The P2 experiment: A future high-precision measurement of the weak mixing angle at low momentum transfer

Dominik Becker, Razvan Bucoveanu, Carsten Grzesik, Kathrin Imai, Ruth Kempf, Matthias Molitor, Alexey Tyukin, Marco Zimmermann, David Armstrong, Kurt Aulenbacher, Sebastian Baunack, Rakitha Beminiwattha, Niklaus Berger, Peter Bernhard, Andrea Brogna, Luigi Capozza, Silviu Covrig Dusa, Wouter Deconinck, Jürgen Diefenbach, James DunneJens Erler, Ciprian Gal, Michael Gericke, Boris Gläser, Mikhail Gorchtein, Boxing Gou, Wolfgang Gradl, Yoshio Imai, Krishna S. Kumar, Frank Maas, Juliette Mammei, Jie Pan, Preeti Pandey, Kent Paschke, Ivan Perić, Mark Pitt, Sakib Rahman, Seamus Riordan, David Rodríguez Piñeiro, Concettina Sfienti, Iurii Sorokin, Paul Souder, Hubert Spiesberger, Michaela Thiel, Valery Tyukin, Quirin Weitzel

Research output: Contribution to journalReview articlepeer-review

112 Scopus citations


We describe the research and development work for the P2 experiment which aims for a high precision determination of the weak mixing angle sin 2θW to a precision of 0.15% at a four-momentum transfer of 4. 5 × 10 - 3 GeV2. This accuracy, comparable to existing measurements at the Z pole, allows for a sensitive test of the Standard Model up to a mass scale of 50 TeV, extendable to 60 TeV. The weak mixing angle is connected to the weak charge of the proton which will be extracted from a measurement of the parity violating cross section asymmetry - 39. 94 × 10 - 9 in elastic electron-proton scattering. A total accuracy of 0. 57 × 10 - 9 is achievable in a measurement time of 11000 h using a 150μA polarized electron beam impinging on a 60 cm liquid hydrogen target. The P2 asymmetry is smaller than any asymmetry measured so far in electron scattering with an unprecedented goal for the accuracy. The use of a solenoid spectrometer with 100% ϕ-acceptance as well as an atomic hydrogen trap polarimeter are new features, which have never before been used in parity-violation experiments. In order to collect the enormous statistics required for this measurement, the new Mainz Energy-Recovering Superconducting Accelerator (MESA) is under construction. Plans for the associated beam control system and the polarimetry are described in this article as well. A liquid hydrogen high-power target with an extremely low noise level of 10 ppm needs to be designed and constructed. We report in addition on the conceptual design of the P2 spectrometer, its Cherenkov detectors, the integrating read-out electronics as well as the ultra-thin, fast tracking detectors. The physics program of the MESA facility comprises indirect, high precision search for physics beyond the Standard Model, measurement of the neutron distribution in nuclear physics, single-spin asymmetries, and a possible future extension to the measurement of hadronic parity violation.

Original languageEnglish (US)
Article number208
JournalEuropean Physical Journal A
Issue number11
StatePublished - Nov 1 2018

ASJC Scopus subject areas

  • Nuclear and High Energy Physics


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