Have tachyons mass

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Tachyons (Greek. tachys: 'fast') are hypothetical particlesFTL particle named for Faster-Than-Light particle) that can move faster than the speed of light! This is according to the special theory of relativitynot explicitly prohibited, only exceeding the speed of light in a vacuum c (almost 300,000 km / s) is not possible. Tachyons, on the other hand, should from the beginning a speed greater thanc have.

Tachyons - Trapped in Another World?

This is theoretically possible if tachyons have a imaginary mass own, m2 <0. However, if their speed drops and becomes comparable to the speed of light, then their energy grows towards infinity, so that they can never fall below the speed of light in a vacuum. Thus, tachyons - should they exist - never penetrate the sub-light speed range. If you look at the Cone of light, a common space-time diagram of the theory of relativity, this is how the tachyons move on space-likeGeodesics, while photons move on light-like (zero geodesics) and matter on time-like geodesics.

Tachyons swap cause and effect

Tachyons contradict this Causality principle! Between events with spacial distance According to Einstein, there can be no signal exchange. If tachyons actually existed, it would be possible that the effect would be temporal in front the cause. That would bring physics, especially thermodynamics (keyword: thermodynamic time arrow based on the 2nd law), into serious difficulties. In addition, a number of unsolvable paradoxes would be possible. For these reasons, the existence of such particles and the veracity of theories which postulate or derive them are negated by most physicists.

Tachyons in non-supersymmetric string theories

In string theories, tachyons occur when the supersymmetry between bosons and fermions is dispensed with. Only the superstring theory guarantees that no tachyons are involved and guarantees the preservation of the valuable and so far always verified Causality principle ('Cause comes before effect'). On the other hand, non-supersymmetric string theories offer interesting phenomena like the Tachyon condensation. In bosonic string theories, a scalar particle or field can assume a tachyonic state in this way.

Tachyons prohibited?

The experimental search for tachyons, after Cerenkov radiation, which is expected with tachyon deceleration during propagation through dense media or the negative (!) mass square in the energy balances of various reactions have so far been unsuccessful. However, the existence of tachyons has not been completely refuted either. Even so, there are good reasons (as shown here) why theymay not existwithout plunging physics into a crisis.

The day arc is explained under the seasons.

Tardyons are all particles that are slower than photons in the same medium. The speed of the tardyons is therefore less than the speed of light in a vacuum cwhich is about 300,000 km / s. The term Luxon encompasses all particles that deal with c move. On the 'other side of the light barrier' one finds the (hypothetical) tachyons.

The almost unmanageable number of particles in physics could be called a 'particle zoo'. A tongue-in-cheek designation, linguistically a metaphor, is: The number and properties of the particles are just as colorful and diverse as the fauna in the zoo. In a strict sense, physicists make a distinction Elementary particlesthat have no further substructure, of composite particles. There are also numerous terms that summarize particles under a certain characteristic.

Wave and particle

The real elementary particles in particle physics are the leptons and the quarks. After everything we know today and what the Standard Model of particle physics says, they are punctiform. Some contemporaries may be reluctant to take note of this punctiformity; ultimately it is a property in the particle image. Quantum theory unmasked the particles as a wolf who sometimes comes along in sheep's clothing and sometimes doesn't: the Wave-particle dualism states that particles can also be described as waves. With the wave, the statement about the point-like shape also becomes obsolete, because waves are extended structures.

Hadrons, mesons, baryons, nucleons - not without it

The construction kit of elementary quarks and leptons now brings the diversity of the particle zoo with it. The six quarks can serve as building blocks for composite particles. This main group is called the hadrons. Hadrons are classified into subgroups: Exactly two quarks combine to form mesons. Baryons, on the other hand, always consist of exactly three quarks. The nucleons (nuclear particles) are the two types of particles in the atomic nucleus, protons and neutrons (and their antiparticles). Both are among the most famous baryons.
The mesons are further subdivided according to certain particle properties, i.e. according to Quantum numbers. The best-known mesons are the pions and the kaons, but there are far more exotic particles, such as charming (they are really called that!) Mesons (which contain c-quarks) or strange mesons (which contain s-quarks), the J / Psi-Particles, Charmonium, Bottomium etc.

further particle properties

These particles can be distinguished from each other very well by quantum numbers such as spin, isospin, weak isospin, parity, electrical charge, color charge, weak charge, hypercharge, weirdness etc.

Hyperons are strange

The hyperons are particularly heavy, strange baryons, which accordingly have completely new constituents than ordinary matter, namely strange quarks (s-quarks). There are also delta baryons and bottom baryons (contain b-quarks).

The three lepton families e, μ, τ

If one abandons quark matter and turns to the second fundamental class of elementary particles, the leptons, one also finds subclasses here. You will be in three generations divided. These are the electron, muon, and baptismal families. The best-known leptons are probably the electron and its antiparticle, the positron. We also know the muons, which are basically 'heavy electrons', and the tauons (tau particles), which are even heavier. The trichotomy (tripartite division) can be performed using the weak isospinsexplained in terms of group theory. The three families were also verified experimentally on the basis of the decay of the neutral Z boson with a 95% certainty. Because the Z-particle can decay into a pair of two leptons, namely lepton and antilepton. In the experiment were only three Decay channels found: electron and positron, muon and antimuon, tauon and antitauon. This is the most important, experimental evidence for the three genera of leptons.

Almost nothing of particles: neutrinos

The neutrinos also belong to the leptons and can be classified into three families: electron neutrino, muon neutrino and tau neutrino. They can even switch between these families and transform into one another, one speaks ofNeutrino oscillation. The neutrinos that come from the sun and are created in the sun as a by-product of thermonuclear fusion (more precisely: pp chain) are subject to this process.

Particle weddings

Leptons can also mate: At very low temperatures, certain solids contain the Superconductors, two electrons together. They form a bound state, which one of the pioneers of superconductivity thinks Cooper pairs is called. The union of these two fermions is of a bosonic nature and suddenly changes the conduction properties of the material. An analogue to the superconductivity of electrons is the superconductivity of the quarks, the so-called color superconductivity. Here fermionic quarks mate to form bosonic diquarks. At high densities, this state of matter becomes relevant and is discussed in connection with neutron stars. The equation of state of neutron star matter would change as a result of the quark pairing.

Force particle and standard model

They are known in quantum field theories Calibration bosons, bosonic particles that mediate the respective interaction (electromagnetic, gravitational, strong, weak). these are

  • the massless, electrically neutral photon of the QED,
  • the mass, charged W bosons and the electrically neutral Z boson of the weak interaction,
  • the eight massless, color-charged gluons of the QCD
  • and the only hypothetical, i.e. not proven, graviton of quantum gravity (for example in string theories).

Taken together, these are 1 + 3 + 8 + 1 = 13 gauge bosons, which physicists assume to exist. In the Standard Model of Particle Physics, there is another important particle that has also not yet been verified experimentally: the Higgs particle. It is particularly massive and has therefore not yet been detected in particle accelerators. The particle physicists hope for verification with each new generation of accelerators (from 2007: LHC at CERN). The Higgs boson is required to turn massless gauge bosons into masses, as in the case of the W particles and the Z particle. The Higgs boson in turn belongs to the class of Nambu Goldstone Bosonsthat are always involved in a spontaneous symmetry breaking. The number of gauge bosons is significantly expanded in the Great Unified Theories: here a further 12 X bosons are derived, which of course due to the immensely high energy regime (E ~ 1016GeV) are far removed from experimental evidence.

After this antipasti: antiparticles and antimatter

The Antiparticle have already been mentioned. For every particle there is the corresponding antiparticle inverted electrical charge. If the particle is its own anti-particle it is called Majorana Particle. It is possible to invert the constituents of composite particles without exception. In this way one can produce antimatter, which, however, has to be well shielded from the surrounding ordinary matter so that it does not only radiate into electromagnetic energy (gamma rays). This process is called pair annihilation or pair annihilation. In 1995, CERN succeeded in producing anti-hydrogen: a positively charged positron ('antielectron') forms an atom with a negatively charged antiproton as the atomic nucleus.

Atoms & Molecules

This leads to what is surely the most well-known particle network: the atom. The atomists around Democritus (460 - 371 BC) referred to in ancient philosophy the indivisible (Grch. atomos) Unity of matter as atoms. It was not until the 20th century that physics was able to prove that what was called atoms was by no means as elementary as assumed. The pioneer wasErnest Rutherfordwho was able to show in his 1911 scattering experiments with α-particles on gold foil that atoms consist of a small, dense atomic nucleus and a surrounding electron shell. The subsequent, decades-long elaboration of the quantum theory finally showed that the electrons do not orbit the atomic nucleus as massive point particles (Bohr's atomic model), but the electrons in 'clouds' (precisely: the absolute square of the Wave function of the electron) are 'smeared' around the atomic nucleus (Orbital model). Linked atoms that Molecules, owe their existence to chemical bonds, which can also be understood in terms of quantum theory. The associated areas of atomic and molecular physics are the orbital model, hybridization, electron bonding, Hartree-Fock theory, homeopolar bonding, etc.

α, β and γ particles

In the radioactivity one knows Alpha particlesassociated with alpha decay, Beta particlesrelated to beta decay and gamma rays emitted during gamma decays. All of these particles send radioactive atomic nuclei (Radionuclides) out. The designation with the first letters of the Greek alphabet was initially due to the ignorance of which particles were involved. Experiments (exploiting the ionizing effects of radioactivity; mist and bubble chambers, deflection in electric / magnetic fields, mass spectrometers, etc.) revealed the true nature of these particles:

  • Alpha particles are helium atomic nuclei, i.e. a combination of two protons and two neutrons.
  • Beta particles are electrons or positrons (which belong to the group of leptons) depending on the type of beta decay.
  • Gamma rays are high-energy, electromagnetic waves above that connect to the range of X-rays.

Bosons, Fermions and Statistical Physics

In the statistical physics all particles are divided into two groups: into bosons, particles with integer spin, and into fermions, particles with half-integer spin. So the differentiating criterion is that Spin. The spin statistics theorem sharply delimits both groups of particles (identical versus distinguishable particles) and postulates an adequate quantum theoretical description for each. The consequences for the structure of matter are considerable and of fundamental importance for physics and the structure of matter (periodic table of the elements, Bose-Einstein condensates, quantum gases, BCS superconductivity, color superconductivity, stability of compact objects due to fermionic degeneracy pressure and much more.).

Quanta

In quantum theory you also have that Quanta given certain names and thus defined particle groups: the Photons have already been discussed and are the quanta of the electromagnetic field. The quantization apparatus of other interactions also leads to other quantum types: The Phonons are the oscillation quanta of the crystal lattice in solid state physics. TheMagnons are the quanta in ferromagnets. Fluxons denote the flux quanta of the magnetic flux in the theory of superconductivity.Vibrons are general, quantized vibrational degrees of freedom, while Rotons denotes quantized degrees of freedom of rotation. Both are used in molecular physics, where a molecule can change its energy state through exchange (emission or absorption) of these quanta. In principle, however, when a thread pendulum is bumped in a banal manner, a large number of vibrons are generated, which bring the pendulum into an excited oscillation state.

cosmological particles

In the cosmology Particle names have also been introduced for fields. In terms of quantum theory, it makes no sense to distinguish between particles and fields because they are 'two sides of the same coin'. He laid the foundation stone for this Wave-particle dualism.
So will inflation with the Inflaton connected; a scalar field in the theory of the quintessence is associated with theCosmon identified and the dark energy or the cosmological constant is identified with the Radion connected.

WIMPs

WIMPs are all particles that - like the leptons - are only subject to the weak interaction, but carry a relatively large mass. They are candidates for the non-baryonic dark matter in the universe. Neutrinos do not belong to the WIMPs because they are too light.

Particles as threads or surfaces

An extension of the particle concept was established by the string theories. All particles, but also other objects, are seen here as vibratory structures. In the one-dimensional case they are called Strings, in the two-dimensional case it is the membranes, in short Bran called and in the general case they are called p-bran with the dimension p. Different particles are generated by the fact that the p-branes have different oscillation states: an overtone is, so to speak, a new particle. It remains to be seen whether the string theories or their superordinate construct, the M-theory, will turn out to be a powerful alternative to conservative particle physics. The string theories are still the key to formulating a quantum gravity, a theory of the gravity of strong fields and small spacetime scales. In the meantime it has got a competing theory in the form of loop quantum gravity.

Speed ​​as a criterion for particle classification

A particle classification based on their speed v relative to the speed of light c in the same optical medium was also undertaken. Here one knows the tardyons with v smaller cwho have favourited Luxons with v equal c and the tachyons with v greater c. The occurrence of tachyons would be against that Principle of causality (Order of cause and effect) violate (but not against the special theory of relativity!), Therefore physicists try to avoid tachyonic theories.

supersymmetric particles

As if this hodgepodge of particles wasn't enough, the physicists in supersymmetry (SUSY) come up with new particles: the SUSY particles. In a well-defined nomenclature, supersymmetric partners to established particles appear here: for example, one speaks of Squarks, Neutralinos and Higgsinos. So far none of these SUSY particles has been discovered experimentally. Therefore, SUSY has so far only been an additional theory that has yet to prove itself.

exercise

You have now got to know a number of particles, often characterized by the suffix -one, e.g. hadrons, bosons, photons, gluons, tachyons, selectrons, tauons and cosmons. In contrast to this, clarify the terms Schoschonen, Kronen and Sponen.

A particle accelerator is a great facility for research into High energy and particle physics. In this research facility, charged particles (ions) are accelerated to high speeds by means of electric and magnetic fields. Once a suitable speed has been reached, the particles are shot at a target. In this collision, a large number of new particles are created, which are detected with various measuring devices. From the investigation of these particle reactions, the physicists deduce which particles were involved in the collision, how they were transformed and which forces were at work.

relativistic effects

The particle speeds are so high, namely close to the vacuum speed of light of around 300,000 km / s, that the effects of the special theory of relativity have to be taken into account: time dilation and Lorentz contraction are the daily business of high-energy physicists. The length contraction manifests itself in the fact that heavy ions, which contain many nucleons, are contracted in the direction of movement: they then no longer have a spherical shape, but rather resemble a pancake in the laboratory system! (see figure under Lorentz contraction)

Fields control particle trajectories

To accelerate and guide the particle beams (English technical term beam) the experimenters use electric and magnetic fields. For this reason, the particles in the beam must be charged, i.e. ionized (technical term:stripped), be. The Lorentz Force F. = q (E. + v × B.) with the electric charge q, the vector of the electric field E., the vector of the magnetic field B. and the vector of the particle velocity v (here in a non-relativistic formulation) provides - with correct orientation of the fields - essentially in the first term for the acceleration in the direction of movement and in the second term for the deflection, so the guidance of the particle beams. Magnetic Dipole fields one uses to deflect the beam while magnetic Quadrupole fields ensure its focus. Without a charge of the accelerated species, the Lorentz forces disappear and neither guidance nor acceleration would be possible.

Why fast particles?

The purpose of particle accelerators is to accelerate particles to high kinetic energies and to release new particles in a final collision with a target. The greater the kinetic energies of the particle beams, the more complex showers of particles (secondary particles) the experimenters can generate in the collision event, which usually results in completely new particle species.
It can be said that the particle accelerator is the most modern form of a microscope. Because the length scale is significantly smaller and goes into the subatomic area. The characteristic scale is in the range of femtometers (10-13 cm), therefore one could use particle accelerator 'Femtoscopes'call. Particle accelerators can be used to experimentally investigate the diversity of particles, the 'particle zoo'.

Construction of a particle accelerator

Particle accelerators are in principle long, evacuated tubes (technical term: Cavities), in which particle beams propagate. Acceleration due to premature collisions would not be possible without a vacuum. The physicists use two methods to make particles collide with one another: The experimenter either shoots the particle bundle at a static target. target); or uses a special design of particle accelerators, the Collider, in which he accelerates two particle bundles separately and finally puts them on a collision course. Colliders have the advantage that the Center of gravity (engl. center of mass energy, short com energy) is significantly larger because the kinetic energies in the Add particle bundles.
There are now various Accelerator architectures with different sizes, geometries, efficiencies and costs. The first accelerators were linear accelerators. linear accelerator, LINAC for short), where the acceleration path is a straight line. In circular accelerators (cyclotron), synchrocyclotron and synchrotron, the acceleration paths are curved (spiral or circular path). The advantage is that multiple acceleration of the beam in multiple revolutions; the disadvantage is the deflection of the beam from the target path by centrifugal forces. The physicists compensate for this with (increasingly stronger) magnetic guide fields.

CERN - The most famous particle accelerator facility in the world

The acronym CERN stands for European Council for Nuclear Researchwhat in German European Organization for Nuclear Research is called (literally translated actually: European Council for Nuclear Research). CERN is the largest and best-known particle physics laboratory in the world. It was founded in 1954, currently has 20 member states and employs almost 3000 people in a wide variety of professions. At CERN in 1989 the Internet was created by Tim Berners-Lee invented!
Modern particle acceleration systems like CERN are large complexes consisting of many LINACs and synchrotrons. The researchers and the global public are eagerly awaiting the completion of the new accelerator named Large Hadron Collider (LHC) End of 2007. The commissioning of the LHC will definitely be exciting, as the explosive research topics mentioned below suggest. In addition to the ion collision experiments, CERN is also produced

  • Neutron beams for structural analysis,
  • Neutrino rays passing through the Gran Sasso massif to be shot as far as Rome in order to investigate the beam with neutrino detection experiments (keyword: neutrino oscillation)
  • Antiproton beams, which are slowed down on so-called deceleration paths, in order to Anti-hydrogen atoms, a form of antimatter.
  • and much more.

Particle beams

According to the particle species being accelerated, one can leptonic accelerators and hadronic accelerators distinguish. Leptonic particle bundles consist primarily of electrons and positrons (the antiparticles of electrons), while hadronic particle species are usually heavy ions (typically stripped gold or lead).

Research into fundamental natural forces

Particle accelerators are the laboratories of high energy physics and are the experimental set-up around whichfour fundamental interactions in physics, namely to study weak interaction, strong interaction, electromagnetic and gravitational interaction. The quantum field theories make many statements that can be verified or falsified in particle accelerators. The effort to unify at high energies has been successfully implemented in the electroweak theory and the Great Unified Theories. The Discovery of the Z particle 1973 at CERN Donald Perkins and colleague was a scientific sensation, as it was from the theorists Vineyard, salam and Glass show predicted (Nobel Prize 1979). It wasn't until ten years after the discovery of the Z particle in 1983 that the two finally became W-particles discovered at CERN: Shot at the synchrotron Carlo Rubbia and Simon Van der Meer Protons on antiprotons and discovered the remaining weakons.

Explosive research topics

The most important research areas in high-energy physics also have astrophysical relevance, because the cosmos naturally produces the highest energies (see e.g. cosmic rays, blazars or big bang).
An important discovery has yet to be made in the Standard Model: the high-energy physicists are trying to do this Higgs boson to discover. The latest generation of particle accelerators are at the critical energy threshold to be able to produce this heavy particle. Here a race breaks out between researchers from the USA (Fermilab) and Europe (CERN). The Higgs particle explains processes in the early universe. In the Higgs mechanism, the particles are given mass.
Experimental signatures of the Supersymmetry searched. So far, none of the required SUSY particles could be detected in particle accelerators. This aspect is also of great interest to cosmologists because these particles may contribute to the dark matter in the cosmos.
Another research area deals with the intensive study of Quark-gluon plasmas (QGP). In the meantime it has been possible to establish this state from free quarks and gluons in experiments. This research topic interests astrophysicists with regard to the question of the equation of state of matter in neutron stars and quark stars.
In the high-energy collisions, the physicists also try to track down the quantum effects of gravity. Particle accelerators prove to be test laboratories for the ideas based on models of the Quantum gravitations are based. The string theories with their extra dimensions can be tested, the limits of general relativity can be explored and the excitation of gravitons can be checked. If the Planck scale should actually be reduced by existing extra dimensions, the so-called TeV quantum gravity can already be investigated with the latest particle accelerators.
For cosmology, accelerator physics is also important because physical states are comparable to those in Big Bang could be generated in the particle physics laboratory. The hope is that with ever better accelerators, ever higher center of gravity energies or energy densities can be produced in order to gradually approach this area. In the future, Leptoquarks and X-Force could possibly be studied in the GUT regime.
A particularly fascinating prospect is that black holes could be produced in the terrestrial laboratory in particularly high-energy collisions. If the TeV quantum gravity scenario is correct, we are also here on the threshold to the dream of the Laboratory physics with black holes to make it come true. Quantitative considerations by many high-energy physicists show that they would not pose a threat to the earth because they are many times smaller than the cosmic black holes. Most scientists agree that such mini-holes must evaporate on extremely short time scales (fm / c) by the emission of Hawking radiation. It may be possible to prove this still hypothetical form of radiation in particle accelerators. More details on this topic can be found in a web article under Black Holes in Particle Accelerators.

Websites of the most famous, international and German particle accelerator facilities

  • CERN in Switzerland,
  • FERMILAB, Fermi National Accelerator Laboratory (UNITED STATES),
  • RHIC, Relativistic Heavy Ion Collider (UNITED STATES),
  • DESY, German electron synchrotron, in Hamburg and Zeuthen,
  • GSI, Society for Heavy Ion Research in Darmstadt,
  • Max Planck Institute for Physics in Munich,
  • Research Center Karlsruhe,
  • Research center Julich.

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© Andreas Müller, August 2007