Challenges for FCC-ee luminosity monitor design

Abstract For cross section measurements, an accurate knowledge of the integrated luminosity is required. The FCC-ee physics programme at and around Z pole sets ambitious precision goal $$10^{-4}$$ 10 - 4 on absolute measurement one order magnitude better relative between energy scan points. determined from rate Bhabha scattering, $$\mathrm {e^+e^- \rightarrow e^+e^-}$$ e + → , where final state electrons positrons are detected in dedicated monitors covering small angles outgoing beam directions. constraints multiple: ( i ) they placed inside main detector volume only about 1 m interaction point; ii centred directions do not satisfy normal axial symmetry; iii their coverage limited by pipe, hand, requirement to stay clear acceptance, other; iv steep angular dependence scattering process imposes a acceptance limits $$\upmu $$ μ rad, corresponding geometrical $${\mathcal {O}}(1\,\upmu \text {m})$$ O ( 1 m ) monitor radial dimensions; v very high bunch-crossing 50 MHz during Z-pole operation calls for fast readout electronics. Inspired second-generation LEP monitors, which achieved experimental $$3.4 \times 10^{-4}$$ 3.4 × (Abbiendi et al. Eur Phys J C 14:373–425, 2000), proposed ultra-compact solution based sandwich tungsten-silicon layers. A vigorous R &D needed ensure that such satisfies more challenging requirements.