Mar Capeáns is a Spanish particle physicist who took up the role of CERN Director for Site Operations in January 2026. She earned a PhD in Particle Physics from the University of Santiago de Compostela in 1995, and was awarded Executive MBA in Management of Technology by the University of Lausanne and EPFL in 2007.​ 

She joined CERN in 1992. From 2012 to 2017, she led the Detector Technologies Group, then moved to the Technology Department as Head of the Planning, Project and Resources Group. In 2019, she served as Upgrade Technical Coordinator for the CMS experiment. From 2021 to 2025, she headed the Site and Civil Engineering Department.

She is editor of the Journal of Instrumentation and serves as an adviser on scientific councils and for competitive funding programmes.