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
157 views

Dose-depth curve of photons vs. protons

The dose-depth curve of protons and photons can be seen in the image below: Now, what I've heard is, that in some cases, proton therapy is advantageous compared to photons, and of course the other ...
1
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2answers
104 views

Why do objects have size? [closed]

What is the reason objects, like coffee mugs, have size?
2
votes
1answer
41 views

For Charmonium, why does the spin-spin interaction mostly affect the $L = 0$ states?

For Charmonium, why does the spin-spin interaction mostly affect the $L = 0$ states? My textbook states that this is because "only then is the wave function at the origin non-vanishing". Could anyone ...
2
votes
4answers
203 views

Orbital angular momentum of nucleus?

For nuclei, I know that it is the $J^{\pi}$ that is usually measured/calculated, which is the spin-parity. I don't see "orbital angular momentum" of a nucleus very often. Now my notion of spin vs. ...
0
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0answers
69 views

Understanding $ee\to h \to ff$ process

can anyone tell me where to find a good reference that talks about $$e^+ e^-\rightarrow H \rightarrow f\bar{f}$$ where this describes an electron-positron annihilation into a Higgs that in term ...
3
votes
3answers
226 views

Are electrons held together by vacuum energy?

If one models the electron as a hollow spherical conductor with charge $e$ and radius $a$ then its electrostatic energy is given by: $$E_{em}=\frac{1}{2}\frac{e^2}{4\pi\epsilon_0a}$$ However if one ...
1
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0answers
51 views

Difference between LO and NLO event generators?

I am performing undergraduate research in particle physics. In our research, we are using two event generators (PYTHIA8 and MC@NLO with HERWIG++) to study open bottom production. I am unsure of the ...
2
votes
1answer
80 views

Pion decay into electron and anti-neutrino

In Peskin and Schroeder Books Chapter 5 subsubection Bound State equation (5.43) $\mathcal{M}(\uparrow \uparrow \rightarrow B)=\sqrt{2M}\int ...
3
votes
3answers
66 views

acceleration of particles - thought experiment

The Large Hadron Collider accelerates particles to 99,9999991 % of the speed of light. And I understand that you need infinite amount of energy to accelerate it to the speed of light. What would ...
0
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0answers
21 views

Do photons exert gravity? [duplicate]

I read about GR today and came across the Bonnor beam. As I understand it, two parallel light beams (in a flat space) will in fact creep – slowly – towards each other. As Wikipedia puts it: On the ...
2
votes
0answers
123 views

Why does the electric dipole moment of the electron tell us about its sphericity? [duplicate]

There are a bunch of experiments that claim to show that the electron is highly spherical by measuring the electron electric dipole moment. See e.g.: ...
0
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0answers
60 views

How to find creation and annihilation operators? [duplicate]

I get confused when trying to find this. Please describe it as simply as possible, but keep in mind I have no budget whatsoever to pay for textbooks, so here goes: How do you find the creation and ...
0
votes
1answer
75 views

Neutrino mass and the Majorana equation

I can't seem find this on the Internet. What does the Majorana equation predict neutrino masses to be (if they were their own antiparticle), and how? (I have little understanding of spinors, btw...) ...
1
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2answers
42 views

Electron-positron scattering: why is this the only diagram?

This is probably a very basic question, but I've been going through all my course materials and looking through various books to find a simple way of figuring this out. But consider the following ...
1
vote
1answer
25 views

Given the quadrupole moment of the nucleus as Q, is it possible to find the order of magnitude of the dimensions of the nucleus?

Given the quadrupole moment of the nucleus as Q, is it possible to find the order of magnitude of the dimensions of the nucleus? ( order of magnitude means approximate value to the powers of ten)
1
vote
1answer
40 views

Why does the nuclear volume scale (roughly) linearly with number of nucleons?

As far as I know, it is the fermi repulsion that gives a collection of protons or neutrons its finite size. But this only acts on indistinguishable fermions. If the protons and neutrons do not repel ...
1
vote
2answers
132 views

How do you accelerate atoms/particles? [closed]

Revision of earlier question. So I'm in 11th grade, and I'm writing a theory for my Physics professor and I need help. I need to know how you can make atoms/particles travel faster in the vacuum of ...
0
votes
1answer
56 views

Repulsion of electric charges

If a take a vacuum tube and put electrons in it and put a negative ion strip or something like that outside the tube will the electrons inside the tube start moving due to the repulsion of charges of ...
0
votes
1answer
124 views

Do most physicists believe that axions exist? [closed]

Is the theoretical justification behind proposing axions sufficiently robust, like, say the Higgs boson prior to its detection, that one should consider the existence of axions as generally accepted ...
2
votes
0answers
20 views

Decay of some particle involved quarks vs mesons as outgoing states

Let's have decay width of some mother particle into the state which involves hadrons. For simplicity, let's assume that creation of hadrons (on diagram) is possible only through electroweak vertices ...
0
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0answers
51 views

Uses of the accidental isomorphism $SO(5)\sim Sp(2)$?

Some of the accidental isomorphisms of low dimensional Lie algebras have very important applications in physics. The theory of angular momentum makes use of the fact that $SO(3)\sim SU(2)$. ...
1
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2answers
80 views

Neutrino Reaction: Is the Following Reaction Allowed?

Is the following reaction allowed and why? $$ \nu_e \to e^- + \mu^+ + \nu_{\mu} $$ I would say it is allowed since individual lepton number and charge are conserved.
2
votes
2answers
60 views

Why are holes (in a semi conductor) regarded as particle?

Can I say that holes in a semiconductors are treated as current-carrying conventional direction ?
2
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0answers
50 views

Running of the Higgs mu term (or: running of individual mass terms in a complicated mass matrix)

I am wondering how to calculate the (one-loop) beta function for an individual mass term that appears in combination with a number of other mass terms in the coefficients of a number of fields. What ...
1
vote
1answer
116 views

Why do the quarks constantly change colors?

In a hadron the quarks constantly change colors.They,then exchange gluons to remain color neutral.For example a red quark becomes blue by emitting a red and anti blue gluon and then the blue quark ...
3
votes
0answers
51 views

Are there resources for simulating and/or theoretically describing solitons?

Recently there are striking new ideas emerging on "lower level" dynamics with respect to quantum mechanics involving fluid mechanics principles, including hints of soliton-like aspects to particle ...
17
votes
5answers
2k views

Why doesn't matter clump together such that it can't be taken apart again?

Given the inverse square law force of gravity shouldn't two particles that are infinitely close to each other be infinitely attracted to one another? For example, suppose the hands of some super deity ...
2
votes
2answers
102 views

Selection rule of Kaon decay to pions

in Peskin QFT page 611, he said the isospin change for $${K^0} \to {\pi ^ + }{\pi ^ - }$$ is 1/2, while isospin change for $${K^ + } \to {\pi ^ + }{\pi ^0}$$ is 3/2. Why? If ${I_3}({K^ + }) = ...
3
votes
4answers
1k views

Magnetic force between two charged particles?

I know the gravitational force between two particles with masses $m_1$, $m_2$: $$ \vec{F} = \frac{Gm_1m_2}{|\vec{r}|^2} \hat{r} $$ And I know the electrical force between two particles with charges ...
0
votes
2answers
85 views

What can happen when 2.3*10^28 positrons collide with 2.3*10^28 electrons? [closed]

I'm interested in this question after a writer friend asked me what happens when a human gets bombarded with positrons. Didn't want to post this under scifi because I want more "scientific" answers... ...
0
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0answers
28 views

Centrality analogue in proton-proton collision

If we look at ion-ion collisions one can represent most observables as a function of centrality (0-5% centrality class event etc.). Is there any possibility to introduce centrality analogue in ...
0
votes
1answer
60 views

Possible Meson decays

For an excited state $D_s^{**+}$ of the $D_s^+$ meson, a possible decay is $$D_s^{**+} \rightarrow D_s^+ \pi^0 $$ For which of the $1P$ mesons, i.e. $1^1P_1, 1^3P_0, 1^3P_1,1^3P_2$, is this decay ...
1
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0answers
34 views

Group theory of quark model [closed]

I am trying to understand the group theoretical aspects of quark model. In chapter 11 - Hypercharge and Strangeness- in the book titled 'Lie Algebras in Particle Physics' by H. Georgi, I am not able ...
2
votes
1answer
46 views

Why is there no $u$-channel in $A_1 + A_2 \rightarrow A_1 + A_2$ scattering?

Two particle species $A_1$ and $A_2$ with respective masses $m_1$ and $m_2$ scatter in a process of the type $A_1 + A_2 \rightarrow A_1 + A_2$. I am required to show that the matrix element ...
0
votes
0answers
52 views

Isothermal Expansion in Real Gases

I understand that for a ideal gas in the case of reversible isothermal expansion, $\Delta U=0$ and $-Q=W$ but in case of a real or van der Waal gases, how can I find $Q$, $\Delta U$ and $\Delta S$?
2
votes
1answer
31 views

Electroweak precision in the future

LEP has measured electroweak precision observables to an extremely good precision ($\sim 0.1\%$). The future linear collider is expected to run far from the W and Z poles so other then higgs and top ...
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0answers
33 views

Reference for the non-perturbative origin of the baryon masses

I'm looking for nice introductions to the non-perturbative generation of the baryon masses.
1
vote
1answer
87 views

Deuteron wave function

The deuteron wave function is given by $$|\psi _d\rangle = a|^3S_1\rangle+b|^3D_1\rangle$$ where all states are normalized. How do we find $b^2$ s.t. the wave function reproduces the magnetic moment ...
4
votes
1answer
198 views

Spin of vector boson in higher dimension

A vector boson $V^{\mu}, \mu = 0,...,3$ has spin 1. To my understanding (correct me if I'm wrong) this is because it transforms as a 4-vector under Lorentz transformation $SO(1,3)$. So the $\mu = ...
1
vote
3answers
138 views

Quark anti-quark pair creation. Do we need a gluon?

What is the difference between these diagrams? Is the presence of the gluon taken for granted in the second one? and EDIT: I just zoomed into the picture, it is not a single quark state. ...
-1
votes
1answer
39 views

Estimate the moment of inertia of nucleus [closed]

How do I estimate the moment of inertia of the rotating nucleus, $^{232}_{90}Th$, using the first order estimate assuming the nucleus does not change shape at high rotational angular momentum? Can you ...
0
votes
0answers
29 views

Difference betwen combinatorial and correlated background in particle physics?

What is the difference, in particle physics experiments, between combinatorial and correlated backgrounds?
2
votes
1answer
51 views

Hard processes in particle collisions

This is in reference to a MC generator called Pythia, but has wider applicability because the phrases are used widely in particle phyiscs, even though I have not managed to find a clear, ...
2
votes
0answers
163 views

effect of a simultaneous local and a global $U(1)$ symmetry breaking

EDIT : I am trying to figure out the effect of symmetry breaking in a $U(1)_Y\times U(1)_Z$ invariant lagrangian where $U(1)_Y$ is local symmetry of the Lagrangian and $U(1)_Z$ is a global symmetry of ...
0
votes
0answers
31 views

What is the limit of directly detecting a resonance?

Some resonances are extremely short-lived. With a lifetime of $10^{-23}$ seconds, they would travel just about the size of the proton ($10^{-15}$ m) even if they traveled at the speed of ...
1
vote
0answers
55 views

Understading triplet Majoron model

In the Higgs triplet Majoron model, the spontaneous breakdown of ungauged lepton number gives rise to two Numbu-Goldstone bosons. But isn’t the SU(2) symmetry also broken? I mean when the neutrak ...
4
votes
0answers
35 views

$ZZ^{(*)}$ decaying to leptons mass spectrum

I was looking the mass spectrum of the $ZZ^{(*)}$: and I was wondering why the shape is the way it is. The peak around 90 GeV is the single Z resonant, what is reason behind the slight peak in the ...
4
votes
1answer
65 views

Rejecting background in $B$-meson decay

I want to reconstruct the $B$ mass from the decay $$ B^0 \rightarrow K^{0*} \gamma \quad\text{ where }\quad K^{0*} \rightarrow K^{+} \pi^{-} $$ and the equivalent antiparticle decay. A key element in ...
0
votes
1answer
51 views

Trace of gamma particle

Can we have a detector, making traces of gamma particles (gamma photons) visible? Usually they are invisible until pair born or something. UPDATE G-M tube can detect gamma particles. Can we put ...
0
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0answers
43 views

Motion of charge particle under electric and gravitational fields

I am working on one experiment in which the charged particle falls under the effect of gravity and passes through the electric field in between. I want to know what is the charge of the particle? ...