This is yet another consequence of the quantum world of subatomic particles.

You might ask 'Much larger mass.? How can the same particle have multiple mass ranges?'. The second process is the production of an off-shell Higgs boson, with a mass considerably larger than its nominal value, albeit with a lower rate. The on-shell production rate has been measured experimentally to about 10% precision by now. In the first process, the Higgs boson is produced with a mass close to its nominal value (on-the mass-shell, or on-shell in short).

The strategy relies on measuring the ratio of the rates of occurrence of two different processes by which the Higgs boson is produced at the LHC. Scientists were at a loss to measure the width of the Higgs boson until a new method was proposed a few years ago. The predicted width of the Higgs boson mass range (about 0.0041 GeV/c 2) is about 200 times too small to be resolved by the detector, unfortunately. Because of this quantum effect, the mass of an unstable particle can vary around its nominal value in a range (called the width) that is inversely proportional to its lifetime. On the other hand, the lifetime is also too long to be measured through the range of possible variations of its nominal mass (125 GeV/c 2), allowed by Heisenberg’s uncertainty principle. The lifetime is almost a billion times too short for the Higgs boson to fly a measurable distance in the detector before decaying into other particles. Measuring the Higgs boson lifetime poses a big experimental challenge, though. For this reason, the experimental measurement of the lifetime of the Higgs boson is very important: It allows us to learn about the strength of its interaction with other particles and provides a window to peek into physics beyond our best current theory, the standard model. A longer lifetime could be even more surprising as it would indicate that the particle is more stable than what the standard model predicts this is equivalent to saying its interaction with other particles is weaker than predicted. A value shorter than what is theoretically calculated could hint at new decay options, potentially into new, undiscovered particles. The lifetime of an unstable particle is connected to the available options for it to decay. Pretty short, isn't it? Compare this number to 880 seconds (about 15 minutes), the average lifetime of a neutron outside an atomic nucleus. Like most other elementary particles, it is unstable and lives only for an extremely short time, 1.6 x 10 -22 seconds, according to the established theory of particle physics (the standard model). The Higgs boson is peculiar in many respects.

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