Electron deuteron scattering with HERA, a letter of intent for an experimental programme with the H1 detector.

This document outlines the case for a programme of electron-deuteron scattering mea- surements at HERA using the H1 detector. The goals of the $e^\pm D$ programme are to map the partonic structure of the nucleon at large $Q^2$ and low $x$, to explore the valence quark distributions at the highest $x$ values, to provide a precise measurement of the strong coupling constant and to investigate the parton recombination phenomena revealed in shadowing and their relationship to diffraction. The importance of these measurements for the under- standing of the perturbative and non-perturbative aspects of QCD thought to be responsible for nucleon structure is discussed, as is the significance of the measurements for future experimental programmes. Some modifications to both the H1 apparatus and the HERA accelerator are necessary to realise this programme; these are presented in the document. Mention is also made of questions that will remain unanswered following the completion of the above programme and the potential role of HERA and of H1 in investigating these questions is outlined.Physicists and Institutes interested in supporting this project are asked to inform Max Klein ([email protected]) and Tim Greenshaw ([email protected]) that they would like to have their names on the Letter of Intent by Wednesday 30th April 2003