CERN’s LHCb Uncovers Two New Particles
The new particles named Ξ_b’ – (Xi_b’ –) and Ξ_b* – (Xi_b* –) had already been predicted by Quantum Chromodynamics (QCD) although, up until this stage, had never been detected. ‘Nature was kind and gave us two particles for the price of one,’ said Matthew Charles of the CNRS’s LPNHE laboratory (Paris IV University).
Like all baryons, each new particle consists of three quarks held together by the strong nuclear force: one beauty (Mb ≈ 4.19 GeV [MS]), one strange (Ms ≈ 101 MeV) and one down quark (Md ≈ 4.1-5.8 MeV) with different ‘spin’ combinations have been identified.
The new particles are similar to protons, although, because they both contain a beauty quark, are considerably heavier. This was critical to their discovery, as Charles highlights: ‘The Xi_b’– is very close in mass to the sum of its decay products: if it had been just a little lighter, we wouldn’t have seen it at all using the decay signature that we were looking for.’
The latest discoveries have been attributed to LHCb’s unparalleled performance and its ‘excellent hadron identification’ capabilities, which as CERN explains: ‘is unique amongst the LHC experiments’ as it allows researchers to separate a very ‘strong and clear signal’ from any background noise.
In addition to mass, researchers were able to study other attributes, such as production rates, particle stability and decay event dynamics—these have all proved to agree with current QCD theory. ‘Testing QCD at high precision is a key to refine our understanding of quark dynamics, models of which are tremendously difficult to calculate.’
The precision of the current LHCb research has been applauded by scientists, as any future particle discoveries, not predicted by the standard model, should be easier to isolate. As Patrick Koppenburg, LHCb physics coordinator concludes: ’If we want to find new physics beyond the Standard Model, we need first to have a sharp picture’.
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