Track simulation and reconstruction in LHCb
Tilburg, J.A.N. van
MetadataShow full item record
The Large Hadron Collider (LHC), due to start operating in 2007, collides protons with a centre-of-mass energy of 14 TeV. LHCb is one of the four experiments along the LHC and is dedicated to measure the decay of B mesons. Simulations of the proton collisions, based on Pythia, are tuned to agree with data from other experiments. Simulations of the detector, based on Geant, show the importance to minimise the amount of material. Currently a particle sees, up to the last tracking station, on average only 12% of an interaction length and 40% of a radiation length. A detailed simulation of the Outer Tracker detector response (digitisation) predicts an average channel occupancy in B events of 4.3%. In the reconstruction, tracks are fitted using the extended Kalman filter method, requiring the use of a reference trajectory. The hit purity is increased from 98.0% to 98.5% by removing hits with the highest chi^2 contribution (>9). The matching algorithm finds so-called long tracks by combining tracks segments found before and after the magnet. The matching efficiency for high-momentum long tracks (p>5 GeV) is 91%. Afterwards, hits from the TT detector are added to the track with an efficiency of 89% and a wrong hit fraction of 6%. The combined performance of the long track algorithms shows a 94% efficiency and 8% ghost rate for p>5 GeV. The momentum resolution of long tracks equals 0.35%. The decay channel B_s0 -> D_s- pi+ will be used to measure the oscillation frequency, Delta m_s, while the decay channel B_s0 -> D_s(*)-+ K(*)+- will be used to measure the CP-violating parameter gamma-2chi. The selection requirements for these decay channels are simultaneously optimised. The expected annual yield equals 85000 for B_s0 -> D_s- pi+ and 4600 for B_s0 -> D_s-+ K+- with background fractions of 0.34 and 0.24, respectively. In addition, 1300 B_s0 -> D_s*-+ K+- events and 200 B_s0 -> D_s-+ K*+- events are expected. A separate sensitivity study shows that, after 1 year of data taking, the oscillation frequency can be accurately measured up to 88 ps^-1 (5 sigma sensitivity limit) and that, after 3 years of data taking, a precision on gamma-2chi of 8.4+-1.1 degrees can be reached.