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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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Direction of chiral symmetry breaking

What happens if one breaks the SU(2) chiral symmetry in a non-real direction(a direction apart from the one that the small masses of hadron's constituents(quarks) dictate). Or equivalently We know ...
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Can neutrinos derive Higgs mechanism mass by a relationship to other particles?

Can faint neutrino mass be strictly a corrective term that derives from a hidden relationship (in an unknown Theory of Everything (TOE) perspective) to another elementary particle that does gain mass ...
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Why are number changing interactions inelastic?

Inelastic processes are those in which the kinetic energy of the initial particles and final particles are not the same. Is this true also for number changing processes such as pair creation or pair ...
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Which books or content should I prefer to understand particle physics operator and representations [duplicate]

I am just a intermediate passout and I want to know which books should I prefer for learning the mathematics of particle physics level like the different representation, operation like Hamiltonian, ...
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What is the origin of neutrino mass? [duplicate]

Standard model shows zero mass for neutrino and seesaw model explains why the neutrino mass is so small. But to show that the neutrino mass is small, the mass should be originated by some mechanism. ...
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CP violation measurement

I have a question regarding the measurement of CP Violation in experiment. How is parity measured in an experiment? I know that in the direct measurement of CP violation we look at a particle process ...
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A body moving along a circular path covers a distance of 3 m in 1 s uniformly [on hold]

A body moving along a circular path covers a distance of 3 m in 1 s uniformly, such that the body returns to its starting point. (i) Is the body moving with uniform speed? Explain. (ii) Is the body ...
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1answer
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A question on the strong interaction and charm number

I know that the particle $P_c(4380)^+$, has quark content $\bar{c}cuud$. Furthermore I know that the reaction $K^-+P_c(4380)^+\rightarrow K^-+J/\psi+p$, is strong and the quark content on the left ...
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Detemining whether a particle is stable with respect to the electromagnetic, EM or strong force

If we have some beautiful hadron , how can we decide based on the quantum numbers and masses of the other beautiful hadrons whether it is stable under the electromagnetic, weak or strong interaction . ...
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Using Isospin symmetry to find the decay width of an interaction

Say we have two decays $\Delta^+\rightarrow \pi^+n$, and $\Delta^+\rightarrow \pi^0p$. I want to show, using isospin symmetry that the probabilities for these decays is in the ratio $\tfrac{Γ(\Delta^+\...
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Can someone explain Technicolor?

I read Wikipedia on Technicolor (and understood some of it - I am not a scientist) Can someone give me a layman's definition? Is the technicolor theory dead now that the Higgs has been found? Can ...
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Confusion on conservation of energy in the beta decay process

In a question,regarding the beta decay process, it is given that. Assuming the anti-neutrino to be massless and possessing negligible energy and the neutron to be at rest, momentum and energy are ...
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Why is the decay $\eta'\rightarrow \gamma + \gamma$ suppressed?

So the $\eta$ meson's dominant decay mode is $\eta \rightarrow \gamma + \gamma$ whereas the dominant mode for $\eta'$ is $\rho+\gamma $ or $\eta + \pi+\pi$. Why does it not decay to two photons ...
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Can someone explain the $ttH$ Coupling?

IS the $ttH$ an actual particle? If so, how can it form? I though the life of the top quark was way to short to form a particle. If it is not a particle, what is meant by coupling.
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How to find the corrsponding expression after working with natural units $\hbar=c=1$?

If one does long calculations in natural units how does one find the right expression in let's say SI units in the end? I know that natural units make the calculations easier and also help to show ...
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Example of calculating phase shifts in scattering theory

I have an extended question to this post: Phase shifts in scattering theory I have read it and also went over the formalism in Sakurai's, Shankar's, and Griffith's. I am now trying to look for ...
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Stale file handle error [migrated]

I am doing particle physics. I am running code on monte carlo samples. I am getting the "Stale file handle" error only when I run on one specific sample. The rest of them is OK. A screen shot of ...
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Why do we need a two-Higgs doublet model and why only one extra doublet is added to the extension?

The general two higgs doublet model can neither give masses to neutrinos without considering a see-saw mechanism nor it can unify gravity with other three forces. To explain dark matter also we have ...
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Does the wave function contain the information of the particle's mass?

It is said that wave function contains "all" the information about a particle but I don't see how I can get the mass from wave function. Further, it is able to judge what kind of particle it is by ...
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Neutrino scattering cross-section in high energy limit

I've come across a problem in out particle physics lecture notes that I have been unable to resolve on my own. I've paraphrased the bits of the notes that are giving me so much trouble: The notes ...
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Tritium decay energy too small for quark model

So $^3$H turns into $^3$He through $\beta^-$ decay, right? The energy of this reaction is only 18.6 keV. However, according to the constituent quarks model, the only thing different between $^3$H ...
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Are pressureless, collisionless and self-interacting dark matter all synonymous?

Is there any distinction between pressureless, collisionless and self-interacting dark matter or does being one imply the other?
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Is positron creation operator times electron creation operator equal to the ground state?

This is part of a larger problem, but the important part is that at one point I have: $$ bb^\dagger+bd+d^\dagger b^\dagger + d^\dagger d + b^\dagger b +db + b^\dagger d^\dagger+d d^\dagger $$ where $...
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Particle decoupling, universe expansion and QFT

A particle (say neutrino) decouples from the plasma in the early universe when its interaction rate $\Gamma$, with the plasma, is slower than the expansion rate $=H = \frac{\dot{a}}{a}$, i.e. $\Gamma &...
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What is the atomic number of an electron, and why is its symbol $\sideset{_{-1}^{\phantom{-}0}}{}{\text{e}}$ in $\beta^{-}$ decay equations?

I'd assume that the atomic number, i.e. the proton number, of an electron is $0$ given that it doesn't have any protons. However, to balance beta minus decay equations, this source seems to claim ...
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Are there anti virtual particles (mediator bosons)?

I have read these questions: Can bosons have anti-particles? Is there a possibility for discovery of anti-graviton, i.e. the graviton antiparticle? Antiparticle for Higgs boson? According to ...
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Pion nucleon scattering [closed]

If the kinetic energy of pion is 190 MeV and the rest mass energy =140MeV. How I can calculate the pion lab momentum and pion center of mass momentum.
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Strange Quark Matter

I am watching a video on neutron stars. The video is discussing the collision of 2 neutron (quark) stars and the ejection of strangelets. That if one of these strangelets comes into contact with ...
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How do I determine how far a muon neutrino of 1 GeV will travel in the atmosphere if it's a product of the decay of a muon?

I have a question that is asking how far a muon neutrino of 1 GeV will travel in the atmosphere is the muon lifetime is $2.2\mu$ sec. This is in the context of muons being created by cosmic rays ...
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Correlation diagram for related branching ratios. How to interpret?

I wonder how to interpret the following diagram and how one can see where to place the diagonal lines? Source:https://arxiv.org/pdf/0809.0608.pdf So my thoughts on this: The two axis are two ...
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1answer
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Photo pair production: differential cross section

In a scientific paper, I need for my Bachelor thesis, the differential cross section for photo pair production $\gamma\gamma\to e^{+}e^{-}$ is given as follow: $\mathrm{d}\sigma = \frac{r_{0}^{2}\...
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1answer
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Is there any experiment going on to test the TWO HIGGS DOUBLET MODEL?

We know that the two higgs doublet model which is a beyond standard model theory predicts five higgs bosons.Is there any experiment that is going on to test this theory and if so have they found any ...
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Measurement of spin asymmetries in semi-inclusive deeply inelastic scattering (SIDIS)

I have been reading several papers regarding the spin asymmetries for SIDIS. One thing I was trying to understand is the method of extraction of symmetries. When I read the single spin asymmetries, ...
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Does the weak force have an attractive/repulsive force observable in everyday life like the other forces?

After the correct comments, this question is not here to compare gravity's and EM's long range forces' energetics and amplitudes to microscopic scattering amplitudes of such forces as weak and strong. ...
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1answer
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Arrow of time and CPT symmetry

It's been a few years since my physics degree. But I've been wondering: if you look at pictures of collisions at CERN, isn't it obvious which way time flows - simply on a probability basis? The ...
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The Strings have a finite size they can vibrate?

as I searched about the Strings theory I found out this explanation: Since the strings have a finite size they can vibrate. All the known particles of nature are just different modes of vibration of ...
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Pair creation and annihilation and Wheeler's one electron universe

I stumbled upon Wheeler's idea that there could be only one electron. If I understood correctly, basically the idea is that one electron moves forward and backward in time such that it appears as if ...
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How would the structure function of protons be different if quarks had spin 0?

I saw this question in a practice exam. I know that the structure functions are not linearly independent but that $F_2(x)=2xF_1(x)$ when the energy is in the order of GeV. The question asks what ...
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Cherenkov light and refractive index

LHCb’s Ring Imaging CHerenkov detector (RICH) is aimed at telling different charged particles apart by measuring their velocity, which, together with an independent measurement of their momentum, is ...
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Galactic or Extra-galactic Cosmic Rays?

If we want to show whether or not a specific Cosmic Ray particle is confined to our galaxy we must use the Larmor radius (relativistic version), $$r = \gamma \, \frac{ m c}{q B}$$ Considering a $10^...
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Why does the conclusion that protons are monopoles has led us to believe that they specifically may have a half-life? [closed]

from Zeldovich, Ya. B.; Khlopov, M. Yu. (1978). "On the concentration of relic monopoles in the universe": "The majority of particles appearing in any quantum field theory are unstable, and they ...
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Vanishing integral in deriving stress-energy tensor from action

In the derivation of the energy-stress tensor for a scalar field (context: Inflation Theory for Cosmology) by varying the action with respect to the metric, the integral over spacetime that is ...
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1answer
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Decay width of the tau lepton

The total decay width of a particle, $\Gamma$, is proportional to the fifth power of its mass, $m$, $$ \Gamma \propto m^5$$ We also know that the dominant decays of the tau lepton are $$\tau^- \to \...
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1answer
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Is there an example of two elementary particles colliding to result in a single elementary particle?

Apologies for the novice question, but I don't know enough particle physics to immediately answer my own questions. I have the following questions. Is there an example of an inelastic collision ...
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1answer
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Expected number of events at a neutrino telescope

When you want to detect neutrinos from an isotropic neutrino sources like a supernova, how can you calculate the number of events? For simplification let's assume the neutrino flux is mono-energetic....
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How solitons are related to particle physics?

Recently, I read a paper about introduction to solitons. Author said that the solutions of sine-Gordon equation can be candidate for modeling elementary particles and there are some applications in ...
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Computing the decay width for Top quark decaying to bottom quark and W boson

I have been trying to calculate the decay width for the $t \rightarrow bW^+$ decay. After having done this numerous times, I can not figure out how the result $$\Gamma = \frac{g^2m_t^3}{64\pi m_W^2}\...
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Understanding the idea behind the super-Poincaré algebra

On the Super-poincaré algebra wiki page (https://en.m.wikipedia.org/wiki/Super-Poincaré_algebra), it says: "If Minkowski space-time belongs to the adjoint representation, then can Poincaré symmetry ...
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1answer
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Which decoupled first? The dark matter or the CMB photons?

According theories that work best for the structure formation which happened first in the history of the evolution of the Universe, the decoupling of dark matter or the decoupling of photons? How sure ...
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In what ways can gravitational wave research help particle physicists? [closed]

Old content (put on hold as too broad) I was massively ill-informed about the experiments that shape the modern particle physics research. For example, I believed that most of the information that ...