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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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Baryon number conservation

Can someone explain me why the Hamiltonian for the nucleon field (derived from the corresponding Lagrangian) $$H_N=\int d^3xN^\dagger(\textbf{x})\Big(-\frac{\nabla^2}{2M_0}+M_0\Big)N(\textbf{x})$$ ...
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How to calculate the differential cross section in the center-of-mass frame for a process $AB \rightarrow CD$?

I'm trying to do Exercise 4.2 in Halzen, Martin's "Quarks and Leptons" In the center of mass frame for the process $AB \rightarrow CD $, show that $$\begin{array} { c } { d Q = \frac { 1 } { 4 ...
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1answer
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How a discrete z2 symmetry removes flavour changing neutral current from Two Higgs Doublet Model?

By applying a discrete Z2 symmetry to the theory of Two Higgs Doublet Model it is ensured that fermions of one type couples to only one doublet. But how FCNC is removed by doing so? Because if all ...
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Why cannot electrons be accelerated by cyclotron?

I was reading about cyclotron and it's working. I found out that electrons cannot be accelerated by this device. The reason I found was that they are too light. But I want to know why exactly ...
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Theory behind the experimental signatures of Higgs-Boson

As I understand it, the Higgs-Boson itself is unstable and has a transient existence. So, the particle detectors cannot detect it directly. Instead, the detectors register all the decay products and ...
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2answers
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Color symmetries in variant QCD

Suppose we only have two colors, for example, red (R) and blue (B) to construct the wave functions of baryons and mesons and that the color symmetry is SU (2) and not SU (3). In this situation, ...
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How $W^{\pm}$ bosons get their electric charge $\pm 1$ as opposed to $Z_0$ that have neutral electric charge?

In the 'Standard Model' book by Y. Grossman and Y. Nir, in chapter 7 (the leptonic standard model) on page 93 after defining the charge of the broken symmetry generator, i.e $Q=T_3+Y$ they say that ...
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If a particle can exert a force on itself,then can we define a whole lot of newtonian mechanics corresponding to it?

I think that it may be a broad question to be answered but if small amount of discussion is possible then it would be very helpful for all of us. Basically,I asked a question on this website a few ...
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Why do I keep getting the lifetime of the W boson as being $10^{-15}$ rather than $10^{-25}$?

I need to calculate the lifetime of the W boson given its decay width. From what I know the lifetime of a particle is calculated by dividing $\hbar$ with the decay width $\Gamma$. From my textbook $\...
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1answer
54 views

Earliest existence of particles and forces

I'm trying to understand the relation between particles and forces during the very early universe--the Planck epoch and subsequent stages as the fundamental forces separated. At what point did the ...
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How do we know that the $W$ and $Z$ bosons aren't composite?

Background to my reasoning: When the strong force was first discovered, it was considered to be the force that interacts between nucleons to keep the nucleus together and that the mediator bosons of ...
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Difference between energy and charge of an electron? [closed]

What is the difference between energy and charge for an outermost electron in a multi-electron atom (theoretically), which is less and which one is relatively more among them?
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A particle of mass $M$ decays into two particles of mass $m_{1}$ and $m_{2}$ [closed]

I can't understand how to get what the problems asks for: A particle of mass M decays into two particles of mass $m_{1}$ and $m_{2}$. A detector measures your energies and moments like this: $$E_{1} =...
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2answers
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Practical applications of modern particle physics? [closed]

I'm a wholehearted supporter of scientific discoveries. "IFLS!" Nevertheless, I'm curious what non-scientists gain from unlocking the mysteries of the universe. I found a lot of articles like these: ...
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Which is more fundamental property of matter: charge or mass? [closed]

I haven't got a whole satisfying answer to this question. I think that matter can exist without charge but it can't exist without mass. Am I correct? So this fact may be answered by asking about the ...
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1answer
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Could $\nu_e+p\rightarrow e^-+\pi^++p$ occur via the weak interaction? If so, how would be the Feynman diagram?

I checked if the reaction conservate baryon number, charge and leptonic number and it seems like it does. But I tried to draw the Feynman diagram and I don't understand how the proton interact, so ...
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1answer
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How lepton numbers and baryon numbers of a particle are decided?

Suppose a new particle is discovered how will it be assigned a lepton and baryon number? Moreover, what difference would it make if the electron had +1 lepton number and a positron -1? The same ...
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How to understand the makeup of neutral pi and eta mesons?

I know that mesons are bosons made up of quark-antiquark pairs. But when I see the list of mesons, I can see that the makeup of neutral pions and eta mesons are noted in a strange way. $$\pi^0=(u\bar{...
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1answer
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Which sterile neutrino are we looking for?

I am trying to wrap my head around sterile neutrinos. As far as I understand it, sterile neutrino is a name for every particle that feels only gravitational force. The most notable example is a right-...
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3answers
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How do we define “mass” in the context of particle physics and relativity?

In laypersons terminology, mass is defined as the amount of matter. However, consider the following: The $W$ and $Z$ bosons have mass. An antiparticle has the same mass as its corresponding particle. ...
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1answer
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Violation of the Law of Conservation of Charge in black hole?

Hey I'm a noob to physics however after reading about black holes and Hawking radiation. If a black hole made entirely out of negatively charged particles (say this black hole is made entirely of ...
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How to determine which force mediates an interaction?

I have been given an assignement gives me a number of interactions, asks me to determine which, among these interactions are permitted under conservation laws (Charge, Baryon number, Leptonic numbers, ...
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1answer
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Monte Carlo Closure Test in Particle Physics

What is the principle behind a MC Closure Test employed while analysing data in particle physics? So, what I understand here is that this test checks if one's code is working properly or not ...
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Particle Scattering: Canonical transform from superpositions of particle mixes

A particle scattering experiment can be seen as specified by the input state and the output state. A state is a superposition of particle mixes, ex.: $ \psi_{in} = \alpha \{e^+ + e^-\} + \beta {\mu^-...
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How to know how the self-energy changes the mass?

Suppose we have a Green's function of the typical form \begin{equation} G(k)=\frac{1}{k^2-m^2-\Sigma(k)} \end{equation} where $\Sigma(k)$ is the self energy of that particle. How exactly can we ...
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The number of particles in PDG, and what the data includes

I checked here for computer-readable PDG particle data, and count about 174 unique particle IDs there, which seems like an awfully small number of particles to be "every particle type there is in the ...
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1answer
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Why does electron-positron annihilation conserve parity?

I think I'm missing something quite basic here but consider the process: $$ e^- + e^+ \rightarrow 2\gamma$$ Fermions have opposite parity to antifermions so the parity quantum number before the ...
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2answers
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if mass is just entrapped energy, what entraps the energy and how they have so different properties?

According to the special theory of relativity, mass is nothing but entrapped energy. If that is true what traps the energy and how they have very different properties?
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Why are physicists so worried about P-symmetry violations, while symmetry is already violated by conventions of intrinsic parity? [closed]

As it is well known, apart from +1 and -1 parities for particles and antiparticles, for intrinsic parity also defined "by convention" parity -1 for some symmetrical particles which are own ...
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How does one modify the decay width of a particle (QFT/Thermal Field theory style) when a particle is travelling through matter

I believe a particle's decay width/rate should depend on whether they are in matter or vacuum, but am unsure of where to find a prescription describing this phenomena. Please could someone point me in ...
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2answers
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Does the wavelenth of matter waves depend upon the kinetic energy of the particle or object?

Do the properties of the waves (wavelength,frequency) emitted by a particle or object depend upon the velocity, or as to say its kinetic energy? Is the De Broglie equation $E = h \nu $ applicable to ...
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How can I show that the angular separation between two muons (that decayed from a Z boson) is $1/{\gamma}$?

I have a very relatavistic Z boson that decays into a pair of muons. The muons are directed at an angle of 90 degrees to the Z flight direction, and I need to show that the angular separation of the ...
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2answers
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Value of $\beta$ in Boltzmann statistics when degeneracy of quantum states is taken into account

The relationship between entropy $S$, the total number of particles $N$, the total energy $U(\beta)$, the partition function $Z(\beta)$ and a yet to be defined constant $\beta$ is: $$S(\beta)=k_BN \...
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2answers
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Is there a 5th fundamental force which may be responsible for the behavior of matter to be wave or a particle?

We already know about the 4 fundamental forces in nature which are gravitational,electromagnetic,weak nuclear and strong nuclear forces. There are several other questions on this website which are ...
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1answer
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Is there a sharp distinction between particles and fields?

The quantisation of the electromagnetic field, proposed originally by Plank, blurs the distinction between particles and fields. 'Point' particles become fuzzy and subject to a wave equation. Also, ...
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2Higgs Doublet Models: Mechanism to set Yukawa Couplings to 0?

I just started having a look at 2 Higgs Doublet Models (2HDM) and came across this: The general idea seems pretty simple. Introduce a second Higgs doublet that acquires a vev. The general Yukawa ...
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1answer
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How did the book derive the following Unitary Operator expression in Mach Zehnder experiment?

I'm reading Renato Portugal's "Quantum Walks and Search Algorithms". In The Postulates of Quantum Mechanics, under the heading 'Evolution Postulate', there is the Mach Zehnder experiment, with the ...
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The existence of Delta baryons was experimentally proven? [duplicate]

If we will look at the table from Wikipedia of their properties, we will find the same mass for all. That looks like a result of some calculation, rather then a result of measurement. Was that ...
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$e^+e^-\rightarrow f\bar{f}$ process in the center of mass frame

In Mark Thomson's Modern Particle Physics, page 152-153, writes the four-momenta of the particles involved in the $e^+e^-\rightarrow f\bar{f}$: $$p1=(E,0,0,+E)$$ $$p2=(E,0,0,-E)$$ $$p3=(E,+\beta E\sin\...
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Formal name for the “pianology” objection towards contemporary particle physics direction of research?

In a popular science book, an interesting objection towards the current direction of particle physics was stated. I tried to search for more on this, but got nowhere. Since I assume this is not an ...
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Particles and associated fields

When a particle is associated with a field. 1) It is said that the excitation of the field produces the particle, 2) it is also said that when the field is quantized, the quanta of the field is ...
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Average number of particles in single particle state meaning

So I was reading Fermi-dirac statistics and there is something that bothers me. I don't fully understand this line: "For a system of identical fermions with thermodynamic equilibrium, the average ...
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1answer
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Flight Tme of Neutrinos between Emission & Absorbtion

At a rough estimate,how long could a neutrino travel before striking a particle which would absorb it,& are there any neutrinos from the early days of the universe still wandering about?
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How do we know the group property of a new particle?

Suppose I have a particle $W'$ which can decay into $\mu$ and $\nu_{\mu}$ and $e$ and $\nu_{e}$. Suppose we know such new gauge bosons come from some additional gauge group added to the Standard ...
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1answer
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Vibrations in Stones and Crystals [closed]

I have read studies done that indicate certain sounds can either disrupt or reinforce the molecular structure (I think this is the terminology used) of living organisms. This is based on the idea that ...
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1answer
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Momentum Four-Vectors particle physics [closed]

I am studying Special Relativity, and am really struggling to get my head around four-vectors. I am looking at the following question. You have a particle of rest mass M and total energy E, which ...
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1answer
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How can pure leptonic interactions be mediated by the weak force?

$\mu^+ \rightarrow e^+ + \nu_e + \bar \nu_\mu$ Consider the above decay, it is given in my lecture notes as a weak force interaction. I thought the weak force was only involved when quarks change ...
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2answers
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Does the concept of compounds between the particles exist in Particle Physics?

Can you distinguish between the two different situations in the picture - a single particle, and a complex of two particles? Is the difference obvious for a physicist? How you would call that kind of ...
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1answer
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Is acceleration of particle by photon a continuous process?

There are a lot of questions, so I assigned a number to each one. Let's assume we have electron which is not moving in some inertial frame of reference. Let this electron be hit by a photon. Since ...
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1answer
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What are direct experimental evidences that quarks exist? [duplicate]

Now we have very established model of quarks explaining fundamental strong interaction. What are experimental proofs for existence of quarks and what is the name of physicist which made them?