Kamran Vaziri and Don Cossairt
Last time we reported the latest Tevatron luminosity record was 228.1E30/cm2/s in the third quarter of 2006. However, the Tevatron did not stop there: the intense effort to improve this machine's performance continues. The latest average luminosity record is 292.4E30/cm2/s. So far the 2007 integrated luminosity is 680.7 inverse picobarns. Both these quantities are important for physics' discovery potential of the elusive Higgs boson, the subatomic particle that, according to physics theory, is linked to an invisible field filtering through the universe. As particles move, the field clings to them, making them heavy and creating mass. It is possible at Tevatron energies, by collecting several thousand inverse picobarns of collision data, we may be able to discover or narrow down the whereabouts of this important particle. CERN's Large Hadron Collider will also be searching for the Higgs.
Another neutrino experiment at Fermilab is the Booster Neutrino Experiment or MiniBooNe. MiniBooNe uses the muon neutrino produced from the decay of particles produced in the interaction of 8 GeV protons with a beryllium target. The decay happens in the 50 meter decay pipe. All particles except the neutrinos are absorbed in the absorber located at the end of the decay pipe and the soil intervening between the absorber and the detector. The experiment has another absorber that is located in the middle of the decay pipe, which will be used to study the effects of a shorter decay pipe (25 m). This absorber is made of iron plates that are normally kept out of the decay pipe, hanging from chains. Last December it was found out that some of these chains were broken and two of the absorber plates had fallen partially in the beam. The experiment had taken about 8.5E20 protons over the last four years. Analysis of the broken chain links showed that hydrogen embrittlement has been the cause of this failure; i.e., hydrogen production in the metal due to a small leakage of radiation has been responsible for the metal fatigue. The chains will be replaced with 304 stainless steel that is also resistant to the other radiolytically produced corrosive compounds in air as well.