During the last two days, I attended the meeting of the High Energy Physics Advisory Panel in Washington, DC. This was the first HEPAP meeting after the Long-Baseline Neutrino Experiment was reconfigured to comply with DOE’s financial guidelines. The discovery by the Daya Bay reactor experiment of a large theta-13 parameter in neutrino mixing, just a few days before the previous HEPAP meeting in March, has opened the gate for important future advances in neutrino physics and removed the major risk for LBNE.
The afternoon of the first day was devoted entirely to the topic of LBNE. Stephen Parke began the discussion with a talk on the physics of neutrinos, and Deputy Director Young-Kee Kim followed with a comprehensive report on the effort she led to reconfigure LBNE into a phased program. She was followed by Milind Diwan, co-spokesperson for LBNE, who described the enormous progress that the collaboration has achieved in the last few years. The collaboration now comprises some 59 institutions and more than 340 collaborators, including both national and international participants.
The members of HEPAP asked many questions and made generally supportive comments on the reconfigured experiment. The proposed configuration for the first phase of LBNE that fits DOE financial guidelines includes a 10-kiloton liquid-argon detector on the surface at Homestake. Such a detector would be adequate for neutrino physics using the Fermilab beam, but would miss potentially important physics in two areas: the study of neutrinos from supernovae collapses and proton decay. Both of these studies require a detector underground at sufficient depth to reduce backgrounds. The second phase of the experiment would place a detector underground at Homestake. Many of the HEPAP members conveyed the desirability to place the far detector underground from the beginning. They urged that the laboratory, the collaboration and the DOE work together to gather the additional resources that would make it possible to place the detector underground in the first phase. LBNE’s CD-1 review is planned for the fall, and we will seek the additional resources between CD-1 and CD-2.
The afternoon session concluded with remarks by Bill Brinkman, director of the Office of Science, who stated that he would like to see the experiment done and would try to move it forward. He also warned us that we should be conscious of the difficulties of constructing a large project like LBNE in view of the priorities set by the administration, which are primarily driven by climate change.
This was also the first meeting of HEPAP after the discovery of the Higgs-like particle at the LHC. We heard talks by scientists from ATLAS and CMS, who provided us with the latest available results, which are enormously impressive. Beyond the discovery of the Higgs-like particle, there is tremendous excitement in understanding the various decay properties and measuring the spin of the observed particle.
Rocky Kolb presented an important report from a committee convened to investigate the opportunities for DOE to contribute to the study of dark energy. One opportunity it identified is a spectroscopic probe that would significantly improve the study of dark energy and that could be accommodated in the time between the start of the Dark Energy Survey, which is close to taking data, and the completion of the Large Synoptic Survey Telescope in the early 2020s. In the U.S. there are at least two projects contending to build a spectroscopic probe. DOE will write a mission need without selecting an experiment at this time, and will proceed to analyze the possibilities and organizational arrangements.
The meeting presentations are available on the HEPAP website.