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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Experimental evidence for Z boson coupling to right handed fermions

I do have a question about electro-weak interactions. I know the Z boson is an admixture of two fields, one that couples only to the left-handed part of the fermions (the neutral field introduced to ...
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34 views

Virtual particles and the scaling effect on valence quarks

Summary from Carrolls: "Particle at the end of the Universe", page 101. Inside a proton there are 3 valance quarks. In addition, there is constant creation and annihilation of gluon, quarks and ...
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67 views

Discovery of spin-3 particle at LHCb

I just read a discussion on the CERN website regarding first observation of a heavy flavored spin-3 particle at LHCb. This appears to be a post from last July. Is there anyone knowledgeable enough in ...
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68 views

Free parameters in the Standard Model

From my understanding of the standard model, I understand that there are 19 or 20 free parameters that we need to put in by hand as, and I'm guessing here, there is as yet no theoretical basis for ...
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11 views

Neutrino cc interaction potential calculation field theoretically

Is there any very good reference where neutrino charge current interaction potential is calculated field theoretically in details ?
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19 views

Alpha particle in vacuum

Does the alpha particle travel in vacuum for ever and ever or can it undergo some transformation eg two protons get separated or the neutron decays etc.?
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60 views

What exactly is quantum spin? [duplicate]

What is "spin" as it relates to subatomic particles? I've heard that it's similar to angular momentum but I've also heard that's not completely the case.
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72 views

Would you please explain this statement please [closed]

As the atoms of a material are brought closer together to form the crystal lattice structure, there is an interaction between atoms, which will result in the electrons of a particular shell of an atom ...
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1answer
18 views

What is the reduced width amplitude of an unstable state?

Particularly used in nuclear physics when describing the lifetime (i.e. partial decay width) of a resonant state (a.k.a resonance) is the term "reduced width amplitude". I have searched online, and ...
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131 views

Can the Unruh effect be confirmed by the LHC?

Two short questions regarding the Unruh effect. There are related answers on this forum and on wikipedia, but I am looking for confirmation of my own intuitive assumptions, so a straightfoward yes or ...
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56 views

Nature of particle spectra at ALICE

I have a question regarding the nature of the particle spectrum at ALICE as a function of momentum. The spectra in question can be seen here. My question is, why is it that the particle spectrum in ...
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1answer
19 views

Excitation energy of carotene using the particle in a box model

I'm practicing for an exam and I came across the following question: The linear, conjugated π-electron system of a carotene molecule comprises 11 atoms and the distance between two atoms is 1.4 Å. ...
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3answers
122 views

What is the difference between the Higgs Boson particle and an electron moving through the Higgs field?

I am watching a lecture by Sean Caroll titled "Particles, Fields, and the Future of Physics". I am not a physicist by any means but enjoy the subject in my spare time hoping to understand it. This ...
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230 views

Evidence that nuclei contain neutrons and protons (other than nucleons appearing if a nucleus is smashed)?

This may seem like a silly question, but I believe this to be very fundamental because the Standard Model of particle physics seems based on the axiom or assumption that neutrons and protons exist ...
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29 views

How can I choose my desired direction in which the electrons travel?

If I take a circular vacuum tube (like a particle accelerator) and try to accelerate the electrons in it with a bunch of magnets and like charged panels to repel or attract the electron in it and ...
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215 views

Fiducial volume in collider/detector physics

I'm trying to make some sense of ATLAS measurements for a personal project to learn how to use Pythia, and part of my work requires me to recreate the distribution for Z boson decay. I encountered the ...
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1answer
51 views

Most general separable solution of free Dirac equation

In relativistic quantum mechanics, the solution of the free Dirac equation is assumed to be $$\Psi(\textbf{r},t)=u(\textbf{p})e^{i(\textbf{p}\cdot \textbf{r}-Et)}$$ How do I know that this is the most ...
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22 views

Why average incoming spins and sum over outgoing spins? [duplicate]

The book by Griffith on elementary particles reads: A typical experiment starts out with beam of particles whose spin orientations are random, and simple counts the number of particles in a given ...
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14 views

How to define the parameter $\beta_{CM}$ of the transformation of pseudorapidity of the referencial LAB to CM

How can I determine $\beta_{CM}$ knowing the energy of the center of mass (CM), and without knowing anything about the particle mass? I have only information about the pseudorapidity in the ...
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1answer
39 views

Predict spread of signal peak in particle physics experiments, due to detector resolution

I am working on an LHCb experiment, in particular the $B^0 \rightarrow K^{*0} \gamma$ decay. The $K^{*0}$ decays into $K^+$ and $\pi^-$. So the decay products of the decay are $\gamma, K^+ $and $ ...
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44 views

Helicity angle of electron in $B^0 \rightarrow K^{*0} \gamma$, with $\gamma \rightarrow e^+ e^-$?

I haven't been able to find the exact definition of a helicity angle, and the ones that I found don't apply to this particular case, because they'd require to boost to the electrons' 4-momentum to the ...
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30 views

What does it mean for a state to have a negative partial decay width?

I don't understand what it means when a particular decay mode has a negative partial decay width. I'm guessing the total decay width for a particular system must always be positive (now that wouldn't ...
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27 views

How can you have odd nuclear spin angular momentum but positive parity or vice versa?

How does it happen that you can get states like $J^\pi=3^+$ or $J^\pi=2^-$? I think this could be because $\pi=(-1)^l$ so you could have an even state in $l$ but the $J=l+s$ sum could be an odd ...
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44 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 ...
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2answers
99 views

Why do objects have size? [closed]

What is the reason objects, like coffee mugs, have size?
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20 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 ...
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49 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. ...
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61 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 ...
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211 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 ...
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25 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 ...
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1answer
52 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 ...
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59 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 ...
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19 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 ...
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79 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.: ...
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52 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 ...
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1answer
48 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...) ...
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36 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 ...
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1answer
21 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)
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1answer
36 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 ...
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2answers
127 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 ...
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1answer
44 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 ...
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1answer
106 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 ...
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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 ...
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36 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 $SO(3)\sim SU(2)$. ...
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68 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.
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51 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 ?
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36 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
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1answer
88 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 ...
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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 ...
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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 ...