Experimental Particle Physics. High energy fission (1953-56), experiments with antiprotons (1955-65), pion-nucleon and nucleon-nucleon scattering with polarized targets (1961-1980), π-N phase shift analyses (1964-70), determination of the spin and intrinsic parity of hyperons using polarized targets (1964-69), search for time-reversal symmetry violations in e-p scattering with a polarized target (1968-71), development of multiwire proportional chambers (1968-70), study of the interactions of high-energy nuclei (1971-80), search for weak right-handed currents in muon decay (1980-85), test of the Standard Model of electroweak interactions using polarized electrons to produce Z°-bosons in the SLD detector at the Stanford Linear Collider (SLC) (1986-1999), gaseous detector development (1997-present), search for neutrino oscillations using the KamLAND detector in Japan (1999-present).
I am presently involved in an experiment to measure neutrino oscillations using the KamLAND detector in the Kamioka mine in Japan. This project is a joint effort of physicists from Japan and the United. Here in Berkeley Professors Stuart Freedman (co-spokesman for the US KamLAND group), Kam-Bui Luk, Hitoshi Murayama as well as colleagues in the LBNL Physics and Nuclear Science Divisions are members of the team that is carrying out this work. Several post-docs and students are also playing crucial roles in this project.
The object of the experiment is to determine whether or not neutrinos oscillate from one species to another in the time interval between when they are emitted and detected. The results bear directly on the fundamental question of whether neutrinos have mass, for only massive neutrinos can oscillate. In the first phase of this experiment we will detect neutrinos originating in a large group of reactors which provide electrical power in Japan. These reactors are all located about 200-300 km from our detector, and calculations indicate that in the absence of oscillations we should detect about two neutrino interactions per day in the fiducial volume of the detector.
The detector itself is a large sphere, 20 m in diameter, filled with a liquid that scintillates when a neutrino produces an interaction. The emitted light is detected by 2000 photomultiplier tubes deployed along the walls enclosing the scintillator volume. Measurement of the timings and amplitudes of the phototube pulses allows reconstruction of the location and energy of each interacting neutrino. This information will then be used to extract the oscillation signal which depends on the masses and energies of the neutrinos, and the distances to the reactor sources. The signal rate will be modulated by the variation in reactor power as a function of time. In a later phase we plan to measure oscillations of solar neutrinos. Together these measurements are expected to be crucial ingredients in the determination of neutrino mass-squared differences and in choosing between competing theoretical models.
The Berkeley group is responsible for the electronics used to read out and process the signals form the 2000 phototubes, and for the calibration of the detector. The electronics has been designed and built here, and is now (Oct. 2001) being tested and installed. It is a state-of-the-art automatic-wave-form-digitization system (AWFD) which will give detailed pulse shape information about the detected signals, and thereby provide us with excellent rejection of unwanted backgrounds. The calibration system, which involves the deployment of radioactive and light sources in the detector, will be crucially important in translating the observed pulses into quantities of physical significance, and in monitoring the stability of the detector response. Detector commissioning will commence in October 2001, and data acquisition is expected to start in early 2002.
In addition to my involvement with KamLAND I am spending some of my time working on polarization-related topics, both experimental and theoretical, for a high-energy linear electron-positron colliders.
“Proposal for US participation in KamLAND,” (unpublished) available from H. Steiner, LBNL Berkeley, can be found on the web at http://kamland.lbl.gov/KamLAND.US.Proposal.pdf
Gudrid Moortgat-Pick and Herbert M. Steiner, “Physics opportunities with polarized e- and e+ beams at TESLA, Eur. Phys. J. Direct C6, 1-27 (2001).
SLD Collaboration (K. Abe, et al.), “A high precision measurement of the left-right Z boson cross-section asymmetry.” Phys. Rev. Lett. 84, 5945 (2000).