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Posts Tagged ‘Intensity Frontier’

The cleanup of the MINOS cavern and the rest of the Soudan Underground Laboratory is complete.

This article first appeared in

Fermilab Today May 25.

Two months after a fire broke out in the access shaft of the Soudan mine, the Soudan Underground Laboratory is again open for operation. Safety officers inspected the mine and laboratory last week and issued a permit for normal occupancy. The officers identified a short list of additional repairs, which will be carried out in the upcoming months. Work also continues on the Soudan mine shaft.

“The cleanup of the laboratory is complete, and the MINOS far detector is ready to take beam data with full magnetic field,” said Fermilab physicist Rob Plunkett, co-spokesperson for the MINOS neutrino experiment. “The small number of components we had to replace was consistent with a normal power outage.”

The 5,000-ton MINOS far detector is located a half mile underground in the Soudan laboratory. In March, fire-fighting foam covered parts of the detector and the lowest part of the magnet coil was partially immersed in water. Laboratory staff gently heated the coil over the past two weeks to dry it out.

The CDMS experiment, located in a cavern adjacent to the MINOS detector, experienced no damage to its equipment except to a backup generator. Its cryogenic system recovered unscathed from the power outage triggered by the fire. CDMS scientists have removed the new particle detectors they were testing before the fire, and they will begin operation of an expanded experiment with more dark-matter detectors in September.

University of Minnesota building code inspectors and ES&H personnel from the university and Fermilab inspected the laboratory last Wednesday. The University of Minnesota manages the Soudan Underground Laboratory.

— Kurt Riesselmann


A cosmic ray shower.

Editor’s note: Bob’s most excellent particle detector adventure, part 7.

Bob Peterson continues to travel with his QuarkNet particle detector around the edge of Africa recording remnants of cosmic rays. This offers a chance to study how cosmic ray recordings differ on land and sea and at different latitudes. The data will be accessible to high school students and teachers in several countries who use similar detectors to learn about particle physics.

Read his previous posts here: The voyage begins, Turning the detector on, Other science on the sea, Particle detectors don’t like light, Enduring a branding for science A teaching moment on the ocean.

11 May 2011
R/V Polarstern
Latitude: 30-56.1 N
Longitude: 14-27.0 W
off the Moroccan coast
Ship course 017° T
Ship velocity 10.8 knots

10 May:
Dawn; the forecast called for a sunny day? What’s that cloud bank out my cabin window? Oh, wait, that’s land! Ah, the Canary Islands right on schedule just as the navigator predicted, and we approach Las Palmas harbor from the south.

The Polarstern receives the pilot at 0945 (he’s late), and the ship proceeds cautiously into the slip. Forty-five minutes later, dock lines are thrown and we are winched tight to the quay and the gangway lowered.

We are here to receive new scientists from Alfred Wegner Institute, or AWI, coming onboard for special training in echo acoustics and bottom profiling. And it gives some of us a chance to feel land. Shore leave is two hours; be back by 1400 or the captain will not be happy. So, I escape. Sure enough the land is moving in a wave-like motion. I must have sea-legs.

Underway again at 1745. The pilot was late again. By 1830, the Canary Islands are falling behind and slipping into the sunset haze.

How IceCube works. Credit: IceCube collaboration

11 May:
Daily, the Polarstern weather technician, Klaus, launches a weather balloon for upper-atmosphere soundings. Michael Walter, my contact from DESY/IceCube, needs these data. I’m intrigued, so Klaus gladly offers to train me to ready and launch the balloons. This will be fun.

All over the world, weather stations and ships launch these balloons simultaneously, and they need to be at 10 kilometers, or 6 miles, altitude by 1200 Coordinated Universal Time, or UTC. So, Klaus prepares and launches the balloon one hour before because it takes that long to reach 33,000 feet. The balloons are filled with helium to about five feet diameter and carry a small data collection transponder called a radiosonde.

Launchings on land are straight forward; the technician steps out of the filing garage and let’s go. On ship, it’s anything but simple. The deck is pitching and rolling, the forward speed sweeps the deck with maybe 35 knots of wind, and the tall crow’s nest in the center of the ship is definitely in the way. There will be no end of grief from the crew if I hang the balloon there. So, Klaus coaches (and laughs) as I learn to manage the recalcitrant, reluctant object, but I’ve now mastered the preparation and launch. Launchings are analogous to a young boy throwing a rock off a cliff; except, it defies gravity. What fun to watch it sail away. I wonder how long I can still see it before it disappears into the haze.

The data returns to the ship in one-second intervals, showing the profiles of atmosphere parameters. The soundings return data on altitude, pressure, temperature, humidity and wind speed and these data might couple to the QuarkNet cosmic ray muon detector (CRMD) data. Michael Walter will use this to correlate to the cosmic ray flux, or flow rate of cosmic ray remnant particles passing through various areas of the sky. I hope that QuarkNet students can do the same. I, too, will return home with the large data sets to compare to the onboard QuarkNet detector.


*Quay: Pronounced “key”. A concrete, stone or metal platform lying
alongside or projecting into water for loading and unloading ships. Similar to a

*Pilot: a master mariner hired by the captain to guide a big ship into confined harbors. They have special local knowledge and training. Still the ship’s captain is ultimately responsible. A pilot job is nice if you can get it, because all have to wait for the pilot. They are notoriously late.

*Winch: A hauling or lifting device consisting of a rope, cable or chain winding around a horizontal, rotating drum, turned by a crank or by a motor or other power source.

*AWI: Alfred Wegner Institute – Research facility that owns and manages the R/V Polarstern.

*UTC: Coordinated Universal Time

*Radiosonde: An instrument carried by balloon or other means to various levels of the atmosphere and transmitting measurements by radio.

*Crow’s nest: A shelter or platform fixed near the top of the mast of a vessel as a place for instruments or lookout.

–Bob Peterson


Editor’s Note:  Fermilab is getting ready for its annual meeting that draws together many of the 2,311 scientists across the U.S. and globe that work with Fermilab as well as staff physicists and engineers. While it could be a time of sadness and reflection with the Tevatron set to shutdown, physicists are finding that Fermilab still has a lot to offer in terms of exciting, ground-breaking science as Fermilab Director Pier Oddone outlines in his weekly column.

This article first appeared in Fermilab Today May 24.

The 44th edition of the Users’ Meeting will take place on June 1 and 2, and it should be very exciting. The Users’ Meeting is a well-established tradition at Fermilab. Every year it showcases results from the entire Fermilab experimental program, alongside discussions of the lab’s future program and presentations from government officials about policies applicable to particle physics. This year we are very fortunate to have the Secretary of Energy, Dr. Steven Chu, presenting the Meeting’s public lecture at 8 p.m. on June 2.

This year has a special edge as we approach the end of data collection at the Tevatron. This remarkable machine is achieving luminosities considered impossible decades ago with antiprotons — more than 4 x 1032 cm-2sec-1 instantaneous luminosity, with 11 femtobarns of accumulated luminosity recently celebrated.

The Tevatron’s two international collaborations CDF and DZero have many achievements of their own, including major discoveries that have established our Standard Model of particle physics. There is still juice left in the Tevatron and we may yet establish processes beyond the Standard Model if some of the collaborations’ recent results are confirmed. We also have hints of unexpected results in the neutrino sector, with neutrino oscillation data from MiniBooNE and MINOS.

Looking to the future, MINERvA is laying the foundation for understanding different nuclear targets, NOvA construction is proceeding well, and there are new proposals to extend MINOS running. The Dark Energy Survey is nearing completion, better detectors are in development for the Cryogenic Dark Matter Search, and the COUPP dark matter search is operating a small prototype at Sudbury and a larger 60 kg prototype in the NuMI tunnel. Pierre Auger continues to provide interesting results with ultra-high-energy cosmic rays. And the LHC is working splendidly and results are coming out at a fast pace.

We are also in a critical year for two long-term projects, LBNE and Project X. In addition to Project X’s broad Intensity Frontier physics program, it can serve as a foundation for a neutrino factory if one is needed to fully understand the physics of neutrinos. Looking even farther ahead, we are studying the feasibility of muon colliders as a path back to the Energy Frontier.
All this activity augurs a great Users’ Meeting next week.

–Pier Oddone, Fermilab director


Antineutrino data from MiniBooNE show the region of oscillation parameter space that is allowed at 90 percent confidence level (solid blue curve)." These results were consistent with findings from LSND, and were among the findings discussed at the Short-Baseline Neutrino Workshop that took place at Fermilab last week. Click on image to see larger version.

This article first appeared in Fermilab Today May 19.

When exciting results are popping up all over the place, it calls for bringing the best minds together from around the world to discuss the findings and make plans for the future. That’s precisely what happened at the Short-Baseline Neutrino Workshop 2011, which took place May 12-14 at Fermilab. More than 100 people from 44 institutions attended.

Neutrinos are a million times lighter than an electron and are electrically neutral, which allows them to pass through matter unaffected, making them difficult to detect. Neutrinos exist in three flavors: muon, electron and tau, and have the ability to transform from one flavor into another, a process known as oscillation.

The purpose of various short-baseline neutrino experiments is to explore questions about neutrinos that travel over a relatively short distance.

Recently, a number of tantalizing results have sprung up from both short and long baseline experiments, which seem to suggest that neutrino oscillations occur under circumstances that were previously believed to not allow them, said Bill Louis, physicist at Los Alamos National Laboratory and workshop co-organizer.

“Even if just one of these results is correct, it may possibly have a profound impact on our understanding of particle and nuclear physics,” Louis said.

Learning more about this area of physics is a key part of Fermilab’s future.

A few months after the Tevatron shuts down, there will be an 11-month period during which scientists will improve on proton sources to better serve experiments at the Intensity Frontier, including neutrino, kaon and muon programs, said Fermilab Deputy Director Young-Kee Kim. Once the complex comes back online, Fermilab plans to resume operation of neutrino beams using both 120 GeV and 8 GeV protons on the neutrino-production targets.

The MiniBooNE detector, shown above, was one project at the recent Short-Baseline Neutrino Workshop that presented interesting results. Photo: MiniBooNE collaboration.

Antineutrino data from MiniBooNE show the region of oscillation parameter space that is allowed at 90 percent confidence level (solid blue curve).” These results were consistent with findings from LSND, and were among the findings discussed at the Short-Baseline Neutrino Workshop that took place at Fermilab last week.
In their lectures, Steve Holmes, project manager for the proposed Project X, and Chris Polly, acting project manager for the future muon g-2 experiment at Fermilab, touched on the topic of the proposed beamlines. Kim further discussed future plans and solicited attendee feedback.

The ensuing discussions yielded a consensus amongst workshop attendees: The beamlines have tremendous potential, but measures will need to be taken to minimize background signals caused by cosmic radiation. Some possibilities include reusing or repurposing already existing equipment, or building additional components, which could result in a high-intensity neutrino beam that would be suitable for future experiments.

Workshop speakers also touched on what can be done in the interim between now and Project X. Among these speakers were: Geoffrey Mills (LANL), who discussed the potential of BooNE, the two-detector version of MiniBooNE; Roxanne Guenette (Yale University), who presented an overview of liquid argon detector applications in the MiniBooNE beamline; and Ryan Patterson (CalTech) and John Cooper (Fermilab), who spoke on what could be accomplished with a third NOvA detector.

See a full list of presenters online.

Louis was most impressed by the quality and diversity of the talks that touched on both experimental and theoretical issues and covered the gamut of neutrino topics.

“The talks were uniformly excellent,” Louis said. “It was just great hearing all of the different possibilities and plans for future neutrino experiments.”

— Christine Herman


This article ran in Fermilab Today May 20.

A new analysis using combined MiniBooNE and SciBooNE data looked for disappearing muon neutrinos building on a MiniBooNE study from 2009.

A new analysis using combined MiniBooNE and SciBooNE data looked for disappearing muon neutrinos building on a MiniBooNE study from 2009.

Kendall Mahn, TRIUMF; and Yasuhiro Nakajima, Kyoto University; were among the experimenters who performed this analysis.
When it comes to neutrinos, it’s best to expect the unexpected.

Previous Results of the Week have showcased a surprising difference between MiniBooNE electron neutrino appearance and electron antineutrino appearance results. In this special result, we present an analysis done by combining MiniBooNE and SciBooNE data to improve our understanding of a MiniBooNE analysis from 2009.

Previously, MiniBooNE looked for an excess of electron neutrino events in a muon neutrino beam over a short distance (0.5 km). Experimenters then conducted the same search using antineutrinos. While the tests were the same, the results were surprisingly different. The neutrino data is consistent with background, but the antineutrino data shows an excess of events consistent with the controversial 1990 results from the Liquid Scintillator Neutrino Detector experiment at Los Alamos National Laboratory.

If this observed difference is due to new physics, the new physics must be rather exotic. The most common explanation for these results uses the idea of sterile neutrinos, which physicists believe are neutrinos that do not have charged partners. Collaborators believe that as the muon neutrino travels, it will sometimes convert into a sterile neutrino, which then would convert into an electron neutrino. We expect that the sterile neutrino is only detectable from this reaction.

If sterile neutrinos exist, then the muon neutrinos should disappear, that is, some of the muon neutrinos will have converted to undetectable sterile neutrinos and the rate of muon neutrinos will be lower than we expect. Let’s say the muon neutrinos constitute a pie before baking. Disappearance is characterized by a missing slice of this pie, as some of the muon neutrinos have changed into sterile neutrinos, which we can’t see.

A previous search for the disappearance of muon neutrinos and muon antineutrinos two years ago compared MiniBooNE data to the predicted number of events at the detector. This is like counting the ingredients and examining the empty pie tin before baking, and then estimating the total pie weight and size after baking without looking at it directly.

Of course, this method is limited by our understanding of the initial number of neutrinos that reach MiniBooNE and the specifics of how they interact, that is, how well we know the ingredients beforehand .

Now, MiniBooNE has teamed up with the SciBooNE experiment to perform an improved analysis on the disappearance of muon neutrinos. SciBooNE, a dedicated cross section experiment shares the same neutrino target and flux as MiniBooNE, but was located in the same neutrino beam closer to the neutrino source. By adding the SciBooNE data to our analysis, we are able to measure the neutrino rate before the muon neutrinos disappear. This is like weighing the pie and inspecting it before baking, and is less dependent on our initial predictions.

The first joint venture of these two experiments observes no muon neutrino disappearance at 90 percent confidence level, which constrains models that require large amounts of disappearance. Our next step will be to look at muon antineutrino disappearance with both experiments, an important step to understanding the nature of new physics, if it exists.

Learn more

— Kendall Mahn and Yasuhiro Nakajima


The NOvA Far Detector (red) and surface building 'placed' inside Soldier Field stadium in Chicago, for a sense of scale of the detector size. The Far Detector measures 51.2 feet wide by 51.2 feet high by 206.7 feet long, or 15.6 meters wide, 15.6 meters high and 63 meters long.

Let me set the scene for you. The NFL season has been cancelled so in an effort to raise money the Chicago Bears have rented out their Soldier Field stadium. The DOE obtained the lease and entrusted a host of physicists to build a particle detector inside the 61,500 seater.

 None of this is true of course (well the coming NFL season may be in a lockout) but it gives you a sense of scale of the NOvA experiment if you compare the size of one of its detectors, the Far Detector, to the football stadium.

The NOvA (NuMI Off-axis electron-neutrino [νe]Appearance) experiment is a neutrino oscillation experiment designed to search for muon-neutrino to electron-neutrino oscillations and is the flagship project for the Fermi National Accelerator Laboratory (Fermilab) Intensity Frontier initiative. NOvA is a two-detector experiment with the smallest of the two a 200 ton Near Detector at Fermilab and the second a 15 kiloton Far Detector situated 503 miles, or 810 kilometers away in Ash River, Minnesota.

The experiment proceeds with an intense beam of muon neutrinos from the NuMI (Neutrinos at the Main Injector) beam at Fermilab. The neutrinos are then directed to travel along a trajectory such that they can be observed by the Near and Far Detectors. The neutrinos that reach Ash River, on the Canadian border, are compared to the neutrinos detected by the Near Detector. We know that neutrinos ”oscillate” or change type as they travel which is why NOvA is searching for the number of neutrinos that have oscillated from muon neutrinos to electron neutrinos, hence electron neutrino appearance: essentially measuring how many electron neutrinos have appeared compared to what is detected at the Near Detector.

So what is so great about knowing that, you may ask. Well, in neutrino physics our understanding of neutrino oscillations is governed by the PMNS matrix – a mathematical description of the probability of the different neutrinos changing from one type to another.

There are six different parameters that are derived from the PMNS matrix. Firstly, you have the three mixing angles theta-13, theta-23 and theta-12. These are essentially the proportions of each of the three known types of neutrinos that combine to form each type like Neapolitan ice cream. For example, electron neutrinos make up the largest share of the mixing angle for the electron neutrino. Second, you have a CP-violating phase which is the breaking of particle-antiparticle (charge conjugation – C) and mirror (parity – P) symmetries . Lastly, you have any two of three mass-squared differences which measure the difference between the masses of the neutrino types. The true nature of these parameters is beyond the scope of this introductory blog but, in short, NOvA aims to make the first measurement of the mixing angle theta-13 and push the search for electron neutrino appearance beyond the current scientific community’s limits by more than an order of magnitude. For a non-zero theta-13, it is possible for NOvA to observe CP violation in neutrinos, which will help us understand why the universe has a matter-antimatter asymmetry, and to establish the neutrino mass ordering or ”hierarchy” of neutrino types from lightest to heaviest.

Before NOvA can make any physics measurements it needs two fully assembled and calibrated detectors, which basically means that we understand what our detector is telling us!

The detectors are totally active, segmented and deploy the technology of liquid scintillator (mineral oil plus 5 percent pseudocumene) contained in highly reflective, rigid PVC extrusion cells to detect neutrino interactions.

The charged particles produced by a neutrino interaction inside the detector cause the liquid scintillator to produce light that is captured by optical fibers and carried to light-sensitive detectors at one end of each cell. The Far Detector will consist of about 400,000 1.6 inch by 2.4 inch by 52.5 feet, or 4 centimeter by 6 centimeter by 16 meter, cells that require approximately 3.2 gallons, or 12 million liters, of scintillator and 8,078 miles, or 13,000 kilometers, of .07-centimeter, or 0.7-millimeter, optical fiber. That is roughly equivalent to having enough fiber to feed through the Earth from Fermilab, near Chicago, to Sydney, Australia! The Near Detector will have the same design but will only be about 1/200th as massive.

The Far Detector is under construction and will begin taking data in early 2013. Due to the segmented nature of the detectors, data can be collected as soon as a section of readout has been installed.

Event display of the first NuMI neutrino event observed by NOvA's NDOS detector. The colored squares are a representation of time and location of the hits recorded by the detector cells. Click on image to see a larger version.

The Near Detector eventually will sit underground at Fermilab in the NuMI beamline but a portion of it has been built as a prototype on the surface. This prototype detector, named NDOS, began running at Fermilab in November and registered its first neutrinos from the NuMI beam in December 2010. The full installation of NDOS was completed in March 2011, at which point the detector entered an ongoing commissioning phase. NDOS is fundamental to understanding the fabrication and assembly procedures to be used in the construction of the Near and Far Detectors as well as inferring detector response and fine-tuning data acquisition systems and event reconstruction algorithms.

This is only the beginning for NOvA and future blog entries will aim to expand on some of the details brushed over here (in particular the underlying physics) as well as provide an insight into the daily activities of NOvA physicists. Who knows, maybe sometime soon NOvA will be putting neutrino physics firmly in the spotlight! For now I leave you with a picture of an event topology display showing the first NuMI beam neutrino event observed by NOvA’s NDOS.

NOvA really is a super experiment!!

— Gavin S. Davies


The number of Latin Americans working on the MINERvA experiment is unusual for a high-energy physics experiment. Among our Latin American collaborators, you’ll find professors, postdocs, graduate students and undergraduate students from countries such as Mexico, Brazil, Peru and Chile.

Cristian Pena in front of the MINERvA detector. Credit: Fermilab/Reidar Hahn

Being part of MINERvA offers many opportunities. For example, graduate students can complete their Ph.D. theses using MINERvA data, and many also have the opportunity to work at Fermilab, where they share ideas and knowledge with other students, postdocs, and professors from around the world. Working on MINERvA provides Latin American scientists the opportunity to perform research at the frontiers of experimental high-energy physics. The projects and studies on which we work are crucial for the experiment and for the neutrino physics program worldwide.

In my particular case, I am from Universidad Técnica Federico Santa María in Valparaíso, Chile. I recently had the opportunity and honor to be at Fermilab for five months working on two different projects. This experience was really exciting and challenging. I really learned a lot of physics and programming, understood more deeply how the experiment works, improved my English, and had the opportunity to meet and work directly with many experienced people in the field.

In terms of my personal life, it was a bit difficult to get accustomed to all the changes, such as language, food and geographical distances (my commute in Chile is just a five-minute walk). And once I got used to these, it started snowing. When I was first told about the weather at Fermilab, I said, “Oh come on. You must be exaggerating”, but clearly I was wrong. I really enjoyed meeting all the people in the collaboration and was interested to find out that Spanish from other Latin American countries is quite different – most people were not able to understand me when I used my spoken Chilean-Spanish. But now all those difficulties are just memories, thanks to the help Guiliano (my Chilean partner and roommate) and I received from the other Latin American folks at Fermilab.

MINERvA detector construction. Credit: Fermilab

When I returned to Chile a month ago, I realized that it would have been much more difficult to have this opportunity 10 years ago. I am really thankful for the efforts of Fermilab and the MINERvA experiment to make this possible, as well as the joint efforts that the Latin American Universities and their governments have made.

The fact that the number of Latin Americans in the MINERvA experiment is large is evidence of the science development which has started in our region. It also reinforces the importance of the efforts that institutions and governments are making to achieve the altruistic goal of developing science in their countries.

I would like to thank Jorge Morfin, who is working really hard to make collaborations like this possible; William Brooks, who is the leader of the experimental high-energy group of Universidad Técnica Federico Santa María and who keeps working to maintain and give the same opportunity to other Latin American students; and Deborah Harris and Kevin McFarland, the spokespersons of the experiment. I also want to thank the whole MINERvA collaboration who is doing a really nice job and pushing really hard to obtain the results the physics community is waiting for.

— Cristian Peña

Related information:
*Read about Cristian earning the Fulbright award

*From Peru to MINERvA

*Fermilab helps increase Mexican high-energy physics research

*Fermilab helps increase Brazilian high-energy physics research


Project X chopper challenge

Thursday, May 5th, 2011

This story appeared in Fermilab Today May 5.

Two Fermilab deflector prototypes being considered for the Project X chopper. In both cases, each rectangular copper plate sets up an electrostatic pulse that kicks the bunch farther and farther away from the beamline, chopping it out.

At the recent Project X collaboration meeting, attendees confronted the proposed accelerator’s wide-band chopper, a system that would allow scientists to cherry-pick particle bunches from beams to be routed to multiple experiments.

Though its design is a formidable challenge, researchers now believe it’s a workable problem.

“The meeting was the first time we were confident there’s a solution,” said Steve Holmes, Project X project manager. “There are options that look like they’ll work.”

The chopper would lend the proposed Project X a kind of maneuverability not seen in other accelerators.

Different particle physics experiments call for different bunch patterns. A chopper helps create the required pattern by using electric fields to selectively pick off bunches from a steady stream of particles. Bunches in the beam that are left alone accelerate toward an experiment’s target.

With only one target, the chopper’s job can be straightforward: leave every nth bunch alone.

With more than one target, as in the case of Project X, the chopper has to send a far more complicated bunch pattern down the particle conveyor belt. It must also work in concert with a splitter, or router, to direct the right bunches to the different experiments.

“A chopper combined with a splitter is a new twist on the idea,” said Sergei Nagaitsev of Fermilab’s Accelerator Division. This new twist will give scientists the freedom to put in any pattern they like while efficiently serving up bunches for multiple experiments.

“We wanted the project to be as flexible as possible,” Nagaitsev said. “So this chopper is one of the strongest selling points for Project X.”

Collaborators from Fermilab, Lawrence Berkeley National Laboratory and SLAC are pursuing various technical options for the system.

“Nobody’s done anything like this before, but it’s the key to making the whole thing work,” Holmes said.

— Leah Hesla


In experimental particle physics, the term “background” refers to events that can be easily confused for signal.  In my last post , I introduced the Mu2e experiment and pointed out that this experiment needs a huge amount of muons (1 million trillion, 1018,  or more) and hopes to be sensitive to even one muon decaying directly into an electron.  To achieve such a single-event sensitivity the sources of backgrounds must be minimized and/or understood extremely well.

So, what is so difficult about that?  Mu2e must have a striking experimental signature that is extremely hard to fake, right?  Not exactly!  The signal for the Mu2e experiment is just a single electron!  Hmmm… That sounds like it could be a problem because every ordinary atom making up the experiment, the building housing the experiment and planet Earth that it sits on is made up of electrons! 

The figure shows the muon-electron conversion energy distribution in light green and the energy distribution for electrons from one of the backgrounds in red. The signal energy is spread out due to the limited resolution of the Mu2e detector (not all of the signal events are measured to have the exact energy produced in the decay). The source of the background shown in red is from muons that decay in orbit (DIO) into an electron and neutrinos. This decay is allowed in the Standard Model. Because of the extra neutrinos produced in the final state, the electron carries less energy than the signal events where the muon decays only to electrons since no neutrinos are involved to take away some of the energy.

So, let’s state the problem again:  the Mu2e experiment wants to stop 1018 muons on a target nucleus, and then be sensitive to even one event in which the muon decays directly into an electron.  It isn’t easy! In fact, the experiment is carefully designed to minimize all potential sources of background events.  

Luckily, the electrons produced from the direct muon-to-electron conversion are special in that their energy will always have the same value 105 megaelectron volts, or 105 MeV.  This is an important point, because now, assuming that we can measure the energy of the electron well, our background has been reduced from “all electrons” to “electrons that have an energy close to 105 MeV” (see the figure at right).  In the case of the Mu2e experiment, this means that we can reduce our total background to less than one event expected over the total running time of the experiment!

Taking this into account, it is clear that the amount of background will depend on how well the experiment can measure the energy of the 105 MeV electron.  In other words, the sensitivity of the experiment depends critically on its ability to resolve the energy of an electron.

Future posts will include a series of “tricks” used by the experiment to control each of the major background sources.

— Craig Group


View this animation to see how Fermilab's Project X would be integrated into the laboratory's Accelerator Complex.

This story first appeared in Fermilab Today April 12.

According to the Nuclear Energy Institute, U.S. nuclear power plants have produced roughly 70,000 tons of radioactive waste over the last four decades. By 2025, scientists expect the amount of wa ste to be roughly 100,000 tons. The nuclear industry faces an ever-increasing waste problem, and Fermilab’s proposed Project X is developing the technologies that may contribute to a solution.

Last week at AccApp’11, an accelerator applications conference hosted by the American Nuclear Society and the International Atomic Energy Agency, Fermilab’s David Johnson explained how Project X could demonstrate the technologies required for accelerator-driven nuclear waste treatments.

“Fermilab has proposed the construction of a high-power proton linac for support of our high-energy physics program, and we are exploring the possibility to expand the application of the project to nuclear physics and energy applications,” Johnson said.

Project X is a proposed high-intensity proton accelerator complex that would support experiments in neutrino and rare processes physics. By using highly efficient superconducting radio frequency cavities, the technology of choice for next-generation accelerators, Project X would create a continuous-wave beam of protons. While the Project X mission is focused on particle physics, the beam that will be produced has uses that go beyond particle physics. The continuous-wave beam—as opposed to a pulsed one—makes it possible for Project X to also support experiments validating assumptions that underlie accelerator-driven waste treatment concepts. It would also demonstrate the associated accelerator and target technologies, Johnson said.

By hitting a lead-bismuth target with protons, a high-power, continuous-wave linac would create fast, or highly energetic neutrons. These fast neutrons would burn up the dangerous radioactive elements in nuclear waste, significantly reducing its half-life. In order to meet the requirements for treating nuclear waste on the industrial scale, the accelerator must operate reliably with virtually no downtime. Johnson explained that by advancing technologies and producing stable accelerator operations, Project X could serve as a proof of concept for the application.

“We would like to get the nuclear community excited about this potential facility,” Johnson said. “We welcome any and all participation.”

– Elizabeth Clements