This summer, the world’s most powerful particle collider will go into hibernation. But before that, it’s delivering some last-minute discoveries: the common proton’s weightier sibling.
In a statement today, CERN’s Large Hadron Collider beauty (LHCb) Collaboration—the Swiss institution’s specialty unit in matter-antimatter research—announced the discovery of an entirely new particle, a heavy proton-like particle with two charm quarks. Compared to an ordinary proton, the particle, named Xi-cc-plus, is about four times heavier and very unstable, lasting around 45 femtoseconds (one femtosecond is one quadrillionth of a second).
The findings were first presented at the Rencontres de Moriond conference and will soon be detailed in a formal scientific paper, according to the LHCb.
Quarks are fundamental particles—meaning they can’t be broken down into smaller parts—that serve as the building blocks of protons and neutrons, according to the U.S. Department of Energy. And these protons and neutrons in turn form larger atoms and molecules that make up all matter.
These quarks come in six different flavors—up, down, charm, strange, top, and bottom—with varying masses and electric charges. These flavors combine in groups of two or three to create composite particles, or hadrons (hence, the Large “Hadron” Collider). For example, protons have two up quarks and a down quark, whereas neutrons have two down quarks and one up quark.
Xi-cc-plus, on the other hand, replaces the two up quarks in protons with charm quarks, which are heavier than up quarks but have the same charge. According to CERN, most hadrons are rarely as stable as the proton, quickly decaying into other, more stable particle forms. Physicists actually predicted this particle’s existence and mass around two decades ago, and the new findings now validate the earlier claims and the relevant theoretical expectations, according to LHCb researchers in a statement from the University of Manchester.
To study these short-lived particles, physicists at the LHC smash together high-energy particles and carefully study the result of the ensuing decay process. This allows them to deduce the properties of the particle produced from the collision. Finding Xi-cc-plus required observing around 915 such events, aided by a 2023 upgrade to LHCb equipment. The recent upgrade produces more collisions and tracks particle decays with greater precision.
Remarkably, Xi-cc-plus is the 80th hadron discovered by all LHC experiments. True, these particles don’t last very long and are excruciatingly difficult to produce. Still, each discovery brings physicists closer to explaining unsolved mysteries surrounding the strong force, the most powerful natural force that binds protons and neutrons.
LHCb spokesperson Vincenzo Vagnoni noted in the statement that Xi-cc-plus will contribute toward testing “models of quantum chromodynamics, the theory of the strong force that binds quarks into not only conventional baryons and mesons [types of composite particles] but also more exotic hadrons such as tetraquarks and pentaquarks.”
The findings also speak to the high returns of “hardware” upgrades to gigantic physics machines. To put this in perspective, the actual discovery of Xi-cc-plus came along in 2024, just one year after the upgrades to LHCb. And again, the LHC is set to get a major upgrade starting this summer—so the next decade should be exciting times for particle physics, indeed.
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Source: Gizmodo