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Posts Tagged ‘neutrino’

Nobel Prize in Physics 2015

Tuesday, October 6th, 2015

So, the Nobel Prize in Physics 2015 has been announced. To much surprise of many (including the author), it was awarded jointly to Takaaki Kajita and Arthur B. McDonald “for the discovery of neutrino oscillations, which shows that neutrinos have mass.” Well deserved Nobel Prize for a fantastic discovery.

What is this Nobel prize all about? Some years ago (circa 1997) there were a couple of “deficit” problems in physics. First, it appeared that the detected number of (electron) neutrinos coming form the Sun was measured to be less than expected. This could be explained in a number of ways. First, neutrino could oscillate — that is, neutrinos produced as electron neutrinos in nuclear reactions in the Sun could turn into muon or tau neutrinos and thus not be detected by existing experiments, which were sensitive to electron neutrinos. This was the most exciting possibility that ultimately turned out to be correct! But it was by far not the only one! For example, one could say that the Standard Solar Model (SSM) predicted the fluxes wrong — after all, the flux of solar neutrinos is proportional to core temperature to a very high power (~T25 for 8B neutrinos, for example). So it is reasonable to say that neutrino flux is not so well known because the temperature is not well measured (this might be disputed by solar physicists). Or something more exotic could happen — like the fact that neutrinos could have large magnetic moment and thus change its helicity while propagating in the Sun to turn into a right-handed neutrino that is sterile.

The solution to this is rather ingenious — measure neutrino flux in two ways — sensitive to neutrino flavor (using “charged current (CC) interactions”) and insensitive to neutrino flavor (using “neutral current (NC) interactions”)! Choosing heavy water — which contains deuterium — is then ideal for this detection. This is exactly what SNO collaboration, led by A. McDonald did

Screen Shot 2015-10-06 at 2.51.27 PM

As it turned out, the NC flux was exactly what SSM predicted, while the CC flux was smaller. Hence the conclusion that electron neutrinos would oscillate into other types of neutrinos!

Another “deficit problem” was associated with the ratio of “atmospheric” muon and electron neutrinos. Cosmic rays hit Earth’s atmosphere and create pions that subsequently decay into muons and muon neutrinos. Muons would also eventually decay, mainly into an electron, muon (anti)neutrino and an electron neutrino, as

Screen Shot 2015-10-06 at 2.57.37 PM

As can be seen from the above figure, one would expect to have 2 muon-flavored neutrinos per one electron-flavored one.

This is not what Super K experiment (T. Kajita) saw — the ratio really changed with angle — that is, the ratio of neutrino fluxes from above would differ substantially from the ratio from below (this would describe neutrinos that went through the Earth and then got into the detector). The solution was again neutrino oscillations – this time, muon neutrinos oscillated into the tau ones.

The presence of neutrino oscillations imply that they have (tiny) masses — something that is not predicted by minimal Standard Model. So one can say that this is the first indication of physics beyond the Standard Model. And this is very exciting.

I think it is interesting to note that this Nobel prize might help the situation with funding of US particle physics research (if anything can help…). It shows that physics has not ended with the discovery of the Higgs boson — and Fermilab might be on the right track to uncover other secrets of the Universe.

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This Fermilab press release came out on July 8, 2015.

Fermilab's Main Injector accelerator, one of the most powerful particle accelerators in the world, has just achieved a world record for high-energy beams for neutrino experiments. Photo: Fermilab

Fermilab’s Main Injector accelerator, one of the most powerful particle accelerators in the world, has just achieved a world record for high-energy beams for neutrino experiments. Photo: Fermilab

A key element in a particle-accelerator-based neutrino experiment is the power of the beam that gives birth to neutrinos: The more particles you can pack into that beam, the better your chance to see neutrinos interact in your detector. Today scientists announced that Fermilab has set a world record for the most powerful high-energy particle beam for neutrino experiments.

Scientists, engineers and technicians at the U.S. Department of Energy’s Fermi National Accelerator Laboratory have achieved for high-energy neutrino experiments a world record: a sustained 521-kilowatt beam generated by the Main Injector particle accelerator. More than 1,000 physicists from around the world will use this high-intensity beam to more closely study neutrinos and fleeting particles called muons, both fundamental building blocks of our universe.

The record beam power surpasses that of the 400-plus-kilowatt beam sent to neutrino experiments from particle accelerators at CERN.

Setting this world record is an initial step for the Fermilab accelerator complex as it will gradually increase beam power over the coming years. The next goal for the laboratory’s two-mile-around Main Injector accelerator — the final and most powerful in Fermilab’s accelerator chain — is to deliver 700-kilowatt beams to the laboratory’s various experiments. Ultimately, Fermilab plans to make additional upgrades to its accelerator complex over the next decade, achieving beam power in excess of 1,000 kilowatts, also referred to as 1 megawatt.

“We have the world’s highest-power beam for neutrinos, and we’re only going up from here,” said Ioanis Kourbanis, head of the Main Injector Department at Fermilab.

Laboratory-made neutrino experiments start by accelerating a beam of particles, typically protons, and then smashing them into a target to create neutrinos. Scientists then use particle detectors to “catch” as many of those neutrinos as possible and record their interactions. Neutrinos rarely engage with matter: Only one out of every trillion emerging from the proton beam will interact in an experiment’s detector. The more particles in that beam, the more opportunities researchers will have to study these rare interactions.

The amped-up particle beam provided by the Main Injector enriches the lab’s neutrino supply, positioning Fermilab to become the primary laboratory for accelerator-based neutrino research. Neutrinos are also made in stars and in the Earth’s core, and they pass through everything — people and planets alike.

“The idea is that if you build a more intense beam, neutrino scientists from around the world will beat a path to your door,” said Fermilab Deputy Director Joe Lykken. “This is exactly what’s happening.”

Fermilab currently operates four neutrino experiments: MicroBooNE, MINERvA, MINOS+ and the laboratory’s largest-to-date neutrino experiment, NOvA, which sends particles from Fermilab’s suburban Chicago location to a far detector 500 miles away in Ash River, Minnesota. The laboratory is working with scientists from around the world on expanding its short-baseline neutrino program and would also serve as host to the proposed flagship Long-Baseline Neutrino Facility and Deep Underground Neutrino Experiment, or DUNE. Scientists aim to address basic questions about the mass and properties of each kind of neutrino as well as the role neutrinos played in the evolution of the universe.

“Reaching this milestone is a fantastic achievement for Fermilab; beam power is everything in our field,” said DUNE co-spokesperson Mark Thomson of the University of Cambridge. “The ability for Fermilab to deliver, yet again, gives the international neutrino community huge confidence in the future U.S.-hosted neutrino program.”

Fermilab is also preparing to operate two experiments for studying muons, short-lived particles that could reveal secrets about the earliest moments of the universe. The increased beam power will also benefit the Fermilab Test Beam Facility, one of the few facilities in the world that provides muons, pions and other particles that researchers can use to test their particle detectors.

Since 2011, Fermilab has made significant upgrades to its accelerators and reconfigured the complex to provide the best possible particle beams for neutrino and muon experiments. With the dedicated work of the Fermilab Accelerator Division, the Main Injector is on track to nearly double its Tevatron-era beam power by 2016.

“Fermilab’s beamline has been a tremendous driver of neutrino science for many years, and the continued improvements to the intensity mean that it will remain a driver for many years to come,” said Indiana University’s Mark Messier, co-spokesperson for the NOvA experiment.

Fermilab is America’s premier national laboratory for particle physics and accelerator research. A U.S. Department of Energy Office of Science laboratory, Fermilab is located near Chicago, Illinois, and operated under contract by the Fermi Research Alliance LLC. Visit Fermilab’s website at www.fnal.gov, and follow us on Twitter at @Fermilab.

The DOE Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.

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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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ELBNF is born

Tuesday, February 3rd, 2015

This article appeared in Fermilab Today on Jan. 27, 2015.

The proposed experiment at the Long-Baseline Neutrino Facility would send neutrinos through the Earth's mantle from Batavia, Illinois, to Lead, South Dakota. Image: symmetry

The proposed experiment at the Long-Baseline Neutrino Facility would send neutrinos through the Earth’s mantle from Batavia, Illinois, to Lead, South Dakota. Image: symmetry

At approximately 6:15 p.m. CST on Jan. 22, 2015, the largest and most ambitious experimental collaboration for neutrino science was born.

It was inspired by a confluence of scientific mysteries and technological advances, engendered by the P5 report and the European Strategy update, and midwifed by firm tugs from Fermilab, CERN and Brookhaven Lab. Going by the placeholder name ELBNF (Experiment at the Long-Baseline Neutrino Facility), the newborn had the impressive heft of 145 institutions from 23 countries.

The new Institutional Board (IB), convened by interim chair Sergio Bertolucci, unanimously approved a Memorandum of Collaboration that launches the election of spokespeople and a process to develop bylaws. The IB also endorsed an international governance plan for oversight of ELBNF detector projects, in concert with the construction of the LBNF facility hosted by Fermilab.

The goal of this international collaboration is crystal clear: a 40-kiloton modular liquid-argon detector deep underground at the Sanford Underground Research Facility exposed to a megawatt-class neutrino beam from Fermilab with the first 10 kilotons in place by 2021. This goal will enable a comprehensive investigation of neutrino oscillations that can establish the presence of CP violation for leptons, unequivocally determine the neutrino mass ordering and strongly test our current neutrino paradigm. A high-resolution near detector on the Fermilab site will have its own rich physics program, and the underground far detector will open exciting windows on nucleon decay, atmospheric neutrinos and neutrino bursts from supernova detonations.

Unlike most births, this one took place at an international meeting hosted by Fermilab; there was room for nearly all the friends and family of accelerator-based neutrino experiments. One of the critical items flagged at this meeting is to find a better name for the new collaboration. Here are a few of my unsolicited attempts:

nuLAND = neutrino Liquid ArgoN Detector

GOLDEN = Giant OsciLlation Detector Experiment for Neutrinos

Think you can do better? Go ahead. My older son, a high-priced management consultant, offered another one pro bono: NEutrino Research DetectorS.

I am too young to have been in the room when ATLAS and CMS (or for that matter CDF and DZero) came into being, but last week I had the thrill of being part of something that had the solid vibe of history being made. The meeting website is here.

Joe Lykken, Fermilab deputy director

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How to make a neutrino beam

Friday, December 12th, 2014

This article appeared in Fermilab Today on Dec. 11, 2014.

Ingredients for a neutrino beam: speedy protons, target, magnetic horn, decay pipe, absorbers. Image adapted from Fermilab

Ingredients for a neutrino beam: speedy protons, target, magnetic horn, decay pipe, absorbers. Image adapted from Fermilab

Fermilab is in the middle of expanding its neutrino program and is developing new detectors to study these ghostly particles. With its exquisite particle accelerator complex, Fermilab is capable of creating very intense beams of neutrinos.

Our neutrino recipe starts with a tank of hydrogen. The hydrogen atoms are fed an extra electron to make them negatively charged, allowing them to be accelerated. Once the charged atoms are accelerated, all of the electrons are ripped off, leaving a beam of positive protons. The protons are extracted into either the Booster Neutrino Beamline (BNB) or are further accelerated and extracted into the Neutrino Main Injector beamline (NuMI). Fermilab is the only laboratory with two neutrino beams. Our two beams have different energies, which allows us to study different properties of the neutrinos.

In the BNB, these protons smash into a target to break up the strong bonds of the quarks inside the proton. These collisions are so violent that they produce new quarks from their excess energy. These quarks immediately form together again into lighter composite short-lived particles called pions and kaons.

Since the pions and kaons emerge at different directions and speeds, they need to be herded together. As a bugle tunes your breath into musical notes, a horn of a different type rounds up and focuses the pions and kaons. The BNB horn looks roughly like the bell of a six-foot long bugle. It produces an electric field that in turn generates a funnel-like magnetic field, which directs all of the dispersed pions and kaons of positive electric charge straight ahead. Particles with negative charges get defocused. By switching the direction of the electric field, we can focus the negatively charged particles while defocusing the positive charges.

The focused particles in the BNB beam travel through a 50-meter long tunnel. This is where the magic happens. In this empty tunnel, the pions and kaons decay in flight into neutrinos, electrons and muons. At the end of the decay tunnel is a wall of steel and concrete to stop and absorb any particle that is not a neutrino. Because neutrinos interact so rarely, they easily whiz through the absorbers and on towards the experiments. And that’s the basic formula to make a beam of neutrinos!

A single neutrino beamline can support many experiments because the neutrinos interact too rarely to get “used up.” The BNB feeds neutrinos to MicroBooNE, and most of them go on through to the other side towards the MiniBooNE detector. Similarly, most of those go on through the other side as well and continue traveling to infinity and beyond. Detectors located in this beam measure neutrino oscillations and their interactions.

The NuMI beamline is designed similarly, but uses a different target material, two focusing horns, and a 675-meter decay pipe. The spacing between the two NuMI horns is adjustable, allowing fine-tuning of the neutrino beam energy. The NuMI beamline has higher-energy neutrinos than the BNB and thus studies different properties of neutrino oscillations.

The NuMI beamline feeds neutrinos to the MINERvA experiment and on through to the MINOS near detector. The NuMI beamline then continues about 450 miles through Earth on toward the MINOS far detector in the Soudan mine in Minnesota. By the time the beam reaches the far detector, it is about 20 miles in diameter! By having a near and far detector, we are able to observe neutrino flavor oscillations by measuring how much of the beam is electron neutrino flavor and muon neutrino flavor at each of these two detectors.

The last of the big Fermilab neutrino experiments is NOvA. Its near detector is off to the side of the NuMI beam and measures neutrinos only with a specific range of direction and energy. The NOvA far detector is positioned to measure the neutrinos with the same properties at a greater distance, about 500 miles away in Ash River, Minnesota. By placing the NOvA detectors 3 degrees to the side of the beam’s center, NOvA will get to make more precise oscillation measurements for a range of neutrino energies.

As more experiments are designed with more demanding requirements, Fermilab may expect to see more neutrino beamline R&D and the construction of new beamlines.

Tia Miceli

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Fermilab published a version of this press release on June 24, 2014.

The 30-ton MicroBooNE neutrino detector is gently lowered into the Liquid-Argon Test Facility at Fermilab on Monday, June 23. The detector will become the centerpiece of the MicroBooNE experiment, which will study ghostly particles called neutrinos. Photo: Fermilab

The 30-ton MicroBooNE neutrino detector is gently lowered into the Liquid-Argon Test Facility at Fermilab on Monday, June 23. The detector will become the centerpiece of the MicroBooNE experiment, which will study ghostly particles called neutrinos. Photo: Fermilab

On Monday, June 23, the next phase of neutrino physics at Fermilab fell (gently) into place.

The MicroBooNE detector – a 30-ton, 40-foot-long cylindrical metal tank designed to detect ghostly particles called neutrinos – was carefully transported by truck across the U.S. Department of Energy’s Fermilab site, from an assembly building it was constructed in to the experimental hall three miles away.

The massive detector was then hoisted up with a crane, lowered through the open roof of the building and placed into its permanent home, directly in the path of Fermilab’s beam of neutrinos. There it will become the centerpiece of the MicroBooNE experiment, which will study those elusive particles to crack several big mysteries of the universe.

The MicroBooNE detector has been under construction for nearly two years. The tank contains a 32-foot-long “time projection chamber,” the largest ever built in the United States, equipped with 8,256 delicate gilded wires, which took the MicroBooNE team two months to attach by hand. This machine will allow scientists to further study the properties of neutrinos, particles that may hold the key to understanding many unexplained mysteries of the universe.

“This is a huge day for the MicroBooNE experiment,” said Fermilab’s Regina Rameika, project manager for the MicroBooNE experiment. “We’ve worked hard to create the best scientific instrument that we can. To see it moved into place was a thrill for the entire team.”

The MicroBooNE detector will now be filled with 170 tons of liquid argon, a heavy liquid that will release charged particles when neutrinos interact with it. The detector’s three layers of wires will then capture pictures of these interactions at different points in time and send that information to the experiment’s computers.

Using one of the most sophisticated processing programs ever designed for a neutrino experiment, those computers will sift through the thousands of interactions that will occur every day and create stunning 3-D images of the most interesting ones. The MicroBooNE team will use that data to learn more about how neutrinos change from one type (or “flavor”) to another, and narrow the search for a hypothesized (but as of yet, never observed) fourth type of neutrino.

“The scientific potential of MicroBooNE is really exciting,” said Yale University’s Bonnie Fleming, co-spokesperson for the MicroBooNE experiment. “After a long time spent designing and building the detector, we are thrilled to start taking data later this year.”

MicroBooNE is a cornerstone of Fermilab’s short-baseline neutrino program , which studies neutrinos traveling over shorter distances. (MINOS and NOvA, which send neutrinos through the Earth to Minnesota, are examples of long-baseline experiments.) In its recent report, the Particle Physics Project Prioritization Panel (P5) expressed strong support for the short-baseline neutrino program at Fermilab.

The P5 panel was comprised of members of the high-energy physics community. Their report was commissioned by the High Energy Physics Advisory Panel, which advises both the Department of Energy and the National Science Foundation on funding priorities.

The detector technology used in designing and building MicroBooNE will serve as a prototype for a much larger long-baseline neutrino facility planned for the United States, to be hosted at Fermilab. The P5 report also strongly supports this larger experiment, which will be designed and funded through a global collaboration.

Read the P5 report.

Fermilab is America’s premier national laboratory for particle physics and accelerator research. A U.S. Department of Energy Office of Science laboratory, Fermilab is located near Chicago, Illinois, and operated under contract by the Fermi Research Alliance, LLC. Visit Fermilab’s website at www.fnal.gov and follow us on Twitter at @FermilabToday.

The DOE Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.

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À l’occasion de l’ouverture de l’appel à candidature 2013 de “Sciences à l’Ecole” pour l’accueil d’enseignants français au CERN durant une semaine, nous publions ces jours-ci le journal quotidien plein d’humour de Jocelyn Etienne qui a suivi ce programme l’année dernière, au mois de novembre dernier.

 

Dans les cavernes des géants
Mercredi 07 novembre 2012

La matinée est animée par un physicien autrichien guide alpin hyperactif dont je n’ai pas saisi le nom mais que je devrais pouvoir retrouver avant la fin du séjour dans un lieu où même le boson de Higgs est détectable (edit : Michael Hoch en fait). Il nous amène voir les sites où se trouvent deux gigantesques détecteurs de particules, CMS et ATLAS, placés à l’endroit où les faisceaux de protons du LHC se rencontrent.

Avant cela, rapide visite dans un site où un bout du LHC est exposé. On y voit les deux conduits dans lesquels les faisceaux de protons circulent quasiment à la vitesse de la lumière, et dans des sens opposés.

DSC04163Quatre fois sur les 27 km, ces 2 tuyaux se croisent pour causer les collisions qui sont analysées par CMS et ATLAS (mais aussi LHCb et ALICE). Le module sur lequel je m’appuie sur la photo comporte aussi des électroaimants supraconducteurs refroidis à -271°C par de l’hélium liquide. Les aimants servent plus ou moins à diriger et comprimer le faisceau, son accélération se faisant en d’autres points à l’aide de champ électrique haute fréquence. Mais tout ça ne peut-être vu en fonctionnement car cela se situe à 100 m sous terre et de plus, les radiations émises pourraient nuire à mon cuir chevelu.

DSC04181

À CMS, c’est le physicien Jean Fay qui nous fait visiter les locaux avec grandes compétence et gentillesse. Bien que l’on ne puisse pas approcher le détecteur (mais l’affiche de la photo donne une idée de sa taille), une salle de contrôle de la bestiole nous est accessible.

DSC04169_CMSLe système d’exploitation est linux car les pannes windows sont à proscrire… C’est le monsieur qui me l’a dit. Je résume sa pensée : « Vindoze, c’est bon pour les présentations poveurpoïnt, et encore… »

Attends, je dois vérifier un truc… non, c’est bon en fait !

Attends, je dois vérifier un truc… non, c’est bon en fait !

Vite, il nous faut retourner vers ATLAS. Il se situe en fait vers le CERN, alors que CMS est diamétralement opposé, et en France si j’ai bien tout compris.

C’est un physicien retraité à l’esprit vif comme un neutrino qui nous guide : Klaus Bätzner. Le site ATLAS est plus orienté vers le public car il est proche du CERN et sans doute plus accessible. Une salle de projection 3D est mise à notre disposition. Équipés de lunettes et d’un casque, la vidéo qu’on nous présente est impressionnante.

La salle de contrôle est pleine de grands écrans, de petits écrans, de claviers, et de gens qui regardent des écrans tout en pianotant sur les claviers. Ils sont comme dans un aquarium et on peut les observer sans trop interférer avec leur comportement. 🙂

Après le déjeuner avalé en vitesse, direction la salle du conseil pour écouter l’excellent Fabrice Piquemal du CNRS nous parler des neutrinos. Ça tombe bien, les détecteurs précédents ne font qu’extrapoler la présence de neutrinos lors d’une collision, par calcul de l’énergie manquante. Les neutrinos ont la fâcheuse tendance à traverser la matière comme qui rigole, et ne vont pas plus vite que la lumière contrairement à une idée faussement répandue.

Le soir, nous nous retrouvons à Genève après avoir sagement suivi la ligne 14. Le dîner se déroule dans un restaurant où des musiciens jouent avec tout ce qui leur passe sous la main : scie, cuillère, cloche, parfois même des instruments de musique à condition qu’ils fassent plus de 3 mètres. Exténué, retour vers 23 h au CERN.

 

À suivre…

Jocelyn Etienne est enseignant au lycée Feuillade de la ville de Lunel.

Pour soumettre sa candidature pour la prochaine session du stage au CERN, c’est par ici.


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This article first appeared in Fermilab Today on June 6.

Sam Zeller won a DOE Early Career Research Award to support her work on liquid argon neutrino dectectors. Photo: Reidar Hahn

Neutrinos are known for escaping capture. They fly through matter and their different types continuously morph into one another. That elusive, shifting behavior challenges nearly every available tool and capability scientists have to sketch their portraits.

With better tools come more detailed portraits. Last month, Fermilab scientist Geralyn “Sam” Zeller received a 2012 DOE Early Career Research Award to advance a detector technology that will capture neutrinos’ attributes with unprecedented detail. The $2.5 million award, spread over five years, will support a proof-of-principle study towards the construction of multi-kiloton liquid-argon neutrino detectors.

“There are some really important questions we want to answer about how neutrinos behave,” Zeller said. “The best chance for answering them is to study neutrinos with this exquisite detector.”

Liquid-argon detectors are practically photographic in their ability to show what happens when a neutrino hits an argon nucleus. Tracks that the resultant particles leave behind are shown in high resolution, and it’s easy to distinguish the various particle types that arise from the interaction.

But information on how neutrinos behave in liquid-argon detectors is sparse. Most of what is known is based on simulations rather than experiment. Also, researchers have typically gathered what they need to know from event displays – pretty pictures of events that, while useful, are relatively light on quantified information.

Zeller, who has been at Fermilab since December 2009, plans to fill the gap with an abundance of new data. The DOE award will support the analysis of neutrino data recently collected by a small (less than 1 ton) liquid-argon detector prototype called ArgoNeuT. In the next few years, Zeller’s team will also generate and analyze neutrino data using Fermilab’s new MicroBooNE detector, a 170-ton liquid-argon detector. Their findings will tell them whether they can get the expected performance out of a detector of much larger scale. They’ll also characterize exactly how neutrinos behave when interacting in argon.

“There’s a big gap in our knowledge of how neutrinos interact,” Zeller said. “We want better information to inform the design of future detectors.”

Zeller’s project leverages the current ongoing U.S. neutrino program with the idea that the community could build, in manageable stages, a liquid-argon detector weighing tens of thousands of tons. Its prodigious size increases scientists’ chance of capturing a neutrino that has changed forms. Combined with its characteristic high precision, the detector would prove invaluable for the proposed Long-Baseline Neutrino Experiment, which will allow scientists to observe neutrino oscillations, as their form-changing is called. It would also be of use for the short-baseline program in looking for a fourth neutrino to add to the family of the known three.

If future neutrino experiments go well, scientists may finally have answers to basic questions surrounding the ghostly particle: which neutrino types are the lightest and heaviest, and do they behave the same as their antiparticles?

The DOE award will fund two postdocs and a dedicated team for the long-baseline program, as well as supporting technical and engineering work.

“There’s an opportunity here because we have these two detectors and the best neutrino beams in the world,” Zeller said. “Now we’re going to try to get as much information out of them as we can.”

Leah Hesla

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What has no thumbs and travels at the speed of light, to within experimental uncertainty?

Hi All,

I will just say this right away, the Borexino, ICARUS, LVD, OPERA, and MINOS Experiments have all independently found, within experimental uncertainty, that neutrinos travel at the speed of light. To enlighten, last September the OPERA Experiment at the Gran Sasso Laboratory, in Gran Sasso, Italy, observed what appeared to indicate that neutrinos travel faster than the speed of light. (More information available from veteran QDers Aiden and Seth).

The reported quantity is time it took neutrinos to travel from CERN to Gran Sasso minus the time it would have taken light. I should also mention that the statistical (stat.) and systematic (sys.) uncertainties are incredibly important.

δt = (Time it took neutrinos to reach GS from CERN) – (Distance between GS and CERN)/(Speed of Light)

Figure 1: Results from four Gran Sasso Laboratory experiments indicating neutrinos travel at the speed of light, to within exerpeimental uncertainty. Reported quantity is time it took neutrinos to travel from CERN to Gran Sasso minus the time it would have taken light. Credit: BERTOLUCCI, Sergio

Figure 2: Results from the MINOS Experiment indicating neutrinos travel at the speed of light, to within exerpeimental uncertainty. Reported quantity is time it took neutrinos to travel from Fermilab to MINOS minus the time it would have taken light. Credit: ADAMSON, Phil

To clarify the situation, this result was not a typical “Hey! We discovered new physics!” result. Had OPERA correctly observed a massive particle traveling faster than light, then we would truly be in the midst of a physic revolution. That is not a hyperbole either. As a result, everyone, theorists and experimentalists alike, put on their scientists hats and scrutinized the result to no end. Much drama ensued and at long last the problem has been resolved. The issue at hand were actually two very subtle effects that worked against each other. The first was that a 5.2 mi (8.3 km) cable was accidentally stretched back in 2008 and systematically introduced a 74 nanosecond delay in the system that recorded the time the neutrinos arrived at the detector. The second issue involved the highly precise master clock system for the entire experiment; it was slow by about 15 nanoseconds. 74 – 15 = 59 nanoseconds was exactly how much sooner the neutrinos were arriving than they were expected.

 

Figure 3: Two previously unaccounted issues regarding the OPERA Experiment. Credit: DRACOS, Marcos

In conclusion, neutrinos may still travel faster than the speed of light. It is unlikely, but still possible. Officially as of today, though, we know that all measurements of neutrinos’ speed show are consistent with the speed of light.

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Neutrino 2012: Day 3+4

Friday, June 8th, 2012

How many types of neutrinos are there? That was Day 3+4’s Big Question.

Hi All,

Your Day 3+4 breakdown is finally here. A lack of internet access is always an issue. At any rate, things were a very great mix of experimental results and theoretical discussions that all pointed to one question: How many types of neutrinos are there in the Universe? According to the Standard Model, which itself is founded on very rich experimental results, there are 3 flavors: electron-neutrino, muon-neutrino, and tau-neutrino. However, it is very possible there are more neutrinos that do not have any charges under the Standard Model. Such neutrinos are called sterile neutrino or singlet neutrinos.

Without further ado: MiniBooNE, Neutrino Anomalies, KamLAND-Zen, EXO-200, and Day 4.

MiniBooNE

A quick breakdown of what the Miniature Booster Neutrino Experiment, or MiniBooNE for short, is all about can be given in the following two slides. Fermilab accelerates protons into a fixed target to produce pions and kaons. The pions and kaons are then directed toward the ground and squeezed together by a system of magnetic fields called “the horn.” The pions then fly for a period of time, decaying into muons, electrons, and neutrinos. The muons further decay into more neutrinos and electrons. When the electron and neutrino beam hits the ground, the electrons are absorbed and the neutrinos pass through the planet. Finally, after popping out in a deep underground Minnesota mine, the neutrino beam flies through the MiniBooNE detector and physics is born.

One of MiniBooNE’s chief scientific goals is to confirm or refute the result of a previous experiment, LSND, which observed an excess of neutrinos. The excess was best described by introducing a single sterile neutrino and we still do not know if the result was a statistical fluke or something more serious.

Figure 1: Summary of the MiniBooNE Experiment at Fermilab with motivation for its science programme. Credit: POLLY, Chris

Figure 2: Breakdown of the MiniBooNE Experiment at Fermilab. Credit: POLLY, Chris

The experiment has announced for the first time with its full dataset, that it has observed an excess number of anti-muon-neutrinos converting to anti-electron-neutrinos. This excess is almost entirely in the lower energy range, i.e., smaller energy transfer between neutrinos and detector, and the experiment is trying vigorously to determine if this has been caused by a previously unknown background.

Figure 3: Results showing an excess in the number of low energy anti-electron neutrinos observed. Credit: POLLY, Chris

When combing the anti-neutrino and neutrino excesses, the overall excess in number of events grows in significance. The two results are consistent with each other, so there is no measurable difference between matter and anti-matter has been observed. If it is there, it is beyond the detector’s capabilities. There are a few ideas to explain the more-than-expected number of neutrinos and they are individually being studied as we speak. A VERY preliminary result (so preliminary I am choosing not the put up the plot here) is that the data is somewhat well-described by assuming the existence of two sterile neutrinos. This actually is more preferred than a single sterile neutrino, so theorists are a bit happy at the moment. 🙂

Figure 4: Results showing an excess in the number of low energy electron-neutrinos and anti-electron neutrinos observed. Credit: POLLY, Chris

Neutrino Anomalies

The prospect of adding a new neutrino to the Standard Model is a tricky issue, let alone adding two. Theoretically it is not terribly difficult but such a step would have very obvious and quickly testable predictions. The first of several theory talks (I am skipping my synopsis of all other theory talks) had a summary of known anomalies from neutrino experiments. LSND and MiniBooNE has already been discussed and the largest. A rather recently discovered discrepancy is the number of neutrinos predicted to be produced by nuclear reactors. The calculation is very well known but had not been updated in years. After recalculating the expected neutrino production rate, the predicted rate was found to be larger than the observed rate. Strictly speaking, all results ARE consistent with the Standard Model and we cannot make any definitive statements based solely on what is listed here.

Figure 5: . Credit: LASSERRE, Thierry

KamLAND-Zen

On to KamLAND-Zen, which stands for Kamioka Liquid Scintillator Anti-neutrino Detector – Zero Neutrino Double β-Decay (pronounced: beta-decay). This experiment has got to be the best example of when an experiment collaboration just stops trying to write its experiment name as a logical acronym. It is still a wicked-cool name. Nuclear β-decay is one of the most well-studied examples of radioactivity where a nucleus in an atom will disintegrate into a lighter nucleus, plus an electron (or a positron), and an anti-electron-neutrino (or a regular electron-neutrino). Some radioactive elements can also undergo the super rare double β-decay where two β-decays occur simultaneously. In the case that a sterile neutrino does indeed exist, then the even more rare neutrino-less double β-decay should be possible. In this situation, two nuclei in an element will disintegrate into two lighter nuclei and only two electrons (or positrons!). KamLAND-Zen is looking for such a decay in the gas xenon but has had no such luck. It has, however, been able to measure the rate of the still-very-rare 2-neutrino-double β-decay in xenon, an impressive feat in and of itself. The experiment was also able to disprove a previous measurement of this rate from a different experiment called DAMA. Here are the results.

Figure 6: KamLAND-Zen's measurement of the half-life of double β-decay in xenon gas. Credit: INOUE, kunio

Figure 7: Summary of KamLAND-Zen's experimental results. Credit: INOUE, kunio

EXO-200

The Enriched Xenon Observatory Experiment, or EXO-200 for short (the 200 is explained on wiki), is KamLAND-Zen’s biggest competitor in the race for finding neutrino-less double-β-decay. The first slide shows how much more data they have since the last time their results were announced. The second slide shows their background and the fact that they have observed almost 22,000 2-neutrino double β-decay events! I cannot describe how cool that is other than say just that: it is really cool that they have so many events. Consequentially, their results are in good agreement with KamLAND-Zen’s results. So sadly, no neutrino-less events.

Figure 8: Details of the EXO-200 Experiment, its analysis, and differences from its previous analysis. Credit: FARINE, Jacques

Figure 9: Results from EXO-200 Experiment. Credit: FARINE, Jacques

Figure 10: Results from EXO-200 Experiment with comparison to other experiments.. Credit: FARINE, Jacques

Day 4

Day 4 was a much needed rest for conference goers. Like most other attendees, I spent the day exploring Kyoto and then working with my adviser on a paper we are hoping to finish soon. In the evening, however, we were treated to a dance performance by real-life geisha dancers. I was unable to get too many photos but below is a good one. The two dancers are both geiko-sans (fully-fledged geisha dancers) but there were also three maikos (apprentice geisha dancers).

Figure 11: Something. Credit: Mine

After the short entertainment, the main event began: a public lecture on the importance of neutrinos and their influence on how the Universe evolved, given by Prof. Hitoshi Murayama, Director of the University of Tokyo’s Institute for Physics and Mathematics of the Universe. Sadly, I was unable to find his slides online, which is especially unfortunate considering his talk was entitled, “Neutrinos May Be Our Mother.” I was able to snap this photo of Prof. Murayama discussing his recent meeting with the Prime Minister of Japan and philanthropist Fred Kavli, of the famed Kavli Foundation. Mr. Kavli’s generous contributions to physics and astronomy have led to the construction of dozens of institutes around the world to focus and have allowed us to concentrate on the most important mysteries of this universe we call home.

Figure 12: Prof. Hitoshi Murayama (Far Left), sharing a picture of his meeting with Mr. Fred Kavli (Second from Right), and Prime Minister Yoshihiko Noda (Far Right). Credit: Mine.

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