Quantum Diaries

I am in office, and am following a live blog of the webcast. http://www.quantumdiaries.org/2012/07/03/higgs-seminar-live-blog-from-… [The Guardian one pointed out below is more informative]

When a single electron collides with another single electron, quantum field theory predicts the scattering probability distribution as a sum of Feynman diagrams. All of them must have two incoming and two outgoing legs, so the only difference between them is the number of internal loops. The basic ones, having no internal loops, is called the "tree level diagrams" (there may be one or more of these). The rest, having internal loops, can be thought of as higher order corrections to the results you get from just the tree-level diagrams. Now, these internal loops are best thought of as vacuum fluctuations that pop out and interact with the two scattering particles. Say two electrons scatter: the tree-level diagram is two electrons approaching, interacting via a virtual photon (the force carrier for electromagnetism) and then going away from each other again. (There is also another tree-level diagram for this.) And then there are higher-order contributions, e.g. from the case where the virtual photon fluctuates into an electron-positron pair, which then decays back into a photon, in between the two electrons. This is good for more detail (but a long series): http://www.quantumdiaries.org/2010/02/14/lets-draw-feynman-diagams/

I don't have a direct link, and this is a little old, but it looks good: http://www.quantumdiaries.org/2012/07/04/new-baby-boson-is-born-weighi… Look carefully at this graph: http://www.quantumdiaries.org/wp-content/uploads/2012/07/Higgs-2gamma-… This graph shows how many pairs of photons were crated, classified by the energy. There are a lot of ways to create a pair of photons, so there is a lot of background noise even if the Higgs Boson doesn't exist. This is roughly the dotted line (it's very difficult to see, because it's almost covered with the red line). The black points are the actual measurements. They almost agree with the dotted line, except in the range of 125-130GeV where there is a bump. In that energy range there are more pairs of photons created than the expected quantity. The energy of the photons is essentially equal to the mass of the HB, but there are some dispersion because of the measurements errors and some quantum effects. The red line is a simulation of how many pairs of photons would appear if the mass of the HB were 126.5GeV. They adjusted that parameter to get the best fit. This red line has a bump near 126.5GeV that is similar to the bump that the measurements have (black dots). The dotted line is very similar, so the red line cover it everywhere except in the bump range. There is a lot of noise, so one possibility is that the bump is only a lucky streak, so they wait until they get a 5 sigma deviation, i.e.…

It's a bit of a subtle point but Majorana anti-neutrinos are still right handed chiral particle and a Majorana neutrino is still a left handed particle. So any particle-antiparticle effects from Delta-CP (or anything else) just becomes a left-right chirality effect. That behavior is built right into the term "Delta-CP", CP stands for charge-parity, meaning it's related to both a charge flip (particle to anti-particle) or a parity flip (left to right). This isn't a full explanation but I'd have to go find some old text-books in order to provide a better one. Here's also a blog post that kinda sorta addresses the same point https://www.quantumdiaries.org/2011/06/19/helicity-chirality-mass-and-…

For anyone interested in a deeper (but not dense) introduction to how and why Feynman diagrams work I’ve found a lot of pleasure going through this blog post below. https://www.quantumdiaries.org/2010/02/14/lets-draw-feynman-diagams/

Funnily enough, the CERN mug in the header image is slightly off. Read more here: https://www.quantumdiaries.org/2011/06/26/cern-mug-summarizes-standard… tl;dr: the joke in particle physics circles goes that the extra "+ h.c." term stands for "hot coffee" instead of "hermitian conjugate"

Just to add to this: The part that comes this initial gluon emission (hadronization) is not very well understood since at this length scale the perturbative (i.e., feynman diagram) approach to QCD breaks down. See e.g. http://www.quantumdiaries.org/2010/12/11/when-feynman-diagrams-fail/

CERN: LEP data confirm train time tables http://cds.cern.ch/record/1726241 CERN: Is the moon full? Just ask the LHC operators http://www.quantumdiaries.org/2012/06/07/is-the-moon-full-just-ask-the…

That's about it. See also http://www.quantumdiaries.org/2012/06/28/why-we-shouldnt-combine-higgs…

Blog Coverage: http://www.quantumdiaries.org/2012/06/03/neutrino-2012-day-1/

special relativity: http://onestick.com/relativity general relativity: http://www.feynmanlectures.caltech.edu/II_42.html quantum electrodynamics: "QED: The Strange Theory of Light and Matter" or http://vega.org.uk/video/subseries/8 standard model: http://quantumdiaries.org/2010/02/14/lets-draw-feynman-diagams conceptual core of quantum mechanics: http://scottaaronson.com/democritus/lec9.html history of quantum mechanics: "The Second Creation" and "The Infinity Puzzle"