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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Deep Ineslastic Scattering for neutron and proton in weak-interaction

I'm studing Deep Inelastic Sacttering theory to study the parton model. I have studied the scattering $$e+q \to e+ q$$ And the structures functions $$F_1 = \frac{1}{2} \sum_q e_q^2 \cdot q(x)$$ and $...
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Parity and chirality

I don't exactly understand how parity is related to chirality. On wikipedia it says that the parity transformation can be thought of as a test for chirality of a physical phenomenon. How those two ...
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Polarized Cross Section and the Spin Density Matrix

I am trying to calculate the spin density matrix for the following process ($t$-Quark on shell): My first method is to split the process into a production and a decay.I have determined the polarized ...
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By which interaction will proton decay? [duplicate]

I learned that proton takes at least $10^{34}$ years to decay. If it will decay one day, will it decay via weak interaction or some other interaction?
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What energy range is considered as a "high-energy" or "low energy" cosmic ray?

I have been studying cosmic ray muons lately, and I'm having trouble with making sense of all the eV values. What is the approxamate range (in eV) for "high-energy" and "low energy"...
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How can we tell whether a double beta decay is neutrinoless or not?

If a double beta decay is neutrinoless, there will be no neutrino carrying the energy away and the electrons should carry the exact amount of energy of the decay. The problem is that because neutrinos ...
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A photon cannot exist if it travels at speed lower than $\mathrm{c}$ in a vacuum, why?

This is known in physics that photons travel only at fixed speed $\mathrm{c}$ in vacuum but also inside a medium going from one atom to the next and taking advantage of the vacuum that exists between ...
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Mott scattering vs Rutherford Scattering

If I am understanding the scattering rate correctly, and that is the nr. of accelerated particles that are scattered in a certain solid angle per unit time, the why the bigger the scattering angle the ...
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Quark model wavefunction separability

When looking at the quark model we say we can write the wavefunction in 4 components, ie $$ |\Psi \rangle = |\Psi_{spatial} \rangle|\Psi_{spin} \rangle|\Psi_{flavour} \rangle|\Psi_{colour} \rangle \...
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Stopping power vs linear energy transfer (LET)

I wonder about the difference between stopping power and linear energy transfer. I would like to refer to http://radonc.wikidot.com/stopping-power-v-linear-energy-transfer-let where it is quite ...
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Why are the quark quantum numbers $S$ and $B$ defined to be $-1$ for $s,b$ ($+1$ for $\bar s,\bar b$)?

For $s,c,b,t$ quarks we have quantum numbers $S,C,B,T$. (For $u,d$ quarks we usually specify charge and baryon number, though we could also specify $U,D$.) The quarks with charge $-1/3,~s$ and $b$, ...
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Double charmed omega baryon to charmed omega baryon via muon capture?

Let’s think of the double-charmed omega baryon as a kind of second-generation proton, and the single-charmed omega as a second-generation neutron. I made up the names “puotron” and “muotron” for ...
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Why does $C$-parity forbid odd number of photons in pion decay, but not in positronium decay? (Martin-Shaw)

I'm reading Martin and Shaw's "Particle Physics." In Section 5.4.1 they show how $C$-parity restricts the number of photons in pion decay to an even number of photons: $$ \pi^0=u\bar u\...
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Magnetising a needle with static electricity using silk cloth

A nautical navigation textbook on my table says that we can magnetise a non-magnetised needle by rubbing it with a silk cloth. I decided to cross check on the internet, and found some experts calling ...
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What will happen if neutrinos are not massless particles? [duplicate]

In beta decay, explain qualitatively What will happen if neutrinos are not massless particles?
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Finite distance propagation for charged particles

Usually, when it comes to studying QFT at a finite distance, the underlying problem is neutrino oscillations. Could it be relevant in some sense to study finite-distance propagation of charged ...
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Required characteristics of particles or forces that support 'psychic phenomena'

In Sean Carroll's book, The Big Picture: On the Origins of Life, Meaning, and the Universe Itself, pg. 156, he talks about how 'psychic phenomena' like moving objects using mind power is not ...
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Median discovery/exclusion significance calculation

I was wondering, when using the Asimov approximations for the median discovery or exclusion significance $$Z_0 = \sqrt{2((s+b) \ln(1+ s/b)-s)}$$ are the expected number of signal s and background b ...
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Can electric charges really be positive and negative?

This question is my extension to this one. Please excuse if it sounds too naive, as I am not a physicist by trade. From the above linked question and answers to it I understand no physical phenomena ...
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Adiabatic turn-on of free multi-particle states

Consider a second-quantized operator $\mathcal{H}_{full}$ describing some interacting QFT, whose action is known on a set of Fock states $\{\mathcal{|F\rangle}\}$, which, in turn, are the eigenstates ...
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Could charm, bottom, and even top matter form under the right circumstances?

Strange matter forms because turning some of the down quarks into strange quarks unlocks lower energy levels, and this can lower the system's overall energy at high densities. If the density was ...
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Definition of single-particle states in the free theory

I like defining single-particle states as simultaneous eigenstates of generators of the Poincare group (basically, the representations of the Poincare group). This is the most fundamental definition ...
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Do neutrinos absorb light?

I have been reading about neutrinos lately. One thing that I found amazing about these, is that their detection is not so easy. My question here is, do neutrinos absorb light?
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What is the official explanation of why the spin-1 $W^{\pm}$ Bosons having a magnetic moment?

How is it possible a spin-1 particle to ever have a magnetic moment? Is there any analytical solution to this?
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Three polarizer experiment question

Can the probabilistic results of multiple polarizer experiments be explained in anyway other than QM?
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An explanation about "why is the Universe charge neutral" [duplicate]

I am new at physics. I have a question: What evidence is there that support the statement that the Universe is charge neutral? Is there anybody explain to me?
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What happens when a frame of reference oscillates with a spinning electron?

If a spinning electron was oscillating back and forth, it would create a magnetic field. If I were to hypothetically oscillate with it, it would appear stationary. So, would I experience its magnetic ...
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Why not one fundamental quantum field instead of several?

Why in the physics of elementary particles is not considered the option of the existence of not several separate, but only one single fundamental quantum field? Like string theory. One fundamental ...
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What would happen to a quark if it could be isolated, into what particles it would change? [closed]

WP defines as quantum charge the $-\frac{1}{3} e$ charge value of the down quark and as elementary charge the -1e of the electron. The elementary quark particle cannot be isolated in the lab and its ...
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In layman's terms, what are $\rm SU$ groups used for in particle physics?

I've looked a lot of other places for an explanation for why $\rm SU$ groups are so ubiquitous in particle physics, but they all look like I'd need to teach myself lie algebra and group theory just to ...
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What makes up and down quarks so special?

One of the ways a lot of different mesons and baryons are grouped is by their up and down quark content. There's also isospin, which is admittedly a subset of a more general symmetry. But the ...
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What is the right insight or intuition regarding difference (if any) between a resonance and a bound but unstable state?

When we introduce quantum mechanics we might ask students to calculate the bound states for a potential well of some finite depth. In an introductory example the well might be $V(r)=0$ for $r < a$ ...
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Experiment on nuclei decay [duplicate]

I have a doubt (I have already made a similar question, but slightly different): If I have a bunch of radioisotopes, and I would measure it decay rate and average lifetime, I measure for a time (...
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Radiation Experiment, Can back radiation increase temperature?

I have just completed an experiments to determine if back radiation can increase the temperature of an object. I wanted to perform an easy experiment that would emulate the effect of back radiation to ...
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Can radio waves be converted to positron and electron when placed in weak electric field?

In particle physics, gamma rays can be converted to positron and electron when placed in strong electric field. My question is: What will happen if radio waves are placed in weak electric field? Will ...
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Could electrons exert pressure on a gas?

What would happen if in a sealed chamber with a gas one injects electrons (by any means of emission)? Would the pressure in the chamber rise? What would happen to the gas (say H)? What would ...
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Decay constant what does it means? [duplicate]

The law of decay is $$\frac{dN}{dt} = -\lambda N ,$$ where $\lambda$ is the decay constant. I read something about $\lambda$ but not really clear.... Someone told that is a probability, someone that ...
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Isolated quark detection [duplicate]

Are there any physical properties or laws that prevent the detection of separate or isolated quarks? I think there is no subparticle in nature living loose like this
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Average lifetime of particles

I have heard that If I have 10^24 particles (for instance) and I observe them for 1 years, I can say that they have an average lifetime at least of 10^24 years. How this is derived? So with N ...
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Has there been an experiment with entangled particles to observe effect on decay time when one is at relativistic speed? [closed]

Has there been an experiment with entangled particles, two of the same, for example two neutrons, where one is left mostly at rest and the other accelerated to relativistic speed to observe if any ...
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Why do we say lepton flavour violation is against the standard model if no symmetries are associated with lepton flavour?

Or if a symmetry does exist what is it? If possible could you compare this to a symmetry that leads to a conservation?
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What is the Lorentz factor γ value in order to find the Larmor precesion frequency for the electron including the Thomas precesion correction?

I want to calculate the Thomas corrected value for the lab frame of the electron's Larmor precesion frequency using this equation: $$\omega_{s(g=2)}=\frac{e B}{m c \gamma}$$ I don't know what Lorentz ...
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Finding the velocity of a bounded quark of a meson

How would you compute the velocity of one of the quarks of a meson, when we have no reference to a reaction or a collision? I initially thought we could use the conservation of energy and momentum to ...
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Why is the Pauli's exclusion principle not violated in the two neutron beams interference experiments?

It is my understanding so far that in this kind of experiments like the one measuring the 4π (i.e. 720° Dirac Belt trick) rotation characteristic of 1/2 spin fermions like neutrons, two neutron beams ...
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How do you make antiprotons?

What is the reaction that makes antiprotons? I'm not a physicist so I might not understand the shorthand.
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Had scientists ever fired single protons/electrons/particles before Einstein's work on the photoelectric effect?

Had scientists ever managed to fire/detect single, individual particles, photons/electrons/etc., before the photoelectric effect was discovered and Einstein's work on it saying that light also acted ...
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Vertex at high $s$ Mandelstam variable

Previously I asked the question Mandelstam variables high-energy limit in which it was said that the result $stu \approx -s^2 t$ for $s$ large was derived in the forward limit ($t \rightarrow 0$) and $...
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Hadronization time

In the process of hadronization what is the characteristic time? I was thinking about at the inverse of $\Lambda_{\rm QCD}$ but can also be a dependence from $\sqrt{s}$. Can anyone help me?
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Could processes and outcomes which are happening in colliders be simulated via mathematical model?

Colliding particles either for the purpose of getting fresh yet unexplained experimental results or as a mean of testing proposed theories appears to be a very crude experimental method. Could area of ...
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Chirality/helicity of anti-particles (again)

Questions (very) closely related to this one have been posted dozens of times, but the joint information (including even lecture notes and books) is incredibly contradictory, so I state my specific ...

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