Iacopo Vivarelli

Particle physics is the study of the fundamental constituents of matter and the forces that act between them. Particle colliders are machines able to accelerate particles at high energies, then collide them together. Colliders are a key instrument for the understanding of how nature works at distances much smaller than the size of an atomic nucleus. I am a member of the ATLAS Collaboration, one of the two general-purpose experiments taking data at the Large Hadron Collider (LHC). For many years I have been searching for evidence of new physics phenomena in the LHC collisions. In particular, I was looking for the production of the so-called supersymmetric partners of the known elementary particles. The lack of evidence for new phenomena lead me to investigate the elephant in the room, that is, the production of the heaviest elementary particle, the top quark. I am in particular interested in rare production processes, where pairs of tops are produced together with a vector boson. The study of these processes could bring a new understanding to the interaction of the top quark with the rest of the Standard Model particles altogether. One of my passions is calorimetry, that is, the process of stopping and destroying particles to measure their energy. I am working together with colleagues in Italy, the US and Korea to build a new type of calorimeter that should dramatically improve the energy resolution of these devices.

Previous academic positions

• Professor of Physics (before Reader and Lecturer) - University of Sussex (Brighton - United Kingdom) - From June 2013 to September 2023.
• Akademischer Rat - Albert-Ludwigs Universität (Freiburg Im Breisgau - Germany) - From May 2009 to May 2013. 
• CERN/INFN fellow - CERN (Geneva - Switzerland) - From January 2009 to April 2009. 
• Post-doctoral Fellowship - Universita' degli Studi (Pisa - Italy) - From July 2005 to December 2008.

Professional Standings

• UK National Contact for ECFA Detector Roadmap and Infrastructures panels. 
• Member of the UK Science and Technology Facilities Council (STFC) Particle Physics Technology Advisory Panel (PPTAP).  
• CERN Scientifica Associate (coordination of research activities on supersymmetry in ATLAS).
• External reviewer for several european research bodies.
• Performing peer reviewing for high-impact factor, major high energy physics journals.
• Member of the Editorial board of the “Symmetry” journal.
• Author of “Review of Particle Physics”, del Particle Data Group. One becomes author of the PDG review only through invitation for excellent research on the field (supersymmetry in this case).
• Director of Teaching and Learning for the School of Mathematics and Physical Sciences - University of Sussex (Aug 2021 - July 2024).
• Senior leadership roles within the ATLAS Collaboration - please refer to the dedicated section below.

Research activities

My research develops mainly in two directions. On one hand, I am a long-standing member of the ATLAS collaboration. My early contributions focused on the assembly and commissioning of the central hadronic calorimeter (TileCal), and on the development of the jet reconstruction and calibration for the early phases of the data taking. I have then focused on data analysis (software and physics): I concentrated on finding a solution to the naturalness problem through the detection of new phenomena in Run 1 and Run 2 collisions. My leadership has been acknowledged by the collaboration giving me the honour and responsibility of coordinating all searches for supersymmetry at the beginning of Run 2. Lacking signals of new phenomena, my most recent contributions have focused on precision measurements of processes of associated top production with vector bosons.

On the other hand, I am firmly convinced that the future of collider physics is in the construction of a lepton collider for precision measurements of the electroweak sector and in particular of the Higgs boson. I have started to ramp up an effort to deliver significant contributions in this area as well. 

The ATLAS Collaboration 

The ATLAS experiment at the European Centre for Nuclear Research (CERN) is built and operated by a large international collaboration of about 3000 physicists and it is in its science exploitation phase. Given the size of the collaboration, ATLAS should be regarded as a large experimental facility with a large international research community affiliated to it. I am a respected member of the worldwide collaboration and I have hold management roles.

• Elected member of the Speaker’s Committee - coordinating and overseeing the presentations of the collaboration to international conferences (April 2023)
•  Elected member of the Publication Committee - overseeing the quality of paper publications for the whole collaboration (March 2020 - March 2022).
• Co-convener of the ATLAS SUSY Working Group - coordinating all ATLAS activities for the search of supersymmetric particles. Coordinating the activities of about 250 scientists. Primary leadership role in ATLAS. (Oct 2015 - Sept 2017).
• Co-coordinator of ATLAS task force (five members) for the redesign of the analysis model (Jan 2013 - June 2013). Co-coordinator of the task force for the implementation of the new analysis model. Coordinating the activity of about 15 scientists (July 2013 - Oct 2014).
• Co-coordinator of the ATLAS analysis activities for the search of stop pair production. Coordinating the activity of about 40 scientists. (Oct 2012 - Sept 2013).
• Co-convener of the ATLAS SUSY group background forum. Coordination of the background estimation activity for SUSY analysis in ATLAS. Coordinating the activity of about 200 scientists. (2011-2012)
• Chairman of the Physics Validation (software certification for physics use). Coordination of a group of 20 physicists. Central leadership role in ATLAS (2008-2009)
• Co-coordinator of the group performing SUSY analysis with b-jets and missing transverse momentum. Coordinating the activity of 25 scientists. (2010-2012)
• Member of the ATLAS Physics Coordination - core management body for physics analysis in ATLAS. (Ex officio, 2008-2009 and 2015-2017)
• Member of the ATLAS Software Project Management Board - core management body for ATLAS software. (Ex officio, 2008-2009)
• Responsible for the Online Data Acquisition of the central ATLAS hadronic calorimeter. (2006-2008)
• Members of the research group I led in the past have had important leadership roles in the collaborations: Co-convener of the Physics Modelling group (J. McFayden), Co-convener of the Analysis Model Software Group (K. Suruliz), Co-coordinators of the Top+X subgroup (K. Suruliz), UK co-convener of the Top Physics Group (T. Stevenson).

Future Colliders 

Starting in 2017, I have initiated a research stream on feasibility studies, software development and detector R&D for future colliders at the University of Sussex. The main activities in this area have focused on the development of a Dual Readout calorimeter prototype for the IDEA detector, which is an innovative detector concept described in the Conceptual Design Reports of both the Chinese and European electron-positron Higgs factories, CePC and FCC-ee. A dual readout calorimeter exploits two independent samplings of the hadronic showers in order to correct on an event-by-event basis for fluctuations in the electromagnetic shower fraction. My main contributions are:

• Calorimeter software infrastructure development - both hands-on and coordination of activities.

• Test beams (2017 and 2018) using the H8 beam line.

• Test of optical fibres for the 2021 prototype, tested at DESY and at CERN.