| Home | Absolute
luminosity determinations in ATLAS are obtained from different methods:
from machine parameters, from the rate of theoretically well
calculated processes like pp-->W/Z and from elastic scattering.
Relative luminosity measurements are provided by the LUCID monitor.
The ALFA system will measure elastic pp-scattering in the coulomb-region at very small scattering angle of a few micro-radians. This implies operating detectors very close to the beam (1-2mm) in Roman Pots 240 m distance from the Interaction Point. With a special beam optics we can obtain from a measurement of the impact of the elastic protons in the ALFA detector the t-value of the event. The detector will consist of a scintillating fibre tracker with a spatial resolution of 30 microns. A fit to the t-spectrum including the Coulomb-Nuclear interference region yields the luminosity and further fundamental physics parameters like the total cross section. The expected precision of the luminosity calibration is about 3 %. |
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| Experimental set-up: two Roman Pot units with two vertical pots at each side of the IP. | Extraction of the Luminosity from the measured t-spectrum | |
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| Locations of the Roman Pots in ATLAS | The Roman Pot Unit houses and positions the pots and connects the system to the beam pipe | |
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| Conceptual design of ALFA | The central ALFA tracker with 20 planes of scintillating fibres in U/V-Geometry |
Last update: Hasko Stenzel, 27.02.2007