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Observation of excess events in the XENON1T dark matter experiment –



The XENON1T detector. Visible is the bottom array of photomultiplier tubes, and the copper structure that creates the electric drift field. Credit: Kavli Institute for the Physics and Mathematics of the Universe

Scientists from the international XENON collaboration, an international experimental group including the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU), University of Tokyo; the Institute for Cosmic Ray Research (ICRR), University of Tokyo; the Institute for Space-Earth Environmental Research (ISEE), Nagoya University; the Kobayashi-Maskawa Institute for the Origin of Particles and the Universe (KMI), Nagoya University; and the Graduate School of Science, Kobe University, announced today that data from their XENON1T, the world’s most sensitive dark matter experiment, show a surprising excess of events. The scientists do not claim to have found dark matter. Instead, they have observed an unexpected rate of events, the source of which is not yet fully understood. The signature of the excess is similar to what might result from a tiny residual amount of tritium (a hydrogen atom with one proton and two neutrons), but could also be a sign of something more exciting—such as the existence of a new particle known as the solar axion or the indication of previously unknown properties of neutrinos.

XENON1T was operated deep underground at the INFN Laboratori Nazionali del Gran Sasso in Italy, from 2016 to 2018. It was primarily designed to detect dark matter, which makes up 85% of the matter in the universe. So far, scientists have only observed indirect evidence of dark matter, and a definitive, direct detection is yet to be made. So-called WIMPs (Weakly Interacting Massive Particles) are among the theoretically preferred candidates, and XENON1T has thus far set the best limit on their interaction probability over a wide range of WIMP masses. In addition to WIMP dark matter, XENON1T was also sensitive to different types of new particles and interactions that could explain other open questions in physics. Last year, using the same detector, these scientists published in Nature the observation of the rarest nuclear decay ever directly measured.

The XENON1T detector was filled with 3.2 tons of ultra-pure liquefied , 2.0 t of which served as a target for particle interactions. When a particle crosses the target, it can generate tiny signals of light and free electrons from a xenon atom. Most of these interactions occur from particles that are known to exist. Scientists therefore carefully estimated the number of background events in XENON1T. When data of XENON1T were compared to known backgrounds, a surprising excess of 53 events over the expected 232 events was observed.

This raises the exciting question: Where is this excess coming from?

Observation of Excess Events in the XENON1T Dark Matter Experiment
The excess observed in XENON1T in the electronic recoil background at low energies, compared to the level expected from known backgrounds indicated as the red line. Credit: Kavli Institute for the Physics and Mathematics of the Universe

One explanation could be a new, previously unconsidered source of background, caused by the presence of tiny amounts of tritium in the XENON1T detector. Tritium, a radioactive isotope of hydrogen, spontaneously decays by emitting an electron with an energy similar to what was observed. Only a few tritium atoms for every 1025 (10,000,000,000,000,000,000,000,000!) xenon atoms would be needed to explain the excess. Currently, there are no independent measurements that can confirm or disprove the presence of tritium at that level in the detector, so a definitive answer to this explanation is not yet possible.

More excitingly, another explanation could be the existence of a new particle. In fact, the excess observed has an energy spectrum similar to that expected from axions produced in the Sun. Axions are hypothetical particles that were proposed to preserve a time-reversal symmetry of the nuclear force, and the Sun may be a strong source of them. While these solar axions are not dark matter candidates, their detection would mark the first observation of a well-motivated but never observed class of new particles, with a large impact on our understanding of fundamental physics, but also on astrophysical phenomena. Moreover, axions produced in the early universe could also be the source of dark matter.

Alternatively, the excess could also be due to neutrinos, trillions of which pass through your body, unhindered, every second. One explanation could be that the (a property of all particles) of neutrinos is larger than its value in the Standard Model of elementary particles. This would be a strong hint to some other new physics needed to explain it.

Of the three explanations considered by the XENON collaboration, the observed excess is most consistent with a solar axion signal. In statistical terms, the solar hypothesis has a significance of 3.5 sigma, meaning that there is about a 2/10,000 chance that the observed excess is due to a random fluctuation rather than a signal. While this significance is fairly high, it is not large enough to conclude that axions exist. The significance of both the tritium and neutrino magnetic moment hypotheses corresponds to 3.2 sigma, meaning that they are also consistent with the data.

XENON1T is now upgrading to its next phase-XENONnT-with an active xenon mass three times larger and a background that is expected to be lower than that of XENON1T. With better data from XENONnT, the XENON collaboration is confident it will soon find out whether this excess is a mere statistical fluke, a background contaminant, or something far more exciting: a new particle or interaction that goes beyond known physics.

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Dark matter detector observes rarest event ever recorded

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'Canada, Canada, Cana…da': Researchers Spot Change To White-Throated Sparrow's Song – NPR




Experienced birders might be familiar with the sounds of the white-throated sparrow. Some say the end of the call sounds like the word Canada repeated several times.


KEN OTTER: Canada, Canada, Canada, Canada.

KELLY: That is Dr. Ken Otter. In 2000 he was doing his first field study in northern British Columbia. He was studying area bird populations and made a discovery.

OTTER: I was working on chickadees, but I noticed that there was white-throated sparrows around.

KELLY: White-throated sparrows – they weren’t known to be in the area, but there they were. And they sounded a bit different.

OTTER: They were going, can-a-can-a-can-a-Canada-da (ph), almost like they were stuttering that last phrase.


KELLY: Otter figured this unusual new tune was maybe specific to this one community of sparrows.

OTTER: It wasn’t until seven or eight years later that we started to realize that the song was actually spreading eastwards.

KELLY: Yeah. In 2004 only around half of the sparrows in Alberta, Canada, were singing the song. By 2014, that had changed. You might say the tweet went viral.

OTTER: All the birds in Alberta were now singing this Western dialect.

KELLY: Now, Otter does not know why exactly this new song has caught on. He imagines this little spark of variation maybe might improve a male sparrow’s chances with the ladies.

OTTER: If there’s a little bit of female preference, which is something we want to test next, then it would be advantageous for males to sing an atypical song. And after a while, it would just take over.

KELLY: In that case, it seems like the white-throated sparrow’s sultry new crooner is here to stay.


KELLY: You’re listening to All Tweets Considered.

Copyright © 2020 NPR. All rights reserved. Visit our website terms of use and permissions pages at for further information.

NPR transcripts are created on a rush deadline by Verb8tm, Inc., an NPR contractor, and produced using a proprietary transcription process developed with NPR. This text may not be in its final form and may be updated or revised in the future. Accuracy and availability may vary. The authoritative record of NPR’s programming is the audio record.

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How can we be alone? – Skywatching –



The latest estimate is that there are around six billion Earth-like planets in our galaxy alone.

However, when we really dig into the issue regarding what makes a planet suitable for life as we know it, this large number could be a considerable understatement.

First, we know about places where liquid water and warmth are available for living things, but otherwise they are very un-Earth-like — such as Europa, one of the moons of Jupiter, where tidal forces warm an ocean hidden under a roof of ice.

For the moment, let’s just stick to the Earth-like planets. The starting point in identifying an Earth-like planet is that it is the right size, it has an atmosphere, and its surface temperature is high enough to support a water ocean.

There also needs to be a water cycle, where water evaporates from the ocean and returns to it as rain. If there are landmasses, they will be irrigated and material will be eroded from the land and taken into the sea as nutrients for living creatures. However, there is a range of conditions under which this may happen.

First, the planet should be in the Goldilocks Zone, where the planet receives enough warmth and light from its star to ensure a high enough surface temperature and to drive a water cycle.

This is where the situation becomes more complicated. Planets, including ours, exist in a thermal equilibrium. Heat from our star warms our world. As the temperature rises, the Earth radiates increasing amounts of infrared, sending heat off into space.

Eventually, the input and output are equal and the planet’s temperature stabilizes. Intriguingly though, if we do this calculation for the Earth, we find our planet should be frozen solid, with a mean temperature more or less equal to the Moon’s, around minus 50C.

This obviously isn’t the case, and the explanation is the greenhouse effect. Gases such as water vapour, carbon dioxide and methane are greenhouse gases, which means they impeded the ability of a planet to re-radiate heat into space.

The result is that in order to meet a balance of input and output, the planet has to be hotter. Planets with lots of greenhouse gases can be further from their stars and still have comfortable temperatures.

Planets with atmospheres low in greenhouse gases must be closer. The atmospheres of young planets are rich in greenhouse gases.

During the 4.5 billion years since the Earth formed, the Sun has brightened steadily, but on Earth living things removed them and replaced them with oxygen, which is not a greenhouse gas, keeping our environment stable and our planet inhabitable.

In the 1970s, James Lovelock proposed the Gaia Hypothesis (Gaia is the Earth goddess), in which he proposed that once life is established, it has a certain power to keep its environment comfortable.

There are two other factors.

First, there are clouds.

Water evaporated from the oceans by solar heat forms clouds, which can reflect solar energy back into space, providing a stabilizing influence. Of course, more energy in the atmosphere can drive more severe weather.

Second, there is dust.

Every day, warm air heated by contact with warm ground rises, carrying dust with it.  This can act as an insulator, keeping in heat, or as a reflector, sending it back out, depending on the grain size and the amount.

In addition to being the right distance from their stars, we need our planets to have an atmosphere and a signature of water vapour.

If we see oxygen, which needs living things to produce and maintain it, we can be pretty sure there are living things.

Maybe fortunately, the distances between stars ensure it will be a long time before we can interfere with our alien brethren or they with us.

  • Jupiter and Saturn rise in the southeast around midnight
  • Mars follows in the early hours.
  • Venus lies low in the sunrise glow.
  • The Moon will reach Last Quarter on the 12th.

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Full buck moon with penumbral lunar eclipse visible in Saskatchewan this weekend – Humboldt Journal



Saskatchewan residents will have the opportunity to view a magnificent full Buck Moon this July in addition to a lunar eclipse. 

Named after the time of year when young bucks begin to grow new antlers from their foreheads, the July full moon marks a time of renewal. With this in mind, the July moon, like the other months of the year, has many names.

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For example, the full moon is also known as the “Thunder Moon.” According to the Old Farmer’s Almanac, the moon was given that name, “because thunderstorms are so frequent during this month.” They note that Native peoples would give distinctive names to each reoccurring full moon to mark the change of seasons. As such, many of these names arose when Native Americans first interacted with colonialists.

The moon also has number of Native American names which, translated directly into English, mean the “Ripe Corn Moon” by the Cherokee, “Middle of Summer Moon” by the Ponca, and “Moon When Limbs of Trees Are Broken by Fruit” by the Zuni.

The full Buck Moon will be at its fullest on July 4.

As the full moon increases in fullness, Humboldt residents will also be able to view a ‘penumbral lunar eclipse’. explains how it is set to begin July 4 at 9:07 p.m. but that it won’t be directly visible from Humboldt at that time.

At 9:24 p.m., “it will be rising but the the combination of a very low moon and the total eclipse phase will make the moon so dim that it will be extremely difficult to view until moon gets higher in the sky or the total phase ends.” 

The moon will be closest to the centre of shadow at 10:29 p.m. (-0.65 Magnitude). It will end at 11:52 p.m.

During this penumbral lunar eclipse, the Earth’s main shadow does not cover the Moon.

Stargazers should opt to travel as far away from city lights as possible in order to avoid light pollution that will obscure the clarity of heavenly bodies. While this works best in more remote places, anywhere that has a higher elevation will also provide more ideal viewing conditions.

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