Decays of light, pseudoscalar mesons into lepton pairs are one possible way of detecting physics beyond the Standard Model. This thesis will focus on the η' → e+e- decay, because only few experiments have studied this decay. By the use of a basic simulation, the feasibility of conducting a search for the  η' → e+e- decay at DAΦNE, a electron-positron collider in Frascati, Italy, was investigated. The simulation implements an idea from previous experiments, where the η' decay was investigated through the e+e- → η' → X process. The results of the simulation show that experiments at DAΦNE could produce an observable signal of the process when the produced η' decays into one of the most probable decay modes. However, in order to draw a definite conclusion, a more detailed study is needed. / Sönderfallet av lätta, pseudoskalära mesoner till ett par av leptoner är ett möjligt sätt att detektera fysik bortom Standardmodellen. Detta examensarbete fokuserar på η’ → e+e- sönderfallet, på grund av att få experiment har studerat detta sönderfall. Genom att använda en enkel simulering, undersöktes möjligheten att studera η’ → e+e- sönderfallet vid DAΦNE, en elektron-positron accelerator i Frascati, Italien. Simuleringen följde samma genomförande som tidigare experiment, där η’ sönderfallet undersöktes genom e+e- → η’ → X processen. Resultaten av simuleringen visar på att experiment vid DAΦNE kan producera en detekterbar signal av processen då de producerade η’ sönderfaller till de mest troliga sönderfallen. På grund av begränsningarna i den utförda simulationen, behöver dock en mer detaljerad studie göras för att dra definitiva slutsatser.

In this master’s thesis the width of the <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Ceta'" /> meson is studied as a function of temperature. We consider a background medium consisting of a pion gas and assume a vanishing net baryon chemical potential. The width is obtained in the framework of large <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?N_%7Bc%7D" /> chiral perturbation theory and we consider terms up to next-to-leading order in the effective Lagrangian. We use a low-density approximation to calculate the width increase due to scattering with pions from the heat bath. The results suggest that the in-medium width for the <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Ceta'" /> may become of considerable size: at a temperature <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?T%5Capprox%2075" /> MeV we find a width increase of <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5CDelta%5CGamma%5Capprox%203-4" /> MeV, comparable to the inverse lifetime of the fireball created in a heavy-ion collision. The <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Ceta'" /> is of particular interested since it is intimately connected to the <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?U(1)_%7BA%7D" /> anomaly of Quantum Chromodynamics (QCD). It has been speculated that <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?U(1)_%7BA%7D" /> may become a symmetry of QCD at high temperatures and studies of the <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Ceta'" /> could indicate if that is the case. Depending on for how large temperatures the results from large <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?N_%7Bc%7D" /> can be trusted, they indicate that the <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Ceta'" /> may be possible to study experimentally in heavy-ion collisions due to its sizable in-medium width.