Particle Physics at the LHC era
Since the start of its operations, the CERN Large Hadron Collider (LHC) has been central to high-energy physics research, delivering groundbreaking data. The highlight of the past decade was the 2012 discovery of the Higgs boson, which completed the Standard Model, the theory that describes matter and the forces acting upon it, and earned François Englert and Peter Higgs the 2013 Nobel Prize. LHC experiments continue to deepen our understanding of matter and forces, offering precise measurements of the Higgs boson and other Standard Model processes, closely aligned with theoretical predictions.
The quest for new physics
Despite its great success in describing the particle interactions and properties, the Standard Model leaves many open questions. It does not explain the mass hierarchy of the particles it predicts and why gravity is so weaker compared to the other forces. It also does not provide a candidate for the dark matter required by astrophysical and cosmological observations.
Physics beyond the Standard Model are therefore crucially required for our understanding of nature to advance. Many theories and models are suggested by the theoretical community in attempts to tackle the Standard Model open questions, and many of these can be probed with the LHC data. The discovery of new phenomena is one of the reasons the LHC was built, and many searches for these have been performed at the experiments. Regardless of the variety and ingenious methodology of these searches, no indication of new physics has been hinted yet. Instead, there has been a broad exclusion of theories, and the survivors had to evolve.
One of the best motivated extensions of the Standard Model, accessible at the LHC, is SUperSYmmetry (SUSY); it makes the hierarchy of mass scales more natural, provides an origin for the dark matter (with the Lightest Supersymmetric Particle, LSP, being a dark matter candidate) and facilitates the unification of the forces.
Despite all these motivations, direct SUSY searches at the LHC have so far not been conclusive, but have imposed tight constraints in the predicted SUSY particle masses, e.g. the SUSY partner of the gluon, gluino, is excluded up to about 2 TeV in models with a light LSP.
Although SUSY, as well as other theories beyond the Standard Model, remain elusive so far, the open questions of the Standard Model are so pressing that it is certain there is something beyond. With the increasing amount of available LHC data, we are on the right track to find what that is.
We are faced with a unique chance to make a unique discovery at the LHC, and history has taught us it may be unexpected. At the LHC experiments, we are looking forward to it.
New Frontiers in Exploration
In addition to the traditional experiments at the LHC, new experiments are emerging to explore previously inaccessible domains of particle physics. One such experiment is FASER (Forward Search Experiment), which aims to detect light, weakly interacting particles that could hold the key to understanding dark matter and other mysteries of the universe. FASER, positioned 480 meters downstream of the ATLAS interaction point, is uniquely designed to search for particles produced at very small angles to the beamline, which are often missed by the larger LHC detectors. By exploring this new frontier, FASER is offering fresh insights into the nature of matter, potentially unlocking further understanding of dark matter, neutrinos, and other elusive phenomena.
With the ongoing efforts of both existing and new experiments, the LHC is providing us with unprecedented opportunities to push the boundaries of our knowledge and uncover the fundamental nature of the universe. We look forward with anticipation, knowing that the next major discovery could be just around the corner.