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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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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286 views

realization of: CFT generating fuction = AdS partition function

An important aspect of the AdS/CFT correspondence is the recipe to compute correlation functions of a boundary operator $\mathcal{O} $ in terms of the supergravity fields in the interior of the ...
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574 views

Could LEP II have discovered a 125GeV Higgs?

LEP II eliminated the Higgs up to 114.5GeV. If it had been run for longer could it have detected a Higgs at 125GeV? I Googled for this without any luck, though I did find a comment that LEP II topped ...
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Hypercharge for $U(1)$ in $SU(2)\times U(1)$ model

I understand that the fundamental representation of $U(1)$ amounts to a multiplication by a phase factor, e.g. EM. I thought that when it is extended to higher dimensional representations, it would ...
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6k 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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850 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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1k views

What is the current status of the anomalous muon magnetic moment?

Many years ago, a discrepancy was found between the experimentally measured value of the muon magnetic moment, and the theoretically calculated value. Shockingly, most physicists were blase about it. ...
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406 views

How are neutrino beams emitted at CERN?

As far I know they come from accelerator collisions, but I have read confusing things like magnetically focused. How could neutrinos be guided magnetically if they aren't affected by the ...
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546 views

Operator that describes particle detector

In non-relativistic QM, the position of a particle is an observable. In QFT, fields are the observables. However, particles must have some sort of position, otherwise we wouldn't see pictures like the ...
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413 views

As the universe expands, the wavelengths of photons are stretched, and energy is lost. What about electrons?

Will electrons, and other particles, also loose energy as they travel through the cosmos? They have wavelengths. Do they get "stretched"? My guess is that the EM force, somehow, counteracts this ...
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How to determine the mass of a quark?

As far as I know quarks are never found in isolation, so how can we determine their rest mass?
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588 views

Wave/particle-duality as result of taking different limits of a QFT

There is an account on dualities in quantum field theories and string theories by Polchinski from last week http://arxiv.org/abs/1412.5704 At the end of page 4, he writes the wave/particle ...
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492 views

Is there any theory for origination of charge?

We have a theory of a Higgs field that describes how a particle gets mass. Since mass and charge both are intrinsic properties of a particle, is there any similar theory for how particles get electric ...
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593 views

How come random matrices can predict energy spectra of heavy atoms?

Some of the applications of random matrices is to find the spectra of heavy atoms in nuclear physics which are usually difficult to find otherwise. How can starting from randomness of some kind, ...
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What is the need for the Higgs mechanism and electroweak unification?

The Higgs mechanism allows massless fields to acquire mass through their coupling to a scalar field. But if the masses cannot be predicted because the couplings have to be fixed, what really is the ...
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115 GeV, 170 GeV, and the noncommutative standard model

Several years ago, noncommutative geometry was used to describe the standard model, somehow yielding a prediction of 170 GeV for the mass of the Higgs boson, a prediction which was falsified a few ...
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What are the alternatives to the Higgs mechanism?

Can someone summarize, with references if possible, all of the alternatives to the simplest model (that requires only a single scalar Higgs field with the Mexican Hat potential) of spontaneous ...
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What are the mathematical problems in introducing Spin 3/2 fermions?

Can the physics complications of introducing spin 3/2 Rarita-Schwinger matter be put in geometric (or other) terms readily accessible to a mathematician?
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If atoms never “physically” touch each others, then how does matter-antimatter annihilation happen?

It is known that matter and antimatter annihilate each other when they "touch" each other. And as far as I know, the concept of "touching" as our brain gets it is not true on the atomic level since ...
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Why are quark types known as flavors?

There are six types of quarks, known as flavors. Why where these types called flavors? Why do the flavors have such odd names (up, down, charm, strange, top, and bottom)?
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Why is stringless supergravity not considered by many to be a candidate theory of quantum gravity?

This paper seems to show that $d=4, N=8$ supergravity is finite. Yet the paper only has three citations in spires, and I certainly haven't heard talk of a new candidate theory of gravity. Why ...
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What does it mean that the neutral pion is a mixture of quarks?

The quark composition of the neutral pion ($\pi^0$) is $\frac{u\bar{u} - d\bar{d}}{\sqrt{2}}$. What does this actually mean? I think it's bizarre that a particle doesn't have a definite composition. ...
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What are bootstraps?

I've heard occasional mentions of the term "bootstraps" in connection with the S Matrix. I believe it applies to an old approach that was tried in the 1960s, whereby - well I'm not sure - but it ...
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873 views

Why don't we normally see the Higgs boson?

I am a physics student and my dad just asked me about the Higgs Boson. I've told him the little I know, that the Higgs field is a field that is supposed to give mass to elementary particles, and that ...
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791 views

So, no Higgs boson then?

There are a lot of articles being posted in the wake of a CERN announcement that they have not observed the Higgs boson in the range of energies so far searched (between 145 and 466 billion eV), e.g. ...
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731 views

How does Annihilation work?

How does annihilation work? I'm wondering why matter and antimatter actually annihilates if they come into contact. What exactly happens? Is that a known process? Is it just because of their different ...
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trying to understand Bose-Einstein Condensate (BEC)

I am a computer scientist interested in network theory. I have come across the Bose-Einstein Condensate (BEC) because of its connections to complex networks. What I know about condensation is the ...
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687 views

Why are there no particles in conformal theories?

In Matt Strassler's recent post (here) he makes the statement that scale invariant (I assume he means conformally invariant, more generally) theories have no particles in them. What's the reason for ...
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463 views

Alejandro Rivero's correspondence: diquarks and mesons as superpartners of quarks and leptons

The idea of “hadronic supersymmetry” originated in the mid-1960s and derives from the observation that baryons and mesons have similar Regge slopes, as if antiquarks and diquarks are superpartners. ...
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334 views

What is the 'bump' near $M_{\mu\mu}\approx 30\text{ GeV}$

In this (attached) Summer 2011 plot from CMS (twiki page), they have a plot of the dimuon invariant mass spectrum across 3 orders of magnitude in energy. There seems to be a 'bump' near ...
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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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446 views

The delay between neutrinos and gammas in a supernova, and the absolute mass scale of neutrinos

In a supernova explosion (of some type), there is a huge amount of neutrinos and gamma rays produced by a runaway nuclear reaction at the stellar core. In a recent comment, dmckee noted that the ...
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Cross-section in relativistic limit: Fermi's golden rule still valid?

In order to calculate the cross-section of an interaction process the following formula is often used for first approximations: $$ \sigma = \frac {2\pi} {\hbar\,v_i} \left| ...
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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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What happens in electron-electron collisions?

What are the results of high energy electron electron collisions? Are other particles created?
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801 views

Do particles behave like electromagnetic waves?

From double-slit experiments we know particles have wave-like behavior: they statistically form an interference pattern. My question is: Is this wave-like behavior similar to the photons' behavior? ...
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948 views

Why can the Euler beta function be interpreted as a scattering amplitude?

The Wikipedia article on the Veneziano Amplitude claims that the Euler beta function can be interpretted as a scattering amplitude. Why is this? In another word, when the Euler beta function is ...
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What would happen if you put your hand in front of the 7 TeV beam at LHC?

Some speculation here: http://www.youtube.com/watch?v=_NMqPT6oKJ8 Is there a possibility it would pass 'undetected' through your hand, or is it certain death? Can you conclude it to be vital, or ...
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535 views

Why is the charmed eta meson its own antiparticle, but the neutral kaon is not?

I have a limited understanding of antiparticles, so this may be why I am unable to explain why certain mesons are their own antiparticles, while others are not. My understanding is that antiparticles ...
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Virtual particles and physical laws

Recently, I was reading about Hawking Radiation in A Brief History of Time. It says that at no point can all the fields be zero and so there's nothing like empty space(quantum fluctuation etc.). Now, ...
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Why not dilute radioactive waste?

Radioactive wastes are dangerous because unstable elements are too concentrated. Originally radioactive elements come from nature where they were very diluted and that's why they were secure. So why ...
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Higgs Boson mass in Electron volts?

Im no physics genius here, I was just interested in the Higgs Boson so I was reading this article : How the Discovery of the Higgs Boson Could Break Physics I came across this Furthermore, ...
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Where does matter come from?

I admit, it's been a few years since I've studied physics, but the following question came to me when I was listening to a talk by Lawrence Krauss. Is there any knowledge of from where matter that ...
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How do $\pi^0$ particles exist?

I have been taught that the $\pi^0$ particle contains either an up quark and an anti-up quark or a down and an anti-down. How can these exist without annihilating? Also, it is its own antiparticle, ...
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980 views

Mixing of quarks, neutrinos… and leptons?

This is a quite simple question: quarks do mix (through the CKM matrix), neutrinos do mix (through the PMNS matrix). Then why do charged leptons not mix?
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Weak force: attractive or repulsive?

We are always told that there are the four fundamental forces or interactions of nature: gravitation, electromagnetism, and the weak and strong forces. We know that gravitation is attractive, that ...
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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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956 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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695 views

What is meant by the phrase “the mass is protected by a symmetry”?

In a particle physics context I've heard this phrase used. I guess it means that the mass of a particle is less than you'd naively expect from $E=mc^2$ after computing the momentum uncertainty ...
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Justification for new theories of Particle Physics and General Relativity

In reference to arxiv:1212.4893v3 and arxiv:1206.5078v2 papers of Ma and Wang, they have proposed new theories in particle physics, the weakton model where quarks and leptons are formed using these ...