International Large Detector. Letter of intent

In the summer of 2007, the GLD concept study group, whose membership was largely based in Asia, and the LDC concept study group, which was mostly based in Europe with a strong north american membership, joined forces to produce a single Letter of Intent for a detector at the International Linear Collider, and formed the ILD concept group. Both the GLD and LDC concepts used the particle flow algorithm for jet reconstruction and a TPC for the central tracker. The basic parameters of the two concepts such as the size of the detector and the strength of the solenoid field, however, were quite different and had to be unified in order to write this letter of intent for ILD. Also, other critical details such as the interaction region design had to be unified. This was a non-trivial task, neither politically nor sociologically. The newly-formed concept study group, the ILD group, created a management team and engaged in intense studies to define the ILD detector concept by scientifically optimising the detector designs. The process has worked remarkably well, and we present here the outcome of this study as well as the large amount of studies that preceded separately by the two older concept groups. The ILD detector concept is now well defined, even though some technology choices are still open. One of the merits of unifying the detector concepts was that it revitalised the studies on physics performance and detector designs. We believe that the level of sophistication of the simulation and physics analyses has reached a high degree of sophistication for a detector group at this stage. This was achieved through collaboration and competition, and is the result of a productive learning process. The unification had also positive effects on the subdetector R and D efforts. Most R and D on detector technologies relevant to the GLD and LDC groups is being performed within the framework of detector R and D collaborations such as LCTPC, SiLC, CALICE, and FCAL which pursue their own goals of detector technology development. Members of the detector concept groups participate in the R and D collaborations and make sure that the detector technologies are successfully applied to the detector concept designs. By the creation of the ILD concept group, the application efforts became more focused. Currently, the ILD management includes subdetector contacts who are also key members of the detector R and D collaborations. This scheme is working efficiently such that we can finish basic R and D in time for the Technical Design Report which is envisaged around 2012. Overall, the ILD group structure is efficient while keeping exibility and openness. Even though we are still short on person power and funding at this time, we believe that we are well positioned to successfully complete a technical design for a detector at the International Linear Collider. The ILD group is firmly committed to the ILD project. (orig.)