Cosmogenic backgrounds, especially 11C, are low thanks also to the 3800-meter water equivalent of overburden and the three-fold coincidence analysis technique. The remaining backgrounds for measurement of CNO solar neutrinos are pep solar neutrinos and radioactive 210Bi. With two breakthroughs in the thermal stability of the detector and the analysis method, the 210Bi rate could be determined precisely and accurately for the CNO neutrino analysis. Finally, the absence of CNO solar neutrinos is disfavored at five sigma significance, and the flux of CNO solar neutrinos is determined to be 7.0+3.0-2.0 x 108 cm-2s-1.

 

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20200723 First measurement of CNO solar neutrinos.pdf