“Once more unto the breach…” Unlike the auspicious scene from Shakespeare’s Henry V, current particle physics is not a battle but a stalemate. However, particle physicists are reanalysing past data, venturing once more beyond the breach to probe the universe in this intellectual quest. The current model of particle physics is the Standard Model (SM), which has expanded our view of the universe by identifying elementary particles, such as quarks and leptons, as the fundamental constituents of matter. Despite these significant advances, a chasm remains as we stand on the precipice of discovering new physics.
Over the last 50 years, particle physicists have known what to look for, yet today there is no single guiding theory to motivate discoveries. Although the SM has been highly successful in providing experimental predictions, it has failed to fully incorporate a theory of gravity and to explain phenomena such as the accelerating expansion of the universe. This situation makes probing the SM analogous to searching a haystack without knowing whether there is even a needle to find.
This has led to a paradigm shift from a theory-driven approach to a bottom-up, data-driven search. Particle physicists now survey and reinterpret existing measurements from particle colliders to test the viability of new models. This effort utilises the CONTUR framework—‘Constraints On New Theories Using Rivet’—which exploits results collected in specific energy ranges with a high degree of model independence. CONTUR compares these measurements to physics beyond the SM. While this approach is highly generic and unlikely to match the discovery potential of direct searches, its breadth of potential models and ability to eliminate inconsistent proposals make it a valuable complementary method.
Measurements have already shown accordance with the SM, allowing CONTUR to set limits on new theories, illuminating the path to new physics beyond the SM and refining the number of viable models. An example of the potency of this method is the recent paper “New Sensitivity of Current LHC Measurements to Vector-Like Quarks,” in which CONTUR reinterpretation software was applied to a class of new physics models involving vector-like quarks (VLQs).
Vector-like quarks are hypothetical quark partners that appear in several extensions of the Standard Model; however, they have eluded experimental constraints because they do not acquire mass through regular mechanisms. VLQs are typically assumed to interact only with the “top” and “bottom” SM quarks. The paper analysed the sensitivity of available measurements to other VLQ interactions using the CONTUR framework.
By using CONTUR, a whole class of VLQ models could be comprehensively probed, and greater constraints could be placed on these models. Notably, the coverage of a broad variety of measurements means that potentially overlooked results are considered. Following the paper’s review, more realistic couplings involving smaller groups of VLQs were noted and quickly analysed, demonstrating the speed and complementarity of CONTUR compared to direct searches. Looking ahead, CONTUR aims to directly incorporate SM predictions and uncertainties, avoiding reliance on second-hand analysis. The method’s scalability and adaptability to novel measurements and models ensure it will be a potent tool in future research.
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