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[en] After ten years of experience with parity-violating electron-proton-scattering, the preparatory work on a new high precision parity-violation experiment in Mainz has begun. Project P2 is bound to measure the weak charge of the proton to a relative uncertainty of 1.9%, which corresponds to a relative uncertainty of 0.15 % for sin2θW. This can be achieved by measuring the parity-violating asymmetry in elastic electron-proton-scattering to a relative precision of 1.7 % at Ebeam∼200 MeV and Q2∼0.005 GeV2. In this proceeding, we will discuss the achievable precision within project P2 as well as the experimental concept and present first results of studies involving Monte Carlo methods.
[en] We present the preliminary value of the measurement of the parity violating asymmetry in the cross section of quasi-elastic scattering of longitudinally polarized electrons on deuteron at backward angles at Q2 = 0.23. The preliminary asymmetry is APVd(Q2 = 0.23) = (−20.77±0.84stat±1.23syst)10−6. From this value a preliminary linear combination of the GMs and the isovector axial form factor GA can be extracted GAT = 1+0.59GMs = −0.53±0.37±0.02. Combining this preliminary linear combination with that extracted from the measurement of the parity violating asymmetry on proton, already publish, it is possible to disentagle the form factors and thus we can obtain a preliminary experimental determination of the isovector axial form factor GAT = 1 = −0.43±0.46
[en] Doppler-free two-photon laser spectroscopy has been employed for excited transitions between the 1S and 2S states in muonium. An unambiguous signal could be observed. The frequency interval was determined to be Δν1S-2S = 2 455 529 002(33)(46) MHz, where the first error arises from statistics and the second one is due to systematic effects which mainly are related to the properties of the high power pulsed laser system. There is agreement with a prior less accurate independent experiment at KEK and with QED theory within two standard deviations. The Lamb shift contributions are tested at the 8 · 10-3 level. The muonium-hydrogen and muonium-deuterium isotope shifts of the 1S-2S transition have a high potential for a precise mass determination of the positive muon. The experiment yields at present m1S-2Sμ = 105.658 80(29)(43) MeV/c2
[en] For modern parity violation experiments it is crucial to measure and monitor the electron beam polarization continuously. In the recent years different high-luminosity concepts, for precision Compton backscattering polarimetry, have been developed, to be used at modern CW electron beam accelerator facilities. As Compton backscattering polarimetry is free of intrinsic systematic uncertainties, it can be a superior alternative to other polarimetry techniques such as Moeller and Mott scattering. State-of-the-art high-luminosity Compton backscattering designs currently in use and under development at JLab and Mainz are compared to each other. The latest results from the Mainz A4 Compton polarimeter are presented. (orig.)
[en] In the frame of a phenomenological approach based on Compton-like Feynman amplitudes, we study the annihilation channel in antiproton nucleon collisions with production of a single charged or neutral pion and a lepton-antilepton pair. These reactions allow us to access nucleon and axial electromagnetic form factors in the time-like region and offer a unique possibility to study the kinematical region below the two-nucleon threshold. The differential cross section in an experimental setup where the pion is fully detected is given with explicit dependence on the relevant nucleon form factors. The possibility of measuring a heavy charged pion in the annihilation channel is also discussed
[en] The PANDA experiment at the new FAIR facility will cover a broad experimental programme in hadron structure and spectroscopy. As a multipurpose detector, the PANDA spectrometer needs to ensure almost 4π coverage of the scattering solid angle, full and accurate multiple-particle event reconstruction and very good particle identification capabilities. The electromagnetic calorimeter (EMC) will be a key item for many of these aspects. Particle energies ranging from some MeVs to several GeVs have to be measured with a relative resolution of 1% ⊕ 2%/√E/GeV . It will be a homogeneous calorimeter made of PbWO_4 crystals and will be operated at -25°C, in order to improve the scintillation light yield. With the exception of the very forward section, the light will be detected by large area avalanche photodiodes (APDs). The current pulses from the APDs will be integrated, amplified and shaped by ASIC chips which were developed for this purpose. The whole calorimeter has been designed in three sections: a forward end-cap, a central barrel and a backward end-cap (BWEC). In this contribution, a status report on the development of the BWEC is presented
[en] Radiative corrections to the annihilation of proton-antiproton into electron-positron are revisited, including virtual and real (soft and hard) photon emission. This issue is relevant for the time-like form factors measurements planned at the PANDA experiment at the FAIR facility, in next future. The relevant formulas are given. A stand-alone Monte-Carlo integrator is developed on the basis of the calculated radiative cross section and its application to the PANDA experiment is illustrated.
[en] 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
[en] Within the FAIR phase-0 project, the use of FAIR equipment at other facilities before the completion of the civil construction is envisaged. The PANDA EMC is a good candidate for FAIR phase-0, due to the advanced state of its development. In particular, the backward endcap (BWEC) of the PANDA EMC, which is developed and built at HIM in Mainz, could be ready by 2020, three years before its foreseen installation. Therefore, possible experiments at the MAMI electron beam facility making use of the BWEC are under consideration. One candidate is the measurement of the π0 electromagnetic transition form factor via the electroproduction on a nuclear Coulomb field. To select this channel, the momentum distribution of the π0 needs to be measured by detecting the decay γ particles in an EMC. Since the relevant γs are emitted at forward angles, where high particle fluxes are expected, the affordable luminosity is limited by the maximum event rate of the detector. Therefore, the total event rate at different scattering angles with various targets need to be determined. Monte Carlo simulations are ongoing and a beam test with a prototype calorimeter was scheduled for January 2018 in order to address these questions. The status of these feasibility studies is presented.