IceCube rules out last Standard Model explanation of ANITA’s anomalous neutrino events
The IceCube Neutrino Observatory is possibly the strangest telescope on Earth. From its home at the South Pole, it sits and waits for fundamental particles called neutrinos to pass through its 5,160 optical detectors buried in the ice. When a neutrino interacts with a hydrogen or oxygen atom in the ice, it produces a signal that IceCube can detect.
But IceCube isn’t the only neutrino experiment in Antarctica. There is also the ANITA (the ANtarctic Impulsive Transient Antenna) experiment, which flies a balloon over the continent and points radio antennae toward the ground. ANITA searches for radio waves because extremely high-energy neutrinos—those hundreds of times more energetic than the ones that IceCube commonly detects—can produce intense radio signals when they smash into an atom in the ice.
From its balloon flights, ANITA claimed to have detected a few events that appear to be signals of these extremely high-energy neutrinos, so the IceCube Collaboration decided to investigate. In a paper submitted today to The Astrophysical Journal, they outline their search for an intense neutrino source in the direction of the events detected by ANITA. The collaboration found that these neutrinos could not have come from an intense point source. Other explanations for the anomalous signals—possibly involving exotic physics—need to be considered.
When ANITA reported signals that looked like extremely high-energy neutrinos, physicists were puzzled. These neutrinos had arrived at an angle that suggested they had just traveled through most of the planet, which is not expected for neutrinos at these energies.
“It’s commonly said that neutrinos are ‘elusive’ or ‘ghostly’ particles because of their remarkable ability to pass through material without smashing into something,” says Alex Pizzuto of the University of Wisconsin–Madison, one of the leads on this paper. “But at these incredible energies, neutrinos are like bulls in a china shop—they become much more likely to interact with particles in Earth.”
Many scientists have since come up with potential explanations for these weird signals, and one possibility is that a really intense neutrino source produced them. After all, if a source produced huge numbers of neutrinos, it is more plausible that one or two made it to ANITA.
So Pizzuto and his collaborators decided to see whether there was an intense neutrino source shooting a beam of neutrinos toward Earth—a point source. To do this, the researchers took eight years of IceCube data and looked for correlations between the locations of the ANITA events and the locations of the IceCube events.
Since the researchers could not know how long a potential point source might have been emitting neutrinos, their analyses used three different and complementary approaches equipped to find coincidences on different timescales. Their analyses also had to account for uncertainty in the ANITA events’ directions because the events do not have definite positions on the sky.
Once they had addressed those challenges, the researchers simulated neutrinos passing through Earth to see how many incident neutrinos would be necessary for ANITA to see one event, and they then did the same for IceCube.
In all three searches, they found no evidence for a neutrino source in the direction of the strange ANITA events. This is particularly intriguing because, due to a process called tau neutrino regeneration, the extremely high-energy events that don’t make it all the way to ANITA should still be detectable by IceCube.
“This process makes IceCube a remarkable tool to follow up the ANITA observations, because for each anomalous event that ANITA detects, IceCube should have detected many, many more—which, in these cases, we didn’t,” says Anastasia Barbano of the University of Geneva in Switzerland, another lead on this paper. “That means that we can rule out the idea that these events came from some intense point source, because the odds of ANITA seeing an event and IceCube not seeing anything are so slim.”
When the ANITA events were detected, the main hypotheses were an astrophysical explanation (like an intense neutrino source), a systematics error (like not accounting for something in the detector), or physics beyond the Standard Model. “Our analysis ruled out the only remaining Standard Model astrophysical explanation of the anomalous ANITA events,” says Pizzuto. “So now, if these events are real and not just due to oddities in the detector, then they could be pointing to physics beyond the Standard Model.”
Ibrahim Safa of UW–Madison, another lead on this paper, says that while it has been an exciting time for physicists trying to explain these events, “it looks like we’ll have to wait for the next generation of experiments, which will increase exposure and sensitivity, to get a clear understanding of this anomaly.”
NAIROBI, Kenya (AP) — The body of Ugandan Olympic athlete Rebecca Cheptegei — who died after being set on fire by her partner in Kenya — was received Friday by family and anti-femicide crusaders, ahead of her burial a day later.
Cheptegei’s family met with dozens of activists Friday who had marched to the Moi Teaching and Referral Hospital’s morgue in the western city of Eldoret while chanting anti-femicide slogans.
She is the fourth female athlete to have been killed by her partner in Kenya in yet another case of gender-based violence in recent years.
Viola Cheptoo, the founder of Tirop Angels – an organization that was formed in honor of athlete Agnes Tirop, who was stabbed to death in 2021, said stakeholders need to ensure this is the last death of an athlete due to gender-based violence.
“We are here to say that enough is enough, we are tired of burying our sisters due to GBV,” she said.
It was a somber mood at the morgue as athletes and family members viewed Cheptegei’s body which sustained 80% of burns after she was doused with gasoline by her partner Dickson Ndiema. Ndiema sustained 30% burns on his body and later succumbed.
Ndiema and Cheptegei were said to have quarreled over a piece of land that the athlete bought in Kenya, according to a report filed by the local chief.
Cheptegei competed in the women’s marathon at the Paris Olympics less than a month before the attack. She finished in 44th place.
Cheptegei’s father, Joseph, said that the body will make a brief stop at their home in the Endebess area before proceeding to Bukwo in eastern Uganda for a night vigil and burial on Saturday.
“We are in the final part of giving my daughter the last respect,” a visibly distraught Joseph said.
He told reporters last week that Ndiema was stalking and threatening Cheptegei and the family had informed police.
Four in 10 women or an estimated 41% of dating or married Kenyan women have experienced physical or sexual violence perpetrated by their current or most recent partner, according to the Kenya Demographic and Health Survey 2022.
TEL AVIV, Israel (AP) — A rare Bronze-Era jar accidentally smashed by a 4-year-old visiting a museum was back on display Wednesday after restoration experts were able to carefully piece the artifact back together.
Last month, a family from northern Israel was visiting the museum when their youngest son tipped over the jar, which smashed into pieces.
Alex Geller, the boy’s father, said his son — the youngest of three — is exceptionally curious, and that the moment he heard the crash, “please let that not be my child” was the first thought that raced through his head.
The jar has been on display at the Hecht Museum in Haifa for 35 years. It was one of the only containers of its size and from that period still complete when it was discovered.
The Bronze Age jar is one of many artifacts exhibited out in the open, part of the Hecht Museum’s vision of letting visitors explore history without glass barriers, said Inbal Rivlin, the director of the museum, which is associated with Haifa University in northern Israel.
It was likely used to hold wine or oil, and dates back to between 2200 and 1500 B.C.
Rivlin and the museum decided to turn the moment, which captured international attention, into a teaching moment, inviting the Geller family back for a special visit and hands-on activity to illustrate the restoration process.
Rivlin added that the incident provided a welcome distraction from the ongoing war in Gaza. “Well, he’s just a kid. So I think that somehow it touches the heart of the people in Israel and around the world,“ said Rivlin.
Roee Shafir, a restoration expert at the museum, said the repairs would be fairly simple, as the pieces were from a single, complete jar. Archaeologists often face the more daunting task of sifting through piles of shards from multiple objects and trying to piece them together.
Experts used 3D technology, hi-resolution videos, and special glue to painstakingly reconstruct the large jar.
Less than two weeks after it broke, the jar went back on display at the museum. The gluing process left small hairline cracks, and a few pieces are missing, but the jar’s impressive size remains.
The only noticeable difference in the exhibit was a new sign reading “please don’t touch.”
VICTORIA – The British Columbia government is partnering with a bear welfare group to reduce the number of bears being euthanized in the province.
Nicholas Scapillati, executive director of Grizzly Bear Foundation, said Monday that it comes after months-long discussions with the province on how to protect bears, with the goal to give the animals a “better and second chance at life in the wild.”
Scapillati said what’s exciting about the project is that the government is open to working with outside experts and the public.
“So, they’ll be working through Indigenous knowledge and scientific understanding, bringing in the latest techniques and training expertise from leading experts,” he said in an interview.
B.C. government data show conservation officers destroyed 603 black bears and 23 grizzly bears in 2023, while 154 black bears were killed by officers in the first six months of this year.
Scapillati said the group will publish a report with recommendations by next spring, while an independent oversight committee will be set up to review all bear encounters with conservation officers to provide advice to the government.
Environment Minister George Heyman said in a statement that they are looking for new ways to ensure conservation officers “have the trust of the communities they serve,” and the panel will make recommendations to enhance officer training and improve policies.
Lesley Fox, with the wildlife protection group The Fur-Bearers, said they’ve been calling for such a committee for decades.
“This move demonstrates the government is listening,” said Fox. “I suspect, because of the impending election, their listening skills are potentially a little sharper than they normally are.”
Fox said the partnership came from “a place of long frustration” as provincial conservation officers kill more than 500 black bears every year on average, and the public is “no longer tolerating this kind of approach.”
“I think that the conservation officer service and the B.C. government are aware they need to change, and certainly the public has been asking for it,” said Fox.
Fox said there’s a lot of optimism about the new partnership, but, as with any government, there will likely be a lot of red tape to get through.
“I think speed is going to be important, whether or not the committee has the ability to make change and make change relatively quickly without having to study an issue to death, ” said Fox.
This report by The Canadian Press was first published Sept. 9, 2024.
