Questions tagged [particle-physics]

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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42 views

How do I determine the rest mass of a $J/\psi$ particle from CMS Dimuon Data?

Essentially, I'm using CMS Dimuon data, from the decay of a $J/\psi$ particle, to prove that momentum is 'conserved' in relativistic collisions. However, I'm unable to find how I can do this. I ...
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6answers
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Why can’t gravitons distinguish gravity and inertial acceleration?

If gravitons mediate the gravitational force, couldn’t the detection of gravitons by an observer be used to distinguish whether they are experiencing gravitational acceleration vs. inertial ...
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How does the ionic radius influence the ion's interaction?

What can we deduce about an ion, its interaction or the structure it is in, based on the ionic radius? My understanding of the concept of the ionic radius is that these are seen almost as having a ...
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How to label the particles observed in a chamber?

Can anybody help to understand how we can label the particles in an interaction in a chamber, for example in the charmed baryon discovery, $$ \nu_\mu + p -> \Lambda^+ + \mu^+ + \pi^+ + \pi^- $$ ...
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Heisenberg's uncertainty [closed]

I'm doing an exercise with the first Heisenberg's uncertainty relation. He asked me: "show that for a particle moving in a circle (with a constant magnitude) $\Delta L \cdot \Delta \theta \sim \...
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Homework: Probability to get spin aligned in delta decay

During my subatomic physics course, we get homework with no particular explanation. This time one of the questions really got us lost. The question is: The ∆+(1920) resonance decays into pρ0. What is ...
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1answer
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B mesons lifetime

I read about a technique called b-tagging in which one can check if a b meson was produced in a collision by looking for a jet which has a secondary vertex within it. The reason is that b mesons are ...
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2answers
132 views

Can a massless particle have both spin and charge?

Can a hypothetical elementary particle, at least in theory (according to the current science), have 0 mass and yet also have both spin and electrical charge (at the same time)?
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Has there been research done on the dependence of particle decay to its immediate surroundings?

The meson particle, Kaon, can decay into pions or leptons + neutrinos. Each decay has its own probabilities as measured and confirmed during experiments. Has there been any research into the ...
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1answer
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Where does the extra energy come during superelastic collison

It is known that in superelastic collison the energy of particles after collison is more than the original particles but how is it possible . I barely could find suitable information on net for a high ...
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We know the length scales of particles, but what are the length scales of bosonic and fermionic fields?

As particles are about 10-15 meters, the fields must be of inferior length scales? Then are they between Planck scales and electron scales? About which scale? Thanks in advance
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Negative Energy in the 4-momentum of an Antiparticle?

By the very definition of an antiparticle, we know that it has a negative energy $E$; which, in natural units, is: $$E = -\sqrt{m^2 + p^2}$$ where the symbols have their usual meanings. Thus, If we ...
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What do sigma confidence levels mean in particle physics?

My level of understanding of Particle Physics is elementary. Suppose say I have conducted an experiment (maybe a poll) with a sample size of $n$, then I can calculate the mean $\mu$ and the standard ...
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1answer
38 views

Muon $g\!-\!2$ experiment at Fermilab

At Fermilab the $g\!-\!2$ Muon experiment is going on which measures the magnetic dipole moment of the muon. Can we explain the difference in prediction of theory and experiment if we introduce preons,...
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2answers
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Why is the flavour space for flavour symmetry defined in terms of low mass quarks?

In the textbook, I am following it describes flavour space with basis up, down and strange quarks. I am not sure why we did not choose up, charm and top as the basis and why only three bases can ...
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Motion of a Particle in a Penning Trap, parameters and solutions

Ideal equations for motion of a charged particle in a Penning Trap are: $$ x(t) = \rho_{+}\cos(\omega_{+}t + \phi_{+}) + \rho_{-}\cos(\omega_{-}t + \phi_{-}) $$ $$ y(t) = (\frac{q}{\lvert q\rvert }) [...
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How would quarks behave in the event of 'The Big Rip'?

I have always heard that you can't get a quark by itself because "the energy required to split them apart is enough to create another." But, in the case of The Big Rip, the idea is that ...
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Which one is more efficient in producing high energy gamma rays?

According to https://apps.dtic.mil/dtic/tr/fulltext/u2/a351472.pdf the big pulsed power accelerator, HERMES III, generate electron beam with peak energy at 22 MeV and average electron energy at 16 MeV ...
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CKM matrix flavour vs mass eigenstate implication for decay of mesons

From reading the answer in Difference between the CKM and the PMNS matrix , I gather that the transition $W\to ub$ where $u$ and $b$ mean flavour eigenstates is not possible, but it is possible where $...
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Confusion on the proof of Goldstone’s theorem

I amd reading a proof Goldstone’s theorem in Zee's QFT book. On page $228$, Zee presents the proof as follows. The conserved charge $Q$ is given by \begin{equation} Q=\int d^D\vec{x}J^0(t,\vec{x}). \...
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1answer
44 views

Why does light hitting a charged particle cause it to oscillate?

I am trying to study the classical Physics interpretation of light hitting a charged particle. Why does light hitting a charge particle, such as an electron, cause it to oscillate? Is it because the ...
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1answer
39 views

Why can only the Higgs particle have a non-zero expected value in a vacuum? [duplicate]

What does the phrase “Due to Lorentz invariance, only the Higgs particle can have a non-zero expected value in a vacuum” mean?
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Calculating the residue as part of Matsubara summation

On page no. $166$ of "Many-body quantum theory in condensed matter physics" by Henrik Bruus & Karsten Flensberg, while explaining the summation of Matsubara frequency, the following ...
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1answer
50 views

Deep inelastic scattering (DIS) and handbag diagram

Here, in page 11, you can see the so-called 'handbag' diagram that explains how a virtual photon emitted in a deep inelastic scattering (DIS) process interacts with a parton. I'm going to use this ...
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1answer
35 views

Length of cloud of virtual particles [closed]

Every subatomic particle which interact with the 3 quantum interactions has a cloud of virtual particles. How big is that cloud and where is its density bigger?
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4answers
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Friction at atomic level

What is happening at atomic Level between two bodies when there is friction force acting between them?
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Is the wave packet of a relativistic quantum particle oblate (flattened) or prolate (elongated)?

A free, non-relativistic wave packet of a quantum particle is usually thought of as having spherical shape. What happens for a particle moving relativistically? For an outside observer, is the wave ...
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5answers
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Are protons bigger than electrons?

In every text/ physics book that I've read, Protons are mentioned as particles that are bigger, way bigger 2000 times to be precise, than electrons...I believed that until a few minutes ago when I ...
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2answers
47 views

Antiproton synthesis

For a pion minus hitting a stationary proton, what are the other particles if an antiproton is to be created among them? A positive pion is possible but the total rest mass energy of the final state ...
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1answer
59 views

Decay of spin-1 particle into two 1/2 particles

If particle of spin 0 decays in rest frame decays in 2 particles the angular distribution will be uniform. How it will change for particle with spin 1 decaying in pair of $e^{-} e^{+}$ for example?
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1answer
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Book on Representations and Group Theory in Particle Physics for Mathematicians

Is there a book for someone who already knows some group theory and theory of group representations on the mathematical side, and just wants something which explains the applications in particle ...
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4answers
252 views

Is it theoretically possible that electrons are made up of quarks just like protons and neutrons? [duplicate]

Before closing it as a dupe of this. Please go through the question once . Is it theoretically possible that quarks make up an electron ( like you may get a particle with the same electronic charge $(-...
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Deep inelastic electron-proton scattering amplitude

In 'QCD and collider Physics' book by Ellis, Stirling and Webber, chapter 4.2 'The parton model from field theory' there is this equation for the amplitude of the process $e^- (k) P \rightarrow e^- (k^...
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Can only two electrons be in ground state? Are the energy levels the same thing as the energy shells? I can't find a straight answer

So for a model like this one, can there be two electrons in one energy level? And I don't understand the Pauli principle that two electrons can't be on the same energy level when there are 2 electrons ...
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2answers
50 views

$\beta$ decay paths question

Can the $\beta^-$ decay proceed by the absorption of a $W^{+}$ boson or the $\beta^+$ by the absorption of a $W^-$ boson? The $\beta^-$ decay is known as the decay of a $d$ quark into an $u$ quark and ...
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1answer
81 views

Murray Gell-Mann's independent discovery of group theory [closed]

In this article I found an interesting remark on how group (representation) theory was introduced into the physical sciences : Murray Gell-Mann developed the “eight-fold way” to explain the spectrum ...
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2answers
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Pauli Exclusion principle: Query

The definition that I have concluded is that: No two fermions can exist in the state, or quantum state, unless they have opposite spins. Am I right in saying this? They can have the same azimuthal ...
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9answers
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Why are all quarks and leptons of this universe the same?

We know the composition of stars by spectroscopic analysis. The EM waves generated by them are blue- or redshifted. We could have said, "Look, the wavelength is slightly different so it may be ...
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1answer
31 views

Help in recovering the Rutherford formula for $ep\to ep$ scattering in the nonrelativistic limit

If the proton were a point charge like the muon, then $ep\to ep$ scattering, the differential scattering crossection is $$\frac{d\sigma}{d\Omega}\Bigg|_{\rm lab}=\Bigg(\frac{\alpha^2}{4E^2\sin^4(\...
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1answer
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How to prove the equivalence of two definitions of hypercharge?

Before introducing top bottom and charm quarks,Strong Hypercharge is defined in the following two ways--- $1.\,\,\,Y=B+S$ where $Y,B,S$ are the hypercharge, baryon number and strangeness respectively. ...
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1answer
78 views

How to write quark composition of $\rm SU(3)$ mesons?

In $\rm SU(2)$, taking up quark and down quark as a doublet we can easily apply the isospin ladder operators to write the combination of 2 quark or 3 quark (baryon) systems. In $\rm SU(3)$ quark model,...
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0answers
62 views

Hamilton operator action in QFT

I have a question about the action of the Hamilton operator in quantum field theory. At the moment I am trying to get into QFT and came across the following commutator relation: \begin{align} [H,\psi] ...
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5answers
186 views

What laws prevent massive particles to travel at the speed of light?

I and a few of my friends have come across an interesting question. Jackson talks about the case where photon has non-zero mass. By adding an extra term to the Lagrangian, he shows how Maxwell's ...
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0answers
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Running coupling constants

I am slightly confused about the coupling constants of the fundamental forces and would really appreciate some help in clearing up this confusion. Some sources(like this one: http://hyperphysics.phy-...
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2answers
64 views

When a particle changes its spin orientation is it instantaneous?

A change of magnetic field caouses an electric field and an associated potential which is as high as the time derivative of the magnetic field.So is it possible that the change of the spin should be a ...
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1answer
26 views

Why in the field theory, particle's motion is described by 0+1 dimensional field theory?

I started reading the lecture notes on Path integral formulation by Ashoke Das. At the very first page of the introduction chapter, he says that - "a theory describing the motion of a particle ...
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Gas ionizing reactor

What would happen if you ionized a gas inside a coil of wire with high voltages? Please correct me if I misunderstood something, but my interpretation is the following: If you reach the diaelectric ...
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1answer
31 views

OPE leading twist = collinear factorisation?

The operator product expansion systematically expands QFT interactions in terms of a sum of local operators. Is the leading twist of this expansion identifiable with collinear factorisation and, if so,...
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1answer
37 views

Distinguishing between quark and gluon jets

How do experimentalists at the LHC differentiate between jets produced by quarks and those produced by gluons. I know that for b quarks there is a b-tagging method, but what do they do for the others ...
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0answers
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What is a simple QFT calculation that could show that some theory of Quantum Gravity might be correct? [closed]

Imagine that we could do QFT calculations with a Hamiltonian that takes GR into account. What is a relatively simple calculation that could show that this theory is more accurate than a "normal&...

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