Beam Me Up
With first beam and a topped-off detector, MiniBooNE gets ready to go

by Mike Perricone

In science, once is not enough. One result isn’t proof. An experiment must be repeatable: someone else must be able to achieve the same result.

The “mini” in MiniBooNE is deceptive. There’s nothing small about the stakes for this short-baseline neutrino oscillation experiment at Fermilab, now mere weeks away from taking its first data. Marking the completion of its detector with a final cup of ultra-pure mineral oil—the last of 250,000 gallons of this translucent liquid—MiniBooNE is about to start the quest to repeat the landmark result of the Liquid Scintillating Neutrino Detector at Los Alamos National Laboratory.

LSND was the first accelerator-based experiment to produce evidence of neutrino oscillations. Confirming that result—nailing down acceleratorproduced neutrinos that change from one flavor to another—would also indicate the existence of an additional flavor or type of neutrino, beyond the three now known. A fourth neutrino would represent another crack in the Standard Model of particle physics, and a milestone and challenge for particle physicists.

“It’s crucial to verify that result with MiniBooNE,” said experiment co-spokesperson Bill Louis, a member of LSND at Los Alamos during its run from 1993 to 1998. “My biggest hopes for MiniBooNE would be that it runs well, takes lots of data, and provides a definitive test of the LSND evidence for neutrino oscillations.”

The MiniBooNE beam came to life in late April, with a stream of particles originating in the Booster accelerator and traveling about three-fourths of the way down the 680-foot beam pipe to a temporary target. The attempt began late on April 26, with first beam recorded at 4 a.m. on April 29. Beam was halted on May 6 to begin work on what’s called “hot handling” of the horn, the device that will be used to focus and direct the intense particle beam onto the permanent target for neutrino production.

“Intense” might actually be an understatement in describing the beam.

“In one year,” said Craig Moore of the lab’s External Beams department, “we will transport more beam at MiniBooNE than we did in all 17 years of the Fixed-Target Program at Fermilab. It’s a very intense beam.”

To control the beam, External Beams has built two concepts into the MiniBooNE operation. The first is “auto-tune,” an automated tuning program to keep the beam properly positioned inside the beam pipe. The second is “e-berm,” an electronic monitoring system intended to help minimize beam loss. Earthen berms are built over accelerators to absorb particles from beam loss; “e-berm” aims at limiting the need for an earthen berm by limiting losses. The concept has been used before at the lab, but this system is an entirely new one developed by Beams Division specialist John Anderson. The system uses toroid magnets for measurements, one at the beginning of the beam line and one at the end. If the measurements are the same at both ends, the beam is intact; if not, beam losses are immediately tracked down and corrected.

Getting the beamline in shape was not without its adventures.

“For some reason, the magnets we installed still had acid inside the lines from their initial cleaning,” said co-spokesperson Janet Conrad of Columbia University. “The Low Conductivity Water (LCW) group worked day and night to flush them so that we could bring up the beamline. Members of MiniBooNE pitched in doing ‘water shift,’ too. It was a good collaboration between us and the lab—the LCW group are really good guys. We really owe them a lot of thanks. They probably saved us three weeks by working so hard.”

Through mid-June, MiniBooNE and External Beams will study and tune the beam, de-bug the instrumentation, and develop the process of moving the focusing horn in and out of the target area. Then the temporary target will be moved out, and beam will be sent all the way down the line to the horn and permanent target to produce the experiment’s first accelerator-generated neutrinos. In its operational stage, MiniBooNE will produce neutrinos by drawing on the 8 GeV beam from the revamped Booster accelerator, the third component in Fermilab’s accelerator chain after the Cockcroft- Walton pre-accelerator and the linear accelerator (LINAC).

With the detector completed, MiniBooNE has already begun tracking cosmic ray events. But first, collaborators took a break to celebrate.

“What did we feel when we topped off the detector? Tremendously happy, excited, and relieved,” said Conrad. “Jennifer Raaf [of the University of Cincinnati] called me the night the detector was finally full. It must have been about 9 p.m. She was ecstatic to be finished. The oil fill work was grueling, messy—and in February, it was cold. She and the other ‘oil sheiks’ did a great job.”

The Cincinnati group had been responsible for testing the oil and filling the 12-meter diameter sphere (about 40 feet) with its 1,550 photomultiplier tubes. It was the culmination of months of effort, pumping oil from tanker trucks that in turn had been filled from railroad tanker cars delivering the purer-than-food-grade oil to the Fermilab railhead. At the celebration on May 3, Deputy Director Ken Stanfield poured the honorary final cupful of oil into the plumbing through a bright red funnel.

“The top-off happened at the same time as our first beam into the MiniBooNE line, so we had lots of parties all at once,” Conrad said. “We started on Thursday with the Beams Division champagne toast. That was very classy and a lot of fun. The next day we had the detector top-off party at the detector hall. Jesse Guerra [of the Mechanical Department] brought balloons that we tied to the muon tracker. And then in the late afternoon, we had the Wilson Hall party. It was a good two days for MiniBooNE.”

There were toasts for jobs well done all along the way: Princeton University for mounting the photomultiplier tubes; Louisiana State University on instrument calibration; the University of Cincinnati on the oil procurement and transfer; Indiana University on the data acquisition system (DAQ); Columbia University, Embry-Riddle Aeronautical University and Bucknell University on the PMT testing; the University of Alabama, University of Michigan, University of Colorado, and University of California-Riverside on software, and Fermilab on the tank construction.

Now MiniBooNE, initiated in 1997, is back to focusing on the future, anticipating final beam tests and then the first neutrino results later in 2002. Those results could lead to an expanded effort, the full-fledged Booster Neutrino Experiment (BooNE) with a longer beam line.

“We’ll run MiniBooNE for at least two or three years,” said Louis. “If indeed we verify the LSND signal, then we’ll want to build a second detector at a different distance. That will be the full BooNE experiment, with which we can make precision measurements of the neutrino oscillation parameters.

The world is watching to see what MiniBooNE will find.

Los Alamos offers a critical link to MiniBooNE— and to Fermilab

The evidence for oscillations from the Liquid Scintillating Neutrino Detector at Los Alamos National Laboratory was the starting point for the science of MiniBooNE.

“The concept of MiniBooNE was born out of our connections with high energy physicists after LSND found such an exciting effect,” said Bill Press, Deputy Laboratory Director for Science and Technology at Los Alamos. “It was clearly necessary to check the LSND results. By working at higher energies at Fermilab, the signal for new physics should be much stronger. This natural evolution will—I hope—lead to the discovery of new physics beyond that discovered by SuperKamiokande [in Japan] and the Sudbury Neutrino Observatory [in Canada].”

Los Alamos Physics Division Leader Susan Seestrom cited LSND as an important component of the lab’s LAMP nuclear physics program, and called the potential for MiniBooNE to confirm the LSND results very exciting.

“I am intrigued by the possibility that a combination of neutrino and anti-neutrino running with MiniBooNE could point us toward CPT violation as a mechanism for reconciling the solar neutrino and accelerator neutrino data,” Seestrom said.

Los Alamos has offered crucial support throughout the construction of the neutrino experiment at Fermilab.

Many of the MiniBooNE detector’s photomultiplier tubes were originally used at LSND, as were some of the electronic components. The LANL group at Fermilab (Vern Sandberg, Geoff Mills, Richard Van de Water, Richard Schirato, Jan Boissevain, Ben Sapp, Camilo Espinoza, Neil Thompson, Gerry Garvey, Hywel White, and experiment co-spokesperson Bill Louis) made critical contributions to the phototubes, electronics, DAQ, oil plumbing and detector design.

In addition to MiniBooNE, Los Alamos has longstanding ties to the Drell-Yan experiments at Fermilab, studying quark effects in nuclei, and is part of the upcoming E906 experiment, designed to measure anti-up / anti-down quark distributions. Recently, Fermilab transferred 400 kg of excess beryllium (worth about $80,000) to Los Alamos to provide a 20 percent increase in the performance of a new Ultra-Cold Neutron source under construction at the laboratory.

The Advanced Hadron Facility, a central capability in LANL’s future plans for nuclear stockpile stewardship, draws on the expertise in accelerator technology from both Los Alamos and Fermilab. The labs are working closely on magnet design for the AHF. Recently, Los Alamos also became a participant in the Sloan Digital Sky Survey, with the telescope located in nearby Apache Point, New Mexico.

“Cross-disciplinary research makes possible breakthroughs in our understanding of Nature that can’t be achieved in other ways,” Press said. “The connection between Los Alamos and Fermilab through MiniBooNE and the Sloan Digital Survey are good examples of both labs trying to foster the connections between different disciplines. After all, everyone is interested in studying physics at the frontiers—we just use different tools to probe that physics from various angles. This type of synergy between nuclear and high energy physics, and between the laboratories, benefits all of us.”

Seestrom said that, as a national security laboratory, Los Alamos placed a high priority on maintaining strong connections to areas of leading edge basic research.

“The distinctions between nuclear and high-energy physics are becoming increasingly blurred,” she said. “This often becomes an obstacle in funding the best scientific work. It is gratifying when an experiment straddling this line can work as well as MiniBooNE has.”