Measurement of neutral current $e^{\pm }p$ cross sections at high Bjorken x with the ZEUS detector

The neutral current $e^{\pm }p$ cross section has been measured up to values of Bjorken $x \cong 1$ with the ZEUS detector at HERA using an integrated luminosity of 187  pb$^{-1}$ of $e^{-} p$ and 142 pb$^{-1}$ of $e^{+} p$ collisions at $\sqrt{s}=318$ GeV. Differential cross sections in x and $Q^{2}$, the exchanged boson virtuality, are presented for $Q^{2} \geq 725 GeV^{2}$. An improved reconstruction method and greatly increased amount of data allows a finer binning in the high-x region of the neutral current cross section and leads to a measurement with much improved precision compared to a similar earlier analysis. The measurements are compared to Standard Model expectations based on a variety of recent parton distribution functions.