Precise density measurement with mu+ for E07 nuclear emulsion at J-PARC

One of the main purposes of the E07 experiment at J-PARC is to understand Lambda-Lambda and Xi-N interactions via double hypernuclei with several nuclides in use of nuclear emulsion. For well understand, we need to precisely measure the masses of hypernuclei by decay daughters of them. To do so, the key point is to know kinetic energies daughters through accurate decision of the emulsion density. At present, the density is obtained by track length alpha rays with monochromatic energy from natural isotopes of Thorium and Uranium series in the emulsion.

In addition to alpha rays, we will count mu+ particles from decay of stopped pi+ mesons in the density measurement to check the results by alphas. The range of mu+ is ~600 micron via also monochromatic energy.

To detect mu+ from pi+ decay, we are developing an automated search method with the Vertex Picker, which scans whole area of the emulsion. The key point of the method is to distinguish mu+ from background of stopping proton. At present, well detection of mu+ was expected by simulation with Geant4.

We will introduce the automatic search method for mu+ particles, and effectivity via density measurement with mu+.