Tagged Questions

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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3
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2answers
26 views

Adding a tracer to the surface of a water droplet

I have a 2 mm water droplet generated by a syringe and falling down. I am using two perpendicular cameras to capture simultaneous frames from it. I need to track the droplet during the time and ...
0
votes
0answers
21 views

Where does the polarity of particles come from? [duplicate]

Going though current lessons, I can clearly see that some particles, electrons, are charged negatively and other, protons, are charged positively. Where does this polarity come from? Knowing that ...
3
votes
2answers
80 views

Is a wave packet physically realizable as a Fourier series?

In QM a wave packet is modeled as an infinite, or almost infinite, Fourier series, and the Fourier transform provides a transformation between momentum space and position space. To what extent is ...
2
votes
0answers
33 views

particle and antiparticle notation

This may be a very simple question but I'm really confused. If $\psi$ represents a particle (a Dirac fermion). What is an anti-particle represented by? Is it $\bar\psi=\psi^\dagger\gamma^0$ or ...
0
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0answers
19 views

Is the continuity (discontinuity) one of the intrinsic properties of all physical objects?

Is the continuity (discontinuity) one of the intrinsic properties of all physical objects? How do we define continuity? Which of the definitions of continuity are used (and why) in physics? This ...
-4
votes
3answers
106 views

how human is affected because of particle accelerator? [on hold]

I saw a TV series The Flash which is about physics fiction. What will happen when the human will caome in contact to bombardment of particle accelerator.
1
vote
0answers
23 views

Why do weak interactions give such slow decay rates, if the analog of the fine structure constant isn't signifigantly small?

Intuitively, it seems as though the reason would be a small value for the coupling constant, as the probability for emitting $W^{-}$ bosons would be low. However, it's value is almost the same as the ...
2
votes
0answers
30 views

Discrete Symmetries: Breaking and Preserving

This is not a question, let's list down all the effects resulting from breaking or preserving of various discrete symmetries, on various observables, be it in condensed matter or in high energy. ...
1
vote
0answers
33 views

Charge Conjugation Operator in Supermultiplet

Consider an $\mathcal{N}=1$ left-handed chiral supermultiplet. The particle content is $$L = (\phi\quad e_L) $$ where $\phi$ is a complex scalar and $e_L$ a left handed Weyl fermion. People usually ...
10
votes
2answers
127 views

Black hole “no hair” theorem

The "no hair" theorem (or conjecture), suggests that black holes can be entirely described by their mass, angular momentum and charge. All other details of the BH formation are lost. Is there a ...
4
votes
1answer
60 views

Is the decay $B\rightarrow K^* \gamma$ decay allowed in the Standard Model?

This is my idea of the Feynman diagram of the $B^0$ to a $K^0$ decay: The photon is radiated off by one of the particles, and by $up$ quarks I just mean ($u$,$c$ and $t$) and their antiquarks. how ...
2
votes
1answer
26 views

How can nuclear decay both annihilate and create?

This'll be back to basics for many of you, but here's something I still don't get. How can nuclear decay of an unstable atom both create and annihilate positron-electron pairs? You have an unstable ...
0
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2answers
51 views

What is the Weak force?

In this Particle Physics books I'm reading it explains Weak force with Beta Decay, a Neutron turns into a Proton after emitting an electron, so after it emits an electron one of the neutrons ...
5
votes
1answer
162 views

Is the particle reaction $π^- + p \to K^- + Σ^+$ possible?

I'm currently going over some undergraduate exams on particle physics and I'm having problems with a specific reaction, namely $$ \pi^- + p \to K^- + \Sigma^+ $$ which, in my opinion, is not allowed ...
1
vote
0answers
48 views

Mechanism of Supersymmetry Breaking (F-term, D-Term, Mediated)

I will make my question clear. SUSY is broken symmetry because we haven't seen superpartners. As far as I know, there are two mechanism of SUSY breaking, F-term and D-Term. Besides, there are some ...
3
votes
1answer
38 views

The differences of R parity and $U(1)_R$ symmetry

I know that we introduce R-parity to avoid proton decay. But some papers introduce $U(1)_R$ Lepton Number, e.g claudia, thomas. I have questions 1.What is the differences of R parity and $U(1)_R$? ...
4
votes
1answer
83 views

Engineering new particles

I am not a physicist, but I have a somewhat philosophical question regarding particle physics. In chemistry, and biology, there is a notion of synthesis, which has led to the creation of novel ...
0
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1answer
35 views

Building blocks of particles in different theories

If I understand it correctly, in most theories in physics we exploit the notion of point, i.e. we have e.g. point-like particles. In string theory, we don't have points, but a notion of string. What ...
6
votes
2answers
594 views

How is antimatter made?

How is antimatter made in laboratory? Can anyone explain, at the particle level, specifically how anti-protons and anti-electrons are made?
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0answers
13 views

What is the difference between wigglers, bending magnets and undulators?

At storage ring of a synchrotron we have three systems: wigglers, bending magnets and undulators, which have influence on the electron flow. Could you answer, what exact difference between them in a ...
1
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0answers
49 views

How to construct singlet and other multiplets from two triplets

Let an $SU(2)$ isotriplet operator is given by\begin{equation}\bar{l^c}i\tau_2\vec \tau l=l^T Ci\tau_2\vec \tau l\sim 3\end{equation} and an isotriplet Higgs field \begin{equation}\vec \Delta\sim ...
3
votes
2answers
281 views

Is there a connection between gluons and photons?

I was wondering if there is any sort of connection between a gluon and a photon since they are both considered massless.
2
votes
1answer
120 views

Is this summary of modern theoretical physics correct?

This is not exactly a physics question; it's more of a question about physics. You'll see what I mean in a minute. My understanding of modern theoretical physics is below. What I want to know is: Is ...
5
votes
1answer
375 views

How can mesons have spin greater than 1?

My understanding was that a meson, being made of a quark and an antiquark (spin 1/2) could only have spin 1 or 0, by addition of angular momentum states. I just saw an article ...
1
vote
1answer
65 views

Is it possible to make superpartner of Standard Model live in Mirror World?

In the ordinary Supersymmetry (SUSY), the superpartner of SM live in SM world (matter world). Then we introduce mirror world with mirror particle live there. I would like to make a new concept that ...
10
votes
2answers
117 views

Why do fermions come in generations, but not bosons?

Why does the $1/2$ spin of fundamental fermions (electrons, quarks, and neutrinos) split them into three variants that differ only in mass, while the integer spins of massless fundamental bosons (e.g. ...
4
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0answers
24 views

What are hadronic uncertainties?

I am reading articles about recent findings at CERN and the possibility of New Physics contributions, and they keep saying that the discrepancies may be due to hadronic uncertainties... What are ...
1
vote
0answers
37 views

How the neutron magnetic moment was measured?

How was the neutron magnetic moment measured? Was the antineutron magnetic moment measured too?
3
votes
2answers
365 views

What is meant by the spin of a particle? [duplicate]

I have been studying that electrons have quantum number called spin quantum number(s), this number can have either +1/2 or -1/2 value. If s=+1/2, the spin is clockwise and if s=-1/2, the spin is anti ...
4
votes
1answer
139 views

Why is Planck's constant the same for all particles?

This question came to me while reading "Where does de Broglie wavelength $\lambda=h/p$ for massive particles come from?". This question has a nice answer that explains that wave number has be ...
6
votes
0answers
205 views

Integration & bremsstrahlung calculation

In this paper (relevant pdf section) that I'm reading, involving the calculation of bremsstrahlung in electron proton scattering (diagram below), the author calculates the integral over outgoing ...
7
votes
2answers
275 views

How detectors in particle colliders can differentiate neutrons from antineutrons?

Their mass is the same. None of them interacts with EM fields. And their decay (around 1000s) is far too slow to see their decay products yet in the detector. How is it then possible to differentiate ...
3
votes
0answers
25 views

Symmetric neutrino mass matrix?

(i) Is there basis in which the $3\times 3$ sub-matrices $m_L$ and $M_R$, of the $6\times 6$ neutrino mass matrix $$m_\nu=\begin{pmatrix}m_L & m_D\\ m_D^T & M_R\end{pmatrix}$$ can be made ...
0
votes
1answer
52 views

Constraints on new unknown stable fermions?

This question is rather speculative, but I would like to ask it anyway. What are the constraints on possibility of discovering new unknown stable fermions of some sort in the future? If I am not ...
2
votes
1answer
24 views

$B^{0}$ decay into $K^{+}$ and $K^{-}$: equally probable?

One of the decay modes of the $B^0$ meson is $B^0 \rightarrow K^{*0} \mu^{+}\mu^{-}$, with $K^{*0} \rightarrow K^+ \pi^-$. But because of the $B$-meson oscillatios, we can also have $ B^0 ...
0
votes
1answer
27 views

Why is a “Semi-leptonic” Decay Mode called so?

Why is a semileptonic decay mode called so? I mean, if there is one lepton amongst the decay products, it should be leptonic, right? If there are two, that should be called bi-leptonic or something ...
1
vote
1answer
47 views

Tetrad choice for Pauli-Lubanski in the massless case

The Pauli-Lubanski pseudovector coincides with intrinsic spin in the rest frame of the particle. In a more general frame, one defines a tetrad and projects the PL vector on it to define intrinsic spin ...
4
votes
1answer
131 views

Does accelerating generate gravitons?

If gravity and acceleration are indistinguishable, then does that mean converting potential energy to kinetic energy generates gravitons... but only temporarily until you stop accelerating?
2
votes
1answer
27 views

“Radiative” particle decay?

This might be a very simple question, so sorry. I have encountered the expression "radiative particle decay" quite a few times now, and none of the sources ever explain what they mean by radiative: I ...
3
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0answers
17 views

Cronin enhancement in p-A collisions

What is the physical picture behind Cronin enhancement in proton-nucleus collisions at intermediate transverse momentum?
2
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1answer
124 views

Group Theoretic definition of a particle

We intuitively have a sense of what a particle means in the conventional sense. But is it possible to have a group theoretical definition of a particle, I mean in terms of irreducible representations ...
0
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0answers
12 views

Penning Trap Simulation

I'm currently working on a particle tracker and I would like to implement a Penning trap. I think I might have a problem with the field of the electrical quadrupole. My idea was to place 2 dipoles and ...
3
votes
0answers
86 views

Computing box diagrams with non-vanishing external momenta

I'm trying to explicitly compute the following box diagram in the Feynman-t'Hooft gauge: If I neglect the impulsion of the $s$ quark, then the final amplitude is given by $$\mathcal{A} \propto ...
2
votes
3answers
90 views

What happens to photons after they hit objects?

If I am not wrong when light hits for example white wall most of the photons are absorbed and transformed into heat and few of the photons at certain wavelength are reflected from the object. So white ...
2
votes
2answers
134 views

What's the symbol for the antiparticle of the delta plus baryon?

It can't be $\Delta^-$ since that is another particle also made up of quarks (not antiquarks). I can think of four possibilities: $\overline\Delta^+$ $\overline{\Delta^+}$ $\overline\Delta^-$ ...
1
vote
1answer
35 views

Simultanously HOT and DENSE in QCD?

Take this form of the QCD Phase Diagram for example: This baryon density is a number density - i.e. number of baryons in some volume. Why are baryon density and temperature regarded as ...
2
votes
2answers
27 views

Meaning of SIS in accelerators

With reference to accelerator facilities, the term "SIS" is often used. e.g. SIS-100, SIS-300 etc. What does SIS stand for, in this context? (The last S is probably for Synchrotron) Google appears ...
9
votes
1answer
159 views

Why Lorentz group for fields and Poincaré group for particles?

Wigner treatment associates to particles the irreps of the universal covering of the Poincaré group $$\mathbb{R}(1,3)\rtimes SL(2,\mathbb{C}).$$ Why don't we consider finite dimensional ...
0
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0answers
30 views

Constant Rayleigh Scattering Cross Section

in the Review of Particle Physics - Interactions of Particles with Matter, there is a plot that gives the cross sections for different interactions of photons with matter. One of them is Rayleigh ...
0
votes
1answer
54 views

Why can't muons be the carriers of the strong interaction?

The strong forces operate up to range of $10^{-15}$ meters. The calculations for Muon reveal that they can be propagator for distances up to $10^{-14}$ meters. Why can't I ignore the factor of 10 and ...