Thursday, 28 February 2013

D mesons flipping

The magnet at the LHCb detector

A result today from the LHCb had me humming:
"On the 18th day of shut-down, my true love sent to me: D mesons flipping".

To put this in English, the Large Hadron Collider's LHCb detector has published highly significant results indicating that they have detected particles called D mesons, oscillating from matter into antimatter. The results come 18 days after the LHC shut down for maintenance.

Their paper, pre-published on arXiv, outlines how the D mesons, the last of the four types of mesons to be 'observed' undergoing this oscillation, were detected to a five-sigma level of certainty.

As science writer Jason Palmer puts it:
"In the complicated zoo of subatomic physics, particles routinely decay into other particles, or spontaneously change from a matter type to their antimatter counterparts. This "oscillation" forms an important part of the theory that attempts to tame the zoo - the Standard Model. Mesons are part of a large family of particles made up of the fundamental particles known as quarks. The protons and neutrons at the centres of the atoms of matter we know well are each made up of three such quarks.
Mesons, on the other hand, are made of just two - specifically one quark and one antimatter quark. Theory holds that four members of the meson family can undergo the matter-antimatter oscillation - the matter and antimatter quarks both flip to their opposites."

The LHCb, which has had a series of stunning results with B mesons, had observed two types of B mesons and a K meson oscillating between matter and antimatter before.  But with this new paper, the team provide evidence that the last of the four types of particles, D mesons, has now been detected undertaking the same type of oscillation.

As Chris Parkes, LHC researcher from University of Manchester said:
"This is a nice moment, it's a sort of completeness.”

It is striking to note that the abstract on arXiv lists 60 authors, with another 550 not cited, due to lack of space. This really underscores the collaborative nature of physics at the Large Hadron Collider.

The results are significant because the LHCb is investigating the unsolved question of why there is more matter than antimatter in the Universe. According to the Standard Model, particles of matter and antimatter come in pairs, and matter and antimatter should obey the same laws.  Therefore, we ought to expect an equal amount of both.  So the question, "where's all the antimatter?" has had physicists scratching their heads for some time. The team at the LHCb, are undertaking some of the most significant and fundamental work to try and answer this question.

LHCb's result comes through two and half weeks after the LHC was shut-down for a lengthy period of maintenance.  But it emphasises just how much science will be carrying on whilst the main detectors are serviced and upgraded. The data collected by researchers during the first phase of collisions will be pored over for years to come, and we should expect more fascinating results like these, in the coming months.


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