Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Quantum Chromodynamics Binding Energy

  1. Jul 28, 2014 #1

    Drakkith

    User Avatar

    Staff: Mentor

    Binding energy is typically used to talk about the amount of energy needed to separate bound particles. This means that it represents the energy lost when particles enter a bound state.

    So, why does this article use the term "binding energy" to talk about the energy/mass content of a proton?

    http://en.wikipedia.org/wiki/Proton#Quarks_and_the_mass_of_the_proton

     
  2. jcsd
  3. Jul 28, 2014 #2
    Good question
     
  4. Jul 28, 2014 #3

    Orodruin

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    Well, in the QCD setting, separating two color charges would require an infinite amount of energy due to confinement so this definition of binding energy would also be a weird one. I will agree that calling it binding energy may be a bit misleading when it is simply the energy contained in the stuff holding the hadrons together.
     
  5. Jul 28, 2014 #4
    I think it still makes sense.

    As it refers to composite objects, and since the composite objects have measurable quantum numbers it is correct to call it a binding energy. For example, the valence content of hadrons is measureable.

    What is not clear to me is how to model a hadron with point like particles, and what quark masses should be used. Lattice qcd does a good job I guess.

    P.s. It doesn't take an infinite amount of energy to separate quarks. It takes a quantifiable energy per unit distance. It takes an infinite amount of energy to separate by an infinite distance. (See lattice qcd results for quark anti quark separation where this is modelled)
     
  6. Jul 28, 2014 #5

    Orodruin

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    This is typically the definition of the zero-point of the potential energy of both gravity and electric potential.
     
  7. Jul 28, 2014 #6

    Drakkith

    User Avatar

    Staff: Mentor

    I still don't see why it's called binding energy.
     
  8. Jul 29, 2014 #7

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    It is a positive energy (visible as mass, and in deep inelastic scattering), and it is related to the QCD bond.
     
  9. Jul 29, 2014 #8

    Drakkith

    User Avatar

    Staff: Mentor

    Can you elaborate on that, MFB?
     
  10. Jul 29, 2014 #9

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    Take a proton, for example: it has 3 valence quarks (two up, one down). Their combined masses (=rest-energy due to special relativity) are about 10 MeV. Without the strong interaction, a collection of those 3 valence quarks at rest would have a mass of 10 MeV.

    As we know, a proton is significantly heavier, which also means it has more energy (at rest). This difference comes from the strong interaction. It is so strong that "naked quarks" don't exist in hadrons. You always have to consider the quark, gluons, virtual quarks and the kinetic energy of all those particles together, and this adds up to a much larger energy. That concept is known as constituent quark. If you add those three and compare it to the actual proton mass, you'll note that you get a negative binding energy again.
     
  11. Jul 29, 2014 #10

    Drakkith

    User Avatar

    Staff: Mentor

    I understand where the mass of the proton comes from, what I don't understand is why it's commonly said that the mass comes from the binding energy if the usual meaning of the term refers to a negative amount of energy. Am I missing something obvious?
     
  12. Jul 29, 2014 #11

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    Well, the mass comes from "the binding process [and everything else going on related to that]" in QCD.
     
  13. Jul 29, 2014 #12

    Vanadium 50

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    The gluon field has an energy E^2 + B^2. That's where the mass comes from. It's called binding energy because it takes an infinite amount of energy to separate the constituents, and E^2 + B^2 is less than infinity.
     
  14. Jul 30, 2014 #13

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    What are E and B here?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Quantum Chromodynamics Binding Energy
  1. Binding energy (Replies: 1)

  2. Binding Energy (Replies: 5)

Loading...