from the strange-but-charming dept.
The LHCb experiment at CERN is a hotbed of new and outstanding physics results. In just the last few months, the collaboration has announced the measurement of a very rare particle decay and evidence of a new manifestation of matter-antimatter asymmetry, to name just two examples.
In a paper released today, the LHCb collaboration announced the discovery of a new system of five particles all in a single analysis. The exceptionality of this discovery is that observing five new states all at once is a rather unique event.
The particles were found to be excited states – a particle state that has a higher energy than the absolute minimum configuration (or ground state) – of a particle called "Omega-c-zero", Ωc0. This Ωc0 is a baryon, a particle with three quarks, containing two "strange" and one "charm" quark. Ωc0 decays via the strong force into another baryon, called "Xi-c-plus", Ξc+ (containing a "charm", a "strange" and an "up" quark) and a kaon K-. Then the Ξc+ particle decays in turn into a proton p, a kaon K- and a pion π+.
From the analysis of the trajectories and the energy left in the detector by all the particles in this final configuration, the LHCb collaboration could trace back the initial event – the decay of the Ωc0 – and its excited states. These particle states are named, according to the standard convention, Ωc(3000)0, Ωc(3050)0, Ωc(3066)0, Ωc(3090)0 and Ωc(3119)0. The numbers indicate their masses in megaelectronvolts (MeV), as measured by LHCb.
Significant results, if a bit quarky.
Paper available online at arxiv.org.
The apparent symmetry between matter and antimatter is puzzling scientists at the European Organization for Nuclear Research (CERN):
One of the great mysteries of modern physics is why antimatter did not destroy the universe at the beginning of time.
To explain it, physicists suppose there must be some difference between matter and antimatter – apart from electric charge. Whatever that difference is, it's not in their magnetism, it seems.
Physicists at CERN in Switzerland have made the most precise measurement ever of the magnetic moment of an anti-proton – a number that measures how a particle reacts to magnetic force – and found it to be exactly the same as that of the proton but with opposite sign. The work is described in Nature [open, DOI: 10.1038/nature24048] [DX].
"All of our observations find a complete symmetry between matter and antimatter, which is why the universe should not actually exist," says Christian Smorra, a physicist at CERN's Baryon–Antibaryon Symmetry Experiment (BASE) collaboration. "An asymmetry must exist here somewhere but we simply do not understand where the difference is."
Previously: Evidence Mounts that Neutrinos are the Key to the Universe's Existence
Matter-Antimatter Asymmetry Confirmed in Baryons
LHCb Observes an Exceptionally Large Group of Particles
Possible Explanation for the Dominance of Matter Over Antimatter in the Universe