Recent findings of neutrino experiments (as of August 2015)

neutrino-flavors_web_CreditT2KIn each second, a trillion naturally occurring neutrinos from the sun and other bodies in the galaxy pass through our bodies but they have no effect because neutrinos rarely interact with matter. In the details explained below you will see how rare the neutrino interaction is. You will also read that human beings have learned to generate intense beams of neutrinos. In recent times the technology have improved to a point where we can generate trillions of neutrinos per second. But, the more interesting story is our ability to detect the neutrinos. Neutrino physics is the future of particle physics. The findings of the neutrino experiments are probably more relevant than the findings of the LHC (Large Hadron Collider) experiments when it comes to answering the most fundamental questions. I sincerely believe that neutrino is the key.

Observations of neutrino oscillations (transformations)

The NOvA experiment started collecting data and reported its first observations of neutrino oscillations. In the NOvA experiment, FERMILAB generates an intense beam of muon type neutrinos. The neutrino detector is placed 500 miles away in Ash River (Minnesota). The detector weighs 14 tons and it is 50 feet tall, 50 feet wide, and 200 feet long. FERMILAB generates trillions of muon type neutrinos per second but the detector can see only a few hundred of those per year because neutrinos normally do not interact with matter. Physicists devised ingenuous methods to detect those rare events when the neutrino interacts with matter.

NOVA-Looking-North-large

There is growing evidence that neutrinos can transform from one type to another. Muon type neutrinos can transform into electron type or tau type neutrinos. The NOvA experiment has been collecting data since February 2015 and they have seen 6 cases of muon type neutrinos transforming into electron type neutrinos [1].

NOVA_FERMILAB

Similar long-distance experiments such as T2K in Japan and MINOS at FERMILAB have seen these muon neutrino to electron neutrino oscillations before. These 6 cases are the first for the NOvA experiment.

By the way, the majority of muon type neutrinos arriving at the NOvA detector have 2 GeV energy – supposedly the energy that maximizes the probability of neutrino oscillation.

Can we differentiate anti-neutrino from neutrino?

This is related to the question of why we see so little anti-matter in the universe. A particle and its anti-particle (electron and positron for example) are always created in pairs. Particle and its anti-particle are created at the same time. So what happened to those positrons?

We know that if a particle collides with its anti-particle the “annihilation” takes place and the matter (mass) contained in the particle and the anti-particle is transformed into light (photons). Obviously, a full scale annihilation did not take place because we see matter everywhere in the universe. If anti-neutrino is fundamentally different from neutrino then we can argue that most of the anti-matter must have transformed into anti-neutrinos.

The conceptual difficulty here is that “anti”ness is defined as particle having the opposite electric charge. Since neutrino has no electric charge anti-neutrino is ill defined. I predict that neutrino experiments will be able differentiate neutrino and anti-neutrino of the same type and we will have to refine our definition of “anti”ness.

T2K and NOvA can also run in anti-neutrino mode. For example, FERMILAB can generate a beam of muon type anti-neutrinos. If the NOvA detector can catch some of those and also observe a small fraction of them turn into electron type anti-neutrinos then we will be a step closer to the goal.

Majorana neutrino

If the NOvA experiment cannot differentiate anti-neutrino from neutrino of the same type then we will pay more attention to the theory developed by Ettore Majorana  who disappeared under mysterious circumstances while going by ship from Palermo to Naples on March 25, 1938.  But to be absolutely sure that neutrino and its anti-neutrino are the same we need to see a neutrino-less double-beta decay which has never been observed. [2]

My prediction: I have already stated in the previous section that I predict that the neutrino experiments will be able to differentiate neutrino and anti-neutrino of the same type. I am also predicting that the neutrino-less double-beta decay will never be observed. It is fun to make bets like this.

Evidence from T2K Experiment in Japan

It is not just the NOvA experiments that I am counting on. The T2K experiment in Japan is making progress too. They recently reported that they are generating beams of electron type anti-neutrinos at the J-PARC facility in Tokai. Their far detector  (Super-Kamiokande ) on the east coast was able to detect 3 of those electron type anti-neutrinos.

t2k-schematic

The next step is to see if these electron type anti-neutrinos are different from electron type neutrinos.

It might take T2K and NOvA data combined to know whether the anti-neutrino is different from the neutrino. The final verdict will come from the planned DUNE neutrino experiment.

DUNE-s

What about the OPERA experiment?

How can we forget the September 2011 announcement by the OPERA experiment claiming that muon type neutrinos were probably moving faster than light in vacuum. That was a false alarm. In March 2012, OPERA researchers blamed this result on a loose fiber optic cable connecting a GPS receiver to an electronic card in a computer.

In 2010, the OPERA experiment announced that it had found its first case of muon type neutrino transforming into a tau type neutrino. In 2012, 2013, 2014 and 2015, it announced its second, third, fourth and fifth cases.

We now know for sure that muon type neutrinos can transform into either tau type or electron type neutrinos. Clear evidence for neutrino oscillations.

OPERA_experiment

Sterile neutrino

All observed neutrinos have left-handed chirality. Obviously, all anti-neutrinos have right-handed chirality but we are not talking about “anti”ness here. You may see my earlier posts mentioning the chirality of neutrinos:

https://sureshemre.wordpress.com/2014/01/08/there-are-no-right-handed-neutrinos/

https://sureshemre.wordpress.com/2014/01/09/only-left-handed-fermions-experience-the-weak-nuclear-force/

Can neutrinos have right-handed chirality? Maybe they exist and they are part of the dark matter. Many experiments are looking for neutrinos with right-handed chirality.

There are different definitions for “sterile” so it is not just neutrinos with right-handed chirality. You can find more information about other types of sterile neutrinos at

http://www.quantumdiaries.org/2014/07/27/sterile-neutrinos/

On the experimental side a new experiment is planned at FERMILAB.

My prediction: experiments will not find neutrinos with right-handed chirality.

Highest energy neutrino ever found

The IceCube experiment at the South Pole is a neutrino observatory. IceCube was built to search for very high energy neutrinos created in the most extreme cosmic environments. IceCube searches for neutrinos from the most violent astrophysical sources: events like exploding stars, gamma-ray bursts, and cataclysmic phenomena involving black holes and neutron stars.

icecube_experiment

The IceCube experiment holds the record in highest energy neutrinos ever detected. [3]. In July 2012, the IceCube Collaboration announced the observation of the two highest-energy neutrinos ever observed to date, with energies around 1000 TeV. These neutrinos were named Bert and Ernie (Sesame Street characters). Later, they detected 2 more with even higher energies. The third one named Big Bird (another Sesame Street character) was a 2200 Tev neutrino. The latest one (a muon type neutrino) announced  on August 5, 2015 by the Symmetry Magazine [4] probably had more than 6000 Tev because it produced a 2000 Tev muon. In comparison, the LHC (Larger Hadron Collider) can accelerate protons to maximum of 13 Tev. We don’t know where these super high energy neutrinos are coming from. The energy contained in a 6000 Tev neutrino is simply mind shattering.

icecube_detector_sm

References

[1] http://www.fnal.gov/pub/presspass/press_releases/2015/NOvA-Neutrinos-Change-20150807.html

[2] http://arxiv.org/abs/1408.2455

[3] https://icecube.wisc.edu/science/highlights

[4] http://www.symmetrymagazine.org/article/august-2015/icecube-sees-highest-energy-neutrino-ever-found

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About Suresh Emre

I have worked as a physicist at the Fermi National Accelerator Laboratory and the Superconducting Super Collider Laboratory. I am a volunteer for the Renaissance Universal movement. My main goal is to inspire the reader to engage in Self-discovery and expansion of consciousness.
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