The Large Hadron Collider, a monumental feat of human engineering and scientific endeavor, has once again pushed the boundaries of our understanding of the cosmos. In a groundbreaking new analysis, the ATLAS Collaboration, one of the primary experiments at the LHC, has unveiled the results of an intensive search for supersymmetric particles, specifically squarks and gluinos, within the titanic collisions of protons. This ambitious investigation delved into the intricate tapestry of high-energy physics, scrutinizing events characterized by the presence of tau leptons, jets, and a peculiar signature of missing transverse momentum. These tell-tale signs are the breadcrumbs left behind by particles that interact only weakly with ordinary matter, hinting at phenomena that lie beyond the Standard Model of particle physics, our current best description of fundamental forces and particles. The data, collected at proton-proton collision energies of 13 and 13.6 TeV, represents a significant leap in the precision and scope of such searches, drawing upon vast datasets generated by the powerful LHC accelerator.
The quest for supersymmetry (SUSY) has been a driving force in theoretical physics for decades. Supersymmetry proposes a symmetry between the two fundamental classes of particles: fermions, which make up matter, and bosons, which mediate forces. In this theoretical framework, every known particle has a hypothetical “superpartner” with a different spin. For instance, quarks, which are fermions, would have squarks as their bosonic superpartners, and gluons, the force carriers of the strong interaction, would have gluino superpartners. The search for these particles is paramount because if supersymmetry is indeed a true symmetry of nature, then these superpartners should exist and, crucially, might be produced in the high-energy collisions at the LHC. Their discovery would revolutionize our understanding of the universe, potentially shedding light on fundamental mysteries like the nature of dark matter and the unification of fundamental forces.
The ATLAS detector, a sophisticated marvel of cutting-edge technology, plays a pivotal role in these investigations. Imagine a colossal, multi-layered camera designed to capture the fleeting aftermath of subatomic particle collisions. Its intricate design allows scientists to measure the energy, momentum, and trajectory of countless particles produced in these energetic events. The analysis focused on events exhibiting missing transverse momentum, a crucial indicator that invisible particles, such as neutrinos or potential dark matter candidates, have escaped detection. The tau lepton, one of the three known charged leptons (along with the electron and muon), is particularly interesting because it is massive and decays relatively quickly, often producing complex signatures that can be used to precisely reconstruct the event kinematics and distinguish New Physics signals from Standard Model backgrounds.
The meticulous processing of the immense amount of data collected by ATLAS is a testament to the collaborative efforts of hundreds of physicists and engineers worldwide. Each proton-proton collision is a unique event, and the ATLAS detector meticulously records the particles it produces. The challenge lies in sifting through this deluge of information to identify those rare events that might signal the existence of new, undiscovered particles. The analysis for squarks and gluinos involved sophisticated algorithms and statistical techniques to isolate potential signals from the overwhelming background of known particle interactions. The sheer volume of data analyzed, spanning billions of individual collisions, underscore the scale of this scientific endeavor.
The inclusion of tau leptons in this search is strategically significant. While electrons and muons are more commonly used in searches for new physics due to their cleaner signatures, tau leptons offer a complementary perspective. Their heavier mass and more complex decay modes can sometimes provide unique handles for disentangling subtle signals from overwhelming backgrounds. By specifically targeting events with tau leptons, the ATLAS Collaboration aimed to enhance their sensitivity to specific supersymmetric scenarios that might otherwise be missed. This diversification of search strategies is essential in the ongoing hunt for physics beyond the Standard Model, ensuring that no avenue is left unexplored in our pursuit of a more complete picture of fundamental reality.
The energy regimes probed by the LHC, particularly at 13 and 13.6 TeV, are crucial for potentially producing these elusive supersymmetric particles. The higher the collision energy, the more massive the particles that can be created, according to Einstein’s famous equation E=mc². Squarks and gluinos are predicted by many SUSY models to be relatively massive, so reaching these extreme energies is a prerequisite for their direct observation. The ATLAS experiment’s ability to operate and collect data reliably at these unprecedented energy levels is a triumph of technological innovation and engineering prowess, enabling physicists to explore hitherto uncharted territories of the subatomic world and push the frontiers of particle physics.
The analysis presented by the ATLAS Collaboration places stringent limits on the possible masses of squarks and gluinos. By not observing a statistically significant excess of events in their targeted signatures, the researchers have effectively ruled out the existence of these hypothetical particles within certain mass ranges. This is a crucial aspect of scientific progress: even null results provide valuable information by constraining theoretical models. These new limits are more stringent than previous searches, pushing the boundaries of what we know about the mass scales at which supersymmetry might manifest itself and guiding future theoretical and experimental investigations.
Understanding the background processes in these high-energy collisions is a critical and often challenging aspect of new physics searches. The Standard Model, while incredibly successful, predicts a vast number of background events that can mimic the signatures of new physics. The ATLAS analysis employed sophisticated simulations of these background processes, validated against control regions in the data, to accurately estimate their expected contribution. This meticulous subtraction of known physics is essential to ensure that any observed excess of events can be attributed to new phenomena rather than statistical fluctuations or misaccounting of known interactions within the complex interplay of fundamental forces.
The strategic selection of event topologies incorporating tau leptons, jets, and missing transverse momentum is designed to maximize sensitivity to specific types of supersymmetric particle production. For instance, the production of gluinos, which are strongly interacting, is expected to be copious at these energies. Gluinos could then decay into quarks and squarks, or into other supersymmetric particles. Similarly, squarks, as superpartners of quarks, would be produced in pairs or in association with other particles. The detailed reconstruction of jets, which are sprays of particles originating from quarks or gluons, alongside the identification of tau leptons and the measurement of missing transverse momentum, allows for a robust reconstruction of the kinematics of these potential decay chains.
The implications of these new constraints on supersymmetric models are profound. Many theories that posit the existence of supersymmetry predict specific mass ranges for these superpartners. By excluding certain mass ranges, the ATLAS results help to refine these theoretical predictions, guiding theorists to develop more specific and testable models. If supersymmetry is to be discovered, its superpartners must lie within the mass ranges that have not yet been excluded by experiments like ATLAS. This iterative process of experimental search and theoretical refinement is the cornerstone of scientific progress in particle physics.
The search for squarks and gluinos has long been a high-priority goal at the LHC, and the results from ATLAS represent a significant milestone in this ongoing endeavor. While direct evidence for these particles remains elusive, the increased sensitivity of the detector and the sophisticated analysis techniques employed have allowed scientists to probe deeper into the energy scales where these particles might exist. The relentless pursuit of fundamental physics at the LHC continues, driven by the hope of unraveling the deeper mysteries of the universe and potentially discovering the new particles that could lead us to a more comprehensive understanding of nature.
The missing transverse momentum signature is a beacon in the dark, pointing towards the presence of particles that leave no trace in the detector. In the context of supersymmetry, this missing momentum could be carried away by the lightest supersymmetric particle (LSP), which in many models is stable, electrically neutral, and weakly interacting, making it an excellent dark matter candidate. The search for squarks and gluinos, by looking for their decay products and the resulting missing energy, is indirectly probing the properties of these potential dark matter constituents of our universe, linking the high-energy frontiers of particle physics to the cosmological mysteries that surround us.
The publication of these results in the European Physical Journal C (EPJC) signifies the rigorous peer-review process and the scientific community’s validation of the ATLAS Collaboration’s meticulous work. The detailed methodology, statistical analysis, and interpretation of the data are all scrutinized by experts in the field, ensuring the robustness and reliability of the findings. This publication not only contributes to the body of scientific knowledge but also serves as a benchmark for future searches and theoretical developments in the complex and fascinating realm of particle physics and the ongoing quest for physics beyond our current understanding of fundamental reality.
The ATLAS experiment continues to operate and collect data at the LHC, with ongoing upgrades and improvements to its detectors and analysis capabilities. This ensures that the search for new physics, including squarks and gluinos, will continue with even greater sensitivity in the future. As the LHC pushes to higher luminosities and potentially higher energies, the chances of discovering these elusive particles, or further constraining their existence, increase. The scientific journey at the cutting edge of physics is one of persistent exploration, and the ATLAS Collaboration remains at the forefront of this thrilling quest for knowledge, pushing the boundaries of what we know and opening new vistas in our cosmic comprehension.
The exploration of new physics at the LHC is not merely an academic exercise; it holds the potential to revolutionize our understanding of the universe at its most fundamental level. The discovery of squarks and gluinos, or any other new particles predicted by theories beyond the Standard Model, would have profound implications for cosmology, astrophysics, and our quest to comprehend the very fabric of reality. The current results, while not revealing these specific particles, are an indispensable step in this grand scientific endeavor, systematically narrowing down the possibilities and guiding the ongoing search for the ultimate laws that govern our universe, a testament to humanity’s insatiable curiosity and relentless pursuit of truth.
Subject of Research: Search for physics beyond the Standard Model, specifically for supersymmetric particles (squarks and gluinos), in high-energy proton-proton collisions.
Article Title: Search for squarks and gluinos in pp collisions at $\sqrt{s} = 13$ TeV and 13.6 TeV in events with $\tau$-leptons, jets and missing transverse momentum using the ATLAS detector.
Article References: ATLAS Collaboration. Search for squarks and gluinos in pp collisions at $\sqrt{s} = 13$ TeV and 13.6 TeV in events with $\tau$-leptons, jets and missing transverse momentum using the ATLAS detector. Eur. Phys. J. C 85, 1437 (2025). https://doi.org/10.1140/epjc/s10052-025-14957-6
Image Credits: Provided by Springer Nature
DOI: https://doi.org/10.1140/epjc/s10052-025-14957-6
Keywords: Supersymmetry, squarks, gluinos, ATLAS detector, Large Hadron Collider, missing transverse momentum, tau leptons, jets, Standard Model, particle physics, high-energy physics.
