# 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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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 $... 1answer 46 views ### Parity and chirality I don't exactly understand how parity is related to chirality. On wikipedia it says that the parity transformation can be thought of as a test for chirality of a physical phenomenon. How those two ... 0answers 42 views ### Polarized Cross Section and the Spin Density Matrix I am trying to calculate the spin density matrix for the following process ($t$-Quark on shell): My first method is to split the process into a production and a decay.I have determined the polarized ... 0answers 42 views ### 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? 2answers 32 views ### 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"... 2answers 59 views ### 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 ... 2answers 161 views ### 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 ... 1answer 26 views ### 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 ... 1answer 73 views ### Quark model wavefunction separability When looking at the quark model we say we can write the wavefunction in 4 components, ie $$|\Psi \rangle = |\Psi_{spatial} \rangle|\Psi_{spin} \rangle|\Psi_{flavour} \rangle|\Psi_{colour} \rangle \... 1answer 21 views ### Stopping power vs linear energy transfer (LET) I wonder about the difference between stopping power and linear energy transfer. I would like to refer to http://radonc.wikidot.com/stopping-power-v-linear-energy-transfer-let where it is quite ... 1answer 41 views ### Why are the quark quantum numbers S and B defined to be -1 for s,b (+1 for \bar s,\bar b)? For s,c,b,t quarks we have quantum numbers S,C,B,T. (For u,d quarks we usually specify charge and baryon number, though we could also specify U,D.) The quarks with charge -1/3,~s and b, ... 1answer 45 views ### Double charmed omega baryon to charmed omega baryon via muon capture? Let’s think of the double-charmed omega baryon as a kind of second-generation proton, and the single-charmed omega as a second-generation neutron. I made up the names “puotron” and “muotron” for ... 1answer 33 views ### Why does C-parity forbid odd number of photons in pion decay, but not in positronium decay? (Martin-Shaw) I'm reading Martin and Shaw's "Particle Physics." In Section 5.4.1 they show how C-parity restricts the number of photons in pion decay to an even number of photons:$$ \pi^0=u\bar u\... 2answers 169 views ### 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 ... 0answers 38 views ### What will happen if neutrinos are not massless particles? [duplicate] In beta decay, explain qualitatively What will happen if neutrinos are not massless particles? 0answers 29 views ### 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 ... 1answer 40 views ### 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 ... 0answers 15 views ### 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 ... 1answer 90 views ### 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 ... 0answers 50 views ### 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 ... 1answer 44 views ### 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 ... 2answers 81 views ### 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 ... 2answers 61 views ### 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? 2answers 72 views ### 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? 0answers 34 views ### Three polarizer experiment question Can the probabilistic results of multiple polarizer experiments be explained in anyway other than QM? 0answers 43 views ### 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? 0answers 35 views ### 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 ... 1answer 163 views ### 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 ... 0answers 47 views ### 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 ... 1answer 112 views ### 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 ... 2answers 123 views ### 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 ... 3answers 92 views ### 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$r < a$... 1answer 29 views ### 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 (... 3answers 103 views ### 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 ... 1answer 53 views ### 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 ... 1answer 32 views ### 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 ... 3answers 216 views ### 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 ... 0answers 29 views ### 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 3answers 88 views ### 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 ... 1answer 80 views ### 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 ... 1answer 49 views ### 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? 0answers 15 views ### 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 ... 2answers 61 views ### 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 ... 2answers 2k views ### 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 ... 1answer 651 views ### How do you make antiprotons? What is the reaction that makes antiprotons? I'm not a physicist so I might not understand the shorthand. 4answers 524 views ### 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 ... 0answers 36 views ### 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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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?