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Posts Tagged ‘Gran Sasso’

This article appeared in symmetry on April 22, 2015.

The world’s largest liquid-argon neutrino detector will help with the search for sterile neutrinos at Fermilab. Photo: INFN

The world’s largest liquid-argon neutrino detector will help with the search for sterile neutrinos at Fermilab. Photo: INFN

Mysterious particles called neutrinos seem to come in three varieties. However, peculiar findings in experiments over the past two decades make scientists wonder if a fourth is lurking just out of sight.

To help solve this mystery, a group of scientists spearheaded by Nobel laureate Carlo Rubbia plans to bring ICARUS, the world’s largest liquid-argon neutrino detector, across the Atlantic Ocean to the United States. The detector is currently being refurbished at CERN, where it is the first beneficiary of a new test facility for neutrino detectors.

Neutrinos are some of the most abundant and yet also most mysterious particles in the universe. They have tiny masses, but no one is sure why—or where those masses come from. They interact so rarely that they can pass through the entire Earth as if it weren’t there. They oscillate from one type to another, so that even if you start out with one kind of neutrino, it might change to another kind by the time you detect it.

Many theories in particle physics predict the existence of a sterile neutrino, which would behave differently from the three known types of neutrino.

“Finding a fourth type of neutrinos would change the whole picture we’re trying to address with current and future experiments,” says Peter Wilson, a scientist at Fermi National Accelerator Laboratory.

The Program Advisory Committee at Fermilab recently endorsed a plan, managed by Wilson, to place a suite of three detectors in a neutrino beam at the laboratory to study neutrinos—and determine whether sterile neutrinos exist.

Over the last 20 years, experiments have seen clues pointing to the possible existence of sterile neutrinos. Their influence may have caused two different types of unexpected neutrino behavior seen at the Liquid Scintillator Neutrino Detector experiment at Los Alamos National Laboratory in New Mexico and the MiniBooNE experiment at Fermilab.

Both experiments saw indications that a surprisingly large number of neutrinos may be morphing from one kind to another a short distance from a neutrino source. The existence of a fourth type of neutrino could encourage this fast transition.

The new three-detector formation at Fermilab could provide the answer to this mystery.

In the suite of experiments, a 260-ton detector called Short Baseline Neutrino Detector will sit closest to the source of the beam, so close that it will be able to detect the neutrinos before they’ve had a chance to change from one type into another. This will give scientists a baseline to compare with results from the other two detectors. SBND is under construction by a team of scientists and engineers from universities in the United Kingdom, the United States and Switzerland, working with several national laboratories in Europe and the US.

The SBND detector will be filled with liquid argon, which gives off flashes of light when other particles pass through it.

“Liquid argon is an extremely exciting technology to make precision measurements with neutrinos,” says University of Manchester physicist Stefan Soldner-Rembold, who leads the UK project building a large section of the detector. “It’s the technology we’ll be using for the next 20 to 30 years of neutrino research.”

Farther from the beam will be the existing 170-ton MicroBooNE detector, which is complete and will begin operation at Fermilab this year. The MicroBooNE detector was designed to find out whether the excess of particles seen by MiniBooNE was caused by a new type of neutrino or a new type of background. Identifying either would have major implications for future neutrino experiments.

Finally, farthest from the beam would be a liquid-argon detector more than four times the size of MicroBooNE. The 760-ton detector was used in the ICARUS experiment, which studied neutrino oscillations at Gran Sasso Laboratory in Italy using a beam of neutrinos produced at CERN from 2010 to 2014.

Its original beam at CERN is not optimized for the next stage of the sterile neutrino search. “The Fermilab beamline is the only game in town for this type of experiment,” says physicist Steve Brice, deputy head of Fermilab’s Neutrino Division.

And the ICARUS detector “is the best detector in the world to detect this kind of particle,” says Alberto Scaramelli, the former technical director of Gran Sasso National Laboratory. “We should use it.”

Rubbia, who initiated construction of ICARUS and leads the ICARUS collaboration, proposed bringing the detector to Fermilab in August 2013. Since then, the ICARUS, MicroBooNE and SBND groups have banded together to create the current proposal. The updated plan received approval from the Fermilab Program Advisory Committee in February.

“The end product was really great because it went through the full scrutiny of three different collaborations,” says MicroBooNE co-leader Sam Zeller. “The detectors all have complementary strengths.”

In December, scientists shipped the ICARUS detector from the Gran Sasso laboratory to CERN, where it is currently undergoing upgrades. The three-detector short-baseline neutrino program at Fermilab is scheduled to begin operation in 2018.

Kathryn Jepsen

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Going underground most days for work is probably the weirdest-sounding this about this job. At Laboratori Nazionali del Gran Sasso, we use the lab to be underground because of the protection it affords us from cosmic rays, weather, and other disruptions, and with it we get a shorthand description of all the weirdness of lab life. It’s all just “underground.”

ss17bis

The last kilometer of road before reaching the above-ground labs of LNGS

Some labs for low background physics are in mines, like SURF where fellow Quantum Diariest Sally Shaw works. One of the great things about LNGS is that we’re located off a highway tunnel, so it’s relatively easy to reach the lab: we just drive in. There’s a regular shuttle schedule every day, even weekends. When there are snowstorms that close parts of the highway, the shuttle still goes, it just takes a longer route all the way to the next easy exit. The ride is a particularly good time to start drafting blog posts. On days when the shuttle schedule is inconvenient or our work is unpredictable, we can drive individual cars, provided they’ve passed emissions standards.

The guards underground keep a running list of all the people underground at any time, just like in a mine. So, each time I enter or leave, I give my name to the guards. This leads to some fun interactions where Italian speakers try to pronounce names from all over. I didn’t think too much of it before I got here, but in retrospect I had expected that any name of European etymology would be easy, and others somewhat more difficult. In fact, the difficult names are those that don’t end in vowels: “GladStone” become “Glad-eh-Stone-eh”. But longer vowel-filled names are fine, and easy to pronounce, even though they’re sometimes just waved off as “the long one” with a gesture.

There’s constantly water dripping in the tunnel. Every experiment has to be housed in something waterproof, and gutters line all the hallways, usually with algae growing in them. The walls are coated with waterproofing, more to keep any potential chemical spill from us from getting into the local groundwater than to keep the water off our experiments. When we walk from the tunnel entrance to the experimental halls, the cue for me to don a hardhat is the first drip on my head from the ceiling. Somehow, it’s always right next to the shuttle stop, no matter where the shuttle parks.

And, because this is Italy, the side room for emergencies has a bathroom and a coffee machine. There’s probably emergency air tanks too, but the important thing is the coffee machine, to stave off epic caffeine withdrawal headaches. And of course, “coffee” means “espresso” unless otherwise stated– but that’s another whole post right there.

When I meet people in the neighboring villages, at the gym or buying groceries or whatever, they always ask what an “American girl” is doing so far away from the cities, and “lavoro a Laboratorio Gran Sasso” is immediately understood. The lab is even the economic engine that’s kept the nearest village alive: it has restaurants, hotels, and rental apartments all catering to people from the lab (and the local ski lift), but no grocery stores, ATMs, gyms, or post offices that would make life more convenient for long-term residents.

Every once in a while, when someone mentions going underground, I can’t help thinking back to the song “Underground” from the movie Labyrinth that I saw too many times growing up. Labyrinth and The Princess Bride were the “Frozen” of my childhood (despite not passing the Bechtel test).

Just like Sarah, my adventures underground are alternately shocking and exactly what I expected from the stories, and filled with logic puzzles and funny characters. Even my first night here, when I was delirious with jetlag, I saw a black cat scamper across a deserted medieval street, and heard the clock tower strike 13 times. And just like Wesley, “it was a fine time for me, I was learning to fence, to fight–anything anyone would teach me–” (except that in my case it’s more soldering, cryogenics plumbing, and ping-pong, and less fighting). The day hasn’t arrived where the Dread Pirate Roberts calls me to his office and gives me a professorship.

And now the shuttle has arrived back to the office, so we’re done. Ciao, a dopo.

(ps the clock striking 13 times was because it has separate tones for the hour and the 15-minute chunks. The 13 was really 11+2 for 11:30.)

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The CUORE-0 collaboration just announced a result: a new limit of 2.7 x1024 years (90%C.L.) on the halflife of neutrinoless double beta decay in 130Te. Or, if you combine it with the data from Cuorecino, 4.0×1024 years. A paper has been posted to the arXiv preprint server and submitted to the journal Physical Review Letters.

Screen Shot 2015-04-09 at 5.26.55 PM

Bottom: Energy spectrum of 0νββ decay candidates in CUORE-0 (data points) and the best-fit model from the UEML analysis (solid blue line). The peak at ∼2507 keV is attributed to 60Co; the dotted black line shows the continuum background component of the best-fit model. Top: The nor-369 malized residuals of the best-fit model and the binned data.370 The vertical dot-dashed black line indicates the position of371 Qββ. From arXiv.

CUORE-0 is an intermediate step between the upcoming full CUORE detector and its prototype, Cuoricino. The limit from Cuoricino was 2.8×1024 years**, but this was limited by background contamination in the detector, and it took a long time to get to that result. For CUORE, the collaboration developed new and better methods (which are described in detail in an upcoming detector paper) for keeping everything clean and uniform, plus increased the amount of tellurium by a factor of 19. The results coming out now test and verify all of that except the increased mass: CUORE-0 uses all the same cleaning and assembly procedures as CUORE, but with only the first of 19 towers of crystals. It took data while the rest of the towers were being built. We stopped taking CUORE-0 data when the sensitivity was slightly better than Cuoricino, which only took half the exposure time of the Cuoricino run. The resulting background was 6 times lower in the continuum parts of the spectrum, and all the energy resolutions (which were calibrated individually for each crystal each month) were more uniform. So this is a result to be proud of: even before the CUORE detector starts taking data, we have this result to herald its success.

The energy spectra measured in both Cuoricino and CUORE-0, displaying the factor of 6 improvement in the background rates.

The energy spectra measured in both Cuoricino and CUORE-0, displaying the factor of 6 improvement in the background rates. From the seminar slides of L. Canonica.

 

The result was announced in the first seminar in a grand tour of talks about the new result. I got to see the announcement at Gran Sasso today–perhaps you, dear reader, can see one of the talks too! (and if not, there’s video available from the seminar today) Statistically speaking, out of these presentations you’re probably closest to the April APS meeting if you’re reading this, but any of them would be worth the effort to see. There was also a press release today and coverage in the Yale News and Berkley Labs news, because of which I’m making this post pretty short.

 

The Upcoming Talks:

There are also two more papers in preparation, which I’ll post about when they’re submitted. One describes the background model, and the other describes the technical details of the detector. The most comprehensive coverage of this result will be in a handful of PhD theses that are currently being written.

(post has been revised to include links with the arXiv post number: 1504.02454)

**Comparing the two limits to each other is not as straightforward as one might hope, because there were different statistical methods used to obtain them, which will be covered in detail in the papers. The two limits are roughly similar no matter how you look, and still the new result has better (=lower) backgrounds and took less time to achieve. A rigorous, apples-to-apples comparison of the two datasets would require me to quote internal collaboration numbers.

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