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The Higgs boson is the last particle in the [[Standard Model]] of [[particle physics]] which has not yet been observed. Its existence was first proposed by Prof. Peter Higgs of Edinburgh University in 1964 as a means to explain the origin of the masses of the elementary particles by the introduction of an fundamental scalar field. This gives all the fundamental particles mass via a process of spontaneous symmetry breaking called the ''Higgs Mechanism''.
{{subpages}}
The '''Higgs boson''' is a massive spin-0 [[elementary particle]] in the [[Standard Model]] of [[particle physics]] that plays a key role in explaining the mass of other elementary particles. The experimental discovery of a particle consistent with the Higgs was announced in a seminar on July 4, 2012.<ref name=Higgs/><ref name=CERN/> This particle was first proposed by Professor [[Peter Higgs]] of [[University of Edinburgh|Edinburgh University]] in 1964 as a means to explain the origin of the masses of the elementary particles by the introduction of an fundamental scalar field. This gives all the fundamental particles mass via a process of spontaneous symmetry breaking called the ''Higgs Mechanism''. The Higgs boson was popularised as the "God particle" by the [[Nobel Prize]]-winning [[physicist]] [[Leon M. Lederman]] in his 1993 popular science book ''The God Particle: If the Universe Is the Answer, What is the Question?'' co-written with science writer Dick Teresi.<ref name=Lederman/><ref name=Fermilab/>


==The Higgs mechanism==


==The Higgs Mechanism==
In the original [[Standard Model]], all bosons were massless. Since the bosons for the Weak interaction have mass, that left an unanswered question in the original [[Standard Model]]. So a scalar field was added, called the Higgs field. The quantum of the Higgs field is called the Higgs boson and it was predicted to have mass.


The Higgs Mechanism is vital in explaining the masses of the electroweak W and Z bosons. To understand the problem in giving mass to the vector bosons let us first consider the QED sector of the Standard Model Lagrangian.
A verbal explanation of how the Weak interaction bosons have mass is as follows. In the [[Standard Model]], the theory that explains experimental observations of [[elementary particle]]s, the [[Quantum chromodynamics|QCD vacuum]] has less symmetry than the force laws governing fundamental interactions.<ref name=Altarelli/> This reduced symmetry situation is not unique, and is found in many systems, among them the ground state of [[ferroelectric]]s and of [[superconductor]]s. In these systems, the greater symmetry of nature is exhibited "on average" by a mosaic of sub-domains individually with reduced symmetry, but statistically exhibiting the greater symmetry of the interactions when all the domains are viewed as an ensemble.


::<math>\mathcal{L}_{QED} = \overline{\psi}(i \gamma^\mu\partial_\mu - m)\psi - j^\mu_{em} A_\mu - \frac{1}{4} F_{\mu\nu}F^{\mu\nu}</math>
In the case of superconductors, the photons, whose exchange mediates the electromagnetic interactions between [[Cooper pairs]], cannot propagate freely because of the presence everywhere of electric charge. In a similar fashion, the Higgs mechanism predicts the symmetry of electroweak interactions is broken by interactions among Higgs bosons in the vacuum, leading (among other things) to non-zero masses for the ''W<sup><big>±</big></sup>'' and ''Z'' weak bosons. In fact, the properties of mass and electric charge stem from interaction with the reduced symmetry vacuum, and are not a result of direct interactions between particles.<ref name=Tully/>


Now consider how things will change if we perform a local phase rotation such that:
==Search for the Higgs boson==
Studies using the Fermilab's [[Tevatron|Tevatron collider]] suggest a range for the mass of the Higgs boson between 115-150 GeV (gigaelectronvolts), assuming the correctness of the Standard Model of particle physics. See review of the experiments:<ref name=Monig/> The observed mass was placed at 125.3±0.6 GeV.<ref name=CERN/>


::<math>\psi(x) \rightarrow \psi'(x) = e^{i \alpha(x)} \psi(x)</math>
The Higgs particle was not made in the Tevatron collider, but by using the high energies of the [[Large Hadron Collider]] in Geneva. This discovery was an early goal of this major international project.<ref name=LHC/> The magnitude of this effort is huge:<ref name=Higgs1/>
::"The data presented yesterday are the latest from the $10.5 billion [[Large Hadron Collider]], a 27-kilometer (17-mile) circumference particle accelerator buried on the border of France and Switzerland. CERN has 10,000 scientists working on the project..."


We would expect the Langrangian to remain invariant under such a rotation since to do otherwise would mean that if I chose a different phase than someone else where we could get different physics results.
The discovery was a bit anticlimactic, as theory has incorporated the Higgs boson for decades. As said by Stephen Hawking:<ref name=HawkingBBC/><ref name=Hawking/>
::“This is an important result and should earn Peter Higgs the Nobel Prize” the physicist predicted. “But it is a pity in a way, because the great advances in physics have come from experiments that gave results we didn’t expect.”


Further experiments will explore the complete mechanism.


==Search for the Higgs Boson==
==References==
{{Reflist|refs=
<ref name=Altarelli>
{{cite book |title=Elementary Particles (Landolt-Börnstein: Numerical Data and Functional Relationships in Science and Technology - New Series / Elementary Particles, Nuclei and Atoms) Volume 21, Subvolume A |author=Guido Altarelli |chapter=Chapter 2: Gauge Theories and the Standard Model |url=http://books.google.com/books?id=lBCyYTobfJ8C&pg=PT19#v=onepage&q&f=false |isbn=3540742026 |year=2008 |publisher=Springer  |pages=p. 2-3
|quote=the fundamental state of minimum energy, the vacuum, is not unique and there is a continuum of degenerate states that all together respect the symmetry...}}
</ref>
 
<ref name=CERN>
{{cite web |title=CERN experiments observe particle consistent with long-sought Higgs boson |date=4 July 2012 |publisher=CERN press office |accessdate=2012-07-05 |url=http://press.web.cern.ch/press/PressReleases/Releases2012/PR17.12E.html}}
</ref>
 
<ref name=Fermilab>
{{cite journal |author=Ivan Semeniuk |date=17 February 2009 |url=http://www.newscientist.com/article/dn16618-fermilab-closing-in-on-the-god-particle.html |title=Fermilab 'closing in' on the God particle |journal=New Scientist}}
</ref>
 
<ref name=Hawking>
{{cite web |url=http://www.slashgear.com/higgs-boson-costs-stephen-hawking-100-bet-04237061/ |author=Chris Davies |date=Jul 4th, 2012 |publisher=Slash Gear |title= Higgs boson costs Stephen Hawking $100 bet |accessdate=2012-07-05}}
</ref>
 
<ref name=HawkingBBC>
{{cite web |url=http://www.bbc.co.uk/news/science-environment-18708626 |date=July 4th, 2012 |publisher=BBC |title= Stephen Hawking on Higgs: 'Discovery has lost me $100' |author=Interview with BBC's Pallab Ghosh |accessdate=2012-07-06}}
</ref>
 
<ref name=Higgs>
Announced at a CERN seminar in Geneva. See {{cite web |title=Higgs boson discovery brings scientists close to understanding mass |publisher=Washington Post |url=http://www.washingtonpost.com/business/higgs-boson-discovery-brings-scientists-lose-to-understanding-mass/2012/07/05/gJQA23iQPW_story.html |author=Thomas Mulier and Jason Gale |accessdate=2012-07-05 }}
</ref>


<ref name=Higgs1>
Quote from {{cite web |title=Higgs boson discovery brings scientists close to understanding mass |publisher=Washington Post |url=http://www.washingtonpost.com/business/higgs-boson-discovery-brings-scientists-lose-to-understanding-mass/2012/07/05/gJQA23iQPW_story.html |author=Thomas Mulier and Jason Gale |accessdate=2012-07-05 }}
</ref>


==References==
<ref name=Lederman>
<references />
{{cite book |author=Leon M. Lederman and R Teresi |year=1993 |url=http://books.google.com/books?id=-v84Bp-LNNIC&printsec=frontcover#v=onepage&q&f=false |title=The God Particle: If the Universe Is the Answer, What is the Question?|publisher= Dell |isbn= 0-385-31211-3}}
</ref>
 
<ref name=LHC>
{{cite web |title=Why do particles have mass? |work=LHC 'big questions' |url=http://www.lhc.ac.uk/17738.aspx  |publisher=Science and Technology Facilities Council |year=2012 |accessdate=2012-07-06}}
</ref>
 
<ref name=Monig>
{{cite journal |author=Klaus Mönig |date=February 12, 2010 |url=http://physics.aps.org/articles/v3/14 |title=Viewpoint: First bounds on the Higgs boson from hadron colliders |journal=Physics |volume=3 |pages=14 |doi=10.1103/Physics.3.14 }} [http://physics.aps.org/pdf/Physics.3.14.pdf Download PDF.]
</ref>
 
<ref name=Tully>
{{cite book |title=Elementary Particle Physics in a Nutshell |author=Christopher G. Tully |url=http://books.google.com/books?id=ZBA2UgZ-MtIC&pg=PA5 |pages=p. 5 |isbn=1400839351 |year=2011 |publisher=Princeton University Press}}
</ref>


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The Higgs boson is a massive spin-0 elementary particle in the Standard Model of particle physics that plays a key role in explaining the mass of other elementary particles. The experimental discovery of a particle consistent with the Higgs was announced in a seminar on July 4, 2012.[1][2] This particle was first proposed by Professor Peter Higgs of Edinburgh University in 1964 as a means to explain the origin of the masses of the elementary particles by the introduction of an fundamental scalar field. This gives all the fundamental particles mass via a process of spontaneous symmetry breaking called the Higgs Mechanism. The Higgs boson was popularised as the "God particle" by the Nobel Prize-winning physicist Leon M. Lederman in his 1993 popular science book The God Particle: If the Universe Is the Answer, What is the Question? co-written with science writer Dick Teresi.[3][4]

The Higgs mechanism

In the original Standard Model, all bosons were massless. Since the bosons for the Weak interaction have mass, that left an unanswered question in the original Standard Model. So a scalar field was added, called the Higgs field. The quantum of the Higgs field is called the Higgs boson and it was predicted to have mass.

A verbal explanation of how the Weak interaction bosons have mass is as follows. In the Standard Model, the theory that explains experimental observations of elementary particles, the QCD vacuum has less symmetry than the force laws governing fundamental interactions.[5] This reduced symmetry situation is not unique, and is found in many systems, among them the ground state of ferroelectrics and of superconductors. In these systems, the greater symmetry of nature is exhibited "on average" by a mosaic of sub-domains individually with reduced symmetry, but statistically exhibiting the greater symmetry of the interactions when all the domains are viewed as an ensemble.

In the case of superconductors, the photons, whose exchange mediates the electromagnetic interactions between Cooper pairs, cannot propagate freely because of the presence everywhere of electric charge. In a similar fashion, the Higgs mechanism predicts the symmetry of electroweak interactions is broken by interactions among Higgs bosons in the vacuum, leading (among other things) to non-zero masses for the W± and Z weak bosons. In fact, the properties of mass and electric charge stem from interaction with the reduced symmetry vacuum, and are not a result of direct interactions between particles.[6]

Search for the Higgs boson

Studies using the Fermilab's Tevatron collider suggest a range for the mass of the Higgs boson between 115-150 GeV (gigaelectronvolts), assuming the correctness of the Standard Model of particle physics. See review of the experiments:[7] The observed mass was placed at 125.3±0.6 GeV.[2]

The Higgs particle was not made in the Tevatron collider, but by using the high energies of the Large Hadron Collider in Geneva. This discovery was an early goal of this major international project.[8] The magnitude of this effort is huge:[9]

"The data presented yesterday are the latest from the $10.5 billion Large Hadron Collider, a 27-kilometer (17-mile) circumference particle accelerator buried on the border of France and Switzerland. CERN has 10,000 scientists working on the project..."

The discovery was a bit anticlimactic, as theory has incorporated the Higgs boson for decades. As said by Stephen Hawking:[10][11]

“This is an important result and should earn Peter Higgs the Nobel Prize” the physicist predicted. “But it is a pity in a way, because the great advances in physics have come from experiments that gave results we didn’t expect.”

Further experiments will explore the complete mechanism.

References

  1. ↑ Announced at a CERN seminar in Geneva. See Thomas Mulier and Jason Gale. Higgs boson discovery brings scientists close to understanding mass. Washington Post. Retrieved on 2012-07-05.
  2. ↑ 2.0 2.1 CERN experiments observe particle consistent with long-sought Higgs boson. CERN press office (4 July 2012). Retrieved on 2012-07-05.
  3. ↑ Leon M. Lederman and R Teresi (1993). The God Particle: If the Universe Is the Answer, What is the Question?. Dell. ISBN 0-385-31211-3. 
  4. ↑ Ivan Semeniuk (17 February 2009). "Fermilab 'closing in' on the God particle". New Scientist.
  5. ↑ Guido Altarelli (2008). “Chapter 2: Gauge Theories and the Standard Model”, Elementary Particles (Landolt-Börnstein: Numerical Data and Functional Relationships in Science and Technology - New Series / Elementary Particles, Nuclei and Atoms) Volume 21, Subvolume A. Springer, p. 2-3. ISBN 3540742026. “the fundamental state of minimum energy, the vacuum, is not unique and there is a continuum of degenerate states that all together respect the symmetry...” 
  6. ↑ Christopher G. Tully (2011). Elementary Particle Physics in a Nutshell. Princeton University Press, p. 5. ISBN 1400839351. 
  7. ↑ Klaus Mönig (February 12, 2010). "Viewpoint: First bounds on the Higgs boson from hadron colliders". Physics 3: 14. DOI:10.1103/Physics.3.14. Research Blogging. Download PDF.
  8. ↑ Why do particles have mass?. LHC 'big questions'. Science and Technology Facilities Council (2012). Retrieved on 2012-07-06.
  9. ↑ Quote from Thomas Mulier and Jason Gale. Higgs boson discovery brings scientists close to understanding mass. Washington Post. Retrieved on 2012-07-05.
  10. ↑ Interview with BBC's Pallab Ghosh (July 4th, 2012). Stephen Hawking on Higgs: 'Discovery has lost me $100'. BBC. Retrieved on 2012-07-06.
  11. ↑ Chris Davies (Jul 4th, 2012). Higgs boson costs Stephen Hawking $100 bet. Slash Gear. Retrieved on 2012-07-05.
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