High-voltage monolithic active pixel sensors for the PANDA luminosity detector and search for the decay e+ e- -> eta c eta pi+ pi- at center of mass energies between 4.23-4.36 GeV at BESIII
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Abstract
Although quantum chromodynamics is regarded as the quantum field theoretical description of the strong interaction, many open questions remain. Especially the existence of so-called exotic states is an open issue. In recent years it has drawn attention to it by the discovery of many new, unexpected states in the charmonium mass region. The properties of these resonances are not consistent with previously known bound states of quantum chromodynamics, i.e. mesons and baryons. The most famous of these states are the X(3872) and the $Z_c(3900)^{pm}$. To reveal the internal structure of these new states, precise measurements of their line shapes are needed. Furthermore, new states have to be searched for to understand the underlying pattern amongst the new states. The BESIII experiment in Beijing and the planned PANDA experiment in Darmstadt will play an important part in this task.
PANDA will use energy scan measurements to determine the line shape of resonances with high precision. The luminosity is needed for the relative normalization of the individual scan points, and enters as a systematic uncertainty into such a measurement. Therefore, PANDA will use a dedicated luminosity detector to measure the luminosity with high accuracy. It will employ four layers of novel silicon pixel sensors (HV-MAPS) to measure the tracks of elastically scattered antiprotons to determine the luminosity. In this work a data acquisition system and a tracking station have been developed. With this setup, the sixth prototype version of the HV-MAPS sensor has been completely characterized, e.g. in terms of the signal-to-noise ratio and the hit detection efficiency.
The second part of this work deals with the search for new resonances at BESIII. The $Z_c(3900)$ was discovered by the BESIII collaboration in the decay $text{Y}(4260)rightarrow J/psi pi^+pi^-$ and has been found in all three charged states by now. Its discovery suggests the existence of the up to now unobserved isospin triplet $eta_cpi^{pm, 0}$ and of the $eta_ceta$ isospin singlet. Using the high statistic datasets at center of mass energies between 4.23 GeV and 4.36 GeV available at BESIII, a resonant substructure in the $eta_ceta$ subsystem of the decay $e^+e^-rightarrow eta_cetapi^+pi^-$ is searched for. As no significant $eta_c$ signal is found, upper limits on the cross section of the reaction $e^+e^-rightarrow eta_cetapi^+pi^-$ at the center of mass energies of 4.23, 4.26 and 4.36 GeV are established to be 3.47, 5.98 and 19.02 pb respectively.