Questions tagged [elementary-particles]

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Probability of forming a proton or neutron with loose quarks?

If I had two unbound up quarks and a down quark or two unbound down quarks and an up quark, what is the probability, if I bring them close together, they stick and form a proton and a neutron, ...
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1answer
124 views

Spin of the particle and degrees of freedom

Wigner showed that irreducible representations of the Poincare group can be listed, depending of the mass being zero or larger then zero, as $2J+1$ dimensional representations where $J$ is half-...
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1answer
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Is an electron an ideal magnetic dipole?

Spin (for example of an electron) is described as an intrinsic form of angular moment, and we often say the electron has therefore magnetic moment, due to this angular moment. Well, I suppose when we ...
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785 views

Electron plasma

Can a plasma consisting of only electrons exist in a stable configuration? I do not mean a plasma consisting of separated protons and electrons, but only electrons in an extreme high density. Systems ...
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1answer
344 views

What effects would a finding of Gravitational Repulsion Between Matter and Anti-Matter in the ALPHA Experiment have on Mainstream Theory?

The actual nature of the gravitational force between matter and anti-matter (attractive or repulsive) remains unsettled: See Are there experiments taking place right now that might show evidence for ...
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1answer
65 views

Do charges have spatial dimension?

I don't know much about anything in physics. I hope you can bear with that. Let me start with my question do charges have any dimension, by this I mean physical dimension like length, breadth, height ...
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1answer
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Behavior (wave or particle) of the photon absorbed by an electron

After being absorbed by an electron, does a photon continue to behave like a particle, or like a wave, or both?
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1answer
42 views

How is the difference in ground and excited state of baryons masses explained within QCD and SM?

How is the difference in ground and excited state of baryons masses ($\Sigma$ and $\Sigma^*$, $\Xi$ and $\Xi^*$ for example) explained within QCD and SM? Is it possible to calculate (predict) this ...
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1answer
108 views

Is any particle allowed within the laws of physics?

In the same way wormholes are possible but not guaranteed to occur naturally, is a theoretical particle possible such as one with a mass of a tonne and a charge of -3, or are there upper and lower ...
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2answers
51 views

Origin of particles at the Big-Bang

When we read writings on the Big Bang, in Planck's time (and even for some who try to imagine what was before), one talk about particles and antiparticles, but where do these particles and their ...
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1answer
43 views

Is PMNS neutrino mixing allowed in the standard model?

Some people say that the standard model does not allow for non-zero neutrino masses: it prevents renormalization, they say. Other people say that massive neutrinos with PMNS mixing are allowed in the ...
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1answer
54 views

Mass of the fundamental particles

I have always wondered that how do scientists measure the mass of a fundamental particle. Obviously they can't weigh it in a conventional machine we use to weigh other things in our daily life. And do ...
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2answers
227 views

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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0answers
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Particles in curved space-time and group representation

It is well-known, that particles in Minkowski space can be constructed as unitary projective representations of the Poincaré group, i.e. isometry group of Minkowski space: $$M_d= \frac{Poincare_d}{SO(...
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1answer
41 views

Traces at pion decay

A negative pion breaks down into a muon and a muon antineutrino. What do the traces of the pion decay look like in a bubble chamber with a vertical, static homogeneous magnetic field? My ideas: The B-...
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1answer
30 views

What is the relationship between the different aspects of mass?

There seem to be several different ways in which mass manifests itself, in particular with reference to fundamental particles: Gravitational mass. Inertial mass. The coupling to the Higgs field. The ...
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1answer
37 views

Derivation of interaction potentials of fundamental forces

In Gauge theory of weak interactions by Greiner and Müller, they show the following superb comparison of the interaction potentials between particles as a function of separation: I have never seen ...
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1answer
44 views

Conserving angular momentum in elementary decay/reaction

I am trying to understand how to conserve angular momentum in a elementary decay/reaction. Consider the elementary reaction: $$ K^{-}(J = 0) +p(J = 1/2) ~\to~ \Omega^{-}(J = 3/2) + K^{+}(J = 0) + K^{...
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1answer
60 views

Difference between strong interaction and weak interaction?

I was looking at a straight forward answer on internet which I am unable to find. Can there be a strong interaction in which transformation of one quark flavour into other takes place(Eg. up quark -&...
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2answers
98 views

What precisely and mathematically does it mean to say gauge bosons as elementary particles?

In standard particle physics textbook, we say that photons, gluons and $W$ and $Z$ bosons are gauge bosons as elementary particles. However the gauge bosons are vector bosons and they carry the form ...
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2answers
151 views

Can a massless particle have both spin and charge?

Can a hypothetical elementary particle, at least in theory (according to the current science), have 0 mass and yet also have both spin and electrical charge (at the same time)?
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1answer
521 views

Is muon muon annihilation already realised?

As muon colliders do not yet exist, has muon-muon annihilation already been realized experimentally?
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1answer
680 views

Mass Resolution- Particle's width in Particle physics?

I'm not 100% sure. but I think that the width of a particle could change depending on the decay channel. for example: The J/psi's mass resolution could be 40 MeV or in other cases 8 MeV. So I would ...
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5answers
5k views

Are protons bigger than electrons?

In every text/ physics book that I've read, Protons are mentioned as particles that are bigger, way bigger 2000 times to be precise, than electrons...I believed that until a few minutes ago when I ...
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2answers
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How can a truly elementary particle decay into other particles? [duplicate]

Consider (for example) the next particle decays: The decay of a Higgs and the decay of a muon [in the diagram of which we also see the decay of (virtual) $W^-$ into an electron and its associated ...
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0answers
34 views

QCD methods - Dirac trace, trace in color space, trace in flavor space

What is meant by the following terms in QCD - Dirac trace, trace in color space, trace in flavor space, etc. Could someone explain with an example (For eg. what's the diffrerence between something ...
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Calculating the quark propagator while dealing with the color, Dirac & flavor matrices all together

$S^+$ is a diagonal matrix in color space, and is given as : $S^+ = S_{rg} ^+ \hat{P_{rg}} + S_b ^+ \hat{P_b}, where, \hat{P_b} = 1_c - \hat{P_{rg}}$ is the projector on blue quarks, $\hat{P_{rg}}$ ...
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1answer
48 views

How to prove the equivalence of two definitions of hypercharge?

Before introducing top bottom and charm quarks,Strong Hypercharge is defined in the following two ways--- $1.\,\,\,Y=B+S$ where $Y,B,S$ are the hypercharge, baryon number and strangeness respectively. ...
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Frequency of photons and speed in media

I'd like to ask a few questions about photons, not as a professional of physics. Frequency: Since it's connected to the frequency of the wave composed by the stream of photons but can be defined for ...
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1answer
79 views

How to transform a given Lagrangian to a Nambu-Gorkov basis?

With reference to the Nambu (or famously, Nambu-Gorkov) transformation in this paper, could someone explain the reason behind using the 3rd Pauli matrix in the Lagrangian after equation (2.3) (would ...
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2answers
94 views

If virtual particles are considered to be just mathematical constructs, does this imply there are no corresponding physical processes?

Some people consider all elementary particles to be non-existent. They tell us that they are changes in the field configurations that last which are called "real particles", while those that ...
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3k views

Why do physicists think that the electron is an elementary particle?

When we first discovered the proton and neutron, I'm sure scientists didn't think that it was made up of quark arrangements, but then we figured they could be and experiments proved that they were. ...
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1answer
52 views

Conservation of chirality in non-weak elementary particle interactions

Chirality is not conserved in propagation (e.g., electron oscillates between left and right chiral). But is chirality conserved in interactions? What is a good reference paper or book for this notion ...
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502 views

Why should I believe that “elementary” particles are indeed elementary?

Atoms were once thought to be indivisible (i.e. have no substructure) until it was discovered that they are made of protons and neutrons. Protons and neutrons in turn are made of quarks, and that's ...
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Parity of Particles

Like charge, spin,etc.. Parity is an intrinsic property of the particle. As I read in Grifith's introduction to elementary particles book , he states parity mathematically but I am not able to see it ...
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2answers
58 views

Entropy always increases. Then why did elementary particles come together to form an atom?

It is generally said that entropy always increases. But after the Big Bang elementary particles came together to form an atom. Isn't that paradoxical ?
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1answer
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Why the mesons $\pi^0$ and $\eta$ are “degenerate”

I don't know anything about elementary particles, but reading the book by Zeidler on p158, table 2.8 one can observe the quark content of baryons and mesons. It is strange that the $\pi^0$ meson has ...
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1answer
63 views

Question about a relativisticaly accelerated harmonic oscillator

How can the speed of oscillation of a harmonic oscillator be affected if somehow it got accelerated to a relativistic speed perpendicular to its oscillation? Can this be compared with the effect on ...
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1answer
39 views

Which is the meaning of these masses?

When reading about the masses of neutrinos in the HDM (Hot Dark Matter) model of the universe, I came across the following equation: $$\tag{1} \sum_i m_{\nu_i} = 92 \Omega_\nu h^2 \text{eV}$$ My ...
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4answers
105 views

Do elementary particles last forever?

I have heard that not even black holes last forever, because of Hawking radiation. But what about elementary particles? Will an electron, for example, exist for all time?
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1answer
85 views

If we had enough energy available in particle colliders, what reactions could show up if the quark and electron fields weren't fundamental?

Suppose the quark and lepton fields weren't the fundamental fields of Nature, but that a "deeper" Lagrangian connected to a generic model of sub-quarks and -leptons would take over the ...
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Haag's comment on the relation between fields and particles

I am very confused by the statement made in Haag's, Local Quantum Physics: Fields, Particles, Algebras (page 46): ... the idea that to each particle there is a corresponding field and to each field a ...
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2answers
72 views

What principle of quantum mechanics tells us that harmonic fluctuations of a field act like localized particles? [duplicate]

"Quasiparticles" are ubiquitous in condensed matter physics, e.g. magnons and phonons, and more generally all particles in quantum field theory are considered the elementary harmonic ...
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1answer
118 views

Which equations of 5 string theories show that elementary particles formed by strings?

It is commonly said that "elementary particles are indeed formed by strings." (from E Witten interview) Which equations of string theory show that elementary particles are indeed formed by ...
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98 views

Electric field associated with a stationary electron

In the framework of QFT, quantum fields are the fundamental objects instead of point-like notion of particles. Particles, at least fundamental ones like electron, are understood to arise as ...
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2answers
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What is the evidence (experimental observation) that elementary particles have spin angular momentum?

From what I have read here, the concept of spin is attributed to a calculation based on a mathematical model using quantum mechanics. For example, How can a particle with no size have angular momentum?...
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An electron has no known internal structure, does that imply it has an unknown one?

I'm currently reading Alonso and Finn's Electromagnetism book. It explains that the spin contributes to the magnetic moment and is somewhat comparable to a rotation of the particle around its own ...
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1answer
47 views

Does tau decay to rho meson + tau neutrino?

In the particle data group table: http://pdg.lbl.gov/2020/tables/rpp2020-sum-leptons.pdf ,only $\tau \rightarrow \pi + \nu_{\tau}$ is documented. But does $\tau \rightarrow \rho + \nu_{\tau}$ as well? ...
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Why do the masses of fundamental particles seem to increase exponentially?

The (15 positive) masses of fundamental particles are measured inputs to the standard model. They seem to increase exponentially when ranked in increasing order, or perhaps follow a power law when ...
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Why do quarks have a fractional charge?

I am aware that evidence exists that strongly suggests the existence of quarks and do not doubt it. It is just simply really weird to me that they can have a fractional charge. While other ...

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