Monday, November 12, 2012

Supersymmetry dealt a blow

The popular physics theory of supersymmetry was dealt a blow by the publishing of a crucial paper by CERN. Physicists who work at the Large Hadron Collider (LHC) look at specific particles, which are unstable. This just means that they split into smaller particles as they decay. Of course, there are many different kinds of smaller particles into which the larger particle can split. Some of the decays rarely happens.

According to the standard model, the decay in the question only happens in three out of 109 B-decays (A B-decay is a decay where a B-meson decays. A B-meson is a particle consisting of a anti-bottom quark and an up, down, strange, or charm quark). The fraction of all decays that lead to a particular final result is also called the branching ratio. So of all the possible decays that the B-meson can do, only 3 x 10-9 of the decays lead to the decay in the paper. Actually, they treat two different B-decays, but the branching ratio of both of them is in the order of magnitude ~10-9 - 10-10. According to Supersymmetry, the branching ratio of these decays is much higher.

What this all comes down to is if we have a billion of the large particles, only one of them splits into a certain combination of smaller particles. Thus, we say that the chance for that certain decay is one in one billion. The article is about one particular kind of decay.

Now, different theories have different chances for that particular decay of happenings. In the standard model, that is one in one billion. In super symmetry, it's maybe one in one million. That means it happens a thousand times more often.

Sometimes, scientists don't know whether a decay actually happens at all. But down at LHC, they've found the decay, so they know it happens. But they've only found it once out of maybe a billion other decays.

While this decay happens rarely, it happens many times in LHC. What's new with this publication is that they are now fairly certain that the amounts of decays they detect aren't some kind of freak accident or a problem with the test. The probability that background processes can produce the observed number of decay candidates is 5x10-4 and corresponds to a statistical significance of 3.5 sigma. That is that if they did the same experiment 5x104 times, one of them would be wrong.

This all comes down to that the standard model predicts that one in one billion decays is that particular decay, but super symmetry predicts maybe a thousand in one billion decays is that particular decay. So, according to SUSY, this decay should have happened many more times than this single one they've found. This means that right now, the standard model seems correct and super symmetry has something wrong.

Monday, November 5, 2012

Hunting for the Higgs Boson

If you're in the East Bay tonight, you should check out the 2012 Segre Lecture at UC Berkeley. Peter Jenni, a CERN Scientist and former ATLAS Spokesperson, will present "Hunting for the Higgs Boson and more at the LHC." 

This annual lecture was conceived as a way for the Physics Department to honor and bring the work of an experimental physicist to the general public. Many renowned experimental physicists have been hosted. The observation of the Higgs Boson at the LHC was easily the biggest science story of the year, so this should be an excellent lecture. It will begin at 5PM in the Pauley Ballroom and is an lecture that any budding astronomer or science enthusiast won't want to miss! Click here to say you're going.

The lecture abstract is as follows:

For the past three years, experiments at the Large Hadron Collider (LHC) have begun exploring physics at the high energy frontier. A rich harvest of initial physics results has been obtained that allows us to test the Standard Model (SM) of elementary particles and to make searches Beyond the SM (BSM), at the highest energy level ever reached in a laboratory. Most exciting is the recent discovery of a new particle that may well be the long-awaited Higgs Boson. This discovery would also establish the postulated electro-weak symmetry breaking mechanism in the SM. Other far-reaching results can be reported for BSM physics searches like Supersymmetry (SUSY) and its implication for Dark Matter in the Universe, Extra Dimensions, and the production of new heavy particles. Besides these physics results, the history and technical challenges of the LHC project, its status, future physics prospects, as well as Cal and LBNL’s prominent role in them will also be covered briefly in this talk.