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Posts Tagged ‘neutrino’

Neutrino 2012: Day 2

Tuesday, June 5th, 2012

When it comes to neutrino experiments, they were all there Day 2: T2K, MINOS, OPERA, ICARUS, and NOνA, and LBNE!

Hi All,

Here is a run down of what happened Tuesday. I will try to post Day 3 things this afternoon, which should be Wednesday morning for the US. An update on the LBNE is at the bottom of the post.

Happy Colliding

– richard (@bravelittlemuon)

T2K

Figure 1: Update of T2K experiment after March 11, 2011 earthquake that struct Japan. Credit: NAKAYA, Tsuyoshi.

The Tokai to Kamoika Experiment, or T2K for short, is a one impressive behemoth of an experiment. Much like MINOS Experiment at Fermilab, you shoot protons into a target to make pions. The pions then decay into neutrinos, and the neutrinos travel 183 mi (295 km) through the Earth to the (Super-, Hyper-) Kamiokande detector in Kamioka, Japan.

When the March 2011 earthquake struck Japan, the proton accelerator at the J-PARC physics lab was heavily damaged, and power throughout the country was effectively shut off. Due to immense leadership of J-PARC’s director, Shoji Nagamiya, the accelerator was back online December 9, 2011, and by December 24, 2011, neutrinos were being observed in Kamioka. It is baffling that despite all this, the experiment still marched on and announced the herculean result it had observed 10 events where a muon-neutrino had converted into electron-neutrino. The predicted results were 9.07±0.93 event assuming sin213=0.1, and 2.73±0.37 events assuming sin213=0.0. Consequently, the experiment was able to measure θ13 itself and found sin213=0.104 +0.060-0.045

Figure 2: Schematic of T2K (Tokai To Kamioka) Experiment. Image: http://www2.warwick.ac.uk/newsandevents/news/t2k

MINOS

The MINOS Experiment at Fermilab is most simply described at the US version of T2K. It is unfair and a disservice to both MINOS and T2K to make that comparison because of the unique features of the experiments, but I have a lot to write. In 2010, MINOS caused a bit of a stir when it measured the mass difference between two of the three anti-neutrinos. The measurement itself was not at all controversial. The issue was that this result differed from the well measured mass difference for regular neutrinos. Here the Fermilab presser that can tell you all about it. On Day 2, MINOS announced that the discrepancy between neutrinos and anti-neutrinos has completely disappeared and that the previous disagreement is believed to have been a statistical fluctuation. It appears that Fermilab has released a new press release this morning explaining things in more detail. Below are the main plots. Oh, and MINOS data also slightly favors inverted hierarchy for anyone interested in that. Fun fact: In its seven years of running, MINOS has used over 1.5 sextillion protons to produce all of its neutrinos.

Figure 3: Preliminary results from the MINOS detector showing best fit value for neutrino mass splitting and mixing angle. Credit: NICHOL, Ryan

 

Figure 4: Preliminary results from the MINOS detector showing best fit value for anti-neutrino mass splitting and mixing angle. Credit: NICHOL, Ryan

Figure 5: Preliminary results from the MINOS detector showing best fit value for neutrino and anti-neutrino mass splitting and mixing angle. Credit: NICHOL, Ryan

OPERA

The OPERA Experiment, or Oscillation Project with Emulsion-tRacking Apparatus, is a fine and mighty experiment capable of one of the most time-consuming tasks in neutrino physics that even tests the patience of sleeping mountains: observing the conversion of tau-neutrinos into muon-neutrinos. Like T2K and MINOS, OPERA gets its neutrinos from pions, which are produced when protons strike a fixed target. Specifically, the experiment uses CERN protons in its first four years of running has used about 14.2 x 1019 protons!

Figure 6: A breakdown, by year, of how many protons the OPERA experiment has observed. Credit: NAKAMURA, Mitsuhiro

OPERA’s defining characteristic is how well it is able to extract out a signal from everything else. Below is an example of a real event in which a neutrino has collided with a nucleus, producing a charge lepton and nucleus somewhat fragments.

Figure 7: An example of a real neutrino event being extracted from the data. Credit: NAKAMURA, Mitsuhiro

The big news from OPERA on Day 2 was the second observation of a muon-neutrino converting into a tau-neutrino! 2 events in over four years; I told you this thing required patience. Here is how the event works.

Figure 8: The OPERA Experiment's second candidate event of a muon-neutrino converting into a tau-neutrino. Credit: NAKAMURA, Mitsuhiro

Here is an explanation of the event.

Figure 9: A breakdown of OPERA's second tau-neutrino candidate. Credit: NAKAMURA, Mitsuhiro

Finally, here is a summary of the status of OPERA’s search tau-neutrinos. It is worth mentioning that the experiment also announced it has observed 19 instances where a muon-neutrino has converted into an electron-neutrino!

Figure 10: A summary of the current status of the OPERA Experiment's search for appearances of tau-neutrinos. Credit: NAKAMURA, Mitsuhiro

A Few Words on ICARUS and NOνA

Due to the lack of time, I will simply say that one can expect big things from ICARUS and NOνA when they both have results. ICARUS has already started running and the gigantic, LHC-Detector-sized NOνA will start running next year when Fermilab flips on its proton beam again. NOνA will be capable of determining whether neutrinos have normal mass hierarchy or inverted mass hierarchy.

 

LBNE

Interesting things happen at conferences, like an impromptu talk added the morning of the second day of events. Long Baseline Neutrino Experiment co-spokesperson Robert Svoboda surprisingly gave an update of the LBNE, the first since its budget was gravely slashed. Much is still being kept internally for another few weeks when the final proposal will be submitted, so I will limit what I say. In summary, there are three options being considered for the experiment for phase 1 construction. Beyond that, it is up to the Funding Lords.

Figure 11: Update of the Long Baseline Neutrino Experiment. Credit: SVOBODA, Robert

Figure 12: Update of the Long Baseline Neutrino Experiment. Credit: SVOBODA, Robert

 

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Neutrino 2012: Day 1

Sunday, June 3rd, 2012

Updated: Tuesday June 5, 2012 13:23 local (Kyoto) time.

Day 1 Events

Hi All,

Sorry for the delay. The conference’s schedule is jammed packed, and not basking in a wireless cloud limits my access to the site. At any rate, Monday was a very productive day. For the first time under a single roof, all the nuclear reactor-based experiments showed their measurement of θ13, the physical quantity that stipulates the probability of two specific neutrinos turning into each other. θ13 (pronounced: theta-one-three) has been extensively covered here if you are interested in reading more about it. Herein lies the purpose of conferences: to allow experimentalists and theorists the opportunity to compare and contrast highly important results from similar experiments. Checking that everyone’s results agree also shows the importance of redundant experiments.

As I mentioned, the conference open with Laureate Jack Steinberger giving a quite overview of the history of neutrinos. He paid quite a homage to his hero Bruno Pontecorvo for his everlasting contributions to physics. Pontecorvo is the definition of a man born ahead of his time. Not only did he first postulate that neutrinos could oscillate back in 1957 (first confirmed in 1998), he also recognized that the rate of detecting cosmic muons was comparable to the rate of radioactive (beta) decay. According to Steinberger, Pontecorvo’s result was largely ignored. Fermi himself “did not think there could be a relationship between the muon… and the electron. It was too much an intellectual jump.”

Fig. 1: Me with Nobel Laurate Jack Steinberger at the first poster session of the Neutrino 2012 Confereince in Kyoto, Japan.

However, it was CERN’s historic Gargamelle Experiment that made Steinberger’s just beam with excitement. The experiment was the first to demonstrate evidence for the existence of the Z boson, the most unique prediction of the Electroweak Theory (Standard Model). He thinks of it as “the most important experiment ever done at CERN” and confirmation of the Electroweak Theory is the “most glorious result at cern.”

A rather interesting talk was a talk entitled “Application of Reactor Anti-Neutrinos.” Nuclear reactors are incredibly useful for physics because they are a controlled source of neutrinos. Unfortunately, plutonium is an inherent byproduct of nuclear reactors. However, we can look at this another way: plutonium-producing reactor is a generous producer of neutrinos. This clever rearrangement of words is the premise of one potential breakthrough in nuclear non-proliferation: uncovering the mass production of Pu via neutrinos. I have to run, but in short “the anti-nutrino has a possibility to monitor reactor operation and Pu contents in operation core.” It reminds me a bit of Laureate Luis Alvarez’s clever use of cosmic rays to image the internal structure of Egyptian pyramids.

 

Happy Colliding

– richard (@bravelittlemuon)

 

Greetings from Kyoto! The sun is high and the solar neutrino rate is brimming.

 

Fig. X: Conference Poster for Neutrino 2012 in Kyoto, Japan (http://neu2012.kek.jp/)

Conference Poster for Neutrino 2012 in Kyoto, Japan (http://neu2012.kek.jp/)

It is Day 1 of Neutrino 2012, an annual conference dedicated to all things neutrino, and today’s talks about about to begin shortly with a welcome from, count them: two Nobel laureates. The first is by Jack Steinberger, co-discoverer of the muon neutrino along with science education advocate Leon Lederman, on the present state of neutrinos, what we know about them, and what we definitely do not know. It is a highly appropriate talk to kick off such an important conference. The second talk is by Makoto Kobayashi, “K” of the famed CKM matrix, and is on the existence of neutrino masses and how that discovery has defined a generation of on-going research.

Okay, time for the bad news. There is no internet in the main lecture hall and, as a consequence, I cannot physically live-blog this week. This is a bit of a disappointment but check back here often for regular updates through the week. After an interesting conversation on the flight over here, I am expecting to hear some very interesting and very new results.

 

Happy Colliding

– richard (@bravelittlemuon)

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Summer is a productive time for us and tends to involve lots of traveling.

 

Fig. 1: My 2010 PDG booklet and my Japan Rail pass. I am not sure which is more important.

Hi All,

As fellow QDer Aidan posted this morning, it is conference season, again! Lots and lots of conferences for all the different sub-sub-fields in physics. Two big ones on my plate are Neutrino 2012, which is about ALL things that begin with the letters n-e-u-t-r-i-n-o and end in the letter -s; and ICHEP 2012, which is the mother-of-all high energy physics conferences. (Much more on ICHEP in a few weeks seeing that I have been invited to be a panelist on the “Social Media in Science Communication” session. Trust me, it will be good.)

Neutrinos are all the rage these days: from #FTLneutrinos to θ13, we are determined to know precisely how neutrinos work. Fortunate for us, there is a huge international conference, imaginatively called “Neutrino,” next week in the gorgeous, ancient city of Kyoto, Japan, and you can definitely count on there be a Quantum Diaries presence. QDer Zeynep Isvan will be around, and, with the suggestion from my chief editor, Daisy, I will be live-blogging the plenary sessions when I can. The programme is also already online, so feel free to check out the topics.

After the conference, however, is when things get kicked into high gear for me. A few months ago I won a NSF summer fellowship to research dark matter in Japan. It is now summer, so for the next three months I will be a visitor at University of Tokyo’s prestigious Institute for the Physics and Mathematics of the Universe, or IPMU for short. I still have plots to make for a meeting today and my first flight is (literally) 24 hours from now. At least I have my trusty messenger bag already packed with two of the more important things: a Japan Rail pass and my 2010 PDG booklet!

See you in Kyoto!

 

Happy Colliding

– richard (@bravelittlemuon)

PS While adding links and sources to the post, I found my IPMU host on Twitter.

PPS More than 3.6 fb-1 worth of data has already been collected by the collider experiments.

 

Fig. X: Conference Poster for Neutrino 2012 in Kyoto, Japan (http://neu2012.kek.jp/)

Fig. 2: Conference Poster for Neutrino 2012 in Kyoto, Japan (http://neu2012.kek.jp/)

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Born in the hearts of stars and nuclear reactors, almost undetectable, nearly as fast as light, able to pass unhindered through everything from planets to people, and confirmed shapeshifters. That role call describes what makes the particles known as neutrinos both exciting and perpetually challenging for physicists on the hunt.

A series of brilliant experiments designed and executed since the 1950s have managed to detect these slippery subatomic wonders, revealing much about their origins, travels, and presence as one of the most abundant particles in the cosmos.

Earlier this week, an international collaboration led by China and the United States at the Daya Bay Reactor Neutrino Experiment in the south of China pinpointed the action behind one of the neutrino’s signature magic tricks: its ability to seemingly vanish entirely. The disappearing act is the product of neutrino oscillations, and the Daya Bay team calculated the final unknown transformation type. The 5-sigma discovery not only helps demystify the neutrino, but it will also guide future experiments in exposing more fundamental mysteries – such as how we exist.

Photomultiplier tubes on the Daya Bay walls.

Sensitive photomultiplier tubes line the Daya Bay detector walls, designed to amplify and record the faint flashes that signify an antineutrino interaction. (Courtesy of Roy Kaltschmidt, Lawrence Berkeley National Laboratory)

“It’s surprising and exciting that this result came so quickly and precisely,” said Brookhaven Lab’s Steve Kettell, who is Chief Scientist for the U.S. at Daya Bay. “It has been very gratifying to be able to work with such an outstanding international collaboration at the world’s most sensitive reactor neutrino experiment.” (more…)

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I’ve let the news aspect of this story die back a little before writing about it. It now appears that the OPERA results were due to a mistake in the end. Rumors have it that it was a bad connector on a fiber optic link between a GPS and a computer that gave a 60ns time shift. New data taking with the tightened connector will be required to verify that this was, in fact, the cause of the problem. See also the Nature page.

Of course this was not a grand surprise, the vast majority of physicists felt that a mundane explanation would be found in the experiment rather than a rewrite of much of fundamental physics. But what I want to explore here is instead, what would you do? And, how does this illuminate the differences between theory and experiment?

The first question was fairly explicitly asked to me by colleagues at a meeting just days after the announcement of the preliminary OPERA “faster-than-light” neutrinos. I stumbled over an answer that I can abstract as “if you make a measurement, you can think about it, and even not believe it, but eventually you publish it” presumably with enough caveats that you aren’t misleading the readers into a different level of confidence in the results that you yourself hold. But I’m not sure if this answer (though probably close to what any official answer would be) is truly correct.

Extraordinary claims do demand extraordinary proof. And at first look the OPERA folks seemed to be extraordinarily careful in their review of their own work. Since the velocity measurement  in the experiment fundamentally comes just from the distance and the time of flight of the particles, a lot of effort went into the metrology and surveying for the distance measurement and a careful evaluation of the clocks involved. But a loose connection seems to have been missed before public announcements and the wild theorist party (see below) that emerged from the smoke at the initial CERN lecture cum press conference.

Connectors are the bane of an experiment. From the horrid Lemo 00 connectors still found all too often in particle and nuclear physics, to the stiff cadmium-plated circular military connectors beloved of the aerospace concerns, down to the simple is-it-really-connected-securely screw terminals on the back of an old power supply, this is where so much debugging time and effort goes. So it seems plausible that the error could be there. But when should it have been found?

I’d want to tear the experiment down and build it back up, re-cable, re-connect, tear everything apart before I’d be willing to claim a major discovery. At the time, the word was that the OPERA folks had put lots of time and effort into trying to find the problem, the mistake, but couldn’t locate it, so the news was released and the world started talking (and writing papers for arxiv) about faster-than-light neutrinos. I think we still don’t have a good enough picture as to the level of due diligence at the experiment. Did folks rebuild all of the timing system multiple times? Did the full signal chain get carefully looked at?

We tend to not be too critical of other physicists, and without knowing what happened within the OPERA collaboration, it’s easy for me to ask these questions without a real response. What experimentalists, in my opinion, need to take away from this is a real understanding of responsibility for being self-critical especially, but not exclusively, if there is a lot at stake. We well know the “solid four sigma” results which fade away in a few months, and yet it happens again and again. We know what will play in the popular press, and we’re careless about how we explain ourselves. (But enough about quantum teleportation illustrated with Star Trek visuals.)

I suspect that more than a few folks within the experiment, as well as outside, got terribly excited by the slim possibility of a major discovery. Within the group, this hopefully did not affect the critical thinking and tear-down of the experiment. Outside, in the larger community, certainly every neutrino experiment discussed very seriously what could be done to make such a measurement, and the theorists started producing papers. Why the results were wrong. Why the results were right, and agreed with their favored ideas. What it means for the rest of physics.

At times like this the cultural divide between theory and experiment never seems larger! A flood of papers since even a slight touch on a big discovery is worth something it seems. And now what? After the experimental error seems to be, well, an experimental error that wasn’t caught for a very long time, what do we think of all of theory papers? Presumably they just fade away, a light bright (?) spot of activity in late 2011 that someone will write a book about in five years, “The Faster-than-Light Neutrino Craze of ’11?” Some people got a little bit of publicity for misunderstanding GPS or for boldly extrapolating the neutrino velocity to higher energies. Is there regret over the waste of time? Or just a little exclamation, “ahhh…those experimentalists not checking their cables.”

More on this as the story develops, and as the water-cooler arguments continue.

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This column by Fermilab Director Pier Oddone appeared in Fermilab Today on Jan. 17.

Last week we hosted the US-UK Workshop on Proton Accelerators for Science and Innovation. The workshop brought together scientists from the United States and the United Kingdom who are working on high-intensity proton accelerators across a variety of fronts. The meeting included not only the developers of high-intensity accelerators but also the experimental users and those involved in the applications of such accelerators beyond particle physics.

At the end of the conference, John Womersly, CEO of the UK’s Science and Technology Facilities Council, and I signed a letter of intent specifying the joint goals and activities of our collaboration for the next five years. We plan to have another workshop in about a year to review progress and explore additional areas of collaboration.

Our collaboration with scientists from the United Kingdom in the area of high-intensity proton accelerators is already well established. We have a common interest in muon accelerators, both in connection with neutrino factories and muon colliders. Both of these future projects require multi-megawatt beams of protons to produce the secondary muons that are accelerated. We collaborate on the International Muon Ionization Cooling Experiment at the Rutherford Appleton Laboratory. MICE is the first muon cooling experiment and an essential step in the road to neutrino factories and muon colliders. We also collaborate on the International Scoping Study for neutrino factories.

In our current neutrino program we are very appreciative of this collaboration and U.K. expertise in the difficult mechanical design of high-power targets, in particular for the MINOS, NOvA and LBNE experiments. The design of these targets is quite challenging as the rapid deposition of energy creates shock waves that can destroy them.The Project X experimental program also depends on having appropriate megawatt-class targets relatively close to experimental set-ups.

One of the primary interests in applications outside of particle physics is the development of intense proton accelerators that could be used for the transmutation of waste or even the generation of electrical power in subcritical nuclear reactors. The accelerators necessary for such subcritical reactors could not have been built just a decade ago, but the advent of reliable superconducting linacs changed that. Several programs abroad are developing such accelerators coupled to reactors. While the United States has no explicit program on accelerator-driven subcritical systems, the technologies that we are developing for other applications, such as Project X, place us in a good position should the United States decide to develop such systems.

Overall, the workshop was very productive and the areas of potential collaboration seemed to multiply through the meeting. Each one of the five working groups is preparing a brief summary of the potential areas of collaboration as well as a specific and focused plan for the next year.

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httpv://www.youtube.com/watch?v=YtuMqjCiymQ&list=UUD5B6VoXv41fJ-IW8Wrhz9A&index=3&feature=plcp

It could be the largest structure ever to be built from plastic. Its footprint of 1,052 square meters will cover an area about the size of a quarter of a football field. Its height will rise past the top of a five-story apartment building. And with 368,640 tubes of white PVC, the structure will have about as many components as some of the largest LEGO structures built in the world.

The NOvA detector will comprise 368,640 PVC tubes that will be filled with mineral oil. A company in Wisconsin extrudes the tubes, which look like extra-long downspouts, in panels of 16. Credit: Rich Talaga, Argonne

But this huge structure, to be constructed in Ash River, Minn., won’t serve as a plastic replica. It will be the skeleton of a fully functional particle detector. Wired with fiber optic cables and filled with 500 truckloads of mineral oil, the 15,000-ton NOvA detector will enable scientists to discover how the masses of the three types of neutrinos—the lightest, tiniest particles known to mankind—stack up.

Last week, the preparations for the assembly of this white PVC behemoth passed a pivotal test. In an assembly building at Fermilab, 40 miles west of Chicago, scientists, engineers and technicians from Fermilab, Argonne National Laboratory and the University of Minnesota successfully operated for the first time the NOvA pivoter, the hydraulic system developed by Fermilab to move and rotate huge, 200-ton plastic blocks for the assembly of the NOvA detector. (See this 3-minute video with a time lapse of the pivoter test and a fly-through animation of the NOvA detector hall.)

“This is a big deal,” said Fermilab physicist Pat Lukens, who manages the assembly of the detector. “Now the focus will shift to Ash River. We will assemble 500 truckloads of plastic modules.”

But this is no ordinary plastic. Argonne’s Rich Talaga and other NOvA collaborators spent many years finding the right ingredients to produce the strongest and most reflective PVC for the 16-meter-long tubes that hold and support the weight of the mineral oil.

“Ordinary plastic tends to deform under pressure,” said Talaga, who worked closely with Fermilab’s Anna Pla-Dalmau. “Think of a plastic coat hanger. It changes shape when you put a sweater on it. We had to find a plastic that has to be strong for 20 years and doesn’t get weaker and rupture.”

Using a machine developed and tested at Argonne National Laboratory, technicians apply special no-drip glue to a NOvA panel to create blocks that are 16 meters by 16 meters square and weigh 200 tons. Credit: Rich Talaga, Argonne

For Extrutech Plastics in Manitowoc, Wisc., a company that makes PVC wall and ceiling panels and other plastic products, the purchase order for the NOvA tubes was the largest ever. The company has begun the production of the PVC panels, which look like 16 extra-long downspouts with a four-by-six-centimeter cross section attached side-by-side. The panels, which must meet the tight specifications for the thickness and uniformity of the NOvA plastic, are shipped to a warehouse rented by the University of Minnesota. There, students and technicians outfit each tube with a fiber optic cable that will capture the faint light that a neutrino creates when it breaks up an atom in the mineral oil. Avalanche photodiodes attached to each fiber will record and amplify the signal, which is then digitized and transmitted to the central data acquisition system.

To make sure that no light gets lost, Talaga and his group used a special PVC formulation that includes large amounts of titanium-dioxide to create a strong plastic that is white and highly reflective.

“The oil doesn’t absorb much light,” said Talaga. “The light created by a neutrino interaction is either absorbed by the walls of the tubes or by the fiber optic cable inside each tube. By making the walls highly reflective, the light bounces back eight, nine or ten times without significant absorption and you see a stronger signal in the fiber.”

To transform the roughly 24,000 plastic panels into one giant particle detector, technicians will place 24 panels next to each other to make a layer of tubes, 16 meters by 16 meters square. After an application of special no-drip glue, the next layer will be placed on top, with the tubes lying perpendicularly to the layer below. Gluing and lifting of the 1,000-pound panels will be done with machines developed and tested at Argonne, where the first set of machines was used to build the test block used on the pivoter at Fermilab.

The Argonne group just finished the installation of the first gluing machine at Ash River. The full-size pivoter, six times as wide as the one tested at Fermilab, is under construction and will be ready for operation early next year. Bill Miller, of the University of Minnesota, who participated in the pivoter test at Fermilab, will lead the assembly of the detector in Ash River. He will supervise local staff, hired by the University of Minnesota for the task.

“We plan to assemble the first block in Ash River this spring,” said Lukens, who’s overseen the development of the NOvA assembly plans for three years. “It will take 18 months to assemble the entire detector.”

Scientists from 28 institutions are working on the NOvA experiment. When operational, the experiment will examine the world’s highest-intensity, longest-distance neutrino beam, generated at the Fermilab.

Engineers at Fermilab designed and tested a hydraulic system that will move and rotate the huge, 200-ton plastic blocks for the assembly of the NOvA detector. Credit: Reidar Hahn, Fermilab

Accelerators will produce a beam of muon neutrinos that will travel straight through the earth to the NOvA detector in northern Minnesota. During their split-second trip to Ash River, some of these neutrinos will turn into electron neutrinos and tau neutrinos. By measuring the composition of the neutrino beam with a small, 222-ton detector at Fermilab and a large detector in Ash River, scientists expect to discover the neutrino mass hierarchy, determining whether there are two light neutrinos and one heavy one, or two heavy ones and a light one.

For photos of the construction of the NOvA detector building in Ash River, see the photo gallery in the October 2011 issue of symmetry magazine.

— Kurt Riesselmann

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Live blog: neutrinos!

Friday, September 23rd, 2011

This is a live blog for the CERN EP Seminar “New results from OPERA on neutrino properties“, presented by Dario Autiero. Live webcast is available. The paper is available on the arXiv.

The crowd in the auditorium (Thanks to Kathryn Grim)

The crowd in the auditorium (Thanks to Kathryn Grim)

15:39: So here I am at CERN, impatiently waiting for the Colloquium to start on the OPERA result. The room is already filling up and the chatter is quite loud. I’m here with my flatmate Sudan, and we have a copy of the paper on the desk in front of us. I just bumped into a friend, Brian, and wished him look finding a chair! (He just ran to get me a coffee. Cheers Brian!)

15:53: Wow, the room is really crowded now! People are sitting on the steps, in the aisles, and more are coming in. The title slide is already up on the projector, and some AV equipment is being brought in. I was just chatting to Sudan and Brian, and we commenting that this is probably the biggest presentation that the world’s biggest physics lab has seen in a long time! As Sudan says, “The whole world is going to be watching this man.”

15:55: Burton and Pauline are here too, getting some photos before the talk begins. Expect to see more (less hastily written) blog posts about this talk!

15:59: We’re not allowed to take photos of the talk itself, but there will be a video feed that you can watch. See this link for details about the live webcast.

16:03: The talk begins. A fairly straightforward start so far. As usual, the speaker introduces the OPERA Collaboration, and gives a bit of background. Nothing ground breaking so far!

16:06: The analysis was performed blind, which means that the physicists checked and double checked their systematic uncertainties before looking at the data. This is a common best practice in these kinds of experiments and it is a good way to eliminate a lot of experimenter bias. The speaker is now discussing past results, some of which show no faster than light speed, and one of which (from MINOS) that shows a small effect which is less than 2σ.

16:16: Autiero is currently discussing the hardware of the experiment. It looks like a standard neutrino observatory setup- large amounts of dense matter (Pb), scintillation plates and tracking hardware for the muons which get produced when the neutrinos interact. By the time the beam reaches Gran Sasso it is about 2km wide! At CERN the neutrinos are produced by accelerating protons at a target, producing pions and kaons, which are then allowed to decay to muons and muon neutrinos. The hadrons are stopped with large amounts of Carbon and Iron, so that only the neutrinos and some muons survive. By the time the neutrino beam reaches Gran Sasso the muons have long since interacted and are no longer present in the beam. The neutrinos have 17GeV of energy when they leave CERN, so they are very energetic!

16:29: The discussion has moved onto the timing system, probably the most controversial aspect of the experiment. The timing challenge is probably the most difficult part of the whole analysis, and the part that particle physicists are least familiar with. Autiero points out that the same methods of timing are commonly used in metrology experiments. For OPERA, the location of each end of the experiment in space and time is determined using GPS satellites in the normal way, and then a “common view” is defined, leading to 1ns accuracy in synchronization. It looks like variations in the local clocks are corrected using the common view method. The time difference between CERN and Gran Sasso was found to be 2.3 ± 0.9 ns, consistent with the corrections.

16:36: Things are made trickier by identifying where in the “spill” of protons a neutrino came from. For a given neutrino it’s pretty much impossible to get ns precision timing, so probability density functions are used and the time interval for a given proton spill is folded into the distribution. We also don’t know where each neutrino is produced within the decay tube. The average uncertainty in this time is about 1.4ns. Autiero is now talking about the time of flight measurement in more detail, showing the proton spills and neutrino measurements overlaid.

16:39: Geodesy is important to this analysis. OPERA need to know the distance between CERN and Gran Sasso to good precision (they need to know the distances underground, which makes things more complicated.) They get a precision of 20cm in 730km. Not bad! Autiero is now showing the position information, showing evidence of continental drift and even an earthquake. This is very cool!

16:47: Two techniques are used to verify timing, using Caesium clocks and optical fibers. These agree to ns precision. The overall timing system is rather complicated, and I’m having trouble following it all!

16:48: I just got a message from a friend who saw this blog via Twitter. Hello Angela! Welcome to all the readers from Twitter!

16:52: Currently discussing event selection at Gran Sasso. Events must have a highly relativistic muon associated with them. (The speed of the muon and slight difference in direction of flight can only increase the measured time of flight.)

16:54: Autiero is telling us about how the analysis is blinded. They used very old calibrations, intentionally giving meaningless results. A novel approach to blinding!

16:56: No evidence of variation with respect to time of day or time of year. So that’s the “Earth moved!” theory sunk.

17:01: Unblinding: Δt = -987.8ns correction to time of flight after applying corrections (ie using up to date calibration.) Total systematic uncertainty is 7.4ns. Time of flight obtained using maximum likelihood. Measured difference in time of flight between speed of light and speed of neutrinos is

\[
\delta t (c-\nu) = (60.7 \pm 6.9(stat) \pm 7.40 (syst)) ns
\]

\[
\frac{c-v_{\nu}}{c} = -(2.4 \pm 0.28 \pm 0.30)\times 10^{-5}
\]

17:03: ~16,000 events observed. OPERA has spent six months checking and rechecking systematic uncertainties. Cannot account for discrepancy in terms of systematic uncertainties.

17:04: “Thank you”. Huge ripple of applause fills the auditorium.

Questions

(These questions and answers are happening fast. I probably make an error or omission here and there. Apologies. Consult the webcast for a more accurate account or for any clarifications.)

17:05: Questions are to be organized. Questions about the distance interval, then the time interval, then the experiment itself. There will be plenty of questions!

17:08: Question: How can you be sure that the timing calibrations were not subject to the same systematic uncertainties whenever they were made? Answer: Several checks made. One suggestion is to drill a direct hole. This was considered, but has an uncertainty associated of the order of 5%, too large for this experiment.

17:12: Question: Geodesy measurements were taken at one time. There are tidal effects (for example, measured at LEP.) How can you be sure that there are no further deviations in the geodesy? Answer: Many checks made and many measurements checked.

17:14: Question: Looking for an effect of 1 part in 105. Two measurements not sufficient. Movement of the Moon could affect measurements, for example. Answer: Several measurements made. Data taken over three years, tidal forces should average out.

17:15: Question: Is the 20cm uncertainty in 730km common? Answer: Similar measurements performed elsewhere. Close to state of the art. Even had to stop traffic on half the highway to get the measurement of geodesy!

17:16: Question: Do you take into account the rotation of the Earth? Answer: Yes, it’s a sub ns effect.

17:23: Question: Uncertainty at CERN is of the order of 10μs. How do you get uncertainty of 60ns at Gran Sasso? Answer: We perform a maximum likelihood analysis averaging over the (known shape) of the proton spill and use probability density functions.

(Long discussion about beam timings and maximum likelihood measurement etc.)

17:31: Large uncertainty from internal timers at each site (antenna gives large uncertainty.) Measurements of timing don’t all agree. How can you be sure of the calibration? Answer: There are advanced ways to calibrate measurements. Perform inclusive measurement using optic fibers. Comment from timing friends in the audience? Audience member: Your answer is fine. Good to get opportunity to work on timing at CERN.

17:33 Question: What about variation with respect to time of day/year? Answer: Results show no variation in day/night or Summer vs Spring+Fall.

17:35: Question: How can you be sure of geodesy measurements if they do not agree? Answer: The measurements shown are for four different points, not the same point measured four times. Clocks are also continually resynchronized.

17:37: Question: Do temperature variations affect GPS signals? Answer: Local temperature does not affect GPS measurements. Two frequencies are used to get the position in ionosphere. 1ps precision possible, but not needed for OPERA.

17:41: Question: Can you show the tails of the timing distributions with and without the correction? Is selection biasing the shapes of the fitted distributions? Answer: Not much dependence on spatial position from BCT at CERN. (Colleague from audience): The fit is performed globally. More variation present than is shown in the slides, with more features to which the fit is sensitive.

17:43: Question: Two factors in the fit: delay and normalization. Do you take normalization into account? Answer: Normalization is fixed to number of events observed. (Not normalized to the cross section.)

17:45: Question: Do you take beam stretching/squeezing into account? Answer: Timing is measured on BCT. No correlation between position in Gran Sasso and at CERN.

17:47: Question: Don’t know where muons were generated (could be in rock.) How is that taken in to account? Answer: We look at events with and without selections on muons.

17:49: Question: Do you get a better fit if you fit to the whole range and different regions? What is the χ2/n for the fits? Answer: We perform the fit on the whole range and have the values of χ2/n, but I can’t remember what they are, and they are not on the slides.

17:50: Question: What about any energy dependence of the result? Answer: We don’t claim energy dependence or rule it out with our level of precision and accuracy.

17:52: Question: Is a near experiment possible? Answer: This is a side analysis. The main aim is to search for τ appearance. (Laughter and applause from audience.) We cannot compromise our main physics focus. E-mail questions welcome!

17:53: End, and lots of applause. Time for discussion over coffee! Thanks for reading!

The start of the neutrinos journey, taken from the OPERA paper.  (http://arxiv.org/abs/1109.4897)

The start of the neutrinos journey, taken from the OPERA paper. (http://arxiv.org/abs/1109.4897)

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Italy visit in March

Tuesday, March 31st, 2009

Quantum Diaries starts again. At its first start in 2005, my friend Zhizhong Xing, a neutrino theorist, contributed a lot of interesting articles. After the Quantum Diaries paused, Zhizhong moves to a Chinese scientists’ blog site, http://www.sciencenet.cn/u/xingzz, keep spreading all kinds of fancy news.

It is said that this restart is more or less motivated by the upcoming release of the movie “Angels and Demons”. I am very impressed by this novel. “Angles and Demons” is written by Dan Brown. A physicist at CERN created anti-matter, which could be used as a MDW (Mass Destruction Weapon), which we failed to search out in Iraq. The anti-matter was stolen and hidden in Vatican to threaten the on-going Pope election. When I heard the news that Quantum Diaries will be restarted, I am preparing for a workshop in Venice, Italy, Neutrino Telescope 2009. Last time I visited Italy was in 2005, soon after I read this novel. I went to Frascatti in suburb of Roma for the Neutrino Factory Workshop. I have been in Roma once in 2000, as a tourist. But I haven’t any impression on the metaphor of the buildings described in Dan’s novel. After the meeting, I came to Roma in the early morning by train. My flight was in the evening. I had one day to investigate these great buildings. The left-baggage office at the train station was crowded incredibly with a 2-hour long queue. Thus I had a very special experience, with a backpack and a luggage, walking along the route in Dan’s novel, up to the Castle Santa Angelo.

Back to the Venice meeting. Venice in March is very beautiful. Italian food and wine are excellent. Of course, the talks and discussions are identically interesting. For example, Prof. Minakata from Tokyo Metropolitan University gave a talk titled “Neutrino non-standard Interactions: Another eel under a willow?”. Actually he means “another loach under a willow”, a Japanese proverb. Loaches like to live under willow trees. This proverb means that just because you caught a loach under the willow tree once, it doesn’t necessarily mean that there will always be a loach there. He asked the audience if they know loach. I am surprised that nobody responded yes. Probably that’s why Minakata San changed the loach to eel. I am no longer a theorist for long time, thus have difficulties to catch point from a bunch of formula in this talk. But I know loach very well. It is common in rice-planting area. Well, there is a famous Chinese dish, called loach in Tofu.

量子日记又重新跟大家见面了。2005年量子日记启动的时候,我的朋友、中微子理论家邢志忠教授曾为大家贡献了不少有趣的文章。量子日记暂停后,志忠又转战科学网博客,坚持不懈,孜孜不倦地提供各种小道消息。

据说这次重新启动与《天使与魔鬼》电影5月15日公映活动有关。《天使与魔鬼》是丹•布朗写的小说,《达•芬奇密码》的姊妹篇。小说的背景是欧洲核子研究中心的科学家维特勒研制出了蕴含着极其强大能量的反物质,结果被人杀害,反物质被人窃取,藏到了梵帝冈,用以要挟即将进行的教皇选举。接到量子日记重新启动的消息的时候,我正在准备去意大利参加“中微子望远镜2009”研讨会。上一次去意大利是2005年,我刚看完《天使与魔鬼》不久,到罗马郊区的Frascatti参加“中微子工厂”研讨会。2000年时候,我曾经到罗马走马观花地旅游过一次,但对书中建筑的种种隐喻完全没有印象。开完会后,第二天清晨坐火车来到罗马。飞机要很晚才起飞,我有将近一天的时间重新看一看。罗马火车站行李寄存处生意兴隆,排了至少两小时的长龙。于是我背着包,拖着行李箱,沿着丹•布朗的路线,一直走到天使堡。

威尼斯的三月非常漂亮,意大利饭和红酒非常好,当然,会议报告也同样有意思。例如,来自东京都立大学的Minakata教授做了一个报告叫“中微子非标准相互作用:柳树下的又一条鳗鱼?”。出处来自日本的一条谚语“柳树下的又一条泥鳅”。泥鳅据说喜欢呆在柳树下,你曾经在柳树下找到了一条泥鳅,但并不意味着在同一个地方还能抓到一条。他问“你们知道泥鳅吗?”,与会的大部分西方人没有反应。我想这也是他题目中把泥鳅改成鳗鱼的原因。我已长久不关心理论物理,因此无法在报告内容的一大堆符号中抓住关键。不过我很熟悉泥鳅,它在适宜种植水稻的水乡是非常常见的。还有一道名菜叫“泥鳅豆腐”。

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