Inside the Large Hadron Collider, protons are accelerated to nearly the speed of light and smashed head-on. At the collision point, a burst of energy is born for an instant, from which new particles can emerge. One of the heaviest is the top quark. It is 180 times heavier than a proton and lives for less time than it takes light to cross an atomic nucleus.
Physicists from the ATLAS experiment analyzed 140 inverse femtobarns of data: that's like having collisions run continuously for several years. They selected events where an electron, a muon, and jets of particles from b-quarks remained after the collision. This combination is the calling card of a top-quark pair decay.
The rate of top-quark pair production depends on the top quark's mass. The heavier the quark, the rarer it appears. By measuring the rate, scientists calculated the top quark's mass. The result matched previous measurements but with smaller uncertainty.
The precise mass of the top quark is not just a number for a reference book. It determines whether the vacuum of our universe is stable. If the top quark were slightly lighter, empty space could suddenly rearrange itself, and the world would vanish in a bubble of a new phase. Fortunately, measurements show we are safe.
The same data set also allowed measuring how often a top quark and a W boson are produced together. These processes are rare but important: they are sensitive to details of quark interactions and could point to new particles not yet discovered.
as written by the authors arXiv:2602.06664
Measurements of the inclusive and differential top-quark pair ($$t\bar{t}$$) cross-sections in proton--proton collisions at $$\sqrt{s} = 13$$ TeV, using 140 fb$$^{-1}$$ of data collected by the ATLAS experiment at the Large Hadron Collider, are presented. Events with an opposite-charge $$e\mu$$ pair and $$b$$-tagged jets are selected, and the inclusive cross-section measurement is used to determine the top-quark pole mass via the dependence of the predicted cross-section on $$m_t^\mathrm{pole}$$. Complementary measurements of $$e\mu b\bar{b}$$ production, treating both $$t\bar{t}$$ and $$tW$$ events as signal, are also provided.
The top quark is the only quark that decays before it can bind with another quark. So it can only be observed through its decay products.
In the TV show 'The Big Bang Theory', the characters discuss top quarks when arguing about particle physics.