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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25 views

Is high temperature **required** for nuclear fusion?

tl;dr : Can fusion be achieved only by speeding up particles to high enough speeds to smash into each other? I know that it is necessary for protons, or any oppositely-charged particles for that ...
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Pseudorapidity: Derive conversion to Cartesian momenta

I am working on the ATLAS opendata as part of a lab course at my uni at the moment and stumbled upon the identity $p_{z} = p_{T}*\sinh(\eta)$ with the pseudorapidity $\eta = -\ln(\tan(\frac{\Theta}{...
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How to know the $C$-parity of a particle?

As a following up to Why does the parity of a meson have a "+1" in it? I have another question: Why does the photon have a $C$-parity of -1? Is it due to some advanced calculation or can I ...
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44 views

Is the strong potential repulsive for high distances?

The negative region in a potential is attractive and the positive region is repulsive. At least in case of the coulomb potential: When having a look at the strong potential it is obvious that the ...
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1answer
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Why does the parity of a meson have a “+1” in it?

The parity of a meson is defined as $ P = (-1)^{L+1} $ where $L$ is the angular momentum. What does the "1" in the exponent represent?
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Measuring strong coupling constant

How can the strong coupling constant be measured?
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28 views

Role of the Yukawa potential

What is the Yukawa potential converging to zero? Afaik the strong potential rises with the distance between quarks, hence, it should rise accordingly.
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62 views

What exactly is a gluon doing when acting as an gauge boson?

The question is in the title. I know that, e.g., W bosons change the flavour in electroweak processes. What do gluons do?
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1answer
65 views

Why is $\Delta^0$ not decaying weakly?

Given the lower decay I wonder why it happens this way. Wouldn't it be possible to decay via a weak process as well?
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2answers
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Difference between left- and right-handed, helicity and chirality

What is the difference? I know there is the (almost) same question What's the difference between helicity and chirality? but when a particle is given as left-handed. Is it helicity or chirality?
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Main decay of $ J / \psi $

The main decay of $ J / \psi $ is $ c \bar{c} \to ggg $. How can this reaction channel be observed? 3 gluons will hadronize immediately, or not?
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1answer
22 views

Why is it that the Callan-Gross relation predicts that quark has spin 1/2?

I'm studying deep inelastic scattering, and currently at the part where they say the Callan-Gross relation: $$F_1 (x) = \frac{1}{2x} F_x (x)$$ where $F_1$ and $F_2$ are the dimensionless structure ...
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1answer
36 views

Asymptotic freedom and momentum exchange

Why is the momentum exchange very high for low distances? For sufficiently short distances or large exchanges of momentum https://en.wikipedia.org/wiki/Asymptotic_freedom While I think about ...
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Energy threshold for photon

I just read https://en.wikipedia.org/wiki/Annihilation#Examples and there is the popular $ e^+e^- \to \gamma \gamma $ reaction described. Is it always possible to produce a $ \gamma $? A photon does ...
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Deeply Virtual Compton Scattering

what are Transition Distribution Amplitudes respectively Deeply Virtual Compton Scatterings ? I'm so unsure about the terms I can't even distinguish (in case they are not really related to each other)....
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Why are there fixed target experiments?

Collider experiments put all their energy into $ \sqrt{s} = 2E $ while target experiments only provide $ \sqrt{s} = \sqrt{2Em+m^²} $. Yet, there are fixed target experiments. Why?
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How does the introduction of the charm quark suppress FCNC?

I did some reading on the GIM mechanism today, and simply fail to understand how it works. I understand how the CKM-matrix can be used to do the basic calculation of the probability of, say, observing ...
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1answer
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Why is $J/\psi$ not being able to decay into $\pi^+\pi^-\pi^0$ (Ozi-rule)?

There are already (very similar) questions like What is the precise statement of the OZI Rule? and Why does charmonium (and phi mesons) not decay via quark and antiquark annihilation? but, to be ...
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Why is this way of deducig the 1 dimensional Maxwell-Boltzmann Distribution wrong?

I asked before how the 1D Maxwell-Boltzmann distribution can be derived. However, I did not get or find an answer to my own method explaining why it is wrong, which I am quite curious about. It is a ...
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33 views

Why don't we consider the Gamow factor when configuring the cyclotron?

Most of the time, during a collision the repulsive force between the protons will beat the attractive force that binds the nucleus together and the whole thing is torn apart. But very occasionally, ...
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1answer
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How to find the most likely decays in 2 hadrons for $\Omega$?

I took a look at the Particle Data Group, and the most likely modes are $\Omega ^{-}\rightarrow \Lambda K^{-}$ (68%) and $\Omega ^{-}\rightarrow\Xi ^{0}\pi ^{-}$ (24%). I have 2 questions: 1) The ...
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Kinetic energy of daughter nuclei after decay given the Q value [closed]

Assume that we know the Q value of the decay ${}^{230}_{90}\rm{Th}\rightarrow {}^{226}_{88}\rm{Ra} + \alpha$, and we make the simplification that the total mass of a nucleus is the number of nucleons ...
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How does Isospin work?

I have been trying to find a good source to explain the concept of isospin thoroughly but everything I have found seems to gloss over it. I have found sources that tell me it is a vector quantity but ...
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2answers
151 views

Physical significance of the decomposition $3\otimes\overline{3}=8\oplus 1$ in meson classification

Under the assumption of $SU(3)$ flavour symmetry of early days, proposed by Gell-Mann and Neeman, among other irreducible representations, the meson octet was obtained. This result from the $SU(3)$ ...
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1answer
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Why is the decay $\omega \rightarrow \eta \pi^0$ forbidden?

I understand that it is due to C conservation, but I'd like some more information - perhaps it's simpler than I'm imagining. Similarly for the decay $\omega \rightarrow \rho \gamma$. Thanks!
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What should be the real error band of a fit function?

This is a question concerning data analysis. It could relate to particle/nuclear physics or other field. Please note that this question has nothing to do with technical problems, and is more of a ...
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2answers
83 views

Why is particle physics called high energy physics? [duplicate]

The highest energy accelerator till date is the LHC which operates at an energy scale of perhaps 10-100 TeV. In SI units this is about $\sim 10^{-6}-10^{-5}$ Joule which is several orders of magnitude ...
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On the size of positronium

How can we simply apply the bohr model on a positronium as the positronium doesn't even have a nucleus or nucleus-like entity like in a hydrogen like atom. Moreover this implies that the first ...
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1answer
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How to optimize the significance for my neural network with the purpose of classifying detector events?

For my Bachelor's thesis, I've created a neural network with the task of classifying FCNC tz-production events. It was trained on data from a Monte-Carlo simulation, and tries to output 0 when ...
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2answers
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Weak interaction and charge conjugation $C$

Does the weak interaction always change the charge of all participating particles? And in this context, what does $C$-violation do then?
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Increasing total anti-neutrino cross section [duplicate]

Is there a method for increasing the total microscopic cross section for an interaction between an anti-neutrino and a nucleus of Titanium 48?
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1answer
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Increase the Inverse Beta Decay Cross Section for Ti-48

Is there a theoretical way to increase the cross section of inverse beta decay for Ti-48? This would be any method for increasing the likelyhood that Ti-48 absorbs an anti neutrino and creates Ca-48 ...
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1answer
37 views

Synchrotron radiation for protons

I know that due to the huge mass difference and dependence of radiated energy on mass, protons lose much less energy in synchrotrons than electrons. Can someone tell me how to calculate the energy ...
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1answer
106 views

On scheme dependence in QFT renormalization

I searched for the answer to my question quite a while and it seems nobody ever asked similar questions or it is written explicitly in any textbooks. The question is, If physical parameters of any ...
4
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1answer
106 views

Is width of particles a consequence of Heisenberg's uncertainty principle?

The uncertainty principle tells us that $$\sigma_x\sigma_p \geq \frac{\hbar}{2}, $$ which means that the more precisely we measure a particle's position, the more imprecise we will know its momentum. ...
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1answer
60 views

How to find theoretically the decay width of a particle-decay process? [closed]

The problem is devided into two parts: First part: There is an interaction Lagrangian for real scalar fields given by L=$\lambda_1 \phi_1 \phi_2\phi_3+\lambda_2\phi_1^2\phi_3$. I need to know how to ...
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Is charge point-like or a smear?

Coulomb gave the law for the force between two static charges while considering them to be points in space. But the differential form of Gauss' Law talks about charge densities, a thing possible only ...
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2answers
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Can we affect the size of the universe with the observation of light?

Adding on to THIS question I would like to take this question a bit further, and forgive my ignorance of the details as I have never taken any formal training on such subjects. But it's said that ...
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2answers
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How do you distinguish between missing momentum from a neutrino and from dark matter?

I thought googling this would give me an answer quite quickly, but actually couldn't find much, so maybe it's a silly question. But I read that dark matter searches rely on measuring missing momentum ...
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1answer
71 views

$K\to \pi \gamma$ decay

I was asked the following question in an exercise sheet: The decay $K \to \pi\gamma$ is absolutely forbidden by a certain conservation law, which is believed to hold exactly. Which conservation ...
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1answer
92 views

What are the basic ingredients in the Standard Model (SM) of particle physics? [closed]

What are the basic ingredients of the standard model (SM) and their applications?
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How does a quark $u$ or $d$ turn into one another?

The pseudo-explanation that the proton is stable because it has a lower mass than the rest is incomplete, because a particle formed by three u: uuu would have still a lower mass. I know that some ...
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Logic for Eq.(9.68) in Griffiths' “Intro. to Elementary Particles” (2nd edition)

Treating charged pion decay $\pi^{-} \rightarrow \ell^{-} + \bar{\nu}_{\ell}$ (where $\ell$ designates a lepton of first- or second-generation) by the representation of the figure below, Griffiths ...
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1answer
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When a Z boson decays into a particle/antiparticle pair, do those particles instantly annihilate each other?

If you look at a Feynman diagram of neutrino-electron scattering, there is the mediation of force by means of a virtual Z boson, and the product of this interaction is just the neutrino and electron ...
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1answer
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Determine/measure energy of neutral particles

I wonder that nobody came up with this question in advance - maybe it is too obvious? However.. How can neutral particles be measured (with respect to their energy in a particle detector)? I know ...
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2answers
347 views

Why does the Higgs boson have electroweak charges $~T_3~$ and $~Y_w~$ but does not have an antiparticle with opposite charges?

(Using $Q=T_3+Y_W$) The Higgs boson has weak isospin $T_3=-\cfrac12$ and weak hypercharge $Y_W=+\cfrac12$. Since every particle has all opposite charges of its antiparticle, why isn't there an anti-...
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1answer
114 views

The Zero Energy Hypothesis and its consequences for particle creation and dualist interactionism

Most attacks on the possibility of dualist interaction cite the conservation of energy as a definitive objection. I have attempted to investigate the validity of this objection, and have found a ...
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1answer
81 views

Where does the extra mass of a $W$ boson come from in particle decay?

I’ve seen everywhere explaining that it can exist because of time/energy uncertainty. I get this. I understand that’s WHY it exists but I’ve still never gotten WHERE the extra mass comes from. Is the ...
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2answers
123 views

How can the 1 dimensional Maxwell-Boltzmann Distribution be derived?

In terms of energy, the 3 dimensional MB Distribution is giving the probability for a particle to have an energy $E \geq E + dE$ is: $$f(E) = \frac{2}{\sqrt \pi} \cdot \bigg(\frac{1}{k_BT}\bigg)^{\...
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Threshold energy of Ti-48 inverse beta decay

Goal: Use anti neutrinos to convert Ti-48 to Ca-48 using inverse beta decay (IBD). The resulting Ca-48 should have the same half-life as natural Ca-48. Question: What is the threshold energy for the ...