Rejection of late conversions in the ALICE TRD trigger

The ALICE Transition Radiation Detector (TRD) provides various level-1 trigger contributions based on the information of individual tracks. Chamber-wise track segments are merged in the Global Tracking Unit (GTU) and used for the on-line reconstruction of transverse momentum (p_t) and electron identification. Based on this information, versatile and flexible trigger conditions were implemented. Amongst others, several triggers on high-p_t electrons were used during Run 1. The dominant background originates from photon conversions in the material in front of the TRD. For the reconstruction of the transverse momentum, the GTU performs a straight line fit under the assumption that the tracks point to the primary vertex. However, electrons from conversions at large radii can falsely point close to the primary vertex and fake high-pt particles. In our improved tracking algorithm, the local curvature of the tracks is exploited to reject electrons from late conversions by approximating their sagitta. After successful tests in simulations, the algorithm was implemented in the GTU preserving the 7 us latency of the trigger decision relative to a level-0 trigger. We present the performance of the late conversion rejection and show prospects for TRD triggers for data-taking in 2016.