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. F

    A Relation between chirality and spin

    When learning about chirality I was very surprised to find that for QED and QCD the decay modes that would produce 2 particles with the same chirality had a Matrix Element of 0, which I took to mean that angular momentum was being conserved. Even the W only decay into RH antiparticles and LH...
  2. A

    A Influence on Neutron spectrum due to energy loss of beam

    Suppose some protons are impacted on a Lithium target to produce neutrons with energies close to the proton energy. If one considers Energy-loss due to proton-target collision (ionization of the target atoms), will this kind of energy loss influence neutron energy spectrum? I am asked by my...
  3. zehkari

    Relativistic momentum of two photons from a decay

    Homework Statement Homework Equations (1) E2 = p2c2 + m02c4 (2) E = γm0c2 (3) E = Eγ1 - Eγ2 (4) p = E / c (5) E = hf (6) λ = c / f The Attempt at a Solution a) Using eqn (1), rearranged p = (E - m0c2) / c , I obtained 2.9 MeV c-1. Not sure if I have the right answer here as I...
  4. Ajdin Palavric

    Using PDFs to Compute the Total Cross Section

    Homework Statement I would like to compute the total cross section of a lepton pair production using parton distribution functions. The main problem I am having is the numerical computation and the order of magnitude I am getting as a final answer, which so far definitely indicates that...
  5. C

    De Broglie wavelength of an electron

    I'm reposting this thread with some editing suggested by fresh_42: 1. Homework Statement Calculate the mass, velocity and the de Broglie wavelength of an electron and an alpha particle, given the kinetic energy K = 2MeV Homework EquationsThe Attempt at a Solution please find attached![/B]...
  6. T

    Axial Transformation of a pion

    Homework Statement I'm considering a non-linear chiral theory where the Lagrangian is in terms of the field #\Sigma = e^{\frac{2i\pi}{f}}# where #\pi# is my pion matrix containing pion, kaon, and #\eta#. I need to calculate the transformation of #\pi# up to order #\pi^2# under an axial...
  7. T

    Day Night Effect of Neutrinos

    Homework Statement I'm trying to solve problem 3 from http://www.ictp-saifr.org/wp-content/uploads/2018/07/hw_ICTP-SAIFR-2.pdf The problem is as follows: Assume that solar neutrinos arrive at the surface of the Earth in the ##\left| \nu_2 \right>## state (a mass eigenstate). Assume this...
  8. J

    I Particle creation, energy density and the Compton wavelength

    The Compton wavelength of a particle is given by $$\lambda=\frac{h}{mc}.$$ One can construct an expression for the energy density ##\rho## of a particle of mass ##m## given by $$\rho = \frac{mc^2}{\lambda^3}=\frac{m^4 c^5}{h^3}.$$ What is the physical significance of the mass scale ##m## in the...
  9. T

    Fraction of solar neutrinos arriving at the Earth

    Homework Statement Consider solar neutrinos of energy 1 MeV (EDIT: 10 MeV not 1 MeV) which are formed at the center of the sun in the ##\nu_2## eigenstate. What fraction of it do you expect to arrive at Earth as ##\nu_\mu## and what fraction as ##\nu_\tau##? Assume that it evolves adiabaticaly...
  10. C

    I Is this outline of particle physics right?

    Just a quick query here: Is the outline of particle physics at the link below right? I have found it very helpful in a general way, but I am only just learning this stuff and don't want to be misled. https://physics.info/standard/concept-map.pdf Thanks!
  11. A

    I Uncertainty of MonteCarlo Simulations: Weight and Error Bars

    Hello everybody, I need a help, primarly a confirmation about my reasoning. I have data from a MonteCarlo simulation of collisions between particles at LHC (made with Madgraph). I have plotted some variables, for example the angle between two final leptons. Then I have normalized the plot to a...
  12. Ramtin123

    A Computing amplitude for divergent loop diagrams?

    I am trying to compute the cross-section for the diagram below with a divergent triangle loop: where ##X^0## and ##X^-## are some fermions with zero and negative charge respectively. I am interested in low energy limits, so you can consider W-propagator as ##\frac {i\eta_{\mu\nu}} {M_w^2}##...
  13. Sophrosyne

    B Creation and annihilation operators in particle physics

    I was recently reading about annihilation and creation operators in particle physics using the model of an harmonic oscillator, and then quantizing it. This is fine. I can understand it. But how does this quantization of the energy of the harmonic oscillator manifest physically? Is it that only...
  14. Ramtin123

    A Three dimensional representation of ##U(1)\times SU(2)##

    Consider a three dimensional representation of ##U(1)\times SU(2)## with zero hypercharge ##Y=0##: $$ L= \begin{pmatrix} L^+ \\ L^0 \\ L^- \end{pmatrix} $$ Then the mass term is given by [1]: $$ \mathcal{L} \supset -\frac m 2 \left( 2 L^+ L^- +L^0 L^0 \right) $$ I am wondering where the...
  15. P

    Courses Is particle physics that important?

    Hey! I will start my third year on the theoretical physics program. I have taken an introduction course in particle physics, just the basics, not much math. (quark and Feynman diagrams the forces and interaction , CRM matrix and cabibbo angle etc. ) Now I'm choosing between relativistic...
  16. M

    Other Navigating a Short PhD in Experimental Particle Physics

    Hello! I am not going to give details about the situation (for obvious reasons) but here it is: I got accepted for PhD to a very good American university, in experimental particle physics and I met a famous professor here who is willing to be my mentor. I talked to some of his old students and...
  17. J

    A Exceptional Quantum Geometry and Particle Physics

    What do you think about the article Exceptional Quantum Geometry and Particle Physics Posted by John Baez https://golem.ph.utexas.edu/category/2018/08/exceptional_quantum_geometry_a.html and the following discussion? It also includes links to the original papers. Exceptional quantum geometry...
  18. Thiwanka Jayasiri

    A Solving WIMP & Dark Matter Equation

    I'm trying to figure out how to arrive at the final expression, as given in the lecture notes. I tried to work this out by myself but getting different figure and units. I've considered the followings, normalize the equation from its values e.g. spins and x parameter, as g~100, x~10(m/t~10)...
  19. A

    B Why is the Higgs boson considered a boson?

    Bosons are described as force carrier particles and, as I understand it, the Higgs mechanism explains why photons are massless, just as all the carriers of the strong nuclear force, the gluons, whereas the weak force bosons have mass. A peculiar type of field is postulated, the ‘Higgs field’. It...
  20. C

    B In night vision equipment, how does 'information' transfer?

    So I read a couple of explanations of how night-vision equipment works. Unfortunately I don't remember the sources but my recollection/understanding is that infrared light is converted into electrons and then into visible light. So my question is how does the information by which I mean (the...
  21. G

    A Charged particles mass before symmetry breaking

    How could electrically charged particles be massless before the symmetry breaking? Wouldn't the energy stored in the electric field contribute to particles mass?
  22. Jimmy Ridley

    Conservation principles and particle-particle reactions

    Please can someone help explain these to me? I have completed a-d but I'm not how e works. I thought gamma was an exchange particle so should it then decay further?
  23. mehdi6

    I Computational particle physics

    Hi to all, I have a random number generator in FORTRAN, which gives a random numbers to my particles initial velocity in three dimension (vx,vy,vz). If, I want to make my particles to embark to move with a specific weight (eg. Maxwellian), what should I do? absv = sqrt(vx*vx+vy*vy+vz*vz) wt=...
  24. C

    I Particle Physics and Quantum Mechanics

    I’m having a hard time, as I begin learning QM, knowing what it applies to, if I can put it that way. Is QM the rules that describe how the particles of the Standard Model interact with each other? Or what is the best way to understand the relationship between what one studies when one studies...
  25. Zypheros_Knight

    B E- p+ collision product energies

    Greetings! This is probably the most simplest of questions but I wanted to ask that which particle carries most of the energy of an electron-proton collision (as in p + e− → n + νe), the neutron or the neutrino? What happens if we use a higher energy proton or electron? For example we use...
  26. C

    I Are resonances formed in the scattering of a baryon and a meson?

    Consider the following reaction of strong interaction (in a scattering process) $$n+\pi^+\to \Lambda_0+K^+\tag{1}$$ Then the particle ##\Lambda_0## formed decays with weak interaction $$\Lambda_0\to \pi^+ +p\tag{2}$$ For each decay process I measure the four momenta of ##K^+##, ##\pi^+##...
  27. C

    I De Broglie relation using four momentum in particle physics

    In particle phyisics four-momentum is used and De Broglie relation is used to understand what lenghts can be "seen" in an experiment. Here (page 6) https://people.phys.ethz.ch/~pheno/PPP/PPP2.pdf it is claimed Where ##Q^2## is not actually "momentum" but its the square of the four momentum...
  28. C

    I Does strong force increase or decrease with aligned spins?

    The deuterium exists only with the proton and neutron of aligned spin, which suggests that the residual strong force is greated with aligned spins, i.e. the binding energy is greater if the spins are aligned. On the other hand the mass of ##\Delta^{+}## is greater than the mass of proton ##p##...
  29. W

    How to treat quark color pairs mathematically

    I am trying to work through a problem in the textbook "Particle Physics in a Nutshell." However, I am realizing how little I actually understand about working through problems involving quark color pairs. Given in the problem is the meson color singlet 1/\sqrt{3}(r\bar{r}+g\bar{g}+b\bar{b})...
  30. Greg Bernhardt

    Insights Interview with Niels Tuning, LHCb Run Coordinator - Comments

    Greg Bernhardt submitted a new PF Insights post Interview with Niels Tuning, LHCb Run Coordinator Continue reading the Original PF Insights Post.
  31. L

    Programs SISSA theoretical particle physics

    I have thought about taking the enterence exam for theoretical particle physics at SISSA this coming July. I was hoping someone here took it in a previous year and could give me some advice. By looking at the old written exams, it seems they are mainly made up from QFT and QM. So my plan was...
  32. Semiconductor

    B Unveiling the Mystery of Invisible Atoms

    If atom are invisible then how can one say that atoms are made up of electrons nucleus and quasi particles.
  33. Soffie

    I What can elastic e-p scattering tell us about the proton?

    I'm already aware that deep inelastic scattering, when an electron of high energy is scattered from a proton, shows us that the proton consists of point-like particles (quarks). However, what does elastic electron proton scattering tell us about the proton? Presumably elastic proton scattering...
  34. L

    Particle The need for getting another particle physics book

    Hi there, my name is Leon and I am a physics undergraduate. Recently I decided to dig into the field of particle physics by getting some related books. I definitely will get some books on quantum field theory (Peskin, Scrednick, mandl and shaw...etc), since qft is a framework of particle...
  35. F

    Center of Mass to lab-frame

    Homework Statement a) [Solved] What is the threshold energy in the center of mass for production of an antiproton in a proton-proton collision? Make sure quantum numbers are conserved. (This one was easy and I manage to solve it) b) In a fixed target experiment calculate the proton beam energy...
  36. M

    Is Quantum-Geometry Dynamics the Key to Solving Modern Physics Conundrums?

    I've always loved physics, since my first science fiction novel in 1971. I won a scholarship to do a Math-Physics double honours program at University of Waterloo in 1977, but was immediately seduced into computer science by the promise of being paid big bucks to play with computers all day...
  37. F

    Relativistic Decay: Calculating Pion Momentum

    Homework Statement A Sigma^+ decays at rest into a neutron and a pion^+ meson, i.e. according to the reaction $$\Sigma \rightarrow n + \pi$$ The n and π masses are assumed known. The kinetic energy of the π + is measured to be 92 MeV. Determine the momentum of the pion. Homework Equations...
  38. Birrabenzina

    High Energy Suggestions for a book on Particle Physics

    Hi everyone, I'm a senior undergrad in an Astrophysics BSc, and I just started my first course in Particle and Nuclear Physics. Our teacher didn't suggest anything as a textbook, and on my own I couldn't find any really relevant/useful book for my course type, and now I'm here, hopefully having...
  39. A

    I Particle physics -- The collision of two Beta particles....

    I would likr to know what would happen if two beta particles were too collide with each other
  40. F

    Speed and direction of b and anti-b quark

    Homework Statement A Higgs particle of mass M is moving in the z-direction with speed $\Beta_H$c compared to the lab system. It decays to a b-quark ans anti-b quark, each of mass m. What is the speed and direction of the b-quark compared to the lab-system, if the Higgs system, (a) it is emitted...
  41. V

    Physics Need advice from a professional

    So I need some advice of someone professional and experienced. I’m 16 just about to sit my GCSEs soon and I’ve got a plan of what I want to do in the future. I reckon for my age I know quite a lot about high end things in Physics to do with quantum physics, special relativity, string theory...
  42. F

    I Exploring Oscillations & Interference in Particle Physics

    I will soon start with the course introduction to QFT and are hence an amateur on the subject. However I could not help but wonder, If particles are describes by oschlliations in a field, how can a "bigger body" be made up of several such oscillation? (A bigger particle is made out of several...
  43. S

    A Meson Compostions: Difference Between π0 and η

    The composition of the π0 is (uu_bar - dd_bar/√2; while the composition of the η meson is (uu_bar + dd_bar)/√2. Why is there a - sign in π0 while is there a + sign in η? How are the signs determined? By the way, can I type Latex symbols on this site? I tried to type the anti up quark by typing...
  44. M

    A Question about the matrix of a pseudoscalar meson

    Hi everyone, I have a question about the ##q_{1}\bar{q_{2}}## to vacuum : $$ \langle 0 |\bar{q_{2}}\gamma_{\mu}\gamma_{5}q_{1}| q_{1}\bar{q_{2}}\rangle$$ That is the first time I try to solve the question like this. How do we calculate the matrix about this question ? Thank you so much!
  45. S

    A How can the LRS model for leptons incorporate the Standard Model group?

    This is a homework problem in a course in particle physics at Cornell University. Assume the Left Right Symmetric (LRS) model for leptons. The gauge group is GLR = SU(2)L×SU(2)R×U(1)X. The Standard Model group SU(2)L×U(1)Y has to be included in the LRS group. Namely, U(1)Y ⊂ SU(2)R×U(1)X. Find...
  46. K

    What are Kaustov's areas of interest in physics?

    Hello everyone.. Myself Kaustov from NIT Trichy, pursuing BTech. in production technology. Very much interested to be a part of physics forum. I have knowledge on Theoretical Astrophysics and Cosmology and also Particle physics. Very much interested to be part of all the discussions and to help...
  47. V

    Interpret constraints on scattering amplitude

    Homework Statement For the following theory: ##\mathcal{L}=\frac{1}{2}[(\partial \phi)^2-m^2\phi^2+(\partial\Phi)^2-M^2\Phi^2]+g\phi^2 \Phi^2## Compute s-channel amplitude for process ##\phi\phi \rightarrow \phi\phi##. Interpret result for ##M>2m##. Homework Equations Scattering amplitude...
  48. It's me

    I How can I access event data for LHCb calorimeters?

    I want to do a project using machine learning on the calorimeter event data of the LHCb. How can I access this data? Is it very difficult to navigate your way through the source code on your own?
  49. A

    High Energy Recommended books in HEP, QFT, QM, GR

    Hi everyone! I'm trying to make a list of recommended books (introductory and advanced). So far, what I was able to search are the following: Particle Physics: - Griffiths: Introduction to Elementary Particles - Thomson: Modern Particle Physics - Nachtmann: Elementary Particle Physics -...
  50. S

    A Symmetries in particle physics

    We often use SO(N) and SU(N) to describe symmetries in particle physics. I am not clear which one to choose when I try to discuss a symmetry. For example, why do we use SU(3) but not SO(3) to describe the symmetry of the three colors of quarks? Similarly, why do we use SU(2) but not SO(2) to...
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