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 can neutrinos oscillate though the lepton flavors have differing masses?
Since the total mass-energy for the neutrino presumably does not change when a neutrino changes lepton flavor, though the mass is different, what compensates for the gain or loss of mass? Does the ...
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1answer
484 views
How does one experimentally determine chirality, helicity, spin and angular momentum?
If I've got an instance of a fundamental particle, how can I separate out the measurements of these three concepts?
(I think) I understand the theory behind them, and why the particles in the ...
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254 views
Are right handed neutrinos actually antineutrinos and vice versa?
Is it experimentally ruled out that right-handed neutrinos are actually antineutrinos, and left-handed antineutrinos are neutrinos ?
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186 views
Why is it common to plot $xG(x,Q^2)$ and not simply $G(x,Q^2)$?
I'm trying to understand the modern description of high-energy scattering processes involving hadrons in the initial states. The phenomenological parton distributions functions play a central role, ...
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53 views
Superconformal Multiplet Calculus in 6D
A convenient method for dealing with off-shell formulations of
supergravity theories is provided by the superconformal multiplet
calculus. This calculus was originally constructed for 4d ${\cal N}=2$
...
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195 views
Universality in Weak Interactions
I'm currently preparing for an examination of course in introductory (experimental) particle physics. One topic that we covered and that I'm currently revising is the universality in weak ...
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224 views
Did the Feynman heuristic of “simple effects have simple causes” fail for spin statistics?
Someone here recently noted that "The spin-statistics thing isn't a problem, it is a theorem (a demonstrably valid proposition), and it shouldn't be addressed, it should be understood and celebrated."
...
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What's the difference between helicity and chirality?
When a particle spins in the same direction as its momentum, it has right helicity, and left helicity otherwise. Neutrinos, however, have some kind of inherent helicity called chirality. But they can ...
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What future technologies does particle physics and string theory promise? [closed]
What practical application can we expect from particle physics a century or two from now? What use can we make of quark-gluon plasmas or strange quarks? How can we harness W- and Z-bosons or the Higgs ...
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1k views
Why is the Higgs boson spin 0?
Why is the Higgs boson spin 0? Detailed equation-form answers would be great, but if possible, some explanation of the original logic behind this feature of the Higgs mechanism (e.g., "to provide ...
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2answers
192 views
What are the main differences between $p p$ and $p \bar p$ colliders
I know that it is somehow related to the parton distribution functions, allowing specific reactions with gluons instead of quarks and anti-quarks, but I would really appreciate more detailed answers !
...
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843 views
Does a particle annihilate only with its antiparticle? If yes, why?
Or to put the question another way - what is the result of a proton-positron collision, or an up quark-charm antiquark collision, etc.? As far as I know, annihilation happens only between particles of ...
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706 views
What if LHC finds SUSY?
Here and on many other forums and blogs people ask the question "What if LHC does not find SUSY?". I would like to ask the opposite. What if it finds it? What would the implications be? Is it going to ...
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101 views
Resonances in high energy physics
I still do not understand what a resonance precisely is. Is it exactly the same as a particle? Or only an excited state?
And why does it make a peak in some diagrams? And which diagrams?
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4answers
663 views
How can a point-particle have properties?
I have trouble imagining how two point-particles can have different properties.
And how can finite mass, and finite information (ie spin, electric charge etc.) be stored in 0 volume?
Not only that, ...
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657 views
Left and Right-handed fermions
Is there a simple intuitive way to understand the difference between left-handed and right-handed fermions (electrons say)?
How to experimentally distinguish between them?
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476 views
What does the data in various stages of analysis from a particle collision look like?
I've been following the news around the work they are doing at the LHC particle accelerator in CERN. I am wondering what the raw data that is used to visualize the collisions looks like. Maybe someone ...
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34 views
Are lens spaces classified via a Weinberg angle?
I am thinking about Kaluza Klein theory in the 3 dimensional lens spaces. These have an isometry group SU(2)xU(1), generically, and in some way interpolate between the extreme cases of manifolds $S^2 ...
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279 views
why certain superpositions of quantum states are supressed?
it has been said that the electron is the fundamental representation of the Poincare group, with only two conmuting observables, $( \sigma , p_{\mu})$. This question regards what is usually called the ...
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374 views
Is the Higgs mechanism a fundamental interaction?
Is the Higgs mechanism a fundamental interaction of the same standing as the strong, weak and electromagnetic interactions? If not, is it mediated by the weak interaction? It seems that all the ...
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298 views
How do you find spin of a particle from experimental data?
So I was wondering, with all this Higgs talk going on, they just detected a particle with a mass of 125 GeV (CMS) or 126.5 GeV (ATLAS). But they still don't know what it is, since there is tons of ...
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1answer
267 views
Why are higher generation of matter unstable?
My secondary school physics textbook has mentioned that protons and neutrons are made up of down and up quarks in different amounts. It has also mentioned that other quarks exist. It states that ...
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4answers
379 views
How can there be a quantum field theory that predicts all particle masses?
Say I have a theory with only one (energy) scale, e.g. one given by the fundamental constants
$$\epsilon=\sqrt{\dfrac{\hbar c^5}{G}}.$$
In this case, where I can't compare to something else, is ...
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3answers
603 views
What actually happens when an anti-matter projectile collides with matter?
I'm trying to understand what would really happen when large quantities (e.g., 10g) of anti-matter collide with matter. The normal response is that they'd annihilate each other and generate an ...
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3answers
560 views
Why does the weak force distinguish left and right handedness?
I'm wondering why the weak interaction only affects left-handed particles (and right-handed antiparticles).
Before someone says "because thats just the way nature is" :-), let me explain what I find ...
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500 views
Why do leptons and quarks mix?
Is the fact that weak eigenstates are not mass eigenstates completely arbitrary? Or is there a deeper reason for the existence of the PMNS and CKM matrices?
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345 views
Is there a connection between the fluctuation-dissipation theorem and the Green–Kubo relations?
Is there a connection between the fluctuation-dissipation theorem and the Green–Kubo relations? I have a hard time finding out if there is a relation and what it is, because the ...
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286 views
What properties of Germanium make it suitable for Dark Matter detectors?
What properties of Germanium make it suitable for Dark Matter detectors?
I tried googling but there was too many results describing the use of Germanium Chrystals at low tempretures for Dark Matter ...
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1answer
246 views
What if the binding energy becomes larger than the rest mass?
Looking at the equation for binding energy and mass defect,
$$
B = m_{\text{free}} - m_{\text{bound}} \\
\Rightarrow m_{\text{bound}} = m_{\text{free}} - B,
$$
my question is the following. Suppose ...
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314 views
Decay of SUSY particles
In discussion of LHC searches for SUSY particles, physicists seem to assume they will decay quickly to the lightest SUSY particle which then remains stable (at least within the time it takes to leave ...
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1answer
110 views
Is the LEP B meson asymmetry evidence for higher dimensions and/or string theory?
According to this blog, new standard model calculations have changed the 3 sigma B meson forward and backward production asymmetry observed at LEP into two anomolies:
A 2.5 sigma B meson production ...
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1answer
268 views
why is there no ninth gluon?
A teacher of mine told me once that there were no ninth gluon because such a one should be white and interact infinitely far, and no one has been observed. Is there also a theoretical reason?
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192 views
Is there literature on a continuous mass spectrum for the Higgs field?
Various masses for the Higgs field are compatible with experiment, but is it possible that the Higgs field is not observable because it has a continuous mass spectrum?
Work in the 60s and 70s on free ...
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141 views
Parton showering in Pythia 6 Monte Carlo generator
I have Pythia Monte Carlo (MC) samples where I can't understand the parton showering model. If I print out full decay chains from the events, each event contains multiple string objects with pdgId 92. ...
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330 views
+100
About defining “baryons” and “mesons”
I want to understand the proof of the claims (of the construction as well as of its uniqueness) of gauge singlet states given around equation 2.13 (page 10) of this paper.
Also does the listing of ...
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$t\bar{t}$ asymmetry
Some weeks ago, there was lots of talk about this CDF paper:
Evidence for a Mass Dependent Forward-Backward Asymmetry in Top Quark Pair Production
where they measured a much higher asymmetry than ...
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7answers
361 views
Are the rest masses of fundamental particles certainly constants?
In particular I am curious if the values of the rest masses of the electron, up/down quark, neutrino and the corresponding particles over the next two generations can be defined as constant or if ...
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3answers
326 views
Has every possible interaction between elementary particles been observed?
There are some interactions that are forbidden by conservation laws, e.g. an electron cannot turn into a positron by conservation of charge and a photon cannot turn into a positron electron pair by ...
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1k views
What is the definition of colour (the quantum state)?
I heard somewhere that quarks have a property called 'colour' - what does this mean?
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559 views
What is the meaning of the word “particle” in particle physics?
I want to use Matt Strassler's definition of the word "particle" as a specific example:
Matt Strassler writes:
(1) "...all the elementary “particles” (i.e. quanta) of nature are
quanta of waves ...
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4answers
352 views
Matter-Antimatter Asymmetry in Experiments?
As I hope is obvious to everyone reading this, the universe contains more matter than antimatter, presumably because of some slight asymmetry in the amounts of the two generated during the Big Bang. ...
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3answers
898 views
How are neutrons produced from cosmic ray particles?
What are the details of how neutrons are produced as a result of cosmic ray particles hitting our planet's atmosphere?
For instance, what is the pathway that creates the highest number of neutrons ...
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3answers
812 views
Why does electron-positron annihilation prefer to emit photons?
If gravitons are massless, and neutrinos nearly so, why aren't pairs of either of them normally expected products of electron-positron annihilations? Are they possible but simply unlikely, or is there ...
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3answers
257 views
References on the non-compositeness of the known elementary particles
What paper(s) or theory(s) describe or prove that the elementary particles that we have determined today cannot be made up of smaller more fundamental particles?
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Origin of lepton/quark generations?
What theoretical explanations exist for the fact that there are three generations of leptons and quarks?
I'm not so much asking why there are exactly 3 generations, but rather what makes electron, ...
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413 views
How are the masses of unstable elementary particles measured?
I am interested in knowing how (Q1) the particle's masses are experimentally determined from accelerator observations.
What kind of particles? They must be as far as we know elementary and unstable ...
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2answers
286 views
Use of Monte-Carlo simulation in High-energy Physics
I've been doing some research into the analysis used in particle physics when determining the significance of a finding (e.g. the recent Higgs candidate was announced as a boson in the 125-126 ...
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3answers
2k views
How to explain the weak force to a layman?
I'm trying to explain in simple terms what the weak interaction does, but I'm having trouble since it doesn't resemble other forces he's familiar with and I haven't been able to come up (or find on ...
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158 views
Compton Scattering
Compton Scattering essentially states that when a photon of a given wavelength hits an electron the energy level of the electron changes and the photon has its wavelength changed. This seems to be ...
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195 views
Is there a simple way to compute some physical constant from Feynman diagram statistics?
I've been playing around writing some software to generate Feynman diagrams for QED, respecting the vertex "rules" described here, and avoiding creating isomorphic duplicates.
So from a starter ...
