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.
Researchers and academics below the full-professor level in Italy are currently busy with an idle exercise - putting together their applications to a selection for would-be assistant and full professors. By the way, this is happening to me as well, so you may understand why this blog has received little attention from me this past week: the occupation is extremely time-consuming.
Becoming university professors in Italy in the last few decades has been a rather complicated business, where the merit of candidates was often overshadowed by favouritisms and private interests.
Today I feel as American as I've ever felt.
I've lived there for a while, and of course as a foreigner I have many things I love and many I hate about this remarkable country. But today, Americans electing Obama as President for four more years send a message. They say that the attempts at creating a more just society, one where some basic rights of citizens are not ran over by the interests of big corporations, are valued by the American people just as some of us living in another continent do.
While New Yorkers (and others on the east US coast) prepare to deal with hurricane Sandy and the possible water surge resulting from the very strong winds and low pressure of the system, a similar situation is expected in Venice on Wednesday; unlike New Yorkers, Venetians are rather accustomed to the phenomenon - familiarly called "acqua alta" (high water) by residents. However, when the level of water is exceptionally high, normal protection systems to shops, offices, and ground floors of homes prove insufficient.
That is probably going to be the case in the evening of October 31st, when the tide is expected to reach to the level of +1.40 meters above average sea level, due to a combination of factors -low pressure, full moon, winds.
As I
reported in a post a few days ago, the Italian sentencing of seven scientists to 6-years imprisonment for their misassessment of the risks of the population of L'Aquila, soon thereafter struck by a powerful earthquake which killed 309 and injured 2000, raised interest and disconcertment worldwide and spurred a debate which is not likely to end soon.
Who is guilty ?
Holiday Chess Riddle
Why Measure The Top Quark Production Cross Section?
The Buried Lottery
Twenty Years Blogging
