Stack Exchange Network

Stack Exchange network consists of 175 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange

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.

1
vote
0answers
34 views

A body moving along a circular path covers a distance of 3 m in 1 s uniformly [on hold]

A body moving along a circular path covers a distance of 3 m in 1 s uniformly, such that the body returns to its starting point. (i) Is the body moving with uniform speed? Explain. (ii) Is the body ...
0
votes
0answers
13 views

Direction of chiral symmetry breaking

What happens if one breaks the SU(2) chiral symmetry in a non-real direction(a direction apart from the one that the small masses of hadron's constituents(quarks) dictate). Or equivalently We know ...
0
votes
0answers
28 views

Can neutrinos derive Higgs mechanism mass by a relationship to other particles?

Can faint neutrino mass be strictly a corrective term that derives from a hidden relationship (in an unknown Theory of Everything (TOE) perspective) to another elementary particle that does gain mass ...
2
votes
1answer
328 views

Bethe Bloch Plot

Why is the stopping power in Bethe Bloch-Plot shown against $\beta\gamma$ on the horizontal axis? Respectively what is the meaning of $\beta \gamma$? Plot taken from here
0
votes
1answer
15 views

Why are number changing interactions inelastic?

Inelastic processes are those in which the kinetic energy of the initial particles and final particles are not the same. Is this true also for number changing processes such as pair creation or pair ...
1
vote
1answer
53 views

Is positron creation operator times electron creation operator equal to the ground state?

This is part of a larger problem, but the important part is that at one point I have: $$ bb^\dagger+bd+d^\dagger b^\dagger + d^\dagger d + b^\dagger b +db + b^\dagger d^\dagger+d d^\dagger $$ where $...
0
votes
0answers
20 views

Which books or content should I prefer to understand particle physics operator and representations [duplicate]

I am just a intermediate passout and I want to know which books should I prefer for learning the mathematics of particle physics level like the different representation, operation like Hamiltonian, ...
1
vote
0answers
22 views

What is the origin of neutrino mass? [duplicate]

Standard model shows zero mass for neutrino and seesaw model explains why the neutrino mass is so small. But to show that the neutrino mass is small, the mass should be originated by some mechanism. ...
15
votes
1answer
1k views

What are the similarities and differences between Stueckelberg mechanism and Higgs mechanism?

What is the difference and similarities between the Stueckelberg mechanism and the Higgs mechanism? They both make the gauge field massive. Is the Stueckelberg mechanism a special case about $U(1)$ ...
1
vote
0answers
30 views

CP violation measurement

I have a question regarding the measurement of CP Violation in experiment. How is parity measured in an experiment? I know that in the direct measurement of CP violation we look at a particle process ...
6
votes
1answer
119 views

Reference on stages of heavy ion collisions in particle physics

Is there any reference (book/review article etc.) where the physics of heavy ion collisions is overviewed? To be absolutely clear about things, I am looking for a introductory review which covers ...
1
vote
1answer
23 views

A question on the strong interaction and charm number

I know that the particle $P_c(4380)^+$, has quark content $\bar{c}cuud$. Furthermore I know that the reaction $K^-+P_c(4380)^+\rightarrow K^-+J/\psi+p$, is strong and the quark content on the left ...
1
vote
0answers
77 views

Can someone explain Technicolor?

I read Wikipedia on Technicolor (and understood some of it - I am not a scientist) Can someone give me a layman's definition? Is the technicolor theory dead now that the Higgs has been found? Can ...
2
votes
1answer
318 views

Similar masses and lifetimes of the $\Delta$ baryons

Why do the four spin 3/2 $\Delta$ baryons have nearly identical masses and lifetimes despite their very different $u$ and $d$ quark compositions?
2
votes
0answers
21 views

Detemining whether a particle is stable with respect to the electromagnetic, EM or strong force

If we have some beautiful hadron , how can we decide based on the quantum numbers and masses of the other beautiful hadrons whether it is stable under the electromagnetic, weak or strong interaction . ...
1
vote
0answers
18 views

Using Isospin symmetry to find the decay width of an interaction

Say we have two decays $\Delta^+\rightarrow \pi^+n$, and $\Delta^+\rightarrow \pi^0p$. I want to show, using isospin symmetry that the probabilities for these decays is in the ratio $\tfrac{Γ(\Delta^+\...
0
votes
0answers
22 views

Confusion on conservation of energy in the beta decay process

In a question,regarding the beta decay process, it is given that. Assuming the anti-neutrino to be massless and possessing negligible energy and the neutron to be at rest, momentum and energy are ...
2
votes
2answers
382 views

Direction of spin of a particle after parity trasformation

I want to get a basic idea of some symmetries in nature and one that I have across is parity. I have read on the internet that parity transformation can be thought of as a mirror transformation. ...
0
votes
0answers
30 views

Why is the decay $\eta'\rightarrow \gamma + \gamma$ suppressed?

So the $\eta$ meson's dominant decay mode is $\eta \rightarrow \gamma + \gamma$ whereas the dominant mode for $\eta'$ is $\rho+\gamma $ or $\eta + \pi+\pi$. Why does it not decay to two photons ...
64
votes
4answers
7k views
+100

How do we know the LHC results are robust?

Nature article on reproducibility in science. According to that article, a (surprisingly) large number of experiments aren't reproducible, or at least there have been failed attempted reproductions. ...
1
vote
1answer
133 views

What is a String Wall?

This question has nothing to do with sound waves, physical strings or walls... I am reading: https://arxiv.org/abs/1709.07091 It states "In the post-inflationary PQ symmetry breaking scenario, ...
2
votes
2answers
74 views

How to find the corrsponding expression after working with natural units $\hbar=c=1$?

If one does long calculations in natural units how does one find the right expression in let's say SI units in the end? I know that natural units make the calculations easier and also help to show ...
3
votes
2answers
779 views

What is the total velocity/force on a particle in fluid?

I am now facing a fluid-particle interaction problem. I would like to simulate particle motion in a fluid. I do know the external force acting on a particle (dielectrophoretic force in this case) ...
1
vote
0answers
42 views

Example of calculating phase shifts in scattering theory

I have an extended question to this post: Phase shifts in scattering theory I have read it and also went over the formalism in Sakurai's, Shankar's, and Griffith's. I am now trying to look for ...
0
votes
2answers
58 views

Can someone explain the $ttH$ Coupling?

IS the $ttH$ an actual particle? If so, how can it form? I though the life of the top quark was way to short to form a particle. If it is not a particle, what is meant by coupling.
6
votes
1answer
158 views

How are the 'physical' isospin zero states determined?

Consider the light mesons. Since $3 \times \bar{3} = 8 + 1$, the states should be grouped into $\mathfrak{su}(3)$ octets and singlets. In the case of the spin zero states (the pseudoscalars), the ...
0
votes
0answers
18 views

Stale file handle error [migrated]

I am doing particle physics. I am running code on monte carlo samples. I am getting the "Stale file handle" error only when I run on one specific sample. The rest of them is OK. A screen shot of ...
0
votes
2answers
41 views

Are pressureless, collisionless and self-interacting dark matter all synonymous?

Is there any distinction between pressureless, collisionless and self-interacting dark matter or does being one imply the other?
1
vote
1answer
18 views

Why do we need a two-Higgs doublet model and why only one extra doublet is added to the extension?

The general two higgs doublet model can neither give masses to neutrinos without considering a see-saw mechanism nor it can unify gravity with other three forces. To explain dark matter also we have ...
2
votes
1answer
63 views

Does the wave function contain the information of the particle's mass?

It is said that wave function contains "all" the information about a particle but I don't see how I can get the mass from wave function. Further, it is able to judge what kind of particle it is by ...
1
vote
1answer
292 views

Decay of a scalar Particle-Symmetry factors

Consider the Lagrangian $$\mathcal{L} = \dfrac{1}{2} (\partial_{\mu}\phi_{1})^2 + \dfrac{1}{2}(\partial_{\mu}\chi)^2 - \dfrac{M_1^2}{2}\phi_{1}^2 -\dfrac{M^2_\chi}{2} \chi^2 - \dfrac{\mu_\chi}{2} \...
1
vote
0answers
32 views

Neutrino scattering cross-section in high energy limit

I've come across a problem in out particle physics lecture notes that I have been unable to resolve on my own. I've paraphrased the bits of the notes that are giving me so much trouble: The notes ...
0
votes
0answers
27 views

Tritium decay energy too small for quark model

So $^3$H turns into $^3$He through $\beta^-$ decay, right? The energy of this reaction is only 18.6 keV. However, according to the constituent quarks model, the only thing different between $^3$H ...
3
votes
1answer
74 views

Cherenkov light and refractive index

LHCb’s Ring Imaging CHerenkov detector (RICH) is aimed at telling different charged particles apart by measuring their velocity, which, together with an independent measurement of their momentum, is ...
1
vote
3answers
66 views

What is the atomic number of an electron, and why is its symbol $\sideset{_{-1}^{\phantom{-}0}}{}{\text{e}}$ in $\beta^{-}$ decay equations?

I'd assume that the atomic number, i.e. the proton number, of an electron is $0$ given that it doesn't have any protons. However, to balance beta minus decay equations, this source seems to claim ...
2
votes
1answer
33 views

Particle decoupling, universe expansion and QFT

A particle (say neutrino) decouples from the plasma in the early universe when its interaction rate $\Gamma$, with the plasma, is slower than the expansion rate $=H = \frac{\dot{a}}{a}$, i.e. $\Gamma &...
45
votes
3answers
4k views

Why don't electron-positron collisions release infinite energy?

Questions of the form: An electron and a positron collide with E MeV of energy, what is the frequency of the photons released. quite often come up in my A Level course (for often fairly arbitrary ...
2
votes
1answer
28 views

Arrow of time and CPT symmetry

It's been a few years since my physics degree. But I've been wondering: if you look at pictures of collisions at CERN, isn't it obvious which way time flows - simply on a probability basis? The ...
0
votes
0answers
23 views

Correlation diagram for related branching ratios. How to interpret?

I wonder how to interpret the following diagram and how one can see where to place the diagonal lines? Source:https://arxiv.org/pdf/0809.0608.pdf So my thoughts on this: The two axis are two ...
1
vote
1answer
47 views

Are there anti virtual particles (mediator bosons)?

I have read these questions: Can bosons have anti-particles? Is there a possibility for discovery of anti-graviton, i.e. the graviton antiparticle? Antiparticle for Higgs boson? According to ...
0
votes
1answer
20 views

Pion nucleon scattering [closed]

If the kinetic energy of pion is 190 MeV and the rest mass energy =140MeV. How I can calculate the pion lab momentum and pion center of mass momentum.
2
votes
0answers
50 views

Strange Quark Matter

I am watching a video on neutron stars. The video is discussing the collision of 2 neutron (quark) stars and the ejection of strangelets. That if one of these strangelets comes into contact with ...
0
votes
0answers
14 views

How do I determine how far a muon neutrino of 1 GeV will travel in the atmosphere if it's a product of the decay of a muon?

I have a question that is asking how far a muon neutrino of 1 GeV will travel in the atmosphere is the muon lifetime is $2.2\mu$ sec. This is in the context of muons being created by cosmic rays ...
0
votes
1answer
38 views

Photo pair production: differential cross section

In a scientific paper, I need for my Bachelor thesis, the differential cross section for photo pair production $\gamma\gamma\to e^{+}e^{-}$ is given as follow: $\mathrm{d}\sigma = \frac{r_{0}^{2}\...
1
vote
1answer
24 views

Is there any experiment going on to test the TWO HIGGS DOUBLET MODEL?

We know that the two higgs doublet model which is a beyond standard model theory predicts five higgs bosons.Is there any experiment that is going on to test this theory and if so have they found any ...
0
votes
0answers
12 views

Measurement of spin asymmetries in semi-inclusive deeply inelastic scattering (SIDIS)

I have been reading several papers regarding the spin asymmetries for SIDIS. One thing I was trying to understand is the method of extraction of symmetries. When I read the single spin asymmetries, ...
4
votes
4answers
97 views

Does the weak force have an attractive/repulsive force observable in everyday life like the other forces?

After the correct comments, this question is not here to compare gravity's and EM's long range forces' energetics and amplitudes to microscopic scattering amplitudes of such forces as weak and strong. ...
0
votes
2answers
58 views

The Strings have a finite size they can vibrate?

as I searched about the Strings theory I found out this explanation: Since the strings have a finite size they can vibrate. All the known particles of nature are just different modes of vibration of ...
2
votes
1answer
355 views

Breit-Wigner vs propagator?

Consider the two Feynman diagrams below: I know for the second that we should use the Breit-wigner curve, but what about the first? If we go about using the propagator: \[\frac{1}{\tilde q^2-m_z^2c^2}...
1
vote
1answer
57 views

Pair creation and annihilation and Wheeler's one electron universe

I stumbled upon Wheeler's idea that there could be only one electron. If I understood correctly, basically the idea is that one electron moves forward and backward in time such that it appears as if ...