The seventh edition of the Large Hadron Collider Physics (LHCP) conference took place in Puebla, Mexico, from 20 to 25 May, hosted by the Benemérita Universidad Autónoma de Puebla (BUAP). With almost 400 participants, the week involved dynamic discussions between experimentalists and theorists on an assortment of topics related to LHC research. These ranged from heavy-ion physics to precision measurements of the Standard Model (SM), including Higgs-sector constraints and searches for hints of physics beyond the SM such as supersymmetry and model-independent high-mass resonance searches.
Results from the wealth of LHC data collected at 13 TeV during Run 2 (from 2015–2018) are beginning to be published. The ATLAS and CMS collaborations presented new results in the search for supersymmetry, setting new limits on supersymmetric parameters. The latest CMS search for top squarks in events with two tau leptons in the final state excludes top-squark masses above 1 TeV for nearly massless neutralinos. The first ATLAS Run 2 measurement for the production of tau sleptons was also presented, excluding masses between 120 and 390 GeV for a massless neutralino. Both of these challenging analyses contain a high amount of missing momentum, originating from the lightest supersymmetric particle and the neutrinos from the tau decays.
Studies involving unusual signatures were popular at the Mexico conference. Disappearing tracks, emerging jets, displaced vertices and out-of-time decays, which would each be indications of new processes or particles being present in the event, were all discussed. These signatures also provide a challenge for detector and algorithm designs, especially at the high-luminosity LHC (HL-LHC).
The recent observation of CP violation in charm quarks (CERN Courier May/June p7) published by the LHCb Collaboration in March was presented. “Long awaited, finally observed!” was the statement from LHCb-spokesperson Giovanni Passaleva. This result, which shows the different decay rates of charm quarks and charm anti-quarks, opens up new avenues of investigation for testing the SM.
The final two days of the conference featured open discussions on recent progress in the upgrades of the LHC and the detectors for the HL-LHC, and on various proposals and design challenges for future colliders. The HL-LHC will be a very challenging environment in which to distinguish particles of interest, as the average number of proton–proton collisions will increase from around 50 to about 200 each time the bunches in the LHC beams cross. For future colliders, circular and linear, delegates agreed that the community must better communicate the motivations and goals for such future machines with governments and the public.
The next edition of the conference will take place in Paris in 2020. Though also taking place during the current long shutdown, many new results with the full LHC Run-2 statistics will be presented, as well as progress on preparing the detectors and the accelerator for Run 3.