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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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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462 views

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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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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377 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'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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Higgs boson and string theory

Assuming Higgs is found at 125 GeV.Is there any direct or indirect consequence on string theory ? Will it be a blow to string theory or models employing string theory ? ...
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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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515 views

Do particle accelerators produce (dangerous) radiation?

I was under the impression that particle accelerators were pretty harmless, but some article said that they produce harmful radiation when you're in the tunnel. Given that the Internet... isn't always ...
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Is there an accepted analogy/conceptual aid for the Higgs field?

Is there an accepted analogy / conceptual aid for the Higgs field? In Physics there are many accepted conceptual aids such as * Schrödinger's cat * Maxwell's Demon * I'm sure I'm missing ...
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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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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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Observed composition of UHE cosmic rays

How much is known about the composition of ultra high energy cosmic rays (say $E>10^{20}\text{ eV}$)? I get the impression that the particles are often assumed to be protons or other heavier ...
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503 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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Is it pions or gluons that mediate the strong force between nucleons?

From my recent experience teaching high school students I've found that they are taught that the strong force between nucleons is mediated by virtual-pion exchange, whereas between quarks it's gluons. ...
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42 views

Dual Pairs in Four Dimensions

Following the conversation here, I am wondering if anyone knows of an example of dual pair with 4-dimensional N=1 SUSY which relates a non-Abelian gauge theory on one side to a theory with a ...
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311 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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250 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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279 views

What dark matter can AMS currently find (or exclude)?

The rumor mill is running again, this time it's about the AMS experiment (Alpha Magnetic Spectrometer) that's going to make a major announcement soon. I suppose they are looking for peaks in gamma ...
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682 views

ATLAS and CMS calorimeters

I was reading this interesting recent review on arxiv about particle identification: Particle Identification In figure 2, there is an interesting comparison between the CMS and ATLAS calorimeter ...
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Derivation of the effective potential between a quark and an anti-quark

Typically in particle physics books (not in QFT books!) I have often seen this statement that the potential between a heavy quark and its anti-quark can be "empirically" represented as $V(r) = ...
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240 views

Gauge symmetries and elementary particles

The Weinberg-Witten theorem (disclaimer: I don't know this wikipedia entry) is usually mentioned as the reason why gravitons may not be composite particles. I do understand the proof of the theorem, ...
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85 views

More forces at low energy?

Just a quick question: In high energy experiments, the fundamental forces are thought to merge into a single force. My question is, in very low energy experiments (very low), do the forces we know ...
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Does the ruling out of TeV scale SUSY breaking disfavor grand unification?

One of the arguments in favor of TeV scale SUSY breaking is that it leads to the appropriate running of the gauge coupling strengths leading to grand unification, i.e. $k_Y = \frac{5}{3}$ instead of ...
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Relation among anomaly, unitarity bound and renormalizability

There is something I'm not sure about that has come up in a comment to other question: Why do we not have spin greater than 2? It's a good question--- the violation of renormalizability is linked ...
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Have I discovered how to calculate the proton's mass using only integers?

Could it be possible that the mass of the proton can be calculated by a series of integer sequences? Or is this just a curiosity? $$\sum_{m=1}^{\infty } \frac{1}{10^{26}(m^2+1)_{2m}}=$$ ...
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What is the difference between a neutron and hydrogen?

Differences? They are both an electron and a proton, since the neutron decays to a proton and an electron, what's the difference between a neutron and proton + electron? so is it just a higher binding ...
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857 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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Do current models of particle physics explain the chemical properties of elements/compounds?

I have a particle system of seven protons and seven (or sometimes eight) neutrons (each formed by their appropriate quarks, etc.) bound together in a state that can be macroscopically described as a ...
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What does the discovery of the Higgs Boson mean for physics?

Will this unite some theories, or cause some other change in physics, and perhaps our undertanding of the universe?
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Does a muon detector on Earth's surface correctly measure the mean lifetime of a muon?

Just a simple question. Does a muon detector on Earth's surface correctly measure the mean lifetime of a muon? I would think the answer is no because most muons detected are created about 15 km above ...
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Why do physicists believe that particles are pointlike?

String theory gives physicists reason to believe that particles are 1-dimensional strings because the theory has a purpose - unifying gravity with the gauge theories. So why is it that it's popular ...
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The life of proton

I have two questions regarding protons 1) Wikipedia says Mean lifetime of a proton $>2.1×10^{29}$ years (stable) Obviously this means practically nothing happens to a proton, but what does ...
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How was the Oh-My-God particle observed?

How exactly was the Oh-My-God particle (ultra-high energy cosmic ray) observed and its energy measured?
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628 views

How are Monte Carlo simulations used in experimental high energy physics?

How are Monte Carlo simulations used in experimental high energy physics? Particularly in studying detectors limitations (efficiencies?) and data analysis. I will appreciate giving a simple example ...
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Why muonium is unstable?

This question is closely related to my previous question Bound states in QED. Muonium is a system of electron and anti-muon. This article in wikipedia claims that muonium is unstable. QUESTION: Why ...
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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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774 views

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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560 views

Why are “heavier” particles harder to detect than “lighter” ones?

Something I have read multiple times that I've never intuitively understood is that "heavier" particles are harder to detect than "lighter" ones... For example, I quote from Stephen Hawking's "The ...
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342 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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Charge of the muon

In the Wikipedia article of Muon, it says ...with unitary negative electric charge of roughly -1 and a spin of 1/2, What are they trying to convey with the "roughly"? Aren't the allowed values ...
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568 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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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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Rank of the Poincare group

There are two Casimirs of the Poincare group: $$ C_1 = P^\mu P_\mu, \quad C_2 = W^\mu W_\mu $$ with the Pauli-Lubanski vector $W_\mu$. This implies the Poincare group has rank 2. Is there a way to ...
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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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What does spin 0 mean exactly?

I heard two definitions: (1) Spin 0 means that the particle has spherical symmetry, without any preferred axis. (2) The spin value tells after which angle of rotation the wave function returns to ...
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327 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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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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Nambu-Goldstone bosons from a quantum anomaly symmetry breaking?

We know that: Nambu-Goldstone bosons come from Goldstone theorem: a spontaneous (continuous)-symmetry breaking of the system leads to massless scalar modes. quantum anomaly: is the anomalous ...
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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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How to distinguish high-energetic muons and electrons in the CMS and ATLAS muon detectors?

At a typical energy of about 100 GeV, a muon has a Lorentz factor of about 1000, an electron about 200.000. The flight time to the detector should be around 30 ns (assuming d= 10m from the collision ...