Important Particles You Often Hear Of 

Higgs Boson: The God particle

• Higgs boson is another particle that you must have heard of. Back in 1960s scientists predicted the presence of a particle that is responsible for giving mass to other particles like electrons, quarks, neutrinos etc. It was called Higgs boson.
• Higgs boson was discovered in 2012 for which Nobel prize was conferred upon in 2013.
• It is Higgs boson that gives mass to everything.
• It is because of Higgs boson that big-bang happened and everything including you and me were created. This is why it is aptly called the god particle.

Neutrino: The ghostly particles

What are neutrinos?

• Neutrinos as you can see in the chart are fermions, particularly leptons.
• Neutrinos are very light, nearly massless.
• It is a lepton without a charge. (unlike electron which is a lepton with a charge)
• Since they are within nucleus they are released whenever there is decay of the nucleus. (radioactivity)
• Whenever a nucleus decays it can give rise to 3 kinds of radiation alpha, beta and gamma. 
  • Alpha: 2 protons and 2 Neutrons moving at high velocity. (very heavy and very fast so high energy)
  • Beta: Very fast electrons (not heavy but very fast)
  • Gamma: High energy radiation (very fast)
• Neutrinos are released whenever there is beta decay. i.e. whenever nucleus of an atom decays with beta radiation there is an accompanying stream of neutrinos.
• Source: Stars, Supernovae, Galaxies, (even) Nuclear reactors.

What is special about them?

• Being almost massless and chargeless they don’t interact with matter. (unlike a photon which is stopped by a wall, your hand, atmosphere etc. or an electron which is neutralized by a proton)

So everything is transparent to neutrinos. Neutrinos pass through everything unimpeded. Note: Every other sub-atomic particle interacts with matter and is affected by it in some way or the other. (absorb, reflect or deflect)

Solar neutrinos

• Neutrinos are present wherever there is radioactivity.
• Sun or stars in general are engines of nuclear fusion where lighter nuclei are fusing to form heavier nuclei. (helium from hydrogen) In the process they release neutrinos.
• Eg: 4 Hydrogen fuse to form 1 helium in our sun. Hydrogen has 1 proton and 1 electron and no neutron. Helium on the other hand has 2 protons, 2 electrons and 2 neutrons. So in a fusion 4 protons and 4 electrons are 2 protons 2 electrons and 2 neutrons. This happen through a series of steps. (details not important for us). Proton become neutron. In the process releases neutrinos.  Fusion in sun produces 10^38 neutrinos each second. About 10^14  solar neutrinos pass through each square meter of the Earth.
• All the neutrinos that are emitted from the sun is coming to us unimpeded because remember they don’t interact with matter like a photon or electron or proton.
• There are trillion and trillions of neutrinos that are hitting you as you are reading this every second and you don’t even feel it.

Neutrino Astronomy (cutting-edge)

• Neutrinos are one of the gateways to heavens. Electromagnetic and gravitational radiations are others.
• Significance: Unlike electromagnetic waves neutrinos travel unimpeded by matter and thus can reveal information about the source as is.
• Recently we have detected neutrinos from a galaxy for the 1st time and this can tell us a lot about galaxy than a picture we get by detecting light from it. (remember neutrinos come unimpeded unlike photons) ICECUBE is the name of the observatory.

Neutrino Observatories

• All neutrino detectors are built underground, under mountain or under ice. This is because all sub-atomic by-products of radiation are absorbed by earth except neutrinos.
• While neutrinos pass unimpeded by matter, on rare occasions a neutrino will strike a neutron and convert it into a proton. This radioactivity that is induced by the neutrino is the basis of earliest neutrino detectors.
• Note: See table below for names of observatories

Solar-neutrino problem: The ‘missing’ neutrinos

• The amount of solar neutrinos detected by the earlier observatories did not match the calculations for the amount of solar neutrinos. Only about 1/3rd was detected.
• This discrepancy in (missing gap of solar neutrinos) is called the solar neutrino problem.

Neutrino oscillation: Answer to ‘missing’ neutrinos

• Physicists have found that neutrinos come in 3 different varieties. (see Standard Model chart)
• In addition, these neutrinos change from one form to another in their journey (details of how it happens is not important for us)
• But what is important is that only one of these types is produced in the Sun.
• In its journey it is found that about two-thirds of solar neutrinos change its form and become other type. This effect is called neutrino oscillation.
• So, neutrino oscillation is the answer to the ‘missing’ neutrinos’ (actually nothing was ‘missing’, only our detectors were not capable of detecting the other types)
• Now we have observatories that detect all three types of neutrinos. (Sudbury Neutrino Observatory in Canada is one of them)

Important Neutrino Observatories

What Standard Model does not explain?

• Gravity, dark matter, dark energy, reason why there is more matter than anti-matter in the universe.

Sensing using fundamental particles

• The basic principle behind sensing we are familiar with is to study the interaction of photons with matter.
• Instead of photons we may study the interaction of other fundamental particles with matter to sense various features.
• Examples include PET scan which uses beam of positrons instead of photons, Muon tomography which used beam of muons to sense.

PET scan

• Studies the hydrogen distribution in body.

Muon tomography

• Was recently used to study a large cavity in Egyptian pyramid recently.
• Muons being negative particles are deflected by electrons of atoms with large atomic number. If we can measure the amount of deflection we can construct volume maps.
• Besides muon tomography is used in 3-D imaging of large structures. Eg: Recently 3D reconstruction of a nuclear reactor was done using muon tomography.