# Tag Info

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Griffiths is using common-among-experts but confusing-to-beginners language. When he says, for example, that a four-vector “belongs to” the four-dimensional representation of the Lorentz group, he doesn’t mean that the four-vector is a member of the representation itself; he means that the four-vector is a member of the representation space, the vector space ...

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In general, particle physics is not NECESSARILY high energy physics. For example quantum electrodynamics describes all interactions of light and matter, not just high energy ones. However, many of the interesting states of matter that we consider in particle physics only exist at high energies. For example, types of quarks besides up and down only exist at ...

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Boson and bosonic are a noun and an adjective, such as fermion and fermionic. To answer your question directly: photon is always a boson, since it has zero spin. However one uses sometimes term bosonic particle to refer to particles that are really not bosons, but exhibit boson-like behavior. For example, excitons do not really have a well-defined spin, ...

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There is no separate word to distinguish the vector of acceleration from its magnitude. The same is true with the word force, which is also both a vector and often described by the same word when talking of its magnitude. Velocity and speed seem to be the exception, probably because speed is an everyday term, " speed of going from town A to town B&...

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A mathematician will give more detailed and rigorous answer. From the physicist point of view, representation corresponds to the way the object transforms under a symmetry group $G$. Let us assign upper index to the object $a^{i}$, that transforms like a column under $G$: $$a^{i} \rightarrow U_j^{i} \ a^{j}$$ This we will call the fundamental ...

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The decay $B_d \to J/\psi K^0_s$ was targeted (successfully!) by the BaBar and Belle experiments that first demonstrated that CP violation occurred for B mesons, as predicted by Kobayashi and Maskawa. This is because it contained a single weak phase (so it could be interpreted unambiguously), had a relatively high branching ratio, and had a very clean ...

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An early use of the term "high energy physics" (1950) is in the title of the Rochester Conference series. The corresponding proceedings can be consulted in the CERN Library

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To probe the world of the very very small, physicists need a probe method that has a very very short wavelength- otherwise it will not be able to resolve detail on very very tiny length scales. Since shorter wavelengths carry higher energy, the science of probing very very small distances using very very short wavelengths is known as high energy physics. ...

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The anti-triplet representation $\bar{\bf 3}$ is presumably the complex conjugate representation of the defining/fundamental $SU(3)$ representation ${\bf 3}$.

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When a particle physics experiment in a collider produces a certain particular outcome whose characteristics are unambiguous and which furnish strong evidence of an important effect or interaction, or direct experimental confirmation of a theoretical prediction, then the physics people refer to that one event as being "gold plated" as in "...

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I would assume that the student means non-relativistic limit (characterized by the non-linear relation between energy an momentum).

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Hardness is resistance to deformation by a sharp point. Toughness is the amount of energy absorbed during deformation (as the object is yielding), up to the point of fracture. It's possible for a substance (like a diamond) to be extremely hard and at the same time exhibit low toughness- where it can be shattered to pieces with a single well-placed hammer ...

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This is perhaps the deepest mystery in understanding quantum mechanics, and the answer is generally only explained in postgraduate level mathematics. We can start by observing that there is randomness in almost any experimental result. Classically, this is understood in terms of experimental accuracy, but it is also a general principle on which we can base ...

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Its called a wave function because it comes in the form $\frac{\partial^2 u}{\partial t^2} = k \frac{\partial^2 u}{\partial x^2}$ (or rather, the multidimensional equivalent of that). That kind of equation models all sorts of waves, the way you and I think of waves. The randomness comes when one wishes to make an observation of the particle's state. The ...

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Motional EMF: Production of electric voltage when moving a conductor perpendicular to a magnetic field. The motion generates the voltage. Hall EMF: Production of electric voltage perpendicular to electric current in a conductor in magnetic field that is perpendicular to the current. The current generates the perpendicular voltage.

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