HEPD-Activities/Intermediate energy physics

PNPI Group Leader:    O.L. Fedin, A.A. Vasiliev

One of the most pressing questions in particle physics is understanding of the ”proton radius puzzle”. The puzzle originated due to a striking discrepancy between the electric charge radius of the proton, extracted from the muonic hydrogen Lamb shift, compared to the CODATA value, based on electron-proton scattering experiments as well as most of the atomic transition measurements in electronic hydrogen.
          To address this puzzle, we a high-precision measurement of the differential ep elastic scattering cross sections in the region of low momentum transfer (0,001 GeV² < Q² < 0,04 GeV²) will be performed at the Mainz Microtron (MAMI). In order to perform this experiment, a new-generation detector consisting of a Hydrogen Time Projection Chamber (TPC) and a Forward Tracking System, will be constructed and a new electron beamline at MAMI will be built. The experimental setup will allow to measure the energy as well as the angle of the recoil proton in combination with the angle of the forward scattered electron. This is a completely new approach compared to previous low-Q² scattering experiments, in which only the scattered electron was detected.
          The advantages of the new method are precise determination of a momentum transfer as well as a low contribution from radiate corrections.
          Recently a possibility of similar experiment with muons are studied by the PNPI team in a framework of a new lagre CERN-based experiment a new experiment that will help settle some of these questions. AMBER, or Apparatus for Meson and Baryon Experimental Research. It will be the next-generation successor of the Laboratory’s COMPASS experiment.
          More information about Project «PROTON» is available in the article "PROJECT FOR PRECISION MEASUREMENT OF THE PROTON CHARGE RADIUS IN AN ELECTRON–PROTON SCATTERING EXPERIMENT", which was published in "HEPD PNPI Main results 2013-2018" – pp.316-325).
          “Meet AMBER” – the next-generation successor of the COMPASS experiment will measure fundamental properties of the proton and its relatives.

Experiment SPASCHARM

PNPI Group Leader:    D.V. Novinsky

The project is aimed at the SPASCHARM setup creation at IHEP for studying the strong interaction spin dependence and the proton spin structure, as well as for determining the mechanisms of the spin asymmetries formation in the particles production.
          As the promising project from 2025, it is planned to form the new channel of polarized protons and antiprotons beams, as well as pions, kaons and some nuclei ones interacting with polarized and unpolarized targets. A technical project for the creation of a magneto-optical channel has been drawn up, indicating all dimensions and the layout of the equipment. The goal of the final project is to study hidden charm states, one- and two-pin asymmetries, spin density matrix, etc.
          The existing project was created on the basis of the equipment of the "PROZA" experiment. The experiment motivation is to obtain data on the single-spin asymmetry of inclusive and exclusive final states in a wide range of kinematic variables. In particular, based on inclusive measurements, most models (for example, Collins, Sievers, “higher twists” models) cannot predict nonzero asymmetry in the central region and describe the dependence on the transverse momentum p_T.
          The first measurements in the year 2018 spring (so far the only set of physical data) were performed on a beam of negative pions with an energy of 28 GeV, interacting with a polarized target (the substance is pentanol).
          The diagram of the setup is presented, which includes three proportional chambers (PC) manufactured in the track detectors department. PC’s (a total of 1200 channels of electronics) were installed at the same time at the facility, and their software was integrated into the data acquisition system.
          A data taking with statistics 5-10 times higher than the existing one is planned for the existing setup within ~ 5 years. It is also planned to modernize the existing installation (Cherenkov counter - ready, hadron calorimeter, muon system).
          (For more details, see the Experiment SPASCHARM.pdf file, as well as the Presentation at the seminar from 2020).

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