Physicist Anne Schukraft of Fermi National Accelerator Laboratory explains.

Have a follow-up question about neutrinos? Ask Anne when she takes over the @symmetrymag Twitter account on Friday, February 17, at noon Central.

You can watch a playlist of the #AskSymmetry videos here.

Have a burning question about particle physics? Let us know via email or Twitter (using the hashtag #AskSymmetry). We might answer you in a future video!

The Standard Model is holding strong after a new precision measurement of a rare subatomic process.

For the first time, the LHCb experiment at CERN has independently observed the decay of the B_s⁰ particle—a heavy composite particle consisting of a bottom antiquark and a strange quark—into two muons. The LHCb experiment co-discovered this rare process in 2015 after combining results with the CMS experiment.

Theorists predicted that this particular decay would occur only a few times out of a billion.

“Our measurement is slightly lower than predictions, but well within the range of experimental uncertainty and fully compatible with our models,” says Flavio Archilli, one of the co-leaders of this analysis and a postdoc at Nikhef National Institute for Subatomic Physics. “The theoretical predictions are very accurate, so now we want to improve our precision to see if our measurement is sitting right on top of the expected value or slightly outside, which could be an indication of new physics.”

The LHCb experiment examines the properties and decay patterns of particles to search for cracks in the Standard Model, our best description of the fundamental particles and forces. The Standard Model is famously incomplete because it does not address issues such as gravity and the presence of dark matter. Any deviations from the Standard Model’s predictions could be evidence of new physics at play.

Supersymmetry, for example, is a popular theory that adds a host of new particles to the Standard Model and ameliorates many of its shortcomings—such as mathematical imbalances between how the different types of particles contribute to subatomic interactions.

“We love this decay because it is one of the most promising places to search for any new effects of supersymmetry,” Archilli says. “Scientists searched for this decay for more than 30 years and now we finally have the first single-experiment observation.”

This new measurement by the LHCb experiment combines data taken from Run 1 and Run 2 of the Large Hadron Collider and employs more refined analysis techniques, making it the most precise measurement of this process to date. In addition to measuring the rate of this rare decay, LHCb researchers also measured how long the B_s⁰ particle lives before it transforms into the two muons—another measurement which agrees with the Standard Model’s predictions.

“It's gratifying to have achieved these results,” says Universita di Pisa scientist Matteo Rama, one of the co-leaders of this analysis. "They reward the efforts made to improve the analysis techniques, to exploit our data even further. We look forward to updating the measurement with more data with the hope to observe, one day, significant deviations from the Standard Model predictions."

This Valentine’s Day, we challenged our readers to send us physics-inspired love poems. You answered the call: We received dozens of submissions—in four different languages! You can find some of our favorite entries below. 

But first, as a warm-up, enjoy a video of real scientists at Fermi National Accelerator Laboratory reciting physics-related Valentine’s Day haiku:

Or read the haiku for yourself:

Reader poems

Thanks to all of our readers who submitted poems! In no particular order, here are some of our favorites:

For now, I’m seeing other quarks, some charming and some strange
But when we meet, I know we will all physics rearrange
For you, stop squark, will soon reveal the standard model as deficient
To me, you are my superpartner; the only one sufficient.
Without you, I just spin one-half of what our world could be
But you and I will couple soon in perfect symmetry.
All fundamental forces, we are meant to unify
In brilliant theory only love itself could clarify
Now though I may seem hypercharged and strongly interactive,
I must show my true colors if I hope to be attractive.
Without you, I just don’t feel really quite just like a top
But I’m confident I will yet find love in the name of stop.

- Jared Sagoff

The gravity that
Pulls my soul to you dilates:
Your beauty slows time.

- Philip Michaels

A Valentine for Two Quarks

Some people wish for one true love,
like dear old Ma and Pa.
That lifestyle’s not for us; we like
our quark ménage à trois.

You see, some like a threesome,
and I love both of you.
No green quark would be seen without
a red quark and a blue.

The sea is full of other quarks,
but darlings, I don’t heed ‘em.
You must believe I don’t exploit
my asymptotic freedom.

And when you pull away from me,
I just can’t take the stress.
My attraction just grows stronger
(coefficient alpha-s).

With you, my life is colourless;
you bring stability.
Without you, I’m unstable,
so I need you, Q.C.D.

I love our quirky, quarky love.
My Valentines, let’s carry on
exchanging gluons wantonly,
and make a little baryon.

- Cheryl Patrick

Will it work this time?
The wavefunction collapses.
Single once again.

- Anonymous

Our hearts were once close; two nucleons held tight
By a force that was strong, and a love that burned bright.
But, that force became weaker as the days faded ‘way,
And with it, our bond began to decay.

I’ve realize that opposites don’t always attract
(Otherwise, the atom would be more compact),
And opposites we were, our differences great,
Continuing this way, we’d annihilate.

In truth, I’ve quite had it with your duality,
Your warm disposition; cold mentality.
We must be entangled - what else can explain
How, though we are distant, you still cause me pain?

We’ve exchanged mediators, but our half-lives were short,
All data suggests we should promptly abort.
Our collision is over, and signatures thereof
Have vanished, leaving us not a quantum of love.

- Peter Voznyuk

Love ignited light,
Eternal and everywhere:
A Cosmic Background

- Akshay Jogoo

Like energy dear
our love will last forever,
theoretically

- L. Brennan

The race is on to build the most sensitive US-based experiment designed to directly detect dark matter particles. Department of Energy officials have formally approved a key construction milestone that will propel the project toward its April 2020 goal for completion.

The LUX-ZEPLIN experiment, which will be built nearly a mile underground at the Sanford Underground Research Facility in Lead, South Dakota, is considered one of the best bets yet to determine whether theorized dark matter particles known as WIMPs (weakly interacting massive particles) actually exist. 

The fast-moving schedule for LZ will help the US stay competitive with similar next-gen dark matter direct-detection experiments planned in Italy and China.

On February 9, the project passed a DOE review and approval stage known as Critical Decision 3, which accepts the final design and formally launches construction.

“We will try to go as fast as we can to have everything completed by April 2020,” says Murdock “Gil” Gilchriese, LZ project director and a physicist at Lawrence Berkeley National Laboratory, the lead lab for the project. “We got a very strong endorsement to go fast and to be first.” The LZ collaboration now has about 220 participating scientists and engineers who represent 38 institutions around the globe.

The nature of dark matter—which physicists describe as the invisible component or so-called “missing mass” in the universe —has eluded scientists since its existence was deduced through calculations by Swiss astronomer Fritz Zwicky in 1933.

The quest to find out what dark matter is made of, or to learn whether it can be explained by tweaking the known laws of physics in new ways, is considered one of the most pressing questions in particle physics.

Successive generations of experiments have evolved to provide extreme sensitivity in the search that will at least rule out some of the likely candidates and hiding spots for dark matter, or may lead to a discovery.

LZ will be at least 50 times more sensitive to finding signals from dark matter particles than its predecessor, the Large Underground Xenon experiment, which was removed from Sanford Lab last year to make way for LZ. The new experiment will use 10 metric tons of ultra-purified liquid xenon to tease out possible dark matter signals. 

“The science is highly compelling, so it’s being pursued by physicists all over the world,” says Carter Hall, the spokesperson for the LZ collaboration and an associate professor of physics at the University of Maryland. “It's a friendly and healthy competition, with a major discovery possibly at stake.”

A planned upgrade to the current XENON1T experiment at National Institute for Nuclear Physics’ Gran Sasso Laboratory in Italy, and China's plans to advance the work on PandaX-II, are also slated to be leading-edge underground experiments that will use liquid xenon as the medium to seek out a dark matter signal. Both of these projects are expected to have a similar schedule and scale to LZ, though LZ participants are aiming to achieve a higher sensitivity to dark matter than these other contenders.

Hall notes that while WIMPs are a primary target for LZ and its competitors, LZ’s explorations into uncharted territory could lead to a variety of surprising discoveries. “People are developing all sorts of models to explain dark matter,” he says. “LZ is optimized to observe a heavy WIMP, but it’s sensitive to some less-conventional scenarios as well. It can also search for other exotic particles and rare processes.”

LZ is designed so that if a dark matter particle collides with a xenon atom, it will produce a prompt flash of light followed by a second flash of light when the electrons produced in the liquid xenon chamber drift to its top. The light pulses, picked up by a series of about 500 light-amplifying tubes lining the massive tank—over four times more than were installed in LUX—will carry the telltale fingerprint of the particles that created them.

Daniel Akerib, Thomas Shutt and Maria Elena Monzani are leading the LZ team at SLAC National Accelerator Laboratory. The SLAC effort includes a program to purify xenon for LZ by removing krypton, an element that is typically found in trace amounts with xenon after standard refinement processes. “We have already demonstrated the purification required for LZ and are now working on ways to further purify the xenon to extend the science reach of LZ,” Akerib says.

SLAC and Berkeley Lab collaborators are also developing and testing hand-woven wire grids that draw out electrical signals produced by particle interactions in the liquid xenon tank. Full-size prototypes will be operated later this year at a SLAC test platform. “These tests are important to ensure that the grids don't produce low-level electrical discharge when operated at high voltage, since the discharge could swamp a faint signal from dark matter,” Shutt says. 

Hugh Lippincott, a Wilson Fellow at Fermi National Accelerator Laboratory and the physics coordinator for the LZ collaboration, says, “Alongside the effort to get the detector built and taking data as fast as we can, we’re also building up our simulation and data analysis tools so that we can understand what we’ll see when the detector turns on. We want to be ready for physics as soon as the first flash of light appears in the xenon.” Fermilab is responsible for implementing key parts of the critical system that handles, purifies, and cools the xenon.

All of the components for LZ are painstakingly measured for naturally occurring radiation levels to account for possible false signals coming from the components themselves. A dust-filtering cleanroom is being prepared for LZ's assembly and a radon-reduction building is under construction at the South Dakota site—radon is a naturally occurring radioactive gas that could interfere with dark matter detection. These steps are necessary to remove background signals as much as possible.

The vessels that will surround the liquid xenon, which are the responsibility of the UK participants of the collaboration, are now being assembled in Italy. They will be built with the world's most ultra-pure titanium to further reduce background noise.

To ensure unwanted particles are not misread as dark matter signals, LZ's liquid xenon chamber will be surrounded by another liquid-filled tank and a separate array of photomultiplier tubes that can measure other particles and largely veto false signals. Brookhaven National Laboratory is handling the production of another very pure liquid, known as a scintillator fluid, that will go into this tank.

The cleanrooms will be in place by June, Gilchriese says, and preparation of the cavern where LZ will be housed is underway at Sanford Lab. Onsite assembly and installation will begin in 2018, he adds, and all of the xenon needed for the project has either already been delivered or is under contract. Xenon gas, which is costly to produce, is used in lighting, medical imaging and anesthesia, space-vehicle propulsion systems, and the electronics industry.

“South Dakota is proud to host the LZ experiment at SURF and to contribute 80 percent of the xenon for LZ,” says Mike Headley, executive director of the South Dakota Science and Technology Authority (SDSTA) that oversees the facility. “Our facility work is underway and we’re on track to support LZ’s timeline.”

UK scientists, who make up about one-quarter of the LZ collaboration, are contributing hardware for most subsystems. Henrique Araújo, from Imperial College London, says, “We are looking forward to seeing everything come together after a long period of design and planning.”

Kelly Hanzel, LZ project manager and a Berkeley Lab mechanical engineer, adds, “We have an excellent collaboration and team of engineers who are dedicated to the science and success of the project.” The latest approval milestone, she says, “is probably the most significant step so far,” as it provides for the purchase of most of the major components in LZ’s supporting systems.

Major support for LZ comes from the DOE Office of Science’s Office of High Energy Physics, South Dakota Science and Technology Authority, the UK’s Science & Technology Facilities Council, and by collaboration members in South Korea and Portugal.

Editor's note: This article is based on a press release published by Berkeley Lab.

Has the love of your life fallen for particle physics? Let the Symmetry team help you reach their heart—with haikus.

On Valentine’s Day, we will publish a collection of physics-related love poems written by Symmetry staff and—if you are so inclined—by readers like you!

Send your poems (haiku format optional) to letters@symmetrymagazine.org by Monday, February 13, at 10 a.m. Central. If we really like yours, we may send you a prize.

For inspiration, consider the following:

When we peer through our telescopes into the cosmos, we can see stars and galaxies reaching back billions of years. This is possible only because the intergalactic medium we’re looking through is transparent. This was not always the case. 

Around 380,000 years after the Big Bang came recombination, when the hot mass of particles that made up the universe cooled enough for electrons to pair with protons, forming neutral hydrogen. This brought on the dark ages, during which the neutral gas in the intergalactic medium absorbed most of the high-energy photons around it, making the universe opaque to these wavelengths of light. 

Then, a few hundred million years later, new sources of energetic photons appeared, stripping hydrogen atoms of their electrons and returning them to their ionized state, ultimately allowing light to easily travel through the intergalactic medium. After this era of reionization was complete, the universe was fully transparent once again. 

Physicists are using a variety of methods to search for the sources of reionization, and finding them will provide insight into the first galaxies, the structure of the early universe and possibly even the properties of dark matter. 

Energetic sources

Current research suggests that most—if not all—of the ionizing photons came from the formation of the first stars and galaxies. “The reionization process is basically a competition between the rate at which stars produce ionizing radiation and the recombination rate in the intergalactic medium,” says Brant Robertson, a theoretical astrophysicist at the University of California, Santa Cruz. 

However, astronomers have yet to find these early galaxies, leaving room for other potential sources. The first stars alone may not have been enough. “There are undoubtedly other contributions, but we argue about how important those contributions are,” Robertson says. 

Active galactic nuclei, or AGN, could have been a source of reionization. AGN are luminous bodies, such as quasars, that are powered by black holes and release ultraviolet radiation and X-rays. However, scientists don’t yet know how abundant these objects were in the early universe. 

Another, more exotic possibility, is dark matter annihilation. In some models of dark matter, particles collide with each other, annihilating and producing matter and radiation. “If through this channel or something else we could find evidence for dark matter annihilation, that would be fantastically interesting, because it would immediately give you an estimate of the mass of the dark matter and how strongly it interacts with Standard Model particles,” says Tracy Slatyer, a particle physicist at MIT. 

Dark matter annihilation and AGN may have also indirectly aided reionization by providing extra heat to the universe. 

Probing the cosmic dawn

To test their theories of the course of cosmic reionization, astronomers are probing this epoch in the history of the universe using various methods including telescope observations, something called “21-centimeter cosmology” and probing the cosmic microwave background. 

Astronomers have yet to find evidence of the most likely source of reionization—the earliest stars—but they’re looking. 

By assessing the luminosity of the first galaxies, physicists could estimate how many ionizing photons they could have released. “[To date] there haven't been observations of the actual galaxies that are reionizing the universe—even Hubble can't deliver any of those—but the hope is that the James Webb Space Telescope can,” says John Wise, an astrophysicist at Georgia Tech. 

Some of the most telling information will come from 21-centimeter cosmology, so called because it studies 21-centimeter radio waves. Neutral hydrogen gives off radio waves of this frequency, ionized hydrogen does not. Experiments such as the forthcoming Hydrogen Epoch of Reionization Array will detect neutral hydrogen using radio telescopes tuned to this frequency. This could provide clinching evidence about the sources of reionization.

“The basic idea with 21-centimeter cosmology is to not look at the galaxies themselves, but to try to make direct measurements of the intergalactic medium—the hydrogen between the galaxies,” says Adrian Liu, a Hubble fellow at UC Berkeley. “This actually lets you, in principle, directly see reionization, [by seeing how] it affects the intergalactic medium.”

By locating where the universe is ionized and where it is not, astronomers can create a map of how neutral hydrogen is distributed in the early universe. “If galaxies are doing it, then you would have ionized bubbles [around them]. If it is dark matter—dark matter is everywhere—so you're ionizing everywhere, rather than having bubbles of ionizing gas,” says Steven Furlanetto, a theoretical astrophysicist at the University of California, Los Angeles. 

Physicists can also learn about sources of reionization by studying the cosmic microwave background, or CMB. 

When an atom is ionized, the electron that is released scatters and disrupts the CMB. Physicists can use this information to determine when reionization happened and put constraints on how many photons were needed to complete the process. 

For example, physicists reported last year that data released from the Planck satellite was able to lower its estimate of how much ionization was caused by sources other than galaxies. “Just because you could potentially explain it with star-forming galaxies, it doesn't mean that something else isn't lurking in the data,” Slatyer says. “We are hopefully going to get much better measurements of the reionization epoch using experiments like the 21-centimeter observations.” 

It is still too early to rule out alternative explanations for the sources of reionization, since astronomers are still at the beginning of uncovering this era in the history of our universe, Liu says. “I would say that one of the most fun things about working in this field is that we don't know exactly what happened.”

Professors and students of physics in Latin America have much to offer the world of physics. But for those interested in designing and building the complex experiments needed to gather physics data, hands-on experimentation in much of Central and South America has been lacking. It was that gap that something called the Escaramujo Project aimed to fill by bringing basic components to students who could then assemble them into fully functional detectors.

“It was something completely new,” says Luis Rodolfo Pérez Sánchez, a student at the Universidad Autónoma de Chiapas, Mexico, who is writing his thesis based on measurements taken with the detector. “Until now, there was no device at the university where one could work directly with their hands.”

Each group of students built a detector, which they used to measure cosmic-ray muons (particles coming from space). But they did more than that. They used a Linux open-source computer operating system for the first time, calibrated the equipment, plotted data using the software ROOT and became part of an international community. The students used their detectors to participate in International Cosmic Day, an annual event where scientists around the world measure cosmic rays and share their data.

The Escaramujo Project is led by Federico Izraelevitch, who worked at Fermi National Accelerator Laboratory near Chicago during its planning stages and is now a professor at Instituto Dan Beninson in Argentina. During the project, Izraelevitch and his wife, Eleonora, traveled with three canine companions on a road trip from Chicago to Buenos Aires, stopping to teach workshops in Mexico, Guatemala, Costa Rica, Colombia, Ecuador, Peru and Bolivia. Many nights found them in spots with no tourist lodging or even places to camp with their van.

“People received us with a smile and gave us a cup of coffee, or food, or whatever we needed at the time,” Izraelevitch says. “People are amazing.” 

In many locations, students took their detector on a field trip shortly after assembling it. The group in Pasto, Colombia, turned theirs into a muon telescope and carted it to the nearby Galeras volcano, where a kind local lent them a power supply to get things running. They studied an effect of the volcano: muon attenuation, or weakening of the muon signal. Students in La Paz, Bolivia, placed the detector in the back of a van and drove it to a lofty observatory, measuring how the muon flux changed with altitude. 

The Escaramujo Project forged direct connections between students at eight universities, who can now use their detectors to collect and share data with other Escaramujo participants.

“This state is one of the poorest states in Mexico,” says Karen Caballero, a professor at UNACH who brought the Escaramujo Project to the university. “The students in Chiapas don’t have the opportunity to participate in international initiatives, so this has been very, very important for them.”

Caballero says there are plans for the full Escaramujo cohort to use their detectors to calibrate expansions of the Latin American Giant Observatory, used for an experiment that began in 2005. LAGO uses multiple sites throughout Central and South America to study gamma-ray bursts, some of the most powerful explosions in the universe, as well as space weather.

While the workshops for the program wrapped up in early 2016, Izraelevitch says he hopes to visit more universities and lead more workshops in the future.

“Hopefully all these sites can continue growing and working as a collaboration in the future,” he says. “These people are capable and have all the knowledge and enthusiasm for being part of a major, first-class experiment.”