A Triplet Track Trigger for Future High Rate Collider Experiments

Abstract

The Large Hadron Collider (LHC) will have a major upgrade, called the High Luminosity LHC (HL-LHC), after which the proton beams will collide with around 7 times the design luminosity of the LHC (L = 10^34 cm^-2 s^-1). There are also studies being conducted for a 100 km large circular hadron collider, called the hadron-hadron Future Circular Collider (FCC-hh), for the post LHC era. It aims to collide proton beams with sqrt{s} = 100 TeV and L ∼30 x 10^34 cm^-2 s-^1. High luminosities allow for a detailed study of elusive processes, for example, Higgs pair production, thus enabling direct measurement of the trilinear Higgs self-coupling (λ). In this regard, a generator level study is presented in the thesis using the HH->bbbb physics channel assuming trigger-less readout at FCC-hh. An average pile-up of〈μ〉~1000 (200) is expected at the FCC-hh (HL-LHC) within a vertex region of ∼10 cm. A vast pile-up complicates object reconstruction and forces trigger systems to increase the thresholds of trigger objects to satisfy bandwidth and storage limitations of an experiment. Hence, there is a need for a trigger that makes a smart selection of hard collision events from a sea of pile-up collisions at the earliest possible stage of a trigger system. Track triggers are attractive candidates for such demanding situations as they have a very good pointing resolution (unlike calorimeter triggers) in addition to a good momentum resolution. A new concept, the Triplet Track Trigger (TTT) is proposed to be used at the very first trigger level. It consists of three closely spaced highly granular pixel (preferably monolithic sensors) detector layers at large radii (∼1 m). It uses a very simple and fast track reconstruction algorithm, that can be easily implemented in hardware. TTT tracking performance studies are presented using full Geant4 simulation and reconstruction for the ATLAS Inner Tracker (at HL-LHC) and reference tracker of the FCC-hh. Very good momentum and z-vertex resolution allow grouping of TTT tracks into several bins along the beam-axis, where jet clustering algorithms run in parallel to form TTT-jets. The TTT allows for excellent pile-up suppression for the HH->bbbb multi-jet signature in〈μ〉= 1000 conditions of FCC-hh. A rate reduction from the 40 MHz bunch collision frequency to 1 MHz (4 MHz) is achieved for a trigger efficiency of ∼60% (80%). A corresponding rough estimate on S/sqrt{B} ∼16 (19) is obtained with negligible systematic uncertainties and total integrated luminosity of 30 ab^-1.