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This document discusses the construction of a Forward Proton Detector (FPD) as a new sub-detector of the DØ detector for Run II. The FPD uses machine magnets along with points measured on the track of the scattered proton to determine the proton momentum and angle.
Events with a leading proton comprise about 40% of the total cross section and are typically described by the exchange of a color-singlet pomeron, about which little is known. The addition of the FPD would facilitate studies of the structure of the pomeron and its dependence on diffractive mass and momentum transfer, determination of the quark and gluon content of the pomeron, search for diffractive production of heavy objects such as W bosons, and studies of hard double pomeron exchange. These topics are ideally studied at the Tevatron due to the large center-of-mass energy available.
The FPD will consist of quadrupole spectrometers which tag outgoing protons or anti-protons with a minimum momentum transfer and a dipole spectrometer which detects anti-protons with a minimum momentum loss. The installation of the quadrupole spectrometers requires that minor modifications be made to the accelerator to create space for the detectors. Preliminary studies show that these modifications are feasible, but a full engineering study is necessary. The physics benefits of the quadrupole spectrometers include acceptance for a large range of proton momenta and tagging of both protons and anti-protons. This allows a full study of hard diffraction in regions of low background, detailed study of double pomeron events, and in addition provides samples of elastic scattering events for alignment and luminosity monitoring.
Small scintillating fiber detectors will be installed in a series of Roman pots to measure the (x,y) coordinates of the proton or anti-proton track, thus allowing the determination of the track momentum and angle. The detectors will use multi-channel photomultiplier tubes which will be interfaced with Central Fiber Tracker trigger boards, resulting in DØ standard data structure and triggering. The FPD will not require any special running conditions and would have minimal impact on the standard DØ physics program except to broaden it.
The document is organized in the following manner. A discussion of the physics motivation is given in Sec. 2, followed by a description of the FPD in Sec. 3 and the hardware in Sec. 4. Triggering and data taking are covered in Sec. 5, followed by a section on accelerator modifications and conclusions.