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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Physical inituition for axial and vector form factors of a hadron

I often see a decomposition of the matrix element $\langle V|\bar{q}\Gamma^{\mu} Q |P\rangle$, where $V$ is a vector particle, for example a vector meson or a photon, $P$ is a pseudoscalar meson, and ...
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126 views

Do photons generate gravitational waves since they affect with their energy the stress tensor?

The gravitational waves are fact. They are produced in a way predicted 100 years before by Einstein. Anything with energy affecting stress tensor of space time produces them. What does it happen with ...
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2answers
50 views

Questions about particles and their forces

Consider the hypothetical scenario where 2 particles are headed for each other in a collision course but neither interact with a common force. Do these particles simply pass through each other?
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36 views

A question relating to the Higgs boson scalar field

Just wondering. The potential for the Higgs boson is given by: $$ V(\varphi)=\lambda(\varphi^{2}-v^{2})^{2} $$ where $v≃$ 246 GeV is the vacuum expectation value required to explain mass in the ...
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1answer
25 views

How to calculate the decay rate of Higgs to lepton pair?

In class, the generic formula we've been given for calculating scattering amplitudes for the weak decay (at low energies so that the interaction is effectively point-like) is $$ M= ...
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3answers
124 views

How can we conciliate the structure of a proton and Coulomb/strong force? [closed]

I was told in answers to my questions that the schematic picture at wikipedia is misleading, that the 3 (valence) quarks are point particles, sit in on the outer edge of a proton (r = .85 ftm) and ...
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0answers
43 views

What causes certain particles to have charge? [duplicate]

The three major measurements for the elementary particles are mass, spin and charge, mass is supposedly achieved through interaction within the Higgs field due to the Higgs effect, spin is the angular ...
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0answers
14 views

What is the meaning of the minimum separation requirement?

In this work, BHsearch done by CMS, they reconstructed and identified objects using certain conditions. And finally, in Page 3, the last paragraph requires that the minimum separation between any two ...
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0answers
41 views

What is the difference between Breit-Wigner mass and pole mass in PDG?

In Review of Particle Physics 2014, page 81, in the baryon summary table, there are usually noticeable differences between Re(pole position) and Breit-Wigner mass, for example, for $N(1440)$, ...
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0answers
68 views

Do all particles have radiative transitions?

Everybody knows that excited electrons can emit photons upon relaxation. A nucleus too (which is not an elementary particle), can be in an excited state and emit gamma rays upon relaxation: (source) ...
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0answers
23 views

Ideas for experiments on the Beamline for Schools at CERN? [closed]

I'm thinking of participating in CERN's Beamline for schools competition. To those who do not know, they offer a batch from a school to conduct their own experiment on a small scale particle ...
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1answer
32 views

Particle lifetime doesn't depend upon longitudinal momentum

I am writing a report on an analysis of the $B_{s}$ meson from CDF data, and as part of the lifetime analysis, I have noted down that: $$\tau = \frac{l_{xy} m_{B_{s}}}{p_{T}}$$ Where $l_{xy}$ is the ...
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1answer
36 views

What is the likelihood of pair production for a high energy photon?

Wikipedia says that pair production is the dominant form of light-matter interaction for photons with a mass equivalence of at least twice the rest mass of the target particle, implying that not all ...
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0answers
35 views

Decay rate and differential cross-section

If I have a $pp-$beam producing an on-shell particle $A$, which then decays into particle $B+C$, then I can find the total cross-section $pp \to A \to B+C+Y$ ($Y$ being inclusive particle which should ...
2
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1answer
175 views

Confirming an inconsistency of the Balitsky-Kovchegov equation between references

I'm comparing the form of the Balitsky-Kovchegov equation, which describes the splitting of low-momentum gluons, between different references, and I'm finding an inconsistency: most sources (1, 2, 3, ...
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2answers
97 views

Proof that 1d lattice displacement by phonons is given $u_{n\pm 1}(t) = A_ke^{i\omega_k t} e^{i knd}e^{\pm i k d}$

I looked in «Kittel - Introduction to solid state physics», Wikipedia and Google for the derivation that: A phonon of wavenumber $k$ displaces the $s$-th atom in a monoatomic 1d crystal lattice by a ...
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0answers
65 views

Electric field inside the “Dees” of a Cyclotron and why no “Cups”

I read about cyclotron and how does it work. Several references say that the particle to be accelerated is only accelerated when it is between the gaps of the "Dees" or the semicircular disc like ...
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1answer
61 views

Is Electron decay period less than stated?

Phys. Rev. Lett. 115, 231802 – Published 3 December 2015 sets a limit on the stability of the electron for decay into a neutrino and a single monoenergetic photon in $\tau\ge6.6\ 10^{28}\ ...
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30 views

Cloud chamber and observations [closed]

What are the best ways to use a cloud chamber to study particles. What would you gain from observations done in a cloud chamber.
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1answer
40 views

Understanding wave functions of matter waves

The wave functions of matter waves give the probability density of the particle being at a certain location. Does this arise because as an outside observer, we have incomplete information about the ...
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4answers
103 views

Where does the energy lost due to light emission come from?

If an object lose energy when it emits light, does that energy come from the mass of the object? Examples: Does a flashlight lose mass when it's turned on? Does a regular object (like a pencil or a ...
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2answers
61 views

Helicities in electron-positron annihilation

Consider the massless limit of a process in which an electron-positron pair annihilates into a virtual photon - the final state doesn't matter. If the electron is massless (or if the energy is high ...
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0answers
17 views

Voltage drop along electron beam

A focused electron beam represents a current and unless the charges (electrons) meet no resistance to their movement there should be a voltage drop along the length of the beam. So, assuming the beam ...
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1answer
35 views

Particle physics books [duplicate]

I am a A-Level student. I have keen interest in physics, especially particle physics. So, I want to know some websites where I can find free books or other study materials to study particle physics as ...
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1answer
62 views

Collision of electron and proton of high energy [closed]

What will happen when proton and electron with high energy like in 100 TeV collide?
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0answers
22 views

Good books to read [duplicate]

I still regard myself as a beginner in the field of physics.. And there are a lot of information I should know, I am in my second year physics, and I need to read books which are not hard to ...
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1answer
62 views

Charged particle/cosmic ray track on sunglasses

I left my (polarized) sunglasses on car dashboard .. . Returned, and immediately noticed a strongly lightened, partially dotted streak across entire left lens, cutting diagonally from "northwest" to ...
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1answer
53 views

Couplings of fields in the Standard Model

Could someone please explain what this task implies: Calculate coupling of fields: $\bar{e}_{R}e_{R}Z, HW^{+}W^{-}, W^{+}\bar{c}_{L}d_{L}$? (Exercise refers to the Standard Model Lagrangian). What do ...
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1answer
66 views

Conceptually speaking, why does synchrotron radiation arrise?

First, a bit of background. I'm a chemist who works with synchrotron-based techniques, but I'm focussed on materials analysis rather than synchrotron physics. I'm struggling to work out where ...
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0answers
32 views

How many Cherenkov photons on the track of the electron? [closed]

I have this problem where a neutrino interacting with deuterium decay in 2 protons and 1 electron. This electron will produced Cherenkov photon. The specific energy loss of heavy water is ...
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3answers
62 views

Photocurrent's dependence on frequency [duplicate]

Sounds like a rookie question, this, but could someone please explain to me why doesn't photocurrent increase when we increase the frequency of the incident radiation? I mean, an increase in frequency ...
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1answer
27 views

Relativistic blast waves in medium of non uniform density

The relativistic outflow of a gamma ray burst drives a shock into the circumburst medium. This medium could have a uniform density $n_0$ or a density profile of the form, $n(r) \propto r^{-2}$. For ...
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3answers
129 views

String models of particle physics

What general features of particle physics are derived/replicated by constructing string models of particle models? How do such models address the fixing of free parameters like the masses and the ...
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0answers
47 views

Can a photon be captured in a grid space representation at a fractional Planck position?

Consider a photon, positioned in space in a finite portion of a grid. Any point of the grid is vertically or horizontally aligned, each distanced by a Planck unit. $l_P = 1.616 199(97) × 10−35 m$ ...
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116 views

Feynman diagram; $\pi^0+\pi^0\rightarrow \pi^++\pi^-$

For the reaction below draw three Feynman diagrams, one that proceeds through exchange of a gluon, one through a photon and one exchanging a weak W-Boson. $\pi^0+\pi^0\rightarrow \pi^++\pi^-$ Which ...
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35 views

When is the spin of an electron changing?

An electron can have a half spin up or down. The up spin can become a down spin to lose his weak charge. But when are electrons changing their spin?
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2answers
586 views

How to understand that Higgs does not imply circular reasoning?

From what I understand about Higgs (boson/field) it gives mass to subatomic particles. When it interacts a lot with the fields it gets a great mass (like a top quark) and when it interacts a little it ...
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1answer
33 views

Is the magnetic dipole moment in charged particles the more survivable property than the electric charge?

After asking about Which of the properties of particles are intrinsic properties and why? it was commented "Charge, spin, lepton number, baryon number definitely. Mass maybe." and "is magnetic dipole ...
5
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2answers
142 views

Fractionally charged Quarks

Just wondering what the evidence is for fractionally charged quarks, is it simply enough to say that as we see deep inelastic scattering of electrons (at high energies) off the nucleus of an atom ...
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2answers
94 views

Why is an electron considered a point-particle?

Apparently, an electron has mass not greatly smaller than a proton (roughly 1/20, I read, the rest being just binding energy) its volume should, therefore, not be a lot smaller, and its radius between ...
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1answer
57 views

Open Source Particle Tracing Software

I am fairly new to this forum. I am designing an ionospheric plasma testing environment in a thermal vacuum chamber and to do so I require some form of multi-physics package for simulations .. such as ...
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2answers
43 views

Why is the intensity of an alpha ray constant along a material?

I'm taking a course in radiation physics and I've come across the following problem: A thin beam of alpha particles of intensity $I_0$ and energy $E_0$ impacts in a material. What is the intensity ...
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2answers
105 views

Is there a natural source of Antimatter in this universe?

I was just asking if there is an natural source of Antimatter in this universe capable of creating simple molecules/compounds? So, any good answers?
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0answers
64 views

What would be the research advances if we discover the gravitational waves? [closed]

As researchers of LIGO (USA) and VIRGO (France/Italy) say that they have discovered gravitational waves thanks to black hole collision today, what would be, apart of the important confirmation of ...
5
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1answer
74 views

Importance of CP violation

To explain the matter-antimatter assymmetry, CP should be violated according to Sakharov conditions. Charge conjugation is required as matter and antimatter have opposite charges but why Parity ...
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1answer
52 views

Is light relative? [duplicate]

I was wondering, if two cars (A and B) are going at different velocities let's say A=90km/h, B=80km/h then if we add the two speeds we get 170km/h meaning they are relative to each other. But if one ...
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2answers
61 views

Is the video “How to Reveal Subatomic Particles at Home”'s explanation of its experiment misleading?

https://www.youtube.com/watch?v=wN_DMMQEhfQ The video asserts that along the path of an electron or muon, a trail of condensation will appear. But from what I understand, if an electron or muon (both ...
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0answers
27 views

How to determine likelihood of baryon decay

If I want to determine the probability of $\Sigma(1385)^+ \to \Lambda^0 + \pi^+$ how would i do this? I know I have to do something with the $J^P$ value of each part of the decay, but I'm not sure ...
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0answers
25 views

Decay of lepton into meson and neutrino using four-momentum

I'm learning about how to use four-momentums and am working through a problem involving the decay of a charged lepton into a charged meson and neutrino. The equation would be: $L^+ \to M^+ + \nu$ ...
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2answers
98 views

Shouldn't atoms of the same element repel each other? [closed]

Shouldn't the same type of atoms repel each other due to electrostatic charge?