Guillaume Unal received his PhD in 1991 from Orsay, working on the W boson mass measurement with the UA2 experiment. He then spent a year conducting early studies on Higgs boson decays to gamma-gamma at the LHC and on the accordion liquid argon calorimeter test beam. From 1992 to 1996, he was a member of the CDF collaboration in the University of Pennsylvania group, working on the observation of the top quark and its first cross-section measurement. From 1996 to 2002, he was part of the NA48 collaboration at CERN in the Orsay group, working on the experiment’s liquid krypton calorimeter and the precise measurement of direct CP violation in the neutral kaon system. In 2002, he joined the ATLAS Collaboration, initially with the Orsay group and, since 2006, with the CERN team.
Since 2002, he has contributed to the calibration, reconstruction, and simulation software of the ATLAS liquid argon calorimeter, as well as to electron and photon identification and energy measurement performance. He has worked on several physics analyses using photons, including Higgs boson searches in the gamma-gamma channel and Higgs boson mass measurements. He served as Higgs group convener (2004-2006), ATLAS Data Preparation Coordinator (2012-2013), e/gamma group convener (2014-2016), Publication Committee Chair (2019-2020), and Physics Coordinator (2021-2022). On 1 March 2025, he began his new role as ATLAS Deputy Spokesperson.