What is Particle physics: Definition and 531 Discussions

Particle physics (also known as high energy physics) is a branch of physics that studies the nature of the particles that constitute matter and radiation. Although the word particle can refer to various types of very small objects (e.g. protons, gas particles, or even household dust), particle physics usually investigates the irreducibly smallest detectable particles and the fundamental interactions necessary to explain their behaviour.
In current understanding, these elementary particles are excitations of the quantum fields that also govern their interactions. The currently dominant theory explaining these fundamental particles and fields, along with their dynamics, is called the Standard Model. Thus, modern particle physics generally investigates the Standard Model and its various possible extensions, e.g. to the newest "known" particle, the Higgs boson, or even to the oldest known force field, gravity.

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  1. Y

    Physical Valentine's Day -- quotes from particle physics magazine

    Here are the quotes https://www.symmetrymagazine.org/article/show-your-affection-with-physics-valentines , I find them funny except for the last one is hurtful, I shouldn't say such a thing for someone on a valentine's day because they would care about the valentine's day, personally I find it...
  2. R

    I Video lectures in Nuclear and Particle physics? (Undergraduate)

    Hi everyone, I was hoping the internet would be filled with video lectures since lots of universities have been forced to conduct online teaching. However, that doesn't seem to be the case. Therefore I was hoping that some of you know of some great video lectures for nuclear and particle...
  3. J

    Water analogy in Particle Physics

    There is something unusual about water. Without atmosphere, water can't exist. It's as if water is part of atmosphere. In vacuum, liquid water can't exist. What other things like water where it needs other aspects like atmosphere to exist? And what is the analogy of water in particle physics...
  4. John Greger

    A What are some example Feynman diagrams in Yang-Mills theory?

    Hi! So I have just been studying Yang-Mills theory advanced quantum field theory. In chapter 72 of Srednicki's book Quantum Field Theory they list the Feynman rules for non-abelian gauge theory. I was asked if I could show some sample allowed diagrams but I could not.. In standard particle...
  5. DanielR1

    I Confused on the premise behind De Broglie's hypothesis

    I'm confused on how De Broglie's hypothesis works. I've attached my thinking in a pdf file below. I'm not an expert in the field of particle physics(I'm only in high school), so there may be some error in my logic(I really think so, or else De Broglie was wrong!(hint:he isn't)) I've also read...
  6. Adams2020

    Mass difference due to electrical potential energy

    I do not really know the relationship between potential energy and mass difference. Isn't the difference in mass of protons and neutrons due to their quarks? (the neutron is made of two down quarks and an up quark and the proton of two up quarks and a down quark.) Please help.
  7. Adams2020

    I Loss of electron & proton energy due to radiation

    Can you compare the energy loss of electrons and protons due to the radiation they emit? In fact, I want to know which of the two loses more energy when it emits radiation.
  8. S

    A High energy symmetry breaking and laws of physics?

    In some models of the beginning of the universe, like for example in chaotic inflation, space would stop expanding in some points, creating Hubble volumes that could experience different spontaneous symmetry breaking, which would result in different properties, such as different physical...
  9. mjmnr3

    Why does a symmetric wavefunction imply the angular momentum is even?

    I looked in the instructor solutions, which are given by: But I don't quite understand the solution, so I hope you can help me understand it. First. Why do we even know we are working with wavefunctions with the quantum numbers n,l,m? Don't we only get these quantum numbers if the particles...
  10. J

    A Griffith's Elementary Particles Section 9.7 Electroweak Unification

    1. On pg. 343 Griffith's expresses the weak current in terms of left-handed doublets. jμ± = ##\bar χ_L##γμτ±##χ_L## ##χ_L## = ##\begin{pmatrix} ν_e \\ e \end{pmatrix}_L## ##\tau^+## = ##\begin{pmatrix} 0 & 1 \\ 0 & 0 \end{pmatrix}## , ## \tau^- ## = ##\begin{pmatrix} 0 & 0 \\ 1 & 0...
  11. Helena Wells

    A Neutrino decay before electroweak breaking

    Most scientists believe neutrinos don't get their mass from the Higgs field due to their tiny mass compared to the next lightest particle(electron).During the electroweak epoch the rest particles were massless but neutrinos shouldn't be. The neutrinos would then decay to the other massless ( i...
  12. Helena Wells

    I Possibilty of flavor oscillation of an electron

    Neutrinos oscillate at different flavors while propagating in space and this is due to their mass.Any particle being massless cannot oscillate between different flavors while leptons with the mass of the electron and above are very unlikely to change their flavor. Will we able to detect a change...
  13. A

    A Energy needed to convert a bound proton to a neutron?

    Hey everyone, I've got a question on converting bound protons into neutrons. a. What are some methods used to achieve the proton-to-neutron conversion in atomic nuclei? I'm familiar with particle scattering off a proton in the nucleus. I'm also aware of (n,p) reactions. Are there any other...
  14. S

    A Confusions on QED renormalization

    In many QFT textbooks, we usually see the calculations of vertex function, vacuum polarization and electron self-energy. For example, one calculates the vacuum polarization to correct photon propagator $\langle{\Omega}|T\{A_{\mu}A_{\nu}\}|\Omega\rangle$, where $|\Omega\rangle$ is the ground...
  15. hagopbul

    Intro Physics Finding Books on Elementary Particle Physics & Special Relativity

    hello all : looking for books to read in this times ,undergraduate level mostly , but i have some problem finding good ones for introductory elementary particle physics other than griffths and for special relativity any recommendations
  16. F

    I Estimating decay yields from fits to these distributions

    I'm currently reading various papers on the violation of Lepton Flavour Universality in rare B-decays and I would appreciate some help in understanding the methodology for measuring the ratios in these decays. Here is a quote from a recent paper from the LHCb collaboration (p.5): My question...
  17. D

    Particle Physics- Isospin states

    Hi, I have attached the question to this post. I understand on the process on getting to the answer in that you use $$\arrowvert 2, 2\rangle=\arrowvert 1,1\rangle \otimes \arrowvert 1,1\rangle$$ and apply the isospin-lowering operator to obtain $$\arrowvert 2,1 \rangle$$. Then I understand you...
  18. J

    Feynman Diagrams for Decay of Δ++ & Ξ- Particles

    Δ ++ → p + π0 Ξ - → Λ0 + π-
  19. J

    A Looking Under the Hood of Feynman Diagrams

    I'm currently working my way through Griffith's Elementary Particles text, and I'm looking to understand what's going on with the underlying Hilbert space of a system described using a Feynman diagram. I'm fairly well acquainted with non relativistic QM, but not much with QFT. In particular, I'd...
  20. W

    I How Can Neutral Currents Be Detected in Particle Physics Experiments?

    In decay processes where no mixing between quark families is present, the mediator of the weak force is the neutral ##Z^0## boson. If that is the case, how is it experimentally possible to detect neutral currents in processes such as: $$\bar{\nu}_\mu + e \rightarrow \bar{\nu}_\mu + e$$ What...
  21. D

    Particle Schwartz and QFT Following Tong's Notes

    Hello, I have been following Tong's notes on QFT and have found them to be a great introduction. I am almost at the end and am trying to figure out how to proceed. I have seen recommendations on David Skinner's notes, but I think I want to use a textbook either with Skinner's notes or maybe...
  22. W

    I Cross Section Formula in Peskin and Schroeder

    On page 105 of Peskin and Schroeder's book it says that the integral over ##d^2b## in the expression: $$d\sigma = \left(\Pi_f \frac{d^3 p_f}{(2\pi)^3}\frac{1}{2E_f}\right) \int d^2b\left(\Pi_{i=A,B} \int \frac{d^3 k_i}{(2\pi)^3}\frac{\phi_i(k_i)}{\sqrt{2E_i}} \int \frac{d^3...
  23. W

    I What are the global symmetries before and after symmetry breaking?

  24. Diyon335

    Fission vs. Fusion question (particle physics)

    Homework Statement: Calculate energy released in the reactions below, and compare them (see full question below) Homework Equations: a) FISSION: 1g of U-235 splits into La-148 + Br-87 b) FUSION: 0.5g of D2O with 0.5g of T20 creates He-4 and a neutron useful equations: E = Δm(c^2) Hey, can...
  25. TechieDork

    B I've heard that particle physics is just like taxonomy and botany

    I've heard it from my classmates that particle physics is just like botany or when physics meets taxonomy. There is even a quote from Enrico Fermi about this "If I could remember all names of these particles I'd be a botanist" I just want to know how true is that.
  26. W

    Physics Leaving Academia While Still Contributing to Physics Research

    There is a Theoretical Physicist by the name of Garret Lisi. He gave a ted Talk on one of his unified physics theories that received a lot of attention. The reason why I am bringing him up is because he left academia after he finished his phd and moved to Maui. During his time there he found...
  27. A

    A Average transverse momentum as a function of the longitudinal momentum

    Hello everybody! I am working on a code in which I need to study the dependence of ##<p_T>## vs ##p_L## (the average transverse momentum and the longitudinal momentum of a particle). I am looking for references, papers, books, etc. concerning this topic, but I have not been so lucky. My...
  28. F

    A Madame Wu Experiment: Doubts & Reasoning

    Hi all, I have some doubts regarding the experiment of Madame Wu. I know a strong magnetic field is used to polarise the ##^{60}Co## nuclei, then we have an anthracene scintillator on the top of the sample which will detect the electron produced in the decay: ##^{60}Co \rightarrow...
  29. F

    Proton Structure: De Broglie Wavelength & Resolution

    Hi all. I'd personally consider the De Broglie wavelength λ=h/p, with p being the momentum of the electron beam. I get $$\lambda \simeq 0.6 \times 10^{-18} m $$ and since the radius of a quark is ## \leq 10^{-19} m ##, the proton structure can't be resolved. I'm quite sure there's something...
  30. FourEyedRaven

    Particle Thomson (Modern Particle Physics) & Schwartz (Quantum Field Theory)

    Hi. Are these two books complementary, or do they have too much in common? https://www.amazon.com/dp/1107034264/?tag=pfamazon01-20 www.amazon.com/Quantum-Field-Theory-Standard-Model/dp/1107034736/ My problem is that I still don't quite understand the difference between university courses in...
  31. W

    Field in the presence of a background electromagnetic field

    Attempt at a solution: $$ -\gamma^{\mu}\gamma^{\nu}D_{\mu} D_{\nu} - im\gamma^{\mu} D_{\mu} + im\gamma^{\nu}D_{\nu} - m^2 =$$ $$ -\gamma^{\mu}\gamma^{\nu}(\partial_{\mu} + ieA_{\mu})(\partial_{\nu}-m) - I am \gamma^{\mu}(\partial_{\mu}+ieA_{\mu})+im\gamma^{\nu}(\partial_{\nu}+ieA_{\nu}) - m^2...
  32. W

    How Does Conservation of Momentum Apply to Particle Decay?

    Attempt at solution: By conservation of momentum: $$P = (M,0,0,0) = p_1 + p_2 = (E_1 + E_2, 0, 0,0)$$ thus $$ M = E_1 + E_2 = 2k^2 + m_1^2 + m_2^2$$ Now $$E_1^2 - E_2^2 = m_1^2 - m_2^2 = (m_1 + m_2)(m_1-m_2)$$ $$ = M(m_1-m_2) = (2k^2+m_1^2+m_2^2)(m_1-m_2)$$ Isolating k: $$ k =...
  33. H

    What do the numbers in the table represent for the transformation of fields?

  34. TheBigDig

    Energy of Two Gamma Rays Produced by Pion Decay

    So I worked out the first part and obtained ##E_1 = 478.8MeV##, ##E_2 = 459.4MeV## and ##p = 0.49 MeV/c## but I can't quite wrap my head around the second part. Normally, I'd use the equation for s but I'm confused since I don't know the angle between the gamma rays.
  35. W

    Particle Would like some particle physics textbook-reading advice

    Hi all, I am in a bit of a funny situation where I need to pick up at least a cursory knowledge of QFT and particle physics in the space of two weeks. I borrowed "QFT and the Standard Model" by Schwartz but I have no idea how I should approach it. Ideally I'd pour through every page, but I...
  36. J

    How to find the decay rate of processes: a→ b+c

    As mentioned above I'm unable to begin because I don't know the relevant equations or method.
  37. J

    Can we have a proton and an antiproton in the 1^S_0 atomic orbital

    I have a belief from something I read on the internet that the superscript 1 means that this is a singlet state so it can only hold one particle but then say 3^S_0 is a triplet so it could hold three. Then the first state I mentioned couldn't have a particle and an antiparticle in it , but the...
  38. J

    Initial states ppbar can proceed to npi^0 with parity conserved

    I'm working on some stuff for particle physics and I had a few questions I wanted to ask . Heres the outline of the problem : Establish which initial states of the ppbar system amongst 1^S_0, 3^S_1, 1^P_1, 3^P_0, 3^P_1, 3^P_2, 1^D_2, 3^D_1, 3^D_2, 3^D_3 the reaction ppbar->npi^0 can...
  39. RicardoMP

    How to determine particle energies in center of momentum frame?

    That said, my approach was to determine the energies and 3-momenta at the center of momentum reference frame for each particle, with a fixed s, and check it corresponds to each one of the above, but I'm having some trouble proving that, for example, E_A=\frac{s+m^2_A-m^2_B}{2\sqrt{s}}. I've...
  40. W

    I Can Two Particle-in-a-Box Systems Interact to Affect Entropy?

    It is interesting to consider why sufficiently slow work does not tend to increase entropy. We can model atoms as a collection of quantum particle-in-a-box’s; Compression work will tend to squeeze the size of these quantum boxes, reducing L. Now, suppose instead that you left this quantum...
  41. K

    Minimum energy positron electron collision producing Z-boson

    Homework Statement Homework Equations m2 = E2 - p2 ([/B]The Attempt at a Solution I got stuck by not knowing how to handle the frames and I thought you can view the Z boson (CoM) frame, but then you simply get that mz = 2me
  42. DennisN

    David Kaplan lecture on Particles and the Nature of Nothing

    I just saw this public lecture and I really enjoyed it (the lecture begins at about 18 minutes into the video). He is an engaging and rather funny speaker. At the end there is a Q&A in which he for instance goes into some of the misconceptions about quantum mechanics. David Kaplan is also one of...
  43. O

    Current produced by photolectrons

    Homework Statement In perspective to the photoelectric effect I found following question: Electric current is charge flowing per unit of time. If we increase the kinetic energy of the photoelecrons (by increasing the energy of the incident photons), shouldn’t the current increase, because the...
  44. S

    Admissions PhD in Particle Physics: Oxford or Imperial?

    Hi all, I recently got accepted to do a PhD into High Energy Physics groups at Oxford, Imperial, UCL, Cambridge and Manchester. My main interest is neutrino physics, which all of these places are offering. However, I am struggling to pick between Oxford and Imperial. I have met and discussed...
  45. S

    Studying Minimal preliminary knowledge for a PhD in particle physics?

    Currently, I am doing a master in mathematical physics. I am interested in particles& field theory and want to apply a PhD in this field. But I am not sure whether I can... I just learned a little high energy physics from Griffth and Peskin' book on elementary particles and QFT. Recently, I...
  46. O

    Statistics physics problem -- atom is in the ground state or excited state?

    I am learning for my exam in particle physics. One topic is statistical physics. There I ran into this question: Consider an atom at the surface of the Sun, where the temperature is 6000 K. The atom can exist in only 2 states. The ground state is an s state and the excited state at 1.25 eV is a...
  47. FourEyedRaven

    I Particle Physics vs Quantum Field Theory vs Standard Model

    Hi. I'd like to ask what are the differences between Particle Physics, Quantum Field Theory and the Standard Model. I see these names of physics courses but I want to confirm if I understand the difference. My understanding is that when students learn particle physics in their undergraduate...
  48. L

    I What does coupling mean in physics?

    I am reading Carroll’s Spacetime and Geometry, and I have seen the word “coupled” used multiple times in seemingly different ways. I have gotten the sense that it means some sort of interaction between particles, but Carroll refers to coupling between matter fields and the curvature of...
  49. Samuel Scarborough

    Physics Navy or Air Force for Particle Physics

    I have been interested in particle physics since I was in High School, but I have struggled to keep my GPA high enough to get me into grad school and I want to serve my country. I decided that the military was the best route to get the experience I needed. I would like to work with lasers to...
  50. jgarrel

    Quantum Field Theory-Mass spectrum of Lagrangian

    Homework Statement We are given the Lagrangian density: $$ \mathcal{L}=\partial^\mu \phi ^* \partial_\mu \phi - m\phi^* \phi +\sum_{\alpha =1} ^2 ( \overline{\psi}^\alpha (i\gamma^\mu \partial_\mu -m)\psi^\alpha -g\overline{\psi}^\alpha\psi^\alpha \phi^* \phi) $$ , where ##\phi## is a complex...
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