Physicists with the ATLAS Collaboration report the first observation of an exotic new particle, which could help deepen our understanding of the mysteries surrounding one of the four fundamental forces in physics.
The achievement was revealed recently at the Large Hadron Collider Physics conference, where researchers said the new particle appeared to display properties strongly suggestive of the Bc*+ meson.
This unique particle is theorized to be a variation of the Bc+ meson, albeit in a more excited form. The observation now brings the total number of new particle discoveries by CERN’s Large Hadron Collider (LHC) to 82.
A New Particle Emerges
Both the newly discovered Bc*+ meson is part of the broader family of Bc+ meson particles, which consist of an antiquark at their bottom and an up (B⁺. ), down (B⁰. ), strange (B⁰. ₛ) or charm quark (B⁺. c) in their top position.
Such particles were once relegated only to theory since the top quark’s short lifetime would seemingly prevent their physical existence. However, confirmation of the Bc*+ meson, which possesses a charm quark and a bottom antiquark, could help move physicists closer to understanding the mysterious strong force, which, along with the weak force, electromagnetism, and gravity, constitutes the four fundamental forces of the Standard Model of particle physics.
Even after many decades, physicists remain in the dark about certain characteristics of the strong force, such as how it can bind quarks together.
Particles that consist of heavy quarks offer physicists a promising means of testing a range of theories about how the strong force functions, and Bc+ mesons are of special significance in such efforts since they provide a pathway for physicists to unravel clues to what, precisely, holds these particles together.
The Newest Member of the Bc+ Family
According to a recent CERN news release, the new particle was generated during extremely high-energy proton-proton collisions at the LHC.
Before decaying into a Bc+ meson and a photon, the new particle was successfully observed, albeit briefly. According to CERN researchers, a detection of the photon coinciding with the properties of decay associated with the Bc+ meson could offer a long-sought “smoking gun” that would demonstrate the Bc*+ meson.
A key issue physicists currently face involves the particle’s mass: it is anticipated that the mass of this particle would clock in at only a tiny bit larger than the Bc+ meson. Because of this, the photon that should emanate from the decay at the time of the particle’s generation would possess so small an amount of energy that it would likely be indiscernible using any conventional methods.
To overcome this, researchers tried a different approach: They decided to look within the ATLAS tracking detector for the photon converting into an electron-positron pair. In theory, the ephemeral, closely spaced charged particle “tracks” would be produced as a result of the primary proton-proton collision.
“These tracks can have transverse momenta as low as 100 MeV – significantly lower than those typically studied in ATLAS analyses,” according to the recent statement. “This required researchers to deploy a dedicated track-reconstruction procedure to be able to successfully reconstruct the photons and thus identify the Bc*+ meson.”
Toward a Better Understanding of the Strong Nuclear Force
According to researchers, the differences measured between the masses of the Bc*+ meson and the Bc+ meson are 64.5 ± 1.4 MeV, which falls well within the expected ranges based on current theoretical models.
While falling within expected ranges, ATLAS Collaboration researchers did note that the observed differences differed slightly from current high-precision calculations for these values. Still, the discovery offers more than enough data to assist in broadening current theories and eventually allow physicists to glean new insights into the mysterious strong force.
“This result provides valuable new input for theoretical models describing the masses of particles containing the heavier quarks and will help to improve the understanding of the strong nuclear force,” the researchers said.
The ATLAS Collaboration’s findings were reported in a new paper, “Observation of a B∗+c meson with the ATLAS detector,” which appeared on the preprint arXiv.org server.
Micah Hanks is the Editor-in-Chief and Co-Founder of The Debrief. A longtime reporter on science, defense, and technology with a focus on space and astronomy, he can be reached at micah@thedebrief.org. Follow him on X @MicahHanks, and at micahhanks.com.