CERN's LHCb experiment unearths two new baryon particles
The particles, known as the Xi_b'- and Xi_b*-, were predicted to exist by the quark model but had never been seen before. A related particle, the Xi_b*0, was found by the CMS experiment at CERN in 2012. The LHCb collaboration submitted a paper reporting the finding to Physical Review Letters.
Matthew Charles of the CNRS's LPNHE laboratory at Paris VI University said, “Nature was kind and gave us two particles for the price of one.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.”
“This is a very exciting result. Thanks to LHCb's excellent hadron identification, which is unique among the LHC experiments, we were able to separate a very clean and strong signal from the background," said Steven Blusk from Syracuse University, in New York. “It demonstrates once again the sensitivity and how precise the LHCb detector is,” he added.
The research team studied the relative production rates, the widths (a measure of how unstable they are) and other details of the decays, of these particles. The results match up with predictions based on the theory of Quantum Chromodynamics (QCD).
QCD is part of the Standard Model of particle physics, the theory that describes the fundamental particles of matter, how they interact and the forces between them.
“If we want to find new physics beyond the Standard Model, we need first to have a sharp picture,” said LHCb’s physics coordinator Patrick Koppenburg from Nikhef Institute in Amsterdam. “Such high precision studies will help us to differentiate between Standard Model effects and anything new or unexpected in the future,” he added
The measurements were made with the data taken at the LHC during 2011-2012. The LHC is currently being prepared, after its first long shutdown, to operate at higher energies and with more intense beams. It is scheduled to restart by spring of 2015.