Researchers affiliated with the CMS Collaboration at CERN’s Large Hadron Collider have conducted an investigation into whether top quarks comport themselves in accordance with Albert Einstein’s principle of special relativity.
Installation of the CMS beam pipe. Image credit: CERN / CMS Collaboration.
Albert Einstein’s renowned theory of special relativity, alongside the framework of quantum mechanics, forms the foundational bedrock of the Standard Model of particle physics.
Central to this theory is the tenet of Lorentz symmetry, which posits that experimental outcomes remain invariant, irrespective of the velocity or spatial orientation with which the experiment is performed.
The tenets of special relativity have demonstrably withstood rigorous scientific scrutiny. Nevertheless, certain theoretical constructs, encompassing specific formulations of string theory, postulate that at exceedingly high energy levels, the principles of special relativity may no longer hold true, leading to experimental observations that are contingent upon an experiment’s orientation within the fabric of spacetime.
Evidence of such potential deviations, or anisotropies, from Lorentz symmetry might manifest at energies considerably lower than those of the Large Hadron Collider (LHC). However, despite prior investigative efforts, no definitive indications have been detected at the LHC or other particle accelerators.
In a recent scientific inquiry, physicists examining data from the CMS experiment scrutinized the LHC for evidence of Lorentz symmetry violation, focusing their analysis on pairs of top quarks—the most massive elementary particles currently cataloged.
“In such a scenario, an anisotropy would imply that the rate at which top-quark pairs are generated in proton-proton collisions at the LHC would exhibit temporal fluctuations,” the researchers explained.
“To elaborate, given the Earth’s rotation on its axis, the directional alignment of the LHC’s proton beams, as well as the average trajectory of top quarks produced in collisions at the core of the CMS detector, dynamically shifts in accordance with the diurnal cycle.”
“Consequently, if a preferred direction exists within the spacetime continuum, the production rate of top-quark pairs would be susceptible to variations corresponding to the time of day.”
“Therefore, the identification of a deviation from a constant production rate would serve as an indicator of a fundamental anisotropy in spacetime.”
The findings from this latest investigation, derived from data collected during the LHC’s second operational phase, are consistent with a stable production rate, thereby reinforcing the validity of Lorentz symmetry and confirming the enduring applicability of Einstein’s special theory of relativity.
Leveraging this outcome, the research team has established stringent upper bounds on the magnitude of parameters that are theoretically predicted to possess zero values when symmetry is perfectly maintained.
The derived limits represent a significant enhancement, improving upon the sensitivity of previous searches for Lorentz symmetry breaking conducted at the historical Tevatron accelerator by a factor of up to one hundred.
“These results lay the groundwork for forthcoming investigations into Lorentz symmetry violation, utilizing top-quark data from the LHC’s third operational run,” stated the scientific team.
“Furthermore, they create opportunities for the detailed examination of processes involving other fundamental heavy particles, such as the Higgs boson and the W and Z bosons, whose study is exclusively feasible at the LHC.
This research was formally presented in the October 2024 publication of the esteemed journal Physics Letters B.
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CMS Collaboration. 2024. Searches for violation of Lorentz invariance in top quark pair production using dilepton events in 13 TeV proton-proton collisions. Physics Letters B 857: 138979; doi: 10.1016/j.physletb.2024.138979
