Higgs-Boson

Higgs boson (H )

The Higgs Boson or Higgs particle is a named after the British physicist Peter Higgs particles coming from the standard model of elementary particle physics. It is electrically neutral, has spin 0 and decays after a very short time.

The Higgs particle is part of the Higgs mechanism, a proposed already in the 1960s, theory according to which all fundamental elementary particles (eg, electron) only get their mass through interaction with the ubiquitous Higgs field. Particle of sufficient energy and luminosity are required for the experimental detection of the Higgs boson and the determination of its mass, which is why the proof failed over several decades. It was only in July 2012, the accelerator CERN has announced the detection of a particle at the Large Hadron Collider, in which it could be either the Higgs boson. After the presumption was confirmed by analysis of additional data, the experimental confirmation as so advanced that François Englert and Peter Higgs was awarded for the theoretical development of the Higgs mechanism of the Nobel Prize for Physics in 2013 applies. The internationally coordinated evaluation of the resulting data will also template for years to: / Resume future in 5 years to test the whole picture and further refine if necessary.

• 2.1 Development of the theory
• 2.2 Experimental Search 2.2.1 Overview
• 2.2.2 results

• 3.1 Supersymmetry
• 3.2 Composite particles

Higgs particle in the standard model

The building blocks of the Standard Model of particle physics can be divided into four groups: The quarks ( the building blocks of atomic nuclei ), the leptons (eg the electron), the gauge bosons ( which mediate the interactions between particles ) and the Higgs field. Through the so-called second quantization of the vivid contrast between particles and waves is canceled in physics, a particle is represented as excited state of the corresponding quantum field. The Higgs boson therefore corresponds to a quantum- mechanical excitation of the Higgs field, which is expressed as the detectable particles. Expressed Pictorial corresponds to the Higgs field of a violin or guitar string, as schwingungsfähigem system with ground state and vibration. The Higgs boson is then similar to the vibration pattern of the string, which was offset by certain energy supply in the characteristic oscillation and stimulated it. This is audible in a string as a sound of a certain pitch. It is this "in- oscillation bringing the string " is due to the required very high energies only in collisions in high -energy particle accelerators. With the detection of the Higgs boson and the evidence for the underlying Higgs field is to be provided.

Higgs mechanism

The Higgs Boson is all the more important for particle physics, because its existence is the Higgs mechanism, an integral part of the Standard Model predicted. The basic for the standard model gauge theory requires mathematical reasons that the gauge bosons, which produce the interactions between other particles themselves are particles without mass. This is the photon, the gauge boson of the electromagnetic interaction, actually given. The Higgs mechanism explains how in the original equation of the theory also massless gauge bosons of the weak interaction (W and Z bosons ) occur with another physical field in interaction and thus appear in all other equations as well as particles with a certain mass. This new field is called the Higgs field. Its elementary excitations are the Higgs bosons. The interaction, which is mediated by the W and Z bosons in turn, thus acquires a short range, outside of which she is extremely weak; it is precisely the " weak interaction ". Thus allowing the Higgs mechanism in a fundamental gauge theory unifying the electromagnetic and weak interactions to electroweak interactions. In addition, the mass of fermionic elementary particles ( quarks and leptons ) is explained by their interaction with the Higgs field.

The mass of the fundamental particles, an earlier than originally prestigious property is thus interpreted as a result of a new kind of interaction. Only the mass of the Higgs boson itself eludes this interpretation, it remains unexplained.

Experimental Evidence

The Higgs boson has, according to previous results, a very large in comparison with most other elementary mass of about 125 GeV/c2 - the equivalent of about two iron atoms (compared to the Z boson has the mass of 91 GeV/c2, the muon 106 MeV/c2, the electron 511 keV/c2, the electron-neutrino less than 2.2 eV/c2 ). In order to raise the center of mass energy required to generate, large particle accelerators are used. Because of its short life of approximately 10-22 s decays the Higgs boson practically at source in other elementary particles, preferably in the with the greatest mass. In the experiments, these decay products and their properties are measured and compared the measurements with computer simulations of the experiment with and without the Higgs boson. In particular, it searches the candidate combinations of decay products to determine whether a certain invariant mass occurs with greater frequency than would be expected on the basis of other known reactions. Since statistical fluctuations can mimic such a signal is only spoken by the discovery of a new particle, in general, when chance on average would need 3.5 million or more attempts to bring ( zufälligerweise! ) such a significant event concluded ( one speaks of a significance of at least 5 σ ). This corresponds approximately to the frequency that the 22 -time tossing a fair two-sided coin 22 times " number" is up.

Higgs boson and the cause of mass

In simplified representations of the Higgs boson is often a flat rate shown as a cause of mass. This is incorrect or imprecise for several reasons: Firstly, it is the Higgs field that is everywhere present with the same intensity and with the elementary particles of the standard model has an interaction through which they behave as if they have a specific, immutable mass. Exceptions are the photons and gluons, because they have no interaction with the Higgs field. Next, the mass of the Higgs boson itself is not explained only from an interaction with the Higgs field, but assumed in the standard model as a prerequisite to allow the Higgs mechanism at all. The resulting mass values ​​of the remaining particles carry but at the weighable mass of usual matter, which ultimately therefore the mass of the atoms, only about 1 percent, because it is based on the equivalence of mass and energy on all the interactions of their constituents. At over 99 % puts the atomic mass in the atomic nucleus whose mass in turn results to about 99 % only of the strong bond between the quarks in its nucleons. Is correspondingly low, the contribution of data generated by the Higgs field mass of quarks and electrons.

History

Developing the theory

1964 developed Peter Higgs, François Englert and Robert Brout and Gerald Guralnik, Carl R. Hagen and Tom Kibble are independently and almost simultaneously the same formal mechanism by which initially massless elementary particles interacting with a background field ( the " Higgs field " ) solid. Although all three work has appeared in succession in the same issue of the journal Physical Review Letters, in which Englert and Brout her manuscript had something more filed, so that their publication was placed in front of those of the other authors you named the field and its particles (the field quantum) alone for Higgs.

The Higgs mechanism was originally developed in analogy to solid state physics and thereby formulated only for abelian gauge theories. After he was transferred in 1967 by TWB Kibble on non-Abelian gauge theories (Yang -Mills theories ), the mechanism could be applied to the weak interaction. This led to the prediction of the - experimentally confirmed in 1983 - the great mass of the responsible for the weak interaction W and Z bosons.

1968 turned Abdus Salam to the Higgs mechanism to the electroweak theory of Sheldon Lee Glashow and Steven Weinberg, and thereby created the Standard Model of particle physics, for which all three were awarded the 1979 Nobel Prize in Physics.

The term " God particle " as used in popular accounts, but not in a reputable science comes from Nobel laureate Leon Lederman Max. Originally Ledermann wanted to publish his book under the title The goddamn particle ("the goddamn particle" ). However, his publisher forced him to change the title, so the book was published in 1993 under a different title: The God Particle: If the Universe Is the Answer, What Is the Question? ( " The God particle: if the universe is the answer, what is the question? " )

Peter Higgs himself rejected the term from God particle because it could be offensive to religious people.

Experimental search

Overview

Two quarks emit W or Z bosons, which combine into a Higgs boson.

The decay of a Higgs boson into two photons

The decay of a Higgs boson in four electrically charged leptons

The above illustrations show in the form of Feynman diagrams left two mechanisms by which a Higgs boson could be produced at the LHC. Right are shown two possible decay paths ( " decay channels " ) for Higgs bosons. The decay of a Higgs boson into two photons leads to equal the mass of the Higgs boson can be produced in an accelerator experiment compared with a model without the Higgs Boson more photon pairs with a center of mass energy or invariant mass. Since the Higgs boson itself does not interact with photons, the decay via intermediate electrically charged particles ( in the diagram above on a charged fermion ) must be made. The decay of a Higgs boson in four electrically charged leptons by means of intermediate Z bosons is, together with the decay into two photons to the important discovery channels for the Higgs boson. By systematically combined search for these decays strong evidence for the existence of a corresponding particle could be found on two independent detectors of the LHC. The local significance in this case is 5.9 σ, what a mistake in the discovery excludes a large extent.

Results

Since many special features such electroweak interactions have experimentally well confirmed the standard model with a Higgs particle is considered as plausible. According to the standard model and experiments with other particles, the mass of the Higgs boson should, if it exists, be no more than 200 GeV/c2. (For comparison: . Proton and neutron have approximately 1 per GeV/c2 ) Had been found in this area no Higgs particle, said some theories a Higgs multiplet in advance which could be realized at higher energies.

Already in 2003 were data analyzes at LEP determine 114.4 GeV/c2 as the lower limit for the mass at CERN. Addition, it was 156-175 GeV/c2 excluded in measurements of the CDF and D0 experiments (2010) at the Tevatron of Fermilab the area.

In December 2011 and February 2012, preliminary reports of the experiments were published at the LHC at CERN, which could be ruled out in different mass ranges with high confidence the existence of a standard model Higgs boson. These data were evaluated from 2011 from particle collisions at energies of about 7 TeV. According to these results is the mass of the Higgs boson, if it should exist, in the range of 116-130 GeV/c2 ( ATLAS ) or 115-127 GeV/c2 (CMS). This first indication of the existence of the particle could be obtained. These detections mass 124-126 GeV/c2 σ was measured with a local significance of more than 3. However, at least 5 σ required for recognition as a scientific discovery in particle physics. In July resulted in a further analysis of the 2011 data by ATLAS a local significance of 2.9 σ at about 126 GeV/c2.

The CDF and DØ groups of the now- defunct Tevatron delivered in March and July 2012 New data analysis, the possible evidence for the Higgs boson in the range 115-135 GeV/c2 contained, with a significance of 2.9 σ.

On July 4, 2012, the LHC experiments ATLAS and CMS published findings that a particle has a mass of 125-127 GeV/c2 found. These additional data were evaluated from 2012 from particle collisions at energies of about 8 TeV. The local significance reached in both experiments 5 σ, with the inclusion of additional channels at CMS, the statistical significance of the reported value is slightly reduced (4.9 σ ). The mass of the new particle were found to be ~ 126.5 GeV / c 2 (ATLAS), and 125.3 ± 0.6 GeV/c2 (CMS).

July 31, 2012 ATLAS improved data analysis by including a further channel, thus increasing the significance to 5.9 σ at a mass of 126 ± 0.4 ( stat) ± 0.4 ( sys) GeV/c2. Likewise, CMS increased the significance at 5 σ with a mass of 125.3 ± 0.4 ( stat) ± 0.5 ( sys) GeV/c2.

To ensure that the particles found is indeed the Higgs boson of the standard model, more data must be obtained and evaluated. In particular, needs to be investigated for the found particles with which frequencies of the various possible combinations of other particles occur in which it decays. Namely applies for the Higgs boson, a specific prediction: the probability to produce a particle in the decay, increases in proportion to the square of the mass of the particle. In November 2012 ( 3) of the ATLAS and the CMS collaboration results on five different decay channels published ( decay in (1) two gamma quanta, (2) four electrons or muons, two electrons / muons and two neutrinos, (4) two leptons, or (5) two bottom quarks ). They do not contradict the predictions of the standard model, but are still subject to large uncertainty ranges, as a final confirmation that could be inferred.

M. Schumacher and C. Weiser wrote in an article in a physics journal in August 2012: "The discovery of a Higgs -like particle after decades of efforts is a milestone in physics, regardless of whether it is ultimately as the Higgs boson of the Standard Model which proves an extended theory or something totally unexpected. "

In March 2013 ATLAS and CMS presented new analyzes confirm that the new particle with the predictions for the Higgs boson is compatible.

Higgs bosons beyond the Standard Model

Supersymmetry

In the minimal supersymmetric standard model ( MSSM ), an extension of the standard model of supersymmetry, there are five Higgs bosons, three "neutral " and two " charged " (the terms "neutral " or " loaded" are as in the electroweak gauge theory defined ):

The A particles is odd with respect to the CP- symmetry, ie it is a pseudoscalar, while the h- and the H - boson CP are just ( scalars ). In addition, the A particles not coupled to the three gauge bosons W , W- and Z.

The h boson has relation to the benchmark scenario used a theoretically allowed maximum mass of 133 GeV/c2 and is therefore regarded as particularly similar to the Higgs boson of the Standard Model.

These five Higgs bosons five more, so-called Higgsinos be postulated in this model as a super affiliate.

Composite particles

The idea that the Higgs boson is not elementary, but a composite particle is treated eg in technicolor theories. It is assumed that a new strong interaction exists and that the Higgs boson is a bound state of this interaction.

Another approach to the explanation of particle masses as an alternative to the Higgs mechanism is based on the assumption that the particles, quarks and leptons previously assumed as fundamental and punctual, be composed of " Haplonen " and their mass is the equivalent of the interaction between the Haplonen. In this picture, also the particle at CERN recently discovered is a composite of Haplonen boson.