D. Becker

Measurement of the axial and the strangeness magnetic form factor of the proton with a P2 backward angle setup

The P2 experiment at the future accelerator facility MESA in Mainz aims for a precise determination of the weak charge of the proton at low momentum transfer. The experimental method is a measurement of the parity violating asymmetry in elastic electron-proton scattering at forward angle. This asymmetry is dominated by the weak charge, but also the proton structure plays a role. Here we consider a back angle measurement, which is more sensitive to the proton structure, and present its possible implications on the main P2 measurement.

Measurement of the weak charge of the carbon-12 nucleus within the P2 experiment in Mainz

The P2 experiment at the MESA facility in Mainz aims to make a high precision measurement of the weak charge of the proton, and a suitable experimental setup is currently being designed [1]. As high precision measurements of the weak charges of different particles and nuclei are differently sensitive to physics beyond the Standard Model in the form of new quantum loop correction parameters, experiments with a range of different target materials are complementary. We introduce first feasibility considerations for the determination of the Weak Mixing Angle via the scattering of electrons from carbon nuclei in a graphite target with the P2 detector setup. In order to make an estimate of the achievable precision we present analytic calculations as well as Monte-Carlo simulations. The results of Geant4 simulations of proposed experimental setups are included.

Study of light backgrounds from relativistic electrons in air light-guides

Abstract The MOLLER experiment proposed at the Thomas Jefferson National Accelerator Facility plans a precision low energy determination of the weak mixing angle via the measurement of the parity-violating asymmetry in the scattering of high energy longitudinally polarized electrons from electrons bound in a liquid hydrogen target (Moller scattering). A relative measure of the scattering rate is planned to be obtained by intercepting the Moller scattered electrons with a circular array of thin fused silica tiles attached to air light guides, which facilitate the transport of Cherenkov photons generated within the tiles to photomultiplier tubes (PMTs). The scattered flux will also pass through the light guides of downstream tiles, generating additional Cherenkov as well as scintillation light and is a potential background. In order to estimate the rate of these backgrounds, a gas-filled tube detector was designed and deployed in an electron beam at the MAMI facility at Johannes Gutenberg University, Mainz, Germany. Described in this paper is the design of a detector to measure separately the scintillation and Cherenkov responses of gas mixtures from relativistic electrons, the results of studies of several gas mixtures with comparisons to simulations, and conclusions about the implications for the design of the MOLLER detector apparatus.

From deep inside to outer space: exploring neutron skins

M. Thiel∗1, S. Baunack1, D. Becker1, J. Diefenbach1, A.Esser1, M.I. Ferretti Bondy1, K.S. Kumar2,3, F.E. Maas1, H. Merkel1, U. Müller1, K.D. Paschke4, B.S. Schlimme1, C. Sfienti1, P.A. Souder5, and A. Tyukin1 1Institut für Kernphysik, Johannes Gutenberg-Universität Mainz, D-55099 Mainz, Germany 2Department of Physics, University of Massachusetts, MA 01003-9337, USA 3Department of Physics and Astronomy, Stony Brook University, NY 11794-3800, USA 4University of Virginia, Charlottesville, Virginia 22904, USA 5Syracuse University, Syracuse, New York 13244, USA E-mail: thiel@kph.uni-mainz.de

P2 - The weak charge of the proton

The goal of the P2 project is a new high precision determination of the electroweak mixing angle θ W . The project has been approved in January 2012 and the experiment will be carried out at the upcoming MESA accelerator facility in Mainz. The experimental method is a measurement of the proton weak charge QW (p) through the parity violating asymmetry in the elastic electron-proton scattering at low values of Q 2 ∼ 0.003 GeV2. We have estimated an achievable fractional precision of 0.15% in the determination of sin2(θ W ), which corresponds to an uncertainty of 2.1% for QW (p). In this article, we discuss the achievable precision within Project P2 and present first results of conceptual studies for the experiment.

Status and prospects of Rn measurements at Mainz

Parity-violating electron scattering is particularly sensitive to the neutron density. The recent PREX experiment at the Jefferson Laboratory (JLab) has demonstrated the feasibility of this method meanwhile outlining its major experimental challenges. On the other side intermediate energy photons are an ideal probe for studying the properties of strongly interacting matter from the nuclear scale down to the sub-nuclear components of the nucleus. Among others, coherent pion photoproduction on nuclei is an attractive approach to obtain information on the existence and nature of neutron skins in nuclei. The simultaneous combination of different techniques allows a systematic determination of the neutron skin of nuclei across the periodic table thus benchmarking modern calculations. Recently a systematic investigation of the latter method has been exploited at the MAMI accelerator. With the future accelerator MESA, the same experimental setup as in the measurement of the weak mixing angle will allow for a measurement of the parity violating asymmetry for longitudinally polarized electrons scattered on heavy nuclei with an accuracy of order 1% such that the neutron radius can be determined with precision competitive with the future PREX measurements.

Status and prospects of Rnmeasurements at Mainz

Parity-violating electron scattering is particularly sensitive to the neutron density. The recent PREX experiment at the Jefferson Laboratory (JLab) has demonstrated the feasibility of this method meanwhile outlining its major experimental challenges. On the other side intermediate energy photons are an ideal probe for studying the properties of strongly interacting matter from the nuclear scale down to the sub-nuclear components of the nucleus. Among others, coherent pion photoproduction on nuclei is an attractive approach to obtain information on the existence and nature of neutron skins in nuclei. The simultaneous combination of different techniques allows a systematic determination of the neutron skin of nuclei across the periodic table thus benchmarking modern calculations. Recently a systematic investigation of the latter method has been exploited at the MAMI accelerator. With the future accelerator MESA, the same experimental setup as in the measurement of the weak mixing angle will allow for a measurement of the parity violating asymmetry for longitudinally polarized electrons scattered on heavy nuclei with an accuracy of order 1% such that the neutron radius can be determined with precision competitive with the future PREX measurements.

Status and prospects of R{sub n} measurements at Mainz

Parity-violating electron scattering is particularly sensitive to the neutron density. The recent PREX experiment at the Jefferson Laboratory (JLab) has demonstrated the feasibility of this method meanwhile outlining its major experimental challenges. On the other side intermediate energy photons are an ideal probe for studying the properties of strongly interacting matter from the nuclear scale down to the sub-nuclear components of the nucleus. Among others, coherent pion photoproduction on nuclei is an attractive approach to obtain information on the existence and nature of neutron skins in nuclei. The simultaneous combination of different techniques allows a systematic determination of the neutron skin of nuclei across the periodic table thus benchmarking modern calculations. Recently a systematic investigation of the latter method has been exploited at the MAMI accelerator. With the future accelerator MESA, the same experimental setup as in the measurement of the weak mixing angle will allow for a measurement of the parity violating asymmetry for longitudinally polarized electrons scattered on heavy nuclei with an accuracy of order 1% such that the neutron radius can be determined with precision competitive with the future PREX measurements.