Thursday, December 13, 2012

The Higgs boson or Higgs particle

CMS Higgs-event.jpg

The Higgs boson or Higgs particle is an elementary particle in the Standard Model of physics. All other particles in the Standard Model have been seen in experiments, but the Higgs boson, first predicted to exist in the 1960s, is difficult to create and detect. It may have finally been discovered in July 2012, but it will take further testing to know for sure. Its discovery (or confirmation of its non-existence) would be monumental[6][7] because it would finally prove the existence of the Higgs field, the simplest[8] and longest standing explanation of how the electroweak interaction divides into electromagnetism and the weak force (known as "symmetry breaking"). Its discovery would also affect human understanding of the universe, confirm how fundamental particles acquire mass, validate the final unconfirmed part of the Standard Model, guide other theories and discoveries in particle physics, and open up "new" physics beyond current theories.[9]
This unanswered question in fundamental physics is of such importance that it led to a decades-long search for the Higgs boson and finally the construction of one of the most expensive and complex experimental facilities to date, theLarge Hadron Collider[10] able to create and study Higgs bosons (if they exist) and related questions. On 4 July 2012, two separate experimental teams at the Large Hadron Collider announced that they had each independently confirmed the existence of a previously unknown boson of mass between 125 and 127 GeV/c2 which physicists suspected eventually will be agreed to be a Higgs boson,[7] and whose known behaviour (up to December 2012) closely matches a Standard Model Higgs boson.
The Higgs boson is named after Peter Higgs, who—along with Brout and Englert, and with GuralnikHagen, and Kibble ("GHK")—proposed the mechanism that suggested such a particle in 1964.[11][12][13] Higgs was the only one who emphasised the existence of the particle and calculated some of its properties.[14] Although Higgs' name has become ubiquitous in this theory, the resulting electroweak model (the final outcome) involved several researchers between about 1960 and 1972, who each independently developed different parts. In mainstream media the Higgs boson is often referred to as the "God particle," after the title of Leon Lederman's book on the topic (1993). However, the epithet is strongly disliked by many physicists, who regard it as both inappropriate and misleading sensationalism.[15][16]

In the Standard Model, the Higgs particle is a boson with no spinelectric charge, or color charge. It is also very unstable, decaying into other particles almost immediately. The Higgs particle is a quantum excitation of one component of the four component Higgs field, a scalar field with two neutral and two electrically charged components, forming a complex doublet of the weak isospin SU(2) symmetry, and with U(1) weak hypercharge of +½ (or +1 depending on convention). The field has a "Mexican hat" shaped potential and takes on a nonzero strength everywhere (including otherwise empty space) which breaks the weak isospin symmetry in its vacuum state. When this happens, three of the four Higgs field components are "absorbed" by the originally massless SU(2) and U(1) gauge bosons (this is the "Higgs mechanism") to become the longitudinal components of the now-massive W and Z bosons. The fourth electrically neutral component separately couples to other particles known as fermions (via Yukawa couplings), causing these to acquire mass as well. The fourth component's quantum excitations manifest as the Higgs boson. Some versions of the theory predict more than one kind of Higgs fields and bosons. Alternative "Higgsless" models would be considered if the Higgs boson is not discovered.

Non-technical overview

In particle physicselementary particles and forces give rise to the world around us. Nowadays, physicists explain the behaviour of these particles and how they interact using the Standard Model—a widely accepted and "remarkably" accurate[17]:22 framework based on gauge invariance and symmetries, believed to explain almost everything in the world we see, other than gravity.[18]
But by around 1960 all attempts to create a gauge invariant theory for two of the four fundamental forces had constantly failed at one crucial point: although gauge invariance seemed extremely important, including it seemed to make any theory of electromagnetism and the weak force go haywire, by demanding that either many particles with mass were massless or that non-existent forces and massless particles had to exist. Scientists had no idea how to get past this point.
Work done on superconductivity and symmetry breaking around 1960 led physicist Philip Anderson to suggest in 1962 a new kind of solution that might hold the key. In 1964 a theory was created by 3 different groups of researchers, that showed the problems could be resolved if an unusual kind of energy field existed throughout the universe. It would cause existing particles to acquire mass instead of new massless particles being formed. By 1972 it had been developed into a comprehensive theory and proved capable of giving "sensible" results. Although there was not yet any proof of such a field, calculations consistently gave answers that were confirmed by experiments, so scientists eventually began to believe this might be true and to search for proof whether or not such a field existed in nature.
If this field did exist, this would be a monumental discovery for science and human knowledge, and is expecte to open doorways to new knowledge in many fields. If not then other, more complicated, theories would need to be explored. The easiest proof whether or not the field existed was by searching for a new kind of particle it would have to give off, known as "Higgs bosons" or the "Higgs particle" (after Peter Higgs who first predicted them in 1964). These would be extremely difficult to find, so it was only many years later that experimental technology became sophisticated enough to answer the question.
While several symmetries in nature are spontaneously broken through a form of the Higgs mechanism, in the context of the Standard Model the term "Higgs mechanism" almost always means symmetry breaking of the electroweak field. It is considered proven, but the exact cause has been exceedingly difficult to prove. The Higgs boson's existence would finally after 50 years confirm that the Standard Model is essentially correct and allow further development, while its non-existence would confirm that other theories are needed instead.

AIP-Sakurai-best.JPGHiggs, Peter (1929) cropped.jpg

Recognition and awards

There has been considerable discussion of how to allocate the credit for a proven Higgs boson, made more pointed by its near-certain Nobel prize in future, and the very wide basis of people entitled to consideration. These include a range of theoreticians who made the Higgs mechanism theory possible, the theoreticians of the 1964 PRL papers (including Higgs himself), the theoreticians who derived from these, a working electroweak theory and the Standard Model itself, and also the experimentalists at CERN and other institutions who made possible the proof of the Higgs field and boson in reality. The Nobel prize has a limit of 3 persons to share an award, and some possible winners are already prize holders for other work, or are deceased (the prize is only awarded to persons in their lifetime). Existing prizes for works relating to the Higgs field, boson, or mechanism include: -
  • Nobel Prize in Physics (1979) - Weinberg and Salam (and a co-creator), for "contributions to the theory of the unified weak and electromagnetic interaction between elementary particles" [99]
  • Nobel Prize in Physics (1999) - 't Hooft and Veltman, "for elucidating the quantum structure of electroweak interactions in physics" [100]
  • Nobel Prize in Physics (2008) - Nambu (shared), "for the discovery of the mechanism of spontaneous broken symmetry in subatomic physics" [27]
  • J. J. Sakurai Prize for Theoretical Particle Physics (2010) - for the original 1964 PRL papers; these were also recognition as "landmark" papers by PRL in its 50 year review (described above)
  • Wolf Prize (2004) - Englert, Brout, and Higgs
  • Weinberg's 1967 paper "A model of Leptons" (which was cited only twice in its first three years) holds the position of most cited paper in particle physics, as at 2012.[101]
The original 1964 papers' authors have not yet been awarded a Nobel Prize, nor have other theorists and experimentalists, although a further Nobel prize is widely expected to be awarded if predictions regarding the Higgs field and boson eventually prove correct and the Higgs boson's existence is proven.[102][103]
Following reported observation of the Higgs-like particle in July 2012, several Indian media outlets reported on the supposed neglect of credit to Indian physicist Satyendra Nath Bose after whose work in the 1920s the class of particles "bosons" is named,[104][105] although physicists have described Bose's connection to the discovery as tenuous.[106]

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