Today new results of Higgs searches have first been shown in Kyoto, at the Hadron Collider Physics conference. Let us see the CMS and ATLAS updates of their measurements in the ZZ-> 4 leptons final state, which constitutes the best signal-to-noise channel to study Higgs properties cleanly and measure mass and spin-parity of the new found particle.

The Hadron Collider Physics symposium opened yesterday in Kyoto. I am not following the works very closely, but I did give a peek at today's talks, which were on the topic of top quark physics.

It has taken a while, but the rare decay of B_s mesons (particles composed of a bottom and an anti-strange quark) to muon pairs has finally been seen. The authors of the find -we cannot yet call it an observation given the scarce statistical significance of the signal- are the members of the LHCb collaboration, one of the four experiments working with the proton-proton collisions delivered by the Large Hadron Collider at CERN.

I read the text below in the Facebook page of a colleague and friend, Christopher Hill. The text was meant as a facebook rant - sort of - but it raises important points. I liked what he wrote and I asked him if I could repost it here to the benefit of a larger audience. He graciously agreed. NB: the title of the post is mine.

Now that the election and Sandy is (sort of) over, I want to post a rant that I didn't think was appropriate before now.

First, Nate Silver. I have heard him called everything from a genius to a wizard to a witch in recent days. He is none of the above. He is a guy who understands mathematics (in particular statistics) enough to be able to use it to predict elections.

The CDF and DZERO collaborations at the Fermilab Tevatron collider just saw published on Physical Review D (PRD 86, 092003) their final combination of their most recent and precise measurements of the mass of the top quark.

This result, which is probably going to be the definitive one by the Tevatron experiments, reaches a precision in the top mass which is comparable to the precision of the scale you have in your bathroom, despite the fact that measuring your body weight is a quite simpler matter than determining the mass of an elementary particle, let alone one which exists for less than a trillionth of a trillionth of a second.

A digression

A journalist I am following on twitter just posted the question in the title of this post. I felt bound to try and give an answer with as simple concepts as I found meaningful. So, what makes a unstable particle unstable ?

One answer is this: a particle is unstable if there is a way, not forbidden by any physical law, to convert its rest-mass into other forms of energy. One may understand this by thinking of entropy: any system left free to evolve will do so in the direction of maximum entropy. So since a single particle state is a very low-entropy system, while the decay products of its disintegration have a multitude of possible configurations and a higher entropy, the system will naturally evolve in that direction.