The quest for the fundamental building blocks of the universe has long been a driving force behind humanity’s scientific endeavors. From the ancient Greeks pondering the nature of atoms to the modern physicists smashing particles at colossal energies, our understanding of reality has constantly evolved, pushing the boundaries of what we perceive as possible. Today, at the forefront of this endeavor stands the Large Hadron Collider (LHC), a marvel of engineering and human ingenuity, and its upcoming upgrade, the High-Luminosity LHC (HL-LHC). This colossal machine, a ring of superconducting magnets buried deep beneath the Franco-Swiss border, is designed to achieve unprecedented collision rates, thus opening new frontiers in our exploration of the cosmos and its underlying physics. The latest research published in the European Physical Journal C by Qureshi, Gurrola, and Flórez offers a tantalizing glimpse into the potential discoveries awaiting us at the HL-LHC, particularly in the realm of supersymmetry, a theoretical framework that proposes a symmetry between fundamental particles that mediate forces and the matter particles that make up everything we see.
The Standard Model of particle physics, our current most successful theory describing the elementary particles and their interactions, has achieved remarkable triumphs, accurately predicting phenomena from the Higgs boson’s discovery to the precise masses of various quarks and leptons. However, it is not without its limitations and unresolved mysteries. The hierarchy problem, the vast difference between the electroweak scale and the Planck scale, and the nature of dark matter, which constitutes a significant portion of the universe’s mass but remains invisible to our current detectors, are just a few of the profound questions that the Standard Model alone cannot answer. Supersymmetry offers an elegant potential solution to these puzzles by postulating that every known particle has a “superpartner” with a different spin. For instance, the photon, the force carrier of electromagnetism, would have a superpartner called the photino, a fermion. This theoretical symmetry, if it exists, could help to stabilize the electroweak scale and provide a natural candidate for dark matter in the form of the lightest supersymmetric particle.
Despite its theoretical elegance, direct experimental evidence for supersymmetry has remained elusive. Searches at the LHC have so far yielded null results, placing stringent limits on the masses of supersymmetric particles, often referred to as sparticles. This has led to a scenario where many proposed supersymmetric models are being pushed to higher mass ranges, making their direct detection increasingly challenging. However, the HL-LHC, with its formidable increase in luminosity – essentially the number of collisions per unit area per unit time – promises to provide a vastly expanded dataset, allowing physicists to probe much higher energy scales and explore fainter signals that were previously inaccessible. This surge in collision events is akin to having a much larger telescope capable of seeing fainter and more distant stars, thus revealing previously hidden cosmic structures.
The research by Qureshi, Gurrola, and Flórez specifically focuses on investigating a challenging but potentially illuminating corner of the supersymmetric parameter space: the “compressed mass spectrum” scenario. In this scenario, the mass differences between the supersymmetric partners of the particles involved in their decay chains are relatively small. This presents a significant experimental hurdle because the decay products, such as leptons or jets, originating from these cascades will have very low transverse momentum, making them difficult to distinguish from the overwhelming background noise of ordinary Standard Model particle production. The subtle energy signatures associated with these decays can easily be lost in the statistical fluctuations of the detector and the high rate of background events.
To address this challenge, the researchers propose a sophisticated analysis strategy leveraging the “vector boson fusion” (VBF) topology. VBF is a distinct mechanism by which certain particles, particularly Higgs bosons and sometimes other massive particles like W and Z bosons, can be produced at the LHC. In VBF events, the colliding protons emit and then scatter two electroweak bosons (W or Z bosons), which then fuse to produce the particle of interest. This production mechanism is characterized by the presence of two forward-tagged jets, originating from the scattered quarks within the protons, with a significant separation in pseudorapidity. These distinct signatures provide a powerful handle for isolating VBF events from the prolific background processes that dominate typical LHC data.
The VBF topology is particularly advantageous for hunting supersymmetric particles in compressed mass spectrum scenarios. The reason for this lies in the distinct kinematics associated with VBF production. The forward-tagged jets in VBF events act as excellent triggers and filters, allowing physicists to select events with a higher probability of containing the desired supersymmetric signature. Furthermore, the specific arrangement of these jets, along with the momentum imparted to the produced particle, can help to suppress background processes that do not typically exhibit such distinct “forward-backward” jet structures. This allows for a cleaner selection of events where supersymmetric particles might be decaying.
The paper details a comprehensive simulation study aimed at quantifying the sensitivity of the HL-LHC to supersymmetric scenarios with compressed mass spectra using the VBF topology. They explore different signature topologies that arise from the decay of supersymmetric particles produced via VBF, focusing on final states that include leptons and missing transverse energy. Missing transverse energy is a key indicator of weakly interacting massive particles (WIMPs), a leading dark matter candidate, which escape detection in the calorimeters. The presence of leptons, such as electrons and muons, provides further handles for identifying and characterizing these events.
A significant portion of the research is dedicated to understanding and mitigating the overwhelming Standard Model background. The authors employ advanced background estimation techniques, including sophisticated data-driven methods, to accurately predict the expected number of background events in various signal regions. This is crucial for making reliable inferences about the presence or absence of new physics. The high granularity and sophisticated trigger systems of the HL-LHC detectors, coupled with the increased collision data, will be instrumental in distinguishing the potentially subtle signals of compressed supersymmetry from the fierce competition of everyday particle interactions.
One of the key challenges in compressed mass spectra is that the decay products often have very soft momentum. This means that even if a decay occurs, the resulting particles’ energy and momentum might be too low to be reliably detected by the experiments. The VBF topology, however, can sometimes provide a boost to these particles, leading to slightly more energetic final states, which improves their chances of being observed. The careful reconstruction of these low-momentum particles, and the precise measurement of missing transverse energy are paramount for success in this regime. The proposed analysis strategy leverages the unique kinematic properties of VBF to enhance the observability of these otherwise elusive signatures.
The study investigates various benchmark supersymmetric models and extrapolates the HL-LHC’s potential to discover or set new exclusion limits on these models. The increased integrated luminosity, which represents the total number of collisions recorded, will unlock the ability to explore much larger regions of the supersymmetric parameter space. Even if no definitive discovery is made, the stringent limits that can be placed will significantly constrain theoretical models, guiding future theoretical developments and experimental searches. This iterative process of searching, constraining, and refining is the hallmark of scientific progress in particle physics.
The researchers emphasize the importance of precise theoretical predictions for these simulations. The accuracy of the background and signal models directly impacts the sensitivity of the analysis. Any uncertainties in these predictions can translate into larger uncertainties in the exclusion power of the experiment. Therefore, ongoing efforts in theoretical physics to improve the accuracy of calculations for Standard Model processes and supersymmetric particle production are vital for maximizing the scientific return of the HL-LHC. The interplay between theoretical advancements and experimental capabilities is what drives the field forward.
The advent of the HL-LHC heralds a new era of precision physics. With its increased data sample, the experiments will be able to perform measurements with unprecedented accuracy, allowing for more sensitive probes of existing theories and sharper discrimination between different theoretical scenarios. For supersymmetry, this means not only searching for direct evidence of sparticles but also potentially probing subtle deviations from the Standard Model that could hint at the presence of new physics at higher energy scales. The compressed mass spectrum scenario, while challenging, represents a critical frontier in this extended exploration.
The implications of discovering supersymmetry, particularly with a compressed mass spectrum, would be profound. It would not only validate a deeply elegant theoretical framework but also provide a compelling explanation for the dark matter puzzle. The lightest supersymmetric particle, often a neutralino, is a prime candidate for the weakly interacting massive particles (WIMPs) that are thought to permeate the universe. The precise mass and properties of such a particle, if discovered, could be directly related to cosmological observations of dark matter abundance, offering a remarkable convergence of particle physics and astrophysics.
In conclusion, the research by Qureshi, Gurrola, and Flórez offers a beacon of hope for those searching for evidence of supersymmetry at the HL-LHC. By focusing on the challenging compressed mass spectrum scenario and employing the powerful vector boson fusion topology, they provide a roadmap for future analyses that could potentially unlock one of the universe’s deepest secrets. The HL-LHC, with its immense data-gathering capabilities, coupled with innovative analytical techniques like those proposed in this paper, is poised to revolutionize our understanding of fundamental physics and potentially reveal the existence of particles that have, until now, remained hidden in the shadows of the cosmos. This pursuit of the unknown, driven by curiosity and relentless scientific inquiry, continues to push the boundaries of human knowledge, promising a future filled with astonishing revelations about the very fabric of reality itself. The scientific community eagerly awaits the first data from the HL-LHC, a pivotal moment that could reshape our cosmic worldview.
Subject of Research: Probing compressed mass spectrum supersymmetry at the high-luminosity LHC with the vector boson fusion topology.
Article Title: Probing compressed mass spectrum supersymmetry at the high-luminosity LHC with the vector boson fusion topology.
Article References:
Qureshi, U.S., Gurrola, A. & Flórez, A. Probing compressed mass spectrum supersymmetry at the high-luminosity LHC with the vector boson fusion topology.
Eur. Phys. J. C 85, 1208 (2025). https://doi.org/10.1140/epjc/s10052-025-14935-y
Image Credits: AI Generated
DOI: https://doi.org/10.1140/epjc/s10052-025-14935-y
Keywords: Supersymmetry, High-Luminosity LHC, Vector Boson Fusion, Compressed Mass Spectrum, Particle Physics
