What is Proton decay: Definition and 40 Discussions

In particle physics, proton decay is a hypothetical form of particle decay in which the proton decays into lighter subatomic particles, such as a neutral pion and a positron. The proton decay hypothesis was first formulated by Andrei Sakharov in 1967. Despite significant experimental effort, proton decay has never been observed. If it does decay via a positron, the proton's half-life is constrained to be at least 1.67×1034 years.According to the Standard Model, the proton, a type of baryon, is stable because baryon number (quark number) is conserved (under normal circumstances; see chiral anomaly for exception). Therefore, protons will not decay into other particles on their own, because they are the lightest (and therefore least energetic) baryon. Positron emission – a form of radioactive decay which sees a proton become a neutron – is not proton decay, since the proton interacts with other particles within the atom.
Some beyond-the-Standard Model grand unified theories (GUTs) explicitly break the baryon number symmetry, allowing protons to decay via the Higgs particle, magnetic monopoles, or new X bosons with a half-life of 1031 to 1036 years. For comparison, the universe is roughly 1010 years old. To date, all attempts to observe new phenomena predicted by GUTs (like proton decay or the existence of magnetic monopoles) have failed.
Quantum tunnelling may be one of the mechanisms of proton decay.Quantum gravity (via virtual black holes and Hawking radiation) may also provide a venue of proton decay at magnitudes or lifetimes well beyond the GUT scale decay range above, as well as extra dimensions in supersymmetry.There are theoretical methods of baryon violation other than proton decay including interactions with changes of baryon and/or lepton number other than 1 (as required in proton decay). These included B and/or L violations of 2, 3, or other numbers, or B − L violation. Such examples include neutron oscillations and the electroweak sphaleron anomaly at high energies and temperatures that can result between the collision of protons into antileptons or vice versa (a key factor in leptogenesis and non-GUT baryogenesis).

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  1. S

    I Can proton/neutron decay be avoided in some conditions?

    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...
  2. S

    I Observing Proton Decay & Antineutrinos

    antineutrino? I was looking at this article, which says that a proton that interacts with an antineutrion transforms (or whatever the proper verb is here) into a neutron & positron. But this begs the question that if we're trying to observe a proton decaying, how would we know that it had not...
  3. G

    I Proton decay at the end of the Universe

    I wish this forum allowed indentation using tabs. Some of these questions are dependent on the answers to others. I have used outline numbers to indicate nested questions. I have BA in physics and mathematics, 40+ years ago. I was thinking (always a dangerous thing). I had some questions. I...
  4. K

    I Exploring the Quark Stars: Hexaquarks and Proton Decay

    Question: Is it believed a "quark star" exists within all neutron stars, or just heavier neutron stars. Do protons actually decay under this pressure (quark soup)? Are Hexaquark bosons able to remain stable beyond the limit of a proton, or would they decay at the same time of a regular...
  5. S

    B Can Protons Decay at High Speeds without Colliding?

    Would a proton decay into smaller particles if you accelerate it into higher speeds without colliding it into another proton?
  6. ohwilleke

    I Proton Decay At The Highest Possible Energies

    Proton decay has not been observed and has been constrained to be extremely rare in ordinary low temperature situations, if it happens at all (the Standard Model says it doesn't happen at all, because there are no lighter decay products that would not violate conservation of baryon number)...
  7. A

    B What is the equation for proton emission after muon capture in heavy nuclei?

    Can anyone tell me what is proton emission equation after muon capture for heavy nuclei?is it same with neutron emission equation??
  8. S

    I The ever-increasing proton lifetime

    I was reading this article discussing how experiments have been able to observe proton decay: https://www.economist.com/news/science-and-technology/21734379-no-guts-no-glory-fundamental-physics-frustrating-physicists It states that after concluding that there has been any evidence of proton...
  9. Ranku

    I Grand Unified Theory and proton decay

    How far ahead are we in Grand Unified Theory? Are we still searching for proton decay?
  10. K

    I New scientist SU(5) Unification without Proton Decay

    new scientist latest issue covers this paper SU(5) Unification without Proton Decay Bartosz Fornal, Benjamin Grinstein (Submitted on 26 Jun 2017 (v1), last revised 13 Nov 2017 (this version, v2)) We construct a four-dimensional SU(5) grand unified theory in which the proton is stable. The...
  11. K

    I Deep Underground Neutrino Experiment proton decay

    is there a reason that Deep Underground Neutrino Experiment which uses 70, 000 tons of liquid Argon doesn't also do double duty work as a proton decay experiment? Argon has plenty of protons and 70, 0000 tons is a lot of material to work with it costs several billion dollars so why not use...
  12. J

    I Is proton decay considered in neutron star models (and LHC)?

    Although it is definitely not simple, there are many reasons to consider that baryon number can be violated, for example: - while baryogenesis there was created more matter than antimatter, - hypothetical Hawking radiation can finally turn any matter (mainly baryons) into massless radiation...
  13. K

    I Implications of no proton decay, simplest GUT ruled out

    Search for Proton Decay via p→e+π0 and p→μ+π0 in 0.31 megaton⋅years exposure of the Super-Kamiokande Water Cherenkov Detector M. Miura (The Super-Kamiokande Collaboration) (Submitted on 12 Oct 2016) We have searched for proton decay via p→e+π0 and p→μ+π0 using Super-Kamiokande data from April...
  14. Anchovy

    A Why lower limits on proton decay lifetimes depend on channel

    If I look at the lower limits on the proton decay lifetime \tau set by, say, Super-Kamiokande, I'll see different lower limits depending on what the proton could decay into, eg. \tau_{min}(p \rightarrow K^{+} \overline{\nu}) < \tau_{min}(p \rightarrow \mu^{+} \pi^{0}) < \tau_{min}(p \rightarrow...
  15. C

    B Proton decay probability (Bayesian or frequentist?)

    If an event has probability occurring say 1/100000000000000000000000000000000 times.. if you do the experiment 100000000000000000000000000000000 times.. you are supposed to get the hit at least once? This is the proton decay experiment.. it's more than the above probability figure.. but if you...
  16. ohad

    A Are there BSM which do not predict proton decay?

    Hi, To my knowledge about BSM (which is not much), all of them require or predict proton decay. Do you know of some of them which do not? Thanks, Ohad
  17. C

    A Proton Decay: The Mystery of Ergodicity

    Why does everyone assume that particles decay is an ergodic random process? After all T is not a symmetry of the Standard Model and I don't see any reason why ensamble averages should be equal to time averages.
  18. C

    The Mystery of Proton Decay: Unveiling the Role of the Higgs Field

    What is so special about the Higgs field that causes protons to decay?
  19. Anchovy

    Calculating proton decay lifetime correctly?

    I'm trying to calculate the SU(5) model's prediction for the lower limit of a proton decay lifetime, for the channel p \rightarrow \pi^{0} e^{+}. I'm following this paper: arXiv:hep-ph/0504276v1 It contains the following equation: As far as I can tell this actually contains a prediction...
  20. Anchovy

    Confused by these proton decay diagrams

    I have some confusion over some diagrams involved in proton decays in SU(5). I've seen a few like this that look weird to me. Here is one I found where the colored Higgs triplet does the job: Straight away I don't know what to make of this because I've only ever seen diagrams where fermions are...
  21. Anchovy

    Proton decay lifetime prediction SU(5)?

    I'm trying to understand how the SU(5) prediction for the proton decay lifetime of \tau_{p} \sim10^{31} yr has been arrived at. I keep seeing it stated that \tau_{p} \sim \frac{4\pi}{g_{5}^{2}} \frac{M_{X}^{4}}{M_{p}^{5}} where g_{5} is the SU(5) coupling and M_{X,p} are the X boson and proton...
  22. Anchovy

    Prerequisites for learning MSSM --> proton decay prediction?

    Hi all, I'm attempting to write something on proton decay (specifically in the p \rightarrow K^{+} \nu channel) and need to understand some theory that predicts it. I'm under the impression that the MSSM is the most straightforward theory. However, I look through introductory texts/documents...
  23. G

    Proton to neutron conversion at relativistic energies

    The reaction p→n+e++νe is common inside nucleus. But it not considered when we talk about free particle and reason is simply given mass of products being larger than reactants. Now my question is if there is a high energy proton having total energy in order of 2 GeV or let it to be 100 GeV (To...
  24. majid313mirzae

    Alpha & Proton Decay: Explaining Unequal Rates

    All nuclei with A > 210 are alpha emitters, yet very few emit protons spontaneously. Yet both decays lower the Coulomb energy of the nucleus. Why is proton decay not more common?
  25. C

    Proton Decay- What happens to the proton after too many decays ?

    Proton Decay- What happens to the proton after "too many decays"? Let me start off by saying that I am not the brightest individual, but I am curious about things from time to time (hence my name and hence why I'm here). So please excuse my stupidity if it shows too much. Anyway, recently, I...
  26. R

    Proton Decay and Our Health: Exploring the Effects of One Proton Decay per Year

    We're made of roughly 10^28 protons. Let's imagine that the average lifespan of a proton were 10^28 years even though it is much higher. That would mean one proton per year would decay in our body. How much harm would one proton decay cause us?
  27. N

    2 Q's about statements in Griffiths' book (regarding proton decay)

    Hello, I'm taking a particle physics class and we're using Griffiths' book "Introduction to Elementary Particles". I was reading in it but two statements in it (on the same page, for reference p33 in the second edition) struck me as weird, and as I would greatly appreciate if anyone could...
  28. D

    All matter being liquid in 10^65 years if proton decay doesn't occur.

    http://en.wikipedia.org/wiki/Timeline_of_the_far_future
  29. V

    Exploring Proton Decay: Visualizing Advanced Concepts

    Hello there, I was just reading some articles on Wikipedia.org and found an article on proton decay. I will quote a part of it: How would that be visualized? I've got a basic understanding of particle physics, but these concepts seem rather advanced, yet, I insist on wanting to understand...
  30. M

    Exploring Proton Decay and HyperKamiokande Experiments

    I am not quite sure wheather this is the appropriate section. (since the question is about an experiment). I wondered about the following -when the Kamiokande-colaboration is going to release new results on proton decay bounds- since their last new bounds where in 2009 (Judging from their...
  31. D

    Is the fate of black dwarfs to become neutron stars without proton decay?

    Will black dwarfs eventually quantum tunnel into neutron stars if proton decay doesn't occur?
  32. A

    Question about proton decay and black hole evaporation

    Just to start, let me reassure you that I am not an LHC alarmist. I understand and agree with the cosmic ray explanation, i.e. earth, the sun, jupiter, and everything else would be a BH if they didn't evaporate. Anyway, I was reading around a little on wikipedia and came to this page...
  33. E

    Has proton decay falsified SO(10) GUT?

    I know that proton decay has falsified SU(5) based around 10e30 years. What proton decay of SO(10)? Are SUSY SU(5) and SUSY SO(10) still viable? If the experiment continues with a null result, what models are next in line to be falsified? Could protons last forever and thus falsfy...
  34. W

    Calculating Proton Decay in a Swimming Pool

    Homework Statement Grand unification theories predict that the proton has a long but finite lifetime. Current experiments based on detecting the decay of protons in water infer that this lifetime is at least 10^32 years. Assume 10^32 years is, in fact, the mean lifetime of the proton...
  35. R

    Future of the universe without proton decay.

    How will the future of the universe be if proton decay does not occur? Does it mean that the degenerate era will last longer?
  36. I

    Proton decay [was: Are atoms 'perpetual machines'?]

    don't all atoms decay? don't even protons decay?
  37. Astronuc

    Zinc-54 undergoes rare 2 proton decay

    From the Alchemist Newsletter (Chemweb.com) An international team of researchers has produced a new isotope of zinc, zinc-54, which they say undergoes the rare process of two-proton decay. The research carried out by Bertram Blank of the CENBG laboratory in France and colleagues could shed...
  38. V

    Can Neutrinos Decay? Examining Proton Decay Theories

    some theorist predicts proton can decay, since the decay of proton does not violate any fundemantal conservation law. My question is, could neutrino decay? How come I have never heard of anyone say neutrino could decay?
  39. Z

    What is the mechanism for proton decay in the Standard Model?

    I recently saw posts indicating that the SM does not have baryon and lepton number as exact symmetries, and in fact allows protons to decay, but with much smaller probabilities than GUT's. What is the mechanism by which such decays can occur (is it non-perturbative?), and what order of magnitude...
  40. G

    Exploring Proton Decay: Theories, Experiments, and Expectations

    Hi, can someone remind me why should we expect a proton to decay? The last I heard, people put detectors around stored protons and expected some of them to undergo spontaneous decay, but nothing was ever detected, suggesting that the half-life of protons was longer than measurable time scales...
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