UK scientists one step closer to finding the missing anti-matter from the Universe | WPN World People News

A subtle difference between matter and antimatter has been observed for the first time by the LHCb experiment at CERN. The observation has been made in the neutral Bs meson system, and submitted for publication on 24 April. This work forms part of studies to understand why the Universe only contains matter when we believe that matter and antimatter were created in equal amounts at the Big Bang.

The LHCb detector

LHCb was specifically designed to look for small differences between matter and antimatter (called CP violation) in particles produced by the LHC. Four neutral meson systems occur in nature; K0, D0, B0 and Bs. CP Violation is already well known in two of these, K0 and B0, and both discoveries led to Nobel prizes. The first observation of CP violation was made in 1964 in the neutral kaon (K0) system leading to the 1980 Nobel prize; and the later discovery in the B0 system confirmed the theoretical description of the phenomenon and led to the 2008 Nobel prize. LHCb has now observed CP violation in Bs mesons, combined states made from beauty and strange quarks, and antiquarks.

Members of the LHCb collaboration analysed 70 trillion proton proton collisions that took place in the heart of the detector. They looked at two variants of a decay of the Bsmeson, namely the decay to the final state K-||+ (a negatively charged kaon and a positively charged pion) and its ‘mirror image’ final state K+||- where all particles are replaced by their antiparticles (a positively charged kaon and a negatively charged pion). A small differences in the rates at which these two decay modes happen demonstrates a difference of behaviour between matter and antimatter.

Just 1000 Bs meson decays within the data had these variants, but this was sufficient to reach five sigma certainty on the difference between matter and anti-matter, the level of proof required in particle physics to confirm a discovery.

Professor Chris Parkes (University of Manchester) is the spokesperson for the UK university groups involved in the LHCb collaboration:

“This is an excellent result, consistent with the Standard Model, so it isn’t unexpected – based on the previous results, we thought that we should be able to make this observation with LHCb. We’ve been able to confirm the discovery so soon due to the sensitivity of our detectors, the quality and quantity of data, and the precision of our analysis.”

"LHCb can make the necessary high-precision measurements of matter-antimatter differences, thereby probing the established theories in particle physics in a complementary way to the direct searches for other new particles which are performed at the LHC", explains Dr Lars Eklund (University of Glasgow), a previous convenor for the physics analysis working group responsible for the latest discovery.

The result is particularly important for the UK team involved in LHCb because major elements of the RICH and VELO parts of the LHCb detector - critical to the discovery - were built by the UK groups.

“The VELO can locate particles to within a hundredth of a millimetre, within millionths of a second,” explains Professor Tara Shears (University of Liverpool), “It is this precision that allows physicists to reconstruct the very short flight distance characteristic of a Bsmeson, on a timescale that allows this signature to be recognised in real time. Only some of these mesons are used for this result - and we need the RICH's ability to identify the kaons and pions those Bsmesons decay into to select them. Both VELO and RICH are key to making this result happen.”

Whilst the discovery gives us an example of the difference between matter and antimatter, the difference in the standard model is too small (by a factor of 1000) to explain why our Universe only contains matter. The conundrum remains as a central question for LHCb and other particle physics experiments to answer. Investigating matter anti-matter differences are also an important method of trying to find new physics from beyond the standard model.

The LHCb collaboration is now focussed on examining the D0 system, the final neutral system in which matter anti-matter differences have not yet been seen.

“If LHCb sees a major CP violation for the D0 system, this could be an indication of new physics beyond the Standard Model,” explains Chris, “LHCb is the best tool for the job!”

Source: UK Science and Technology Facilities Council