Neutrinos are teaching us more and more about nucleon
structure, nuclear dynamics, and the Standard Model. Recent
results from neutrino oscillation experiments as well as
improved neutrino sources and detectors have rekindled
interest in neutrino scattering physics at relavitely low
energies (1 GeV). Neutrino cross section results in this
energy region from the MiniBooNE experiment will be
presented.
[D2.002] TWIST, A Precision Measurement of the Muon Decay Spectrum.
David Gill (TRIUMF)
TWIST, the TRIUMF Weak Interaction Symmetry Test, has taken data in the first simultaneous precision measurement of the muon decay parameters \rho, \delta, and P_\mu\xi. The ultimate goal of the experiment is to determine each of these parameters to a few parts in 10^4. With this precision TWIST will confront several proposed extensions to the Standard Model. For example, TWIST will be sensitive to right-handed W bosons with masses up to 800 GeV without needing to make assumptions about the form of the right-handed CKM matrix.
The TWIST spectrometer is made up of 44 drift chambers and 12 proportional chambers mounted in a 2 T solenoidal magnetic field. The chambers are divided symmetrically by a stopping target in the center of the spectrometer where highly polarized positive muons are stopped. The confining field results in a large angular and energy acceptance for the decay positrons that are tracked through the wire chambers. Decay rates of several kHz allow for the collection and analysis of very large data samples making TWIST a systematics-dominated experiment. Data are being analyzed at present that are expected to provide intermediate results for \rho and \delta to ~10^-3.
The TWIST experiment will be described, and the current
state of the data analysis will be discussed.
[D2.003] Neutron-Proton Correlations in N=Z Nuclei Above 56Ni
C.J. (Kim) Lister (Physics Division, Argonne National Laboratory, Argonne IL 60439)
The effects of short-range T=1 pairing correlations between
pairs of protons or neutrons are ubiquitous in intermediate
and heavy mass near-stable nuclei and influence almost all
aspects of their behavior. In principle, correlated
neutron-proton pairing fields should also play a role,
either with T=1 geometry, analogous to normal pairing, or
with deuteron-like T=0 geometry. In practice, these
neutron-proton pairing correlations are only expected to be
important where the wave function overlap is good,
particularly when the Fermi levels are equal, i.e. in N\simZ
nuclei. This requirement, combined with the desirability of
a high level density and numerous particles for stable
collective BCS pairing fields, limit the nuclei which are
good candidates for study of neutron-proton pairing to a
region between nickel and tin which lie very near the proton
dripline and have only recently become accessible for
detailed experimental study. In this talk I will review the
state of investigation into neutron-proton correlations and
their significance. I will briefly visit the very active
area of theoretical investigation into this topic, then
focus most of the talk on experimental signatures for
correlations and their measurement, past, present and
future. Information can be gleaned from binding energies,
backbending, electromagnetic transition rates and transfer
reactions. This research is supported by the U.S. department
of Energy under contract number W-31-109-ENG-38.
[D2.004] The emiT Experiment: A Search for Time Reversal Invarience Violation in Polarized Neutron Beta Decay
Hans Pieter Mumm (University of Washington)
The emiT experiment tests time reversal symmetry in the \beta-decay of polarized free neutrons by searching for the T-odd, P-even triple correlation (the product of the neutron spin and cross product of decay product momenta). The detection of this correlation above the small effect from final state interactions would be a direct indication of time reversal symmetry violation, independent of charge conjugation-parity. A Number of extensions to the Standard Model, such as lepto-quarks, can give rise to this correlation yet do not generate measurable electric dipole moments (EDMs). Consequently, the emiT experiment is complementary to EDM measurements, and, it is important to place the strongest possible limits in neutron decay. The emiT collaboration has published a result [1] from its first run. A second run of the emiT experiment has recently been completed. We will discuss the analysis and constraints on time reversal violation obtained from this greatly improved data set. This work was supported by the National Institute of Standards and Technology, the US DOE Office of Nuclear Physics, and the NSF Division of Physics.
[1] Phys. Rev. C. 62, 055501, (2000).