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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147 views

Møller scattering: twisted?

I am studying the Møller scattering, but I don't know how to get the twisted diagram from the S-matrix. Has anybody a good explanation?
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94 views

Spin of a decay product

A particle A decays into particles B, C and D. The spin of A, B and C particles is 1/2 each. What are the possible spins of particle D? My attempt is the following: Since B and C have spin 1/2 ...
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237 views

Neutrino power plant

Suppose there is a material that interacts with 50% of high-energy neutrinos. To what temperature such material will heat up naturally here on Earth? What power can be extracted from it?
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65 views

Weak decays classification

Sir, We often read about Cabibbo Favourite, Singly Cabibbo Suppressed and Doubly Cabibbo Suppressed decays. I have two questions: I understand that the suppressed decays are rarer but why are ...
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90 views

Intensity of particles with zenith angle dependence

The intensity of particles come to sea level depend to the zenith angle $I=Iv (\cos(z))^n$, where $z$ is the zenith angle and $n$ depend to the particle. I know the vertical intensity depend to the ...
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409 views

Charged pion decay and spin conservation

Charged pions $\pi^\pm$ decay via an intermediate $W$ to (e.g.) a lepton-neutrino pair. The pions being scalar (spin-0) particles and the intermediate $W$ having spin 1, how is spin conserved in ...
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46 views

Limits on stable charged particles

Are there generic model-independent limits on massive stable charged particles (say 10-500GeV)? I mean SU(2)/color singlets with just a hypercharge. For example the LEP search (CERN-EP/99-075) was ...
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156 views

Parton Distribution Functions, average cross section of the nucleon

Say we are given the scattering cross section for neutrinos from $d$ and $\bar{u}$ quarks as $\frac{d\sigma^{d}}{dQ^2}=\frac{G_F^2}{\pi}$, $\frac{d\sigma^{\bar{u}}}{dQ^2}=\frac{G_F^2}{\pi} (1-y)^2$, ...
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228 views

Strong decays of baryons via quark-antiquark pairs

I have the doubly charmed $\Xi_{cc}^{++}$ consisting of ccu quarks. This is meant to decay via strong force, producing a light baryon (cud/uuc/udc etc...) and a quark-antiquark pair along with a ...
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82 views

Chirality when moving around legs in Feynman diagrams

Assuming one has the following term in a Lagrangian: $$ g (\overline{A_R} B_L)(\overline{C_R}D_L) $$ where A,B,C,D correspond to spin 1/2 Dirac particles and the subscripts $R$ and $L$ denote left- ...
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113 views
+50

should the Z0 decay at the same rate that the neutral pion?

The original title of the question was "In a composite Higgs..." and so the sub-questions were done around this theme: Should the decay rate of Z0 be related to the decay of the "higgs" composite ...
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109 views

Eternal clocks and 4D spacetime crystals

There was a recent article about the creation of 4D spacetime crystals based on recent theory proposed by Frank Wilczek. This theory is based on breaking time translational symmetry which basically ...
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95 views

Remaining Potential Experimental Particle Physics Discoveries at the TeV Scale?

With the discovery of the Higgs Boson, some have been calling it the end of experimental particle physics for our generation, due to the fact that all of the particles predicted by the standard model ...
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155 views

What results from particle collision would ensure the existence of the graviton?

I understand that particles are smashed together to try to enable us to detect some sort of graviton presence but we can't actually detect a graviton due to the fact that it 'exists' in some extra ...
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225 views

Can the mass of longitudinal and transverse W bosons be measured separately?

Some higgsless unified models of particle physics predict that the mass of longitudinally polarized W bosons and the mass of transversely polarized W bosons are different. In those models, a ...
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146 views

About the decay of Higgs into 2 Z bosons

I need to know if I understand this point. The factor of HZZ vertex in the SM Lagrangian is half the value of the Feynman rule which appears in Diagrammatica. When I calculate the decay of Higgs ...
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232 views

Does electron go through a forbidden state when annihilate with positron?

Let's consider an electron-positron pair with total spin equal to zero. When it annihilates it can not emit only one photon because it would have zero momentum and nonzero energy. The pair emits two ...
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291 views

Has CERN recently found evidence for a Z-prime boson?

In the recent Higgs seminar at 73:38 Guido Tonelli the spokesman for CMS, makes a mistake and refers to a Z-prime in a context that would imply that they see them frequently. He swiftly backpedals ...
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23 views

Upsilon full decay width? (and reference request)

The decays of 1S, 2S, 3S states of the $\Upsilon$ meson are according the particle data group surprisingly stable, but not as stable as a typical weak-only decay. Some electromagnetic decays, such as ...
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27 views

Covariant projection method - Meson bound states

I have seen many papers that discuss the production or decay of mesons ( quark bound states ) to make use of the covariant projection method where the product $\upsilon\bar{u}$ of the quark spinors ...
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14 views

Collision symmetry and measuring the asymmetry in the Drell-Yan process

I saw a talk the other day about an asymmetry in the Drell-Yan process caused by CP-violation: Apparently one way this can be measured (ATLAS is doing this) is to collide protons and observe the ...
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36 views

Is there a local canonical ensemble partition function for a Bose-Einstein gas?

The grand canonical partition function for a Bose-Einstein gas is $$ Z_{\text{grand bos}} = \exp \left( \sum_{j=0}^{\infty} -\ln \left( 1-e^{\beta(\mu-\epsilon_j)} \right)g_j \right) $$ where $\beta$ ...
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34 views

Is there any difference in mixing and oscillation of neutral mesons?

I have often read about neutral Kaon oscillation or neutral B meson mixing. Both are described by the similar box diagrams. So I want to know if we can say neutral kaon mixing and D meson oscillation. ...
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22 views

No bottom quark in parton distribution function

CTEQ6M Parton Distribution: http://www.scholarpedia.org/article/Introduction_to_Parton_Distribution_Functions My understanding is that bottom/top quarks can exist (at least temporarily) as ...
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54 views

Is the Higgs field responsible of only 1% of the proton mass?

This post is a sequel of: Where does the majority of the mass of the usual matter come from? The following answer of @hft: Your question asks why the "current quark masses" [see ...
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48 views

Thomas precession and neutron star accretion discs

Assuming, based on this wikipedia article Accretion Discs That accretion discs surrounding neutron stars are composed of a gas and / or plasma. That the accretion disc material can achieve a ...
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67 views

What are the differences between the Jetphox, Pythia and Herwig event generators?

I know Jetphox is a parton-level event NLO generator program. But I want to know more about other generator programs such as Pythia and Herwig. What are the differences? I am undergraduate student so ...
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65 views

What are these arcs in bubble chamber photos?

In photos such as this one, or this one (too large to fit inside post), what are the highly frenzied arcs that are really prominent in these photos? Are they simply physical walls in/of the ...
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17 views

Origin and motivation of various flavor symmetries in the neutrino sector

Flavor symmetries of various kinds (for example, $\mu-\tau$ permutation symmetry, or the scaling symmetry, or $S_3$ symmetry) are sometimes assumed between neutrino flavours to "reproduce" the ...
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39 views

Total cross section of particle decay

Suppose a particle A travelling along the $z$-axis and decays into particles B and C. The cross section is given by $$\frac{d\sigma}{d\cos\theta^*} = k(1+\cos\theta^*)^2$$ where $k$ is a constant ...
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36 views

What does conservation of strangeness imply for the nature of interaction?

If the conservation of strangeness holds for a decay, then the possible interactions are Strong, Electromagnetic and Weak. But how does one determine which one is it, out of the three?
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37 views

Why doesn't the decay mode of negative omega conserve rest mass?

There are 3 modes of decay via which a $$\Omega ^{-}$$ particle can decay This is one of the decay: $$\Omega ^{-} \rightarrow \Xi ^{0} + \pi^{-}$$ Baryon number is conserved. Strangeness number is ...
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43 views

How is an atom ionized by electron impact?

Can someone walk me through in detail what happens when an atom is ionized by colliding with an electron? I would prefer a solid example so I can understand it more concretely. What I think:- -The ...
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36 views

Deceleration of spherical particle in fluid

If I know the initial velocity of a particle entering a fluid, how can I calculate its deceleration over time ? What parameters would I need to know ? Viscosity of the fluid, weight of the particle ...
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12 views

What theory is used to describe photonuclear reaction and photodisintegration?

Assumption: electroweak interaction Background: I am interested in interactions of photons with matter. I just like to know at what point we can purely use the limiting case of QED and where we have ...
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40 views

Pion decay exercise in Griffiths books

I have questions about pion decay problem. In Griffith "Introduction to Elementary Particles" 1st edition, 1987, question number 10.10 : Analyze $\pi^-$ decay as a scattering process, using the ...
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54 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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50 views

Is there a typology of different fundamental physical objects?

As I understand it (and of course, I may be wrong!).... In classical mechanics, all objects are basically the same in the sense that They are composed of atoms bunched together. These atoms occupy ...
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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 ...
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29 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 ...
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25 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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28 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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100 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 ...
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53 views

Where do ultra-high-energy cosmic rays come from?

Physicists have detected an amazing variety of energetic phenomena in the universe, including beams of particles of unexpectedly high energy but of unknown origin. In laboratory accelerators, we can ...
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23 views

Techni-Higgs Particle

I read online that a professor from Denmark alleged that the particle that was found in Cern is not necessarily Higgs Boson, it has many characteristics that match with the "god particle" , but it ...
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15 views

Upper bound to annihilation cross section into heavy particles

For a process in which two relativistic particles annihilate to produce two or more heavy(er) particles of mass $M$: Is it true that the cross section $\sigma_{ann}$ cannot be larger than ...
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44 views

Why do weak interactions give such slow decay rates, if the analog of the fine structure constant isn't signifigantly small?

Intuitively, it seems as though the reason would be a small value for the coupling constant, as the probability for emitting $W^{-}$ bosons would be low. However, it's value is almost the same as the ...
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44 views

Charge Conjugation Operator in Supermultiplet

Consider an $\mathcal{N}=1$ left-handed chiral supermultiplet. The particle content is $$L = (\phi\quad e_L) $$ where $\phi$ is a complex scalar and $e_L$ a left handed Weyl fermion. People usually ...
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121 views

Mechanism of Supersymmetry Breaking (F-term, D-Term, Mediated)

I will make my question clear. SUSY is broken symmetry because we haven't seen superpartners. As far as I know, there are two mechanism of SUSY breaking, F-term and D-Term. Besides, there are some ...
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74 views

How to construct singlet and other multiplets from two triplets

Let an $SU(2)$ isotriplet operator is given by\begin{equation}\bar{l^c}i\tau_2\vec \tau l=l^T Ci\tau_2\vec \tau l\sim 3\end{equation} and an isotriplet Higgs field \begin{equation}\vec \Delta\sim ...