In 2005, the NA48 / 2 collaboration at CERN published an evidence for pionium production and decay in decays of charged kaons, studying mass spectra of daughter pion pairs in the events with three pions in the final state: .< ref name = hep-ex / 0511056 >

However, pion production events drain 20 % of the energy of a cosmic ray proton as compared with only 0. 1 % of its energy for electron positron pair production.

The much larger total energy losses from pion production result in the pion production process becoming the limiting one to high energy cosmic ray travel, rather than the lower-energy light-lepton production process.

The pion production process continues until the cosmic ray energy falls below the pion production threshold.

* UHECR protons accelerated in astrophysical objects produce secondary electromagnetic cascades during propagation in the cosmic microwave and infrared backgrounds, of which the GZK-process of pion production is one of the contributors.

Measurements of the production cross section of pions on various nuclear targets showed that the pion has odd parity.

A direct measurement of the production of pions on a liquid hydrogen target, then not a common tool, provided the data needed to show that the pion has spin zero.

The experiment used a pion beam to produce pairs of hadrons with strange quarks in order to elucidate the puzzling production and decay properties of these particles .< ref >

Many new technologies are being pioneered for this experiment, including the use of liquid metal jets as a pion production target, under test in the MERIT experiment, the use of Fixed Field Alternating Gradient ( FFAG ) accelerators, under test in the EMMA experiment, and liquid hydrogen energy reduction cavities for reducing the divergence in the muon beam during the intermediate stages.

In 1949 he became a professor at Columbia University, the same year he received the Nobel Prize in Physics, after the discovery by Cecil Frank Powell, Giuseppe Occhialini and César Lattes of Yukawa's predicted pion in 1947.

In this case, the center of mass frame for the pion is just the frame where the pion is at rest, and the center of mass does not change after it disintegrates into two photons.

Its large solid angle coverage ( near hermetic ), vertex location with precision on the order of 10 μm ( provided by a silicon vertex detector ), good pion – kaon separation at multi-GeV momenta ( provided by a novel Cherenkov detector ), and few-percent precision electromagnetic calorimetry ( CsI ( Tl ) scintillating crystals ) allow a list of other scientific searches apart from CP violation in the B meson system.

: No-one doubted at the time that this particle was elementary, but a few years later, this hyperon, the proton, the neutron, the pion and other hadrons had lost their status of elementary particles as they turned out to be complex particles too consisting of quarks and antiquarks.

The pion was first proposed to exist by Yukawa in the 1930s as the primary force carrying boson of the Yukawa Potential in nuclear interactions, and was later observed at nearly the same mass that he originally predicted for it.

This interaction has a very different dependence on the energy of the pion — it vanishes at zero momentum.

Gell-Mann, along with Maurice Lévy, developed the sigma model of pions, which describes low energy pion interactions.

This factor of 200 is from two sources: the pion has only about ~ 130 times the mass of the leptons, but the extra energy appears as different kinetic energies of the pion or leptons, and results in relatively more kinetic energy transferred to a heavier product pion, in order to conserve momentum.

After the two photons are formed, their center of mass is still moving the same way the pion did, and their total energy in this frame adds up to the mass energy of the pion.

The expansion parameter is the pion energy / momentum.

Adler's seminal papers on high energy neutrino processes, current algebras, soft pion theorems,

It is in particle units nearly kT = 160 MeV, about 15 % above the energy mass of the lightest hadron, the pion.

Experimentally, it is observed that the masses of the octet of pseudoscalar mesons ( such as the pion ) are much lighter than the next heavier states, i. e., the octet of vector mesons ( such as the rho meson ).

Other important experiments studied the angular correlation between electron-positron pairs in neutral pion decays, and established the rare decay of a charged pion to an electron and neutrino ; the latter required use of a liquid-hydrogen bubble chamber.

An example of a virtual pion pair that influences the propagation of a kaon, causing a neutral kaon to mix with the antikaon.

The particle called a muon is a lepton which is produced in the upper atmosphere by the decay of a pion.

Hideki Yukawa showed in the 1930s that such a potential arises from the exchange of a massive scalar field such as the field of the pion whose mass is.

The spinpolarizabilities and are dominated by destructively interfering components from the pion cloud

They studied the decay of an " atom " made from a deuterium nucleus ( d ) and a negatively charged pion ( π < sup >–</ sup >) in a state with zero orbital angular momentum L = 0 into two neutrons ( n ).

A deuteron nucleus is made from a proton and a neutron, and so using the forementioned convention that protons and neutrons have intrinsic parities equal to + 1 they argued that the parity of the pion is equal to minus the product of the parities of the two neutrons divided by that of the proton and neutron in deuterium, (− 1 )( 1 )< sup > 2 </ sup >/( 1 )< sup > 2 </ sup >, which is equal to minus one.

In particle physics, proton decay is a hypothetical form of radioactive decay in which the proton decays into lighter subatomic particles, such as a neutral pion and a positron.

In theoretical physics, quantum chromodynamics ( QCD ) is a theory of the strong interaction ( color force ), a fundamental force describing the interactions between quarks and gluons which make up hadrons ( such as the proton, neutron or pion ).

For example, a neutral pion ( which decays electromagnetically ) has a life of about 10 < sup >− 16 </ sup > seconds, while a charged pion ( which decays through the weak interaction ) lives about 10 < sup >− 8 </ sup > seconds, a hundred million times longer.

This work led in 1946 to the discovery of the pion ( pi-meson ), which proved to be the hypothetical particle proposed in 1935 by Yukawa Hideki in his theory of nuclear physics.

In 1949 he published a calculation of the lifetime of the neutral pion, which anticipated the study of anomalies in quantum field theory.

: The discovery of this new unstable antiparticle which decays in ( 1. 18 ± 0. 07 )· 10 < sup >− 10 </ sup > s into an antineutron and a negative pion was announced in September of that year:

The idea was that the nucleon with its pion cloud obtains an electric dipole moment under the action of an electric field vector which is proportional to the electric polarizability.

( The winner that year was Cecil Frank Powell of England who discovered the pi-meson or pion, which had been predicted a dozen years earlier.

Other gluons, which bind together the proton, neutron, and pion " in-flight ," are not shown.

A neutral pion which decays inside the EM calorimeter can replicate this effect.

Examples for bosons are the neutral pion, the photon, and the Z boson which are identical to their antiparticles.

In Skyrme's model, reproduced in the large N or string approximation to quantum chromodynamics ( QCD ), the proton and neutron are fermionic topological solitons of the pion field.

A related experiment measured the mass difference between the charged and neutral pions based on the angular correlation between the neutral pions produced when the negative pion is captured by the proton in the hydrogen nucleus.

One hypothetical example is proton decay where a proton ( B = 1 ; L = 0 ) would decay into a pion ( B = 0, L = 0 ) and positron ( B = 0 ; L = − 1 ).

A Feynman diagram of a strong proton – neutron interaction mediated by a neutral pion.

Its momentum range is up to 3 GeV for pion / kaon discrimination and up to 5 GeV for kaon / proton discrimination.