The weird new physics of neutrinos

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Already beyond the Standard Model

We already know neutrinos break the mold of the Standard Model. The question is: By how much?

For Symmetry Magazine:

Tested and verified with ever increasing precision, the Standard Model of particle physics is a remarkably elegant way of understanding the relationships between particles and their interactions. But physicists know it’s not the whole story: It provides no answer to some puzzling questions, such as the identity of the invisible dark matter that constitutes most of the mass in the universe.

As a result, in the search for physics beyond the Standard Model, one area of notably keen interest continues to be neutrinos.

In the Standard Model, neutrinos come in three kinds, or flavors: electron neutrinos, muon neutrinos and tau neutrinos. This mirrors the other matter particles in the Standard Model, which each can be organized into three groups. But some experiments have shown hints for a new type of neutrino, one that doesn’t fit neatly into this simple picture.

[Read the rest at Symmetry Magazine]

Blowing up high-mass stars with low-mass neutrinos

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Low-mass particles that make high-mass stars go boom

Simulations are key to showing how neutrinos help stars go supernova.

For Symmetry Magazine:

When some stars much more massive than the sun reach the end of their lives, they explode in a supernova, fusing lighter atoms into heavier ones and dispersing the products across space—some of which became part of our bodies. As Joni Mitchell wrote and Crosby Stills Nash & Young famously sang, “We are stardust, we are golden, we are billion-year-old carbon.”

However, knowing this and understanding all the physics involved are two different things. We can’t make a true supernova in the lab or study one up close, even if we wanted to. For that reason, computer simulations are the best tool scientists have. Researchers program equations that govern the behavior of the ingredients inside the core of a star to see how they behave and whether the outcomes reproduce behavior we see in real supernovae. There are many ingredients, which makes the simulations extraordinarily complicated—but one type of particle could ultimately drive supernova explosion: the humble neutrino. [Read the rest at Symmetry Magazine]

Are neutrinos their own worst enemies?

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EXO-200 resumes its underground quest

The upgraded experiment aims to discover if neutrinos are their own antiparticles

For Symmetry Magazine:

Science is often about serendipity: being open to new results, looking for the unexpected.

The dark side of serendipity is sheer bad luck, which is what put the Enriched Xenon Observatory experiment, or EXO-200, on hiatus for almost two years.

Accidents at the Department of Energy’s underground Waste Isolation Pilot Project (WIPP) facility near Carlsbad, New Mexico, kept researchers from continuing their search for signs of neutrinos and their antimatter pairs. Designed as storage for nuclear waste, the site had both a fire and a release of radiation in early 2014 in a distant part of the facility from where the experiment is housed. No one at the site was injured. Nonetheless, the accidents, and the subsequent efforts of repair and remediation, resulted in a nearly two-year suspension of the EXO-200 effort.

Things are looking up now, though: Repairs to the affected area of the site are complete, new safety measures are in place, and scientists are back at work in their separate area of the site, where the experiment is once again collecting data. [Read the rest at Symmetry Magazine….]

A net for neutrinos at the bottom of the sea

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Casting a net for neutrinos

The KM3NeT experiment will catch the elusive particles using the Mediterranean Sea

For Symmetry Magazine:

Like ordinary telescopes, KM3NeT operates in darkness—but there the resemblance ends. The Km3 Neutrino Telescope (where km3 means a cubic kilometer) is a suite of detectors that sits at the pitch-black bottom of the Mediterranean Sea, 3.5 kilometers below the waves and strong currents of the surface.

KM3NeT needs this absolute night to see the faint amount of light from ghostly neutrinos striking water molecules. Neutrinos pass through most material as though it weren’t there, which is why detectors need to be so big to spot them—more volume means more chances to see a neutrino interact. When completed, KM3NeT will be the largest neutrino detector in the world, made of about 1.3 trillion gallons of seawater. [Read the rest at Symmetry Magazine]

Why are neutrino masses so tiny?

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Neutrinos on a seesaw

A possible explanation for the lightness of neutrinos could help answer some big questions about the universe.

For Symmetry Magazine:

Mass is a fundamental property of matter, but there’s still a lot about it we don’t understand—especially when it comes to the strangely tiny masses of neutrinos.

An idea called the seesaw mechanism proposes a way to explain the masses of these curious particles. If shown to be correct, it could help us understand a great deal about the nature of fundamental forces and—maybe—why there’s more matter than antimatter in the universe today. [Read the rest at Symmetry Magazine….]

Traces of particles from the first second after the Big Bang

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Signs of neutrinos from the dawn of time, less than a second after the Big Bang

First unambiguous observation of the cosmic neutrino background

From Ars Technica:

The first 400,000 years after the Big Bang are inaccessible to us by using light; the material that filled the entire cosmos made it opaque. However, neutrinos interact very little with ordinary matter, so they could travel right through the opaque mess. Lots of these low-mass, fast-moving particles were formed in the first second after the Big Bang, so they could provide a sensitive probe of some of the very earliest moments in the Universe.

Unfortunately, these primordial neutrinos have never been detected directly, and they may have too little energy for us to ever detect them. But a new paper published in Physical Review Letters showed an unambiguous indirect detection using measurements of the cosmic microwave background light. This article marks the first clear measurement of the cosmic neutrino background, which is a significant confirmation of one of the major predictions of the Big Bang model. [Read the rest at Ars Technica…]

Why are there three copies of each type of particle?

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The mystery of particle generations

Why are there three almost identical copies of each particle of matter?

For Symmetry Magazine:

The Standard Model of particles and interactions is remarkably successful for a theory everyone knows is missing big pieces. It accounts for the everyday stuff we know like protons, neutrons, electrons and photons, and even exotic stuff like Higgs bosons and top quarks. But it isn’t complete; it doesn’t explain phenomena such as dark matter and dark energy.

The Standard Model is successful because it is a useful guide to the particles of matter we see. One convenient pattern that has proven valuable is generations. Each particle of matter seems to come in three different versions, differentiated only by mass.

Scientists wonder whether that pattern has a deeper explanation or if it’s just convenient for now, to be superseded by a deeper truth. [Read the rest at Symmetry]