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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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Is there an equivalent of black body radiation for other particles?

So all objects composed of matter emit black body radiation, which is photons of various frequencies. Is there an equivalent of black body radiation for other processes? Is there gluon black body ...
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How is the fraction of a particular neutrino species calculated?

Suppose we assume that a neutrino is formed in the $\left| \nu_2 \right>$ eigenstate. Then, \begin{align} \left| \psi(x, t) \right> &= \left| \nu_2 \right> e^{-i\phi_2} \\ &= \left(...
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27 views

Muon decay - Type of interaction

Why does weak interaction occur when a muon decays? Why can't electromagnetic interaction occur when a muon decays?
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117 views

Is this Feynman diagram possible?

I have been introduced to Feynman diagrams in a particle physics University module and I just created this diagram to practice checking conservation laws: I have been told that charge, baryon and ...
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56 views

Trapping particles in a laser beam (photophoretic trapping)

so to make a long story short this topic to me is very confusing but I would really like to achieve the effect. Basically in photophoretic trapping from what I understand it is the lowest density ...
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109 views

Why is boson spin number related to attraction and repulsion?

The accepted answer to this question says Since the electroweak interaction is mediated by spin 1 bosons, it is the case that "like (charge) repels like and opposites attract". Another answer ...
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32 views

High spin for $Δ^{++}$ resulting from angular momentum of pion in relation to proton

When a pion (Spin 0) collides with a proton (Spin 1/2) the result can be a Δ++ (Spin 3/2). When I tried to look up how the resulting Spin is possible, I came about an answer I do not understand. It ...
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47 views

How 'tightly' can accelerator pipes turn?

I am designing a particle accelerator for a class. I want to know how tight of a turn an accelerator pipe can make; is there a defined maximum? Is there a calculation that needs to be made ...
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36 views

exchanged momentum in Compton scattering

I am trying to resolve a confusion regarding scattering kinematics. I am considering Compton scattering, i.e. a photon with four-momentum $k$ scatters on an electron with four-momentum $p$, the final ...
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1answer
74 views

Nuclear Instability and Q value in Alpha decay

Alpha decay: $(Z,A) \rightarrow (Z-2,A-4)+ ^4_2He $ According to the book: "Nuclear and particle physics" by Williams, $Q_\alpha$ is the measure of available energy to permit an alpha decay. It is ...
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97 views

COM frame in Relativistic particle physics

I have a home work: Consider a head-on collision of a 'bullet' of rest mass $M$ with a stationary 'target' of rest mass $m$. Prove that the post-collision γ-factor of the bullet cannot exceed:$$(m^...
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In order to observe a structure of length order of 1 femtometer, how large kinetic energy must the electron have?

According to the de Broglie relation, $\lambda=h/p$ where $h$ is the (not reduced) Planck Constant and $p$ is the magnitude of the relativistic 3-momentum. So, it should be that $\lambda$ should be ...
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54 views

What particles can move in the light-cone coordinates?

Are only relativistic particles able to move in the light-cone coordinates? Are non-relativistic particles also able to move in the light-cone coordinates?
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Why not build a particle accelerator on ground level? What is the shallowest feasible depth to build one?

Assume you wanted to build a particle accelerator in a non-commerical/non-residential area. It costs more money the deeper you want to build it, therefore you want to build it as close to ground ...
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1answer
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Useful Momentum Relation for Relativistic Particles [closed]

I've seen that $$p = \sqrt{(\frac{E}{c})^2-(mc)^2} = \frac{1}{c} \sqrt{{E_k}^2 + 2 E_0 E_k}$$ for a relativistic particle on hyperphysics and in my modern physics class. I understand that the first ...
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Value of regularization scale

After regularising a transition amplitude, we end up with an expression which depends on regularisation scale. This means that our physical observables like cross section will be a function of ...
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1answer
89 views

Computing integrals for divergent loop amplitudes?

I am trying to compute the cross-section for the diagram below with a divergent triangle loop: $\qquad\qquad\qquad\qquad\qquad$ where $X^0$ and $X^-$ are some fermions with zero and negative charge ...
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2answers
69 views

How are particles in a collision chosen?

In synchrotron particle colliders, how are the particles which are collided chosen? For the most part, collisions of different types of particles don't do anything like you might expect in a video ...
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1answer
113 views

Rho and Omega meson mixing

I am new to particle physics. So this might seem to be a trivial question. I read about $\omega$ and $\phi$ meson states being written in terms of octet and singlet state. In the same way, can $\...
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2answers
98 views

Why neutrino energy threshold in inverse muon decay is so high

In the interaction: $$\rm \nu_\mu + e\to\nu_e+\mu$$ the $\nu_\mu$ energy threshold to produce the process is $m_\mu^2c^2/2m_e$, which gives a $\sim10~\rm GeV$ threshold. For the same muon neutrino ...
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32 views

Which structure function is G(x)?

I found a question about structure functions where they ask what is the $F_2(x)$, $xF_3(x)$ and $G(x)$ shape as a function of $x$ (for a given $q^2=10$ GeV$^2$) and also as a function of $x$. I found ...
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1answer
106 views

What are significant applications of the Higgs Boson itself in the standard model?

I understand that the Higgs Field grants mass to all the matter in the universe, and is equally distributed in all parts of it, but it was the Higgs Boson that was discovered at the LHC, and ...
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42 views

How much energy is stored in the charge when electron and positron are created?

I had asked "The energy of electron formation becomes mass, charge, spin and momentum. How much becomes the charge? We know how much becomes mass: E = mc^2. What is the equation for the charge?". ...
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91 views

Matter effects contributing in solar, atmospheric and reactor neutrino oscillations

Neutrino oscillations are affected by the matter effects. For solar neutrinos, which are exclusively neutrinos of $\nu_e$ type, the matter effects can be contributed by (i) the solar plasma, (ii) ...
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301 views

How can infinite density exist?

Thinking in mind, infinite density is where there is no space between particles correct me here if i'm wrong. Inside a blackhole at the core. So if there are 2 particles touching each other Then ...
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Is translational/rotational KE conserved when diatomic molecules collide?

When two diatomic molecules of a gas collide, is the collision elastic or inelastic? Is rotational KE also conserved/not conserved? My guess is that translational KE is conserved while rotational KE ...
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2answers
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isospin conservation for total isospin or third component of isospin?

In strong interaction, is total isospin or 3rd component of isospin conversed or they are both conserved? Thank you!
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Electric field energy contribution of proton to its inertia

Quoting from the book Introduction to elementary particles by Griffiths. Here two refers to proton and neutron. Heisenberg’ proposed that we regard them as two “states” of a single particle, the ...
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1answer
63 views

Width of $\eta$ meson mass peak?

In an experiment an $\eta$ meson is produced with total energy $E _ { 0 } = 2000$ MeV in the laboratory frame. Estimate the width of the $\eta$ mass peasured in a calorimeter that has an energy and ...
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32 views

How can you explain the number of jets for signal and background components in pp to WZ?

I'm looking for events where a W and a Z boson is produced from collision of two protons, with backgrounds coming from top-antitop production, production of 2 Z bosons and Drell-Yann processes (...
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0answers
36 views

How can you explain the shape of the three lepton invariant mass plot in the case of proton-proton collisions

I'm looking for events where a W and a Z boson is produced from the collision of two protons, with backgrounds coming from top-antitop production, production of 2 Z bosons and Drell-Yann processes (...
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0answers
60 views

How can you explain the shape of the W mass peak in a transverse mass plot in the case of WZ production

I'm looking for events where a W and a Z boson is produced from collision of two protons, with backgrounds coming from top-antitop production, production of 2 Z bosons and Drell-Yann processes (...
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1answer
41 views

Can an energy-momentum four vector include the quantities of all objects in a closed system?

Say I have a particle moving along the $x$-axis in the Earth's reference frame. It decays into an upsilon and a proton, each of which has an energy of 60 GeV. They are traveling in opposite ...
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Why is the muon decay a Flavor Changing Charged Current (FCCC) process?

One way of understanding why the muon decay $$\mu^-\to e^-+\bar{\nu}_e+\nu_\mu\tag{1}$$ is a Charged Current (CC) process is to write the intermediate step through which the decay (1) proceeds i.e., $$...
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2answers
122 views

What is meant by the absolute scale of the neutrino mass?

In this review titled "Pieces of the Flavour Puzzle" the author Ferruccio Feruglio wrote in the introduction that "The origin of the parameters in the flavour sector of the Standard Model (SM), ...
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How does particle physics use deep neural networks to find particles?

Does anyone use deep learning: RNN, CNN or any other architecture of deep neural networks to asses the standard model or to detect new or unseen particles? What's the status these days in this ...
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Mean free path for $3\rightarrow 1$ scattering

I want to calculate the mean free path of an antineutrino in nuclear matter where it can undergo the reaction $p+e^-+\bar{\nu} \rightarrow n$, which I imagine will involve calculating the rate of that ...
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The significance of the infinite electric charge relating to renormalisation in QED

This question is related Significance of electrical fields of infinite objects but is not a duplicate, imo. My question is based on reading Frank Close's book "The Infinity Puzzle", which on page 42 ...
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1answer
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What is meant by “the symmetry of an interaction”?

My understanding of a symmetry is this: apply an operation (e. g. parity inversion) to a system. If it behaves the same afterwards, it is symmetric under that operation. Now, quite often I see ...
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1answer
105 views

Tensor Product Explanation

I'm currently doing a research project involving 3 particle spins and have developed a simple function for the Hamiltonian: I understand how to code my work but the physics behind it is unfamiliar ...
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1answer
52 views

What formula is used to make exclusion plot in the direct detection of dark matter?

The idea of direct detection of dark matter is that a dark matter particle striking some underground target will cause the target nucleus to recoil. From the recoil, one can determine the scattering ...
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1answer
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What do the points on a Dalitz plot represent

I have read that a Dalitz plot is nothing but the plot of $m_{12}^2$ vs $m_{23}^2$, and that the dots correspond to "events". However, this doesn't really tell me anything. My question can boil down ...
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How does gravitational time dilation affect how we age?

Suppose you could live on Jupiter without dying from anything except age, how much longer would you be able to live there compared to how long you could live on Earth?
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high $p_T$ and low $p_T$ b-jet energy correction factor

For b-jets, to get the true transverse momentum using the reconstructed $p_T$, we use a correction factor $p_{T}^{gen}/p_{T}^{reco}$ obtained using MC. Now suppose I make a plot of $p_{T}^{gen}/p_{T}^{...
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1answer
146 views

The antiparticle of photon is itself

I'm not sure whether this question is redundant, but I think it is probably not due to the focus of the question. We might say that photon does have antiparticle and it is photon it self. I know for ...
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1answer
93 views

Interpretation of the adjoint Dirac equation

Adjoint spinors $\bar{\psi}$ satisfy the adjoint Dirac equation $$ \bar{\psi} \left( \gamma^{\mu} \, p_{\mu} - mc \right) = 0 \; $$ (I'm using the terminology and units of Griffiths' "Intro. to ...
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If the PETRA accelerator only goes up to 45GeV, how can we know that Lambda of quark/lepton constituents would be greater than 750GeV?

If the PETRA accelerator only goes up to 45GeV, how can we know that Lambda of quark/lepton constituents would be greater than 750GeV, according to the 1983 article New Tests for Quark and Lepton ...
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1answer
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Annihilation of matter and antimatter of different kind

What happens when antimatter of an atom interacts with matter of another atom? For example, if I collide antihydrogen and helium. I always heard that collision or interaction of antimatter and matter ...
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Four-fermion “contact” interactions differing from those arising from the Standard Model

In the 1998 article Compositeness Test at the FMC with Bhabha Scattering, it states that: It was pointed out that the existence of quark and lepton substructure will be signalled at energies well ...
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How does Bhabha scattering imply the existence of quark/lepton substructure?

In the 1983 journal article New Tests for Quark and Lepton Substructure which covers some science and mathematics behind quark and lepton composition (theoretical). It says: Bhabha-scattering ...