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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What is the width of a decay and why is it given in energy units?

I'm reading Thomson, Modern Particle Physics, and in chapter 16 he says the width of the decay of the Z boson is $\Gamma_Z =2.452 \pm 0.0023$GeV. He also says the total width of the decay is the sum ...
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2answers
324 views

What's smaller: a neutrino, or a string from string theory [on hold]

I've recently read an article that stated "If an atom were as big as the solar system, a neutrino would be the size of a golf ball". I watch the science channel, and on (I believe) the show How the ...
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2answers
66 views

Can neutrinos interact by the EM interaction and gravity?

A definition of a lepton is: A particle that does not interact by the strong force but does by the 3 other forces.$^1$ Neutrinos are leptons, so from the above definition one would expect it to ...
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22 views

Does Compressing Energy over a Multiverse Dimensional Rupre Create Mass? [on hold]

my question is only on a specific method of creating mass through super collapsation of enormous amount of energy in at a singular point or point of singularity.
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1answer
56 views

Doesn't quantum uncertainty disprove string theory? [duplicate]

String theory states that the oscillations of little strings are responsible for all the particles in and the evolution of the universe. The specific type of particle created by a string depends on ...
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2answers
107 views

Sufficient conditions for a interaction to be classified as weak, strong, …?

Let us say I have been given the equation of a interaction/decay/etc. between particles: $$X+Y\rightarrow A+B$$ Are their any sufficient conditions that we can use to determine the type of interaction ...
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1answer
46 views

The interpretation of bubble and oyster Feynman diagrams?

I am reading 'A Guide To Feynman Diagrams in the Many Body Problem' By R.D.Mattuck, in which their is reference to oyster and bubble Feynman diagrams, shown respectively below. In these diagrams I ...
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46 views

How to understand CP-violation in kaon systems with Feynman diagrams and matrix elements?

I am trying to understand CP-Violation in the Kaon system using feynman diagrams and matrix element. Here is a slide from Mark Thomson corresponding exactly to what I am looking for (http://www.hep....
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55 views

Internal structure of electrons and quarks

I have some questions about experiments to probe the internal structure of electron and quarks. What type of experiments were done, in the recent years, to probe the internal structure of the ...
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1answer
34 views

Alpha Particle moving through a magnetic field [closed]

How would I find the acceleration of an alpha particle moving through a magnetic field given the force of the magnetic field, the charge, the initial velocity and the strength of the magnetic field.
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49 views

Mathematical method of Physics [closed]

Please any one can tell me how to get lecture of mathematical method of physics complete course online download complete lecture series. Which professor best for this subject please guide me how to ...
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0answers
27 views

At what density and conditions would Californium-251 reach a supercritical mass? [closed]

If I were to obtain a sample of Californium-251 that weighs 1mg, how would I make that sample reach a supercritical state at which it would create a cataclysmic nuclear detonation? In a sphere, at -...
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45 views

Running of $\alpha$ and scattering amplitudes

Consider a QED scattering process $e^-+e^-\rightarrow e^-+e^-$. The scattering crosssection at the tree-level depends on the square of the fine-structure constant $\alpha$ (apart from the electron ...
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3answers
497 views

How would cold neutrinos get trapped by stars?

Continuing on from the cool physics Q&A'd on the threads Where are all the slow neutrinos?, Is it possible that all "spontaneous nuclear decay" is actually "slow neutrino" ...
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0answers
63 views

Connection between Veneziano amplitude and Regge amplitude

I have tried to read about Regge theory, and I continue to run my head against the Veneziano formula, which is said to produce correct Regge trajectories by eg. t'Hooft at page 6 here: http://www....
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3answers
44 views

Can we give particle with no mass, mass? [duplicate]

Is it possible to take a particle with no mass and give it mass. For example light? Or increase mass?
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1answer
66 views

Definition of a meson? [closed]

I am looking for a definition of a meson that does not include the quark model. After some research I have come across this definition: A meson is a particle that is (1) believed to be ...
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1answer
28 views

Particle Data Group book

Many PDG data books have 'July' marked on their covers, does this mean they are published (and made available on their website) in July? When is it expected to be available this year? (date or month ...
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1answer
68 views

Which theoretical models are there between quantum mechanics and cosmology? [closed]

I'm an enthusiast/hobbyist right now and I'm quite curious about the subject of understanding which scales come between the quantum scale (ab initio/first principles) and the macroscopic scale. After ...
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5answers
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If particles are points, then aren't atoms empty space?

Zero dimensional points do not take up space, so then wouldn't everything in the universe be literally empty? Or is there something that I'm missing?
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3answers
345 views

Why Do Glueballs Have Mass, When Individual Gluons Are Massless?

From Wikipedia Glueballs Glueballs are predicted by quantum chromodynamics to be massive, notwithstanding the fact that gluons themselves have zero rest mass in the Standard Model. Glueballs with ...
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2answers
336 views

Is it possible that all “spontaneous nuclear decay” is actually “slow neutrino” induced?

This thought was inspired by a comment from the current leading answer, by @Sentry, to the question Where are all the slow neutrinos? This [slow-neutrino induced nuclear decay] will still be an ...
29
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5answers
4k views

Do massless particles really exist? [duplicate]

I was in doubt, so I went to wikipedia. There it says "the photon has zero rest mass", but on the side description it says the mass is $<1.10^{-18} \:\mathrm{eV}/c^2$. So is the mass of the photon ...
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Where are all the slow neutrinos?

The conventional way physicists describe neutrinos is that they have a very small amount of mass which entails they are traveling close to the speed of light. Here's a Wikipedia quote which is also ...
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Basic calculus of the adjoint spinor being transformed under parity

In Modern Particle Physics (p.287) Thompson says that under the parity transformation of the adjoint spinor we have $$\bar u=u^\dagger\gamma^0\rightarrow^p (\hat Pu)^\dagger\gamma^0= u^\dagger\gamma^{...
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1answer
31 views

Constructing singlet from doublets

Can we construct a gauge invariant term using the SU(2) doublet $l_L=(\nu_e e)^T$ and $(l_L)^c=C\bar{l}^T_L$? Since, both are doublets under SU(2), and $2\times 2=3+1$, I wonder what will be the ...
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Calculating photon number density inside a volume on whose surface the energy flux is known

I have the power spectrum for a galaxy of radius $R$, which we can approximate as a sphere at some distance $D$. Now, on earth we can measure the power spectrum which is given as a list of tuples, ( $...
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28 views

How to calculate off shell decay channel's branch ratio

I know for the on shell decay, the branch ratio equal partial decay width divide by total decay width. But for off shell decay, for example , $H\to WW^*$, one of the $W$ is off shell, how to calculate ...
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1answer
68 views

Is there a problem with our currently known fundamental particles?

Many scientists are searching for particles even more fundamental than leptons, quarks, gluons, etc. and (from what I know) string theory tries to hypothesize one elementary "thing" that everything is ...
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20 views

LHCb Peaking Background

I was reading a paper on the estimation of the branching fraction of B+ to K pi pi gamma. I was wondering whether you could clarify the meaning of peaking background. Thanks!
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1answer
15 views

Is in the area where the aurora's are also more cosmic ray?

On our poles the aurora's are the effect of high energy particles and photons comming from the sun (solarwind) and of cosmic ray. Those rays are interacting with the oxygen and nitrogen molecules/...
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1answer
28 views

Why are vector mesons identified by the adjective vector?

vector mesons are mesons with total spin 1 and odd parity (usually noted as JP = 1−). Compare to a pseudovector meson, which has a total spin 1 and even parity. coming from a mathematics ...
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32 views

Pair production of quarks

I was reading about pair-production of particles by photons, and in every place that I read, only the electron/positron production was said. So I had the following doubt, is it possible to have a ...
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720 views

Is there strong interaction between electrons?

I am not familiar with quantum mechanics at all. But I remember when I was at high school, we learned that strong interaction keeps protons next to each other while they repel each other because of ...
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How to know the cross section in this Fig

I wonder how to calculate the cross section of ( p p > gamma gamma b b~) (blue region) in the opposite plot, the y-axis is the number of events divided by 100 GeV with luminosity = 100 $\mbox{fb}^{-1}...
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1answer
267 views

Understanding CP-violation from a toy model of two fermions and a scalar boson

Consider a field theory given by the following Lagrangian $$\mathcal{L}_{int}=y\overline{\psi_1}\psi_2\phi+y^*\overline{\psi}_2\psi_1\phi^\dagger$$ where $\phi$ is a complex scalar field, and $\psi_1,\...
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4answers
122 views

How can fields interaction give rise to particles?

We say light a matter-wave, meaning along with its wave property it shows particle nature. But how can fields interaction (electric and magnetic) give rise to particles (photon)? I wish someone could ...
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Can we see/detect things which don't have electrons

Whenever we sees a thing the process happening at atomic level is the electrons of that stuff absorbs the energy from packets and goes to higher state and then comes to ground state and emits ...
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0answers
21 views

Why Weyl fermion in Weyl semimetals(WSM) have high mobility only at low temperature?

I read several papers reporting high Weyl fermion with very high mobility in WSMs such as TaAs, NbAs, WTe2 and so on. However, this high mobility looks like (=Weyl fermion) always appears at only low ...
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27 views

What is meant by interactions being mediated by force-carrier particles?

When a photon interacts with an electron, what is observed to happen? Force-carrier particles are described as the mediators of these interactions. What does this mean and how is this concluded?
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67 views

Do photons interact with everything?

Suppose you shoot a beam of photons in a particle collider. Are there any particles in which the photons do not interact with? Q2: What is an interaction between particles?
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56 views

Why isn't proton radiation by decay on earth known in nature?

Perhaps asking for why isn't appropriate in physics, but as there is neutron and alfa radiation what causes proton radiation not to be very common in nature (in laboratory it is seen although)
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1answer
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Weak decay iff or if strangeness changes? [duplicate]

I know that for a decay if the strangeness changes then the decay is a weak decay because strangeness is conserved in both strong decays and electromagnetic decays. However, is it also true that if a ...
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2answers
128 views

What is the meaning of the size of an elementary particle in QFT? What is the meaning of a point particle? [duplicate]

I have often seen people refer to the size of a particle being at most a given value, or a particle being a point particle, in the context of quantum field theory. Examples are the Wikipedia entry on ...
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1answer
34 views

Why could the Tevatron collider only exclude high masses of the Higgs boson?

I wish to know why the Tevatron collider could only exclude high masses of the Higgs boson ($158-175~\rm{GeV/c^2}$). The two mainly facts you must to consider are that the Tevatron uses energies off $...
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1answer
33 views

How do flavoured mesons decay?

I've seen (Cf. Griffiths' book) many diagrams of weak interaction of the type $q_1 \rightarrow q_2 + W^{\pm}$ (which are justified ultimately in terms of CKM transition values). But I don't understand ...
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2answers
42 views

Is uniqueness a fundamental property of nature? [closed]

The Laws of nature are universally applicable and at every point in force. Together they shape our universe but are all "shapes" unique? For example, is it possible that there is a second identical ...
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68 views

How is one element capable of radiating (almost) every wavelength? [duplicate]

Black bodies are considered as emitting all wavelengths. A incandescent light bulb has (nearly/almost) also the continuous blackbody spectrum near-perfect color rendition. In this bulb is only one ...
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2answers
101 views

Generalisation of a particle in QFT

In classical mechanics, we assumed a particle to have a definite momentum and a definite position. Afterwards, with Quantum mechanics, we gave up the concept of a time-dependend position and momentum, ...
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283 views

How it is possible to mediate a weak interactions by very heavy particle such as Boson?

When considering a weak decay interaction such as leptons , the weak force is mediate by huge particle such as bosons (W+ or W- ). How it is possible to have a such heavy particle within less massive ...