ATLAS Tile Muon trigger extension to the barrel region - contribution to improve Heavy Flavour Jets tagging in Pb-Pb collisions


  • Call:

    IDPASC Portugal - PHD Programme 2016

  • Academic Year:

    2016 / 2017

  • Domain:

    Experimental Particle Physics

  • Supervisor:

    Agostinho Gomes

  • Co-Supervisor:

    Helena Santos

  • Institution:

    Faculdade de Ciências - Universidade de Lisboa

  • Host Institution:

    Laboratório de Instrumentação e Física Experimental de Partículas

  • Abstract:

    Bunches of particles collide at the LHC at a frequency of 40 MHz, but only a very small fraction of the collisions are interesting for physics analyses. The main role of the Trigger and Data Acquisition system of ATLAS is to select and store about 400 interactions per second for further analysis. In order to achieve this goal, the trigger system is divided mainly in two levels. The first one is hardware based, while the following uses dedicated software algorithms to confirm the selection done by the first level trigger. One important problem to solve is the high rate of fake muons originating in the beam halos, or by accidental coincidence of hits of charged particles, like protons, pions or kaons, in the muon spectrometer. These fake muons, in turn, produce high rate of fake heavy flavour jets (collimated sprays of particles) erroneously tagged as containing muons from B-meson decays. The HL-LHC Phase 2 upgrade of the Front end electronics of the hadronic calorimeter of the ATLAS experiment, Tilecal, will allow the usage of digital data in the first level of event selection. The trigger digitization at the first stage of event selection results in two main improvements - a larger signal to noise ratio and a better handling of the super-imposed signals from different bunch crossings. Such a feature will play a particular role in muon triggers. The muon trigger should collect the information of three layers of muon stations to decide upon the identification of an event as containing muons. However this is not always possible either in the case of low pT muons or due to limited coverage. Taking advantage of a well known and clear signal of Tilecal last radial layer (D-cells) it is possible to improve the rejection of non-collision backgrounds in low-pt muon triggers in regions that are not instrumented with three stations. During Run2 Tilecal will use the third radial layer for 1<|eta|<1.3 to help the L1 Muon End-Cap trigger to reject fakes produced by beam remnants. This is now in its final stages of commissioning using proton collisions data. The extension of the first level of event selection including Tilecal D-cells is called Tile-Mu Trigger. Although the third radial layer of Tilecal also covers |eta|<1 its current limited coverage is a decision based on the small signal to noise ratio in this |eta|<1 range. The extension of this trigger to the full eta range covered by Tilecal needs to be evaluated at the HL-LHC conditions. The student will use data of the current run 2 to check the feasibility of the Tile-Mu Trigger in the central barrel region when extrapolating to the HL-LHC conditions. Particular attention will be given to the Tilecal demonstrator prototype electronics and high voltage system required for the integration of the Tilecal barrel D cells in the Tile-Mu Trigger. The student will participate in the validation of the demonstrator prototypes and in the development of the respective high voltage system. The student will explore the Tile-Mu Trigger in order to improve the efficiency and purity of Heavy Flavour Jets tagging. Furthermore, such a project implies the participation in Run 2 (2015-2017) LHC data acquisition, both p+p and Pb+Pb collisions, namely shifts and data quality monitoring. The project will contribute to the development of the ATLAS Upgrade trigger algorithms and, as such, will be integrated in the Software Upgrade program of the ATLAS experiment. A complementary data analysis on Heavy Flavour Jets making use of this development is foreseen.