Stringent limits on - and Lorentz-invariance violation from ~meson decays
Using 13 TeV proton-proton collision data from the LHCb detector, this study establishes the most precise constraints to date on CPT and Lorentz invariance violation in the meson system, measuring the CPT-violating parameter and setting limits on Lorentz-violating parameters at the level within the Standard Model Extension framework.
Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
At the heart of modern physics lies a set of rules so fundamental that they define how the universe behaves. Two of these rules are CPT symmetry and Lorentz invariance. CPT symmetry is the idea that if you were to reverse time, swap every particle with its opposite (antimatter), and flip the universe like a mirror image, the laws of physics would remain exactly the same. Lorentz invariance is the principle that these laws do not change depending on how fast you are moving or which direction you are facing. For decades, these principles have held up under every test, forming the bedrock of our understanding of reality. However, some theories about the deepest layers of the universe, such as those attempting to explain gravity, suggest that these rules might break down at incredibly high energy levels. If they do, the effects would be tiny, hidden deep within the behavior of subatomic particles, waiting to be uncovered by instruments of extreme precision.
A team of scientists working with the LHCb detector at CERN has taken a fresh, highly sensitive look at this question using particles called B0s mesons. These are short-lived particles containing a bottom quark that are created when protons smash together at nearly the speed of light. The researchers focused on how these particles decay, or fall apart, into other particles over time. Specifically, they watched for a subtle interference pattern that would appear if the rules of CPT symmetry or Lorentz invariance were slightly broken. In a world where these symmetries hold perfectly, the decay of a particle and its antimatter twin should follow a perfectly predictable rhythm. If the symmetries were violated, that rhythm would wobble in a specific way, changing depending on the time of day as the Earth rotates and the particles' orientation shifts relative to the stars.
To find these wobbles, the team analyzed a massive collection of data gathered between 2015 and 2018. They sifted through billions of collisions to isolate nearly 380,000 instances where a B0s meson decayed into a specific set of daughter particles: a Ds meson and a pion. This specific decay path is particularly useful because it is very clean and predictable, making it easier to spot any tiny deviations from the expected behavior. The scientists then built a detailed mathematical model of how these particles should behave if the universe follows the standard rules, and they compared this model against the actual data. They looked for signs that the decay rate changed as the Earth turned, which would indicate that the laws of physics were different depending on the direction the particles were moving through space.
The result of this exhaustive search was a confirmation that the universe, at least at the energy scales tested, obeys these fundamental rules. The researchers found no evidence of the wobbles that would signal a violation of CPT symmetry or Lorentz invariance, though a comparison of the oscillatory and constant hypotheses yielded a significance of 1.8 standard deviations, which is compatible with a statistical fluctuation. They measured the parameters that would describe such a violation and found them to be consistent with zero, within a very small margin of error. In fact, their measurements are the most precise ever made for this type of particle, pushing the sensitivity to a level where they can rule out any violation down to a scale of roughly one part in ten to the power of fourteen. This means that if these symmetries are broken, the effect is so incredibly small that it is currently invisible to even the most powerful detectors on Earth.
This work does not just confirm what we already suspect; it tightens the constraints on any new theories that propose the universe is more chaotic at its deepest levels. By proving that the B0s meson behaves exactly as predicted, regardless of the time of day or the direction of its travel, the study reinforces the idea that the laws of physics are indeed universal and unchanging. The researchers have effectively closed the door on a wide range of possibilities for how these symmetries might break, leaving physicists with a clearer, albeit more challenging, path forward in their quest to understand the fundamental nature of reality. The universe, it seems, remains stubbornly consistent.
Drowning in papers in your field?
Get daily digests of the most novel papers matching your research keywords — with technical summaries, in your language.