The Higgs boson or Higgs particle is an elementary particle proposed in the Standard Model of particle physics. The Higgs boson is named after Peter Higgs who, along with others, proposed the Higgs mechanism in 1964.The existence of the Higgs boson and the Higgs field would be associated with the simplest of several methods that attempt to explain why some elementary particles have mass. This theory suggests that an invisible field permeates all space, this field has a value other than zero everywhere, even in its lowest energy state, and therefore, other elementary particles acquire mass when interacting with him. In particular this mechanism justifies the mass of the W and Z vector bosons, which differentiates them from other bosons that mediate fundamental interactions, such as the photon.
The same theory predicts the existence of the Higgs boson, the smallest possible excitation of the field, and, as this would be detectable, has been a long search in particle physics. According to the standard model Higgs boson interacts with all particles with mass, 2 has no spin or electric charge or color, and as the name suggests is a boson. It is very unstable and quickly decays, its. In some variants of the Standard Model can be several Higgs bosons. If it is established that the Higgs does not exist, other proposed models in which the Higgs is not involved could be considered.
Because of its possible role in the production of a fundamental property of elementary particles and, above all, the book The God Particle: If the Universe Is the Answer, what is the question? Lederman Leon, winner of the Nobel Prize for Physics in 1984, the Higgs has been dubbed the God particle in popular culture, though practically all scientists consider it a exaggeration.
One of the main goals of the LHC at CERN in Geneva, Switzerland, whose experiments began in 2010, was to prove the existence of the Higgs and measure its properties which would allow physicists to confirm this cornerstone of modern theory. Previously also tried in LEP (CERN's previous accelerator) and Tevatron (Fermilab, near Chicago in the U.S.).
On July 4, 2012 at CERN is presented preliminary results of joint analysis of data taken by the LHC in 2011 and 2012. The two main accelerator experiments (ATLAS and CMS) announced the observation of a new particle "compatible with the Higgs boson," with a mass of about 125 GeV/c2. The study of the properties of the new particle, to confirm whether it is for the boson or the other possibility, you need even more time and data.
History of Higgs Boson Theory
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| A trace of the hypothetical Higgs boson in a collision simulated proton-proton. |
The Higgs mechanism is a process by which the vector bosons can be obtained explicitly invariant mass without breaking gauge invariance. The proposal for the mechanism of spontaneous broken symmetry was first suggested in 1962 by Philip Warren Anderson and in 1964, developed into a full relativistic model independently and almost simultaneously by three groups of physicists: for François Englert and Robert Brout, The properties of the model were further considered by Guralnik Higgs in 1965 and 1966. The papers showed that when a gauge theory is combined with an additional field that spontaneously breaks the symmetry of the group, the gauge bosons can acquire a finite mass consistently. In 1967, Steven Weinberg and Abdus Salam were the first to apply the Higgs mechanism of electroweak symmetry breaking and showed how a Higgs mechanism could be incorporated into the electroweak theory of Sheldon Glashowde, when it became the model standard particle physics.
The three articles in 1964 were recognized as a milestone for the 50 th anniversary celebration of the Physical Review Letters. Its six authors also were honored for their work with the Award of J. J. Sakurai partículas for Theoretical Physics (the same year a dispute arose, in the event of a Nobel Prize, up to 3 scientists would be eligible, authors accredited with 6 items) .Two of the three articles of PRL (by Higgs and GHK) equations containing the hypothetical field that eventually became known as the Higgs field and hypothetical terms, the Higgs boson. The subsequent article Higgs, 1966, showed the decay of the Higgs mechanism, only a massive boson can decay and the decays can demonstrate the mechanism.
Article of the Higgs boson is massive, and a closing statement Higgs writes that "an essential feature" of the theory "is the prediction of incomplete multiplets of scalar and vector bosons." In the article by GHK boson is massless and massive states are decoupled. The reviews of 2009 and 2011, Guralnik says that the GHK model the Higgs is only an approximation of lowest order, but not subject to any restrictions and gains mass to higher orders, adding that the article was the only GHK to show that there is no massless Goldstone boson in the model and give a complete analysis of the general mechanism of Higgs.
In addition to explaining how the mass is acquired by vector bosons, the Higgs mechanism also predicts the relationship between the masses of W and Z bosons and their couplings among themselves and with the standard model of quarks and leptons. Subsequently, many of these predictions have been verified by precise measurements colliders LEP and SLC, overwhelmingly confirming that some sort of Higgs mechanism takes place in nature, but has not yet figured out exactly why it happens. It is expected that the results of the search for the Higgs boson provides evidence about how this is done in nature.
Cornering the Higgs boson
Before 2000, data collected at the Large Electron Positron collider, (LEP) at CERN for the Higgs boson mass the standard model, had allowed a lower bound of 114. GeV/c2 experimental with a confidence level of 95 % (CL). The same experiment has been a small number of events that could be interpreted as resulting from Higgs boson with a mass of about 115 GeV, just above this cut, but the number of events was insufficient to draw conclusions definitions.
In the Tevatron at Fermilab, there were also ongoing experiments searching for the Higgs boson. From July 2010, the combined data from experiments CDF and DØ at the Tevatron were sufficient to exclude the Higgs boson in the range of 158 -175 GeV/c2 at 95% of Results Preliminary CL.From July 2011 extended the excluded region for the range of 156-177 GeV/c2 at 95% CL.
Data collection and analysis in the search for Higgs intensified since 30 March 2010, when the LHC began operating at 3.5 TeV. Preliminary results of the ATLAS and CMS experiments at the LHC, from July 2011, exclude a Higgs boson of the standard model in the mass range 155-190 and 149-206 GeV/c2 GeV/c221, respectively, 95% CL.
From December 2011, the search had narrowed to about 115-130 GeV region with a specific focus around 125 GeV, where both the ATLAS experiment and the CMS report an excess of events independently, which meant that in this energy range were detected in a number greater than the expected patterns of particles compatible with the decay of a Higgs boson. The data were insufficient to show whether these excesses were due to background fluctuations (ie, random chance or other causes), and their statistical significance was not big enough yet to draw conclusions or even to count formally as an "observation "but the fact that two independent experiments have shown excesses around the same mass was considerable excitement in the physics community particulars.
On December 22, 2011, the collaboration of DØ also reported limits on the Higgs boson within the minimal supersymmetric standard model (MSSM), an extension of the standard model. Proton-antiproton collisions (pp) with a mass energy of 1.96 TeV allowed them to set an upper limit for the production of Higgs boson in MSSM from 90 to 300 GeV and excluding as β> 20-30 for the masses Higgs boson below 180 GeV (as β is the ratio of the two values of the vacuum expectation of the Higgs doublet) .
For all this, in late December 2011, was widely expected that the LHC may provide sufficient data to exclude or confirm the existence of the Higgs boson of the standard model by the end of 2012, when his collection of 2012 data (in energy of 8 TeV) has been examined.
During the first part of 2012, the two working groups continued LHC data updates tentative December 2011, which largely were being confirmed and further developed. Updates were also available in the group was analyzing the final data from the Tevatron. All this continued to highlight and strengthen the same region of 125 GeV, which was showing interesting features.
On July 2, 2012, the ATLAS collaboration further published analysis of data from 2011, excluding boson mass ranges from 111.4 GeV to 116.6 GeV, 119.4 GeV to 122.1 GeV and 129.2 GeV to 541 GeV . They observed an excess of events corresponding to the hypothesized Higgs boson mass around 126 GeV from a local meaning of sigma 2,9. On the same date, the contributions of the DØ and CDF announced further analysis that increased their confidence. The significance of the excess energies between 115-140 GeV now was quantified as standard deviations of 2.9, corresponding to a probability of 1 in 550 to be due to statistical fluctuation. However, this was still far from sigma confidence 5, therefore, the results of the LHC experiments are needed to establish a discovery. They exclude the ranges of the Higgs mass of 100-103 and 147-180 GeV.
Discovery of a new boson
In an internal memo at CERN, the April 21, 2011, is contextualization rumor that LHC physicists had first detected the Higgs boson.
The internal memo talks about the observation of a resonance at 125 GeV, just the kind of phenomenon would be expected if it had been found to detect a Higgs boson in this energy range. However, the high number of observed events, up to thirty times more than those predicted in the standard model of particle physics, surprised themselves investigation.
On June 22, 2012 CERN announced a seminar covering the provisional findings for the year 2012. and soon after began to spread in the media, rumors that this would include a major announcement, but it was unclear if was a stronger signal or a discovery formal. 4 In July 2012, CMS announced the discovery of a boson with mass 125.3 ± 0.6 GeV/c2 with a statistical significance of sigma 4,9,36 and ATLAS of a boson with mass ~ 5.28 sigma 126.5 GeV/c2 This complies with the formal level necessary to announce a new particle that is "consistent with" the Higgs boson, but scientists have not positively identified, pending further analysis and collection of data.
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| Summary of interactions between the particles of the standard model |
On July 4, 2012 CERN announced, with the presence of several scientists, including himself theorist Peter Higgs of the subject, which was detected by the Hadron Collider, a boson with similar characteristics to what is expected from Boson Higgs.38 The data to estimate a minimum value 114.4 GeV experimental mass, consistent with the Higgs boson of the standard model, with a confidence level of 95% .Two independent teams at CERN reached similar conclusions: the CMS with 2,100 scientists and researchers 3.000 Atlas. Experimentally it has been a small number of events at the collider inconclusive LEP at CERN. These have been interpreted as a result of the Higgs bosons, but the evidence is not conclusion, is expected that the Large Hadron Collider, at CERN, can confirm or deny the existence of the boson. If so, They try to understand what type of Higgs boson was.
Rolf Heuer, CERN's director, said "We have a discovery. We have found a new particle consistent with a Higgs boson" and "Matches a Higgs boson as required for the standard model."
Theoretical properties
Many of the properties of the Higgs boson, as described in the standard model are fully determined. As the name suggests, is a boson with spin 0 (which is called a scalar boson). Has no electrical charge or color charge therefore does not interact with the photon or with gluons. However interacts with all particles that have mass model: quarks, charged leptons and the W and Z bosons of the weak interaction. Their coupling constants, which measure intense as each of these interactions are known: its value is greater the greater the mass of the corresponding particle. In the original version of the standard model did not include neutrino masses and, therefore, an interaction between them and the Higgs. Although this could explain the neutrino masses, in principle, its origin may have a nature distant. The Higgs boson is also its own antiparticle.
The standard model does not predict, however, the Higgs mass, which is to be measured experimentally, nor the value of some parameters that depend on this: the Higgs coupling constant to himself as intensely measuring two Higgs bosons interact with each other - or the shelf life. In first approximation, the Higgs mass can take any value. However, the mathematical consistency of the standard model imposes lower bounds between 85 and 130 GeV/c2, and upper bounds between 140 and 650 GeV/c2. The experiments performed at accelerators LEP and Tevatron, and later in the LHC experimental bounds imposed to the value of the Higgs mass-always assuming the standard model behavior. In July 2012 the two experiments by searching for the Higgs LHC, ATLAS and CMS, presented results that exclude mass values outside the range 123-130 GeV/c2 as ATLAS and CMS as 122.5 to 127 GeV/c2 (both ranges with 95% confidence level) .In addition, they announced the discovery of a boson with properties compatible with the Higgs with a mass of about 125-126 GeV/c2. Its half-life with that mass would be about 10-22 s, one part in ten thousand trillion a second.
