117 research outputs found

### Cross Section Uncertainties in the Gallium Neutrino Source Experiments

The 51Cr neutrino source experiments play a unique role in testing overall
operations of the GALLEX and SAGE solar neutrino experiments. Recently Hata and
Haxton argued that the excited-state contribution to the 71Ga cross section for
51Cr neutrino absorption might not be known reliably, despite forward-angle
(p,n) measurements. A large-basis shell model calculation reported here
indicates that the unusual situation they envisioned - destructive interference
between weak spin and strong spin-tensor amplitudes - does occur for the
transition to the first excited state in 71Ge. The calculation provides a
counterexample to procedures previously used to determine the 51Cr cross
section: the predicted (p,n) cross section for this state agrees with
experiment, while the BGT value is well outside the accepted
3-standard-deviation limit. The results argue for a shift in the interpretation
of the source experiments: they become more crucial as measurements of the 71Ga
detector response to 7Be solar neutrinos, and less definitive as wholly
independent tests of 71Ge recovery and counting efficiencies.Comment: 14 pages, 2 figures, Revte

### Uncertainties in the Solar Neutrino Flux

I discuss three issues relevant to solar neutrino flux measurements: cross
section uncertainties in pp chain reactions, uncertainties in the GALLEX/SAGE
response to 7Be and 51Cr neutrinos, and the implications of helioseismology for
nonstandard suns with mixed cores. A few comments are also offered on electron
neutrino to tauon neutrino oscillations, cosmologically interesting neutrino
masses, and recent proposals for supernova neutrino observatories.Comment: Neutrino 98 Talk; 8 pages, 5 figure

### Solar Models With Accretion. I. Application To The Solar Abundance Problem

We generate new standard solar models using newly analyzed nuclear fusion cross sections and present results for helioseismic quantities and solar neutrino fluxes. The status of the solar abundance problem is discussed. We investigate whether nonstandard solar models with accretion from the protoplanetary disk might alleviate this problem. We examine a broad range of models, analyzing metal-enriched and metal-depleted accretion and three scenarios for the timing of accretion. Only partial solutions are found. For metal-rich accreted material (Z ac gsim 0.018) there exist combinations of accreted mass and metallicity that bring the depth of the convective zone into agreement with the helioseismic value. For the surface helium abundance, the helioseismic value is reproduced if metal-poor or metal-free accretion is assumed (Z ac lsim 0.09). In both cases a few percent of the solar mass must be accreted. Precise values depend on when accretion takes place. We do not find a simultaneous solution to both problems but speculate that changing the hydrogen-to-helium mass ratio in the accreted material may lead to more satisfactory solutions. We also show that, with current data, solar neutrinos are already a very competitive source of information about the solar core and can help constraining possible accretion histories. Even without helioseismic constraints, solar neutrinos rule out the possibility that more than 0.02 M â from the protoplanetary disk were accreted after the Sun settled on the main sequence. Finally, we discuss how measurements of neutrinos from the CN cycle could shed light on the interaction between the early Sun and its protoplanetary disk

### Fundamental Symmetries and Conservation Laws

I discuss recent progress in low-energy tests of symmetries and conservation
laws, including parity nonconservation in atoms and nuclei, electric dipole
moment tests of time-reversal invariance, beta-decay correlation studies, and
decays violating separate (family) and total lepton number.Comment: 11 pages, 5 figures; plenary talk presented at PANIC0

### Exact Solutions for Matter-Enhanced Neutrino Oscillations

The analogy between supersymmetric quantum mechanics and matter-enhanced
neutrino oscillations is exploited to obtain exact solutions for a class of
electron density profiles. This integrability condition is analogous to the
shape-invariance in supersymmetric quantum mechanics. This method seems to be
the most direct way to obtain the exact survival probabilities for a number of
density profiles of interest, such as linear and exponential density profiles.
The resulting neutrino amplitudes can also be utilized as comparison amplitudes
for the uniform semiclassical treatment of neutrino propagation in arbitrary
electron density profiles.Comment: Submitted to Physical Review D. Latex file, 8 pages. This paper is
also available at http://nucth.physics.wisc.edu/preprints

### Nuclear Spin-Isospin Correlations, Parity Violation, and the $f_\pi$ Problem

The strong interaction effects of isospin- and spin-dependent nucleon-nucleon
correlations observed in many-body calculations are interpreted in terms of a
one-pion exchange mechanism. Including such effects in computations of nuclear
parity violating effects leads to enhancements of about 10%. A larger effect
arises from the one-boson exchange nature of the parity non-conserving nucleon-
nucleon interaction, which depends on both weak and strong meson-nucleon
coupling constants. Using values of the latter that are constrained by
nucleon-nucleon phase shifts leads to enhancements of parity violation by
factors close to two. Thus much of previously noticed discrepancies between
weak coupling constants extracted from different experiments can be removed.Comment: 8 pages 2 figures there should have been two figures in v

### The Effective Field Theory of Dark Matter Direct Detection

We extend and explore the general non-relativistic effective theory of dark
matter (DM) direct detection. We describe the basic non-relativistic building
blocks of operators and discuss their symmetry properties, writing down all
Galilean-invariant operators up to quadratic order in momentum transfer arising
from exchange of particles of spin 1 or less. Any DM particle theory can be
translated into the coefficients of an effective operator and any effective
operator can be simply related to most general description of the nuclear
response. We find several operators which lead to novel nuclear responses.
These responses differ significantly from the standard minimal WIMP cases in
their relative coupling strengths to various elements, changing how the results
from different experiments should be compared against each other. Response
functions are evaluated for common DM targets - F, Na, Ge, I, and Xe - using
standard shell model techniques. We point out that each of the nuclear
responses is familiar from past studies of semi-leptonic electroweak
interactions, and thus potentially testable in weak interaction studies. We
provide tables of the full set of required matrix elements at finite momentum
transfer for a range of common elements, making a careful and fully
model-independent analysis possible. Finally, we discuss embedding
non-relativistic effective theory operators into UV models of dark matter.Comment: 32+23 pages, 5 figures; v2: some typos corrected and definitions
clarified; v3: some factors of 4pi correcte

### Nuclear Physics without High-Momentum Potentials: Constructing the Nuclear Effective Interaction Directly from Scattering Observables

The traditional approach to nuclear physics encodes phase shift information
in a nucleon-nucleon (NN) potential, producing a nucleon-level interaction that
captures the sub-GeV consequences of QCD. A further reduction to the nuclear
scale is needed to produce an effective interaction for soft Hilbert spaces,
such as those employed in the shell model. Here we describe an alternative
construction of this effective interaction, from QCD directly to the nuclear
scale, that is direct and precise. This eliminates the need for constructing
and renormalizing the high-momentum NN potential. Instead, continuum phase
shifts and mixing angles are used directly at the nuclear scale. The method
exploits the analytic continuity in energy of HOBET (Harmonic-Oscillator-Based
Effective Theory) to connect bound states to continuum solutions at specific
energies. The procedure is systematic, cutoff independent, and convergent,
yielding keV accuracy at NNLO or N$^3$LO, depending on the channel. Lepage
plots are provided.Comment: 9 page

### Combined effect of coherent Z exchange and the hyperfine interaction in atomic PNC

The nuclear spin-dependent parity nonconserving (PNC) interaction arising
from a combination of the hyperfine interaction and the coherent,
spin-independent, PNC interaction from Z exchange is evaluated using many-body
perturbation theory. For the 6s-7s transition in 133Cs, we obtain a result that
is about 40% smaller than that found previously by Bouchiat and Piketty [Phys.
Lett. B 269, 195 (1991)]. Applying this result to 133Cs, leads to an increase
in the experimental value of nuclear anapole moment and exacerbates differences
between constraints on PNC meson coupling constants obtained from the Cs
anapole moment and those obtained from other nuclear parity violating
experiments. Nuclear spin-dependent PNC dipole matrix elements, including
contributions from the combined weak-hyperfine interaction, are also given for
the 7s-8s transition in 211Fr and for transitions between ground-state
hyperfine levels in K, Rb, Cs, Ba+, Au, Tl, Fr, and Ra+.Comment: Revtex4 preprint 19 pages 4 table

### Solar Neutrinos: Status and Prospects

We describe the current status of solar neutrino measurements and of the
theory -- both neutrino physics and solar astrophysics -- employed in
interpreting measurements. Important recent developments include
Super-Kamiokande's determination of the neutrino-electron elastic scattering
rate for 8B neutrinos to 3%; the latest SNO global analysis in which the
inclusion of low-energy data from SNO I and II significantly narrowed the range
of allowed values for the neutrino mixing angle theta12; Borexino results for
both the 7Be and pep neutrino fluxes, the first direct measurements
constraining the rate of ppI and ppII burning in the Sun; global reanalyses of
solar neutrino data that take into account new reactor results on theta13; a
new decadal evaluation of the nuclear physics of the pp chain and CNO cycle
defining best values and uncertainties in the nuclear microphysics input to
solar models; recognition of an emerging discrepancy between two tests of solar
metallicity, helioseismological mappings of the sound speed in the solar
interior, and analyses of the metal photoabsorption lines based on our best
current description of the Sun's photosphere; a new round of standard solar
model calculations optimized to agree either with helioseismology or with the
new photospheric analysis; and, motivated by the solar abundance problem, the
development of nonstandard, accreting solar models, in order to investigate
possible consequences of the metal segregation that occurred in the proto-solar
disk. We review this progress and describe how new experiments such as SNO+
could help us further exploit neutrinos as a unique probe of stellar interiors.Comment: 82 pages, 11 figure

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