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How do Physicists know the Higgs Field imparts mass?

  1. Jul 30, 2015 #1
    I can understand using calculations to determine if a particular quark configuration will work and not decay instantly, but how do calculations determine which particles or fields will have a specific influence over space-time if they weren't able to control the particle or field at will?

    How can physicists say that the Higgs Field is responsible for imparting mass if they are not able to control and measure the field directly?

    What, in the scientific community, actually determined that the Higgs Field imparts mass and not some other unknown field that maybe pops into existence for a short time?
     
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  3. Jul 30, 2015 #2

    Orodruin

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    So let us get one thing straight first: All fields exist everywhere at every time. It is excitations in the fields, what we call particles, which may be created or destroyed in physical properties.

    The Higgs boson has all of the properties required for the corresponding field (or more accurately, its vacuum expectation value) to give masses to the other massive elementary particles. This is based on measurements and observations of how the Higgs boson behaves.
     
  4. Jul 30, 2015 #3

    ohwilleke

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    The short answer is that we can't be 100% sure that this is what happens.

    Version 0.9 of the Standard Model didn't have a Higgs field. This version worked great except that all fundamental particles were massless and we knew that this wasn't true because electrons, for example, had mass. So, several people semi-independently came up with the most parsimonious theory that could impart mass to the fundamental particles in a manner consistent with the rest of the theory, which is a Higgs field with a Higgs boson. Experiments were able to infer from things like the W and Z boson masses and the strength of various coupling constants what the Higgs vev would have to be (246.2 GeV more or less) if this theory was correct, but it wasn't exactly clear what the mass of Higgs boson was under this theory and nobody had seen it.

    Then, not so long ago, we discovered a boson whose properties are a dead ringer for the Higgs boson predicted by the theory at 125-126 GeV of mass.

    Therefore, either the Higgs mechanism imparts SM fundamental particle with mass just as predicted, or it is some other mechanism that works exactly the same way in all respect that we have observed so far but might differ in some respect that we have not yet observed.

    In the meantime, it is convenient to assume the former for the sake of discussion and say that this is why mass is imparted, until anyone comes up with a good alternative that reproduces the boson we've called the Higgs boson with the properties that it has and the particle masses that we see in the Standard Model.

    This convention is similar to the convention of stating your own opinion without the preface "I think" because it is always implied when you make a statement of opinion that it is your own unless you say otherwise.
     
  5. Jul 30, 2015 #4

    mfb

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    If the Higgs field leads to the particle masses, their coupling strength to the field should be proportional to those masses, and we can test those couplings with the Higgs boson. If the Higgs is not responsible for masses there is no reason to expect such a relation.

    That's what experiments see, excellent agreement over multiple orders of magnitude:

    http://atlas-physics-updates.web.cern.ch/atlas-physics-updates/wp-content/uploads/2015/03/fig_17-513x492.png

    sqr_m6summary_fitmu.png


    The Standard Model makes even more predictions for its Higgs field and the particle - and all measured properties of the particle agree with those predictions.
     
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  6. Jul 30, 2015 #5

    Vanadium 50

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    This is a little like "How do we know The Odyssey was written by Homer and not another blind poet of the same name?"
     
  7. Jul 31, 2015 #6

    I'll be a little more specific. Are the physicists stating that they do not have a true and defined "entity" for the so-called Higgs Field and therefore, are simply stating that whatever is imparting mass of particles is to be called the Higgs FIeld?

    But then, even if the Higgs Field isn't relating to anything specific at this moment, only a field that imparts mass, how, in the end, did they come to prove that a particular field was imparting mass. How can you actually confirm this without being able to manipulate the field directly and possible "turn" it on or off, or increase or reduce its effect.
     
  8. Jul 31, 2015 #7

    Orodruin

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    What do you even mean by this? A field is not something you can hold in your hand. All fields are everywhere and everytime, physics is describing how the fields behave. The Higgs field as an entity is not more abstract than the electric field.

    This may come as a shock, but physics (and science in general) is not about proving something is true, it is about finding a good description of how the world behaves. There are certain things which can never be proven in a strict sense, but that could be falsified if they were not true. Such theories are good theories. Take the photon mass for example, according to the SM it is massless, but we can never prove this, just put better and better upper limits on the mass. Likewise, we can consider the effects of the Higgs field and come to the conclusion that all of the predictions which should be true if the Higgs mechanism is responsible for electroweak symmetry breaking are correct within current experimental accuracy. There is the saying that "If it walks like a duck and quacks as a duck ..."

    Do you think you can turn the electric field off? (This is a rhetorical question, the answer is "no you cannot")
     
  9. Jul 31, 2015 #8

    Vanadium 50

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    This question can be recast as "how do you know it's the Higgs field and not some other field with the same observable properties?" I don't know how to answer this. I don't even know what an answer would look like.
     
  10. Jul 31, 2015 #9
    You are confused how science works.

    Physicists don't work with absolute truths. History teaches us that it's unwise to assume that you know something with 100.00000000% certainty.

    Physicists have *theories*. They don't pretend that these theories are the ultimate truth.

    What they do say is: "I have such and such mathematical model, I use it to predict results of experiments, then I do the experiments, and the results are very close to the prediction of my theory. So this theory is good (so far)".

    Physicists do not, can not, and don't have to "prove" (what that even means?) that Higgs field imparts mass.

    Physicists want to have a theory whose "mathematical kitchen" is (a) logically consistent, and (b) predicts observed experimental results well. So far, theory which postulates that there is the Higgs field, and it gives particles nonzero rest masses, works well. If anyone comes up with another working explanation which is "better" (simpler, more elegant, ...) some can adopt that explanation instead.
     
  11. Jul 31, 2015 #10

    EXACTLY.

    The same way we know that a fluctuating magnetic field is responsible for EMF induced in a conductor, because we are able to excite it at will for testing, and its not simply the electron breaking orbitals due to random anomalies.

    It's not that I want to Higgs to be non-existent. To me the Higgs (particle and field) is as important as the possibility of antimatter propulsion. The reason I want to know if physicists are proving the Higgs Field exists because they are able to manipulate/interact it at will, is because being able to directly manipulate a mass imparting field, referring to advancements in the far future, seems to be what would be responsible for a civilization being able to develop vehicles that travel near or even surpassing the speed of light.

    The same way discovering the graviton and proving the discovery through direct manipulation would allow for massive vehicles and development outside of our atmosphere.
     
  12. Jul 31, 2015 #11

    ShayanJ

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    That's based on your ignorance of what is Higgs{mechanism, field, boson}!
    The Higgs field is not like a machine that you give a massless particle and it gives you a massive particle any time you like, under any situation you like. Higher than a certain energy scale, the world has a particular symmetry and particles are massless. When the energy is decreased, that particular symmetry is broken and some of those particles gain mass through Higgs mechanism which is caused by the Higgs field choosing a particular ground state among the infinite number of equivalent choices it has(thus the breaking of the symmetry). The Higgs boson is an excitation of the Higgs field. There is nothing here that we can exploit!
     
  13. Jul 31, 2015 #12

    Vanadium 50

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    I think you are confusing "knowledge" with "ability to manipulate". I know there is a star called Vega. I cannot manipulate it. I know the Earth's core is made largely of iron. I cannot manipulate it.
     
  14. Jul 31, 2015 #13
    I understand your point, but it's possible scientists figured out the core was largely made of iron by testing a series of ferromagnetic metals and their densities, and assumptions based on the material recovered from meteorites. Also in part to understanding why compasses pointed in the same direction.

    I just read up that scientists state planetary cores must be liquid or convection wouldn't take place. A test that could be done on the surface.

    Once again, It's not about disproving the Higgs; I just want to know how a conclusion came to be.

    Discovery is something I embrace heavily. If a singularity were to sustain itself in the LHC, well then at least we tried.

    So, let's break it down here then. The energy graphs above are used to show a high correlation between mathematical models.

    Mass and energy are correlated. May be this is where I'm having a hard time understanding how the physicists came to their conclusion. They were measuring changes in energy?

    So, how can this be considered as true mass? If the energy states of the particles drop back down again or even, somehow, reach absolute zero, would that eliminate their inertia?

    Yes, I understand the Higgs Field doesn't take away, only excite. So, I'm not asking what would happen if the Higgs Field reduced a particle's energy to absolute zero.

    If energy levels are being measured, would saying the Higgs field imparts mass be the same as stating a fluctuating magnetic field imparts kinetic energy into an electron?
     
    Last edited: Jul 31, 2015
  15. Jul 31, 2015 #14
    I take it you are still asking "How can physicists say that the Higgs Field is responsible for imparting mass?"

    The answer I already tried to give to you is that they compared predictions of the Higgs theory with experimental evidence. There are many predictions to test. ("They were measuring changes in energy?" I dont exactly understand what you are asking here).

    For one, if there is a Higgs field, it must be possible to have excitations in it - hence, one of the tests was the search that this excitation (which is Higgs boson) is in fact observed.

    The next test was to test whether this newly discovered boson decays exactly as Higgs theory says it should: see
    http://profmattstrassler.com/articl...del-higgs/decays-of-the-standard-model-higgs/
     
  16. Jul 31, 2015 #15

    ohwilleke

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    Keep in mind, that the main empirical evidence for the existence of a Higgs field, the mass of the Standard Model particles, was already known to exist and had mostly been measured with some precision (a few were discovered later), when the Higgs field was invented. The problem that forced scientists to hypothesize the Higgs field was not a problem with some strange new observation that had to be reconciled. Instead, the problem was a big fat disaster in the middle of their beautiful U(1)*SU(2)*SU(3) gauge theory. Their equations perfectly described the electromagnetic force, the weak force and the strong force except for one huge glaring flaw. All the particles in their equation were massless at a very fundamental level.

    This sucked, because the physicists trying to invent the theory knew that this wasn't true and that if this one problem with their equations could be solved that they would have this great physics theory that described almost everything in the world almost perfectly.

    The Higgs mechanism was the simplest, easiest way to solve this big glaring flaw in the mathematical structure of their theory so that fundamental particles could have mass again, although it required the creation of a new field and a new boson carrying that field, and thirteen new experimentally measured physical constants (six quark Yukawas, three charged lepton Yukawas, the W boson coupling to the Higgs boson, the Z boson coupling to the Higgs boson, the Higgs boson self-coupling constant, and the Higgs boson vev) (n.b. these thirteen constants have only eleven or twelve independent degrees of freedom and are not a minimal set of physical constants generated by the Higgs mechanism).

    In addition to causing the Standard Model which previously had just massless fundamental particles to work correctly in a world with particles that have well defined rest masses, there were basically two other consequences of the Higgs mechanism, which are empirically verifiable and have largely been verified. These consequences were basically side effects of the fix that they put into their equations that they would have preferred to do without, because they predicted things that hadn't yet been observed and didn't seem necessary, but were a price that they had to pay in order to come up with some possible solution that would make the math work out rigorously. What were these two side effects?

    1. There exists a Higgs boson which has certain properties with that are a function of its mass but otherwise were perfectly defined when it was invented and put into the equations. This was an implication of the Higgs mechanism that was not directly detected until almost half a century later. I remember that as recently as a year or two before the discovery there were serious arguments in favor of several alternatives to the Higgs mechanism about which many scholarly research articles were published that didn't require a Higgs boson (such as Technicolor). These alternatives were actively under consideration because it was looking like there might not be a Higgs boson, in which case that Higgs mechanism must be wrong. And alternatives to the Higgs mechanism would have been adopted if the LHC had failed to discover a Higgs boson, because the exclusion range of the search for it had been pretty much narrowed down to the point where it would be found where it was indeed found, or it would exist nowhere at all because reality didn't use the Higgs mechanism.

    If the masses of particles in the Standard Model arose by some other means, it would be a stunning coincidence that a particle whose reason for predicted existence and predicted properties exist solely to carry out this mass generation process in the Standard Model, just happened to exist just as predicted for some totally unrelated reason. Once we knew the mass of the Higgs boson, we instantly knew every single one of its other properties with extreme precision because they were predicted by a Standard Model that uses the Higgs mechanism to generate fundamental particle mass, and so far all of those properties (e.g. lifetime and width, decay products, spin, parity, and relationship to the top quark and W boson masses). This just wouldn't happen exactly like that if anything else were going on.

    2. When renormalization is used in the Standard Model to predict how a particular interaction will behave at a particular momentum energy transfer scale in an interaction, the physical constants of the Standard Model mentioned above and also various coupling constants of the Standard Model evolve according to their respective beta functions with the energy scale of the interaction. Basically every physical constant in the Standard Model evolves in this way with energy scale, in part, because many of them arise via the Higgs mechanism.

    For example, in an interaction taking place at 5000 TeV, the mass of the Higgs boson would be materially lower than it is in a 2 GeV interaction energy scale. The strength of the Higgs field is one of the many physical constants of the Standard Model that varies with energy scale due to renormalization group evolution.

    The renormalization of masses in the Standard Model with energy scale that has been observed over the past few decades (mostly before the Higgs boson was discovered) would not happen in the manner that it does if masses in the Standard Model arose in a manner different from the Higgs mechanism unless the alternative had exactly the same impact on the beta functions of physical constants as the Higgs mechanism does (which would make it almost indistinguishable from the predicted Higgs mechanism, bar one or two adjustable parameters, anyway).

    Keep in mind that the Higgs field is a pretty boring spin-0 field that can't do nearly as much cool stuff as more complicated spin-1 or spin-2 fields. Basically, it is a field that always has a value that is just a single number at any given point in space-time (with no direction or vector or tensor attached) which is exclusively a function of the energy scale involved in the interaction that you are using the Standard Model to analyze. Increase the energy scale, and it gets weaker, reduce the energy scale and it gets stronger up to the limiting case of the vacuum expectation value of 246.2 GeV, end of story.

    Crudely speaking, it gets weaker when it is hot and stronger when it is cold, but takes huge many orders of magnitude changes in energy scale to change in any discernible way at all. Basically, the only relevance this change in field strength with energy scale has is in near Big Bang-like conditions and because it has implications for the stability of the vacuum which is only metastable (on a time scale of roughly the age of the universe). Ignoring its renormalization won't deeply throw off your calculations with a fairly ordinary range of conditions.

    Pretty much any alternative field that imparted mass to the fundamental particles of the Standard Model would also have other side effects which aren't observed, because the Higgs mechanism is the simplest possible solution to the mathematical hole that they had in their theory, which is why several independent people once that they knew what the problem was came up with basically the same solution.
     
    Last edited: Jul 31, 2015
  17. Jul 31, 2015 #16

    Orodruin

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    Why do you refer to this as a "boring" property? It is the one property which allows the Higgs to have a Lorentz invariant vacuum expectation value and this is why we need a scalar field to do "Higgs magic". I would say spontaneously breaking SU(2)xU(1) is also "cool stuff", as you put it.
     
  18. Jul 31, 2015 #17

    ohwilleke

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    I call it boring because it doesn't produce complex chains of interactions the way that the spin-1 force fields do.
     
  19. Jul 31, 2015 #18

    Orodruin

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    Define "complex chains". I will give you that gauge fields are awesome, but that does not mean scalar fields aren't.
     
  20. Aug 1, 2015 #19

    mfb

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    That's exactly equivalent to the measurements of the Higgs boson, those results are related to properties of the Higgs field.
     
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