#b-mesons

[startswithabang]

Ask Ethan: Could An Unexplained Decay At The LHC Demolish The Standard Model?

“I want know more about the last announcement from the LHCb [collaboration] about CP Violating asymmetry in a charged B meson decay. What [does] this mean and/or this is a hint for new physics beyond the Standard Model??”

I hear your whining all the time. “The LHC is such a waste. They haven’t found anything other than the Higgs.” Well, maybe you’re not paying attention to the right things, then? The Standard Model is so successful because it makes exquisite predictions for how the composite particles we produce in accelerators ought to live and decay. Well, we have a series of particles, the mesons that contain bottom quarks, that clearly aren’t obeying the rules of the Standard Model. The most robust puzzle we have about this is known as the Kπ puzzle, since there’s a large and significant difference between the CP-asymmetry of neutral and charged B-mesons that decay to kaons and pions.

Could this be the hint of new physics beyond the Standard Model we’ve waited for for so long? Don’t count the LHC out yet, and keep looking for new anomalies!

[wildcat2030]

Four years after its closure, researchers working with data from the Stanford Linear Accelerator Center’s particle physics experiment BaBar (pictured right, in Menlo Park, California) have used the data to make the first direct measurement confirming that time does not run the same forwards as backwards – at least for the B mesons that the experiment produced during its heyday. The application of quantum mechanics to fundamental particles rests on a symmetry known as CPT, for charge-parity-time, which states that fundamental processes remain unchanged when particles are replaced by their antimatter counterparts (C), left and right are reversed (P), and time runs in the reverse direction (T). Violations of C and P alone were first seen in radioactive decays in the 1950s, and BaBar was used to confirm violations of CP in B meson decays in 2001. To keep CPT intact, that implies that time reversal is also violated, but finding ways to compare processes running forward and backward in time has proven tricky. Theoretical physicists at the Universityof Valencia in Spain worked with researchers on BaBar to exploit the fact that the experiment had generated entangled quantum states of the meson Bzero and its antimatter counterpart Bzero-bar, which then evolved through several different decay chains. By comparing the rates of decay in chains in which one type of decay happened before another, with others in which the order was reversed, the researchers were able to compare processes that were effectively time reversed version of each other. They report in Physical Review Letters today that they see a violation of time reversal at an extremely high level of statistical significance.