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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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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2answers
54 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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0answers
43 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 ...
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1answer
96 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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39 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 ...
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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 ...
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2answers
79 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^ + }) = ...
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4answers
702 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 ...
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2answers
76 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... ...
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0answers
20 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 ...
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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 ...
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28 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 ...
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1answer
38 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 ...
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0answers
33 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 $\Delta S$?
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1answer
27 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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32 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.
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1answer
65 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 ...
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1answer
176 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 = ...
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3answers
107 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. ...
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1answer
34 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 ...
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0answers
24 views

Difference betwen combinatorial and correlated background in particle physics?

What is the difference, in particle physics experiments, between combinatorial and correlated backgrounds?
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1answer
34 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, ...
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0answers
155 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 ...
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0answers
28 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 ...
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0answers
46 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 ...
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22 views

Cosmological and astrophysical bounds on physics beyond SM [closed]

There are many cases when cosmological and astrophysical observations make restrictions on particle physics models. For example, some axion models are rejected by white dwarf luminocity functions, ...
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34 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 ...
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1answer
63 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 ...
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1answer
46 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 ...
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0answers
35 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? ...
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1answer
50 views

Uniform $p$-values in $\chi^2$ fit?

I seem to have gotten myself confused about uniform $p$-values assuming the null hypothesis. This is related to how we interpret the results. Say I have a $\chi^2$-distribution which I got from ...
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0answers
26 views

How much cheaper and smaller on average is SiPM technology over conventional PMTs?

I've heard it said that some of the major advantages of silicon photomultipliers are its low cost and compactness when compared to widely used photomultiplier tubes, but haven't found much information ...
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3answers
107 views

What “is” energy in sub-atomic particles?

This question may be simple or not, I don't know but I can't find the answer anywhere. The electromagnetic spectrum is the range of light particles in different wavelengths and is supposed to be ...
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1answer
84 views

How to make sure that two electrons collide head to head?

In high energy experiments, people smash particles into particles. But how to make sure that they really run into each other, instead of just passing by?
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1answer
30 views

Definition of a symbol $s_{NN}$ appearing in particle physics

What is the meaning of $s_{NN}$ in particle physics? See e.g. here http://www4.rcf.bnl.gov/brahms/WWW/thesis/karabowicz_phd_thesis.pdf page 18 in the pdf. What is its relation to energy? I ...
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1answer
95 views

Can we measure the electron spin independently of its magnetic moment?

What experimental evidence do we have for the intrinsic angular momentum of the electron (its spin)? I am specifically interested in whether we have a value for this that is independent of the ...
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1answer
37 views

beginners question: neutral and charged current in elastic scattering

Consider scattering process: $\nu_x + e^- \to \nu_x + e^-$ Why does this only undergo weak neutral current interaction for $\mu$ and $\tau$ neutrinos but can involve exchange of either $W$ or $Z$ for ...
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1answer
33 views

Particle physics plots: on the x-axis, Mass or (Mass)$^2$?

This might be very silly, but I have seen particle physics graphs plotted against $mc^2$ and others plotted against $(mc^2)^2$, which is actually the invariant $p_{\mu}p^{\mu}$. Is there a physical ...
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1answer
51 views

Why, in particle physcis experiments, the background is sometimes a decaying exponential?

Take, as an example, the Higgs boson finding: But the same is found in many other particle physics detector graphs... **Why is the shape of the background a decaying exponential? ** At least ...
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1answer
151 views

braiding bosons or fermions around majorana fermion

Majorana fermions are described by their topological charge. My question is whether we can see the topological charge of Majorana fermions by braiding a boson or a fermion around it ? Is the only ...
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2answers
89 views

Could Dark Energy just be particles with negative mass?

Title speaks for itself. Dark matter: We see extra attractive force, and we posit that there are particles which create such a force, and use the measure of that force to guess their locations. Dark ...
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1answer
94 views

How do scientists measure the spin-parity of a resonance?

I have seen many plots and data tables which display the cross-section vs. center of mass energy for a particular nuclear reaction at a given angle. Here is an example. You can see that there are a ...
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3answers
165 views

Is simulating the entire universe possible?

Is it concievable that we may one day simulate the entire universe with every single particle, field and law of physics factored in? Can n number of particles (say the number of particles that make up ...
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2answers
103 views

Can one proton attract two electrons?

Suppose that in an empty space there is only one proton. This proton would have created a field of positive charge which should attract possible negative electrons, so now we add two electrons on ...
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0answers
19 views

Resonant Depolarization at LEP: Simple Explanation?

I'm looking for a simple explanation of how the idea of resonant depolarization can be used to measure the beam energy at the Large Electron-Positron Collider (LEP). I understand that the amount of ...
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0answers
20 views

Calculation of removing a nucleon from a nucleus

I would like to calculate the energy needed to remove one nucleon - proton or neutron - from a nucleus. What is the equation to be used?
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4answers
136 views

What would happen if two electrons fuse?

Two electrons repel each other naturally; however, if protons can be forced to fuse, can electrons technically fuse too? What would be the product if two electrons fuse?
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How do you build a Lagrangian in particle/nuclear physics? (A specific example)

I know that the terms in the Lagrangian needs to be scalars (with respect to Lorentz symmetry etc.). Also I know that [see C. G. Tully (EPP) p. 85] in general, for $\psi$ in the fundamental ...
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1answer
220 views

Mølller scattering

I came across Mølller scattering today (which is just a fancy name for electron-electron scattering. I'm confused as to why there are two tree level Feynman diagrams for this process: Check out the ...
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1answer
39 views

Is anything without mass an EM wave?

For the longest time I thought the distinction between matter wave and other types of wave is the non-relativist mass of the "thing" under discussion. Photons are EM wave, electrons are matter waves. ...