Kamran Vaziri and Don Cossairt
The start of the Fermi National Accelerator Lab (Fermilab) accelerator's summer shutdown is now officially August 6. The duration of the shutdown is at least 8 weeks and may be longer; Accelerator Operations is now gathering work lists so they can organize schedules for the shutdown work. One of the main drivers for the duration of the shutdown is the installation of collimators and dampers in the Main Injector, which will make slip-stacking to NuMI part of normal operations. So far there are 200 jobs proposed for the shutdown. It is expected that at least another 100 jobs will be added to the queue before August 6. The Accelerator Safety Group is busy reviewing the proposed jobs, joggling schedules to minimize dose to workers, and constructing plans to maintain doses as low as reasonably achievable (ALARA).
The Main Injector continues with slip-stacking studies, and set a new record on June 25 for the amount of beam in the machine, at 4.6E13, with very good transport efficiency. This intensity is what the NuMI experiment can expect after the shutdown, when the accelerators come back up in October. The NuMI experiment is currently working to have a spare target prepared for receiving this higher intensity beam. In addition, during the last quarter NuMI passed an accumulated 3E20 protons on target since beam data-taking started.
The big news at Fermilab was the announcement of the first results of the MiniBooNE neutrino experiment. In the 1990s the Los Alamos Liquid Scintillator Neutrino Detector (LSND) experiment announced the observation of neutrino oscillation. This is a process in which a neutrino from one lepton changes flavor to a different type of lepton neutrino. The LSND observations also suggested the presence of a fourth, or "sterile" type of neutrino, with properties different from the three standard neutrinos. The existence of sterile neutrinos would throw serious doubt on the current structure of particle physics, known as the Standard Model of particles and forces. The MiniBooNE results resolve questions raised by observations of the LSND experiment in the 1990s that appeared to contradict findings of other neutrino experiments worldwide. MiniBooNE researchers showed conclusively that the LSND results could not be due to simple neutrino oscillation.