Omer Penek 

Catching Fundamental Physics with Borexino and FAIR - From Proton Fusion in the Sun to Proton Collisions in the Lab

Abstract:
Searching for solutions to fundamental physics questions is a broad and challenging task. Many experiments and profound models are needed in order to make a step towards understanding the unknowns of our Universe. Here, important physics processes are given by proton-proton and proton-nucleus reactions since hydrogen is the most abundant element of visible matter in the cosmos.

At energies around keV and under certain thermodynamical conditions, two protons can undergo nuclear fusion to create a deuteron. One of the most important natural sources of nuclear fusion is the Sun emitting neutrinos from its core with _MeV endpoint energies. Borexino, a radiopure liquid scintillator detector with 280 tonnes of active mass, located at the Laboratori Nazionali del Gran Sasso in Italy operated between May 2007 until October 2021 and gave significant contributions to the measurement of low-energy solar neutrinos from the dominant proton-proton (pp) chain (branching fraction _99%) and the sub-dominant Carbon-Nitrogen-Oxygen (CNO) cycle (branching fraction _1%). Neutrinos from the CNO cycle have been measured by Borexino with a high statistical significance for the first time in 2020 after being predicted by Bethe and Weizacker more than 80 years ago.

When going to higher energies at several GeV, proton-proton collisions enable access to subnuclear scales. For precision analyses, fixed target experiments become relevant. As an example, the planned Facility for Anti-proton and Ion Research (FAIR) in Darmstadt, Germany serves as an example of a facility pursuing such a proton-on-proton program. In this context, charm productions can be studied by measuring dileptonic final states, which are e.g. relevant for the investigation of the proton structure.

Motivated by the research I was involved in over the past years, in this talk, I will present recent achievements of Borexino focusing on its precision spectroscopy of pp chain and CNO cycle solar neutrinos including novel techniques in the spectral analysis. Moreover, I will give an overview of the physics potential at FAIR with a focus on charm production including the advantages of kinematic methods. I will conclude with a brief discussion on building a bridge between (astro-)neutrino physics and hadron physics.