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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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Quantization during phase transition

Consider a scalar field $\phi(t,\vec{x})$ in $\mathbb{R}^{1,3}$ with the following lagrangian $$ \mathcal{L} = \frac{1}{2}\partial_\mu\phi\partial^\mu\phi - V(\phi) $$ where $V(\phi)$ is such that ...
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0answers
22 views

Bosonic commutation relations for force carriers?

Why are force carriers bosons? The easiest answer that I can give myself is that the gauge field $A_\mu$ is introduced like this: $$ \partial_\mu \rightarrow D_\mu = \partial_\mu+ieA_\mu, $$ so it ...
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0answers
38 views

Can a system that has no energy ,generate energy from nothing? [on hold]

Let's imagine a simple story : In the beginning there was NOTHING ,0 spacetime , 0 energy , 0 matter,no darkness,no light,no cold,no heat,0 dimensions, just absolute NOTHINGNESS.For energy to exist ...
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2answers
66 views

Can a proton and an electron annihilate in a gravitational field?

According to this Physics.SE comment, it is gravitationally allowed, though very unlikely, for a proton and an electron to annihilate yielding two photons. Is that correct? If so, why? (In ...
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1answer
149 views

separation between two Gaussian distributions

I do not understand when two Gaussian distributions are considered separated, given the resolution of the variable. Let us suppose we want to know if the difference between two times of flight is ...
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0answers
23 views

Charge operator applied to matrix multiplets

In the context of SM ($SU(3)_C\otimes SU(2)_L\otimes U(1)_Y$) the charge operator is $Q_{SM} = T_3 + \frac{Y}{2}\mathbb{I}_2$ and gives us the fermions charges. Here $T_3=\frac{1}{2}\sigma_3$ is the ...
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3answers
105 views

Difference between $W^-$ and $\pi^-$

Maybe it's a very naif question, but what is the difference between a $W^-$ and a $\pi^-$? I mean they both change a $d$ into a $u$ right? $d \rightarrow u W^- \quad \text{and} \quad d \rightarrow ...
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0answers
20 views

Decay of (pseudo)scalar particles

I consider the process $\phi\rightarrow\bar{\psi}\psi$, where $\phi$ is (pseudo)scalar and $\bar{\psi}$, $\psi$ are anti-fermion and fermion, respectively. So, how I can distinguish the process with ...
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1answer
51 views

Is every particle sustained ripple in its respective field?

This is neither a homework nor a calculational question, but more of a conceptual one. I was wondering can every particle; that is, the ones indivisible (because divisible ones can be broken down ...
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1answer
35 views

Maximal Parity violation in Weak interactions

In 1956 Lee and Yang proposed parity violation of the weak interactions to explain the $\theta-\tau$ puzzle. The following year, 1957, Madam Wu and collaborators found that in the $\beta$ decay of ...
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1answer
151 views

Normalisation factors for Monte Carlo backgrounds

I am currently starting to get involved in particle physics. I often hear of normalization factors for Monte Carlo backgrounds denoted by $\mu$. So for example if someone talks about his normalization ...
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39 views

Assuming standard pressure and temperature, how far would a given air molecule move in 1 hour

I'm trying to calculate how far a given Air Molecule would actually traverse in a room in 1 hour assuming standard states (i.e. thermal equilibrium and approximately standard temperature and pressure.)...
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1answer
157 views

On-shell Condition for physical particles in QFT

Last year Prof. Ashoke Sen proved Soft Theorems for gravitons for generic theories of gravity. The papers are exceptionally well-written and I think I understand most of it (partly due to the lecture ...
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1answer
32 views

Inverse Compton scattering

Given a collision between a high energy cosmic ray proton (~$10^{20}$ eV) and a CMB photon, I want to calculate the final energy of the photon. I know to proceed, I use the following conservation of ...
4
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1answer
153 views

How should I think of monopoles in a 3+1D lattice $U(1)$ gauge theory?

The Hamiltonian for 3+1D compact $U(1)$ gauge theory on a cubic lattice is of the form \begin{equation} H = J\sum_{\text{links}\ l}E^2_{l}+ g \sum_{\text{plaquettes}\ P}\cos(\Phi_P), \end{equation} ...
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1answer
13 views

Why can't the electrons in Lamb-Retherford Experiment transition from 2S to 2P(j=1/2)

This experiment reveals metastable state and uses the fact that an electron in 22S1/2 can't go to the ground state as ∆l=0 is restricted. But I was thinking why doesn't electron go to 22P1/2 and then ...
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2answers
30 views

Finding the value of $r$ for which the radial function, $P(r)$, has a maximum? [on hold]

In my (university) particle physics course, I am asked to find the values of $r$ for which the function $P(r)$ of a $2s$ Hydrogen electron has its maximum values. Here, $r$ denotes the distance in ...
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0answers
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Why can't large momentum effective theory be applied to fragmentation function?

Large momentum effective theory was proposed in 2013 by Prof. Xiang-Dong Ji. The idea is to numerically solve PDF in lattice QCD via so-called quasi-PDF in finite momentum frame. Such method is ...
2
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1answer
28 views

What is $\mathbb{Z}_2$ Parity?

While reading about exotic decays of Higgs boson one of the simplest interaction that we come up with which leads to BSM decays is: $$\Delta L = \frac{\zeta}{2}s^{2}|H|^{2}.$$ This is the ...
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0answers
31 views

How to find energy levels formula for symmetric triangular potential well [on hold]

As some of you already know that the asymmetric triangular potential well has the energy level where an here refers to the airy function a1 =2.338, a2=4.088, a3=5.521 and a4= 6.787 and V=eFz (F here ...
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2answers
4k views

What is the definition of colour (the quantum state)?

I heard somewhere that quarks have a property called 'colour' - what does this mean?
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2answers
1k views

Correlation between outstanding hints in experimental particle physics

The 115 GeV ATLAS Higgs with enhanced diphoton decays has gone away but there are several other recent tantalizing hints relevant for particle physics, namely CoGeNT's 7-8 GeV dark matter particle ...
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0answers
33 views

Quark flow diagram for $\rho^0 \rightarrow \pi^0+\gamma$

So $\pi^0=\frac{1}{\sqrt{2}}(u\bar{u}-d\bar{d})$ and $\rho^0=\frac{1}{\sqrt{2}}(u\bar{u}-d\bar{d})$ except with a higher angular momentum, this angular momentum is taken by the photon. How do I ...
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4answers
2k views

What is needed to claim the discovery of the Higgs boson?

As I understand the Higg's boson can be discovered by the LHC because the collisions are done at an energy that is high enough to produce it and because the luminosity will be high enough also. But ...
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0answers
18 views

Why Proca Term forbidden in Schwinger Model?

In my QFT Lecture we considered the Schwinger model with a Proca term. Solving the eom for the Stueckelberg field and plugging it back into the original Lagrangian, we receive an effective Lagrangian ...
2
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1answer
152 views

How does the Fine Structure Constant Vary with Energy?

Like my topic, how does the fine structure constant vary with energy? I looked it up and found: $$\alpha_{eff}(q^2) = \frac{\alpha}{1-\frac{\alpha}{3\pi}\ln(\frac{-q^2}{Am_e^2})}$$ , where $\alpha^{-1}...
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1answer
34 views

Antiproton production threshold

Why is the antiproton threshold on cern 6* m_p and on uspas it is 7 * m_p?
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0answers
53 views

How can i calculate the frequency of a gluon? [closed]

After conducting research I believe I could use the frequency formula for a photon to calculate the frequency of a gluon, but I have a paradox. My issue is that in order to calculate frequency you ...
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4answers
188 views

How does natural unit make sense? [duplicate]

Both the fundamental constants $\hbar$ and $c$ have dimensions. In particular, $[\hbar]=ML^2T^{-1}$ and $[c]=LT^{-1}$. But in natural units, we make them dimensionless constants of equal magnitude. ...
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4answers
7k views

Books for particle physics and the Standard Model

I know classical physics, quantum mechanics, special relativity, and basic nuclear physics. I would like to get into some particle physics. Where can I find a good introduction? It might be useful ...
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2answers
60 views

Why can't a particle interaction $A + B \rightarrow C$ conserve energy and momentum at the same time?

I learned that in the Feynman diagram for electron photon scattering, the intermediate particle represented by the middle solid line must be a virtual particle because it violates energy-momentum ...
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1answer
43 views

Are Generations and Families of elementary fermions one and the same?

I've seen both terms being used in papers and it seems to me they essentially mean the same thing referring to three generations of leptons and quarks as families. Is this true or are there some ...
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1answer
149 views

Matter effects in neutrino oscillation

The neutrino oscillation probability in matter is given as: where Now what I do not understand is that "As the energy increases, the probability of oscillation within the sun through the matter ...
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2answers
692 views

What is the 'bump' near $M_{\mu\mu}\approx 30\text{ GeV}$

In this (attached) Summer 2011 plot from CMS (twiki page), they have a plot of the dimuon invariant mass spectrum across 3 orders of magnitude in energy. There seems to be a 'bump' near $M_{\mu\mu}\...
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0answers
31 views

Parton distribution function in terms of Fock space kets

To my understanding, I can (at least, formally) express the (unnormalized) PDF for a certain constituent of a composite state as $$ f(x)=f\left(\dfrac{k}{K}\right)=\sum_j m_j^{(k)}|\langle\psi_j^{(k)}|...
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2answers
118 views

Can material that has no magnetic properties be magnetically aligned?

Can a strong magnetic field be applied to material that has no magnetic properties have a residual magnetic field show the same behavior of a magnet? Example: Could a stick be magnetized where would ...
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1answer
817 views

Experimental boundaries for size of electron?

There is some confidence that electron is a perfect point e.g. to simplify QFT calculations. However, searching for experimental evidence (stack), Wikipedia article only points argument based on g-...
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1answer
157 views

From isospin of nucleons to hadrons

To my understanding, isospin was introduced for nucleons (neutrons and protons) because of their similar properties. When it was found out that they are made up of quarks, naturally the quarks could ...
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1answer
96 views

Collision of two electron beams as an experimental test of the Standard Model? [closed]

I understand from this link that no experiments that collide two electron beams (cf. electron-position beams) at high energy were ever done. Assuming the standard model (SM), such a collision should ...
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1answer
165 views

Special Relativity - three body problem

I have a problem with solving three-body problem in special relativity. I know that in general this problem doesn't have good solution, but I have a specific case when it should be good answer. ...
2
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1answer
81 views

Why atomic masses are quoted with reference to an isotope?

Is there any fundamental reason why atomic masses are quoted with respect to a certain element such as an arbitrary C-12 isotope whose mass has been set to 12 unit exactly? Previously, chemists have ...
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0answers
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Why my cloud chamber won't work?

let me briefly introduce myself, I'm a highschool student from Indonesia, I'm currently making a cloud chamber for my science fair project, I did what the videos on youtube told me, but for some ...
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1answer
30 views

Does two Higgs doublet model predicts two Higgs bosons?

Does 2HDM predict two higgs boson? Why two doublets are needed? I need a simplified answer as i am new to BSM
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1answer
157 views

Longitudinal mode of $W$ and $Z$ boson after SSB

Can it be "proven" from the dynamics of Spontaneous symmetry breaking that the Goldstone bosons get absorbed as the longitudinal degrees of freedom (DoF) of the W and Z bosons? A massless gauge boson ...
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1answer
22 views

How we know that the $\rho(1700)$ meson is in D-wave?

I was reading about Regge radial trajectories for $\rho$ meson and I found that we have two given by the values of the orbital angular momentum, $L=0$ and $L=2$. With this part, I feel OK. But, when ...
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1answer
30 views

Size of transversal momenta in Multi-Regge kinematics?

Considering a scattering process in which $2$ incoming particles annihilate and produce $n-2$ other particles, one can consider the particle momenta $p_i^\mu$ (with $i=1,2,3,...,n$) to be in so called ...
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3answers
165 views

What constitute the secondary particles beam when a high energy proton beam hits a target material?

Basically I want to know what particles emerge along with high energy photons(not sure about it) as the second beam when a specific high energy proton beam is incidented upon a target material such as ...
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3answers
16k views

What happens in electron-electron collisions?

What are the results of high energy electron electron collisions? Are other particles created?
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1answer
36 views

Special Relativity for Synchrotron Radiation

For the last few hours, I tried to solve an exercise about synchrotron radiation but can't get to a solution. I think there are some concepts about special relativity that I didn't understand during ...
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0answers
22 views

What is meant by an “Any Energy” efficiency curve for a particle detector?

So I'm simulating a silicon detector with an electron source incident on it. I need to get 2 efficiency curves, one "photo-peak" and one "any energy". I've got the photo peak one, but I don't ...