Arnau Brossa Gonzalo 1993–2024

Arnau Brossa Gonzalo, a postdoctoral researcher at the Galician Institute of High Energy Physics (IGFAE) working on the LHCb experiment, died in Santiago on 21 July 2024 following complications from a climbing accident.

Arnau obtained his degree in physics at the University of Barcelona in 2016, specialising in theoretical physics. He continued there for his master’s in astrophysics, particle physics and cosmology, with a thesis on the LHCb experiment.

In 2017 he embarked on his PhD studies in particle physics at the University of Warwick. His thesis, entitled “First observation of B⁰ → D^*(2007)⁰K⁺π^– and B⁰_s → D^*(2007)⁰K^–π⁺ decays in LHCb”, won the Springer Thesis Prize for outstanding PhD research. This was the first LHCb measurement of B decays involving fully reconstructed neutral D^*mesons, which are particularly challenging due to the soft neutral particles emitted in the D^* → Dπ⁰ and D^* → Dγ decays. These modes are nonetheless extremely important to understand as they are backgrounds to a wide range of other studies, including those used for precision measurements of the CKM angle γ.

Following the completion of his PhD, Arnau joined the LHCb group at IGFAE in 2022 to work further on the LHCb experiment, first as a postdoctoral researcher and later as a Juan de la Cierva researcher. He then joined the lepton-flavour-universality group at IGFAE, taking on a leading role in the measurement of the ratios of semileptonic-decay branching fractions to final states with tau leptons relative to muons, denoted R(D) and R(D^*). Arnau had rapidly established himself as an expert in this area, and in early 2024 he had taken on convenership of the LHCb subgroup that was dedicated to this and to similar charged-current lepton-flavour-universality tests.

Arnau’s warmth, kindness, dedication, intelligence and competence will be deeply missed by his many friends at the institute in Santiago and in the LHCb collaboration.