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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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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
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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 ...
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1answer
27 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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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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0answers
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How can i calculate the frequency of a gluon? [on hold]

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
168 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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2answers
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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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0answers
39 views

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
78 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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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
94 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
27 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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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 ...
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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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0answers
24 views

Feynman Diagram Calculus [closed]

I need to calculate the transition probability of this process: e- ----> photon+photon+ e- Using the feynman rules I obtain the element: $\langle f|\Delta|i\rangle=\langle u^s(p)\epsilon_{\mu}\...
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0answers
18 views

Cloud Chamber fluid and temperature

I am working on a cloud chamber and, even if i did some research, i still have problems developing the theory behind. People talk about the temperature and gradient of temperature as a fundamental ...
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0answers
24 views

How does binding energy change as more fermions interact?

The subject is few-body quantum mechanics. Given a system of $N$ identical fermions (spin 1/2) interacting through pairwise potentials $V_{ij}$, how does the binding energy change between $N$ and $N+1$...
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1answer
86 views

Why doesn't observing a photon collapse it's wave function into a B or W3 boson?

According to electroweak theory, the photon ($\gamma^0$) and weak bosons ($W^+, W^-, Z^0$) are all linear combinations or superpositions of the weak hypercharge boson ($B$) and the weak isospin bosons ...
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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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1answer
43 views

What does the photon feel when it hits an asteroid on its path to earth [duplicate]

If a photon was approaching earth, after 1 minute(from earths reference frame) an asteroid comes on the photons path. And it hits the asteroid, but from the photons reference frame time doesn't pass ...
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0answers
23 views

The fine structure constant and the strength of interaction between two particles

In my notes, the following is mentioned: We consider the scattering of a beam particle with energy $E$, momentum $p$ and charge $ze$ off a charge distribution $\rho (x)$ of total charge $Ze$. We ...
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1answer
57 views

Derivation of speed of light using particle theory

The speed of light can be calculated by Maxwell's equations, which tell us that light is an electromagnetic wave. How does the particle theory of light account for the constant speed of light?
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3answers
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In particle colliders, according to QM, how are two particles able to “collide”?

According to QM, we know that The act of measurement forces a particle to acquire a definite (up to experimental errors) position, so in a particle collider, like the one in CERN, by which means ...
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1answer
72 views

Comparison between $\rho^0$ and $J/\psi$ decay mode

Why must a hadronic decay of the $J/\psi$ meson include (at least) three gluons? Why is the decay mediated by a single gluon allowed for the $\rho^0$ meson?
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0answers
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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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1answer
36 views

What is the effect of isospin on the proton or neutron alone, i.e. not in a doublet?

So I start with a proton $p$. I extend my "physical" space by means of the internal degree of freedom of isospin, so that I know write $p$ in a higher dimensional space: $$ p = \left( \begin{array}{...
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1answer
77 views

How do Fermions with $0$ weak hyper charge couple to electro-weak force?

If you have two fermions (with spin $\pm \frac{1}{2}$) that form a weak-isospin doublet and their respective right-handed fermions which are weak-isospin singlets, what would it imply if the doublet ...
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0answers
35 views

Does the background shift affects the renormalization group equations?

In Section 21 of "Quantum Field theory" by Mark Srednicki, it is shown that there are two equivalent ways to get the quantum action of the shifted field $\phi'= \phi-\tilde{\phi}$, where $\phi$ is the ...
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1answer
37 views

Can a neutron decay into a proton + muon (+ muon-neutrino)

Can a neutron, if it has enough kinetic energy, decay like: $ \hspace{0.3cm} n \rightarrow p + \mu^- + \bar{\nu}_\mu $ I assume it's not allowed since it's not on the possible decay modes on the ...
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3answers
97 views

Can there be charges in free space without it being on some particle?

We see leptons and quarks possessing charges. Can there be charge in free space devoid of matter(neither leptons nor quarks or anything else)?
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0answers
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How do you find the distance x of a ball jumping of a cliff with a permanent force applied? [duplicate]

Im reposting, since i needed to post my approach to solving it so it doesnt seem like im using this for homework. Everything is given except delta x which you need to find. No friction and the force ...
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1answer
53 views

Antiparticles, CPT and leptogenesis

When people are being careful they'll tell you that antiparticles are the CPT conjugates of particles. You can't say that they are C conjugates or CP because these, while they do reverse the charge, ...
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0answers
24 views

The basics of neutrino telescopes

I'm trying to understand the basic operation of the ANTARES neutrino telescope. Here is what I've gathered: The detection of neutrinos relies upon the detection of muons. Cosmic rays and neutrinos ...
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1answer
44 views

Can electrons “build up” energy?

We're studying the photoelectric effect. My book says that according to the classical wave model, there is no reason for electron emissions to occur almost right after turning on the light source. It ...
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1answer
31 views

Particle Double slit

How was the Particle Double Slit Experiment really done? To be precise, what kind of double slits were used and how can such slits be small enough, especially for electrons and buckys balls?
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2answers
71 views

How are composite hadron fields related to elementary quark fields?

(This question is related to: A pedagogical exposition of the hadron physics?) I'm a mathematician who has been trying to learn quantum field theory for a while. I've gone through large parts of ...
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0answers
29 views

Muons that decay in plastic scintillator

I have a question on the energy of the muons that decay in a plastic scintillator. In these notes, at page 4, fourth line from the end, it is mentioned that muons with less than about 50 MeV will ...
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1answer
38 views

What was the prediction of the standard electroweak theory about the $W$ and $Z$ boson masses?

The standard electroweak theory has two coupling constants $g$ and $g^\prime$. In this theory, the $W$ mass and $Z$ mass are given by $$M_W=\frac{1}{2}gv,~M_Z=\frac{1}{2}(g^2+g^{\prime 2})^{1/2}v$$ ...
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0answers
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Looking for entry level books to understand the math in particle physics [duplicate]

I have a basic understanding of leptons, bosons, hadrons, etc (particles in particle physics). What I would like to begin to understand is the math behind particle physics. Can someone recommend ...
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2answers
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Why are the generations of leptons/quarks regarded as fundamental particles?

My understanding is that 'fundamental' pertains to there being a distinct quantum field corresponding to the particle. I ask the question above based on the fact that the heavier generations of ...
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1answer
58 views

How does the negative energy solution to the Dirac equation predict the antielectron?

Please, can someone explain how the negative energy solution can be used to predict the existence of the antielectron?
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2answers
131 views

How are pulsed neutron sources created and when are they used in particle accelerators?

Are pulsed neutron sources beams of neutrons that are not created continuously? If so what is the benefit of having a discontinuous beam of neutrons rather than a continuous one? Under what conditions ...
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2answers
55 views

Nuclear Physics Brainstorm Question

I was wondering how it could be possible to artificially overcome the strong nuclear force, allowing for the nucleons to be released from each other. If you can't think of any possible solution, is ...
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0answers
45 views

Can supersymmetry be disproved? [duplicate]

Recently there are a lot of news about the plans to build the FCC accelerator, with many claims of possibilities to find new particles, for example like those suggested by theories of supersymmetry. ...
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1answer
61 views

When/Why Did Physics Discard The Point Charge As An Accurate Representation? [closed]

Is there anything about the implications of the "early" quantum theory of Schrodinger equation, wave-particle duality, or the two slit experiment that conflicts with the idea of a point charge? Did ...
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0answers
23 views

Diagrammatics of a current-current correlation function $\langle 0| T\{J^{\mu}(x) J^{\nu}(0)\}|0\rangle$

Say $J^{\mu} = \bar{\psi} \gamma^{\mu} \psi$ is the QED current. While it is clear to me how to compute something like $$\langle 0 |T\{ \bar \psi(x) \psi(0)\} |0\rangle$$ using a Feynman diagram ...
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2answers
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What is the difference between a neutrino and an electron neutrino?

So, what is the difference between a neutrino and an electron neutrino? Like how does the term 'electron' made a difference? Also, what is the difference between an antineutrino and an electron ...
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1answer
61 views

The Majorana condition and C violation

Is the Majorana condition $$ \psi = \psi^c = C \overline{\psi}^T, $$ general? The point is often made that Majorana particles should be defined by CPT symmetry and not C as generally theories do not ...
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2answers
90 views

Are neutrinos just different states of a single particle, in essence?

When Neutrino oscillation phenomenon is analysed quantum mechanically, it is said that, \begin{align} |\nu_e \rangle &= \cos(\theta) | \nu_1 \rangle + \sin(\theta) |\nu_2 \rangle,\\ |\nu_\mu \...
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2answers
60 views

How does particles move in waves? radiation?

I'm reading about particles for a project and had a question. I read that particles don't move forward in a wave, the simply oscillate up and down, and that gives it the wave look. But if they don't ...