First Hint of CP Violation in the Neutrino Sector

The latest report on T2K results has been published[1], and it looks good for the upcoming long neutrino baseline experiment at DUNE and T2HK. The result may suggest that these two upcoming experiments may finally nail down CP violation in neutrinos, which will be a substantial advancement in our understanding on why there are more mater than antimatter in our universe.

The discovery of substantial leptonic CP violation would be groundbreaking. Its observation, together with evidence that a quantity known as lepton number has been violated (that is, not conserved), would provide strong circumstantial evidence for leptogenesis as the origin of the matter–antimatter imbalance.

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[1] T2K collaboration, Nature v.580, p.339 (2020).

Electron Neutrino Losses It's Mass By Almost Half

A new experimental result out of KATRIN has cut the upper limit of the mass of electron neutrino by half, to 1.1 eV. This was reported at the recent conference and in a recent preprint.

I suppose if I want to be accurate, I should say it is the electron antineutrino, since they measured this from beta decays, but nowadays, we don't have a clear cut idea of the difference between the neutrino and its antiparticle. For all we know, they can possibly also be a Majorana particle.

I'll be giving this report to my students in the general physics class, and see if they can convert the 1.1 eV into "kg". :)

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How Do You Detect A Neutrino?

Another Don Lincoln video, and this time, it is on a topic that I had a small involvement in, which is neutrino detection.



My small part was in the photomultiplier photocathode used for detection of Cerenkov light that is emitted from such a collision between the "weak boson" and the nucleus. We were trying to design a photodetector that has a large surface area as compared to the current PMT round surface.

In any case, this is a good introduction to why neutrinos are so difficult to detect.

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How Do You Make Neutrino Beam?

This new Don Lincoln's video is related to the one he did previously on the PIP-II upgrade at Fermilab. This time, he tells you how they make neutrino beams at Fermilab.



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Neutrinos Come Knocking For Astronomy

I feel as if these are the golden years for astronomy and astrophysics.

First there was the discovery of gravitational waves. Then a major astronomical event occurred, and we were able to detect it using the "old" standard technique via EM radiation, and via the detection of gravitational waves from it. So now astronomy has two different types of "messengers" to tell us about such events.

Well now, make way for a third messenger, and that is ubiquitous neutrinos. Two papers published in Science last week detected neutrinos (along with the accompanying EM radiation) from a "blazer". The neutrino detection part was made predominantly at IceCube detector located in the Antarctica.

Both papers are available as open access here and here. A summary of this discovery can be found at PhysicsWorld (may require free registration).

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Super Kamiokande and Extremly Pure Water

This is a rather nice overview of Super Kamiokande, a neutrino detector in Japan. It has produced numerous ground-breaking discoveries, including the confirmation of neutrino oscillation many years ago. Unfortunately, the article omitted an important incident at Super-K several years ago when there was a massive implosion of the phototubes.

The article has an interesting information that many people might not know about extremely pure water, the type that is used to fill up the detector tank.

In order for the light from these shockwaves to reach the sensors, the water has to be cleaner than you can possibly imagine. Super-K is constantly filtering and re-purifying it, and even blasts it with UV light to kill off any bacteria.

Which actually makes it pretty creepy.

"Water that's ultra-pure is waiting to dissolve stuff into it," said Dr Uchida. "Pure water is very, very nasty stuff. It has the features of an acid and an alkaline."
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Another tale comes from Dr Wascko, who heard that in 2000 when the tank had been fully drained, researchers found the outline of a wrench at the bottom of it. "Apparently somebody had left a wrench there when they filled it in 1995," he said. "When they drained it in 2000 the wrench had dissolved." 

In other words, such pure, deionized water is not something that you want to drink.

And this leads me to comment on this silly commercial of PUR drinking water filter. It showed an ignorant public complaining about lead in the drinking water, even though he was told that the amount is below the safety level.



A drinking water contains a lot of other dissolved minerals, any one of which, above a certain limit, can be dangerous. Even that PUR commercial can only claim that it can REDUCE the amount of lead in the drinking water, not completely removed it. It will not be zero. So that guy should continue complaining about lead even with PUR filter.

If this person in the commercial is representing the general public, then the general public needs to be told that (i) you'll never be able to get rid completely of all contaminants in drinking water and (ii) pure water will dissolve your guts! This is why we set safety levels in many things (360 mrem of radiation per year, for example, is our acceptable, normal background radiation that we receive).

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Fermilab Accelerator Complex

This is a neat animation video of the Fermilab Accelerator Complex as it is now, and all the various experiments and capabilities that it has.



Of course, the "big ring", which was the Tevatron, is no longer running now, and thus, no high-energy particle collider experiments being conducted anymore.

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First Observation of Neutrinos Bouncing Off Atomic Nucleus

An amazing feat out of Oak Ridge.

And it’s really difficult to detect these gentle interactions. Collar’s group bombarded their detector with trillions of neutrinos per second, but over 15 months, they only caught a neutrino bumping against an atomic nucleus 134 times. To block stray particles, they put 20 feet of steel and a hundred feet of concrete and gravel between the detector and the neutrino source. The odds that the signal was random noise is less than 1 in 3.5 million—surpassing particle physicists’ usual gold standard for announcing a discovery. For the first time, they saw a neutrino nudge an entire atomic nucleus.

Currently, the entire paper is available from the Science website.

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The Search For Neutrinoless Double Beta Decay

This is a nice and simple article on why we are searching for the neutrinoless double-beta decay.

In this new study, physicists are seeking so-called neutrinoless double-beta decay. Normally, some radioactive atoms' unstable nuclei will lose a neutron via beta decay — the neutron transforms into a proton by releasing an electron and a tiny particle called an electron antineutrino. A mirror image can also occur, in which a proton turns into a neutron, releasing a positron and an electron neutrino — the normal-matter counterpart to the antineutrino. Double-beta decay happens when two electrons and two antineutrinos (the antimatter counterparts of neutrinos) are released: basically, the beta decay happens twice. Scientists have long theorized a neutrinoless version of this process — something that would suggest that the two neutrinos annihilated each other before being released from the atom. Essentially, the neutrino behaves as its own antimatter sibling.

A large portion of high-energy physics experiments around the world are done using neutrinos (Daya Bay, MINOS, NOvA, SuperK, etc...).  It won't surprise me one bit that the another major discovery will be made with these particles.

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CP Violation in Neutrino Oscillation

It is always nice when non-science media carries physics news. Unfortunately, often times, the accuracy is lacking and, in many cases, gives misleading ideas. This is one such case.

It is reporting on the news about CP violation in neutrino oscillation from muon neutrinos and muon antineutrinos that was reported in last week's 2016 ICHEP.

At the T2K experiment, researchers looked for a difference between neutrinos and antineutrinos oscillations. Their findings, announced at the International Conference on High Energy Physics in Chicago, suggest that there are — more muon neutrinos were found changing into electron neutrinos than muon antineutrinos changing into electron antineutrinos.

The researchers, who had expected to detect 23 electron neutrinos and seven electron antineutrinos, observed 32 electron neutrinos and 4 electron antineutrinos.
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If confirmed with a greater level of certainty, this would point to a violation of charge-parity (CP) symmetry in neutrinos. CP symmetry tells us that a system remains unchanged even if two fundamental properties — charge and parity, which refers to a 180-degree flip in spatial configuration — are reversed. If a violation of CP symmetry is confirmed, it would not only hint at the existence of physics beyond the Standard Model — a theory of almost everything — it would also help us understand why the universe is completely devoid of antimatter.

There's nothing wrong with the report. However, it is inaccurate with regards to what it left out. If you don't know any better, you'd think that this is something new, and that this is the first instance of CP violation. This is not true. CP violation has been seen in other particle systems. So there is no longer a question on whether such violation exists. What is new here is that it is the first time it is observed in neutrino oscillation.

This is why science reporting is difficult. You need someone who has a wide breadth of knowledge in many fields to be able to not only report things accurately, but also give a full view of it. There's nothing inaccurate here in what was included. But the inaccuracy occurs on what was omitted, and therefore, not giving a general reader a more complete state of knowledge of the field.

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Still No Sterile Neutrinos

IceCube has not found any indication of the presence of sterile neutrinos after looking for it for 2 years, at least not in the energy range that it was expected.

In the latest research, the IceCube collaboration performed independent analysis on two sets of data from the observatory, looking for sterile neutrinos in the energy range between approximately 320 GeV and 20 TeV. If present, light sterile neutrinos with a mass of around 1 eV/C² would cause a significant disappearance in the total number of muon neutrinos that are produced by cosmic-ray showers in the atmosphere above the northern hemisphere and then travel through the Earth to reach IceCube. The first set of data included more than 20,000 muon-neutrino events detected between 2011 and 2012, while the second covered almost 22,000 events observed between 2009 and 2010. 

I think there are other facilities that are looking for them as well. But this result certainly excludes a large portion of the "search area".

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Kamioka, Japan

With the recent Nobel Prizes in physics going to various discovery related to neutrinos, this Nature article is highly appropriate. We usually do not get a glimpse of the site where many of these experiments are performed. So it is nice to have a bit of a background on Kamioka, Japan, and also the various neutrino detectors and experiments that had gone on there. Considering that this is the place where Kamiokande, Super-Kamiokande, and the KamLAND experiments were done, this is a major site for neutrino-based studies.

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More On Neutrinos

People seem to want to learn more about neutrinos! With the latest Nobel prize being awarded to the discovery of neutrino mixing, it is a good time to have some general article on what we know about neutrinos. John Beacom has written a rather nice article here that should give you an idea of the physics of neutrinos and why it is an important study.

It just struck me as a rather interesting development. When SNO and Super-K were discovering all this, there was hardly any neutrino experiment in the US. Oh, there was plenty of US participation, but neutrino experiments were not big or a priority. This is understandable because, back then, the Tevatron was still going strong and LHC hasn't completely come into force yet. Now, how things have changed considerably. With the Tevatron gone and the center of high energy physics collider having shifted to CERN, the US is now trying to be a major player in neutrino studies, with MINOS, NOvA, and the proposed LBNE. In DOE/funding lingo, the US has abandoned the "Energy Frontier" and has gone into the "Intensity Frontier".

I believe there are still huge amount of amazing physics to be discovered from neutrinos. So it will be interesting how all these new generation of neutrino detectors will pan out.

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2015 Nobel Prize Work Free To Read

As a follow-up from yesterday's announcement of the 2015 Nobel Prize for Physics, the APS has made available the publications that are directly related to award to the two recipients this year.

Evidence for Oscillation of Atmospheric Neutrinos

Measurement of the Rate of ν_e + d → p + p +e ⁻ Interactions Produced by ⁸B Solar Neutrinos at the Sudbury Neutrino Observatory

Direct Evidence for Neutrino Flavor Transformation from Neutral-Current Interactions in the Sudbury Neutrino Observatory

Notice my earlier point, as you look at the authors list on each of these papers, that they were a huge amount of collaborators on these projects.

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2015 Nobel Prize For Neutrino Oscillation Discovery

The 2015 Nobel prize in physics went to Art McDonald and Takaaki Kajita for the discovery of neutrino oscillation at SNO and SuperKamiokande, respectively.

Now, for those readers who are not familiar with all this, do not get the impression that these two were working all by themselves and then discover these. They did not. There were huge number of people who were working on these projects, and the papers they produced listed a large number of authors. However, these two were either the leading scientist or the most prominent/significant figure representing each group. This is not unusual for an experimental discovery, especially in elementary particle physics, where the most prominent figure is singled out for the award.

When I read this, I must admit that I was a bit surprised. Not surprised that they are awarding it for the discovery of neutrino oscillation - it IS a major discovery. I was surprised because I somehow thought that this discovery had already been awarded the Nobel prize already! I mean, it was such a significant moment, and it is now already accepted that neutrino oscillation is a fact, that I somehow assumed the  Nobel prize had already been awarded for this discovery years ago. Obviously, I hallucinated that one.

Maybe the Nobel committee were debating all this time on who should deserve to receive the prize, considering the huge number of people involved, with several prominent physicists deserving it on each group.

In any case, the prize for this discovery was long overdue.

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Neutrino Week, In Summary

I mentioned the "Lost In Translation" problem of the Fermilab press release on the NOvA result. Jon Butterworth has a better article that describes clearly the NOvA result, and also includes the detection by IceCube of the highest energy neutrino ever recorded.

But I hate to say that I was more fascinated by his footnote:

¹Fermilab is in the Chicago suburb of Batavia. The neighbouring suburb is Geneva, Illinois. The means that the current and previous high-energy record-holding machines were built next to a Geneva. Rumours that part of China is to be renamed have just started.

Geneva, China?

Still, I wouldn't be surprise if China does go ahead on its own and build its own collider.

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NOvA Neutrinos - A Slight Lost In Translation

OK, this post is making two different points, and try not to miss both of them, because one of them reinforces my stand that what you say may not exactly be what they understood.

This press release out of Fermilab announced the observation of neutrino oscillation by the NOvA detectors. This is crucial for NOvA to show that they can detect what has already been shown to exist, because it is their mission to study this more carefully and to make specific measurements on this phenomenon.

That's my first point, and that's the main news. Now comes the second point. Another "news"  article took that Fermilab press release, and reported it. But read how it has been presented in the beginning.

Scientists have witnessed their first evidence of oscillating neutrinos, taking a huge step forward in particle physics. The new findings confirm that the extraordinary detector built for the project not only functions as planned but is also making great progress toward its goal of a major leap in our understanding of these particles.

Now this is important, because it comes in at the very beginning of the news article and it sets the tone for the entire report. But read it carefully. If you don't know any better, reading the first sentence will give you the impression that this is the first ever sighting of oscillating neutrinos! 
Since they got this from Fermilab's press release, did the press release itself made the same mistake? Let's take a look. The Fermilab's press release wrote this:

Scientists on the NOvA experiment saw their first evidence of oscillating neutrinos, confirming that the extraordinary detector built for the project not only functions as planned but is also making great progress toward its goal of a major leap in our understanding of these ghostly particles.

Notice the subtle but important difference. Fermilab's press release indicated that this is the first observation of neutrino oscilation by NOvA scientists! Of course, those of us in the know are aware that this statement is indicating that the new NOvA detector has detected what it SHOULD detect, and this is a major milestone in the commissioning of any new instrument, i.e. it should detect what have already been detected to make sure everything is working as it should. It doesn't mean that this neutrino oscillation is the first detection anywhere!

But this is what frequently happens. I don't know the quality of news reporting on "Science World Report", but that is irrelevant because this time of "mistranslation" happens regularly when non-experts tries to interpret or understand scientific reporting. It is why what you write needs to be looked at in several different angles and from background of people who are ignorant of not  only the subject matter, but also the progress in that area. A person reading the news report will think that this is the first ever evidence of neutrino oscillation, when that is clearly false.

The Fermilab news release should look at this type  of misreporting, and see if they need to make their press releases even more "simplified" so that people aren't mislead into thinking the same way as the news report. We must always be vigilant of the fact that what we wrote and what we meant may not be exactly what they understand.

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IceCube Neutrinos Are Truly Cosmic

Latest data analysis from IceCube concludes that the neutrinos that had been reported are consistent with them having a cosmic origin.

Two groups have now analyzed a larger data set (covering years 2010 to 2013). The first work, conducted by the IceCube collaboration, identifies a total of 137 high-energy neutrinos (above 35 tera-electron-volts). The team shows that the number of tracks to showers is incompatible with exotic flavor ratios, such as 1:0:0 and 0:1:0. A similar analysis was performed by theorists at Italy’s Gran Sasso Science Institute in L’Aquila and the Gran Sasso Laboratories in Assergi. They focus on a higher energy range (above 60 tera-electron-volts) and find the ratio of tracks to showers is consistent with several astrophysical (nonexotic) models. Future data and analysis, which may include a method for tagging tau neutrinos, could eventually distinguish between these different source models.

I want to always try to impress upon people reading this, especially non-scientists, on how this is an example of "Physics doesn't just say what "What comes up, must come down". It must also say when and where it comes down!" In other words, there must be a strong QUANTITATIVE aspect of physics.

In this example, just detecting neutrinos is not sufficient (i.e. you found out that what goes up, must come down). The energy of the neutrinos, the interaction channels, etc...etc. are strict, mathematical descriptions that make numerical predictions (i.e. when and where it comes down). Only when the data are compared to these models can one distinguishes the type and nature of these neutrinos. Without the quantitative aspect of the physics, a neutrino will look like any other neutrinos.

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Cyclotron Radiation From One Electron

It is a freakingly cool experiment!

We now can see the cyclotron radiation from a single electron, folks!

The researchers plotted the detected radiation power as a function of time and frequency (Fig. 2). The bright, upward-angled streaks of radiation indicate the radiation emitted by a single electron. It is well known theoretically that a circling electron continuously emits radiation. As a result, it gradually loses energy and orbits at a rate that increases linearly in time. The detected radiation streaks have the same predicted linear dependence, which is what allowed the researchers to associate them with a single electron. 

Of course, we have seen such effects for many electrons in synchrotron rings all over the world, but to not only see it for one electron, but to also see how it loses energy as it orbits around is rather neat. It reinforces the fact that we can't really imagine electrons "orbiting" around a nucleus in an atom in the classical way, because if they do, we would detect such cyclotron radiation and that they will eventually crash into the nucleus.

But I also find it interesting that this has more to do with the effort in trying to determine the mass of a neutrino independent of the neutrino mass oscillation via measuring the electrons mass to high accuracy in beta decay.

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No Violation of Lorentz Invariance In Neutrino Oscillation

The more they test it, the more convincing it becomes.

Another test of the Lorentz invariance has been reported, and this time it is in the neutrino oscillation.

Neutrinos could be a sensitive probe of LV through their oscillation behavior. They are known to oscillate between three flavors (electron, muon, and tau), but Lorentz violations could cause additional oscillations that would modify how the signal depends on neutrino energy and path length (i.e., the distance a neutrino travels between creation and detection). Past searches have failed to find LV oscillations in reactor neutrinos. The Super-Kamiokande experiment—an underground neutrino observatory in Japan—has now reported a characterization of atmospheric neutrinos accessing much greater ranges in neutrino energy and path length than previous tests, giving it greater sensitivity to LV oscillations. The data showed no LV signature, allowing the researchers to place the first-ever limits on LV oscillations between muon and tau neutrinos. For other flavor oscillations, they improve on previous limits by factors of a thousand or more.

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