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February 8th, 2007Anne-Marie Magnan - Imperial College London 1 Update on clusterisation studies for MAPS Comparison between 2 methods of clustering Geant4/LCIO problem with 5 μm cells
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February 8th, 2007Anne-Marie Magnan - Imperial College London 2 IDEAL vs REAL cases IDEAL = just geant4 information for the hits. REAL = Geant4 E init in 5x5 μm² cells Sum energy in 50x50 μm² cells E sum Apply charge spread E after charge spread 50 um Add noise to signal hits with σ = 120 eV (1 e- ~ 3 eV 40e- noise) + noise only hits in a 1 cm² tower : proba 10 -5 ~30 hits for 5σ threshold. ● ● ● ● 5 um %E init
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February 8th, 2007Anne-Marie Magnan - Imperial College London 3 Counting vs basic clustering First method Always : factor x2 in the last 10 layers to account for the double tungstene thickness. Counting = Clustering = –Loop over hits classified by number of neighbours, –number of neighbours < 8 : count only 1 (or 2 for last 10 layers) and discard the neighbours. –8 neighbours AND one of the neighbour has 8 neighbours : count 2 (or 4) and discard the neighbours.
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February 8th, 2007Anne-Marie Magnan - Imperial College London 4 Results for 20 and 30 GeV
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February 8th, 2007Anne-Marie Magnan - Imperial College London 5 2nd method Minimisation method Let’s consider 9 cases : hits having between 0 and 8 closest neighbours. E is defined per event i by : with N ij the number of hits having j neighbours for the i th event, and w j the weights that have to be optimised. The average energy for M events is then defined by : We optimise the quantity X : to find the weights, fixing w 0 =1.
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February 8th, 2007Anne-Marie Magnan - Imperial College London 6 Results of 2nd method weightw0w0 w1w1 w2w2 w3w3 w4w4 w5w5 w6w6 w7w7 w8w8 10 GeV 10.8608830.9456810.3028170.3370080.2110530.2806820.0514401-0.327783 20 GeV 13.441952.107750.7151020.8588280.5427010.7895380.174164-0.500572 30 GeV 11.990861.829460.6362830.80790.3931660.6213650.143223-0.0650524
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February 8th, 2007Anne-Marie Magnan - Imperial College London 7 Comparison of 3 methods
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February 8th, 2007Anne-Marie Magnan - Imperial College London 8 Check of minimisation Reapplying the weights on the same sample : check : 22.36/409.9 = 0.05454 minim : 0.05446
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February 8th, 2007Anne-Marie Magnan - Imperial College London 9 Problem with small cells (5x5 μm²)
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February 8th, 2007Anne-Marie Magnan - Imperial College London 10 Just by curiosity : optimised cell size ? IDEAL energy, with only 100 events per point…
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