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Tesi etd-09292010-155947

Thesis type
Tesi di laurea specialistica
Validation study of the online signal reconstruction in the ATLAS hadronic Tile Calorimeter
Corso di studi
relatore Roda, Chiara
Parole chiave
  • LHC
  • TileCal
  • Optimal Filtering
  • validation
Data inizio appello
Riassunto analitico
The Large Hadron Collider (LHC) that is operating at the CERN laboratory is a<br>proton-proton collider that will provide one bunch collision each 25 ns at a nominal<br>center-of-mass energy of 14 TeV and at a peak luminosity of 10^34 cm−2 s−1 . These<br>conditions allow to investigate the Standard Model predictions and to test many<br>critical areas like the Higgs Boson mechanism in the framework of a wide range of<br>scenarios.<br> <br> Currently the LHC is being tuned and produces collisions at s = √7 TeV with a<br>luminosity of about 10^31 cm−2 s−1 .<br> The experimental conditions however impose severe constraints on the detector<br>structures, electronics and performances in order to cope with the huge amount of<br>data and to be able to select the interesting events with reasonable precision at the<br>Bunch Crossing frequency of 40 MHz.<br> ATLAS is a detector situated on the LHC ring. This thesis deals with its central<br>hadronic calorimeter, TileCal, which is a sampling calorimeter with steel as absorber<br>material and plastic scintillator tiles as active medium; groups of tiles and steel plates<br>form the TileCal cells. The cells are coupled to wave-lenght-shifter bers, which<br>transport the scintillation light to two photomultipliers. The output signals are then<br>properly shaped and digitized by the front-end electronics, which is composed of<br>about 10000 channels.<br> The Tile Calorimeter is complemented by a triple calibration system that allows<br>equalization and monitoring of the signal at various stages. A radioactive source,<br>pushed by an hydraulic system across the calorimeter, generates a signal in the<br>scintillator tiles, allowing to equalize the response of each cell; a laser pulse, injected<br>at the input of the photomultiplier, is used to test the stability of the complete<br>readout chain; finally a dedicated Charge Injection System allows to test the response<br>of the front-end electronics for each channel.<br> A dedicated algorithm, the Non-Iterative Optimal Filtering method (OF-NI), is<br>executed in Digital Signal Processors and is responsible for the online reconstruction<br>of the signal time and amplitude. The reconstruction rate for the whole calorimeter<br>cannot exceed the Level 1 Trigger output rate of 100 kHz, otherwise the event signal<br>is completely lost. This is far from a simple effort due the large amount of background<br>events.<br> In this thesis the focus is on validation aspects of the OF-NI reconstruction for<br>the TileCal signal, mainly using the tools provided by the Charge Injection System; a<br>preliminary analysis of the signal reconstruction in proton collision is also presented.<br> It will be shown that a good understanding of both the hardware and the al-<br>gorithm implementation is required in order to validate the reconstruction and to<br>evaluate the systematics induced on the signal amplitude and time.<br> In the last part of the thesis a timing monitor is presented which allows to control<br>the stability and the performances of the signal reconstruction.<br> This work is part of the contribution to the Tile Signal Reconstruction<br>And Validation Task Force, a group dedicated to the validation of the online<br>signal reconstruction in TileCal.<br>