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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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?
4
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2answers
145 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
146 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?
3
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2answers
154 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 ...
21
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4answers
2k 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 ...
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1answer
54 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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4answers
2k views

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 ...
8
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2answers
181 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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0answers
24 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?
2
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1answer
48 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
56 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 ...
3
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3answers
113 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
132 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
498 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
votes
1answer
138 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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0answers
27 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
76 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
613 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 ...
7
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2answers
139 views

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
54 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
85 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
117 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
52 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 $$E = 2m_ec^2-\frac{e^2}{4\pi\varepsilon_0r},$$ ...
4
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1answer
178 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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0answers
24 views

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 ...
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1answer
86 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
236 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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0answers
54 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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0answers
24 views

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 ...
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1answer
69 views

How experimentalists put bounds on new physics at the LHC?

I would like to understand how experimentalists search for new physics at the LHC. Lets imagine I want to use the LHC data to put a bound on the coupling of some new physics effective operator, say, ...
4
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1answer
33 views

Why could the Homestake experiment only detect electron neutrinos

The Homestake experiment measured the incoming electron neutrino flux via $$\nu_{e}+ Cl^{37} \rightarrow Ar^{37} +e^{-}$$ Why does this reaction not apply to the other neutrino flavours? i.e. what ...
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0answers
25 views

What does a completely negative Greens function in frequency mean?

What can a Greens function of frequency mean when it is always negative? The Greens function is for the photons as the following: (It's derived by Matsubara method to enter the thermal effects and the ...
3
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2answers
991 views

Is deuterium a boson or a fermion?

I want to know if deuterium is a fermion or boson. Please give me a descriptive answer. I tried the formula that is the combination of protons and electrons which gives odd number but the answer is ...
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2answers
129 views

can we detect the photons in the interaction of two charged bodies?

if the interaction of two charged bodies is through the photon exchange: 1) how much is the energy of these photons and how do we calculate their energies? 2) can these photons be detected by a photon ...
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1answer
52 views

If we rub glass particles with paper , will there be any charge induction in glass particles?

If we rub glass particles with paper , will there be any charge induction in glass particles ? I know if you rub with silk they do get charged, but i want to know specifically for glass and paper.
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0answers
13 views

how to completely remove the charge from the glass bubble particles?

Do you have any idea on how to completely remove the charge from the glass bubble particles (25-32 micrometer diameter)? Thanks
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1answer
125 views

The Center of Mass for proton-proton collisions at the LHC

If bunches of protons are being circulated in both directions of the LHC collider with each proton having an energy $E_p=7$ $TeV$, then using the following "Lorentz Invariant Quantity" expression, ...
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1answer
105 views

Energy of resultant photons from meson decay

I am a little unsure how to answer the following question, Find the energies of two photons emitted in opposite directions along the pion's original line of motion if the pion has a r.m.e of 500MEV ...
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0answers
92 views

Radiation Safety of some Particle Accelerators in CERN?

I am trying to study the radiation safety and what kind of roles are required there with particle accelerators. Radiation safety groups of CERN is here. I contacted their a few members of them. I ...
2
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2answers
178 views

Isn't the Coulomb interaction a photon interaction between two charges?

Isn't the Coulomb interaction a photon interaction between two charges? if yes then what does the following text mean? (Many-particle Physics by Gerald D. Mahan.)
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2answers
64 views

A Quantum Telephone [duplicate]

You are an astronaut, traveling through space, but you ran out of fuel and need to get a hold of Houston immediately. How do you do it? You previously gave Houston one of two quantum particles that ...
0
votes
1answer
86 views

Convolution of Gaussian with exponential decay?

I need to convolve an exponential decay (defined as the exponential $Ae^{-\lambda t}$ from $0$ to $+\infty$) with a Gaussian of known standard deviation $\sigma$, in other words I need to compute the ...
0
votes
1answer
182 views

What gives the higgs boson mass? [duplicate]

In light of the discovery of the Higgs boson. The Higgs Boson is a force particle which interacts with matter particles. My question is what does the Higgs Boson interact with to give itself mass.
0
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4answers
85 views

Frequency of a photon

in classical physics frequency represents how many cycles in one unit time, but I do not know how we define a frequency for a particle? what does it mean for a particle to have a frequency, the book I ...
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0answers
15 views

What is 'transparency rate' for ionization chambers?

I was reading a paper a little while ago and I saw that the author noted the 'transparency rate' of an ionization chamber. The ionization chamber had field shaping wires at the entrance and exit that ...
0
votes
1answer
76 views

Why is rho to two pions not allowed? [duplicate]

Why is the $\rho^0 \rightarrow \pi^0 + \pi^0$ decay not allowed? I have seen this question but I am not satisfied with the answers. The $J^{PC}$ of the $\rho$ and $\pi$ are $1^{--}$ and $0^{-+}$ ...
5
votes
2answers
178 views

Width of the decay of Higgs boson into dimuon

According to Standard model, the partial width of the decay of Higgs into dimuon (up to tree level) is: $$\Gamma\approx\frac{m_H}{8\pi} \left(\frac{m_{\mu}}{\nu}\right)^2$$ with the Higgs mass ...
0
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1answer
139 views

What is the general definition of signal acceptance?

Suppose I have a beyond Standard Model theory and want to test it. I want to test if some experiments, say conduced in LHC, show signals of the theory. In this case, what is "signal acceptance"?
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1answer
41 views

Materials on charged black brane

everybody! Does anyone know some good materials on charged black branes in AdS/CFT and the role of chemical potential in theses cases?
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1answer
173 views

Relating momentum fraction to rapidity in a high-energy collision

It's a well-known result in particle physics that in an underlying interaction like this: assuming $p_0^-,p_{0\perp},m_0\ll p_0^+$, $m_1$ and $m_2$ are small, but $p_{1\perp}$ and $p_{2\perp}$ are ...