# Questions tagged [elementary-particles]

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### Is there a reason, other than mass hierarchy, that we associate each quark generation with a particular lepton generation?

The Standard Model contains three generations of quarks, and three generations of leptons. We generally pair off these generations into the "light" generation ($e, \nu_e, u, d$), the "medium" ...
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### What are the allowed $W$ bosons in Muon decay?

I am curious about the allowed Feynman diagrams in Muon decay and whether the $W$ boson can be either the $W^+$ or $W^-$. Muon decay follows the reaction: \mu^-\rightarrow e^-+\...
48 views

### Can string theory explain why the charge of the positron and of the proton are equal? [duplicate]

There is not much more to elaborate. Can string theory say why electrons and protons have exactly opposite charge? And thus why hydrogen atoms are neutral? I guess that the answer is no, because ...
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### Approximating the wave functions of multiple electrically charged elementary particles as a function of time and position

As I understand it the wave function of a free particle in natural units is defined by the equation $$\Psi(\vec{r},t)=\left(\frac{a}{a+it/m}\right)^\frac{3}{2}e^{-\frac{{\vec{r}}^2}{2(a+it/m)}}$$ with ...
81 views

### Minimal size of physical entities

I know that per current knowledge there are layers of size of physical entities going from elementary particles to molecules (and from molecules to molecular structures such as bricks or organism ...
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### How do we know that the charges in an electron and a proton are equal? [duplicate]

An electron and a proton have opposite charges. But how can we be so sure that they have equal amount of charge but opposite? Can't there be a slight difference?
50 views

### Is it possible for a charged particle to have no spin? [duplicate]

Can a charged point particle ever have spin zero? If not why?
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### Question about quantum fields, elementary particles, and quantum numbers, and fundamental forces

As I understand it the allowable spin states of elementary particles is tied to the number of space and time dimensions, so for any two universes with the same number of space and time dimensions the ...
36 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-...
27 views

### Can Target in x-ray emit L alpha without emitting K alpha? Also can hydrogen emit characteristic x-ray?

Is it not possible that incoming electron excite the hydrogen atom and then when it de-excites it releases radiation? Here please don't answer no because hydrogen is light. My actual query is can ...
175 views

### Why doesn't string theory predict the existence of infinitely many elementary particles?

I'm a physicist, but my knowledge of string theory is extremely minimal. My naive conceptual understanding is that the vacuum is modeled as a certain topology (and geometry?) for the spacetime, and ...
48 views

### Quantum particle definition

I'm reading a-lot of articles lately which mention "quantum particle" I was wandering what defines quantum particle in opposed to "regular particle"? from what I've read on the web, there are two ...
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### How can electrons and quarks be composite?

There are theories suggesting that the electrons and quarks are not elementary particles, but instead are composite particles of two or more yet undiscovered elementary particles. However ...
88 views

### What does color represent in quarks?

Im sure I'm pretty undereducated to be asking a question like this, but what do the colors represent in quark chromodynamics? A I understand it, each color represents a sort of charge, but what kind ...
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### Are all bound states entangled?

In QM, a bound state is a special state of a particle subject to ta potential such that the particle tends to remain localized in space. The potential may be external or it may be the result ...
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### How to interpret air movement when we breath in terms of fundamental laws of nature?

How to interpret the movement of air in nose in the two parts of breath : inspire and expire in terms of the 4 interactions of nature, gravitational, electromagnetic, weak, strong interactions ?
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### Pauli's exclusion principle in elementary particles

Elementary particles such as Quarks obey Pauli's exclusion principle since they exist in three colors (RBG). Where as electrons which is also elementary that does not have any color quantum numbers ...
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### Can elementary particles quantum entangle?

I just want to know if elementary particles, such as a quark, can entangle with another elementary particle of the same kind. If so, does entanglement for elementary particles follow the same ...
6k views

### Is there anything in the universe that cannot be compressed?

I've always thought that there is nothing in the universe that cannot be compressed or deformed under enough force but my friend insists that elementary particles are exempt from this. My thought is ...
100 views

### Half life of elementary particles

Do elementary particles have half life? Can we theoretically calculate half of a particle which is in complete isolation?
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### Why do electrons have rest energy?

E=mc² so inserting the value of m and c we get 0.511 MeV for electron but then what does this energy account for coz according to me electrons are not made up of any particles so this doesn't account ...
75 views

### Why don't strings have a Planck mass? (version 2)

The Energy $E$ of a fundamental string due to its length $L$ goes like $$E\sim TL$$ where string tension $T$ is given by $$T \sim \frac{1}{l_P^2}$$ (Using natural units $\hbar=c=1$ with planck ...
108 views

### Why don't strings have a Planck mass?

I understand that strings have a size of roughly the Planck length $l_P$ of $10^{-35}$ m. If that is the case then one would expect that their mass would be roughly the Planck mass which is an ...
216 views

### If quarks don't exist individually how can we say baryons are made up of three quarks?

We know the composite subatomic particles are made up of odd number of quarks (at least 3 for baryons ) or combination of quarks and antiquarks (mesons). My question is if they don't exist ...
51 views

### Possible Feynman diagram for $\tau^+ \rightarrow p \mu^+ \mu^-$ and $\tau^+ \rightarrow \bar{p} \mu^+ \mu^+$?

I want to know the possible Feynman diagram for these two lepton family, lepton and baryon number violating tau decays. These decays are forbidden in the Standard Model. But the further extension of ...
80 views

### Are there compelling reasons not to organize the elementary particles by charge and spin? [closed]

I don't like the way the standard model is currently displayed (see second picture for reference). It does a poor job of abstracting the information into something understandable. As far as I ...
126 views

### Do elementary particles have a density?

The SM supposes elementary particles are structureless unless composite objects like hadrons. For bosons, that can occupy the same state, we can define energy or mass density. The same happens but ...
125 views

### Can there be interference between a proton and an electron?

For example, we know that we can interfere two different electrons or two different protons by employing them in a double-slit experiment. Now suppose, we mix protons and electrons and shoot them ...
1k views

### How are quarks elementary when they can become leptons? [duplicate]

From a recently reignited [casual] curiosity into particle physics thanks to the Fermilab YouTube channel, I read about the g-2 experiment, followed by muons, naturally. Muons, it turns out have short ...
6k views

### When an electron changes its spin, or any other intrinsic property, is it still the same electron?

I am not asking why an intrinsic property, like spin can have more then a single value. I understand particles (electrons) can come to existence with either up or down spin. I am asking why it can ...
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### How do we know that the $W$ and $Z$ bosons aren't composite?

Background to my reasoning: When the strong force was first discovered, it was considered to be the force that interacts between nucleons to keep the nucleus together and that the mediator bosons of ...
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### Which sterile neutrino are we looking for?

I am trying to wrap my head around sterile neutrinos. As far as I understand it, sterile neutrino is a name for every particle that feels only gravitational force. The most notable example is a right-...
58 views

### Sizes of Elementary Particles

Present observation shows that elementary particles have no internal structure, and have no real size as they are described by wavefunction. Something that therefore confuses me is that on a lot of ...
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### why do quantum fields exist? [closed]

Why did the big bang give rise to the quantum fields it did, could the big bang have created the universe any other way? and why not more elementary particles?
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### Are fundamental particles more than their properties?

Parent questions: What came first, neutrons or electrons? Why saying that during electron capture the electron is converted to a neutrino? Background: various nuclear phenomena show the ...
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### What gives an electron its charge? [duplicate]

What exactly gives electrons a charge? I understand how in molecules, an imbalance between electrons and protons give ions charges and I also understand that there is really no positive or negative ...
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### Branching fractions for the 125 GeV Higgs boson

Calculating the branching fractions of a Higgs boson $m_h=125\,\text{GeV}$ into a muon and an anti-muon, and a $b$-quark and an anti-$b$-quark from the decay formula \Gamma=\frac{\alpha_{w}}{8 \...
4k views

### Can two people see the same photon?

In a dark room there are two people and a very faint candle. Then the candle emits one photon. Is it true that only one person can see the photon? Why? And are there any experiments? Edit 2019/4/23: ...
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### Is there an example of two elementary particles colliding to result in a single elementary particle?

Apologies for the novice question, but I don't know enough particle physics to immediately answer my own questions. I have the following questions. Is there an example of an inelastic collision ...
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### Why is Higgs Field a scalar field?

I am reading the book ‘Introduction to Particle Physics’ by Martin and Halzen. In the section about the Higgs Field the book considers the scalar field that interacts with a vector field. Using ...
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### Is there a weak hypercharge : spin-3/2 analogy?

So I was not trained as a particle physicist, but I left a table of particles on a post on Hacker News based on what little I do understand about the conservation of weak hypercharge and weak isospin. ...
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### Is there any Feynman diagram for Baryon/Hyperon decay with missing energy?

I am reading the hyperon decays with missing energy this paper tells for the prospects of baryon decays with missing energy I want to know some of the Feynman diagrams for hyperon decays. Can anyone ...
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### Why do we use this diagram/model for elementary particles?

The model of elementary particles is analagous to the periodic table, which is organized not only beautifully, but also functionally. The typical model for the elementary particles that pops up ...
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### Would manganese, iron, osmium,fluorine or nitrogen cations hold a higher linear energy transfer than carbon cations?

Is linear energy transfer in particle radiation therapy directly proportional to the particles' density? I.e directly proportional to the mass and inversely directly proportional to the volume? If ...
69 views

### What elementary particles have properties that vary by spin direction?

This table of elementary particles indicates that electron spin = 1/2. My understanding is that electron spin may proceed in two directions which may be denoted by spin sign and that electron spin ...
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### Two possible directions of the B field in relation to the E field in radio waves. How induce the left-handed direction?

In vacuum the two field components of a radio wave are directed perpendicular on each over. $\mathbf{E}$, $\mathbf{B}$ and $\mathbf{k}$ form a right hand system ($\mathbf{k}$ is the direction of ...
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### Shape of electron [duplicate]

Today, in the BBC Science section, a headline reads that the Imperial College of London has determined that the shape of the electron is completely spherical. In a physics book I'm reading now, the ...
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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 ...