Physics and Outlook for Rare, All-neutral Eta Decays
Physics and Outlook for Rare, All-neutral Eta Decays

Author:

Publisher:

Published: 2014

Total Pages:

ISBN-13:

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The $\eta$ meson provides a laboratory to study isospin violation and search for new flavor-conserving sources of C and CP violation with a sensitivity approaching $10{̂-6}$ of the isospin-conserving strong amplitude. Some of the most interesting rare $\eta$ decays are the neutral modes, yet the effective loss of photons from the relatively common decay $\eta \rightarrow 3\pi0̂ \rightarrow 6\gamma$ (33$\%$) has largely limited the sensitivity for decays producing 3-5$\gamma$'s. Particularly important relevant branches include the highly suppressed $\eta \rightarrow \pi0̂ 2\gamma \rightarrow 4\gamma$, which provides a rare window on testing models of $O(p6̂)$ contributions in ChPTh, and $\eta \rightarrow 3\gamma$ and $\eta \rightarrow 2\pi0̂ \gamma \rightarrow 5\gamma$ which provide direct constraints on C violation in flavor-conserving processes. The substitution of lead tungstate in the forward calorimeter of the GluEx setup in Jefferson Lab's new Hall D would allow dramatically improved measurements. The main niche of this facility, which we call the JLab Eta Factory (JEF), would be $\eta$ decay neutral modes. However, this could likely be expanded to rare $\eta'(958)$ decays for low energy QCD studies as well as $\eta$ decays involving muons for new physics searches.

Measurement of the Branching Ratio for Eta-meson Decay Into a Neutral Pion and Two Photons
Measurement of the Branching Ratio for Eta-meson Decay Into a Neutral Pion and Two Photons

Author: Jason William Brudvik

Publisher:

Published: 2007

Total Pages: 240

ISBN-13: 9780549130093

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This dissertation presents the results of a measurement of the branching ratio for the rare decay eta → pi0gammagamma. The experiment was carried out in the A2 hall of the Mainz Microtron facility at the Institut fur Kernphysik, on the campus of Johannes Gutenberg Universitat Mainz, in Mainz, Germany. The experiment used the Glasgow-Mainz Tagger, which is a recoil-electron spectrometer, to determine the energy of the incident photons. The principal detector is the Crystal Ball, a highly segmented multiphoton spectrometer covering nearly 4pi steradians surrounding the experimental target. There is also a forward detector, TAPS, which is a multiphoton spectrometer arranged as a downstream wall of detectors. Furthermore, our setup includes an instrument used to differentiate between charged and neutral particles called the Particle Identification Detector, and a liquid hydrogen target. The kinematic-fit technique was used to select the eta → pi 0gammagamma events. The major backgrounds, namely eta → 3pi0 and eta → gammagamma decay and 2pi 0 production were measured simultaneously. The result for the branching ratio is BR(eta → pi0gammagamma) = (2.0+/-0.7) x 10-4. This corresponds to a partial width of Gamma (eta → pi0gammagamma) = 0.26 +/- 0.10 eV. This result is somewhat smaller than the result of recent experiments, it is consistent with theoretical calculations based on Chiral Perturbation Theory.