Beam Energy Overview
This topic is principally concerned with setting the absolute
energy scale of the colliding beams. Precise knowledge of the
collision energy is needed to make mass measurements in both threshold
scans and direct reconstruction using kinematic fits. The beam
energy scale may also be useful to monitor detector calibrations
at high energy using lepton pair production. The top mass measurement
(at threshold) and the Higgs mass measurement (via direct reconstruction)
both point to a target precision of roughly 100 PPM.
The following is a list of obvious topics and questions. Please
feel free to suggest additional questions, provide answers, or
express an interest in thinking about any of these issues.
- Is 100 PPM enough for high energy running?
- Are there other threshold scans (sLeptons for example) which
could use higher precision?
- Is this precision needed all the way up to 1 TeV?
Potential Beam Instrumentation
- WISRD-style spectrometer
- BPM-style spectrometer (RF or conventional)
- Moller/Bhabha scattering
- Other ideas (Spin precession, compton scattering, resonant
photon production, ...)
Potential Detector Measurements
- Radiative returns
- Mu-pair spectrometry (using tracking)
- What is the possible variance of beam energy on short time
- How precise do we need real-time measurements (pulse to pulse
or train to train)?
- What are the likely correlations with other parameters (lumi,
- Possible to measure anything downstream during collisions?
General Questions (all techniques)
- How much time is required to reach target precision?
- How sensitive is this technique to backgrounds?
- How sensitive is this technique to radiation?
- How often does this technique need calibrating at Z-pole,
and for how long?
- Estimated cost in $$$ and in terms of operational difficulty?
- Possible detector technologies (fiber target, visible synchrotron,
- Optics issues
- Possible to measure energy spectrum as well?
- Radiation sensitivity
- BPM stability
- Sensitivity to disrupted beam
- Possible upstream?
- Necessary detector precision/stability
- Impact on operations
- Acceptable event rate, time needed to reach target precision
Documentation and References
November 5, 2004