understanding higgs boson and subatomic particles

7/27/2019 Understanding Higgs Boson and Subatomic Particles

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Understanding Higgs Boson

There aremore than200 subatomic particles known today; not all of them are stable

though--exist of as short a while as a millionth of a second. The action of forces is

understood to be due to exchange of "force" particles. The Standard Model is the one that isagreed upon by most as the complete explanation of subatomic particles categorized

according their forces--the weak, the strong and the electromagnetic. So, it is proposed by

the Standard Model that mass of everything is created due to thing's interaction with the so

called Higgs Field which is everywhere, even in Vacuum. The reason why this field was

thought to exist was upon observing the mass of electron being 40 times that of its original

inside a crystal lattice--under the effect of attraction from surrounding atoms. This same

interaction inside the crystal has a particle equivalent--the phonon; Higgs field has particle

Higgs Boson.

weak force,a fundamental forceof nature that underlies some forms ofradioactivity, governsthe decay of unstable subatomic particlessuch as mesons, and initiates the nuclear fusion

reaction that fuels the Sun. The weak force acts upon all known fermionsi.e., elementary

particles with half-integer values of intrinsic angular momentum, or spin. Particles interact

through the weak force by exchanging force-carrier particles known as the Wand Zparticles.

These particles are heavy, with masses about 100 times the mass of a proton, and it is their

heaviness that defines the extremely short-range nature of the weak force and that makes

the weak force appear weak at the low energies associated with radioactivity. The wholepoint of LHC is in being able to find a particle with mass less than 1 TeV as per theory. This

particle is supposed to most likely be observed with W and Z particles[the particles which are

the reason of existence of Weak Forces] emitted during collision reactions common to all

accelerators. W and Z particles were verified to exist in a CERN experiment back in 1986. The

interesting thing about the W and Z particles is that they are to Weak Forces what photon is

to Electromagnetic Forces and yet the mass of W and Z is some 200,000 times that of

photon[yes, it is not massless for experimental physicist]. This pushed physicists to think

what give a specific mass to a thing. Bosons are either vector or scalars. So, let's first of allread a bit about different sub-atomic particles.

Sub-atomic Particles

First the proton was identified and later the neutron. This seemed to be all that was needed

to explain the composition of the hundreds of different nuclei. But the picture began to get
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complicated as mesons and antiparticles such as the positron were found. More particles

were discovered.

The Coding of Qualitative Information About Particles

Particles seemed to fall into groups and it was convenient to code that qualitative

information about group membership as numbers, usually 0 and 1, 1 if the particle had a

certain characteristic and 0 if not. Charge could be coded as +1, 0 and -1. Heavy particles

associated with the nucleus of atoms such as proton, neutron and mesons were called

baryonsand given a baryon number B equal to 1. This distinguished them from the lighter

particles such as the electron which were called leptonsand had a baryon number equal to 0.

After the neutron was discovered and its properties, except for charge, were found to be so

similar to the proton Werner Heisenberg conjecturedthe proton and neutron were simply

different states of the same particle, Heisenberg characterized the property that

distinguished a proton nucleon from a neutron nucleon as isospinand gave the proton an

isospin of +1/2 and the neutron nucleon an isospin of -1/2.

When certain particle transitions were found not to occur even though they did not violate

the conservation of energy and conservation of charge and the other conservation principles

some physicists conjured up a strangenessproperty of particles and a corresponding

conservation principle, the conservation of strangeness number to explain the

nonoccurrence of transitions. The transitions did not occur because they did not conserve

the strangeness number, again 0 and 1.Further Observations

When small stars die and their source of fusion energy is gone, gravity overcomes the

pressure of their gasses. The atoms are stripped of their electrons, and the nuclei and

electrons are compressed more and more until some other force, if one strong enough exits,

balances gravity.

In white dwarf stars it is the pressure of the electrons that stops the contraction. What is left

is still familiar, a gas of electrons and the nuclei of the atoms. Yet if the star is too massive,

more than about 1.4 times the Sun's mass, the pressure the electrons exert on one another

is not enough to stop gravity. Now electrons and protons collide within the nuclei with

enough energy to form neutrons. Since there are exactly as many electrons as protons in the

star, only neutrons now exist. It is the pressure of the neutrons on one another, physically

staying out of each other's space, that keeps the star from catastrophic collapse under the


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force of its own gravity. The star is a giant nucleus!

With a little more than twice the Sun's mass, the neutron pressure is not enough, and the

star gives in to the inevitable. We do not know of any other force that will stop the collapse

of a very massive star. The result we see from outside is a black hole. What happened to the

neutrons? Neutrons are squeezed down into their component quarks, the fundamentalparticles of matter as we know it.Just as protons, neutrons and electrons make up atoms,

there are subatomic particles that make up protons and neutrons. An electronseems to bestructureless. A protonis made of 2 up quarksand 1 down quark, while 1 up quark and 2down quarks make a neutron.. The electron's antiparticle, its exact opposite, is the positronwith +1 unit of charge. Put the two together in a collision and what do you get? That's right.

Nothing but energy. How do quarks give the proton +1 charge and no charge to theneutron? It turns out if the "up" quark has +2/3 of a unit of charge, and the "down" quark

has -1/3 unit, then it works just right. A neutron has a tiny bit more mass than a proton,

which is why it will decay into a proton and an electron given about 15 minutes outside a

nucleus. Since one kind of quark can change into another kind, and there are a zoo of other

particles as well, this is even more confusing. There are neutrinos, produced inside starswhen fusion occurs. They zip through us and the Earth all the time but hardly ever interact

with baryons. Cold dark matter is abundantly present in our galaxy and others, providing the

glue that holds stars in their orbits. We do not know what it is, but there seems to be more

of it than the baryons that we can touch.neutrino,elementary subatomic particlewith noelectric charge, very little mass, and 1/2unit ofspin. Neutrinos belong to the family of

particles called leptons, which are not subject to the strong force. Rather, neutrinos are

subject to the weak forcethat underlies certain processes of radioactive decay. There are

three types of neutrino, each associated with a charged leptoni.e., the electron, the muon,

and the tauand therefore given the corresponding names electron-neutrino, muon-

neutrino, and tau-neutrino. Each type of neutrino also has an antimattercomponent, called

an antineutrino; the term neutrinois sometimes used in a general sense to refer to both the

neutrino and its antiparticle.

meson,any member of a family ofsubatomic particlescomposed of a quarkand anantiquark. Mesons are sensitive to the strong force, the fundamental interactionthat binds

the components of the nucleus by governing the behaviour of their constituent quarks.

Predicted theoretically in 1935 by the Japanese physicist Yukawa Hideki, the existence of

mesons was confirmed in 1947 by a team led by the English physicist Cecil Frank Powellwith

the discovery of the pi-meson(pion) in cosmic-rayparticle interactions. More than 200

mesons have been produced and characterized in the intervening years, most in high-energy
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particle-accelerator experiments. All mesons are unstable, with lifetimes ranging from 10 8

second to less than 1022second. They also vary widely in mass, from 140 megaelectron

volts (MeV; 106eV) to nearly 10 gigaelectron volts (GeV; 109eV).The decay rate of the pi-

meson into two photons was used to support the hypothesis that quarks can take on one of

three colours.Studies of the competing decay modes ofK-mesons, which occur via the

weak force, have led to a better understanding ofparity(the property of an elementary

particle or physical system that indicates whether its mirror image occurs in nature) and its

non-conservationin the weak interaction. CP violation(the violation of the combined

conservation lawsassociated with charge [C] and parity[P]) was discovered first in the K-

meson system and is under investigation in B-mesons (which contain bottom quarks).

Quarksassociate with one another via the strong forceto make up protonsand neutrons, inmuch the same way that the latter particles combine in various proportions to make up

atomic nuclei. There are six types, or flavours, of quarks that differ from one another in their

mass and charge characteristics. These six quark flavours can be grouped in three pairs: up

and down, charm and strange, and top and bottom. Quarks appear to be true elementary

particles; that is, they have no apparent structure and cannot be resolved into something

smaller. In addition, however, quarks always seem to occur in combination with other quarks

or with antiquarks, their antiparticles, to form all hadronsthe so-called strongly interacting

particles that encompass both baryonsand mesons.The interpretation of quarks as actual

physical entities initially posed two major problems. First, quarks had to have half-integer

spin(intrinsic angular momentum) values for the model to work, but at the same timethey

seemed to violate the Pauli exclusion principle, which governs the behaviour of all particles

(called fermions) having odd half-integer spin. In many of the baryonconfigurations

constructed of quarks, sometimes two or even three identical quarks had to be set in the

same quantumstatean arrangement prohibited by the exclusion principle. Second, quarks

appeared to defy being freed from the particles they made up. Although the forces binding

quarks were strong, it seemed improbable that they were powerful enough to withstand

bombardment by high-energy particle beams from accelerators.

These problems were resolved by the introduction of the concept ofcolour,as formulated inquantum chromodynamics(QCD). In this theory of strong interactions, whose breakthrough

ideas were published in 1973, colour has nothing to do with the colours of the everyday

world but rather represents a property of quarks that is the source of the strong force. The

colours red, green, and blueare ascribed to quarks, and their opposites, antired, antigreen,

and antiblue, are ascribed to antiquarks. According to QCD, all combinations of quarks must

contain mixtures of these imaginary colours that cancel out one another, with the resulting
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particle having no net colour. A baryon, for example, always consists of a combination of

one red, one green, and one blue quark and so never violates the exclusion principle. The

property of colour in the strong force plays a role analogous to that ofelectric chargein the

electromagnetic force, and just as charge implies the exchange ofphotonsbetween charged

particles, so does colour involve the exchange of massless particles called gluonsamong

quarks. Just as photons carry electromagnetic force, gluons transmit the forces that bind

quarks together. Quarks change their colour as they emit and absorb gluons, and the

exchange of gluons maintains proper quark colour distribution.
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understanding higgs boson and subatomic particles

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