What is Neutrino: Definition and 389 Discussions

A neutrino ( or ) (denoted by the Greek letter ν) is a fermion (an elementary particle with spin of 1/2) that interacts only via the weak interaction and gravity. The neutrino is so named because it is electrically neutral and because its rest mass is so small (-ino) that it was long thought to be zero. The rest mass of the neutrino is much smaller than that of the other known elementary particles excluding massless particles. The weak force has a very short range, the gravitational interaction is extremely weak, and neutrinos do not participate in the strong interaction. Thus, neutrinos typically pass through normal matter unimpeded and undetected.Weak interactions create neutrinos in one of three leptonic flavors: electron neutrinos (νe), muon neutrinos (νμ), or tau neutrinos (ντ), in association with the corresponding charged lepton. Although neutrinos were long believed to be massless, it is now known that there are three discrete neutrino masses with different tiny values, but they do not correspond uniquely to the three flavors. A neutrino created with a specific flavor has an associated specific quantum superposition of all three mass states. As a result, neutrinos oscillate between different flavors in flight. For example, an electron neutrino produced in a beta decay reaction may interact in a distant detector as a muon or tau neutrino. Although only differences between squares of the three mass values are known as of 2019, cosmological observations imply that the sum of the three masses (< 2.14 × 10−37 kg) must be less than one millionth that of the electron mass (9.11 × 10−31 kg).For each neutrino, there also exists a corresponding antiparticle, called an antineutrino, which also has spin of 1/2 and no electric charge. Antineutrinos are distinguished from the neutrinos by having opposite signs of lepton number and right-handed instead of left-handed chirality. To conserve total lepton number (in nuclear beta decay), electron neutrinos only appear together with positrons (anti-electrons) or electron-antineutrinos, whereas electron antineutrinos only appear with electrons or electron neutrinos.Neutrinos are created by various radioactive decays; the following list is not exhaustive, but includes some of those processes:

beta decay of atomic nuclei or hadrons,
natural nuclear reactions such as those that take place in the core of a star
artificial nuclear reactions in nuclear reactors, nuclear bombs, or particle accelerators
during a supernova
during the spin-down of a neutron star
when cosmic rays or accelerated particle beams strike atoms.The majority of neutrinos which are detected about the Earth are from nuclear reactions inside the Sun. At the surface of the Earth, the flux is about 65 billion (6.5×1010) solar neutrinos, per second per square centimeter. Neutrinos can be used for tomography of the interior of the earth.Research is intense in the hunt to elucidate the essential nature of neutrinos, with aspirations of finding:

the three neutrino mass values
the degree of CP violation in the leptonic sector (which may lead to leptogenesis)
evidence of physics which might break the Standard Model of particle physics, such as neutrinoless double beta decay, which would be evidence for violation of lepton number conservation.

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  1. marce

    I Neutrinos and theoretical necessity

    - One of the most fascinating particles for me , have always been neutrino's because of them balancing between mass and massless properties. So the question 'why was this needed' in the context of the weak force has led me to the question : as with attempts to explain 3 generations of particles...
  2. R

    A A liquid crystal of Potassium-42 Chloride for directional neutrino detection

    I've been speculating on a method of neutrino detection that uses beta decay instead of scintillation for the detection of neutrinos and was curious about its viability. Potassium-42 can be synthesized by colliding Calcium 40 with protons. It has a half-life of 12.36 hours and decays into...
  3. H

    I What is the Freeze-Out Temperature of WIMP Particles?

    I'm studying the freeze-out moment of different particles and I have few questions that I can't find answer about the Wimp particles. First of all, the freeze-out temperature of the wimp particles is around 0.4-40gev much higher than 1 mev for the neutrinos. Thus, that means that the freeze-out...
  4. Vanadium 50

    I How do the collider experiments measure the mass of the W boson?

    A few months ago, there was a discussion on the W mass. It unfortunately degeneratd with posters attacking the honesty of the researchers. A pity, because we never got into the issues involved in making a sub 100 ppm measurement. The first problem is that the decay is W to lepton + neutrino...
  5. pinball1970

    I What are the implications of neutrino detection at the LHC?

    Article below https://phys.org/news/2023-08-neutrinos-cern-large-hadron-collider.amp Publication here. https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.131.031801
  6. S

    B Neutrino physics -- What are the project goals for the Jiangman underground observatory (JUNO)?

    Jiangman underground observatory (JUNO) is a setup at china which is used for detection of neutrino and their oscillation so far as I know. What is the basic goal of making this setup, Are they interested to observe the effect of neutrino on earth i.e neutrino may rise the temp of earth or some...
  7. mfb

    I New IceCube results next Thursday (June 29)

    Join us to hear exciting IceCube results! It'll involve neutrinos, but beyond that I don't know what it is about. It will be something important or they wouldn't make a press conference. I don't expect a relation, but it's interesting that NANOGrav has some news the same day.
  8. James1238765

    I Evaluating the quark neutrino mixing matrix

    The mixing of the 3 generations of fermions are tabulated into the CKM matrix for quarks: $$ \begin{bmatrix} c_{12}c_{13} & s_{12}c_{13} & s_{13}e^{-i\sigma_{13}} \\ -s_{12}c_{23}-c_{12}s_{23}s_{13}e^{i\sigma_{12}} & c_{12}c_{23}-s_{12}s_{23}s_{13}e^{i\sigma_{13}} & s_{23}c_{13} \\...
  9. fresh_42

    I How Will FASERν Transform Our Understanding of Neutrinos at High Energies?

    https://journals.aps.org/prd/pdf/10.1103/PhysRevD.104.L091101 And here is the pop science summary: https://www.sciencealert.com/for-the-first-time-neutrinos-may-have-been-detected-at-the-large-hadron-collider Which results can be expected?
  10. H

    A What is the achievable accuracy of neutrino speed measurement?

    Is the accuracy of 10^-12 s achievable in measuring a neutrino's speed with current experiments? I have come across a number of papers stating the accuracy is in the order of nanoseconds. This is much lower accuracy than the measured speed of photons. I believe it is due to the difficulties in...
  11. G

    Photon and Neutrino detector and photon trawl device

    Summary:: Hello I am a writer and presently working on treatment for a science-fiction story. So I am not a scientist, just a neophyte interested in science and wanting to write a fiction that would not be too far-fetched and that would make some sense for everyone, including the scientific...
  12. R

    I A test for a superluminal neutrino?

    The neutrino has been puzzling since its proposal and its experimental confirmation. There have been experimental anomalies with it for every experiment designed to test it. One fact that might be quite key is that measurements of the mass-square of the neutrino has consistently shown it to...
  13. R

    I Can Oscillations Explain Neutrino Anomalies?

    The Solar neutrino deficit: The solar neutrino deficit is a problem where fewer neutrinos from the Suns internal nuclear processes are detected here on Earth than expected. The atmospheric neutrino deficit: A similar problem occurs with atmospheric neutrinos where fewer are detected coming...
  14. strangerep

    A Proof that neutrino flavor oscillation implies nonzero neutrino mass?

    [This is a reference request.] I'm dissatisfied with the "proofs" I've found so far. E.g., in Kayser's review from 2008, in the paragraph following his eq(1.4), he assumes a propagation amplitude Prop##(\nu_i)## of ##\exp(-im_i \tau_i)##, where "##m_i## is the mass of the ##\nu_i## and...
  15. mfb

    I New cosmological neutrino mass constraint: sum<0.09 eV at 95% CL

    arXiv: On the most constraining cosmological neutrino mass bounds From neutrino mixing we know that an inverted order (two "heavy" neutrinos, one light neutrino) needs a sum of masses of at least ~0.09 eV, while the normal order (two light, one "heavy") can have a sum as low as ~0.05 eV. The...
  16. peguerosdc

    In 2 consecutive decays, determine max and min energies for a particle

    Hi! Instead of just describing my procedure and all my derivations, I really just want to ask if my approach makes sense (actually I have 2 options) to calculate the maximum energy. I am considering c=1 and the problem suggests to consider the neutrino massless: For the first decay, ##Z...
  17. nomadreid

    I Probability of neutrino switching: more massive, more probable?

    In Scientific American, July 2020, the article "The Darkest Particle" by Louis and Van de Water, page 46, discussing the hypothetical sterile neutrino, there is the sentence: "Because sterile neutrinos are likely to be more massive than the regular flavors, however, particles could make the...
  18. 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...
  19. Arman777

    A N-body simulation with varying neutrino mass

    I am trying to find a picture of the N-body simulations that shows the LSS. Particularly I am looking for different neutrino masses without the CDM. For instance pictures likes this But with more varying/different neutrino masses. I am looking for articles
  20. Coltrane8

    I Neutrino Helicity and Spin Uncertainty

    In the context of non relativistic quantum mechanics, or better, if I consider the neutrino's mass to be zero, the phrase seems to me puzzling. What I know is that if I know the direction of motion, I know the spin projection onto that direction, say ##\hat{z}##-direction. But to not violate...
  21. A

    How do scientists use water Cerenkov detectors to detect neutrinos?

    Assuming that this sphere has a radius of 50kpc, I've converted to m (1.543e21) and plugged into the area equation for a total area of 2.992e43 m^2. From here I've talked myself into circles, and I honestly don't know where to go next. Any help or guidance would be greatly appreciated!
  22. mfb

    I T2K sees ~3 sigma evidence for neutrino CP violation

    Publication: Constraint on the matter–antimatter symmetry-violating phase in neutrino oscillations Edit: arXiv: Constraint on the Matter-Antimatter Symmetry-Violating Phase in Neutrino Oscillations Article: Neutrino Asymmetry Passes Critical Threshold Previous measurements already hinted at...
  23. Timboo

    B Tau neutrino flux in IceCube data

    What does this new find signify, i think we may be shortly due for something bad about to happen https://www.universetoday.com/144900/neutrinos-have-been-detected-with-such-high-energy-that-the-standard-model-cant-explain-them/https://arxiv.org/abs/2001.01737...
  24. Arman777

    I Calculating the Maximum total neutrino mass by using cosmological boun

    In an article its written, $$\Omega_{\nu} = \frac{\rho_{\nu}}{\rho_{crit}}=\frac{\sum m_{i,\nu}n_{i,\nu}}{\rho_{crit}} = \frac{\sum m_{\nu}}{93.14h^2eV}$$ Now I am trying to derive this for myself but I could not. Can someone help me ? So the values are, ##\rho_{crit} = 1.053 75 \times...
  25. Arman777

    Calculating the mass of the neutrino for a relativistic case

    I came across a question that states What mass would a neutrino need to still be relativistic today (T = 2.37K) ? So for a particle to be relativistic we need ##pc \gg mc^2## Well Neutrino was relativistic in the early universe, so I took the time when the neutrino decoupled which is...
  26. M

    A Parameters of neutrino interactions in targets?

    The interaction of neutrinos should be proportional to the amount of material that it goes through. If i want to calculate the number of interactions that i could expect when a neutrino beam go through different materials, the first thing that comes to mind is the nuclei of the targets, as the...
  27. Physics4Eva

    I Unraveling Neutrino Confusion: Ettore Majorana's Theory

    I was looking into neutrinos and found that a man named Ettore Majorana proposed neutrinos and antineutrinos are the same thing. If this could be true, antineutrinos emitted during double beta decay could annihilate one another and vanish. However, this would violate lepton number conservation...
  28. Michael Price

    A Measurements and electroweak gauge invariance/transformations

    Most gauge transformations in the standard model are easy to see are measurement invariant. Coordinate transformations, SU(3) quark colours, U(1) phase rotations for charged particles all result in no measurable changes. But how does this work for SU(2) rotations in electroweak theory, where...
  29. E

    A Future of the electron neutrino mass limits

    In five years also experiment KATRIN will give either the upper bound of electron neutrino mass (0,2 eV) or even the mass of the electron neutrino. https://www.katrin.kit.edu/ My question is, what we can expect from the astronomical and non-astronomical measurements to improve these data? I...
  30. lLehner95

    Longitudinal distribution for a neutrino beam

    In the center of mass frame of reference i found that ##p^{*}=\frac{[(M^{2}-m_{\nu}^{2}-m_{K}^{2})^{2}-4m_{\nu}^{2}m_{K}^{2})]^{1/2}}{2M}##. I don't know how to find the momentum distribution ##p_{L}(\theta)## considering that i have 2 different mesons with a specific number ratio...
  31. M

    Calculate the energy release of an atom

    First of, I have no idea what I'm supposed to do with the neutrinos and the photons. Can somebody explain how to handle these? The rest of what I tried is quite straight forward $$\begin{align*}\Delta E &= 4M_p - M_{He} - 2 M_e + E_{\text{Neutrino and Photons}}\\&= 4M_p - (2[M_p+M_n]-E_B) - 2...
  32. szcsongor

    Consequences of a fourth neutrino type

    Hi, I got this question on a recent astronomy course but can't really find the right answer (rough translation from Swedish): If there was a fourth neutrino type it would have affected Universe's development the following way: a. more photons and more He-4 generated b. less photons and less...
  33. bob012345

    Neutrino vs. Photon Momentum at Fixed Energy

    I'm interested in knowing the ratio of momentum for a neutrino vs. a photon when both have the same energy. Alternatively, my spaceship engine can release 1GW of either a photon beam or a neutrino beam. How much relative thrust will the neutrino beam give me for the same energy (and power) as...
  34. T

    A How Does the Majorana Neutrino Behave in Matter?

    For a Majorana neutrino in matter we have the equation $$(i\gamma^{\mu}\partial_{\mu}-A\gamma_{0})\nu_{L} = m\overline{\nu_{L}}.$$ A is to be considered constant. Squaring, in the ultra-relativistic limit one obtains the dispersion relation $$(E-A)^{2}-p^{2} \simeq mm^{\dagger}$$ i.e. $$p...
  35. 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...
  36. Radwan Parvez

    A Neutrino Electron Scattering In The Standard Model Approach

    Previously I posted a problem concerning Electron-neutrino scattering, but as I couldn't describe the problem clearly, so I am trying to post the problem using latex codes to present it in the correct way. For a couple of months, I am trying to calculate the invariant amplitude of the Neutrino...
  37. Radwan Parvez

    A Neutrino Electron Scattering In The Standard Model Approach

    For a couple of months, I am trying to calculate the invariant amplitude of the Neutrino electron scattering in the standard model (SM) approach where I am not considering any kind of approximation and using the SM propagator for W Boson and Z Boson. I tried to do as following, find out the...
  38. 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...
  39. S

    I Do black holes accumulate neutrinos?

    Do black holes accumulate neutrinos ? Do the neutrinos that fall in, decay in some way , maybe interact with the condensed matter, or just stay "parked" in perpetual loops ?
  40. 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...
  41. K

    I Sterile neutrino and the early universe?

    What are the effects considered by the presence of sterile neutrinos and the early universe, and the neutrino decoupling era?
  42. Simon Peach

    B Discussing Sterile Neutrino Candidacy as Dark Matter

    I would like to hear what the opinions are. Could sterile neutrino's be dark matter? I'm sure this has been discussed if not here then somewhere.
  43. J

    I Neutrino masses and oscillation

    <Moderator's note: Spin-off from another thread: https://www.physicsforums.com/threads/does-red-shift-approach-infinite-near-time-zero.948696/.> We do, however, have a lower limit, because of the solar neutrino experiment: too light and the neutrinos wouldn't have enough proper time to...
  44. K

    A How is the Neutrino Flux Measured in Accelerator Neutrino Experiments?

    How does the neutrio flux can be measured by a near detector of the accelerator neutrio experiments,such as T2K? As I know neutrino interactions with the matter in the near detector is too low,and so how they can count the neutrino flux by counting the produced particle from the interaction?
  45. ShayanJ

    A Problem with neutrino oscillations

    The phenomena of neutrino oscillations (as I understand it) is based on the idea that neutrino mass eigenstates are not the same as the flavor eigenstates and being in a definite mass eigenstate means the paticle has no definite flavor and vice versa. But this doesn't make sense to me, because...
  46. N

    I "Thermal" neutrino generation?

    Consider the Sun. It radiates energy by generating EM radiation. However, Sun is not transparent to EM, and therefore energy can only escape from the surface using this mechanism. Hot plasma below the surface generates and absorbs gazillions of photons, but they are "trapped" there. But EM is...
  47. K

    I Neutrino Mass: Exploring the Oscillation Phenomenon

    Why is there an assumption that if neutrinos didn't have mass they would move at the speed of light? and how does the fact they oscillate prove they have mass?
  48. ohwilleke

    I What false hints of new physics were most notable?

    Sometimes experimental or observational evidence from credible physicists points to new physics and then turns out to be wrong due to statistical flukes, experimental error or a theoretical analysis mistake. What cases of this happening do you find most notable, what showed that the hints were...
  49. A

    I Why Does π+ Decay to Muon and Muonic Neutrino?

    I am having a question in mind that why π+ decays to muon and muonic neutrino ,why no electron and electronic neutrino?
  50. ohwilleke

    I Can Majorana Neutrinos Oscillate Between Neutrino and Antineutrino States?

    Background The Standard Model conserves baryon number, which is equal to (quarks divided by three) minus (anti-quarks divided by three) and lepton number, which is equal to leptons minus antileptons, separately, except in sphaleron processes which conserve B-L, but not B or L separately. There...