# Tag Info

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If you have a scattering event with particles going IN and OUT, so we send the IN particles and measure the OUT particles. A virtual particle is just any particle contributing to the event which isn't in the IN or OUT state, i.e. it is created and destroyed during the event. The reason particles like this can exist is due to quantum fluctuations of the ...

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Yes there are "virtual" Higgs bosons. A virtual particle isn't really a particle but a ripple / disturbance in a field. So a virtual electron is a ripple in the electron field. A virtual higgs is a ripple in the higgs field. Virtual particles are just a convenient conceptual model for describing field disturbances in terms of particles. Matt Strassler ...

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The general two-particle state will look like $\displaystyle \int dp_1 dp_2 \psi(p_1,p_2) a^\dagger_{p_1} a^\dagger_{p_2}| 0\rangle$ Here $\psi(p_1,p_2)$ is the momentum-space wavefunction. Since the creation operators commute, only the symmetric part matters, so we may as well take $\psi(p_1,p_2)=\psi(p_2,p_1)$ (there would be a minus sign if they were ...

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Your interpretation is not correct. The propagator $D_{\mu\nu}(x-y)$ describes the amplitude for a photonic field perturbation to go from $x$ to $y$, with the implicit picture that you have a "source" $J(x)$, and a "sink" $J(y)$, which are perturbing the vaccuum. However, a field perturbation is not a real particle (for instance, in the photon case, the ...

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You can get information about size, shape and rotation of the emitting object. I would start here: http://cds.cern.ch/record/378753/files/9902020.pdf

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A higgs boson is created at an accelerator just like any other particle, by converting energy to mass, according to the famous equation $$E = mc^2$$ If you take the LHC as example, then protons are accelerated to nearly light speed, having enough energy to create particles as heavy as the higgs. For a particle to decay it needs phase-space (i.e. the ...

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It is incorrect to say that the energy of a string directly gives us the mass of the particle. While it is true that more the oscillations on the string, higher the mass, the relation between the oscillations and the mass it not that of a simple proportionality. What's really happening is that the string has some energy $E$ (due to oscillations on it) and a ...

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Most gamma rays from $pp$ collisions come from neutral pions ($p+p\to p+p+\pi^0$), you'd first have to do some relativistic momentum & energy conservation to determine the energy of the neutral pion. It's easiest if you consider the two subsequent reactions: $$p+p\to p+\Delta^+ \\ \Delta^+\to p+\pi^{0}$$ (it's up to you to figure out the kinematics). ...

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You cannot direct an individual photon, only the probability of the photon going into a given direction. In interactions that you are describing, a complicated one, at the center of mass, the probability distribution will depend from which level the photon emerged, if it comes from a quadrupole or higher moment charge distribution of the quark charges in ...

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On your first question: absolutely, energy gravitates (or induces curvature in spacetime) the same way that mass gravitates. If you read general relativity, you will learn that it is in fact the Stress-Energy Tensor that is the source of gravitational interaction (or equivalently spacetime curvature). Energy can be localized very easily; a parallel-plate ...

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There are two neutrinos involved, so there is a spectrum. Both the maximum and the minimum are easy to get. The most energetic case involves the two neutrinos being emitted in the same direction and the electron recoiling. By treating the neutrinos as massless (an acceptable approximation) we get $$pc + \sqrt{m_e^2 c^4 + p^2 c^2} = m_\mu c^2 \,,$$ which ...

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Usually, Cronin effect is given in terms of the central-to-peripheral nuclear modification factor for $dAu$ collisions at midrapidity $$R^h_{CP}(p_t)= > \frac{(1/N^C_{coll})dN^h/p_tdp_t(C)}{(1/N^P_{coll})dN^h/p_tdp_t(P)}$$ where $C$ central, $P$ reipheral, $N_{coll}$ the average number of inelastic $NN$ collisions.If hadronization is ...

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The time delay between neutrinos and photons does not tell us directly about the absolute mass of the neutrinos. The time delay between a neutrino of mass $m$ and a massless neutrino does: $$\Delta t = \frac{d}{v} - \frac{d}{c} \approx 0.5 \left(\frac{mc^2}{E}\right)^2 d,$$ where $\Delta t$ is the time delay in seconds, $v \approx ... 2 Here is the diagram you are discussing: It seems you are worried by the angular momentum carried by the W+. The W+ is a virtual particle in this reaction. In virtual paths the particle is off mass shell and its mass is unphysical, and angular momentum as a part of a four vector will be a complicated function also having unphysical measure, so ... 1 The W is massive so can be in the spin 0 state (or$s=-1, 0, 1$in general). The photon is massless so does not have this "longitudinal" polarization. For the massive vector boson, the relevant symmetry group is the little group$SO(3)$, and for the photon it is$SO(2,1)$. 2 The most general relationship is $$c(b) = \frac{\int_0^b \frac{\mathrm{d}\sigma}{\mathrm{d}b}\mathrm{d}b}{\int_0^\infty \frac{\mathrm{d}\sigma}{\mathrm{d}b}\mathrm{d}b} = \frac{1}{\sigma_\text{inel}}\int_0^b \frac{\mathrm{d}\sigma}{\mathrm{d}b}\mathrm{d}b\tag{1}$$ (source, one of many). In practice, we usually use the Glauber model to describe heavy ion ... 1 Positrons can be easily produced in pair production reactions, when gamma rays with energy more than 1 MeV interact in the field of a nucleus, so there is no problem in producing them at accelerator sites or even from decay products of reactor cores. For LEP in particular the positrons were generated by using an electron beam hitting a target that would ... 0 It looks like the following article is relevant: http://arxiv.org/abs/hep-ph/0402256 (published in Nucl. Phys. A). (The phrase you quote is probably from lectures http://www.physik.uni-bielefeld.de/~borghini/Teaching/HIC-Seminar/SoSe2013/Francois_SPhT2006-1.pdf by one of the authors of the article): "The Cronin effect was discovered in proton-nucleus ... 0 You are asking about a cloud chamber, not a bubble chamber. The processes observed are similar to both, the technique is different, the bubble chamber being a very precise and sophisticated instrument. Here are some tracks in a cloud chamber: The general procedure was to allow water to evaporate in an enclosed container to the point of saturation ... 1 Well, the particles won't always follow circular paths (for instance, the particles in this video). But, if you apply a constant magnetic field across the chamber, charged particles moving in the field will be deflected according to the Lorentz Force Law. The centripetal acceleration for a particle moving in a circle is$a=\frac{v^2}{r}$, where$v$is the ... 0 It boils down to balancing the centripetal force, $$\vec{F}=\frac{mv^2}{r}\hat{r}$$ with the magnetic force $$\vec{F}=q\vec{v}\times\vec{B}$$ Equating these and considering the perpendicular velocity, we get $$\frac{mv_\perp^2}{r}=qv_\perp B$$ Which can easily be solved for$q/m$: $$\frac{q}{m}=\frac{v_\perp}{rB}$$ Thus, if you know the strength of the ... 1 So, I believe that at least one of the now closed experiments (LEP, Tevatron, Hera, ...) might have published their framework and data, but I couldn't find anything on the net. Does anyone know of such a case? I have found this misconception, that the framework and the data might be published or even should be published. It is like asking for a mission ... 3 They mean that the ionized molecules become the "seed" or "basis" or "nucleus" (= form centers) for the formation of tiny liquid water drops / bubbles. The drops / bubbles can easily form around some "seeds" (centers). Ionized molecule is enough to become such a "seed". 5 The interaction mediated by a massive boson will produce interaction potential of Yukawa type: $$V(r) = - \frac{\alpha_\chi}{r} e^{-mr},$$ As is well known, a scalar exchange leads to a universally attractive potential, whereas a vector exchange will attract particles to antiparticles, but repel pairs of particles or pairs of antiparticles. For Z-boson ... 2 Now that we know the mass of the Higgs boson, which system would be better for the production of Higgs bosons, the LEP ramped up or the LHC? LHC was designed as a discovery machine, whereas LEP was designed as a precision machine that would clarify the discoveries of SPS, the previous hadron collider at CERN. I think it was Feynman who said , I ... 5 It's a scenario that has heavy scalars and relatively light gauginos, so it's one example of a class of "split SUSY" or "mini-split SUSY" scenarios that have survived most of the constraints. In this kind of scenario, collider bounds put the lightest superpartners, namely the winos, above about 270 GeV. Gluinos are constrained to be somewhere north of a TeV, ... 0 I think that this problem doesn't have an exact answer. Some time ago, I talked about this with the astrophysicist Paolicchi (this is the asteroid named after him) who works on the field. The conclusion is that debris are produced at random and you can only impose some ("few") constraints globally, say on big branches of the asteroids belt or of planetary ... 1 Our studies of elementary particles have concluded that there are four fundamental interactions between them, and, as all matter is composed ultimately of elementary particles all matter is governed by these four. The strength of the fundamental interactions is given by the coupling constants which are constants multiplying the integrals which describe the ... 1 The confusion comes because you are thinking of probability waves, which is what the interference pattern from elementary particles through the double slit experiment are, as if they are classical waves. Current day physics accepts that the fundamental framework of nature is quantum mechanical. Classical mechanics, classical electromagnetism are emergent ... 1 Scalar fields do transfer momentum in classical physics. Just take a look at acoustic signals in a gas. A strong sound can cause your windows to rattle. A well known example of energy transference by means of sound (pressure waves) is demonstrated with tuning forks. Quantum theory speaks of sound as particles (phonons), the discrete quanta of quantized ... 0 At very low energy one can consider effective forces such as Vanderwaals forces and induced dipole magnetic forces ("split off" from the electromagnetic force), or the nuclear force ("split off" from the strong interaction). "Very low energy" is basically the world you see around you through your own eyes, so I'm sure you can make up more examples yourself. ... 6 As far as I understand, due to conservation of angular momentum, the resulting system of neutral pions would need to have angular momentum 1, therefore, the identical neutral pions would be in an anti-symmetric state, which does not seem possible as they are bosons. Note that a neutral rho meson can decay into two neutral pions and a$\gamma$, although this ... 1 This thread will inevitably descend into a semantic and/or philosophical discussion unless we have some at least somewhat precise notion of what it means for particles to be the "same". In modern physics, elementary particles are fundamentally treated quantum-mechanically, and in quantum mechanics, they are modeled as being exactly the same in the following ... 0 I'd say two electrons can differ, e.g., by their spin projection on some axis. 0 All elementary particles of a particular type, e.g. all electrons, are excitations of the same quantum field, and are all identical and indistinguishable. Because of the uncertainty principle, one cannot distinguish such particles by even their trajectories. 0 Muonic atoms should be stable in electron-degenerate matter (white dwarf material) as long as the Fermi energy is more than$m_\mu - m_e$. This is more or less exactly a analogy with neutron stability in the nucleus where the the protons are effectively in a degenerate state. Any answer has to forbid electrons (which isn't going to be possible as they share ... 9 I believe that the "roughly" term is applied because of the associated experimental error when measuring its charge. The same cannot be said to the electron because "we" decided to make the electron the reference charge. So, the reference charge is definitely -1. However the muon charge must be measured. According to this paper, Muon Mass and Charge ... 3 Now that we have seen the Higgs boson, all the particles predicted by the Standard Model have been discovered. The penultimate particle to be discovered was the tau-neutrino at Fermi-Lab in 2000. The antepenultimate particle to be discovered was the top quark, also at Fermi-Lab in 1995. For a complete timeline, see e.g. this wiki page. There are, of ... 1 First of all, it is the NATURAL behavior of ALL particles (with our without mass), to move along time-like geodesics (if they're massive) or null geodesics (if they are mass-less). So they could accelerate relative to each other (without any external or external forces). Moving along geodesics could pull the particles together or even scatter them to the ... 2 MHV amplitudes are not really any more important than next-to maximal helicity violating amplitudes ($NMHV$) or$N^kMHV\$ amplitudes. You need all of them to compute a general scattering amplitude. Basically, scattering amplitudes for non-Abelian Yang Mills theories are very complicated to compute for more than 4 particles, so people work on formulating ...

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Until recently, quark masses were thought to be one-third of a protons' (612 "electrons"). Now, experimentalists state "bare quark mass" to be about one percent of this at any given moment (based upon their observations). But a difference exists between how positive and negative charges carry mass because the more massive quarks (e.g. "top") are positive ...

3

Neutrino mass is not in conflict with electroweak theory. One can introduce neutrino masses by modifying the Higgs or lepton sector of the Standard Model. The simplest method, that which you propose, is introducing a right handed neutrino with a Yukawa coupling with the left handed neutrino (extending the lepton sector). The right handed neutrino, however, ...

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