ATLAS Thesis Award 2020 goes to Dr. Luigi Marchese, Postdoc in the group of Prof. G. Dissertori.

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Luigi Marchese is one of the winners of the 2020 ATLAS Thesis Award. Luigi graduated at the University of Oxford in 2019, analyzing data collected by the ATLAS experiment. The ATLAS collaboration is composed by more than 5000 members from 181 institutions and about 1200 PhD students. Each year in February, ATLAS celebrates the work of its PhD students selecting the outstanding contributions to the collaboration.
During his PhD, Luigi contributed to several activities of the ATLAS collaboration. His thesis describes different measurements which led to three publications.

He played a leading role in the measurement of the Higgs Boson width. The Higgs boson is a fundamental particle in the Standard Model, the best model we have to describe the fundamental building blocks in the Universe. The Higgs boson is believed to have had a key-role in the evolution of the Universe right after the Big Bang. It is responsible for giving mass to all the fundamental constituents of matter. After more than forty years of Higgs hunting, on the 4th of July 2012 the discovery of a new boson - consistent with the expected Higgs boson in the Standard Model of particle physics - was reported by the ATLAS and CMS collaborations at CERN. However, the Higgs boson is an unstable particle, it decays (i.e. disintegrates) into other particles. The rate at which it decays is a fundamental property of the particle. Indeed, the Higgs Boson was discovered because it produces an excess of events in the mass distribution of its disintegration products.

For a particle which decays quickly, such as the Higgs boson, the mass distribution has an intrinsic spread, the so called “width” of the particle. The faster it decays, the wider the bump. By measuring the width of the excess, one can check in how many different ways the Higgs boson is decaying. This might include decays to new invisible particles, such as dark matter particles, since these decays will influence the width, making it wider. This measurement is an important test of the Standard Model and also a window into new physics. In his thesis, Luigi reported on one of the two most precise constraints of the Higgs Boson width.
In parallel to this contribution, he also worked on some studies of detector performance. In order to perform important measurements, such as the Higgs Boson width or the Higgs boson mass, physicists need to first study the reliability of the detectors when traversed by fundamental particles. This should be done in real LHC proton-proton collisions and in simulated collisions. Luigi studied the performance of the ATLAS muon detectors. Muons are fundamental particles similar to electrons but heavier, and thus able to travel farer across in the ATLAS experiment and reach the muon spectrometer, the outermost part of the detector. Luigi’s work introduced new reliability tests to prove the consistency between the simulation and real data.

All these physics results required huge statistics. When the LHC is on, it produces over 600 million proton-proton collisions per second in the ATLAS detector corresponding to 1 Petabyte/s of data to be collected. The data acquisition process is a huge effort which requires eight people in the ATLAS Control Room all day and night when the detector is on. Luigi actively contributed to data taking operations in the ATLAS Control Room, where he was a shift leader, responsible for the shift crew and data taking during several shifts.

ATLAS is a collaboration of more than 5000 members. Such a huge community requires a massive organization. During his PhD, Luigi was selected as a member of the ATLAS Early Career Scientist Board, a group of seven young scientists. The board worked with the collaboration spokesperson and the ATLAS management to improve the life of the ATLAS members, with a special focus on the early career scientists. As a member of the board, Luigi contributed to several activities reported in this external page post of the ATLAS blog.

At CERN Luigi was also an ATLAS tour guide and he showed students/people the magic behind the scenes of the ATLAS cavern, 100 meters underground. In 2017 and in 2018 he was invited to represent the young community during the visit to CERN of Hon. Boris Johnson and Dr Patrick Vallance, Chief Scientific Adviser to the UK Government.

In addition to his ATLAS work, he also performed a measurement with the CDF collaboration in the Unites States, which led to a third publication.
After graduating, Luigi joined the CMS collaboration and ETH Zürich. He is now a Postdoctoral researcher in the Dissertori group and coordinates the activities of the safety and control system for the ECAL sub-detector. He also contributes to the upgrade of the detector for the HL-LHC.

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