«AB-Note-2005-030 BDI On the Potential Use of Zero Degree Calorimeters for LHC Luminosity Monitoring H. Schmickler – CERN 1211 Geneva 23 - CH S. ...»
Due to the coincidence technique the background rates can be measured and corrected to a high precision, provided the machine is stable enough to have long integration times.
The feature of theZDCs of being linear of 5 orders of magnitude offers the possibility to convey absolute luminosity calibrations from TOTEM like measurements at very low luminosities to operational luminosities up to 1033.
It should be kept in mind that during Pb-Pb running periods of LHC the ZDC’s record a calculable cross section, as described in ref.1. This provides a potentially very useful calibration of the absolute luminosity determination by other means.
2.6 Role of Timing Measurements 2.6.1 Beam Proﬁle The intrinsic timing resolution of the ZDC is of order 150 psec. Since we digitize the time over threshold for each bunch crossing we can use this to calculate the location along the beam axis of a collision and in real time produce a distribution of the luminous region.
This real-time plot is often used at RHIC during r.f. commissioning, for example.
2.6.2 Commissioning Beam Crossing Angle The longitudinal proﬁle of the luminous region has several other potential roles in commissioning. For example, at some point during commissioning a ﬁnite crossing angle (150µrad) between beams will be introduced to prevent parasitic collisions between bunches outside the IR. It would be nice to have a commissioning tool that measures the actual angle.
Several times during RHIC operation a ﬁnite crossing angle was (unintentionally) introduced. This angle was seen very easily as soon as either beam underwent a displacement. This happened during vernier scans or simple luminosity tweaking.
Since under a transverse displacement of x cms the Zinteraction moves by
References  A. J. Baltz, C. Chasman and S. White, Nucl. Instr. And Meth. A417, 1 (1998).
 C. Adler et al., Nucl. Instr. And Meth. A470, 488 (2001).
 M. Chiu et al. Phys. Rev. Lett. 89 (2002) 012302, nucl-ex/0109018.
 A discussion of the role of ZDC in diffractive measurements at RHIC and LHC can be found in S.White, ”Inelastic Diffraction at Heavy Ion Colliders” - http://www.arxiv.org/pdf/nuclex/0501004 and to be published in Nucl. Phys. B..