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Wednesday, May 21, 2014

SIMPLIFIED : WHAT IS HIGGS BOSON?

The first post on this blog was quite a while ago/(Here's the link in case you want to take a look.) The post had all the known and easy facts but for a few days,I really wanted to do a post with more depth and penetration into the topic.In all the websites that I have checked,it might be quite difficult for some to understand the actual fact.Thanks to CERN's website (www.cern.org) that this concept indeed got so much more well-explained to me.So,in this post,I will be explaining step by step,asking questions in every step to get the whole concept easier.Hope that this helps!

Question 1 : WHAT IS HIGGS BOSON?

On 4 July 2012, the ATLAS and CMS experiments at CERN's Large Hadron Collider announced they had each observed a new particle in the mass region around 126 GeV. This particle is consistent with the Higgs boson but it will take further work to determine whether or not it is the Higgs boson predicted by the Standard Model. The Higgs boson, as proposed within the Standard Model, is the simplest manifestation of the Brout-Englert-Higgs mechanism. Other types of Higgs bosons are predicted by other theories that go beyond the Standard Model.


Protons collide at 14 TeV in this simulation from CMS, producing four muons. Lines denote other particles, and energy deposited is shown in blue (Image: CMS)

Question 2 : WHAT IS THE BROUT-ENGLERT-HIGGS MODEL?


In the 1970s, physicists realized that there are very close ties between two of the four fundamental forces – the weak force and the electromagnetic force. The two forces can be described within the same theory, which forms the basis of the Standard Model. This “unification” implies that electricity, magnetism, light and some types of radioactivity are all manifestations of a single underlying force known as the electroweak force.
The basic equations of the unified theory correctly describe the electroweak force and its associated force-carrying particles, namely the photon, and the W and Z bosons, except for a major glitch. All of these particles emerge without a mass. While this is true for the photon, we know that the W and Z have mass, nearly 100 times that of a proton. Fortunately, theorists Robert Brout, François Englert and Peter Higgs made a proposal that was to solve this problem. What we now call the Brout-Englert-Higgs mechanism gives a mass to the W and Z when they interact with an invisible field, now called the “Higgs field”, which pervades the universe.

A Higgs boson decays to 4 leptons in this collision recorded by the ATLAS detector on 18 May 2012 (Image: ATLAS)

Question 3 : How would you explain that? 

Just after the big bang, the Higgs field was zero, but as the universe cooled and the temperature fell below a critical value, the field grew spontaneously so that any particle interacting with it acquired a mass. The more a particle interacts with this field, the heavier it is. Particles like the photon that do not interact with it are left with no mass at all. Like all fundamental fields, the Higgs field has an associated particle – the Higgs boson. The Higgs boson is the visible manifestation of the Higgs field, rather like a wave at the surface of the sea.



The Big Bang Explosion

Question 4 : What is Weak Force?

Weak force, a fundamental force of nature that underlies some forms of radioactivity, governs the decay of unstable subatomic particles such as mesons, and initiates the nuclear fusion reaction that fuels the Sun. The weak force acts upon all known fermions—i.e., elementary particles with half-integer values of intrinsic angular momentum, or spin. Credit : (www.britannica.com)

Question 5 : What is Standard Model?

Matter particles

All matter around us is made of elementary particles, the building blocks of matter. These particles occur in two basic types called quarks and leptons. Each group consists of six particles, which are related in pairs, or “generations”. The lightest and most stable particles make up the first generation, whereas the heavier and less stable particles belong to the second and third generations. All stable matter in the universe is made from particles that belong to the first generation; any heavier particles quickly decay to the next most stable level. The six quarks are paired in the three generations – the “up quark” and the “down quark” form the first generation, followed by the “charm quark” and “strange quark”, then the “top quark” and “bottom (or beauty) quark”. Quarks also come in three different “colours” and only mix in such ways as to form colourless objects. The six leptons are similarly arranged in three generations – the “electron” and the “electron neutrino”, the “muon” and the “muon neutrino”, and the “tau” and the “tau neutrino”. The electron, the muon and the tau all have an electric charge and a sizeable mass, whereas the neutrinos are electrically neutral and have very little mass.

Forces and carrier particles

There are four fundamental forces at work in the universe: the strong force, the weak force, the electromagnetic force, and the gravitational force. They work over different ranges and have different strengths. Gravity is the weakest but it has an infinite range. The electromagnetic force also has infinite range but it is many times stronger than gravity. The weak and strong forces are effective only over a very short range and dominate only at the level of subatomic particles. Despite its name, the weak force is much stronger than gravity but it is indeed the weakest of the other three. The strong force, as the name suggests, is the strongest of all four fundamental interactions.
Three of the fundamental forces result from the exchange of force-carrier particles, which belong to a broader group called “bosons”. Particles of matter transfer discrete amounts of energy by exchanging bosons with each other. Each fundamental force has its own corresponding boson – the strong force is carried by the “gluon”, the electromagnetic force is carried by the “photon”, and the “W and Z bosons” are responsible for the weak force. Although not yet found, the “graviton” should be the corresponding force-carrying particle of gravity. The Standard Model includes the electromagnetic, strong and weak forces and all their carrier particles, and explains well how these forces act on all of the matter particles. However, the most familiar force in our everyday lives, gravity, is not part of the Standard Model, as fitting gravity comfortably into this framework has proved to be a difficult challenge. The quantum theory used to describe the micro world, and the general theory of relativity used to describe the macro world, are difficult to fit into a single framework. No one has managed to make the two mathematically compatible in the context of the Standard Model. But luckily for particle physics, when it comes to the minuscule scale of particles, the effect of gravity is so weak as to be negligible. Only when matter is in bulk, at the scale of the human body or of the planets for example, does the effect of gravity dominate. So the Standard Model still works well despite its reluctant exclusion of one of the fundamental forces.

So far so good, but...


...it is not time for physicists to call it a day just yet. Even though the Standard Model is currently the best description there is of the subatomic world, it does not explain the complete picture. The theory incorporates only three out of the four fundamental forces, omitting gravity. There are also important questions that it does not answer, such as “What is dark matter?”, or “What happened to the antimatter after the big bang?”, “Why are there three generations of quarks and leptons with such a different mass scale?” and more. Last but not least is a particle called the Higgs boson, an essential component of the Standard Model.

Question 6 : What is Strong Force?

Strong force, a fundamental interaction of nature that acts between subatomic particles of matter. The strong force binds quarks together in clusters to make more-familiar subatomic particles, such as protons and neutrons. It also holds together the atomic nucleus and underlies interactions between all particles containing quarks.(Credit : www.britannica.com)

Question 7 : What is a W boson?

Discovered in 1983, the W boson is a fundamental particle. Together with the Z boson, it is responsible for the weak force, one of four fundamental forces that govern the behaviour of matter in our universe. Particles of matter interact by exchanging these bosons, but only over short distances.
The W boson, which is electrically charged, changes the very make up of particles. It switches protons into neutrons, and vice versa, through the weak force, triggering nuclear fusion and letting stars burn. This burning also creates heavier elements and, when a star dies, those elements are tossed into space as the building blocks for planets and even people.
The weak force was combined with the electromagnetic force in theories of a unified electroweak force in the 1960s, in an effort to make the basic physics mathematically consistent. But the theory called for the force-carrying particles to be massless, even though scientists knew the theoretical W boson had to be heavy to account for its short range. Theorists accounted for the mass of the W by introducing another unseen mechanism. This became known as the Higgs mechanism, which calls for the existence of a Higgs boson.

As announced in July of 2012 at CERN, scientists have discovered a boson that looks much like the particle predicted by Peter Higgs, among others. While this boson is not yet confirmed as the Higgs boson predicted to make sense of the electroweak force, the W boson had a large part in its discovery.


The W boson

Question 8 : What is a Z boson?


Discovered in 1983 by physicists at the Super Proton Synchrotron at CERN, the Z boson is a neutral elementary particle. Like its electrically charged cousin, the W, the Z boson carries the weak force.
The weak force is essentially as strong as the electromagnetic force, but it appears weak because its influence is limited by the large mass of the Z and W bosons. Their mass limits the range of the weak force to about 10-18 metres, and it vanishes altogether beyond the radius of a single proton.
Enrico Fermi was the first to put forth a theory of the weak force in 1933, but it was not until the 1960s that Sheldon Glashow, Abdus Salam and Steven Weinberg developed the theory in its present form, when they proposed that the weak and electromagnetic forces are actually different manifestations of one electroweak force. 
By emitting an electrically charged W boson, the weak force can cause a particle such as the proton to change its charge by changing the flavour of its quarks. In 1958, Sidney Bludman suggested that there might be another arm of the weak force, the so-called "weak neutral current," mediated by an uncharged partner of the W bosons, which later became known as the Z boson.

This image taken by the UA1 experiment at CERN on 30 April 1983 was later confirmed to be the first detection of a Z particle (Image: UA1/CERN)
Question 9 : Who received the Nobel Prize for the discovery?
Peter Higgs,Francois Englert.Robert Brout died in 2011,thus being unable to receive the Nobel Prize.

Robert Brout


François Englert (left) and Peter Higgs at CERN on 4 July 2012, on the occasion of the announcement of the discovery of a Higgs boson by the ATLAS and CMS experiments (Image: Maximilien Brice/CERN)


Question 10 : Why is the discovery of Higgs Boson so significant?
This is because this would prove to be the one of the greatest successes in Particle Physics.The Higgs Boson explains the Higgs field,which would help us in understanding the major secrets of the universe.

Members of the ATLAS and CMS collaborations react with jubilation at CERN as the announcement is made (Image: Maximilien Brice/CERN)
My Caption (A nerd's Caption) : Oh Wow! Look there - nerds!

Credits : www.cern.org
www.britannica.com
www.wikipedia.org
Maximillan Brice (CERN)
physics.edu.bu
ATLAS
CMS
UA1
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