What is Deep Inelastic Scattering?

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Since I’ll be writing about the Deep Inelastic Scattering Workshop this week, I was planning to make a pre-conference introduction post explaining in some detail what DIS actually is. But as it turns out, one of the plenary talks tomorrow is devoted to exactly that subject — plus I’m really tired after traveling for about 18 hours and walking around the city for another four or so. So I’ll start with a quick introduction and update this with more information tomorrow.

Deep Inelastic Scattering

Deep inelastic scattering itself is a particular type of physical process that occurs when a hadron (a particle made of quarks and gluons, such as a proton) collides with a lepton (a particle that, as far as we know, has no constituents).

  • It’s “deep” because the lepton has very high momentum as measured in the proton’s reference frame, so the way it behaves in the interaction can depend on very small features of the proton’s structure.
  • It’s “inelastic” because some of the kinetic energy of the original two particles is lost. In modern DIS, that energy goes into splitting the proton into many outgoing particles.
  • It’s “scattering” because the lepton is deflected and comes out at a different angle than it came in at. Measurements of that angle can be useful in characterizing the collision.

DIS processes were used to make the first measurements of the number of quarks in the proton, among other things. (A favorite of mine among those other things is geometric scaling, which is related to what I’ll be talking about at this conference — but the details will have to wait for another blog post.)

Related Topics

Of course, if you limit yourself to actual deep inelastic scattering (leptons on protons), there’s only so much physics you can do. Yes, there are many interesting ways to analyze the data that comes from DIS collisions in electron-proton accelerators, but there are many more interesting ways to analyze the data that comes out of colliding protons with other protons, or electrons with nuclei, or nuclei with nuclei, and so on. All of this stuff falls under the second part of the conference title, “Related Topics.” Basically, DIS is kind of the “poster child” for all of the various particle physics processes which involve strong interactions, so it gets to be featured in the name of the conference, but the topics that are going to be covered span the entire range of work being done with QCD.