Tag: Neutrinos

Two new Neutrino experiments enable Physicists to measure the heat being generated in the Earth’s core and may have discovered a new particle and new physics beyond the Standard Model.

I’ve written about neutrinos several times now in this blog. (See posts of 30July2017, 2December 2017 and 6June2018.) Neutrinos are known as ghost elementary particles because they interact so rarely, so weakly with other particles. In fact, although billions of neutrinos are passing through your body every second you’ll be lucky if a single neutrino interacts with you during your entire life.

Fusion reaction that powers the Sun. Two neutrinos are released in the process, the particles shown as white balls.. (Credit: Quora)

Most of those neutrinos come from the fusion processes that produce the energy of our Sun but there are also anti-neutrinos whizzing about that mostly come from the decay of radioactive elements in the ground along with the fission reactions in nuclear reactors. I’ve often considered it amusing that fusion, which takes lighter elements and combines them into heavier elements, produces a lot of neutrinos while fission and nuclear decay, which break down heavy elements, produce mainly anti-neutrinos.

Beta decay of the Carbon 14 nucleus produces a Nitrogen nucleus while emitting an electron and an anti-neutrino. (Credit: Radiation Dosimetry)

For almost fifty years now scientists have been using neutrinos in order to study our Sun, and learned a great deal about neutrinos in the process. Neutrino detectors consist of large containers of water that capture the neutrinos while photomultiplier tubes that line the inner walls of the container detect the faint light produced by those captures. The detectors themselves are buried deep within mine shafts in order to minimize the interference caused by cosmic rays. These ‘neutrino telescopes’ detect no more than a handful of neutrinos a day but those few particles have lead to many important discoveries.

The walls of neutrino telescopes are covered with photomultiplier tubes that collect the light emitted by neutrino captures. (Credit: Sci-news.com)

Now another neutrino observatory is using anti-neutrinos, known as geoneutrinos to study the interior of the Earth. The Borexino detector, located at the Laboratori Nazionali del Gran Sasso in Italy and containing some 1000 metric tons of water has been in operation now since 2007. Buried 1400 meters beneath the Earth’s surface in the Gran Sasso massif near Rome, Borexino has succeeded in capturing 53 geoneutrino events. (It’s worth noting that during that time the detector was also capturing Solar neutrinos.)

The design of the Borexino neutrino telescope. (Credit: ScienceDirect.com)

And those 53 anti-neutrinos were enough to allow the theoreticians to answer a question that has long perplexed geologists and geophysicists, how much of the Earth’s internal heat is being generated by the decay of radioactive elements? Thanks to the data provided by Borexino we now know, with an 85% confidence level, that just about half of the heat in our planet’s core comes from nuclear decay. In fact the data obtained by Borexino has even allowed physicists to estimate the amounts of the radioactive elements Uranium and Thorium remaining inside the Earth.

Thanks to Borexino we now have actually measured the amount of heat being generated in Earth’s core by radioactive decay! (Credit: NBC News)

Borexino will continue to capture geoneutrinos, and each new detection will increase the accuracy of the results. There are also plans to build a larger detector at Gran Sasso so in the years to come geoneutrinos may tell us even more about the makeup of the interior of the Earth.

Now if you think that calculating the energy generated in the Earth’s core based on just 53 detections of elementary particles is pretty amazing well there are a group of physicists attached to the Antarctic Impulsive Transient Antenna (ANITA) experiment in Antarctica who think that the detection of three particles could overturn the standard model of particle physics.

ANITA is a completely different sort of neutrino detector than Borexino, but one that is only sensitive to the very highest energy neutrinos, those with energies far greater than that of neutrinos coming from either the Earth or Sun. ANITA is intended to study the neutrinos associated with high-energy cosmic rays from quasars or black holes or supernovas.

The way ANITA detects these high-energy neutrinos is that while in space the neutrinos are moving at almost, but not quite the speed of light in a vacuum as they pass through the Antarctic ice they are actually moving faster than the speed of light in ice! Such particles will give off a kind of radiation known as Askaryan radiation until their speed is reduced below that of light, or they leave the ice. The radiation that these high-energy neutrinos give off happens to be in the microwave region of the electro-magnetic spectrum, a type of radiation that we humans are very good at detecting. Your cellphones operate in the microwave region for example.

The ANITA detectors are lifted into the stratosphere by a helium balloon. (Credit: The Scientific Community on Antarctic Research)
The ANITA Experiment catches EM waves giving off by ultra-high energy neutrinos as they skim through the Antarctic ice sheet. (Credit: ResearchGate)

Funded by NASA, the ANITA experiment therefore consists of an array of 40 microwave antennas that are lifted into the stratosphere over the Antarctic by a helium balloon in order to maximize their coverage area. Operating on an every other year basis ANITA has now flown four times and detected numerous signals associated with high-energy neutrinos that have taught physicists a great deal about the neutrino component of Ultra High Energy Cosmic Rays (UHECR).

Launch of the ANITA Experiment. The detector will remain aloft for about four months during the Antarctic summer. (Credit: Jeff Filippini)

Three of those detections however seem to come directly up from beneath the detector, as if they’ve come through the entire Earth, something high-energy neutrinos should not be able to do. Remember the whole time that they’re passing through solid material the neutrinos are giving off Askaryan radiation.

So if these three particles weren’t the sort of neutrinos that physicists are familiar with, what were they? Some new form of neutrino? Or an entirely new type of particle beyond the Standard Model? Three detections do not give enough evidence for a definitive answer but ANITA is only one of a number of experiments that are giving indications of physics beyond the Standard Model.

Further flights with ANITA are planned, as are other experiments designed to give a clearer picture of what these strange particles might be. Physicists have never been happy with the Standard Model, which fails to answer as many questions as it does answer. How long it will take to understand what is beyond the Standard Model, and what experiment will finally succeed in making the breakthrough is anybodies guess. You can be certain however that physicists will keep on looking until they find those answers.

The Ice Cube Experiment. High Energy Physics at the Bottom of the World.

Physicists who study the way the Universe works at its simplest, most fundamental level do so by examining the collisions between elementary particles like the electron, quarks and neutrinos. The higher the amount of energy in those collisions the more we can learn about their behavior, the more we learn about the rules by which the universe is built. This is why physicists need to build such powerful particle accelerators such as the Large Hadron Collider at CERN.

However every day the Earth is struck by particles coming in from outer space with billions of times as much energy as the most powerful ever produced by human science. These particles are called the Ultra High Energy Cosmic Rays (UHECR) and physicists would love to be able to use their enormous energy in their experiments. The problem is that we never know exactly where on earth the most powerful of these particles are going to strike so how do we study them? How do we get them inside our instruments so that we can study them? Obviously in order to catch these UHECR you need a really big detector, and a lot of patience.

Enter the Ice Cube Experiment down in Antarctica. This experiment uses a cubic kilometer of the ice on that frozen continent as a detector for UHECR collisions. (That’s a block of ice one-kilometer long by one-kilometer wide by one-kilometer deep) The image below shows the experiments control facility sitting on the Antarctic ice.

The Ice Cube Experiment’s above ground (ice) Control Center (Credit: Scientific American)

The Ice Cube Experiment was constructed by drilling eighty-six, one-and a half kilometer deep holes into the ice and inserting long strings of ultra sensitive light detectors (Called Digital Optical Modules or DOMs) into the holes. (There are 5,160 of these DOMs total) Deep within the ice the only light that will be possible for the DOMS to detect will be that which is given off by the UHECR as they collide with atoms in the ice. The image below shows the overall layout of the Ice Cube Detector.

The Layout of the Ice Cube Experiment (Credit: Ice Cube Collaboration)

The light given off by these fast moving particles is called Cherenkov radiation, which is best known as that eerie greenish-blue glow around a nuclear reactor. Just what Cherenkov radiation is requires a little bit of explanation.

Cherenkov radiation coming from a Nuclear Pile (Credit: Reed Z)

We all know that nothing can travel faster than the speed in a vacuum. However the speed of light in transparent materials, like air or water or glass or ice is lower than the speed of light in a vacuum. So what happens when a sub-atomic particle like a proton is traveling through ice faster than the speed of light in ice? Well, what happens is the particle emits energy in the form of Cherenkov radiation until its velocity is below the speed of light in ice and it is this Cherenkov radiation that the DOMs of Ice Cube detect. The image below shows one of the DOMs.

One of Ice Cube’s Digital Optical Modules (DOMs) (Credit: The Ice Cube Collaboration)

The primary type of elementary particle that Ice Cube is designed to study are neutrinos and yes I know I talk about neutrinos all of the time (See posts of 30 July 2017, 2 December 2017 and 6 June 2018). Over the last twenty years however we have learned so much about our Universe by studying neutrinos and we have the possibility of learning more about Supernova, Gamma Ray Bursts, Blazars and even the Big Bang itself by studying the high-energy neutrinos given off by those events.

In fact according to two recent papers from the teams of scientists running Ice Cube a neutrino event that was detected by Ice Cube on 22 September of 2017 has been traced back to it original source, a Blazar designated as TXS 0506+056. Objects like Blazars have been observed in the past with optical and radio telescope along with X-ray and gamma ray telescopes and now the Ice Cube Detector as well. The image below shows graphically what a detection by Ice Cube looks like.

The Highest Energy Event yet measured by the Ice Cube Experiment (Credit: The Ice Cube Collaboration)

As you might guess there are already plans to expand Ice Cube. Called Ice Cube Gen-2 the design calls for a detector that could be as large as four kilometers in diameter. Such a large detector could record hundreds of events every day that are millions of times as powerful as those produced at CERN. Ice Cube Gen-2 will benefit from the knowledge gained in the construction of the current Ice Cube in an effort to reduce cost.

It’s as simple as this, the more different ways we look at the Universe the more we learn about the Universe. The Ice Cube experiment in Antarctica is a new way of looking and I think that we’re going to learn a lot. If you’d like to learn more about the Ice Cube Experiment click on the link below to be taken to the experiment’s website.

http://icecube.wisc.edu/

Have Sterile Neutrinos been detected? Some experiments say yes, others say no.

Regular readers of this blog will have noticed that I have a deep interest in particle physics, also called high-energy physics, and in particular the so-called ‘ghost particle’ of the atom, the neutrino. Well after all my degrees are in physics and studying how the most elementary particles that exist interact is certainly the most basic way to understand how the Universe itself works. Also, my grad school advisor’s own research concerned neutrinos.

Neutrinos are a hot topic right now and a soon to be published paper is going to turn the temperature way up. The MiniBooNE experiment, which I discussed in some detail in my post of 2Dec2017, is detecting more neutrinos that calculations predict that it should and one possible explanation for the excess would be the existence of a fourth type of neutrino, a sterile neutrino. MiniBooNE is a cooperative experiment at Fermilab outside of Chicago, which produces the neutrinos the MiniBooNE detector. The image below shows the layout of MiniBooNE.

Layout of the MiniBooNE Experiment (Credit: Fermilab)

O’k a little background first describing the fermion or matter side of the standard model of elementary particles. Since the 1960s physicists have known that all of the matter we see around us, all of the atoms are built from four different particles. There is a pair of quarks called up and down who themselves make up the familiar protons and neutrons in the atom’s nucleus. There’s also a pair of leptons, the electron and the neutrino but while the electron orbits around the nucleus the neutrino is a ‘ghost particle’, rarely interacting with other particles.

If you think that sounds weird it gets worse. In the extremely high-energy collisions we generate in our modern atom smashers we have found that each of those four particles has two heavier, more massive cousins. The cousins of the up quark for example are called the charm and top quarks. The charm and top are identical to the up in every way except being more massive. They have the same electric charge, the same spin, the same weak charge, and same colour charge.

Similarly the down quark has two cousins named strange and bottom while the electron’s cousins are the muon and tau. Why these heavier cousins should even exist we have no idea but they certainly do.

There are three neutrinos as well but they simply called the electron-neutrino, the muon-neutrino and the tau-neutrino because they have the have the bazaar ability to oscillate from one type into another. One of the first attempts to study this oscillation property was called the Liquid Scintillator Neutrino Detector (LSND) at the Los Alamos back in the 1990’s. When the LSND found a surprising excess in the number of neutrinos some theoretical physicists suggested the existence of a fourth kind of neutrino, a sterile neutrino that would interact even less than normal ‘active’ neutrinos but which would oscillate like the others, in other words after a period of time it would become one of the other types. (I know how crazy that all sounds and I will tell you the math is almost easier to understand than the description!)

Other experiments quickly tries to find additional evidence of sterile neutrinos but failed. Both the Underground Oscillation Project with Emulsion-Tracking Apparatus Experiment in Switzerland and the Ice Cube Neutrino Observatory failed to discovery any hint of sterile neutrinos in their data. Physicists began to believe that there must have been some problem with the LSND data or its analysis. The Images below show the Ice Cube Neutrino Observatory in Antarctica.

Ice Cube Neutrino Observatory Credit: South Pole Doc)

Ice Cube Experiment Layout (Credit: Inspire.hep)

But now MiniBooNE has found the same signature of sterile neutrinos as the LSND had making physicists scratch their heads and wonder, what’s going on here? Perhaps one clue is that both LSND and MiniBooNE employ photomultiplier tubes to detect the energy released by a neutrino interacting with another particle while Ice Cube and the Underground Oscillation Project use other techniques. But whether the photomultiplier tubes are enabling the detection of sterile neutrinos, or are causing a false signal that is being interpreted as sterile neutrinos is as yet completely unknown. The image below shows the photomultiplier Tube array in the LSND. When in use the chamber is filled with water for the neutrinos to interact with.

Photomultiplier Tubes are a common technique for detecting Neutrino interactions (Credit: Amusing Universe)

Neutrinos have been leading physicists on both an exciting and yet very twisted journey ever since Wolfgang Pauli first predicted their existence back in the 1930s. I’m certain that there are a few more twists still to come.

 

 

 

Drexel Physics Seminar: Doctor Sowjanya Gollapinni on the current state of research on Neutrinos, the Ghost Particle of the Atom.

I took in a physics seminar at my old alma mater Drexel University on November 30th. I like to stop down once in a while to see what’s changed, a lot, as well as see who’s there that I still remember, seems like fewer each time.

The topic of the seminar was certainly one that interested me, Neutrinos; a kind of sub-atomic particle so difficult to detect it has been called a ghost particle. The German physicist Wolfgang Pauli first predicted the existence of neutrinos as a way of making the books balance in the radioactive process called beta (β) decay. Careful studies of the process showed that some energy was missing, and the angular momentum before and after didn’t match. Pauli suggested that if another particle was involved, one without electric charge and little or no rest mass, it could account for the differences while being very difficult to detect. The images below show the Nobel Laureate along with a diagram of the β decay process.

Wolfgang Pauli (Credit: Public Domain)

Beta Decay Process (Credit: Public Domain)

So difficult were neutrinos to detect that it took more than twenty years to prove that they existed. In fact neutrinos react with normal matter so rarely that while about ten billion (billion with a b) neutrinos are flying through your body every second only two or three will interact with a particle inside you during your entire life. Even today the way we study neutrinos is to arrange for zillions to fly through a detector so sensitive it can measure the properties of the one or two that interact.

Arranging that intense beam of neutrinos, and building that detector is the job of Doctor Sowjanya Gollapinni of the University of Tennessee at Knoxville. Dr. Gollapinni is one of the chief researchers of the MicroBooNE experiment currently running at Fermilab outside of Chicago along with being one of the chief designers of the future Deep Underground Neutrino Experiment (DUNE).

The MicroBooNE, BooNE stands for Boosting Neutrino Experiment by the way, is a new type of detector using a design known as a Liquid Argon Time Projection Chamber (LArTPC). In the detector scattering events (really just two particles bouncing off of each other) between neutrinos and Argon atoms occur inside a very large, uniform electric field. The electric field pulls the ionized atoms generated by the collision toward an incredibly fine mesh of detecting wires. The resulting data plots are then interpreted to determine the kind of neutrino (see below) as well as its energy. The images below show the first high-energy neutrino collision captured by MicroBooNE along with the first recorded cosmic neutrino event.

First Recorded Neutrino Event at MicroBooNE (Credit: MicroBooNE, Fermilab)

First Cosmic Neutrino event at MicroBooNE (Credit: MicroBooNE, Fermilab)

One of the reasons I like MicroBooNE so much is that it uses the Fermilab Tevatron as its source of high-energy neutrinos. The Tevatron was the world’s most powerful ‘atom smasher’ until the Large Hadron Collider (LHC) at CERN took the top spot in 2008. In the world of particle physics however being number two gets you nothing so the physicists at Fermilab have been working hard to reconfigure their equipment in order to continue to study new physics and MicroBooNE is a big part of that effort.

After talking about some of the results from MicroBooNE Dr. Gollapinni spent a little time talking about the next generation neutrino detector known as the Deep Underground Neutrino Experiment or DUNE. As shown in the figure below, DUNE will have two detectors, one just a short distance from the neutrino source at Fermilab while the second will be buried deep inside the Homestake Mine in South Dakota, a distance of 1300 kilometers away. When completed the DUNE detectors will be 400 times larger then MicroBooNE providing 400 time the data.

DUNE experimental setup (Credit: DUNE, Fermilab)

Now the reason for having a second detector a long distance away is to give the neutrinos produced at Fermilab time in order to change from one type or flavour of neutrino to another. You see one of the things we do know about neutrinos is that there are three flavours. One flavour is associated with the familiar electron, a second is associated with a particle called the muon who is like a heavy cousin of the electron while the third is associated with an even fatter cousin called the Tau particle. Even stranger is the fact that the three flavours will oscillate from one kind to another. Learning more about this oscillation process is one of the major goals of DUNE.

At the end of her discussion Dr. Gollapinni mentioned some preliminary but very exciting news. The results so far from MicroBooNE and several other neutrino experiments indicates, just indicates right now, the possible existence of a fourth flavour of neutrino, which would be a stunning result if proving to be true. Right now it’s just an indication, hopefully the DUNE experiment, scheduled to start collecting data in 2024, will give us the answer.

During the question period one of the students who were attending asked Dr. Gollapinni how many flavours of neutrino she thought there were and she answered ‘Well if we find a fourth it’ll be a Nobel Prize and that’s enough for me’.

I certainly wish her luck.

The Deep Underground Neutrino Experiment (DUNE) and why are Neutrinos so Important Anyway.

Over the past month or so I’ve published a series of posts describing what I see as the decline of science in America (28June to 12July2017). Well today I have some good news. Just this week construction has begun on the Deep Underground Neutrino Experiment or DUNE.

DUNE is a collaboration between two already existing physics labouratories. The Sanford Underground Research Facility (SURF) which is buried 2km deep in the old Homestake gold mine outside of Lead, South Dakota along with Fermilab outside of Chicago, the site of America’s most powerful particle accelerator, second only to the LHC at CERN in Europe.

By the way the Homestake mine first became a physics labouratory back in the 1960s when the first Neutrino telescope was build there to measure the flux of neutrinos coming from the Sun. An experiment that provided the first direct evidence that the Sun gets its energy from hydrogen fusion reactions.

The idea behind the DUNE experiment is that Fermilab will use its accelerator to generate an intense beam of the sub-atomic particles called Neutrinos, a particle that has been called the ghost particle because they only interact very rarely with other particles. To give you an idea of how rarely an interaction occurs, every second thousands of Neutrinos are going right through your body but over your entire lifespan only a handful will interact with a particle inside you.

That beam of Neutrinos from Fermilab will be aimed very precisely at SURF where the world’s largest Neutrino Detectors are now being installed. The 2000km trip underground will mean almost nothing to the Neutrinos; a few may be absorbed but only very a few. There will also be an identical detector array right at the output of Fermilab’s accelerator so that scientists can study what happens to the Neutrinos during their 2000km journey. The picture below shows a diagram of the planned setup of the DUNE experiment.

DUNE Experimental Layout (Credit: Fermilab)

You may ask, if only a few Neutrinos are absorbed in 2000km of rock won’t even fewer be captured by the detectors in South Dakota. Yes, absolutely, but the scientists will be able to measure precisely every characteristic of every single Neutrino that is detected.

So, what do the scientists hope to learn from DUNE, why are Neutrinos so important anyway? Well, first of all there is increasingly strong evidence that Neutrinos are actually far more numerous than the electrons and quarks that make up what we think of as matter. In a sense scientists simply don’t enjoy knowing so little about such an important particle.

There are some more well defined problems that we hope DUNE can help to solve. For one, the there’s the question why the Universe, or at least our part of it, is so dominated by matter with so little anti-matter. From all of our experiments at places like Fermilab the Universe should be composed of equal parts matter and anti-matter and Neutrinos may hold the key to understanding the imbalance.

Physicists also hope that a greater understanding of Neutrinos will give us greater insight into fundamental forces, gravity, electromagnetism and the nuclear forces. Understanding Neutrinos is also important because they play a large role in some of the most energetic events in the Universe, everything from supernova to black hole formation.

Despite the recent lack of support for science from our government it’s still true that America’s scientists are second to none and the DUNE project demonstrates how they will always find a way to do new and important work. If you’d like to read more about the DUNE experiment the links below will take you to the SURF and Fermilab WebPages for DUNE.

http://www.dunescience.org/

http://lbnf.fnal.gov/