1. Bangabasi College, Kolkata
Schizophrenic neutrinos…. What we learn from their Multiple personality disorder ?
Dr. Partha Ghosh
Senior Lecturer
Department of Physics
Bangabasi College, Kolkata

2. What are neutrinos?
Put forward by Pauli (1930) to explain the misleading continuous β-spectrum.
Are emitted along with electrons and share energy along with them.
Are tiny, dimensionless particles with spin ½ and zero electric charge.
Were detected experimentally by Reines & Cowan in 1965.

3. Where do neutrinos appear in the Standard Model ?
MATTER (Fermions)
Quarks : up (u) & down (d), charmed (c) & strange (s), top (t) & bottom (b)
Leptons: electron (e) & electronic neutrino (νe), muon (µ) & muonic neutrino (νµ), taon (τ) and taonic neutrino (ντ)
INTERACTION (Bosons)
Strong: Pion(π) & gluon(g)
Electromagnetic: photon(γ)
Weak: W+,- & Z
Gravitational: graviton
& above all,
The HIGGS

4. Do neutrinos possess Mass?
Helicity or handedness is an important property of elementary particles.
Neutrinos are always left handed & since according to Higgs mechanism, handedness changes when interaction takes place with The Higgs, Standard model shows that neutrinos can never acquire mass.
Otherwise an observer moving with velocity c while overtaking would observe a spinning massive neutrino moving in opposite direction, i.e, would see a right handed neutrino. Since right handed neutrinos are not observed, hence neutrinos should be exactly massless.
Right handed counterparts are actually antineutrinos.

5. BUT, NOW THE SCENARIO IS OTHERWISE !
The Super-Kamiokande (SK2) experiment in Japan (1998) and Sudbury Neutrino Observatory (SNO) in Canada were detecting νµ and νe from cosmic rays.
The neutrinos reacted with water molecules in the detector to emit fast muons/electrons, producing Cherenkov radiation.Sensitive PMT’s could detect them, but there was a directional asymmetry.
These experiments have shown that neutrinos OSCILLATE, i.e, νe↔νµ↔ντ, changing their identity from one form to another.And OSCILLATION would not have been possible if neutrinos were exactly mass-less!

6. WHAT WAS FOUND ACTUALLY ?
Expected value N(νµ) ≈ 2N(νe) was not observed in the atmospheric neutrinos coming from all directions, ratio was nearly equal to unity for some.
Anomaly could not be resolved even after thorough revision of flux calculation, reaction rates, detector limitations or consideration of some extra-terrestrial events.
There was a zenith angle dependence of νµ flux, larger deficit was in the up coming direction.
The disappearance of νµ is proportional to their flight distance and inversely proportional to their energy.
Discrepancy with theory was also noticed among solar, reactor and beam neutrinos.

7. NEUTRINO OSCILLATION, FINALLY….
The strange disappearance of some kind of neutrinos can be attributed to a hitherto unknown phenomenon, NEUTRINO OSCILLAIONS.
Given proper conditions, a neutrino of one kind can change into a different one. Not only that, it transforms back and forth as it sails along its path.
The frequency of this continuous makeover depends upon their energy, as well as the distance traveled by them.
This bizarre duality can be understood by a uniquely simple Q.M calculation, assuming that neutrinos are indeed MASSIVE, instead of being MASSLESS.

8. THE QUANTUM MECHANICS BEHIND…..

9. IMPLICATIONS OF MASSIVE NEUTRINOS
The masses of neutrinos are very small to be measured accurately, what we have till now is the upper limit of their mass differences.
The Standard Model has suffered a blow and needs to be revisited.
The concept of Dirac neutrinos and Majorana neutrinos were put forward to explain how they gain mass via Higgs mechanism.
An extension from Superstring Theory was also proposed, which conceptualizes the right handed neutrinos to be present, but not in the 4-D space-time as per our sense of perception, but in extra dimensions. Presence of both kinds allow them to be massive.
The sacred distinction between matter and antimatter is also being proposed to be abandoned, so that inter conversion of neutrinos to antineutrinos and vice-versa is allowed. Under that circumstances, neutrino mass may reveal why in our Universe, matter is in excess over antimatter, or WHY DO WE EXIST, after all.

10. Thanx for bearing with me…..
Nevertheless, a lot more theory and experiment needs to be done, & ….We have miles to go, miles to go before we sleep…..
Thanx for bearing with me…..