LHCb inner tracker: Technical Design Report

Abstract

The LHCb experiment [1] is designed to exploit the large bb production cross section at the LHC in order to perform a wide range of precision studies of CP violating phenomena. The copious production of Bd, Bs and Bc mesons and b-baryons, together with the unique particle-identification capabilities of the LHCb detector, will allow the experiment to perform sensitive measurements of CP violating asymmetries in a variety of channels that are beyond the reach of the current generation of CP-violation experiments. Since bb pairs at the LHC are predominantly produced at small angles with respect to the beam axis, the LHCb detector has been designed as a single-arm forward spectrometer. Its acceptance extends out to 300 mrad in the horizontal bending plane of the 4Tm dipole magnet and to 250 mrad in the vertical plane. The forward acceptance of the spectrometer is limited by the LHC beam-pipe which follows a 10 mrad cone. A side view of the LHCb detector is shown in Figure 1. The main tracking system consists of four planar tracking stations: one station (\TT") is located in between RICH1 and the magnet, three stations (\T1-T3") are located between the magnet and RICH2. Two detector technologies are employed in stations T1-T3: the outer region of these stations, away from the beam-pipe, is covered by the straw-tube drift chambers of the Outer Tracker, which has been described in an earlier TDR [2]. The innermost region around the beam-pipe, where particle densities are highest, is covered by silicon microstrip detectors | the Inner Tracker described in this document. An isometric view of the sensitive elements of one Inner Tracker station is shown in Figure 1.1. It covers a cross-shaped area around the beam pipe, approximately 120 cm wide and 40 cm high. Each station consists of four detection layers, with two ±5º stereo views sandwiched in between two layers with vertical strips. The overall sensitive surface of the three Inner Tracker stations amounts to approximately 4.2m2. Large strip pitches of approximately 200 μm and read-out strips of up to 22 cm length will be employed in order to minimise the number of read-out channels. The approximately 140 cm wide and 120 cm high TT station is entirely covered by silicon microstrip detectors. Inner Tracker and TT station together form the Silicon Tracker project, and in order to indicate the overall size of the project, a brief description of the layout of this station is given in section 1.2. However, the TT station is outside the scope of this document and will be described in a future TDR.