LHCb at CERN: evidence of rare Bd decay into two muons

Scientists at the University of Manchester have reported evidence of a rare decay seen at the LHCb experiment at CERN, according to Interesting Engineering. The decay, called Bd to mu mu, is one in which a beauty quark decays into two muons, particles similar to electrons but somewhat heavier. Estimates suggest it occurs only once in 10 billion beauty particles, which is why it had not been observed before interestingengineering.com. The signal appeared after a major upgrade of the detector, following more than 40 years of searching.

The upgraded LHCb detector

LHCb differs from the ATLAS and CMS detectors: it is a forward spectrometer. Instead of looking in all directions, it concentrates on the forward region of the beamline to study the behavior and decay of beauty and charm quarks interestingengineering.com.

Beauty quarks are heavier than up and down quarks and are produced in large numbers at the LHC. However, they exist for only about one and a half trillionth of a second before decaying. Researchers from the University of Manchester have worked on the LHCb upgrade for more than a decade and a half. The upgraded experiment collects data at five times the rate that was possible before interestingengineering.com.

The UK contribution to the upgrade is the Vertex Locator, a silicon pixel detector placed five millimeters from the beams. It lets scientists pinpoint where particles are produced and where they decay interestingengineering.com.

Significance and the zeptoverse

The statistical significance of the result is 3.2 sigma, below the 5 sigma threshold required to call it a major physics discovery. The measurements remain consistent with the Standard Model interestingengineering.com.

Precise measurements of beauty-quark decays can reveal the influence of new particles that may be too small to be detected directly at the LHC. The rarer a decay is, the more sensitive it can be to such influence. The result points to a way of studying particles and forces at the scale of a zeptometre, a billionth of a trillionth of a meter. The corresponding space is called the zeptoverse. Further work there could reveal signs of physics that the Standard Model cannot explain interestingengineering.com.

Chris Parkes, Head of the Department of Physics and Astronomy at the University of Manchester, who took part in the upgrade, said the decay is remarkably unlikely. Conor Fitzpatrick, Deputy Physics Coordinator of the LHCb collaboration, said the team is glad to have finally seen the elusive signal interestingengineering.com.

The upgraded experiment is to collect data until the early 2030s. A further upgrade could raise data collection by another order of magnitude interestingengineering.com.

LHCb at CERN sees evidence of rare Bd decay into two muons at 3.2 sigma

The upgraded LHCb detector

Significance and the zeptoverse

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