What is Antiparticles: Definition and 47 Discussions

In particle physics, every type of particle is associated with an antiparticle with the same mass but with opposite physical charges (such as electric charge). For example, the antiparticle of the electron is the antielectron (which is often referred to as positron). While the electron has a negative electric charge, the positron has a positive electric charge, and is produced naturally in certain types of radioactive decay. The opposite is also true: the antiparticle of the positron is the electron.
Some particles, such as the photon, are their own antiparticle. Otherwise, for each pair of antiparticle partners, one is designated as the normal particle (the one that occurs in matter usually interacted with in daily life). The other (usually given the prefix "anti-") is designated the antiparticle.
Particle–antiparticle pairs can annihilate each other, producing photons; since the charges of the particle and antiparticle are opposite, total charge is conserved. For example, the positrons produced in natural radioactive decay quickly annihilate themselves with electrons, producing pairs of gamma rays, a process exploited in positron emission tomography.
The laws of nature are very nearly symmetrical with respect to particles and antiparticles. For example, an antiproton and a positron can form an antihydrogen atom, which is believed to have the same properties as a hydrogen atom. This leads to the question of why the formation of matter after the Big Bang resulted in a universe consisting almost entirely of matter, rather than being a half-and-half mixture of matter and antimatter. The discovery of charge parity violation helped to shed light on this problem by showing that this symmetry, originally thought to be perfect, was only approximate.
Because charge is conserved, it is not possible to create an antiparticle without either destroying another particle of the same charge (as is for instance the case when antiparticles are produced naturally via beta decay or the collision of cosmic rays with Earth's atmosphere), or by the simultaneous creation of both a particle and its antiparticle, which can occur in particle accelerators such as the Large Hadron Collider at CERN.
Although particles and their antiparticles have opposite charges, electrically neutral particles need not be identical to their antiparticles. The neutron, for example, is made out of quarks, the antineutron from antiquarks, and they are distinguishable from one another because neutrons and antineutrons annihilate each other upon contact. However, other neutral particles are their own antiparticles, such as photons, Z0 bosons, π0 mesons, and hypothetical gravitons and some hypothetical WIMPs.

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  1. orochi

    A The Symmetry of Antiparticle Isospin Doublets in Particle Physics

    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...
  2. J

    A Charge conjugation in quantum gravity

    The charge associated with gravitational interactions is the mass. In the Standard Model, charge conjugation is the "flippin" of all kinds of charges (electric, color, etc). So, if we were to, say, incorporate quantum gravity in a beyond the Standard Model theory, what would the full charge...
  3. F

    A Exploring the Existence of Baryons with Positive Strangeness

    Hi all, I read on "Intoduction to Elementary Particle Physics" (A. Bettini) that baryons with positive strangeness cannot exist. I don't know what to conclude from this sentence: sigma-baryons have negative strangeness, since there's a sigma as valence quark. But these baryons have, of course...
  4. J

    I Is the ground state energy of a quantum field actually zero?

    I start by outlining the little I know about the basics of quantum field theory. The simplest relativistic field theory is described by the Klein-Gordon equation of motion for a scalar field ##\large \phi(\vec{x},t)##: $$\large \frac{\partial^2\phi}{\partial t^2}-\nabla^2\phi+m^2\phi=0.$$ We...
  5. Malek

    B Are Antiparticles the Key to Understanding the Universe?

    There is an assumption in cosmology say that there is another universe Composed of antiparticles? I mean that the atom composed of positron rather than an electron, anti-proton rather than a proton and anti-neutron rather than a neutron.
  6. parshyaa

    B What are antiparticles and what do they do?

    What are antiparticles and what do they do? How do we know that they do exist? Could you explain these in layman's term,because I don't know much about quantum mechanics.
  7. T

    A Is Negative Mass Related to Antimatter in Physics?

    In physics we cannot easily imagine “negative” energy for a particle (not a field) in order to have “negative” mass, although the first concept of Dirac for antiparticles was that they were “holes” that were opposite to particle existence and there was a minus in front of mc2.Regardless of...
  8. martin25p2

    I Relationship between negative mass, energy and antimatter

    What is the relationship between negative energy, negative mass and antiparticles? I have read some articles but I am still confused. Does negative mass exist? Does negative energy exist with the exception of the Kasimir effect which I understand. Are antiparticles really only the negatice...
  9. binbagsss

    A Quantum Field theory profound insight antiparticles

    Hi, I have recently began studying quantum field theory and have just seen how the quantization of the complex scalar field, noting that there is invariance of the action under a phase rotation shows the existence of antiparticles. I just have a couple of questions, apologies in advance if...
  10. James - STARS

    A Antiparticles in Garrett Lisi's E8 Theory

    Greetings all :) I would like to know please how antiparticles fit into Garrett Lisi's E8 Theory. Thanks!
  11. haushofer

    I Antiparticles and Einstein's energy-momentum relation

    Dear all, in a lot of undergraduate textbooks you find the claim that antiparticles can be motivated by Einstein's energy-momentum relation ## E^2 = p^2 + m^2 ##, which has both 'negative' and 'positive energy' solutions. In the context of a single wave function this is problematic. In the...
  12. T

    ELI5: Antiparticles in Feynman Diagrams

    Hi!, I am studying for an introductory course in QED and Feynman Diagrams. Everything we see is like a first order approach and I am having some trouble understanding antiparticles in Feynman Diagrams: Why is it that we put an antiparticle that is leaving as if it is entering the interaction...
  13. PeterDonis

    Antiparticles of Standard Model gauge bosons

    From a recent thread: Is this true of gluons? Doesn't the color charge invert under CPT? (For example, a red-antigreen gluon's antiparticle would be a green-antired antigluon.)
  14. F

    Quantum Recommended Textbooks for Quantum Field Theory and Antiparticles

    Hello All, I was wondering if anybody could recommend some really good, graduate-level textbooks or sources on quantum field theory and antiparticles. I've browsed through several QFT titles, but if anyone has any books they think would be a good grad-level introduction I'd be grateful...
  15. kq6up

    Can antiparticles annihilate different types of particles?

    The title says it all. For example can an anti-neutron annihilate with an electron? Thanks, Chris
  16. D

    Antiparticles are regular particles going backward in time?

    First I would like to say that I'm sorry if this question has been asked before- I'm new here. I was reading QED by Richard Feynman, and he mentioned that any given antiparticle is just it's regular particle counterpart moving backwards in time. How is this possible? I thought that it was only...
  17. S

    Particles and antiparticles in compex field

    Hi. I am confused about something related to the creation of particles/antiparticles in a complex scalar field. I read in the literature that \phi(x)|0\rangle describes the creation of a particle at point x . But given that \phi(x) = \int \frac{d^3 p}{\sqrt{(2\pi)^3 2E_p}}...
  18. L

    Dirac spinor and antiparticles

    An electron field is a superposition of two four-component Dirac spinors, one of them multiplied with a creation operator and an exponential with negative energy, the other multiplied with an annihilation operator and an exponential with positive energy. So I assume one Dirac spinor creates a...
  19. C

    Antiparticles identical in qft

    Has anyone ever heard of treating a particle and antiparticle as identical based on the formalism of quantum field theory? The argument given is that the creation operator for a particle is the annihilation operator for its antiparticle, but I can't find this idea of treating them as identical...
  20. M

    What is the Connection Between Antiparticles and Vacuum in Physics?

    1.does antiparticles really travels backwards in time or is it just used to describe feynman diagrams and diracs negative energy states. 2.what does vacuum really means physically is it just a state in the fock space from which other particle states are created or it really means something...
  21. ShayanJ

    Understanding the Differences Between Particles and Antiparticles

    I've been trying to understand the exact differences of a particle and its corresponding antiparticle.I know maybe the best way is via checking that the two particles annihilate each other when came to contact or not.But I'm talking about their properties now. In some places,it is written that...
  22. G

    The destruction of particles and antiparticles

    In the First Three Minutes Steven Weinberg wrote: The word "destroy" really throws me off. When I think of destroy I think of complete elimination from existence, such as when you destroy a house it is completely gone, the timber may still remain but the house no longer exists. With...
  23. R

    A-V Couplings for Antiparticles

    Hey everyone, I was wondering how the ca and cv vary for weak interactions with antiparticles. It seems that they must be different. Perhaps this is incorrect, but if this is the case I am not sure how there is a difference between e eantineutrino-> e eantineutrino differs from e eneutrino->e...
  24. A

    Do SUSY particles have antiparticles counterparts?

    Well, all of this is theoretical, but I asked myself this because I never heard about antimatter in a SUSY particle context.
  25. T

    The Limitations of the Dirac Sea in Explaining Particle Motion

    I'm not sure if my interpretation is correct, but this Dirac Sea interpretaton does as far as I understand this, tell us that every energy level from -infinity to a certain energy level E<0 is filled with anti-particles. And this should be true for every single location in the universe. If...
  26. J

    A question on virtual antiparticles and Hawking Radiation

    I know that Hawking Radiation is caused by the separation of virtual particles on the event horizon of a black hole, but I do not understand why the antiparticle is always the particle from the pair that falls into the black hole. It seems to me that the gravitational effects of the black hole...
  27. S

    Antiparticles vs virtual particles

    Im a grade 12 student and I just started reading black holes aint so black in the brief history of time. However, I'm having a hard time distinguishing a difference between these two particles. What is a difference? thanks!
  28. P

    Is fission or fusion of antiparticles possible?

    Is fission or fusion of antiparticles possible?
  29. M

    Photon Exchange - Frequency? And uncharged antiparticles

    I wondered about the photon exchange mechanism when my AP physics teacher taught about it. Essentially, it's like shooting a basketball back and forth. I don't see the attractive part, but's that what the analogy was on the internet thing used. I assume it's in the math, anyway. But my...
  30. S

    Spin of Particle and Antiparticle: Same or Different?

    So a simple question, really: Given a particle, will its antiparticle always have the same spin or not? And if not, in which cases will the spin be different? Thanks in advance.
  31. T

    How one can deduce the existence of antiparticles

    Hi together ... I wonder how one can deduce the existence of antiparticles from the Klein-Gordon equation. Starting from (\frac{\partial^2}{\partial t^2} - \nabla^2 + m^2) \Psi(t,\vec{x})=0 one gets solutions \Psi(t,\vec{x})=\exp(\pm i (- E t + \vec{p} \cdot \vec{x})) leading to E^2=p^2 +...
  32. J

    On Feynman diagrams, why do antiparticles have their arrows pointing backwards

    ...compared to normal particles? I was told this was something about, for a particle moving forward in spacetime, its antiparticle can be considered as moving backwards in space time. but that really doesn't mean anything to me. what's wrong with putting a forward arrow on an...
  33. A

    How do antiparticles behave in the presence of gravity?

    Can someone tell how antiparticles affected by gravitational force? The same way as particles or opposite? Thanks.
  34. B

    Particles & Antiparticles: What is the Deal with Photons?

    I was recenlty watching a lecture by Feynman where is talks about particles, and how all particles have anti particles. A photon is a particle but I can't find any discussion about a anti photon. Reason?
  35. R

    Statistical mechanics of antiparticles

    I have some questions that my teacher was unable (and unwilling) to answer in class, so I thought I'd ask them here. The chemical potential \mu=\left(\frac{\partial U}{\partial N}\right)_{S,V} is given by the derivative of the energy with respect to particle number at constant volume and...
  36. B

    Uncertainity Principle , particles and antiparticles

    Is Uncertainity Principle is applied during particle antiparticle generation and is it a deterministic principle related to their positions and momentum in space ?
  37. F

    Heuristic explanation of why quantum mechanics plus SR imply antiparticles

    heuristic explanation of why quantum field theory imply antiparticles I'm looking for a heuristic explanation of why quantum mechanics plus special relativity requires antiparticles, Does anybody want to take a crack at it? Or am I asking for the impossible?
  38. F

    Can Antiparticles be Visualized in Particle Detectors?

    Can antiparticlees be seen or can they only be detected?
  39. K

    Would baryons and their antiparticles interact via the strong interaction?

    And would the potential be equal in magnitude yet opposite in sign? If you were to approximate a yukawa potential for some baryon and had it "near" its antiparticle, what would the potential look like. The same for a baryon and another baryon but opposite? This would just be like a...
  40. N

    Quark Structure of Particles & Antiparticles: Rules & Order

    I am asking this question because I did not get it clarified in any of the books I have read. What is the rule for having the quark structure of an antiparticle given the structure of the particle?Is it always OK to put bar on the quark symbols of the corresponding particle? Specifically,I...
  41. T

    Do antiparticles really go back in time?

    do antiparticles really go back in time?
  42. R

    Why Are Photons Emitted in Neutral Particle Annihilations?

    It is well known that photon is a quant of electromagnetic field. It is also well known that the electromagnetic field is produced by charged particles. Assume that some neutral particle annihilates with its antiparticle. Why a photon is emitted as a resuilt, not a quant of some other field?
  43. D

    Is the Charge of a Positron the Same as a Proton?

    I was reading that the antiparticle of a particle is the same, except it has an opposite charge, which cancels it out. if the charge of an electron is -1.60 x 10^-19, would that make the charge of the positron +1.60 x 10^-19? but isn't that also the charge of the proton? I must be missing...
  44. N

    Antiparticles: only distinct propery is C(Q)?

    [Q0]Is the only distinct difference between a particle and antiparticle the charge? Does it apply to Quarks Electron Proton Neutron(does it have a antiparticle?) Neutrinos. FCPs(do FCP have charge? well light doesn't but does a gluon...and what's the other one called not the graviton)...
  45. C

    Particles connected to Antiparticles

    Consider a particle-antiparticle creation, let's say an electron and a positron. I am curious if there is any lasting connection* between particles and the antiparticles that they were born with (in terms of the physics of their interaction). Has anyone ever predicted or observed such a...
  46. P

    Particles, Antiparticles, and Superpartners

    so electrons would have an antiparticle called a positron? and it's possible that the electron also has a superpartner called a selectron? if so would the positron also have a superpartner?
  47. G

    What Are Antiparticles and Their Role in the Universe?

    I've been reading a lot lately, stephen hawkings mostly, a few others as well, but its difficult. The more things i read on the same subjects the better i understand the fundamental ideas, but its still difficult. One thing i have trouble grasping is anti particles. I've never been introduced to...