The search for proton decay
Much rests on the existence of proton decay, and yet we've never seen a proton die. The reason may simply be that protons rarely decay, a hypothesis borne out by both experiment and theory. Protons on average will outlast every star, galaxy and planet, even the ones not yet born.Indeed, a proton is made up of 3 quarks (2 up and 1 down). However, while neutrons are also made up of 3 quarks in a different combination (1 up and 2 down) they also contain the mono-charge components of electrons, neutrinos and photons.
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. Therefore, protons will not decay into other particles on their own, because they are the lightest (and therefore least energetic) baryon.
Photons could conceivably decay, but new analysis of the cosmic microwave background shows that a visible wavelength photon is stable for at least 1018 years. For a photon to decay, it must have a mass—otherwise there'd be nothing lighter for it to decay into.
The proton is a baryon and is considered to be composed of two up quarks and one down quark. It has long been considered to be a stable particle, but recent developments of grand unification models have suggested that it might decay with a half-life of about 1032 years.
Protons are stable because the proton is the lightest baryon. All other baryons must decay into the proton [*]. Therefore only physics beyond the Standard Model (which as yet remains undiscovered) can cause the proton to decay. The most natural scale for that to be at is at the GUT scale or above.
A hadron is any particle that is made from quarks, anti-quarks and gluons. In particular, you will understand that a proton is made of two up quarks, a down quark, and a large number of gluons and of quark-antiquark pairs.
The idea that quarks can never be isolated is called confinement. Each type of quark has an antiquark, and quark-antiquark pairs can be created out of energy in particle collisions.
First, the
proton p is composed of the three quarks uud, so that its total charge is +(23)qe+(23)qe−(13)qe=qe + ( 2 3 ) q e + ( 2 3 ) q e − ( 1 3 ) q e = q e , as expected.
How Does it Work?
| Table 2. Quark Composition of Selected Hadrons |
|---|
| Particle | Quark Composition |
|---|
| π+ | u¯d |
| π− | ¯ud |
| π0 mixture | u¯u u u ¯ , d¯d d d ¯ mixture |
Pions (commonly shortened to a π) are a type of meson, which are subatomic particles made of a combination of quarks and antiquarks. Since antiquarks are antimatter, they will annihilate the same type (known as a flavour) of quark if they come near it.
The proton is a spin 1/2 particle (fermion), the pions are spin 0 particles (bosons). The orbital angular momentum quantum number can only be an integer, so there is no way that angular momentum can be conserved. The proposed decay cannot occur.
Longer answer: All mesons are unstable, with the longest lived mesons existing for a few hundredths of a microsecond. This means they don't have to obey as many conservation laws, like baryon conservation. This means that all mesons have a lower energy state to decay into via the electroweak interaction.
The pion is a meson. The π+ is considered to be made up of an up and an anti-down quark.
Baryons need 3 quarks to maintain color neutrality (1 red, 1 blue, 1 green) and with 6 types of quarks, that's 216 possible combinations, but the top quark doesn't form any baryons, so that leaves 75 possible Baryons - which is the number listed in the list of Baryons.
In particle physics, a hadron /ˈhædr?n/ ( listen) (Greek: ?δρός, hadrós; "stout, thick") is a subatomic composite particle made of two or more quarks held together by the strong force in a similar way as molecules are held together by the electromagnetic force.
Hadrons are particles that feel the strong nuclear force, whereas leptons are particles that do not. The proton, neutron, and the pions are examples of hadrons. Leptons feel the weak nuclear force. In fact, all particles feel the weak nuclear force.
A baryon is a composite subatomic particle.
The most stable baryons are protons and neutrons, so most building blocks of matter are baryons. Baryon comes from the Greek word βαρύς (barys) for heavy. At the time of their naming, most known elementary particles had lower masses than the baryons.Electrons and positrons are *not* made up of quarks. They are in a separate "family" of particles known as LEPTONS. Leptons and quarks are "fundamental" (indivisible) particles. Leptons do not experience the "strong" or "hadronic" force that protons and neutrons do.
So in answer to the question "What are electrons made up of?" is, electrons are made up of charge, mass, and angular momentum. To make an electron, reach out across the electric field (which is otherwise just sitting there) and introduce enough wiggle to create −1.602×10−19 coulombs of charge.
Baryons are hadrons that can decay into or are protons. Mesons are hadrons that do not decay into protons, such as: pions and kaons. Pions and kaons can be positive, neutral and negative. Baryons and mesons aren't fundamental particles and so can be split into smaller particles known as quarks.
There are six leptons, three of which have electrical charge and three of which do not. They appear to be point-like particles without internal structure. The best known lepton is the electron (e-). The other two charged leptons are the muon( ) and the tau( ), which are charged like electrons but have a lot more mass.
Mesons are intermediate mass particles which are made up of a quark-antiquark pair. Three quark combinations are called baryons. Mesons are bosons, while the baryons are fermions. There was a recent claim of observation of particles with five quarks (pentaquark), but further experimentation has not borne it out.
The kaon (also called the K0 meson), discovered in 1947, is produced in high-energy collisions between nuclei and other particles. It has zero electric charge, and its mass is about one-half the mass of the proton. It is unstable and, once formed, rapidly decays…
Quark
| A proton is composed of two up quarks, one down quark, and the gluons that mediate the forces "binding" them together. The color assignment of individual quarks is arbitrary, but all three colors must be present. |
|---|
| Composition | Elementary particle |
|---|
| Types | 6 (up, down, strange, charm, bottom, and top) |
A neutron (udd) decays to a proton (uud), an electron, and an antineutrino. This is called neutron beta decay. (The term beta ray was used for electrons in nuclear decays because they didn't know they were electrons!) Frame 1: The neutron (charge = 0) made of up, down, down quarks.
The sigma is a baryon which contains a strange quark. The only baryon with a strange quark which is less massive than the sigma is the neutral lambda baryon. The neutral sigma can decay to the lambda without violating conservation of strangeness, so it proceeds rapidly by the electromagnetic interaction.
Strange quarks can be found in particles such as kaons and some hyperons. Scientists began noticing strangeness when these particles did not decay as quickly as their masses would have suggested they would have.
Neutral pion decays
meson has a mass of 135.0 MeV/c2 and a mean lifetime of 8.4×10−17 s.
