Measurement of the branching fraction of to D+ → K- K+K+ in the LHCb experiment

Full text: The world's most powerful particle accelerator, Large Hadron Collider (LHC), is located near Geneva built around 100 m underground. For 2010 and 2011 it has collided opposing beams of 3.5 TeV protons and now the beam energy has increased to 4 TeV per beam. The LHCb experiment, one of the four main detectors in the LHC, is devoted to study CP violation and rare decays in the b and c-quark sectors. CP violation is one of the necessary ingredients to explain the difference between matter and anti-matter observed in the Universe, since they were created in equal amounts during the Big-Bang. According to the Standard Model, the CP violation in the charm sector is very small compared to the s and b systems. LHCb has the appropriate conditions to collect charm data with an outstanding statistics. So if it finds any asymmetry larger than the expected from the SM, it will open door to New Physics. We report a measurement of the branching fraction of the doubly Cabibbo suppressed mode D+ → K- K+K+ relative to the Cabibbo-favored mode D+ → K- π+π- as a first step of a Dalitz plot analysis and CP violation measurement. Based on the signal signature, we choose the discriminating variables which distinguish between signal and background. We then select values (cuts) which allow us to not only select the signal but also maximize the statistical significance, so that, performing mass fits, we determine the yields. The efficiency was sub-divided into specific contributions, for instance, trigger and particle identification, because this way some of the contributions can be directly obtained from data and do not depend on the simulations. In this analysis we made use of 2011 LHCb data of about 1fb-1 and due to the excellent performance of the LHC and LHCb we can improve the measurement of the branching fraction with respect to the previous experiments. (author)