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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“Double-counting” in particle detectors

Apparently, when analysing events from particle detectors, one may incur in double-counting, which happens when a physics object appears as a single object of its own type, but it may also be ...
5
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1answer
62 views

What CP violating processes do we know of?

So, after going over my particle physics notes and some introducing literature, it seems the currently known processes we experimentally confirmed to be CP violating are Kaon mixing (an indirect ...
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1answer
43 views

The counting of all possible baryons quark combinations

I would like to ask how do you count the number of possible quark combination that could possibly exist in a baryon. I know certain spin symmetry or orbital momentum symmetry have to be conserved. But ...
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2answers
135 views

Global symmetry and particle multiplets

In chapter 20, of Peskin and Schroeder's quantum field theory book, they start with a comment that a global symmetry that is manifest lead to particle multiplets with restricted interactions. Can ...
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1answer
52 views

What does 'channel' mean?

I see many plots like the following that graph counts per channel, I know what a 'count' is, but I don't know what a 'channel' is. Could somebody please explain to me? My guess is that it is that ...
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179 views

Is the electromagnetic mass real?

In his Lectures on Physics vol II Ch.28-2 Feynman calculates the field momentum of a moving charged sphere with charge $q$, radius $a$ and velocity $\mathbf{v}$. He finds that the total momentum in ...
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2answers
260 views

How are quarks and leptons detected experimentally?

How are quarks and leptons (including subatomic particles) detected in the laboratory,especially when most hadrons and leptons have a lifespan for a considerable small amount of time?Also how do we ...
5
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1answer
94 views

Current knowledge of Higgs

What is the current knowledge about the Higgs field after its discovery in the LHC? Does it exactly mimic the standard model Higgs? Does this knowledge rules out the possibility of other Higgs ...
2
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1answer
99 views

Isospin of the neutral sigma baryon

I was typing up another answer on P.S.E. and I wanted to use the fact that the decay $$\Sigma^0\longrightarrow\Lambda^0+\gamma$$ does not occur strongly as an example of isospin conservation. But then ...
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1answer
40 views

Sphaleron interactions erase baryon asymmetry?

The sphaleron interactions in the standard model is $(B-L)$ conserving and $(B+L)$ violating. Each sphaleron transition causes $\Delta B$ and $\Delta L$ to change by the same amount so that ...
2
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1answer
81 views

Do particle decays happen instantly?

For example, let's say a W boson decays into an electron and a neutrino. Is there some transition? Does the boson fade out while the decay products fade into existence? Or does this happen in the ...
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0answers
31 views

Why Does Electron Revolve around nucleus? [duplicate]

Actually why does electron revolve around nucleus. Considering Simple atom, hydrogen atom where a single electron revolves around the nucleus. It is said that the electrostatic force of attraction ...
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4answers
4k views

If two photons collide, does the resulting particle have zero velocity?

If two photons traveling in opposite directions along the same line collide, will the resulting particle have a velocity of zero relative to the rest of time space in the instant of the collision?
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19 views

intuition about Gauge in Hall bar geometry with 4 leads

Please tell me about the kind of gauge I should use for calculating the resistance in a 4 lead hall bar geometry.As when I use Landau gauge it will make my leads transitionally invariant only along ...
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0answers
58 views

How to theoretically determine electric charges of $W^{\pm}$ bosons?

I just realised that I don't remember how to conclude theoretically that $W^{\pm}$ bosons have electric charges of $\pm 1$. After some searching I'm quite surprise that I couldn't find a satisfying ...
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1answer
64 views

Baryogenesis via Leptogenesis

Baryon number is directly violated through electroweak anomaly and so does the Lepton number, for each transition from one vacuum to another. The two violations are of equal amount $\Delta B=\Delta ...
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2answers
221 views

Why would electrons have Weak Charge? [closed]

Electrons (and, their cousins Muon and Tau) carry Weak Charge having value $-1/2$. If you believe in Strong Anthrophic Principle Why does electrons carry Weak Charge? If you don't believe in Strong ...
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3answers
60 views

In the Higgs boson experiments, why are protons used?

Why are protons used to create Higgs particles at CERN? Can anyone please explain the concepts very simply? (How to explain this to a layman?)
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2answers
89 views

Could synchrotron radiation be produced by a gravitational field instead of a magnetic field?

I know that synchrotron radiation is produced when a charged particle is accelerated radially by a magnetic field, but I was wondering if synchrotron radiation could also be produced by an uncharged ...
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1answer
65 views

Where does the mass of a nucleon originate in an atom?

The mass of the three quarks in the nucleons make up only about one to two percent of the mass of the nucleons. What makes up the other 98 percent?
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47 views

Summing up independent mass measurements to recover $Z$ boson mass

I am trying to calculate the $Z$ boson mass from a list of $\mu^+\mu^-$ data (momentum). We have been asked to make five blocks of data from the total amount of 10k. Then calculate the mass via ...
3
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2answers
239 views

How we see laser light if it travels in a straight path? [duplicate]

Light travels in straight path, and our eyes detects an object's reflected light then we see the object. So if laser light is going in a straight path, how come we can see laser light?
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2answers
130 views

Where does the electric force come from if an electron has no definite location?

Say electron A is nearby another electron (B), so that they may repel each other. Electron B is in a position eigenstate (so it has a definite position). But electron A is not. How does electron A ...
3
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1answer
120 views

Number conservation of bosons and fermions

Why is the number of bosons not conserved while the number of fermions is conserved? Does it have something to do with the Pauli exclusion principle?
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2answers
128 views

How to calculate the tree-level probability amplitude for the electron-positron to muon-antimuon process?

Consider the following process: $e^+ + e^- \rightarrow \mu^+ + \mu^-$. I'm trying to calculate the probability amplitude of such a process in leading order. In leading order the amplitude is given ...
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4answers
1k views

How come “smaller, weaker” particles are more massive (have higher energies)?

Something has always struck me as counter-intuitive: when reading about high-energy experiments such as the LHC, they are always looking for stuff on a really small scale with MASSIVE energies. I ...
2
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1answer
39 views

Eigenstates of total isospin, I

In the book from which I'm studying particle physics (by Mark Thompson) it is stated that states of two quarks of third component of isospin = 0 (like ud or du) are not eigenstates of the total ...
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Could we make things out of newly discovered particles?

Right now, all of the "stuff" that has been created in the world is made of protons, electrons, and neutrons. I'm aware that particles other than these have much shorter lifetimes. But I've also heard ...
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176 views

Can a superpartner be less massive than its SM counterpart?

Theoretically, can a superpartner be less massive than its standard model counterpart? I realize there are experimental constraints.
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21 views

Introducing inert superfield in R-symmetry model in extended MSSM

Some papers, e.g, Chakraborty et al, Frugiuele and Gregoire introduce inert superfield doublet $\hat{R}_d$ and $\hat{R}_u$. I have a question, what is the role of these inert superfields?
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1answer
45 views

Ambiguity in assigning intrinsic parity

We know that, fermions can have intrinsic parity either $\eta_P=+1$ or $=-1$. How does one then fix the intrinsic parities ofthe elementary particles, uniquely? Again, the intrinsic parity of a baryon ...
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1answer
50 views

Stopping power diagram

I'm currently looking at this figure, but I'm not sure how to interpret it. If I'm not mistaken, the energy loss of the muon (This is a muon that penetrates copper) is on the y-axis. But does that ...
2
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3answers
97 views

Can “particle” waves break as ocean waves do?

I have heard about electrons surfing on wake fields which got me thinking. Are there analogs to reefs for these waves and can these waves break as ocean waves do when they hit a reef?
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2answers
111 views

SU(3) antiquark triplet transformation

I'm reading a rather elementary particle physics text, Modern Particle Physics by Thomson. He is staying away from the heavy group theoretic stuff. He derives the transformation law for an SU(2) ...
3
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1answer
323 views

Charged current vs. neutral current neutrino interactions

I am doing research related to the detection potential of neutrino detectors and, in looking up the various neutrino interaction channels that exist in each detector, I have found the interactions ...
3
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1answer
115 views

Why Majorana phases cannot be removed?

Why is the extra two Majorana phases in the PMNS matrix cannot be removed if neutrinos are Majorana fermions? Or in other words, why are the Majorana phases cannot be absorbed into the redefinition of ...
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26 views

How to calculate U-spin for baryons

I am trying to calculate U-spin for sigma baryons. I don't know why U-spin for (sigma+) and (sigma-) and (sigma*+) is 1/2 but for (sigma*-) is 3/2? I know that (sigma+) and (sigma-) are octet and ...
2
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0answers
63 views

If tachyons were real, where would they originate from? [closed]

If the hypothetical tachyon existed, where would it possibly originate from? or is this question off the realms within the current state of physics. Also what are some ways physicist have tried to ...
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1answer
557 views

What happens when an atom absorb electron/photon?

I'll give you a scenario or two, and please tell me what will happen and that shall answer my question. Thanks in advance. Scenario 1: Will an atom absorb an electron with kinetic energy greater ...
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Why cross section of $e^+ e^- \to \bar{q} q$ is 3 times larger than $e^+ e^- \to \mu^+ \mu^-$?

I know the usual answer: quarks carry color charge (let us denote them r,g,b), antiquarks anti color charge, and since the initial state ($e^+ e^-$) does not carry any color charge (and color is ...
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1answer
53 views

Soft-Supersymmetry Mass (Direct contact term)

I found this term/operator in some papers that can generate masses, e.g Riva-Biggio-Pomarol(2012), Fox-Nelson-Weiner $\int d^4\theta \frac{X^\dagger X}{M^2}Q^\dagger Q$ Could anyone explain about ...
3
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0answers
79 views

Field Lagrangian <--> Particle Lagrangian

The action-functionals describing the motion $\mathbf{x}:[a,b]\to \mathbb{R}^3$ of a free particle of mass $m$ and the evolution $\varphi:[a,b]\times \Omega\to \mathbb{R}$ of a free scalar field of ...
4
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1answer
113 views

String Theory: Why should(n't) the string snap?

My question is related to a comment in the margin of the popularising site The Official String Theory Web Site. There are two basic types of string theories: those with closed string loops that ...
0
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1answer
38 views

does electron - positron pair annihilation occur when E is negative?

Suppose I release an electron-positron pair from rest at a distance of $r$. Then the particles attract each other and collide. The total energy $E$ is $$E = 2m_ec^2-\frac{e^2}{4\pi\varepsilon_0r},$$ ...
3
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1answer
143 views

Can the Higgs condensate be described in terms of creation operators?

In superconductivity, the BCS condensate can be described in terms of 2 creation operators (the 2 electrons of the pair) acting on the vacuum. I'm wondering whether a similar description can be given ...
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How to calculate D0->K+K- decay with QCD factorization?

I am studying the decay of D0->K+K- and I calculated the result of Branching Ratio by Naive QCD and I wrote all the equations for amplitude and branching Ration and Hamiltonian and... for this decay ...
2
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1answer
81 views

Is it possible to single out a proton, electron, neutron?

I've read that it's nearly impossible to take a proton from an element. But if it's "nearly" impossible then it is possible to some degree. If this has happened, what is exactly the process of taking ...
5
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1answer
227 views

Making precise the statement “particles are excitations in a quantum field”

I've been trying to self teach QFT lately. I find that the basic physical idea makes sense, and I can keep up with the mathematical formalism without too much trouble, but I'm having trouble ...
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53 views

What is a nucleon field?

A nucleon is either a proton or a neutron. A field is, as John Gribbin says, a physical quantity that has a value for each point in space and time. But what is meant by a nucleon field? Can anybody ...
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How come plasmon resonances of metals are capable of being tuned to different wavelengths?

I read in this article that plasmon resonances though being a pre-determined property of a metal are capable of being tuned to other wavelengths when these same metals are made into tiny ...