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LHC CMS Experiment Tests for Quark Substructure

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LHC CMS Experiment Tests for Quark Substructure

Generated: 2026-04-30 · API: Gemini 2.5 Flash · Modes: Summary

LHC CMS Experiment Tests for Quark Substructure

Clip title: Is There Something Smaller Than Quarks? Experimental Test Author / channel: Anton Petrov URL: https://www.youtube.com/watch?v=THuOlazRwx4

Summary

This video addresses a fundamental question in particle physics: whether quarks, currently considered elementary particles by the Standard Model, possess any internal structure. The speaker highlights that for a long time, based on our best understanding of the universe and the Standard Model, quarks have been believed to be point-like, with no smaller constituents. However, a recent experiment conducted at the Large Hadron Collider (LHC) by the CMS collaboration aimed to test this hypothesis by probing the smallest scales of matter yet.

To provide context, the video traces the history of our understanding of matter, from ancient Greek philosophical concepts of indivisible “atoms” to modern discoveries. It recounts how, over centuries, matter was progressively broken down: molecules (proven by Einstein), then atoms (discovered by Rutherford to have nuclei), followed by protons and neutrons within the nucleus, and finally, quarks within protons and neutrons (discovered in 1968). By the 1970s, the Standard Model codified these 17 fundamental particles, with the Higgs boson being the last confirmed in 2012. Intriguingly, the video introduces the “preon” hypothesis, proposed in 1974, which suggests that quarks themselves might be composed of even smaller particles, potentially simplifying the complex “particle zoo” and offering a more elegant explanation for their properties.

The CMS experiment at the LHC sought to discover these hypothetical preons by colliding protons at extremely high energies. Researchers meticulously measured the “dijet angular distribution” – the scattering angles of particle jets produced from these collisions. Deviations from predicted angles would indicate that quarks have an internal structure. The experiment probed quarks down to an unprecedented scale of approximately 10^-20 meters, about 10,000 times smaller than a typical proton, using data collected between 2016 and 2018.

The crucial finding of the experiment was that there was absolutely no evidence of internal structure within quarks at the scales probed. All observed scattering angles perfectly matched the predictions of the Standard Model, reinforcing the idea that quarks behave as point-like particles. This result currently sets the most stringent limit on “quark compositeness.” While the experiment also searched for other phenomena beyond the Standard Model—such as extra spatial dimensions, quantum black holes, or signs of dark matter—no significant new discoveries were made. The conclusion is that as of mid-2026 (the video creator’s stated reference point), the Standard Model of physics appears to be largely correct, though still recognized as incomplete as it cannot explain gravity, dark matter, or dark energy. The speaker suggests that if preons do exist, they might be much, much smaller than what was detectable in this experiment, possibly requiring even higher energy collisions (e.g., 37 teraelectron volts) at future LHC runs to potentially reveal this next layer of reality.

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