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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What do the overlines above some terms in the Standard Model represent? [closed]

Why do some terms in the Standard Model, like the Theta parameter (among others) sometimes have a little dash or bar, like an overline, above them? What does it mean?
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What is the formula/method to calculate the range and energy loss by electron passing through an medium?

I want to know how it is calculated that an electron having certain energy will pass how much distance inside an material (solid). Actually I want to shoot an electron from vacuum to air and for not ...
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What is the the importance of neutrino in modern physics? [closed]

In my understanding, a neutrino is a Fundamental particles that only interact via weak interaction and gravity. It oscillates between different flavours which means it has mass. Ongoing research is ...
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Correct answer on a multiple choice question regarding the effect of beta decay on lead [closed]

$^{210}_{82}\text{Pb}$ emits two beta particles and it is transformed into Polonium. After that the Polonium emits one alpha particle and gets transformed back into $\text{Pb}$. The nuclear decay ...
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What is the maximum spin of a particle? (Both theoretically and observed)

I know that the elementary fermions are spin 1/2 and the elementary bosons are spin 1 (except the potential graviton), but are what is the highest known spin of any elementary particle (including ...
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Popular Research Areas in Theoretical Particle Physics [closed]

To quote a section written by Joseph Conlon in his book "Why String Theory?": The fashionable areas vary hugely with time. At one time it was proton decay and grand unified theories, at ...
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Oscillation of charm meson [duplicate]

In the LHC they have found a meson(the charm meson) which oscillates between itself and its antiparticle and they have also found there is a difference in mass between the charm meson and the ...
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1answer
54 views

Is there a hard clear division between a particle and a wave? [duplicate]

My limited understand is that photons can we both or is a particle and a wave. But they have 0 weight(?) I found this quote today: "Quarks, like all elementary particles, are excitations of a ...
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1answer
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Partition design in regard to double slit experiment

Has a totally blocking physical partition ever been used in between the slits in order to keep a particle waves to join after having gone through the two slits?
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1answer
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How can i shoot accelerated electron directly into the air?

I am trying to do an experiment in which I have to first accelerate the electron to 10eV and then shoot into the air directly. I need some kind of membrane which allows electron to pass and keep ...
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Gell-Mann-Okubo linear formula

I know that quadratic form of Gell-Mann-Okubo is $$ M = a_0 + a_1 Y + a_2 \left[ I \left( I + 1 \right)-\frac{1}{4} Y^2 \right] $$ using isospin and strangeness it can be rewritten to $$\frac{N + \Xi}...
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Can we use Shrink rays plus Nano-particles to send robots to the past [closed]

We could use shrink ray's to enter the quantum realm, I researched about Muon, Higgs-boson, and quark particles, at least one of them can be used for a shrink ray, but I'm not asking if we could build ...
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What do these straight lines in the graph mean?

Does it mean thermal equilibrium? If the answer is yes, then how do we get to the molecular dissociation stage when we have already reached thermal equilibrium in vibrational mode? Because equilibrium ...
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How is energy photon emission balanced? [closed]

A neutral pion has a rest energy of 135 MeV and a mean life of If it is produced with an initial kinetic energy of 80 MeV and decays after one mean lifetime, what is the longest possible track this ...
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1answer
58 views

How to determine the number of physical parameters in Yukawa couplings?

Suppose we have a Lagrangian containing a series of Yukawa couplings between fermions $\psi_i$ and scalars $\phi_i$, $$\mathcal{L} \supset y^k_{ij} \phi_k \overline{\psi}_i\psi_j + \rm h.c., $$ where $...
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General 2-body decay [duplicate]

I have the 2-body decay rate: $$|\vec{p}_1| = |\vec{p}_2| = \frac{[(M^2 - (m_1 + m_2)^2)(M^2 - (m_1 - m_2)^2)]^{1/2}}{2M}$$ $$d\Gamma = \frac{ \left| \mathcal{M} \right|^2}{32 \pi^2} \frac{|\vec{p}_1|...
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82 views

The electric charge of quarks

How can we determine the electric charges of quarks? And what are the values? The color charge is not the electric charge... How do we even know their electric charge? I would think that there are ...
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Am I correct in understanding that everything in the Universe is entangled with everything, only to varying degrees?

Since all quantum fields directly or indirectly constantly interact with each other, can we say that everything in the universe is entangled with everything, only to varying degrees?
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How does the Higgs boson get its mass? [duplicate]

I understand that Higgs boson gives other particles mass. But how does it get its own mass? Does it interact with another field?
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1answer
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Particle momentum in collision expressing in Mandelstam variable

Consider the s channel process, I use the metric convection $+---$ instead, the constraints are: Conservation of four momentum: $p_{1}^{\mu}+p_{2}^{\mu}=p^{\mu}$ and on mass shell condition $p_{i}^{2}=...
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Entropic factor of electron-positron annihilation [closed]

In this question, user Nicolau Saker Neto states that "The distinction between enthalpy and Gibbs free energy in such subatomic reactions is completely negligible, as the entropic factor is ...
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3answers
60 views

Pair production from one gamma photon to an electron and positron

According to this Wikipedia article, the Electron–positron annihilation forms two gamma photons from an electron and a positron collision. However, according to this other article from Wikipedia, pair ...
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Why can't I assume the quarks inside a hadron move together?

Looking at the following Feynman diagram: Using conservation of energy, we can see that in the rest frame of $D^0$, the energy of $K^-$ is higher than its rest energy. Meaning, it is in motion. I ...
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Why are the parity quantum numbers of low lying hadrons what they are?

So you can get the flavour and angular momentum from the $SU(3)_F$ symmetry and rotational symmetry respectively but I haven't seen how these models predict the parity of these states (and similarly ...
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1answer
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Photon-Gluon annihilation in QCD

I am starting to learn about QCD, and I wanted to calculate the squared matrix elements for photon-gluon annihilation into a quark and an anti-quark. However, I am having trouble writing down the ...
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2answers
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Why isn't electron spin a real rotation? [closed]

When an electric current flows, a magnetic field is created. Then, isn't the magnetic field of a magnet also caused by an electric current?
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1answer
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Effective description of the EM interaction of protons by modifying the original Dirac equation [duplicate]

Dirac equation describes elementary fermions (e.g., electrons, muons, etc). When coupled to electromagnetic fields, the $g$-value comes out to be equal to $2$ which is exactly the value for the ...
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Application of Lie groups in particle physics [duplicate]

Is there a simple answer to the question, how lie groups are used in particle physics?
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Fermi-Dirac vs. Maxwell-Boltzmann distribution in the early universe plasma

From my studies, I remember that the quantum effects relative to the bosonic or fermonic nature of the particles play a role only in the conditions of degenerate gas: when the plasma is very dense and ...
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1answer
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Relation between Decay Rate and Annihilation Cross Section

In particle kinematics and realistic observable, one typically works with scattering cross sections and decay rates. If one has an expression for a decay rate for a particle of a certain type to decay ...
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How to reduce an integral in phase space to an one-dimensional form?

I've been trying for a very long time to show that the following integral: $$I_D=2{\displaystyle \int} \, {\displaystyle \prod_{i=1}^3} d \Pi_i \, (2\pi )^4\delta^4(p_H-p_L-p_R) |{\cal M}({e_L}^c e_R ...
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1answer
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Symmetry factor of a Feynman Diagram

I saw there are already many questions here about the symmetry factor of Feynman diagrams but most of them are about theories that contain only scalars. My question is: What is the symmetry factor of ...
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How can we detect particles that have no electric charge?

Particle accelerators look for electric changes, but what if particle has no effect on other particles or an electric charge, would we not detect it?
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Fundamental Particles (Quarks) and Quantum Fields

From what I have understood while studying quantum and particle physics is that all the particles are excitations of their respective fields. This makes me wonder if elementary particles like quarks ...
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1answer
60 views

What prevents us from considering the magnetic dipole of subatomic particles to be as fundamental as the charge

After the discovery that subatomic particles have a magnetic field, explanations were sought. Ultimately, it boiled down to the fact that electric circuit currents in the particles are responsible for ...
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Proving that neutron and antineutron are not the same particles [closed]

How can you prove that the neutron and antineutron are not the same particles knowing that neutron is not a stable particle?
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Have we ruled out the Minimal Supersymmetric Standard Model (MSSM)?

This question is inspired by a Physics Stackexchange question posted 8 years ago (The future of supersymmetry). The question that I have is very similar to the question in the above link, except that ...
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Particle decay, decay rate [closed]

I have a questions about the article Particle decay two-body decay. $$|\vec{p}_1| = |\vec{p}_2| = \frac{[(M^2 - (m_1 + m_2)^2)(M^2 - (m_1 - m_2)^2)]^{1/2}}{2M}$$ $$(M, \vec{0}) = (E_1, \vec{p}_1) + (...
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2answers
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Is there a relationship between the properties of different charges of a fundamental particle?

To begin with, I'm a high school student and so my understanding of QFT is quite basic. Due to this, I'd prefer a simple answer (it would be great if it's yes/no) along with a very basic explanation. ...
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1answer
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How can charm mesons conserve charge?

If a charm meson can change from particle to antiparticle. Then how can charge be conserved if they have different charges. what am i missing?
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1answer
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Meaning of “Minimal” in “Minimal Supersymmetric Standard Model”

From what I am aware of, the LHC has ruled out the Minimal Supersymmetric Standard Model (MSSM), or at least highly constrain it. "Minimal" means that supersymmetry is introduced into the ...
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Difference among invariant, helicity, and scattering amplitude

As for particle physics, I would like to know difference among invariant amplitude, helicity amplitude, and scattering amplitude. What the difference among them?
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Is “Particle Phenomenology” done by Particle Theorists or Particle Experimentalists?

I came across the term "Particle Phenomenology", which is "the application of theoretical physics to experimental data by making quantitative predictions based upon known theories" ...
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Form Factors in Particle Physics

I am having trouble understanding how people parameterise hadronic matrix elements in terms of form factors. For example the decay of a pseudoscalar B to a vector meson: $$ \langle V(k, \eta) | \bar q ...
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1answer
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Future Plans for Searches for Supersymmetry in the LHC

Due to the failure of the LHC to discover supersymmetry so far (July 2021), the simplest and the likeliest supersymmetric models (e.g. the MSSM) have been ruled out, and the confidence in ...
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Switching from Research in Experimental Particle Physics to Theoretical Particle Physics [duplicate]

It is quite common for physicists to change research areas in the middle of their careers. However, given that currently there's a big difference between experimental particle physics and theoretical ...
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Switching to Theoretical Particle Physics as an Experimental Particle Physicist [closed]

It is quite common for physicists to change research areas in the middle of their careers. However, given that currently there's a big difference between experimental particle physics and theoretical ...
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1answer
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Why did the fundamental forces of nature break symmetry in the order they did?

First gravity broke loose, then the strong force and finally there was the separation of the weak and the electromagnetic force? Is this a logical sequence? I guess it has to do with temperature/...
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Dalitz Plot Analysis and Kinematics

I have trouble understanding the fundamental properties of Dalitz plots. For example the Dalitz plotz for the J/Psi (which is treated as unknown) to 3pion decay: I.e. we now have the invariant masses $...
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Do particle decays with different products have different decay rates?

https://en.wikipedia.org/wiki/Particle_decay#Probability_of_survival_and_particle_lifetime lists the mean lifetime of particles. But particles may decay in different ways, so is the mean lifetime the ...

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