Performance of missing transverse momentum reconstruction for the ATLAS detector in the first proton-proton collisions at at $\sqrt s$= 13 TeV

In June 2015 the Large Hadron Collider restarted collisions at a centre-of-mass energy of 13 TeV. Preliminary studies of the first data collected by the ATLAS experiment, corresponding to an integrated luminosity of about 6 pb$^{-1}$, offer a good opportunity to test both the performance of the missing transverse momentum ($E_{\text{T}}^{\text{miss}}$) reconstruction with data and its agreement with simulation. $E_{\text{T}}^{\text{miss}}$ is calculated from calibrated and corrected physics objects using a track-based soft term. The $E_{\text{T}}^{\text{miss}}$ performance is studied in two complementary topologies with and without genuine $E_{\text{T}}^{\text{miss}}$, $W \,{\rightarrow}\, e\nu$ and ${Z \,{\rightarrow}\,\mu\mu}$. General $E_{\text{T}}^{\text{miss}}$ distributions are shown comparing data with the expectation from the simulated signal and relevant background samples. The $E_{\text{T}}^{\text{miss}}$ resolution and its response as a function of the transverse momentum of the reconstructed $Z$ boson are also studied.