Speaker Oleg Kiselev (GSI)
Abstract
The physics of the proton as the charged nuclear building block of matter is at the core of interest in the quest for understanding nature. We plan to build a Time-Projection-Chamber (TPC)-based active target detector for the µ-p elastic scattering experiment at COMPASS facility at CERN, aiming at measurement of the proton radius with about a factor 10 smaller uncertainty on the electromagnetic corrections compared to electron scattering, and thus contributing to solve the so-called “proton radius puzzle”.
Application of an active target technology in particle and nuclear physics attracted high attention in the last years due to the difference to a classical TPC, the detector gas also serves as the reaction target. A reaction can occur anywhere within the detector’s active volume and these reactions can be measured over a broad range of energies for many types of beam, from electrons and muons up to the heavy ions. The vertex of the reaction and the parameters of the recoil particles can be determined on an event-by-event basis with very high efficiency and solid angle coverage, and with very low energy threshold. We propose usage of a high-pressure hydrogen-filled ionization chamber without gaseous amplification; due to for the measurement of the proton radius via muon-proton scattering, best possible energy resolution is a key feature of the detection setup.
Last year, a test experiment with a small-size active target prototype has been performed and shown feasibility of the proposed experiment. The experimental concept of the future experiment and few preliminary results of the test experiment will be presented. Details of the other active targets together with the experimental results using those detectors will be also shown.