ILC Vertex Detector Issues and Thoughts

The ILC is intended to perform precise measurements of new particles produced with the low cross sections characteristic of high energy e+e− collisions. Figure 1 shows cross sections and event yields for a 500−1fb data sample for various established and hypothetical processes. Cross sections are low, typical event yields for supersymmetric particles are a few thousand per channel. The angular distributions due to s-channel spin 1 exchange are forward peaked, putting a premium on good coverage of the forward direction. Although the range of new physics to be studied at the ILC is not yet clear, there are a few flagship measurements which can drive detector design. One example is the set of measurements of Higgs couplings to quarks and bosons. These measurements, which will span more than two orders of magnitude in mass and coupling strength, require excellent separation of b, c, and light quark vertices. A related measurement is the self-coupling of the Higgs. Here the signal reaction, e+e− → ZHH → qqbbbb with four b-jets must be separated from backgrounds like tt→ bbcscs, ZZZ, and ZZH. This physics requires efficient B tagging and excellent b/c separation in complex events. Different constraints on the vertex detector come from measurements like heavy quark forward-backward asymmetry. Here the emphasis is on forward tracking with flavor tagging and determination of the charge of the parent b quark. Whether the ultimate focus is on Higgs, supersymmetry, or other new physics phenomena, it is likely that precise measurements of heavy quark jets and their decay vertices will play a crucial role [1] in ILC physics.