Matter and Forces of Nature at Quantum level

Particles of nature can be put in two large distinct groups- Bosons and Fermions, based on their overall spin. Bosons correspond to Bose-Einstein statistics and possess integer spin such as 0, 1, 2 while Fermions correspond to Fermi-Dirac statistics and exhibit odd half integer spin such as ½, 3/2 so on. Fermions cannot exist in same quantum state at same place at the same time. This is known as Pauli Exclusion Principle. Bosons on the other hand can and do exist at same place, at the same time in same quantum state. Gluon, Photon, W, Z, Higgs and still hypothetical Graviton are Bosons. W and Z Bosons have spin of 1 and carry the weak force field which holds nucleons together to form atomic nucleus. Gluons exhibit a spin of 1 and carry strong force field which keeps Quarks together to form Protons and Neutrons. Photons also have a spin of 1 and carry Electromagnetic field responsible for Electromagnetism. Higgs Boson has a spin of 0 and it carries the field responsible for mass of particles. Particles become massive when they interact with the Higgs field. Particles such as Photons pass straight through this field without interacting and therefore have zero mass. Gravitons are supposed to have a spin of 2 and carry the field responsible for Gravity. Of these field carrying Bosons only W Boson carries charge. Charge carried by W Boson has a value of -1. Photon and Gluon are massless because they are not affected by Higgs field. Gravitons also are predicted to be massless. W Boson carries mass of 80.4 GeV/c², Z Boson Carries mass of 91.2 GeV/c² and Higgs Boson carries mass of 125.3 GeV/c². Apart from these there are composite Bosons such as Mesons. One Quark and one Antiquark held together by strong field is named Meson. Both constituting Quarks have odd half integer spin and therefore are Fermions, giving Meson an integer overall spin of either 0 or 1. Mesons are very short lived. They quickly decay into more fundamental particles. Charged Mesons decay into Electrons and Neutrinos. Sometimes they decay into intermediate particles which then further decay to Electrons and Neutrinos. Pion, Kaon and J/Ψ are Mesons. Atomic nucleus can be a Fermion or Boson depending on number of Protons and Neutrons contained. If the number is even then it’s a Boson, otherwise it is a Fermion. Depending on whether it is a Boson or Fermion, some strange properties are observed in Elements.

Quark and Lepton are Fermions. So far we know of six Quarks named Up, Down, Charm, Strange, Top and Bottom, all having spin of 1/2. There is an anti particle pair for each one of them. They all carry fractional charge and they all have mass. Up Quark carries charge of +2/3 and Down Quark carries charge of -1/3. A Proton is two Up Quarks and a Down Quark held together by three Gluons. Since overall spin is half integer, Proton is a type of composite Fermion classified under the name of Baryon- particles made of three Quarks. Before 1987 it was thought that spin of Protons is a resultant of spin of its three constituent Quarks. But the 1987 European Muon Collaboration test indicated that this was not correct. It turned out that Quarks contribute only a very little, 25% at most to the overall spin of Protons. Scientists at RHIC have come up with conclusive evidence that contribution of Gluons to overall spin of Protons is almost same as that of Quarks, a value in the range of 20% to 30% of total Proton spin. Remaining spin might be coming from orbital angular momentum of Quark-Gluon system buzzing around confined by the weak force. Confinement might also be contributing to mass of Proton apart from the Higgs field contribution. Missing spin problem was named Proton spin Crisis. Neutron is another composite Fermion made of two Down Quarks and one Up Quark held together by three Gluons. Because it is made of three Quarks, Neutron also is a Baryon. Baryons are strongly interactive in nature. Protons can exist freely for extremely long time, free Neutrons on the other hand have a mean lifetime of 881.5±1.5 s. At the end of life, free Neutrons decay into Proton, Electron and Electron Antineutrino. Nucleus of a Carbon-13 atom is also a composite Fermion as it is formed by six Protons and seven Neutrons, making overall spin odd half integer.  

Electron, Electron Neutrino, Muon, Muon Neutrino, Tau and Tau Neutrino are six known Leptons with a spin value of 1/2. Electron, Muon and Tau carry a charge of -1 while the three Neutrinos are neutral. Antiparticles of all six Lepton are also Fermionic. Leptons are weakly interactive Fermions and have lower mass than Baryons, Electron and Electron Neutrino being least massive with mass of .511 MeV/c² and less than 2.2 eV/c² respectively. Electrons are stable, Muons have lifetime 2.197 microseconds, Tau have lifetime of .2906 Picoseconds while lifetime of the three Neutrinos is unknown. 

Composite particles made of Quarks, Antiquarks and Gluons are classified as Hadrons. Fermionic Baryons are made of three Quarks and Bosonic Mesons are made of one Quark and one Antiquark and therefore are Hadrons. Baryonic Hadrons can be put in three groups- Baryons made of one type of Quark, Baryons made of two types of Quark and Baryons made of three types of Quark. Baryonic Protons and Neutrons are most common Hadrons in nature. Pion and Kaon are confirmed Mesonic Hadrons. All Mesons are highly unstable and quickly decay into other more stable particles such as Electrons.

Exotic Baryons and Exotic Mesons are composite particles grouped as Exotic Hadrons. Some of them are confirmed to exist while some other still remain hypothetical. Composite particles made of four or more Quarks and Antiquarks and Gluons are collectively called Exotic Baryons. As of August 2015, two Pentaquarks made of four Quarks and an Antiquark have been discovered at Large Hadron Collider. Dibaryon or Hexaquark and Skyrmion are exotic Baryons predicted to exist but have not been detected yet. Glueballs, composite of Gluons and Tetraquark are exotic Meson candidates. Z(4430) is a charged Tetraquark whose existence is confirmed by LHCb experiment.

For Every particle in standard model an anti particle exists. Anti particles are same as particles except for their charge which is opposite. For example nucleus of antiatom is negatively charged but the Positrons whirling around are positively charged making the antiatom neutral. Particle and anti particle if brought together, annihilate each other converting into energy. If all matter in Universe is replaced with #Antimatter and flow of time is reversed, the anti matter world thus formed will be a mirror image of our everyday matter world with identical nature. In science it is known as Charge-Parity-Time Reversal symmetry or CPT symmetry. Matter and Antimatter particles are always produced in pair. Equal number of particles and anti particles should have been created at Big Bang. Then why there is so little anti matter in known Universe against amount of Matter? This is one of the questions LHC will try to answer in its future runs. Scientists have hints that laws of nature do not apply equally to Matter and Antimatter. A very small amount of matter may have survived mutual annihilation during early days of Universe causing it to be as we find it today. Using ALICE experiment a team of scientists at CERN confirmed in August 2015 that Matter and Antimatter indeed are perfect mirror of each other and should completely annihilate one another whenever they meet. Baryon Antibaryon symmetry experiment gave same conclusion.

Standard model is incomplete. It still cannot explain Gravity and Dark Matter. Experiments at LHC are aimed at solving these problems. Scientists there will try to detect Graviton, particle supposed to carry Gravitational field and weakly interactive massive particles or WIMPS which are supposed to compose Dark Matter. Detection of either one of these will be an epochal moment for humankind.

References:
1) https://arxiv.org/pdf/1105.4992.pdf
2) http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/disfd.html
3) https://home.cern/about/updates/2015/08/alice-precisely-compares-light-nuclei-and-antinuclei

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