Neutrino Astrophysics

Cristina Volpe
We summarize the progress in neutrino astrophysics and emphasize open issues in our understanding of neutrino flavor conversion in media. We discuss solar neutrinos, core-collapse supernova neutrinos and conclude with ultra-high energy neutrinos.

Accelerator on a Chip

Could tiny chips no bigger than grains of rice do the job of a huge particle accelerator? At full potential, a series of these “accelerators on a chip” could boost electrons to the same high energies achieved in SLAC National Accelerator Laboratory’s 2-mile linear accelerator in a distance of just 100 feet. This could make accelerators a lot smaller and more affordable.

The Gordon and Betty Moore Foundation has awarded $13.5 million to an international collaboration led by Stanford University, to develop a working prototype of such an accelerator over the next five years. SLAC and two other national labs provide key in-kind contributions in support of this expansive university effort.

Here’s how “accelerator on a chip” works: Electrons enter the chip and travel through a microscopic tunnel that has tiny ridges carved into its walls. When scientists shine an infrared laser on the chip, the light interacts with those ridges and produces an electrical field that boosts the energy of the passing electrons. In experiments at SLAC, the chip achieved an acceleration gradient, or energy boost over a given distance, roughly 10 times higher than the SLAC linear accelerator can provide.

There’s a lot of work to do to make this technology practical for real-world use. For instance, creating a full-fledged tabletop accelerator will require a more compact way to get electrons up to speed before they enter the chip; the Moore Foundation’s funding will help scientists work on that, and ideally create a prototype the size of a shoebox.

On the plus side, the accelerator on a chip uses commercial lasers and can be manufactured with low-cost, mass-production techniques.

Scientists think a series of these tiny chips could greatly reduce the size and cost of particle accelerators for a variety of applications. For example, the technology could help make compact low-cost accelerators and X-ray devices for security scanning, medicine, biology and materials science. Small, portable X-ray sources could improve medical care for people injured in combat and reduce the cost of medical imaging in hospitals.


The puzzle of the origin of elements in the Universe

A rare nuclear reaction that occurs in red giants has been observed for the first time at the Gran Sasso National Laboratory in Italy. This result was achieved by the LUNA experiment, the world’s only accelerator facility running deep underground.

The LUNA experiment at the INFN Gran Sasso National Laboratory in Italy has observed a rare nuclear reaction that occurs in giant red stars, a type of star in which our sun will also evolve. This is the first direct observation of sodium production in these stars, one of the nuclear reactions that is fundamental for the formation of the elements that make up the universe. The study has been published in Physical Review Letters.

LUNA (Laboratory for Underground Nuclear Astrophysics) is a compact linear accelerator. It is the only one in the world installed in an underground facility, shielded against cosmic rays. The experiment aims to study the nuclear reactions that take place inside stars where, like in an intriguing and amazing cosmic kitchen, the elements that make up matter are formed and then driven out by gigantic explosions and scattered as cosmic dust.

For the first time, this experiment has observed three “resonances” in the neon-sodium cycle responsible for sodium production in red giants and energy generation (the 22Ne(p,g)23Na. In the same way as in acoustics, a “resonance” is a particular condition that makes the reaction inside the star extremely likely. LUNA recreates the energy ranges of nuclear reactions and, with its accelerator, goes back in time to one hundred million years after the Big Bang, to the formation of the first stars and the start of those processes that gave rise to mysteries we still do not fully understand, such as the huge variety in the quantities of the elements in the universe.

“This result is an important piece in the puzzle of the origin of the elements in the universe, which the experiment has been studying for the last 25 years”, remarked Paolo Prati, spokesperson for the LUNA experiment. “Stars generate energy and at the same time assemble atoms through a complex system of nuclear reactions. A very small number of these reactions have been studied in the conditions under which they occur inside stars, and a large proportion of those few cases have been observed with this accelerator”.

LUNA uses a compact linear accelerator in which hydrogen and helium beams are accelerated and made to collide with a target (in this case, a neon isotope), to produce other particles. Special detectors obtain images of the products of the collisions and identify the reaction to be examined. These extremely rare processes can only be detected in conditions of cosmic silence. The rock surrounding the underground facility at the Gran Sasso National Laboratory shields the experiment against cosmic rays and protects its measurements.

LUNA is an international collaboration involving some 50 Italian, German, Scottish and Hungarian researchers from the National Institute for Nuclear Physics in Italy, the Helmholtz-Zentrum Dresden-Rossendorf in Germany, the MTA-ATOMKI in Hungary and the School of Physics and Astronomy of the University of Edinburgh in the UK.

Read more at and (Three New Low-Energy Resonances in the 22Ne(p,g)23Na Reaction)

Scientists Mix Matter and Anti-Matter to Resolve Decade-Old Proton Puzzle

Fans of science and science fiction have been warned that mixing matter with anti-matter can yield explosive results. And that’s just what physicists were counting on, in hopes of blowing wide open a puzzle that has confounded them for the last decade.

The puzzle comes from experiments that aimed to determine how quarks, the building blocks of the proton, are arranged inside that particle. That information is locked inside a quantity that scientists refer to as the proton’s electric form factor. The electric form factor describes the spatial distribution of the quarks inside the proton by mapping the charge that the quarks carry.

Nuclear physicists have used two different methods to measure the proton’s electric form factor. But the deeper that they probe inside the proton, the more the results from these two different methods disagree. Eventually, the measurements provided by one method amount to about five times the quantity yielded by the other. This huge discrepancy is much larger than the experimental uncertainty in the measurements.

“The proposed solution for the discrepancy is that the analysis of one set of measurements was too simplistic,” says Larry Weinstein, a professor of physics at Old Dominion University. “And that if we include something that is known as the two-photon effect, they both should agree.”

The effect is a result of the manner in which nuclear scientists conduct their probes of the proton. The proton is probed by bombarding it with energetic electrons and observing how the two particles interact. Most of the time, this interaction consists of the electron exchanging a single virtual photon with the proton. A virtual photon is just a packet of energy that an electron gives up to the proton as it collides with the particle. But sometimes, the electron interacts with the proton differently; it may conjure up two virtual photons that it passes on to the proton…. Continue reading Scientists Mix Matter and Anti-Matter to Resolve Decade-Old Proton Puzzle


Nuclear War from a Cosmic Perspective

 We humans have invested great resources and ingenuity in building the Spectacular  Thermonuclear Unpredictable Population Incineration Device, (acronym S.T.U.P.I.D.), whose two adjustable knobs determine its explosive power X and the probability P that it goes off spontaneously in any given year.

We humans have invested great resources and ingenuity in building the Spectacular Thermonuclear Unpredictable Population Incineration Device, (acronym S.T.U.P.I.D.), whose two adjustable knobs determine its explosive power X and the probability P that it goes off pontaneously in any given year.

Max Tegmark
I discuss the impact of computer progress on nuclear war policy, both by enabling more accurate nuclear winter simulations and by affecting the probability of war starting accidentally. I argue that from a cosmic perspective, humanity’s track record of risk mitigation is inexcusably pathetic, jeopardizing the potential for life to flourish for billions of years.