Particle physics Definition and 509 Threads

Using the identity for the dot product of Pauli matrices: 𝜎𝑖⋅𝜎𝑗=𝜎𝑖𝑥𝜎𝑗𝑥 + 𝜎𝑖𝑦𝜎𝑗𝑦 + 𝜎𝑖𝑧𝜎𝑗𝑧. How to express this purely in terms of 𝜎𝑧, as x and 𝑦 components change spin states

The first two went fine, but i got stuck at the third one and the rest. For the third: I had that the up quark remains the same as one is needed in a pion and that the anti-strange forms an anti-down and strange. But first, I dont know really why that exactly would be the case. Secondly I dont...

Any conductor with resistance will develop an electric field. This electric field "leaks" outside the conductor, though its strength falls off with the cube of distance. https://www.physicsforums.com/threads/electric-field-outside-of-a-current-carrying-wire.431870/ So, shouldn't it be possible...

I will be applying to graduate programs in theoretical particle physics this winter in the US (for the Fall 2025 intake) and I would appreciate some help with finding appropriate programs/schools. My interests (and experiences) are a weird mix of hep-th and hep-ph, so, I would like to look for a...

I am looking for instructions from you to find out a good university to enroll to a PhD program in Astrophysics and particle physics or a similar study. I have completed my 4 year BSc(Hons) Special in Theoretical Physics with a grade of second class upper division in Sri lanka. My specialized...

Hi, I would like some feedback on my draft of a SOP for a grad school application for particle physics. I am mostly targeting places in the US. I am finding it difficult to identify areas I should focus on and areas that are not as important. I read that such a statement should focus on research...

I would like to know if this thought makes any sence or if i'm missing something Heisenberg principle states that: ΔxΔρ ≥ ħ/2 ⇒ Δρ ≥ ħ /2Δx If we consider a scenario where we increase the precision of our measurement of position, we have Δx ⇒ 0 the principle implies: Δρ ≥ ħ/2Δx → Δρ ⇒ ∞...

Are there any GUTs where the proton never decays? One should write such a theory, perhaps me... :oldbiggrin:

Can energy be stored in a single particle without it being lost over time? I mean, photons would be an exampld in principle, but they get redshifted as the universe expands and become less energetic as time goes by We could store that energy in form of kinetic energy for individual...

I was wondering whether the decay of neutrons and protons (if they happen to be able to decay, as it is predicted by some GUTs) could be avoided in some cases. Let's begin with neutrons: In principle neutrons have a very short time when they are isolated (around 10 minutes) and they suffer...

How do we normally calculate the partial width Γi for a decay involving gluons.Consider the following example: in the first example, I know that one can estimate the partial width Γ1 using CKM matrix elements to get "Γ1 is directly proportional to V2cb V2cs ."Now, for the second diagram it is...

The first thing we need for this is to define what a particle is... It is an object that has specific intrinsic properties and is described by a wave sign How to measure it? This is done by the interaction of the particle to be measured with the measurement system. When measuring, the wave...

I am given the ckm matrix and told that B0s decay to Ds- and pi+ with a branching frcation of 3x10-3. I am then asked to find the branching fraction for other decays. I have done this easily enough for decays like B0s to Ds-K+ by using the ckm matrix elements. However the J/psi meson is a charm...

Is it realistic to switch from atomic theory to nuclear or high energy theory?

The binding energy per nucleon for each element has a specific pattern. It increases from hydrogen to iron and then decreases again. What is the fundamental reason why the binding energy per nucleon has this pattern? According to my investigation, the range of action of the strong force is...

Hello there! Recently, I was awarded a governmental scholarship to study for a PhD at the University of Cambridge. I am interested in particle detectors (development or characterisation) and am okay with analysis work. Is anyone here studying or has studied at the University of Cambridge and...

I have been banging my head against this for a few weeks now; tweaking the simulation, adjusting my calculations, and searching around the web to try to find an answer. I can't post questions on CERN's Fluka help forum so this seemed like the best option. I really appreciate any help you can...

At low photon energies, the probability of the photoelectric effect to occur increases, but the probability of the photoelectric effect to happen also increases when going towards most inner shells like K shell but inner shells require much more photon energies to be broken, so isn't there a...

So my first thought was that I can just use Fourier trick and integrate: $$ F(q^2) = \int_V \rho(r) \cdot e^{ i \frac{ \vec{q} \cdot \vec{r} }{h} } d^3r $$ $$ F(q^2) = 2\pi \rho_0 \int_0^{\infty} r^2 \cdot e^\frac{-r}{R} dr \cdot \int_0^{\pi} \sin{\theta} \cdot e^{ -i \frac{q \cdot r...

Can you explain to me the reason why Thomson Scattering can not explain what happens when light meets an electron at low intensity, and what does that have to do with light being a wave or particle or relativistic/QM effects? https://en.wikipedia.org/wiki/Compton_scattering

An electron and muon collide head-on, with energies 35 GeV and 50 GeV, the following reaction takes place: $$ e^- + \mu^+ \rightarrow \nu_e + \nu_{\vec{\mu}} $$If the electron neutrino has energy of 25 GeV, and collides at angle 20 with respect to incoming electron direction, what is the muon...

I am currently learning about the coalescence model and femtoscopy, and am very confused about what resonances are. I read here (https://www.quantamagazine.org/how-the-physics-of-resonance-shapes-reality-20220126/?utm_source=pocket_saves) that they are, as all particles, an excitation of the...

There is an interesting paper by Arkani-Hamed and collaborators (https://arxiv.org/abs/1607.06821) to address the hierarchy problem. There, they consider many possible models of fundamental particle physics where they all have an exact copy of the Standard Model but with different Higgs...

How does a photon interact with EM field of a nucleus thus exchange momentum and recoil the nucleus when pair production happens?

I'm trying to fill a conceptual gap I have in the history of physics In 1922 Stern and Gerlach make their experiment, proving that electrons have intrinsic angular momentum, however it takes a while for people to understand this. At first they think this is somehow caused by quantization of...

Why is breaking radiation stronger than accelerating radiation? Why is it that when an electron comes accelerating toward a nucleus radiate weaker than when it goes decelerating away from the nucleus? Is it because when it decelerates, at the same time it changes direction? Or is it because it...

I already have a PhD in Nanoscience and Nanotechnology and I will start an M.S. in Physics at SJSU next Monday (August 21 2023). I am interested in Particle Physics. A professor at my institution working in the field told me the following "For you, since you already have a PhD, I don’t think it...

We know from molecular spectroscopy that incoming light on a molecule can change a molecule's rotational, vibrational and electronic energy levels. If the incoming light is, on the far-infrared and microwave region the molecule gets rotational energy.(microwave spectra) on the near-infrared...

We know that when a high energy gamma ray(E >= 1022 keV because the total energy of 1 electron at rest and 1 positron at rest is 511 keV) passes near a high Z(atomic weight) atomic nucleus interacts with the electrical field of the nucleus and there is a probability that this high energetic...

Hi everyone How can i prove that the propagator is And then

I was able to solve b) but I am confused for a). I understand that in the proton-antiproton collision, only two quarks (one from proton and other from anti-proton) can be combined to get a virtual photon that in turn creates muon and anti-muon. I don't understand what would happen to the other...

1) We know in case of beta decay if there is excess of protons or neutrons in the nucleus beta decay take place. Force involved - weak interaction Reason involved - to stabilize, to obtain proton neuton 1:1 ratio in the nucleus. E. g., Beta minus - Carbon 14 transforms into Nitrogen 14 2) Case...

Hi every one.How can i prove the below equation? And then that it's Lorentz invariant quantitude ? Thanks for your help

TL;DR Summary: Given a pentaquark: (a) Determine the isospin multiplet it belongs to. (b) Calculate a kind of a Gottfried Sum Rule for this pentaquark-neutrino or -antineutrino scattering. Hello everybody, I'm having a bit of a trouble with the exercise below as it deals with a pentaquark and...

How did you find PF?: Google Search I am in 8th grade and 10 hours a day free time and i am highly motivated to learn some particle physics. What should i start with?

I am currently a sophomore in HS, and I have a science fair project next year. I want to do something interesting- I don't want to put in barely any effort and do something that everyone has done, like 'growing plants in different light levels'. I would ideally like to do something with...

Free Kindle via Amazon, both part 1 and part 2 Part 1: https://www.amazon.com/dp/B00OD49Z96/?tag=pfamazon01-20 Part 2: https://www.amazon.com/dp/B00OD49Z00/?tag=pfamazon01-20 Enjoy

There are several "bumblebee" models [1], [2] where Lorentz invariance is violated usually resulting from a local vector or tensor field acquiring a nonzero vacuum expectation value We do not know whether we are in the true vacuum state or in a "false"/metastable vacuum state that could decay...

Griffiths "introduction to elementary particles" serves a great introduction as a first course on particle physics for undergraduate students. But what are the possible alternatives of this textbook? Like being more beneficial in the long run, more time-consuming, for aspired students. But it...

Several texts state the vertex HQET Feynman rule as : igTijvμ\frac{1}{1+\slashed{v}} with the reasoning for vμ presented as being due to the QCD interaction vertex being between two heavy quark propagators, which are \frac{1+\slashed{v}}{2v.k}, giving ...

I have been tasked with calculating amplitudes of a B meson decaying to a photon and lepton/lepton anti-neutrino pair ,upto one loop and have pretty much never seen this thing before. I will ask my questions along the way as I describe what I am doing. This factorization theorem seems to go thus...

Hi, I am doing my PHD in Nuclear/Particle Physics and I am getting all of the information I am using from papers, which are very specific. I feel like I am lacking general knowledge, which is likely to be tested in the defense. Do you know any book where I can get a better overview on Nuclear...

In Quarks & Leptons: An Introductory Course in Modern Particle Physics by Halzen and Martin page 42 reads: I do not understand what the issue is, however. What do they mean by "we want... to transform in exactly the same way"? Didn't they just show that they do transform in exactly the...

I join as a 69 year old retired electrical engineer who is interested in physics. I have particular interest in particle physics and quantum mechanics. I don't expect to provide answers on this forum, but I do intend to ask questions.

Just to keep this from being a long post: I went to a local CSU for Materials Science and Engineering in the fall of 2018 after graduating high school in the spring of 2018. I really like learning about everything that makes up the world around me, and why things are the way they are, and in...

As seen in the summary, my question is purely hypothetical and I understand that it would most likely be impossible to happen (or I just haven't read enough). The concept that quarks and leptons are the fundamental particles of the universe has existed for a while now - therefore we know that...

In a head-on collision between the proton and electron, what is the squared 4-momentum transfer between the two particles. Starting with the difference in momentum of the electron with the 4-vectors before and after the event: $$(P-P')^2=P^2+P'^2-2P\cdot P'$$ The circumstances are such that the...

I had been studying this topic from various textbooks and review articles and I am confused about some terminologies and concepts. The question I have typed in this PDF. [Mentor Note -- Added screenshot of PDF contents]

I was reading this article at Wikipedia that says particle physics predicts that the cosmological constant is 10^120 larger than per observation: https://en.wikipedia.org/wiki/Anthropic_principle

The question may be ambiguous but it's really simple. One says that the baryon octet is the D(1,1) representation of SU(3), but then uses the same one for mesons. D(1,1) means one quark and one antiquark, which corresponds perfectly to mesons. But how can it explain baryons? My information and...