Luminosity Overview

This topic covers the issues related to understanding the luminosity delivered at the interaction point. In addition to the instantaneous and total integrated luminosity, many physics analyses also require a detailed understanding of the differential luminosity spectrum (dL/dE) resulting mainly from the large beam-beam interactions in the collision process. All foreseen measurements of particle masses, for example, are highly sensitive to the exact shape of this luminosity spectrum. Methods for optimizing the delivered luminosity will also be considered in this topic, due to the significant overlap in required instrumentation.

The following is a list of topics and questions which is almost certainly incomplete. Please feel free to suggest additional questions, provide answers, or express an interest in thinking about any of these issues.

Physics Questions

• Which analyses require an absolute luminosity measurement, and with what precision?
• What is the ultimate precision required on the luminosity spectrum?
• What are the relative luminosity requirements for threshold scans at high energy?
• What relative luminosity precision is required to calibrate the energy scale at the Z-pole?

Potential Beam Instrumentation

• Beamstralung monitor
• Pairs monitor
• Laser Wire
• 'Wire' scanner at point of high dispersion
• Radiative bhabha monitor
• Deflection scans
• Bunch length monitor

Potential Detector Measurements

• Bhabha acolinearity
• Low-angle bhabha scattering

Operational Questions

• What is the possible variance on short time scales?
• How precise do we need real-time measurements?
• What are the likely correlations with other parameters (energy, polarization, etc.)?
• How often are invasive measurements required?
• How easy is it to trade luminosity for energy spread?
• Just what is the strategy for optimizing delivered lumi?

Detector Questions

• Where does the luminosity spectrum monitor go?
• What sort of alignment tolerance is needed for the acolinearity measurement?
• How much time is needed to reach the target precision?
• How does an IP boost effect this measurement?

Machine Questions

• What kind of instrumentation is really needed to understand the collision process?
• How well can dL/dE be predicted?
• How can the bunch length be measured, and how important is this?
• Can a pairs monitor be made to work?
• What is currently envisioned for IP instrumentation, and where does this fit?