Extra dimensions vs. supersymmetric interpretation of missing energy events at a linear collider
The photon plus missing energy signature is a primary handle on two important classes of theories. Theories with large extra dimensions predict the production of photons in association with Kaluza-Klein excitations of the graviton. In supersymmetric theories with superlight gravitinos, photons can be produced in association with gravitino pairs. The signatures for these two theories are compared, and it is found that they can be distinguished by studying the photon energy distributions and scaling of the cross section with center-of-mass energy. Both these methods fail, however, if there are six extra dimensions. In that case, additional phenomena predicted by the theories would be required to narrow down the underlying causes of the photon plus missing energy signal. We also study the ability of these measurements to determine the number of extra dimensions.