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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Why is the energy shift due to a 'sagging' potential negative and independent of box size?

Consider a box of width $L$ and the composed of the following potential $$V(x)=\frac{V_0x(x-L)}{L^2}, x\in[0,L]$$ and $V(x)=\infty$ elsewhere. Using perturbation theory - with a square box as the ...
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31 views

How would one go about drawing a Feynman diagram of color screening and anti-screening in QCD?

Title really explains this one. I'm not sure how to put together a diagram of the lowest order for colour screening and anti-screening in QCD. Seems to be a lack of diagrams for this in the ...
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44 views

How to draw Feynman diagram for K^- + p -> Sigma^0 + pi^0 — superposition in diagram

I'm trying to draw the Feynman diagram for the reaction $$K^- +p \rightarrow \Sigma^0 + \pi^0$$ I have two problems: How to draw the $\pi^0 = (u\bar u + d\bar d)/\sqrt 2$, a superposition of ...
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1answer
43 views

Pion decay: why is the positron electron neutrino decay suppressed?

I'm reading through M. Thomson's Modern Particle Physics to better understand why the positron electron neutrino decay channel is suppressed relative to the muon and muon neutrino decay route. I know ...
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1answer
35 views

What experimental measurement could be used to show that a neutrino is a Majorana and not a Dirac particle?

I've just been reading something on the concept that neutrinos could be Majorana particles and not Dirac fermions. I was wondering what experimental measurement could show/prove that neutrinos are in ...
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0answers
54 views

Explanation of graphs from CERN [closed]

I have a few questions about these kinds of graphs What is the name of this type of graph? What does the width of the peak mean? If the points are data points, how was the curve created/predicted? ...
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35 views

Gravitational entropy [duplicate]

In the beginning (big bang), mass was evenly distributed (if you consider an elementary particle as an extended object, like a circle on a very thin cylinder, with a radius near the Planck length, but ...
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1answer
16 views

Semileptonic decay of neutral D meson: branching ratios?

I am looking for the branching ratio of the semileptonic decay of the neutral $D^0$ meson: BR($D^0 \to \pi^+e^-\bar\nu_e$) = ? According to the PDG book the branching ratio for $D^0 \to ...
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1answer
44 views

What determines the color of photon that is emitted from an exited atom?

I understand the principle of how light is emitted from an atom. What I don't know is why neon atom is red and copper is green when exited? Is is the distance between the electron to protons or the ...
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0answers
29 views

Are alpha and beta rays also generating electromagnetic rays?

To discover radio waves in 1886, Hertz used electric sparks between two iron balls. These sparks caused radio waves which generated a current between other balls. The oscillating charges caused a ...
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3answers
109 views

Why is $np$ always equal to $n_i^2$?

For you guys who studied semiconductor physics must be familiar with the equation: $$np=n_i^2$$ I can understand why this is true for the intrinsic case (the broken bonds would always provide ...
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1answer
47 views

Fine structure constant and unit conversion [closed]

In a paper I'm reading, the author writes down the following formula: $$\Gamma=\dfrac{\alpha^2}{576\pi^3}\dfrac{\left(4+z\right)^2}{z}\dfrac{m^5}{m^2_\pi f_\pi^2}$$ $\Gamma$ is a function of $m$ (in ...
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1answer
68 views

How do I calculate the differential cross section with respect to the transversal momentum?

First of all, sorry for my English, my first language is German. My problem is: I calculated the matrix element of the quark-gluon-Compton process (q+g -> gamma + q). With the kinematics of ...
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0answers
47 views

I want to know about the quantization of mass [duplicate]

Is mass quantized? If yes, then why do we see all amounts of mass? Well , can it be said quantized just for smaller masses?
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1answer
34 views

Differential cross-section for a 2-particle process in the LAB frame

This should really be a straightforward calculation, but somehow, I keep confusing myself and failing over and over again. I did the calculation so many times that I don't even know what I'm looking ...
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1answer
123 views

How do (and don’t) particles emerge from fields?

I am aware of the following field- and particle-like notions: QFT particle, a unit of excitation in (the Fock space of) a QFT; SR field, an extremal $A = A(\mathbf x)$ of a Lorentz-invariant action; ...
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3answers
3k views

How can an electron fake a jet?

This is a question for experimentalists. I have seen in several ATLAS papers (see for example chapter 4 in arXiv:1602.09058, 6th paragraph), that after objects have been correctly identified, any jet ...
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16 views

Conjugation Operator General Question

I’m sitting here reading my particle physics book, and the Conjugation Operator is defined as: $C = -(-1)^{S+1}(-1)^{L}$, where $L = $ relative angular momentum for the $q\overline{q}$ pair for a ...
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0answers
42 views

Neutrino interaction probability [closed]

Just a quick question, if a single 1GeV neutrino (muon neutrino) were fired at a block of iron with a given density, $\rho$, and the neutrino-nucleon interaction cross section is $\sigma$, what would ...
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0answers
57 views

What is more fundamental $E=\hbar \omega$ or $E=c\hbar k$?

Let us say I have a massless particle (not necessarily a photon) then in a medium where $\omega \ne c k$ (e.g. a dispersive medium) what is the energy of the particle? As my title indicates are think ...
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1answer
12 views

Adjoint Dirac equation (in momentum form) from Dirac eq in momentum form method

I just wanted to check the method I have formulated for the derivation for the adjoint Dirac equation using Gamma matrice notation. This is a problem from the very excellent "Modern Particle Physics" ...
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1answer
29 views

Motion of an electric charge within an electric field with two electric charges

Assume that air resistance and gravity are negligible and the only significant force acting in the scenario is the electric force. There are two electric charges, both with an equal and positive ...
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1answer
50 views

Sequence of topics for studying quantum theory (Research strategy) [duplicate]

I am trying to learn about the higher level basics of physics. I want to cover up all that is included in particle physics/quantum physics. Now being in high school, I only know partially about ...
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1answer
27 views

Taking Measurements of Quantities in QM

I have a quick question relating to Annihilation and Creation operators, and in taking observables in general. Let's say, for instance, that I prepare a particle so that I consider the projection of ...
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45 views

Calculating statistical significance of peak over background in counting experiment

I histogrammed the invariant masses of particular events in a counting experiment. There is a specific peak which towers over the expected exponential background. How can I give the statistical ...
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2answers
38 views

Evaluating double-slit experiment for wave-particle duality

Is it possible that the wave-like behavior of particles in double slit experiments is just an outcome of particle distribution? Can we regard or treat a normal or Gaussian distribution as wave-like? ...
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1answer
79 views

How does the uncertainty principle relate to quantum fluctuations?

I found a webpage that just kind of mentions the uncertainty principle lightly but doesn't really go into detail as to why we need it in the first place when considering quantum fluctuations and ...
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1answer
40 views

What are all charge-like quantum numbers?

What are all charge-like quantum numbers? In particle physics there are often things (like charge conjugation) that apply to all charge like quantum numbers. Everytime I read something about ...
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1answer
553 views

Why is the charmed eta meson its own antiparticle, but the neutral kaon is not?

I have a limited understanding of antiparticles, so this may be why I am unable to explain why certain mesons are their own antiparticles, while others are not. My understanding is that antiparticles ...
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1answer
45 views

Why positron emission is unlikely to occur for nuclei with an excess of neutrons?

Is it because a neutron decays into a proton and electron rather than a positron. Which type of nucleus emits positron and which emits electrons . Is it something to do with beta plus and beta minus ...
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1answer
34 views

Symbol $p^{0}$ of particle [closed]

This is a very trivial question, but I cannot seem to find the answer anywhere in a textbook or the internet. My question is, what particle is represented by this symbol? $$p^{0}$$
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1answer
50 views

Magnetic field of rotating capacitor [duplicate]

Does the rotating charged capacitor (both plates) produce magnetic field? and what about rotating both plates in opposite directions?
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If matter and antimatter repel, how do we know other galaxies aren't made of antimatter? [duplicate]

Wikipedia's article on antimatter says this: There is considerable speculation as to why the observable universe is composed almost entirely of ordinary matter, as opposed to a more even mixture ...
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41 views

Lepton and strangeness conservation [closed]

Do I have a misunderstanding here at all? The question states: One of the following equations represents a possible decay of the K$^+$ kaon. \begin{align}\mathrm K^+&\to\pi^++\pi^0\\\mathrm ...
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1answer
35 views

Derivation for the most probable macrostate for distinguishable particles using lagrange's method of undetermined multipliers

We have an expression for $\Omega$ (occupation of each macrostate) in terms of $n_i$ (occupation numbers) . We want to find the $n_i$ which maximises $\Omega$. We now that ...
3
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1answer
72 views

Interpreting the Cross Section Ratio R

Below is experimental data for the ratio $$R=\frac{\sigma(e^+e^-\rightarrow hadrons)}{\sigma(e^+e^-\rightarrow\mu^+\mu^-)}$$ as a function of the centre of mass energy $\sqrt s$. I am interested in ...
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1answer
30 views

Adjoint momentum Dirac equation

So we have the commonly quoted momentum space version of the Dirac equation and the adjoint Dirac equation: $$ (\gamma^{\mu}p_{\mu}-m)u=0 $$ Often, we are asked to show that the adjoint momentum ...
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1answer
41 views

Wavefunction of a system of particles

A three-dimensional volume $V$ contains a certain number $N$ of electrons and they can't escape the volume $V$. Assume for simplicity that the potential $\mathcal{V}(\mathbf{r})$ is zero in all the ...
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0answers
44 views

Lagrangian derivation of Thomson scattering cross section (ie photon-electron)

Does anyone know a quick way to obtain the classical Thomson scattering scattering cross section (for photons scattering on electrons) from quantum mechanics/quantum field theory, avoiding the lengthy ...
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1answer
88 views

How does Bremsstrahlung occur in a vacuumized particle accelerator?

In our electrodynamics course we have learned that accelerating a charged particle will lead to a loss of energy in the particle due to Bremsstrahlung. The exact amount of power radiated away is given ...
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0answers
37 views

Identical Particle Wavefunctions

Consider the process $$\rho^0\rightarrow\pi^0+\pi^0$$ The $\rho^0$ has $J=1$ whilst the two pions have $S_{tot}=0$ and thus require $L_{tot}=1$ by conservation of angular momentum. Consequently this ...
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2answers
102 views

How can $\Lambda^0$ and $\Sigma^0$ both have $uds$ quark content?

Title says it all: How can $\Lambda^0$ and $\Sigma^0$ both have $uds$ quark content? Doesn't this make them the same baryon?
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1answer
27 views

The highest photon energy ever measured and transplanckian energies

What is the highest energy of we have measured of a photon by any physical experiment? Has a transplanckian energy photon been measured? Can we study them -if they exist- with special relativity?
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1answer
56 views

Tree Level Feynman Diagrams of Electron Positron Interaction

Consider the interaction $$e^-+e^- \rightarrow e^-+e^-$$ The following is a tree level Feynman diagram for this: We can also make the paths of the two electrons on the right hand side cross over and ...
3
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1answer
45 views

Symmetry responsible for equality of masses of particles

During my studies of basic particle physics the following question came up. What symmetry is responsible for equality of masses of particles and their antiparticles? In particular, is this symmetry ...
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0answers
25 views

Topics important in electrodynamics for particle physics

Say I'm going to study Griffith's electrodynamics, what are the important topics in it, for particle physics? Like Maxwell equations etc.
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16 views

Can energy be organised into elemental form other than hydrogen?if yes,then how?

I wanted to know whether energy can be organised into elemental form easily. If is so then , can antimatter be generated in a similar way other than pointing high intensity laser at some metal foils ...
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30 views

Helicity of massive particle at high enengy

We know that massless spin-1 particle like photon only has two helicity state (-1,1), what about the helicity of massive spin-1 particle (W boson) at very high energy? Does it have helicity 0 state ...
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72 views

How do single photons travel from here to there

I know there have been similar questions but I'm still unclear what the overall consensus is. (1) I assumed and have read that photons travel in straight lines unless deflected by gravity but there ...
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0answers
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The energy of our universe [duplicate]

Is there a substantial basis for the claim that the total energy of our universe is zero? I just read a bit of Hawking's writing in which he comes to this conclusion through inflation theory, but i ...