Speaker
Description
Past experiments have revealed discrepancies in the consistency of the data from neutron form factor measurements, suffering from systematic uncertainty of the neutron detection. Measurements of the neutron's magnetic form factor $G^n_M$ suffer from insufficient detection efficiency whereas measurements of the neutron's electric form factor $G^n_E$ suffer from large backgrounds and low statistics. To overcome these shortcomings, a high rate neutron polarimeter has been developed by the A1 collaboration at the Institute for Nuclear Physics in Mainz, Germany extending their three-spectrometer apparatus at MAMI. It will measure $G^n_E$ over a large range of momentum transfers of $0.2 < Q^2 < 1.6 \text{ GeV}^2$ with consistent settings via double-polarized electron-deuterium quasi-elastic scattering. To reach an unprecedented statistical accuracy and high detection efficiency, the polarimeter must cope with several Mcps of background while providing precise timing of significantly less than 500 ps for position measurements as well as neutron time-of-flight measurements to deduce their momentum. In combination with a high resolution magnetic spectrometer analyzing the momentum of the scattered electrons, the reaction's kinematics can be precisely reconstructed. To meet the high rate capability and timing precision requirements, the signals of the plastic scintillators are discriminated by custom-made front-end electronics based on the ultrafast multi-channel NINO ASIC, encoding the signal time-over-threshold into the output signal width. Digitization is performed by TRB3 boards with multi-hit capability covering a total of 574 channels. Their FPGA-based high precision TDCs measure leading as well as trailing edges of the NINO output signals with negligible dead time and hardware resources compared with conventional ADCs or sampling ASICs. The precise time-over-threshold information allows walk corrections and background suppression by reconstructing the signal amplitudes to deduce the related energy deposits. In April 2019, the first pilot experiment at a momentum transfer of $0.6 \text{ GeV}^2$ has been performed. Preliminary results will be discussed in January 2020 at the 58th International Winter Meeting on Nuclear Physics in Bormio, Italy.
| Topic | Hadron Physics |
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