Papers by richard paolino
Nuclear Spin-Dependent Parity Nonconservation in Diatomic Molecules
Nuclear spin-dependent parity nonconservation (NSD-PNC) effects arise from couplings of the Z0 bo... more Nuclear spin-dependent parity nonconservation (NSD-PNC) effects arise from couplings of the Z0 boson (parameterized by the electroweak coupling constants C2P,N) and from the interaction of electrons with the nuclear anapole moment, a parity-odd magnetic moment. The latter scales with the nucleon number A of the nucleus as A^2/3, while the Z0 coupling is independent of A; the former will be the dominant source of NSD-PNC in nuclei with A>20. The most precise result on NSD-PNC to date comes from a measurement of the hyperfine dependence of atomic PNC in ^133Cs, but this effect can be dramatically enhanced in diatomic molecules. We outline an experimental program to take advantage of this enhancement with over ten suitable molecules with which we can extract the relative contributions of the anapole moment and the electroweak Z0 couplings. This will increase the available data on nuclear anapole moments, as well as reduce the uncertainties in current measurements of C2N and C2P. We report on improvements in the design of our pulsed molecular beam experiment and the current status of our efforts.
Molecular Probe for Electroweak Physics
Parity nonconservation (PNC) arises in atoms and molecules due to neutral current electroweak (EW... more Parity nonconservation (PNC) arises in atoms and molecules due to neutral current electroweak (EW) interactions. Our experiment is sensitive to nuclear spin-dependent (NSD)-PNC including electron-vector times nucleon-axial (VeAn) interaction due to Z^0exchange. VeAn terms are suppressed in the Standard Model (SM) making NSD radiative corrections from weak interactions within the nucleus, known as nuclear anapole moments, significant to the overall NSD-PNC signal. We report on our experiment using rotational hyperfine (HF) levels of well understood diatomic molecules to study NSD-PNC. Initially, one state, B, of a pair of opposite parity HF ground states, A and B, of the molecule is depleted. In the interaction region (IR), A and B are Zeeman shifted to near degeneracy in order to amplify perturbative state mixing caused by NSD-PNC interactions. Interference with Stark-induced mixing is revealed using laser-induced fluorescence from B emerging from the IR. This technique is applicable to a wide class of molecules and the variety of nuclei within so that VeAn and anapole contributions to NSD-PNC can be deciphered. This will yield new anapole results and constrain VeAn coupling constants to up and down quarks which are at present poorly characterized SM parameters.
Extensions to the Standard Model (SM) typically include new heavy particles and new mechanisms fo... more Extensions to the Standard Model (SM) typically include new heavy particles and new mechanisms for CP violation. These underlying phenomena can give rise to electric dipole moments of the electron and other particles. Tabletop-scale experiments used to search for these effects are described. Present experiments are already sensitive to new physics at the TeV scale, and new methods could extend this range dramatically. Such experiments could be among the first to show evidence for physics beyond the SM.
Nuclear Spin-Dependent Parity Violation in Diatomic Molecules
Nuclear spin-dependent parity nonconservation (NSD-PNC) effects arise from exchange of the Z^0 bo... more Nuclear spin-dependent parity nonconservation (NSD-PNC) effects arise from exchange of the Z^0 boson (parameterized by the electroweak coupling constants C2P,N) between electrons and the nucleus and from the interaction of electrons with the nuclear anapole moment, a parity-odd magnetic moment. The latter scales with the nucleon number A of the nucleus as A^23, while the Z^0 coupling is independent of A; the former will be the dominant source of NSD-PNC in nuclei with A >=20. The most precise result on NSD-PNC to date comes from a measurement of the hyperfine dependence of atomic PNC in ^133Cs, but this effect can be dramatically enhanced in diatomic molecules by bringing two levels of opposite parity close to degeneracy in a strong magnetic field. Level crossings have been observed in ^138BaF as a precursor to the test for parity violation in ^137BaF. We report on our measurements and planned design improvements to improve sensitivity in preparation for the parity violation experiment.
Progress towards a Nuclear Anapole Moment Measurement in ^137BaF
We report progress in our experiment to measure nuclear spin- dependent parity violating effects.... more We report progress in our experiment to measure nuclear spin- dependent parity violating effects. Our first goal is to measure the nuclear anapole moment of ^137BaF. We have developed an intense, cold beam of BaF molecules by laser ablation and supersonic expansion. This beam is injected into a homogeneous 0.5 T magnetic field. The field is measured and shimmed with an array of custom broadband NMR probes and commercial room-temperature shim array. We have observed Stark-induced transfer between two Zeeman-rotational sublevels of ^138BaF as a function of magnetic field, indicative of the Zeeman-tuned level crossing of these two states. A similar level-crossing in ^137BaF will be used to amplify the effect of the nuclear anapole moment to an observable level.
Progress Towards a Measurement of the Electric Dipole Moment of the Electron
We have proposed a measurement of the electric dipole moment of the electron (de) using the metas... more We have proposed a measurement of the electric dipole moment of the electron (de) using the metastable a(1) (^3&+circ;) state of the PbO molecule. A non-zero measurement of de within the next few orders of magnitude beyond the current limit of (6.9 ± 7.4) x 10-28 e-cm[1] would be clear evidence for physics beyond the standard model. We will present recent results from and improvements to our experiment including a proof of principle for the experiment, recent data on the initial state preparation using stimulated microwave Raman transitions, and a new detection system. The new detection system uses Winston Cone optical concentrators and large-area, low-noise, high speed, photodiode-based fluorescence detectors with fast overdrive recovery [2].[1] B. C. Regan, Eugene D. Commins, Christian J. Schmidt, and David DeMille, Phys. Rev. Lett. 88, 071805 (2002) [2] S. Bickman and D. DeMille, Rev. Sci. Instr. 76,113101 (2005).
Electroweak Physics in Molecules
We report on recent progress of our program to measure nuclear spin-dependent parity nonconservat... more We report on recent progress of our program to measure nuclear spin-dependent parity nonconservation (NSD-PNC) in electron-nucleon interactions. We probe enhanced NSD-PNC signals from the mixing of rotational/hyperfine states in diatomic molecules that are Zeeman shifted to near degeneracy. The NSD-PNC effect arises from two main sources: the electron-vector/nucleon-axial ( VeAn ) tree-level neutral current (a Z^0-mediated coupling parameterized by electroweak constants C 2P,N ), and a hyperfine term resulting from coupling of the nuclear anapole moment (a magnetic moment induced by intra-nuclear electoweak interactions) to the electron's magnetic dipole moment. The VeAn term is independ. of the nucleon number A of a given nucleus and is suppressed in the Standard Model, while the anapole term scales as A^0.5ex2-0.1em/-0.15em0.25ex3making it the dominant source of NSD-PNC in nuclei withA>20. Measurements in molecules containing nuclei over a large range of A should allow us to disentangle the two NSD-PNC contributions, increasing available data on nuclear anapole moments and reducing uncertainties in current measurements of C2P and C2N. Progress includes demonstration of an increased-flux molecular beam source, and a substantial improvement of molecular detection efficiency using a new scheme.
Nuclear Spin-Dependent Parity Nonconservation in Diatomic Molecules
Nuclear spin-dependent parity nonconservation (NSD-PNC) effects arise from couplings of the Z0 bo... more Nuclear spin-dependent parity nonconservation (NSD-PNC) effects arise from couplings of the Z0 boson (parameterized by the electroweak coupling constants C2P,N) and from the interaction of electrons with the nuclear anapole moment, a parity-odd magnetic moment. The effects of the anapole moment scale with the nucleon number A of the nucleus as A^2/3, while the Z0 coupling is independent of A; the former will be the dominant source of NSD-PNC in nuclei with A > 20. To date, the most precise result on NSD-PNC comes from a measurement of the hyperfine dependence of atomic PNC in ^133Cs. However, the effects of NSD-PNC can be dramatically enhanced in diatomic molecules. We outline an experimental program to take advantage of this enhancement. We have identified over ten suitable molecules; from measurements on the nuclei in these molecules we can extract the relative contributions of the anapole moment and the electroweak Z0 couplings. This will increase the available data on nuclear anapole moments, as well as reduce the uncertainties in current measurements of C2N and C2P. We report on the design of our pulsed molecular beam experiment and the current status of our efforts.
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Papers by richard paolino