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    Quantum Diaries

    quantumdiaries.org · Publication · on HN since 2011

    Quantum Diaries is a blog where particle physicists, many at CERN, explain high-energy physics and life in research.

    Visit blogHN submissions
    PhysicsScience
    What HN says

    HN links it for Higgs announcement live blogs and for explanations of Feynman diagrams, which one commenter calls a pleasant introduction.

    Stats for nerds
    28HN people shared it
    22linked in comments
    125story points
    Apr 2020last shared
    2012people per year2020

    Top posts on HN

    1. 1
      Higgs seminar - live webcast from CERN
      1 person · 41 points · first shared 2011 · 6 comments on HN
    2. 2
      Is science merely fiction?
      1 person · 26 points · first shared 2013 · 6 comments on HN
    3. 3
      Where do we stand on the Higgs boson search?
      1 person · 14 points · first shared 2011 · Discussion on HN
    4. 4
      Is the moon full? Just ask the LHC operators [2012]
      3 people · 8 points · first shared 2012 · Discussion on HN
    5. 5
      High Energy Physics Software and You
      1 person · 5 points · first shared 2011 · Discussion on HN
    6. 6
      A sigma here, a sigma there...
      1 person · 5 points · first shared 2012 · Discussion on HN
    7. 7
      Can the LHC solve the dark matter mystery?
      1 person · 4 points · first shared 2013 · Discussion on HN
    8. 8
      LHCb at CERN confirms new exotic state, possible tetraquark
      1 person · 3 points · first shared 2014 · Discussion on HN
    9. 9
      Cause and Effect: A Cornerstone of Science or a Myth?
      1 person · 3 points · first shared 2023 · 1 comments on HN
    10. 10
      Science: The Art of the Appropriate Approximation
      1 person · 3 points · first shared 2012 · Discussion on HN

    What HN people wrote when they linked it

    • gus_massaMar 2013

      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-weighing-in-at-about-126-gev/

      Look carefully at this graph: http://www.quantumdiaries.org/wp-content/uploads/2012/07/Higgs-2gamma-ATLAS.jpg

      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.…

    • semi-extrinsicNov 2016

      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/

    • 0PingWithJesusApr 2020

      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-the-higgs/

    • ad510Jul 2017

      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"

    • yashevdeJul 2018

      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-model-but-is-off-by-a-factor-of-2/

      tl;dr: the joke in particle physics circles goes that the extra "+ h.c." term stands for "hot coffee" instead of "hermitian conjugate"

    • untiltedJul 2016

      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/

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