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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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Fields or Particles [duplicate]

What is more fundamental, particles or fields? I keep reading what appears to be conflicting answers on this, but I am sure it is just a limitation of my understanding. I have heard some physicists ...
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Corresponding particle-antiparticle solutions for Klein-Gordon equation

For free particle solutions in a box, the following 4 solutions are possible(Not all 4 are independent though) as $$\psi_+=A_+ \exp{\frac{i}{\hbar}(px-Et)}\\\psi_+^*=A_+^* \exp{\frac{-i}{\hbar}(px-Et)}...
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Do electrons have third component of isospin?

From what I've read, it seems like there are two types of isospin: the strong and the weak. I guess this means that leptons have no strong isospin, but they do have weak isospin. Am I right? I am a ...
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Removing zero-counts in exponential decay measurement

I'm doing an experiment where I'm measuring the mean-lifetime of muons. I have a set of data points for the number of decays against time, resembling an exponential distribution (of course). But in ...
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Is it possible to add energy to an antiparticle?

The title says most of it but the more drawn out version is. If you were to add energy to a single particle or antiparticle in a pair, what would be the effects, if it is possible to do.
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Why should $\nu_\mu\to \nu_e$ oscillations be expected to be unobservable in short baseline experiments?

The blog here says On the other hand, several rogue experiments refuse to conform to the standard 3-flavor picture. The most severe anomaly is the appearance of electron neutrinos in a muon ...
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Universe under Point Reflection — or why is the Neutrino not its own anti-particle?

The spin of a anti-neutrino points into the same direction as its momentum. The spin is a cross-product, so under point reflection it remains the same, whereas the momentum gains a factor of $(-1)$. ...
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The simple harmonic oscillator model relating particles and fields in QFT

In all of the introductory Quantum Field Theory texts I gave read so far, (such as Zee, Srednicki, Luke), there is an introduction to the concept of fields as operators, following the simple harmonic ...
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Lecture notes by Rudolf Mössbauer

Rudolf Mössbauer was an excellent lecturer. He gave lectures on Neutrino Physics, Neutrino Oscillations, The Unification of the Electromagnetic and Weak Interactions and The Interaction of Photons and ...
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Do antiquarks cancel quarks out?

I heard that antiquarks are just like antimatter. Does that mean that they cancel quarks out? If so, does that mean that there are more quarks than antiquarks?
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Unitarity violation: sign inconsistency in Quigg

In Gauge Theories of the Strong, Weak, and Electromagnetic Interactions, C. Quigg explains how the process $\nu \overline{\nu} \rightarrow W^+ W^-$ violates unitarity at high energy unless we add the $...
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Could there be elementary particles with electric charge $> 2e$?

There are many quantum field theories, which extend the Standard Model and have new particles. For example, X boson of Georgi-Glashow model has charge $4e/3$ and some Higgs models involve a Higgs ...
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charge particle collisions

If a lithium +1 cation falls toward a fluorine -1 anion, slowly in vacuum, can they find a stable 'orbital'? If not an 'orbital' will they form some kind of stable two-body linear oscillator?
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Electro magnetic field

If an emf is produced in a dc motor, would it be possible to use the motor somehow as a generator or source, taking power out of it rather than putting power into it? How might this be done?
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How exactly does the intensity of light affect photoelectric phenomena?

We were taught that the intensity of light is equal to the rate of flow of photons per unit area times the energy of each photon(planck’s constant times its frequency) then would that mean the ...
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Is a nucleus a collection of quarks or a collection of neutrons and protons? [duplicate]

I do not much about particle physics. But people say that neutron and proton are composed of quarks, and in turn a nucleus is composed of neutrons and protons. Therefore, the question is, is this ...
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In the Quantum eraser experiment, Why doesn't detector D1 or D2 cause wave function collapse?

I thought measurement at detectors is what collapes the wave function. So why aren't these detectors causing collapse? Why is there an interference pattern?
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Fusion methodologies

Forgive my naivety but it seems to me all the attempts to create useful fusion concentrate on high temps or high pressures or both and samples of fusible material consisting of multiple nuclei. Is ...
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Composite particles and Weinberg Witten (WW) theorem

I am quite familiar with the proof of Weinberg Witten (WW) theorem. One major result which follow from WW is that the graviton cannot be a composite particle. I have 2 questions here: How do we tell (...
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Surjectivity of momentum mapping

I have to show that the following mapping of momenta is surjective. The mapping $\{p_i^{\mu},p_j^{\mu},p_k^{\mu}\}\rightarrow\{\tilde{p}_{ij}^{\mu},\tilde{p}_k^{\mu}\}$ is given by $$ \tilde{p}_k^{\...
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3-particle phase space in $d$ dimensions

recently I came across a problem concerning the 3-particle phase space. I am trying to show, that the 3-particle phase space for massless particles with momenta $p_1$, $p_2$ and $k$ is given by $$ d\...
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Constraints on RH component of fermion triplet under $SU(2)_L$

Consider a fermion $\chi$ whose left-handed part is in a triplet representation of $SU(2)_L$: $$ \chi_{L} = (\chi^1,\chi^2,\chi^3)_L^{\ \ \text{T}}. $$ The charged current of $\chi_L$ (i.e. its ...
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How can a single particle hit many pixels in Large Hadron Collider?

In the Large Hadron Collider, the way particles are detected (specifically in ATLAS) is analogous to detecting photons using a photodiode(analogous is an exaggeration, but will suffice for the ...
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Hawking said virtual particles can almost become real particles, following closed trajectories. What does that mean?

Here's hawking quote from his latest book. Brief Answers to the Big Questions "When space-time gets warped almost enough to allow travel into the past, virtual particles can almost become real ...
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Using relativity to calculate the radius of a cyclotron when accelerating protons to 0.99c

If I need to find the minimum radius necessary to have a fixed target collision of $10^{10}eV$ with two protons, and the traveling proton is going 0.99c in a cyclotron of 8 Tesla. Do I need to ...
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Equivalence between $t$ and $u$ channels

Reading about QFT diagrams, I've seen examples like Bhabha scattering where the channel $u$ wasn't necessary due to the final states are distinguisable for being made of the different particles and ...
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Which direction does “the mirror” in the Wu experiment flip?

I have seen two different setups for the Wu experiment: One where the "imaginary" mirror flips the experiment along a plane parallel to the magnetic field and one where the mirror is aligned ...
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What is a non-resonant decay?

In particle physics, what is non-resonant decay? How does it manifest itself in invariant mass frame? Does it not peak? It has to peak, right, otherwise, how would anyone know, that there is a decay ...
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In the Standard Model of particle physics, why we ignore the gravitation force?

In the Standard Model of particle physics, we consider only three forces, my question is about the gravitation force why we ignore?
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Mathematical Research Vs Project (undergraduate) [closed]

This question may not be appropriate for this site, and if so should be closed by a moderator. I'll ask it anyways though. Im currently a junior in my undergraduate degree (math & physics). I am ...
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The production of $b$ ($b$ bar) quarks

I have a question, please if there anyone helps me to understarnd how we distinguish the production pair of quarks $b$ ($b$ bar) it comes from a QCD background or comes from higgs decay?
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Explaining the concept of background noise and signal in Higgs decay to 4 leptons or 2 gammas using an analogy of matlab simulation

I am not sure if this is the right forum to ask this question. But my main concern is to explain the idea of background/signal in Higgs decaying to 4 leptons or 2 gammas. I am absolutely not trying to ...
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What does a fundamental particle really look like? [closed]

After reading a lot and trying to understand people explain it, I made an image in my mind that "fundamental particles are a given position in space to which is given properties", these properties ...
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How does inertia work at the particle level?

I've read recently that the mass of a proton is mostly not given by the Higgs mechanism. But rather it's given by the energy of quarks moving around inside the proton and gluons and other internal ...
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Is this reaction even allowed? [closed]

$$p+p\rightarrow p+n+\pi^+$$ According to coservation laws, is this Allowed or Forbidden? If Allowed what type of interaction is this :- Strong, EM. or Weak? Why? From conservation of Charge &...
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How time dilated is the average particle relative to the big bang? [duplicate]

Particles created during the being bang have experienced time dilation by means of gravitation and general acceleration for the past 13.8 billion years. On average, how time dilated is the average ...
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Why exactly is Neutronium-4 unstable and how to explain Marqués' experimental results?

Wikipedia states: A tetraneutron is a hypothetical stable cluster of four neutrons. The existence of this cluster of particles is not supported by current models of nuclear forces. There is some ...
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Relation between momentum and momentum uncertainty

I have read the following sentence in a section which is explaining why particle accelerators need such high energy: As we require high precision position measurement, the Heisenberg uncertainty ...
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Dark matter relative velocity

In Dark Matter Indirect Detection literature, it is usually said that the relative velocity of dark matter particles in the galactic halo is about $$ v \sim 10^{-3}c$$ See for an example this lecture ...
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Lamb Shift and virtual particles [closed]

Can someone explain about the Lamb Shift?
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Higgs decay at higher energies

If I look at the expected Higgs decay BR's vs. $m_H$ the WW and ZZ dominate over the tt decay mode in the over tt threshold region. From the mere couplings: $g_{ffH} = \sqrt2 m_f /v$ $g_{VVH} = 2 ...
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How can I understand the reaction rate of WIMP dark matter intuitively?

I'm reading a cosmology textbook(sorry it's Japanese) and stacked at statement that If the mass of WIMP is enough smaller than 100GeV, the reaction rate is represented as $\langle \sigma_a |\mathbf{\...
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How can individual neutrinos have different amounts of energy?

Photons have no mass, travel at the speed of light, and their energy is related to their frequency. Neutrinos have a very small mass, travel at almost the speed of light; what is their energy related ...
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Quantum entanglement with different particles

I ve been searching for some techniques that are used to create quantum entangled pairs. I can see that almost all of them are related with photons and rarely electrons. Are there other methods that ...
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The Lorentz-invariant particle spectrum

Before the question, I need to mention some necessary definitions. The rapidity is defined as: $$y=\frac{1}{2}\ln\frac{E+p_z}{E-p_z}=\frac{1}{2}\ln\frac{1+v_z}{1-v_z}=\tanh^{-1}(v_z)$$ where $v_z=...
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What particle interaction is most important for maintaining the equilibrium of a main sequence star?

For main sequence stars like the sun, balance against gravitational collapse is achieved with the pressure of the underlying plasma. My question is how much of this pressure is accounted for by ...
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A question about isospin of pion and kaon

In Ch.18 of the textbook An Introduction to Quantum Field Theory by Peskin and Schroeder, on P.611 when discussing QCD renormalization of the weak interaction, two operators ${\cal O}^{1/2}$ and ${\...
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Is the photon pair generated from the electron-positron annihilation entangled?

Is the photon pair generated from the electron-positron annihilation entangled? And would they work as a source of entangled photons suitable for experiments in quantum optics?
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How far can a moving object embed itself

Let's say we have an electron moving at 10% the speed of light toward a 10 cm thick block of pure carbon. How do we calculate the distance that the electron travels into the carbon? Even though there ...
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Collision of a photon with a quasi-free particle

What is a quasi-free proton? How does the wavelength of a photon change when it collides with a quasi-free particle, e.g. a quasi-free proton?