Département de Physique Nucléaire

Institut de recherche sur les lois fondamentales de l'Univers

The HAPPEx2 experiment measures a combination of the weak form factors of the protons at a low Q² of 0.1 GeV/c². Combined with the already known electromagnetic form factors they allow us to get the strange quark contribution in the charge and current distributions inside the nucleon. These new observables are reached through the parity violating asymmetry in scattering of polarized electrons off a proton target.
The combination with the SAMPLE and/or ⁴He experiments provides us with a very nice separation of the electric and magnetic parts. Stringent constraints are put on the stange radius and magnetic moment for the first time.

Proposal (psorpdf).

Experimentally, the low Q² kinematics are reached thanks to the insertion of a septum magnet between the cryo-target and the entrance window of the Hall A spectrometers. Small scattering angles in the range of [4-8] degrees can then be catched in the acceptance with a beam energy of 3.2 GeV.

Saclay's realisations:

In charge of the electron detector.

Involved in the new C++\ROOT analysis software 'PAN' .