Pion

In particle physics, a pion (or a pi meson, denoted with the Greek letter pi:
π
) is any of three subatomic particles:
π0
,
π+
, and
π
. Each pion consists of a quark and an antiquark and is therefore a meson. Pions are the lightest mesons and, more generally, the lightest hadrons. They are unstable, with the charged pions
π+
and
π
decaying with a mean lifetime of 26.033 nanoseconds (2.6033×10−8 seconds), and the neutral pion
π0
decaying with a much shorter lifetime of 84 attoseconds (8.4×10−17 seconds). Charged pions most often decay into muons and muon neutrinos, while neutral pions generally decay into gamma rays.

The exchange of virtual pions, along with vector, rho and omega mesons, provides an explanation for the residual strong force between nucleons. Pions are not produced in radioactive decay, but commonly are in high energy collisions between hadrons. Pions also result from some matter-antimatter annihilation events. All types of pions are also produced in natural processes when high energy cosmic ray protons and other hadronic cosmic ray components interact with matter in Earth's atmosphere. In 2013, the detection of characteristic gamma rays originating from the decay of neutral pions in two supernova remnants has shown that pions are produced copiously after supernovas, most probably in conjunction with production of high energy protons that are detected on Earth as cosmic rays.[1]

The concept of mesons as the carrier particles of the nuclear force was first proposed in 1935 by Hideki Yukawa. While the muon was first proposed to be this particle after its discovery in 1936, later work found that it did not participate in the strong nuclear interaction. The pions, which turned out to be examples of Yukawa's proposed mesons, were discovered later: the charged pions in 1947, and the neutral pion in 1950.

Pion
Quark structure pion
The quark structure of the pion.
Composition
π+
:
u

d


π0
:
u

u
or
d

d


π
:
d

u
StatisticsBosonic
InteractionsStrong, Weak, Electromagnetic and Gravity
Symbol
π+
,
π0
, and
π
TheorizedHideki Yukawa (1935)
DiscoveredCésar Lattes, Giuseppe Occhialini (1947) and Cecil Powell
Types3
Mass
π±
: 139.57018(35) MeV/c2

π0
: 134.9766(6) MeV/c2
Electric charge
π+
: +1 e

π0
: 0 e

π
: −1 e
Spin0
Parity−1

History

Nuclear Force anim smaller
An animation of the nuclear force (or residual strong force) interaction. The small colored double disks are gluons. Anticolors are shown as per this diagram (larger version).
Pn Scatter Quarks
The same process as in the animation with the individual quark constituents shown, to illustrate how the fundamental strong interaction gives rise to the nuclear force. Straight lines are quarks, while multi-colored loops are gluons (the carriers of the fundamental force). Other gluons, which bind together the proton, neutron, and pion "in-flight," are not shown.

Theoretical work by Hideki Yukawa in 1935 had predicted the existence of mesons as the carrier particles of the strong nuclear force. From the range of the strong nuclear force (inferred from the radius of the atomic nucleus), Yukawa predicted the existence of a particle having a mass of about 100 MeV. Initially after its discovery in 1936, the muon (initially called the "mu meson") was thought to be this particle, since it has a mass of 106 MeV. However, later experiments showed that the muon did not participate in the strong nuclear interaction. In modern terminology, this makes the muon a lepton, and not a meson. However, some communities of astrophysicists continue to call the muon a "mu-meson".

In 1947, the first true mesons, the charged pions, were found by the collaboration of Cecil Powell, César Lattes, Giuseppe Occhialini, et al., at the University of Bristol, in England. Since the advent of particle accelerators had not yet come, high-energy subatomic particles were only obtainable from atmospheric cosmic rays. Photographic emulsions based on the gelatin-silver process were placed for long periods of time in sites located at high altitude mountains, first at Pic du Midi de Bigorre in the Pyrenees, and later at Chacaltaya in the Andes Mountains, where the plates were struck by cosmic rays.

After the development of the photographic plates, microscopic inspection of the emulsions revealed the tracks of charged subatomic particles. Pions were first identified by their unusual "double meson" tracks, which were left by their decay into a putative meson. The particle was identified as a muon, which is not typically classified as a meson in modern particle physics. In 1948, Lattes, Eugene Gardner, and their team first artificially produced pions at the University of California's cyclotron in Berkeley, California, by bombarding carbon atoms with high-speed alpha particles. Further advanced theoretical work was carried out by Riazuddin, who in 1959, used the dispersion relation for Compton scattering of virtual photons on pions to analyze their charge radius.[2]

Nobel Prizes in Physics were awarded to Yukawa in 1949 for his theoretical prediction of the existence of mesons, and to Cecil Powell in 1950 for developing and applying the technique of particle detection using photographic emulsions.

Since the neutral pion is not electrically charged, it is more difficult to detect and observe than the charged pions are. Neutral pions do not leave tracks in photographic emulsions or Wilson cloud chambers. The existence of the neutral pion was inferred from observing its decay products from cosmic rays, a so-called "soft component" of slow electrons with photons. The
π0
was identified definitively at the University of California's cyclotron in 1950 by observing its decay into two photons.[3] Later in the same year, they were also observed in cosmic-ray balloon experiments at Bristol University.

The pion also plays a crucial role in cosmology, by imposing an upper limit on the energies of cosmic rays surviving collisions with the cosmic microwave background, through the Greisen–Zatsepin–Kuzmin limit.

In the standard understanding of the strong force interaction as defined by quantum chromodynamics, pions are loosely portrayed as Goldstone bosons of spontaneously broken chiral symmetry. That explains why the masses of the three kinds of pions are considerably less than that of the other mesons, such as the scalar or vector mesons. If their current quarks were massless particles, it could make the chiral symmetry exact and thus the Goldstone theorem would dictate that all pions have a zero mass. Empirically, since the light quarks actually have minuscule nonzero masses, the pions also have nonzero rest masses. However, those weights are almost an order of magnitude smaller than that of the nucleons, roughly[4] mπv mq / fπmq 45 MeV, where m are the relevant current quark masses in MeV, 5−10 MeVs.

The use of pions in medical radiation therapy, such as for cancer, was explored at a number of research institutions, including the Los Alamos National Laboratory's Meson Physics Facility, which treated 228 patients between 1974 and 1981 in New Mexico,[5] and the TRIUMF laboratory in Vancouver, British Columbia.

Theoretical overview

The pion can be thought of as one of the particles that mediate the interaction between a pair of nucleons. This interaction is attractive: it pulls the nucleons together. Written in a non-relativistic form, it is called the Yukawa potential. The pion, being spinless, has kinematics described by the Klein–Gordon equation. In the terms of quantum field theory, the effective field theory Lagrangian describing the pion-nucleon interaction is called the Yukawa interaction.

The nearly identical masses of
π±
and
π0
imply that there must be a symmetry at play; this symmetry is called the SU(2) flavour symmetry or isospin. The reason that there are three pions,
π+
,
π
and
π0
, is that these are understood to belong to the triplet representation or the adjoint representation 3 of SU(2). By contrast, the up and down quarks transform according to the fundamental representation 2 of SU(2), whereas the anti-quarks transform according to the conjugate representation 2*.

With the addition of the strange quark, one can say that the pions participate in an SU(3) flavour symmetry, belonging to the adjoint representation 8 of SU(3). The other members of this octet are the four kaons and the eta meson.

Pions are pseudoscalars under a parity transformation. Pion currents thus couple to the axial vector current and pions participate in the chiral anomaly.

Basic properties

Pions, which are mesons with zero spin, are composed of first-generation quarks. In the quark model, an up quark and an anti-down quark make up a
π+
, whereas a down quark and an anti-up quark make up the
π
, and these are the antiparticles of one another. The neutral pion
π0
is a combination of an up quark with an anti-up quark or a down quark with an anti-down quark. The two combinations have identical quantum numbers, and hence they are only found in superpositions. The lowest-energy superposition of these is the
π0
, which is its own antiparticle. Together, the pions form a triplet of isospin. Each pion has isospin (I = 1) and third-component isospin equal to its charge (Iz = +1, 0 or −1).

Charged pion decays

PiPlus muon decay
Feynman diagram of the dominant leptonic pion decay.

The
π±
mesons have a mass of 139.6 MeV/c2 and a mean lifetime of 2.6033×10−8 s. They decay due to the weak interaction. The primary decay mode of a pion, with a branching fraction of 0.999877, is a leptonic decay into a muon and a muon neutrino:


π+

μ+
+
ν
μ

π

μ
+
ν
μ

The second most common decay mode of a pion, with a branching fraction of 0.000123, is also a leptonic decay into an electron and the corresponding electron antineutrino. This "electronic mode" was discovered at CERN in 1958:[6]


π+

e+
+
ν
e

π

e
+
ν
e

The suppression of the electronic decay mode with respect to the muonic one is given approximately (up to a few percent effect of the radiative corrections) by the ratio of the half-widths of the pion–electron and the pion–muon decay reactions:

and is a spin effect known as helicity suppression. Its mechanism is as follows: The negative pion has spin zero, therefore the lepton and antineutrino must be emitted with opposite spins (and opposite linear momenta) to preserve net zero spin (and conserve linear momentum). However, because the weak interaction is sensitive only to the left chirality component of fields, the antineutrino has always chirality left, which means it is right-handed, since for massless anti-particles the helicity is opposite to the chirality. This implies that the lepton must be emitted with spin in the direction of its linear momentum (i.e., also right-handed). If, however, leptons were massless, they would only interact with the pion in the left-handed form (because for massless particles helicity is the same as chirality) and this decay mode would be prohibited. Therefore, suppression of the electron decay channel comes from the fact that the electron's mass is much smaller than the muon's. The electron is thus relatively massless compared with the muon, and thus the electronic mode is almost prohibited.[7] Although this explanation suggests that parity violation is causing the helicity suppression, it should be emphasized that the fundamental reason lies in the vector-nature of the interaction which demands a different handedness for the neutrino and the charged lepton. Thus, even a parity conserving interaction would yield the same suppression.

Measurements of the above ratio have been considered for decades to be a test of lepton universality. Experimentally, this ratio is 1.230(4)×10−4.[8]

Besides the purely leptonic decays of pions, some structure-dependent radiative leptonic decays (that is, decay to the usual leptons plus a gamma ray) have also been observed.

Also observed, for charged pions only, is the very rare "pion beta decay" (with branching fraction of about 10−8) into a neutral pion, an electron and an electron antineutrino (or for positive pions, a neutral pion, a positron, and electron neutrino).


π

π0
+
e
+
ν
e

π+

π0
+
e+
+
ν
e

The rate at which pions decay is a prominent quantity in many sub-fields of particle physics, such as chiral perturbation theory. This rate is parametrized by the pion decay constant (ƒπ), related to the wave function overlap of the quark and antiquark, which is about 130 MeV.[9]

Neutral pion decays

The
π0
meson has a mass of 135.0 MeV/c2 and a mean lifetime of 8.4×10−17 s.[10] It decays via the electromagnetic force, which explains why its mean lifetime is much smaller than that of the charged pion (which can only decay via the weak force).

Anomalous-pion-decay
Anomaly-induced neutral pion decay.

The dominant π0 decay mode, with a branching ratio of BR=0.98823, is into two photons:


π0
2
γ
.

The decay π0 → 3γ (as well as decays into any odd number of photons) is forbidden by the C-symmetry of the electromagnetic interaction. The intrinsic C-parity of the π0 is +1, while the C-parity of a system of n photons is (−1)n.

The second largest π0 decay mode (BR=0.01174) is the Dalitz decay (named after Richard Dalitz), which is a two-photon decay with an internal photon conversion resulting a photon and an electron-positron pair in the final state:


π0

γ
+
e
+
e+
.

The third largest established decay mode (BR=3.34×10−5) is the double Dalitz decay, with both photons undergoing internal conversion which leads to further suppression of the rate:


π0

e
+
e+
+
e
+
e+
.

The fourth largest established decay mode is the loop-induced and therefore suppressed (and additionally helicity-suppressed) leptonic decay mode (BR=6.46×10−8):


π0

e
+
e+
.

The neutral pion has also been observed to decay into positronium with a branching fraction of the order of 10−9. No other decay modes have been established experimentally. The branching fractions above are the PDG central values, and their uncertainties are not quoted.

Pions
Particle name Particle
symbol
Antiparticle
symbol
Quark
content[11]
Rest mass (MeV/c2) IG JPC S C B' Mean lifetime (s) Commonly decays to

(>5% of decays)

Pion[8]
π+

π

u

d
139.570 18 ± 0.000 35 1 0 0 0 0 2.6033 ± 0.0005 × 10−8
μ+
+
ν
μ
Pion[10]
π0
Self [a] 134.976 6 ± 0.000 6 1 0−+ 0 0 0 8.4 ± 0.6 × 10−17
γ
+
γ

[a] ^ Make-up inexact due to non-zero quark masses.[12]

See also

References

  1. ^ M. Ackermann; et al. (2013). "Detection of the Characteristic Pion-Decay Signature in Supernova Remnants". Science. 339 (6424): 807–811. arXiv:1302.3307. Bibcode:2013Sci...339..807A. doi:10.1126/science.1231160. PMID 23413352.
  2. ^ Riazuddin (1959). "Charge Radius of Pion". Physical Review. 114 (4): 1184–1186. Bibcode:1959PhRv..114.1184R. doi:10.1103/PhysRev.114.1184.
  3. ^ R. Bjorklund; W. E. Crandall; B. J. Moyer; H. F. York (1950). "High Energy Photons from Proton-Nucleon Collisions". Physical Review. 77 (2): 213–218. Bibcode:1950PhRv...77..213B. doi:10.1103/PhysRev.77.213.
  4. ^ Gell-Mann, M.; Renner, B. (1968). "Behavior of Current Divergences under SU3×SU3". Physical Review. 175 (5): 2195–2199. Bibcode:1968PhRv..175.2195G. doi:10.1103/PhysRev.175.2195.
  5. ^ von Essen, C. F.; Bagshaw, M. A.; Bush, S. E.; Smith, A. R.; Kligerman, M. M. (1987). "Long-term results of pion therapy at Los Alamos". International Journal of Radiation Oncology*Biology*Physics. 13 (9): 1389–98. doi:10.1016/0360-3016(87)90235-5. PMID 3114189.
  6. ^ Fazzini, T.; Fidecaro, G.; Merrison, A.; Paul, H.; Tollestrup, A. (1958). "Electron Decay of the Pion". Physical Review Letters. 1 (7): 247–249. Bibcode:1958PhRvL...1..247F. doi:10.1103/PhysRevLett.1.247.
  7. ^ Mesons at Hyperphysics
  8. ^ a b C. Amsler et al.. (2008): Particle listings –
    π±
  9. ^ Leptonic decays of charged pseudo- scalar mesons J. L. Rosner and S. Stone. Particle Data Group. December 18, 2013
  10. ^ a b C. Amsler et al.. (2008): Particle listings –
    π0
  11. ^ C. Amsler et al.. (2008): Quark Model
  12. ^ D. J. Griffiths (1987). Introduction to Elementary Particles. John Wiley & Sons. ISBN 0-471-60386-4.

Further reading

  • Gerald Edward Brown and A. D. Jackson, The Nucleon-Nucleon Interaction (1976), North-Holland Publishing, Amsterdam ISBN 0-7204-0335-9

External links

  • Mesons at the Particle Data Group
2S7 Pion

The 2S7 Pion ("peony") or Malka is a Soviet self-propelled cannon. "2S7" is its GRAU designation.

It was identified for the first time in 1975 in the Soviet Army and so was called M-1975 by NATO (the 2S4 Tyulpan also received the M-1975 designation), whereas its official designation is SO-203 (2S7). Its design is based on a T-80 chassis carrying an externally mounted 2A44 203 mm gun on the hull rear.

Algebraic notation (chess)

Algebraic notation (or AN) is a method for recording and describing the moves in a game of chess. It is based on a system of coordinates to uniquely identify each square on the chessboard. It is now standard among all chess organizations and most books, magazines, and newspapers. In English-speaking countries, the parallel method of descriptive notation was generally used in chess publications until about 1980. Some older players still use descriptive notation, but it is no longer recognized by FIDE.

Algebraic notation exists in various forms and languages and is based on a system developed by Philipp Stamma. Stamma used the modern names of the squares, but he used p for pawn moves and the original file of a piece (a through h) instead of the initial letter of the piece name. This article describes standard algebraic notation (SAN) required by FIDE.

Allosmaitia strophius

Allosmaitia strophius, the Strophius hairstreak, is a butterfly of the family Lycaenidae. It is found from southern Brazil, north to Sinaloa, Mexico. Strays can be found as far north as Texas.

The wingspan is 22–32 mm. Adults are on wing year-round in Central America. In Texas, a stray was reported in November.

The larvae feed on the flowers of Malpighia species.

Chess piece

A chess piece, or chessman, is any of the six different types of movable objects used on a chessboard to play the game of chess.

Greisen–Zatsepin–Kuzmin limit

The Greisen–Zatsepin–Kuzmin limit (GZK limit) is a theoretical upper limit on the energy of cosmic ray protons traveling from other galaxies through the intergalactic medium to our galaxy. The limit is 5×1019 eV, or about 8 joules (the energy of a proton travelling at ~99.99999999999999999998% the speed of light). The limit is set by slowing interactions of the protons with the microwave background radiation over long distances (~160 million light-years). The limit is at the same order of magnitude as the upper limit for energy at which cosmic rays have experimentally been detected. For example, one extreme-energy cosmic ray, the Oh-My-God Particle, which has been found to possess a record-breaking 3.12×1020 eV (50 joules) of energy (about the same as the kinetic energy of a 95 km/h baseball).

The GZK limit is derived under the assumption that ultra-high energy cosmic rays are protons. Measurements by the largest cosmic-ray observatory, the Pierre Auger Observatory, suggest that most ultra-high energy cosmic rays are heavier elements. In this case, the argument behind the GZK limit does not apply in the originally simple form, and there is no fundamental contradiction in observing cosmic rays with energies that violate the limit.

In the past, the apparent violation of the GZK limit has inspired cosmologists and theoretical physicists to suggest other ways that circumvent the limit. These theories propose that ultra-high energy cosmic rays are produced nearby our galaxy or that Lorentz covariance is violated in such a way that protons do not lose energy on their way to our galaxy.

Handicap (chess)

Handicaps (or "odds") in chess are variant ways to enable a weaker player to have a chance of winning against a stronger one. There are a variety of such handicaps, such as material odds (the stronger player surrenders a certain piece or pieces), extra moves (the weaker player has an agreed number of moves at the beginning of the game), extra time on the chess clock, and special conditions (such as requiring the odds-giver to deliver checkmate with a specified piece or pawn). Various permutations of these, such as "pawn and two moves", are also possible.

Handicaps were quite popular in the 18th and 19th centuries, when chess was often played for money stakes, in order to induce weaker players to play for wagers. Today handicaps are rarely seen in serious competition outside of human–computer chess matches. As chess engines have been routinely superior to even chess masters since the early 21st century, human players need considerable odds to have practical chances in such matches.

Jack Steinberger

Jack Steinberger (born May 25, 1921) is an American physicist who, along with Leon M. Lederman and Melvin Schwartz, received the 1988 Nobel Prize in Physics for the discovery of the muon neutrino.

List of Brazilian inventions and discoveries

Brazilian inventions and discoveries are items, processes, techniques or discoveries which owe their existence either partially or entirely to a person born in Brazil or to a citizen of Brazil.

Bradykinin by Mauricio Rocha e Silva, Wilson Teixeira Beraldo and Gastão Rosenfeld

Chagas disease, pathogen, vector, host, clinical manifestations and epidemiology discovery, by Carlos Chagas

Chest photofluorography by Manuel Dias de Abreu

Epidemic typhus, pathogen discovery, by Henrique da Rocha Lima

Pion by César Lattes, one of the discoverers

Schistosomiasis, disease cycle discovery, by Pirajá da Silva

Jatene procedure by Adib Jatene

Caller ID by Nélio José Nicolai

Airplane (first unassisted flight) by Alberto Santos-Dumont

Wristwatch request by Alberto Santos-Dumont to Louis Cartier

DRE voting machine, the first Direct-Recording Electronic Voting Machine was implemented in Brazil by Judge Carlos Prudêncio in the Southern City of Brusque, back in 1989

Personal stereo (the father of the Walkman) by Andreas Pavel (later sold to Sony)

Anti-ophidic serum by Vital Brazil, he is also credited as the first to develop anti-scorpion and anti-spider serums, in 1908 and 1925, respectively

Automatic transmission using hydraulic fluid by José Braz Araripe and Fernando Lehly Lemos.

Mariana Pion

Mariana Alejandra Pion Núñez (born 19 December 1992) is a Uruguayan footballer who plays as a midfielder for Brazilian club Osasco Audax. She was a member of the Uruguay women's national team.

Meson

In particle physics, mesons ( or ) are hadronic subatomic particles composed of one quark and one antiquark, bound together by strong interactions. Because mesons are composed of quark subparticles, they have physical size, notably a diameter of roughly one femtometer, which is about 1.2 times the size of a proton or neutron. All mesons are unstable, with the longest-lived lasting for only a few hundredths of a microsecond. Charged mesons decay (sometimes through mediating particles) to form electrons and neutrinos. Uncharged mesons may decay to photons. Both of these decays imply that color is no longer a property of the byproducts.

Outside the nucleus, mesons appear in nature only as short-lived products of very high-energy collisions between particles made of quarks, such as cosmic rays (high-energy protons and neutrons) and ordinary matter. Mesons are also frequently produced artificially in cyclotron in the collisions of protons, antiprotons, or other particles.

Higher energy (more massive) mesons were created momentarily in the Big Bang, but are not thought to play a role in nature today. However, such heavy mesons are regularly created in particle accelerator experiments, in order to understand the nature of the heavier types of quark that compose the heavier mesons.

Mesons are part of the hadron particle family, and are defined simply as particles composed of an even number of quarks. The other members of the hadron family are the baryons: subatomic particles composed of odd numbers of valence quarks (at least 3), and some experiments show evidence of exotic mesons, which do not have the conventional valence quark content of two quarks (one quark and one antiquark), but 4 or more.

Because quarks have a spin of ​1⁄2, the difference in quark number between mesons and baryons results in conventional two-quark mesons being bosons, whereas baryons are fermions.

Each type of meson has a corresponding antiparticle (antimeson) in which quarks are replaced by their corresponding antiquarks and vice versa. For example, a positive pion (π+) is made of one up quark and one down antiquark; and its corresponding antiparticle, the negative pion (π−), is made of one up antiquark and one down quark.

Because mesons are composed of quarks, they participate in both the weak and strong interactions. Mesons with net electric charge also participate in the electromagnetic interaction. Mesons are classified according to their quark content, total angular momentum, parity and various other properties, such as C-parity and G-parity. Although no meson is stable, those of lower mass are nonetheless more stable than the more massive, and hence are easier to observe and study in particle accelerators or in cosmic ray experiments. Mesons are also typically less massive than baryons, meaning that they are more easily produced in experiments, and thus exhibit certain higher-energy phenomena more readily than do baryons. For example, the charm quark was first seen in the J/Psi meson (J/ψ) in 1974, and the bottom quark in the upsilon meson (ϒ) in 1977.

Parity (physics)

In quantum mechanics, a parity transformation (also called parity inversion) is the flip in the sign of one spatial coordinate. In three dimensions, it can also refer to the simultaneous flip in the sign of all three spatial coordinates (a point reflection):

It can also be thought of as a test for chirality of a physical phenomenon, in that a parity inversion transforms a phenomenon into its mirror image. All fundamental interactions of elementary particles, with the exception of the weak interaction, are symmetric under parity. The weak interaction is chiral and thus provides a means for probing chirality in physics. In interactions that are symmetric under parity, such as electromagnetism in atomic and molecular physics, parity serves as a powerful controlling principle underlying quantum transitions.

A matrix representation of P (in any number of dimensions) has determinant equal to −1, and hence is distinct from a rotation, which has a determinant equal to 1. In a two-dimensional plane, a simultaneous flip of all coordinates in sign is not a parity transformation; it is the same as a 180°-rotation.

In quantum mechanics, wave functions which are unchanged by a parity transformation are described as even functions, while those which change sign under a parity transformation are odd functions.

Pión District

Pion District is one of nineteen districts of the province Chota in Peru.

Posterior ischemic optic neuropathy

Posterior ischemic optic neuropathy (PION) is a medical condition characterized by damage to the retrobulbar portion of the optic nerve due to inadequate blood flow (ischemia) to the optic nerve. Despite the term posterior, this form of damage to the eye's optic nerve due to poor blood flow also includes cases where the cause of inadequate blood flow to the nerve is anterior, as the condition describes a particular mechanism of visual loss as much as the location of damage in the optic nerve. In contrast, anterior ischemic optic neuropathy (AION) is distinguished from PION by the fact that AION occurs spontaneously and on one side in affected individuals with predisposing anatomic or cardiovascular risk factors.

Protein pigeon homolog

Protein pigeon homolog also known as gamma-secretase activating protein (GSAP) is a protein that in humans is encoded by the PION gene.

QCD vacuum

The Quantum Chromodynamic Vacuum or QCD vacuum is the vacuum state of quantum chromodynamics (QCD). It is an example of a non-perturbative vacuum state, characterized by non-vanishing condensates such as the gluon condensate and the quark condensate in the complete theory which includes quarks. The presence of these condensates characterizes the confined phase of quark matter.

Shasanka Mohan Roy

Shasanka Mohan Roy (born 2 September 1941) is an Indian quantum physicist and a Raja Ramanna fellow of the Department of Atomic Energy at the School of Physical Sciences of Jawaharlal Nehru University. He is also a former chair of the Theoretical Physics Group Committee at Tata Institute of Fundamental Research. Known for developing Exact Integral Equation on pion-pion dynamics, also called Roy's equations, and his work on Bell inequalities, Roy is an elected fellow of all the three major Indian science academies – Indian Academy of Sciences, Indian National Science Academy, and National Academy of Sciences, India – as well as The World Academy of Sciences. The Council of Scientific and Industrial Research, the apex agency of the Government of India for scientific research, awarded him the Shanti Swarup Bhatnagar Prize for Science and Technology, one of the highest Indian science awards, for his contributions to Physical Sciences in 1981.

Tau (particle)

The tau (τ), also called the tau lepton, tau particle, or tauon, is an elementary particle similar to the electron, with negative electric charge and a spin of 1/2. Together with the electron, the muon, and the three neutrinos, it is a lepton. Like all elementary particles with half-integer spin, the tau has a corresponding antiparticle of opposite charge but equal mass and spin, which in the tau's case is the antitau (also called the positive tau). Tau particles are denoted by τ− and the antitau by τ+.

Tau leptons have a lifetime of 2.9×10−13 s and a mass of 1776.86 MeV/c2 (compared to 105.66 MeV/c2 for muons and 0.511 MeV/c2 for electrons). Since their interactions are very similar to those of the electron, a tau can be thought of as a much heavier version of the electron. Because of their greater mass, tau particles do not emit as much bremsstrahlung radiation as electrons; consequently they are potentially highly penetrating, much more so than electrons.

Because of their short lifetime, the range of the tau is mainly set by their decay length, which is too small for bremsstrahlung to be noticeable. Their penetrating power appears only at ultra-high velocity and energy (above petaelectronvolt energies), when time dilation extends their path-length.As with the case of the other charged leptons, the tau has an associated tau neutrino, denoted by ντ.

Thermo-dielectric effect

The thermo-dielectric effect is the production of electric currents and charge separation during phase transition.

This interesting effect was discovered by Joaquim da Costa Ribeiro in 1944. The Brazilian physicist observed that solidification and melting of many dielectrics are accompanied by charge separation. A thermo-dielectric effect was demonstrated with carnauba wax, naphthalene and paraffin. Charge separation in ice was also expected. This effect was observed during water freezing period, electrical storm effects can be caused by this strange phenomenon. Effect was measured by many researches - Bernhard Gross, Armando Dias Tavares, Sergio Mascarenhas etc. César Lattes (co-discoverer of the pion) supposed that this was the only effect ever to be discovered entirely in Brasil.

Xu Beihong

Xu Beihong (Chinese: 徐悲鴻; Wade–Giles: Hsü Pei-hung; 19 July 1895 – 26 September 1953), also known as Ju Péon, was a Chinese painter. He was primarily known for his Chinese ink paintings of horses and birds and was one of the first Chinese artists to articulate the need for artistic expressions that reflected a modern China at the beginning of the 20th century. He was also regarded as one of the first to create monumental oil paintings with epic Chinese themes – a show of his high proficiency in an essential Western art technique. He was one of the four pioneers of Chinese modern art who earned the title of "The Four Great Academy Presidents".

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