Measurement of the Z boson cross-section in - Harvard University ...

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Chapter 4: Data Collection and Event Reconstruction 112 are built: EM clusters, used for electron and photon identification, and combined clusters, using information from both EM and hadronic calorimeters, and used for jet finding. The clustering proceeds in three steps. In the first step, the available η − φ space is divided up into a grid of towers of size ∆η × ∆φ. For EM clusters, ∆η =∆φ =0.025, while for combined clusters, ∆η =∆φ =0.1 [107]. Within each tower, the energy of cells in each longitudinal layer is summed into a tower energy. In the second step, a window of a fixed size is moved across each element of the tower grid in steps of ∆η and ∆φ, and the transverse energies of all towers in the window is summed. If the window transverse energy is a local maximum and above a threshold, a cluster seed is formed. The threshold is 3 GeV for EM clusters and 15 GeV for combined clusters. At this point, for combined clusters, the seeds are directly transformed into clusters; cluster quantities such as position and energy deposition per layer are calculated based on the cells encompassed by the sliding window. For EM clusters, however, there is an additional step in which clusters of different sizes are built depending on the hypothesized particle type and the location of the cluster in the calorimeter. In general, the cluster must be large enough so that it contains most of the energy deposited by the particle. But including more cells in a cluster also means potentially including more noise, so the actual number is a trade-off between these two factors. Topological clustering technique Topological clustering attempts to reconstruct three-dimensional ‘energy-blobs’ in the calorimeter. It starts with a seed cell, and adds to the cluster any neighboring cell if its energy is significantly above the noise level. The resulting clusters have a
Chapter 4: Data Collection and Event Reconstruction 113 variable number of cells, in contrast to the sliding window approach. Separate EM and hadronic clusters are built. In the first step, all cells with a signal-to-noise ratio above a threshold tseed are put into a seed list; tseed = 6 and 4 for EM and hadronic calorimeter cells respectively [107]. The noise is defined as the expected RMS of the electronics noise added in quadrature to the expected pile-up noise. The cells in the seed list are ordered according to their tseed, and form proto-clusters. Next, all neighboring cells of a seed cell are considered. If a neighboring cell is not in the seed list and has a signal-to-noise ratio above a threshold tneighbor, it is added to the proto-cluster. tneighbor = 3 and 2 for EM and hadronic calorimeter cells respectively. If the neighbor is adjacent to more than one proto-cluster, the proto-clusters are merged. A neighbor of a neighbor is added to the cluster if it has a signal-to-noise ratio above a threshold tcell; tcell = 3 and 0 for EM and hadronic calorimeter cells respectively. The procedure is repeated until the seed list is empty. In a busy environment, especially in the endcap and forward calorimeters, clusters thus formed can grow very large if some energy is deposited between incoming parti- cles. However, overlapping showers can be separated by identifying local maxima in a cluster. After the initial clusters are formed, they are therefore searched for local maxima. If multiple local maxima are found in a cluster, that cluster is split between them. After they have been formed, the energies of both types of clusters are at an uncalibrated scale, often referred to as the raw or EM scale. At this point, topological clusters can be calibrated to the local hadronic energy scale. The clusters are first
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Measurement of the Z boson cross-se
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Contents Title Page . . . . . . . .
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Contents vi Electron reconstruction
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List of Figures 1.1 Proton structur
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List of Figures x 6.17 Muon pT scal
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List of Tables xii 6.18 Decompositi
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Acknowledgments xiv mate Niels van
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Chapter 1: Introduction and Theoret
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Chapter 2 The Accelerator and the E
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Chapter 2: The Accelerator and the
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Chapter 6: Event Selection 163 - In
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Chapter 6: Event Selection 167 with
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Chapter 6: Event Selection 169 Entr
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Chapter 6: Event Selection 171 Entr
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Chapter 6: Event Selection 173 T p
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Chapter 6: Event Selection 177 6.2.
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Chapter 6: Event Selection 189 Reco
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Chapter 6: Event Selection 191 smea
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Chapter 6: Event Selection 193 Firs
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Chapter 6: Event Selection 197 Para
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Chapter 6: Event Selection 199 the
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Chapter 7: Background Estimation 20
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Chapter 8: Properties of Z bosons a
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Chapter 9: Discussion and Outlook 2
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Appendix A: Event list 245 Candidat
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Appendix A: Event list 247 Candidat
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Appendix B: Comparison of muon curv
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Bibliography 251 [13] S. Ask. Statu
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Bibliography 253 [44] S. Frixione,
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Bibliography 255 [75] N. E. Adam an
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Bibliography 257 [102] The TOTEM Co
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