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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Is it possible to create a new element that doesn't exist in the universe?

When I say something new I do not refer to something already made like H,O etc and when I mean something new I do not refer to a transformation like tritium to helium and gold. If so how ?(I mean is ...
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What's with the very slightly larger mass of the neutron compared to the proton?

Neutron mass: 1.008664 u Proton mass: 1.007276 u Why the discrepancy? On a related note, how does one go about measuring the mass of a neutron or proton, anyway?
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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 others when they "touch" each others. 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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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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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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609 views

Was the Higgs mass correctly predicted by asymptotic safety of gravity?

This paper was published in Phys Lett B in 2009, and predicted the Higgs mass to be 126 GeV based on the asymptotic safety of gravity. Is this prediction taken seriously by the theory community, or is ...
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648 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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868 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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Do gamma matrices form a basis?

Do the four gamma matrices form a basis for the set of matrices $GL(4,\mathcal{C})$? I was actually trying to evaluate a term like $\gamma^0 M^\dagger \gamma^0$ in a representation independent way, ...
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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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Particle physics getting started

I know classical physics, quantum mechanics, special relativity, basic nuclear physics. I would like to get into some particle physics. I want to get into that higgs boson, lepton, quark things :D ...
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If particles are excitations what are their fields?

After reading these : http://www.symmetrymagazine.org/article/july-2013/real-talk-everything-is-made-of-fields http://www.physicsforums.com/showthread.php?t=682522 It was clear to me that all ...
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252 views

Can the weak force create a bound state?

My understanding is that the exchange of Z bosons could yield an attractive or repulsive "force" between two fermions. For most combinations the electromagnetic or strong interactions will take place. ...
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446 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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54 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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Concept of a point particle in quantum mechanics

A point particle is usually thought of as structureless and without dimension. However, given that Heisenberg's uncertainty principle prohibits us from knowing the position of a particle exactly, what ...
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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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618 views

Why is the decay of a neutral rho meson into two neutral pions forbidden?

Why is the decay of a neutral rho meson into two neutral pions forbidden? (Other modes of decay are possible though.) Is it something with conservation of isospin symmetry or something else? Please ...
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286 views

Precise statement of Mermin–Wagner theorem

Roughly speaking, Mermin-Wagner theorem states that continuous symmetries cannot be spontaneously broken at finite temperature in systems with sufficiently short-range interactions in dimensions ...
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Why does $\mathcal L = -\frac14 F^{\mu\nu} F_{\mu\nu}$ imply Photons are massless?

The Lagrangian $\mathcal L = -\frac14 F^{\mu\nu} F_{\mu\nu}$ with $F_{\mu\nu} = \partial_\mu A_\nu - \partial_\nu A_\mu$ results in the four-potential's equation of motion $$ \underbrace{\partial^\mu ...
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CP Violation of the CKM Matrix

Considering the relation between the $SU(2)_{WEAK}$ partners of the $|u \rangle$, $|c \rangle$, and $|t \rangle$ mass eigenstates and the corrseponding downtype eigenstates $ \left( ...
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352 views

Did CDMS identify dark matter?

A recent paper by the CDMS collaboration (PRL here and free text here) makes this statement in the abstract: This blind analysis of 140.2 kg day of data taken between July 2007 and September 2008 ...
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777 views

How do I know the proton isn't made of 3 anti-down quarks?

I have a proton, how do I know that it is made of 2 up quarks and 1 down quark or if it is made of 3 anti-down quarks, each with different color charges? This question is also applicable to the ...
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Baryogenesis only at the Planck scale, or none at all?

I can think of three general ways of explaining why the universe contains more matter than antimatter: (1) Near the Planck time, the universe had zero baryon asymmetry, but at some later time, ...
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998 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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398 views

Dynamical supersymmetry breaking and Witten index

Witten index, defined as ${\rm Tr}(-1)^F$, makes know if supersymmetry is spontaneously broken or not for a given model. But it is known that supersymmetry can be also broken dynamically and one can ...
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Weinberg angle measurement methods

I was reading up on the history of $W/Z$ bosons today and I got a little puzzled. I always assumed that people measured $M_Z$ and $M_W$ and then derived the Weinberg angle. But it appears that they ...
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Is there a fundamental particle that gives rise to energy?

I was wondering if there exist a particle analogous to the Higgs boson that gives rise to energy, I´m sorry it´s not the big question but I feel confused about how the universe works, also I have been ...
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301 views

Propagator of a scalar in position space

In his lecture on Supersymmetry and Grand Unification, Leonard Susskind "derives" the propagator for a scalar field from dimensional analysis. He says for a particle going from $x$ to $y$ (where x and ...
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222 views

Charge neutrality of the Universe: evidences and theories

I've always wondered why the number of protons in the Universe exactly matches the number of electrons. They are such different particles with totally different cross sections. So, first of all, is ...
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551 views

Proton Radius Puzzle, Is it possible that proton's radius differ depending on how you measure it? What does that even mean?

I just read this NewScientist article, and I was stunned by its results. So I found the original paper here on arxiv. In the introduction of the paper it is stated: The recent determination of ...
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Is broken supersymmetry compatible with a small cosmological constant?

I understand that we can find the energy of a bosonic field in its vacuum state via $E_{vac}^{(B)} = \sum_{\vec{k},s} \frac{1}{2}\hbar\omega_{\vec{k},s}^{(B)}$ and a fermionic one similarly, ...
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632 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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What are the main algorithms the LHC particle detectors use to reconstruct decay pathways?

I am just starting to look into how we understand the data from particle collisions. My question is, what are the algorithms or ways that these detectors interpret the data? Are there standard ...
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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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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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Anti-matter as matter going backwards in time? (requesting further clarification upon a previous post)

I understand this question has already been asked here, however, I don't have enough reputation points to place a comment (I suppose that's the reason) on a specific answer to request a reference. A ...
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126 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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147 views

What is chirality?

I actually wanted to make the title as "What is the difference between chirality and helicity"? But I didn't do that because I don't understand properly what chirality is. I have gone through this ...
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Lie algebra of axial charges

Starting from the lagrangian (linear sigma model without symmetry breaking, here $N$ is the nucleon doublet and $\tau_a$ are pauli matrices) $L=\bar Ni\gamma^\mu \partial_\mu N+ \frac{1}{2} ...
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Where is the “true” Higgs if the LHC 125 GeV signal is rather a higher dimensional radion than a SM Higgs?

In this article, Lumo introduces and explains the idea (presented by the original authors in this paper) that the LHC signal at about 125 GeV could alternatively be interpreted as a higher ...
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Are mesons color polarized?

The binding of quarks in mesons baffles me. It's an Occam's Razor thing. Since a meson is a colorless, the simplest way to bind its two quarks together is to use a $U(1)$ Cartan subalgebra of ...
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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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What is the difference between 'running' and 'current' quark mass?

When looking at the PDG, there is a difference between the 'running' and the 'current' quark masses. Does anyone know which is the difference between these two?
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What is the difference and similarities between Stueckelberg mechanism and Higgs mechanism?

What is the difference and similarities between Stueckelberg mechanism and Higgs mechanism? They both make the gauge field massive. Is the Stueckelberg mechanism a special case about U(1) gauge fields ...
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Possible implications of Quark Quartet

Today on Nature's website appeared a news about the discovery of a quark quartet (formed from two quarks and two antiquarks). They say that this particle containing four quarks is confirmed. This is ...
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Are oscillations of electron chirality experimentally observable?

Is there any plausible experiment by which chirality oscillations in electrons could be observed experimentally, such as through some analogy to neutrino oscillation experiments?
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How well is the $\rho$ and $\omega$ coupling universality measured?

Is there any good recent experimental data that tests whether the $\rho$ coupling constant depends only on the isospin multiplet of the produced particle? EDIT: I got a downvote, so I should explain ...
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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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Can a third type of electrical charge exist?

Upon reading my book on physics, it mentions that there are only two discovered types of electric charges. I wonder if there could be a third type of elusive charge, and what type of effects could it ...