Of Particular Significance

The Standard Model Higgs

What is the Standard Model Higgs particle? It is the simplest form of Higgs particle that could be present in nature, a ripple in the simplest possible form of Higgs field that could be present in nature. And what is the Higgs field? It (or something very like it) is a crucial ingredient in our universe as we know it.  (Read the Higgs FAQ for more details, or watch my video clips from my public talk at the Secret Science Club)

  • The Higgs field (as with all fields) is something that has a value everywhere in space, but unlike most fields we come across it is not zero on average — it has a non-zero value everywhere in space.
  • The Higgs field interacts with many of the particles of nature (and their own corresponding fields) including particles as diverse as the electron, the top quark, and the W and Z particles. (You can read about the known elementary particles of nature here.)
  • All of the known apparently-elementary particles get their masses because the Higgs field has a non-zero value. The stronger is their interaction with the Higgs field, the larger is their mass.
  • [Note: if you have read somewhere that the Higgs particle gives mass to the other particles, you should disregard it. That statement is simply wrong.  The Higgs field does that job.]
  • If the Higgs field was zero on average, then the universe would be a very different place; in particular, there would be no atoms, and thus no ordinary matter (and no earth and no humans.)
  • We know very little about the Higgs field, except that it does what I’ve just described. We don’t actually know if it is one field, or several. We don’t know if it is an elementary field, or a field that is itself made from other fields. How are we going to find out?
  • That’s where the Higgs particle (or particles) comes in. The Higgs particle is to the Higgs field as the vibration pattern of a violin string is to the violin string itself. If you want to know what a violin string is made of, and how tightly it is wound, pluck it. Study the vibrations of the string. If you want to know what the Higgs field is made of, give it a whack (with a proton-proton collision at the Large Hadron Collider [LHC]) and watch it ripple. Those ripples are Higgs particles; study them.
  • Sometimes people say the LHC was built to find the Higgs particle. This is wrong. The LHC was built to understand the Higgs field. The particle is a means to an end, not an end in and of itself.
  • Even with a Higgs field, there may not be an observable Higgs particle, though it will take us ten years to be sure of that. But this can only happen if there are other new phenomena for us to discover at the LHC.  (Why? Long story…)
  • The first step along the road toward understanding the Higgs field is to study the simplest possible version of that field, and the ripple that you can make when you disturb it: the simplest possible Higgs particle. These are called the Standard Model Higgs field and the Standard Model Higgs particle.

There are three articles nested below this webpage that will explain to you the program to search for the Standard Model Higgs particle (as of December 2011), and how and why, if we find a candidate, we’ll study it in such great detail.

  1. How you make the Standard Model Higgs particle
  2. How the Standard Model Higgs particle decays
  3. How you search for and study the Standard Model Higgs particle

35 Responses

  1. There is no way to stop or even steer physicists of all denominations who are drawn with a passion of discovery to whatever end awaits us in applying all their collective minds in the pursuit of what binds or destroys mankinds’ knowledge of how the universe works.

  2. Professor Strassler,
    What is the current status regarding the role or relevance of Higgs field as related to the model(s) of origin of our universe, vis-a-vis the Big Bang Theory, Inflationary Cosmology, or any other models?
    How such conceived roles, if any, stack against the widely accepted role on mass of elementary particles?
    Thank you for comments.
    DJC ,

  3. Dear Dr.Stassler,
    The 5th point, “[Note: if you have read somewhere that the Higgs particle gives mass to the other particles, you should disregard it. That statement is simply wrong. The Higgs field does that job.]”
    I remember that you said when a top-left quark (left chirality) meets a Higgs bosob and then turn into a top-right quark, and turns back (like oscillation). According to the 5th point statement, that statement about meeting Higgs bosons is not an exact statement but just an approximation?

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  5. I’ve been following Your articles on Higgs. Highly informative, thank you. Yet, I have a few questions:
    1. What determines the strength of particle interaction with the Higgs field? Why photon doesn’t interact with it at all and the top quark does strongly? Is there some kind of charge involved?
    2. If W and Z bosons interact with the Higgs field, as You stated above, why there’s separate mechanism (the Higgs mechanism) that gives them mass, when they already should have mass from interaction with the Higgs field?
    3. In what way does the vev give mass to the particles? I though it was through virtual Higgs boson, but You write the boson has nothing to do with it. Come to think of it, for the virtual Higgs to be playing a role, there should be some disturbance in the Higgs field, but it’s not the disturbance, it’s just its normal value.
    4. Considering the above, does the Higgs boson “do something useful”?

    1. 1. We do not know the answer — with the exception of the W and Z, where we sort of know: the strength of the weak force is the same as the strength of the Higgs interaction with the W and Z particles, so that relates, for instance, the lifetime of the W particle, which decays to quark pairs or lepton pairs, to its mass, which comes from the Higgs field. But of course we don’t know what determines the strength of the weak force, so in that sense we don’t know there either. For the quarks and leptons, here are numerous ideas, and no hints as yet as to whether any of them is right. Many of us hope that the LHC might give us insight into that question.

      2. Your question seems a little confused, so I might have to ask you to reask it, otherwise my answer may not really be appropriate to what you want to know. What do you mean “when they already should have mass from interaction with the Higgs field?” The Higgs mechanism is the obtaining of mass of the W and Z by interacting with the Higgs field when the Higgs field becomes non-zero. So your phrasing “why X, when Y” is confusing, because X=Y.

      3. Virtual Higgs particles do not give mass to the various particles. The constant Higgs field will do the job just fine. So your conclusion is essentially correct; there are always disturbances going on spontaneously in the vacuum of our quantum world, but they are not responsible for the masses of the W, Z, leptons and quarks being non-zero. (However, there is much more to say about the role of those disturbances, not merely of Higgs fields but of all the others, in nature — but it cannot be done in a few lines. Stay tuned for an article on that someday.)

      4. 🙂 For the moment, the most useful thing it does it tell us a lot about the Higgs field and the Higgs mechanism. “Usefulness” is kind of a loaded term — useful to who? Mostly I would say that we don’t know of anything crucial that it does in the following sense: if you make the Higgs particle decay so fast that it essentially isn’t there, or if you make it as heavy as you are allowed to (about 800 GeV), there isn’t any common process in nature, or even rather rare one, that is affected very much. In fact that’s one reason why we don’t [mmm… didn’t?] know its mass, or other properties. But there’s plenty we don’t know about the universe — its early history, dark matter, etc. The Higgs particle (or particles) may turn out to be essential in the generation of the baryon-antibaryon asymmetry or in the amount of dark matter in the universe. That we simply don’t know yet.

      1. Thank You for the answers.
        Ad 2. I suppose it will be best if I just explain what I apparently wrongly understand about the matter in hope of a correction.
        – leptons and quarks get their mass through the Higgs field vev but force-carriers don’t interact with the Higgs field;
        – W and Z get their mass thanks to H+, H- and A0 in the Higgs mechanism, so not in the interaction with the field itself;
        Hence the statement “The Higgs field interacts with many of the particles of nature (and their own corresponding fields) including particles as diverse as the electron, the top quark, and the W and Z particles.” suggests I got something wrong.
        Ad 3. Then CERN is conveying misinformation 🙂
        Ad 1. Is it at least know why photons and gluons (and possibly gravitons) don’t interact with the Higgs field? And why the’re all happen to be bosons?

        1. Ok – yes, you are confused about a subtle point.

          W and Z particles DO interact with the Higgs field and DO get their masses from the Higgs field (just like top quarks and electrons etc.)

          AND ALSO

          in the process W+, W- and Z absorb H+, H- and A0

          Essentially: a massive W+ is a mixture of the original massless W+ and the H+. This is the key technical trick of the Higgs mechanism for giving mass to a spin-one particle.

          In other words, you were sort of right about the H+, H- and A0, but not quite; and so you missed the fact that the W+ doesn’t *get* its mass from H+, but absorbs it as part of becoming massive due to the non-zero Higgs field.

          So no, it doesn’t have anything to do with whether things are bosons or fermions. Higgs particles don’t interact with gluons directly because of other symmetries that forbid it. And they don’t interact with photons for a more complicated application of symmetries in the problem. [I say symmetries here but I do warn you that is slightly loose talk — really there are certain subtle constraints, not symmetries, at work.]

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A decay of a Higgs boson, as reconstructed by the CMS experiment at the LHC