News (2014/04/10)

Two items of news to report this week (well, one and a half at least). The half-piece of news is that I'm working on a new blog post which will hopefully be posted some time next week (although it might take until the week after).

The real news is that the LHC has confirmed the existence of Z(4430), a so-called "exotic hadron". Hadrons are composite particles made of quarks (and held together by gluons). According to the quark model, hadrons can only form in one of two ways: a quark-antiquark pairing (known as a meson) and in a quark triplet (know as a baryon).

The most common hadrons in the universe are protons and neutrons which form atomic nuclei. Protons consist of 2 up-type quarks and 1 down-type quark ("uud") while neutrons consist of 1 up quark and 2 down quarks ("udd"). The names and details of quark types, which are known as "flavours", is not something I will go into here, as it is an interesting enough topic to deserve its own post (although a proper explanation for the layperson would need a little more than that I think).

The quark model is a simple one though and does not describe all of the dynamics permitted by quantum chromodynamics ("QCD", the part of the Standard Model that describes strong interactions). This leaves open the door for exotic hadrons which are not mesons or baryons. Z(4430) is one such exotic hadron.

It was first 'discovered' in 2007 (although 5-sigma confirmation didn't come until 2008) and has now been observed at the LHCb experiment at 13.9-sigma accuracy. This means the chances of the observation being a statistical fluke are $1$ in $1.579\times10^{43}$ (a very, very, very large number indeed). It is believed to be a tetraquark made up of 1 charm quark, 1 charm antiquark, 1 down quark and 1 up antiquark ("ccdu").

While perhaps not as exciting as, for example, the BICEP2 result recently, this confirmation is still a very interesting result and will hopefully spur on further developments in the search for exotic hadrons.