Questions tagged [particle-physics]

Particle physics is the study of the fundamental forces of nature as they are embodied in the interactions of elementary and composite particles at high energies and short time and distance scales.

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Are electric force and strong force equal in magnitude?

Should the electric force and the strong force be equal for a nuclei to be stable? Because if perhaps, the strong force is now more than that of the electric force, then shouldn't the nucleus collapse ...
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Stern-Gerlach experiment

In the Stern Gerlach experiment, one can determine the value of $j$ (eigenvalue of $J^2$) by counting the number of discrete lines formed on the screen. For instance, if I count 7 discrete lines on ...
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The evolution of parton distribution functions (PDFs) is always soft?

I am currently studying the PDFs evolution of the proton. In all books I've use to study this topic (Halzen & Martin and Leader & Predazzi) and in all papers I've seen the graphs of the ...
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How does QFT describe an electron in a magnetic field?

Is the electron represented by some kind of wavepackage (localized in space) or by a Fock state and not localized in space? Does then a collapse of the wavefunction occur when one sees the points of ...
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Does a Higgs Boson propagate in space? [closed]

Since a Boson my first guess is that it can propagate through space however because its zero elementary spin compared to the spin 1 of other Bosons I guess it has not helicity. Does this mean that for ...
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Are there things with different physical attributes that serve exact same purpose in a system? [closed]

I’ve been puzzling about this cross-disciplinary concept for the last week. Can you think of any two things that have different physical make up that serve the exact same purpose? For instance, ...
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Subquantum kinetics as an emerging new physics? [closed]

What do the Stackexchange physics community think of Subquantum Kinetics (SQK)[1], as a new emerging physics paradigm to explain phenomena on the microscopic and macroscopic/astronomical levels? ...
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Does String Theory predict things like Unruh effect and Hawking radiation?

I've seen the other post about this, but the answer only discusses Unruh effect rather than String theory. Hawking radiation and Unruh effect solidify fields as the universe's fundamental objects. ...
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Does photon energy affect deflection of a beam of light in a gravitational field? [duplicate]

Does photon energy affect deflection of a beam of light in a gravitational field? According to general theory of relativity angular deflection of a beam of light in a gravitational field is $$φ = \...
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Does laser trap atom cooling change the electron shell levels?

Do the electron orbits change during the cooling of the atom in a laser trap? When cooling down, do the electrons come closer to the nucleus of the atom or do they move away? Or do the electrons leave ...
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Is metaphysics a subject that should replace physics and philosophy? [closed]

I'm really seeking some insight and the following may seem opinionated, but it's really my observations and I could be wrong and I'm completely open to hear thoughts and correction from anyone. If ...
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Do electrons combine to form a single particle

I was reading about exchange interactions and stumbled across this website that was discussing symmetry and the exchange interaction. The website stated The exchange interaction is originated from ...
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Would the Rutherford gold-foil experiment work inside of an alcohol cloud chamber?

Basically as the question asks, if you set up an alcohol vapor cloud chamber with the gold foil inside, wouldn't you be able to "see" the alpha particle's path the entire time? It just seems ...
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2 answers
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What causes an electron and proton to combine into a neutron?

I know that electrons and protons can interact with each other via the weak force to form a neutron and an electron neutrino. This can happen as a result of electron capture or during the formation of ...
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Gyromagnetic precession of electron inside a homogeneous electrostatic field?

Would an electron placed inside a homogeneous electrostatic field (i.e. the static field between the parallel plates of a fully charged capacitor) in addition to being accelerated towards the ...
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Is spin of elementary particles same as the rotation of a planet? [duplicate]

By the word spin of elementary particle, one would imagine the particle to be rotating around its own axis, just like a planet rotates, but is it actually true? While spinning does an elementary ...
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Can we detect and measure color charge?

I was listening to the "Why This Universe" podcast about dark matter and Dr. Dan Hooper mentioned briefly that electric and color charge can be readily detected. Can color charge be ...
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Can a x ray see its own reflection ? / Is opisitional force present between two x-ray transmitters? [closed]

If you downstage a particle exselerater to the point before a black Hole is created ,would an x-ray see its self before the big bang,I which creates the black hole?
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Black $p$-brane solution

Im trying to confirm that the metric (11) in the paper below is a solution to Einstein's equations (6). I tried to use the metric and extract $\lambda=(1-(r_+/r)^{D-3})^{1/2-\gamma/2(D-3)}$ and $R=r(1-...
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Are the sources in QFT just particles?

I'm reading A. Zee's Quantum Field Theory in a Nutshell, where he introduces QFT using path integral formulation. One thing that I'm not sure I got correctly is this: Zee adds a source term to the ...
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Signal "reflection" in mass distribution

A paper I am reading shows a plot with an invariant mass distribution with roughly two peaks, one at lower mass and another at higher mass. The paper says that the lower mass peak is a "...
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1 vote
1 answer
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How do alpha particles heat the plasma in tokamaks and what does that trajectory look like?

In a tokamak, a toroid with toroidal and poloidal magnetic fields, Deuterium and Tritium (D-T) fuse at ~10 keV to produce an alpha particle (3.5 MeV) and neutron (14.1 MeV). The magnetic fields ...
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Is the Higgs field stronger in the presence of mass?

An EM field from a transmitter is stronger at the source than a light-year away. A magnetic field is stronger at the magnet than 1000 km away. A gravitational field is stronger near the mass than ...
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Does the Higgs field create time? [closed]

In my ongoing series of time questions, here is another. Particles with mass experience time, example, radioactive particles decay at a predictable rate and in accordance with time dilation. Massless ...
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Are neutrons and protons stable inside atomic nuclei?

Some people naturally assume that atomic nuclei are made of protons and neutrons. That is, they are basicly clumps of protons and neutrons that each maintain its separate existence, like pieces of ...
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Confusion about probability densities of the MB Distribution

The probability of a particle being at speed $v$ or its corresponding energy $E$ via the MB Distribution $f(v)$ and $f(E)$ is $$f(v)\cdot dv=f(E)\cdot dE$$ To make this equation valid, either the $dE$ ...
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Gravity affects neutrons

A long time ago I asked whether gravity affected subatomic particles. An experimental physicist kindly explained that it's known to affect neutrons. Get a neutron source, and send a beam of neutrons ...
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photoproduction process (vector mesons)

I am reading a paper on photoproduction. I have a question about the following statement: We propose "Z(4430)$^{\pm}$ can be produced by the meson photoproduction process $\gamma$p$\rightarrow$...
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The Dirac equation predicted the positron. Does the Dirac equation also suggest the existence of muons?

The Dirac equation is given by: $$ (i\partial \!\!\!/ - m) \psi(x) = 0$$ It famously predicted positrons by suggesting negative energy solutions. First it was solved with the 'Dirac sea' and positrons ...
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What kind of experiment could measure the total sphericity of the electron's monopole charge $E$-field? [duplicate]

As far as I know this was never experimentally undertaken with a high precision measurement, probably by measuring the $E$ interaction field around the monopole charge of an isolated electron (i.e. ...
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1 vote
1 answer
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On weak interaction and right-handed particles

The weak interaction involving $Z^0$ boson has the following expression for its current: $$ g_{\rm{z}}J_\mu^Z = \frac{g_{\rm{w}}}{\cos \theta_W} \bar{u}\gamma_\mu \left\{g_L\frac 1 2(1-\gamma_5)+g_{R}\...
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Is mass spectrometry convenient to separate elements in a mixture?

Are particle accelerators coupled to spectrometers ever used to separate and extract different components of a mixture? If so, how much substance can be treated per day in this way? Would it be a ...
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1 answer
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Mesons sea and valence contribution

I want some clarity regarding sea and valence quarks. Is sea quarks and gluons contribute in the properties of mesons like masses, spin distribution etc. and how they will contribute?
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Phase space of $\phi$-Meson decay

A $\phi$-Meson can decay into an electron-positron-pair or a pair of Kaons. In which decay is the phase space bigger?
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On neutral Kaon mixing

Kaons are not eigenstates of $CP$: $$ CP|K\rangle =|\overline K\rangle\\ $$ Why do we need to mix them? One answer I read is "since they both decay into $2$ or $3$ pions". Couldn't they ...
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1 vote
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What determines if a pair of properties/variables have an uncertainty relationship?

One of the most common definitions of the Uncertainty Principle is that it states one cannot measure both the position and momentum of a particle to a "perfect" accuracy (probably not the ...
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4 votes
1 answer
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Does QFT Imply Strings the Same Way that String Theory Implies Branes?

It is part of every introductory course on string theory (e.g. Tong) that the open bosonic string in $D = 26$ dimensions with Neumann-Neumann boundary conditions for directions $a \in \{0,\dots,p\}$ ...
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Why doesn't environmental decoherence completely prevent from happening the quantum tunnelling of macroscopic objects? [duplicate]

A macroscopic object has the order of Avogadro’s number of particles. That’s over $10^{23}$. So the probability of all of them tunneling, at the same time, is on the order of that original small ...
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2 votes
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Amplitude of fermion decay with Majorana mass insertion

Consider the following Lagrangian, $$ L \supset \frac{1}{2} m \overline{\psi}\psi^C + g \phi\, \overline{\chi}\,P_R\,\psi + \rm{h.c.} $$ where $\psi$ is a heavy fermion with a Majorana mass $m$, $\phi$...
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Boost of massless particle (eq 2.5.44) from Weinberg QFT

In volume 1 of Weinberg QFT, equation (2.5.44), the general boost of one-particle state L(p) from standard momentum vector $K^\mu=(0,0,k,k)$ to $p^\mu$ is expressed as $$L(p)=R(\hat{p})B(\frac{|p|}{k})...
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Mass of Antiparticles

Why do the mass of anti-particles have to be exactly equal to the particles ? What I learnt from Srednicki Chapter 23 is that to support charge conjugation symmetry (C-symm) of Lagrangian, mass of ...
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-1 votes
1 answer
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A spin-1/2 particle A undergoes the decay $A \to B + C + D $, where it is known that B and C are also spin-1/2 particles

The complete set of allowed values of the spin of the particle D is? Now the answer that I am getting is: 'Spin of the left side and combined spin of the products must be same to conserve the spin ...
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1 vote
1 answer
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On the quark composition of baryons

Baryons are made of three quarks, in the form $\vert qqq \rangle$. If we consider just the isospin doublet $u$ and $d$, there are 8 total possibilities: Now, the first 4 are respectively $\Delta^{++}...
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Experimental results for the measurement of Positron lifetime / Positron decay [duplicate]

It is assumed that the positron, being the antimatter particle of the electron, is stable. I am interested in finding experimental results or experiments which have measured the positron lifetime in a ...
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On synchrotron oscillations

Citing from Buckets and Bunches: taking a closer look at LHC: Imagine two particles in a bunch: particle $A$ which has energy (or momentum) corresponding properly to the RF frequency, and particle $B$...
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3 votes
2 answers
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Why do we give so much importance to energy, i.e., the conserved quantity under time symmetry?

In almost all equations—from GR to QFT—energy conservation is a tool for solving those equations, but we know that energy on large scales is not conserved. Why do we still use this (not) conserved ...
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What's is the energy spectrum of Xray generated by Xray tube?

The energy spectrum of Xray generated from Xray tupe looks like the shape in the following picutre. As we know the continuos spectrum is contributed from bremsstrahlung. And in the high energy ...
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2 votes
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On the analogy between RF cavities and parallel RLC circuits

Every superconductive radio-frequency cavity can be seen as a parallel RLC circuit, as shown in the picture below: The thing is every parallel RLC circuit acts like a band-stop filter: at the ...
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2 votes
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Charged fermions have both chiralities, with the same mass. Shouldn’t neutrinos, also massive, have both chiralities, though with different masses?

Thanks to answers a previous question, I have realised the difference between helicity, a non-Lorentz-invariant quantity, and the Lorentz invariant chirality. Let me summarise what I understand, ...
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On slip factor and phase transitions in particle accelerators

In a uniform magnetic field $B$, a particle with mass $m$, charge $q$ and initial velocity $v$, undergoes a centripetal force (Lorentz force) which makes it travel on a circular orbit, with angular ...
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