Chasing the higgs

Since December many words has been written about the Higgs search in the high energy physics. Recently I have read in the Spanish translation of the "Scientific American" (called "Investigación y Ciencia") a text (not a peer reviewed article) about the Higgs that I think is specially good for newbies in this field.


Usually the blog who talks about the Higgs often uses many technical words and graphics. Nothing to say about the images drawings like:

From cms web site

In my words (I'm a computer scientist, neither this is peer reviewed!). When you remove everything from a portion of the space to have it in the highest possible vacuum, there is still something there. This vacuum have some entity, a non zero field that fills everything. This field, dramatically can make you think in the idea of the ether, but it's should be completely different.


The standard model have some mathematical transformations (usually named symmetries) who not only gives beauty to the theory, it has many behaviour consequences specially in between the interactions.


Physicist knows very well the fundamental interactions (electromagnetic, nuclear week, and strong, and also the oldest we know even if it's the one we know less about, the gravitation). This forces are a consequence from this mathematical symmetries in the standard model. This explains many properties of the particles, except one "small" detail: the mass.


This symmetries in the model says that the mater particles shouldn't have mass, but we know it's there. Even more, the force carrier particles shouldn't have mass, and in general they hasn't, but the bosons W and Z have mass.


In the 60's, Sheldon Glashow, Steven Wienberg and Abdus Salam (they are 1979 Physics Nobel Price)  introduces the Higgs mechanism  (proposed 1962 by Philip Warren Anderson and developed in 1964 by three independent groups, in one of them were Peter Higgs). The idea is simple, this field can be imagined like a viscose liquid who fills completely all the space, and the friction on this liquid gives to the particles what we see as mass. The waves made on this liquid when the particles agitates it, are the the higgs particles.


Some particles flow better in this higgs field, and looks like they have a very small mass. Some others have a big interaction and looks like very massive. And there are particles who didn't interact at all with it, being unmassed.


What are high energy physics colliders searching for? It's highly difficult to detect the higgs particles itself, and much more complicate because they decay very fast. But what it's possible to detect are the products of this disintegrations. What the LHC (and its predecessors) is trying to see in the detectors (specially Atlas and CMS) are this subproducts of the disintegration. Even that this events where they appear, are very difficult to detect.


The LEP (LHC predecessor were the tunnel is the same) has set a lower limit in 114GeV and the highest level would be at 800GeV. But with the results published in the 13th of December, this window has been reduces with a trust of the 95%, in two smaller windows. One between 600GeV and 800GeV (but other experimental results may exclude this window). and the most hopped window is between 115GeV and 128GeV (indirect results of the LEP studies also points to this window). Even more, this window have a substantial probability to have the higgs in between 125GeV and 126GeV.


But this doesn't mean that the higgs exist. There is also a probability that the higgs doesn't exist and the excesses detected are statistical fluctuations and systematic errors... This 2012 the analysis will have much more data. Last week there were the LHC performance workshop where has been decided the setup for the collider this year. Beams energy increased to 4TeV (collisions @ 8TeV), bunches separation of 25ns (they were 50ns, means the double of bunches in the beam, with a pile-up effect), and reduced the beta-star parameter to increase the luminosity (from 1m to 60cm).


21th of March will start again the beam operations.


Update 20120213: Some news point to 4 TeV beam (colliding at 8TeV) with 50ns bunch separation and beta-star at 0.6. Not very different that 2011 configuration, but enough to have  the 16.5/fb collisions predicted to be enough to find the Higgs.