The primary experimental goal of studies of hadronic parity nonconservation (PNC) has long been the isolation of the isovector weak nucleon–nucleon interaction, expected to be dominated by long-range pion exchange and enhanced by the neutral current. In meson-exchange descriptions, this interaction, together with an isoscalar interaction generated by and exchange, dominates most observables. Both amplitudes have been used to compare and check the consistency of experiments, yet no evidence for isovector hadronic PNC has been found. We argue that the emphasis on isovector hadronic PNC was misplaced. The large- expansion provides an alternative and theoretically better-motivated simplification of effective field theories (EFTs) of hadronic PNC, separating the five low-energy constants (LECs) into two of leading order (LO) and three of next-to-next-to-leading order (NLO). We show that this large- LEC hierarchy accurately describes all existing data on hadronic PNC and discuss opportunities to further test th...

A New Paradigm for Hadronic Parity Nonconservation and Its Experimental Implications

A short review is presented of experiments designed to detect parity nonconservation (PNC) in the interaction between nucleons. A recent measurement of PNC in proton-proton scattering is described, and some of the methods which were developed to reduce systematic errors to less than or equal to 2 x 10/sup -8/ are discussed. The results of this experiment and of other measurements on PNC are compared to theoretical predictions.

Parity violation in the nucleon-nucleon interaction

The NPDGamma experiment measures the parity-violating asymmetry in γ -ray emission in the capture of polarized neutrons on liquid parahydrogen. The sensitivity to the asymmetry for each detector in the array is used as a parameter in the extraction of the physics asymmetry from the measured data. The detector array is approximately cylindrically symmetric around the target and a step-wise sinusoidal function has been used for the sensitivity in the previous iteration of the NPDGamma experiment, but deviations from cylindrical symmetry necessitate the use of a Monte Carlo model to determine corrections to the geometrical factors. For the calculations, source code modifications to MCNPX were done in order to calculate the sensitivity of each cesium iodide detector to the physics asymmetry. We describe the MCNPX model and results from calculations and how the results are validated through measurement of the parity violating asymmetry of γ -rays from neutron capture on chlorine.

Monte Carlo calculation and verification of the geometrical factors for the NPDGamma experiment

In our paper four Mӧssbauer spectra of ordinary chondrites (previously classified by a classical method based on determining the ratio of ferrosilite (Fs) to fayalite (Fa) with an electron microprobe) are presented and discussed. These are the Mӧssbauer spectra of two ordinary chondrites type H (Pultusk and Grzempach), one ordinary chondrite type L (Hyattville) and one type LL (NWA 6287). These meteorites were compared, using their Mӧssbauer spectra with the following four other samples: a fragment of a rock that fell near Leoncin in Poland (sample No. 1), a fragment of a rock found in the vicinity of Pultusk in Poland (sample No. 2), a meteorite specimen bought on the meteorite exchange (sample No. 3) and a stone object whose decline was observed in Europe (sample No. 4). The spectrum of sample No. 1 is very similar to the spectrum of ordinary chondrite of type LL. This observation was confirmed using 4M method (previously created by us). The spectrum of sample No. 2 differs significantly from the spectrum of sample of the Pultusk meteorite. In the spectrum of sample No. 3, a clear signal from iron-nickel alloy and troilite can be observed. This fact allows us to state that sample No. 3 is a fragment of rock that was created in cosmic conditions. Sample No. 4 has a Mӧssbauer spectrum similar to the spectrum of terrestrial magmatic rocks. This observation does not clearly determine where the examined object comes from. This work demonstrates the usefulness of Mӧssbauer spectroscopy in recognizing samples that are fragments of meteorites.

/pdf/mossbauer-spectroscopy-as-a-useful-method-for-distinguishing-hgbd3r1v7t.pdf

Mӧssbauer spectroscopy as a useful method for distinguishing between real and false meteorites

The NPDGamma experiment measures the asymmetry in γ -ray emission in the capture of polarized neutrons on liquid parahydrogen. The beam polarization is measured using 3 He spin analysis, but this measurement does not account for the contribution of depolarization from spin–flip scattering primarily due to orthohydrogen in the bulk liquid. This is a systematic effect that dilutes the experimental asymmetry and is modeled using Monte Carlo. Methods for tracking neutron spin in MCNPX were developed in order to calculate the average neutron polarization upon capture for use as a multiplicative correction to the measured beam polarization for the NPDGamma experiment.

Monte Carlo calculation of the average neutron depolarization for the NPDGamma experiment

The NPDGamma experiment measures the parity-violating (PV) gamma asymmetry from polarized cold neutrons captured on protons at the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory (ORNL). The (PV) neutron spin asymmetry A
 γ
 of photons from polarized cold neutron capture on protons is proportional to the ΔI=1 long range weak meson coupling $h_{\pi }^{1}$
 between nucleons in the hadronic weak interaction (HWI). Liquid para-hydrogen production data taking concluded in April 2014 and once the background aluminum asymmetry measurements are complete, the PV asymmetry A
 γ
 can be extracted. Preliminary results of the analysis of A
 γ
 are presented.

Status of the NPDGamma experiment

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Status of the NPDGamma experiment