Neutrino Oscillations in the Precision Era

With the discovery of a modest size for the mixing angle $theta_{13} sim 9^circ$ by the Daya Bay collaboration at $>$5 sigma (cite{dayabay}) the science of neutrino oscillations has shifted to explicit demonstration of CP violation and precision determination of the CP phase in the 3-flavor framework. Any additional contributions from new physics to the oscillation channel $ u_mu to u_e$ could be uncovered by multiple constraints in the ($theta_{13}, delta_{CP}$) parameter space. In long-baseline experiments such constraints will require examination of the oscillation strength at higher $L/E$ where the effects of CP violation will be large. For the fixed baseline of 1300 km for the Long-Baseline Neutrino Experiment (LBNE, Fermilab to Homestake), it will be important to examine oscillations at low energies ($<1.5$ GeV) with good statistics, low backgrounds, and excellent energy resolution. The accelerator upgrades in the Project-X era have the potential to offer the beams of the needed intensity and quality for this advanced science program. In this paper we examine the event rates for high intensity, low energy running of Project-X and the Fermilab Main Injector complex, and the precision in the ($theta_{13}, delta_{CP}$) space. In this paper we have examined the baseline distance of 1300 km in detail, however we point out that much longer distances such as 2500 km should also be exmained with a beam from FNAL in light of the new understanding of the neutrino mixing.

Report on the Depth Requirements for a Massive Detector at Homestake

This report provides the technical justification for locating a large detector underground in a US based Deep Underground Science and Engineering Laboratory. A large detector with a fiducial mass in the mega-ton scale will most likely be a multipurpose facility. The main physics justification for such a device is detection of accelerator generated neutrinos, nucleon decay, and natural sources of neutrinos such as solar, atmospheric and supernova neutrinos. In addition to the physics justification there are practical issues regarding the existing infrastructure at Homestake, and the stress characteristics of the Homestake rock formations. The depth requirements associated with the various physics processes are reported for water Cherenkov and liquid argon detector technologies. While some of these physics processes can be adequately studied at shallower depths, none of them require a depth greater than 4300 mwe which corresponds to the 4850 ft level at Homestake. It is very important to note that the scale of the planned detector is such that even for accelerator neutrino detection (which allows one to use the accelerator duty factor to eliminate cosmics) a minimum depth is needed to reduce risk of contamination from cosmic rays. After consideration of the science and the practical issues regarding the Homestake site, we strongly recommend that the geotechnical studies be commenced at the 4850ft level in a timely manner.

Recent Results from the MINOS experiment

MINOS is an accelerator neutrino oscillation experiment at Fermilab. An intense high energy neutrino beam is produced at Fermilab and sent to a near detector on the Fermilab site and also to a 5 kTon far detector 735 km away in the Soudan mine in northern Minnesota. The experiment has now had several years of running with millions of events in the near detector and hundreds of events recorded in the far detector. I will report on the recent results from this experiment which include precise measurement of $|Delta m^2_{32}|$, ~analysis of neutral current data to limit the component of sterile neutrinos, and the search for $ u_mu to u_e$ conversion. The focus will be on the analysis of data for $ u_mu to u_e$ conversion. Using data from an exposure of $3.14times 10^{20}$ protons on target, we have selected electron type events in both the near and the far detector. The near detector is used to measure the background which is extrapolated to the far detector. We have found 35 events in the signal region with a background expectation of $27pm 5(stat)pm 2(syst)$. Using this observation we set a 90% C.L. limit of $sin^2 2 theta_{13} < 0.29$ for $delta_{cp} = 0$ and normal mass hierarchy. Further analysis is under way to reduce backgrounds and improve sensitivity.

Report of the US long baseline neutrino experiment study

This report provides the results of an extensive and important study of the potential for a U.S. scientific program that will extend our knowledge of neutrino oscillations well beyond what can be anticipated from ongoing and planned experiments worldwide. The program examined here has the potential to provide the U.S. particle physics community with world leading experimental capability in this intensely interesting and active field of fundamental research. Furthermore, this capability could be unique compared to anywhere else in the world because of the available beam intensity and baseline distances. The present study was initially commissioned in April 2006 by top research officers of Brookhaven National Laboratory and Fermi National Accelerator Laboratory and, as the study evolved, it also provided responses to questions formulated and addressed to the study group by the Neutrino Scientific Advisory Committee (NuSAG) of the U.S. DOE and NSF. The participants in the study, its Charge and history, plus the study results and conclusions are provided in this report and its appendices. A summary of the conclusions is provided in the Executive Summary.