| 1 | ------------------------------------------------------------------------
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| 2 | SoftKiller FastJet contrib
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| 3 | ------------------------------------------------------------------------
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| 4 |
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| 5 | The SoftKiller FastJet contrib aims to provide an implementation of
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| 6 | the pileup removal technique introduced in
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| 7 |
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| 8 | SoftKiller, a particle-level pileup removal method
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| 9 | Matteo Cacciari, Gavin P. Salam, Gregory Soyez
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| 10 | arXiv:1407.0408
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| 11 |
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| 12 | The SoftKiller class progressively kills soft particles in order of
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| 13 | increasing pt until half of the event is empty (i.e. rho is zero).
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| 14 | It is constructed using
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| 15 |
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| 16 | SoftKiller soft_killer(double rapmax, double grid_spacing,
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| 17 | Selector sifter = Selector());
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| 18 |
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| 19 | with
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| 20 |
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| 21 | rapmax the maximal (absolute) rapidity extent of the grid
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| 22 | tile_size the requested grid spacing (or equivalent tile size)
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| 23 | sifter when provided, the soft killer is applied
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| 24 | only to particles that pass the sifter (the
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| 25 | others are kept untouched)
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| 26 |
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| 27 | For a given event, the SoftKiller is then applied to an event as follows
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| 28 |
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| 29 | vector<PseudoJet> event;
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| 30 | vector<PseudoJet> killed_event = soft_killer(event);
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| 31 |
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| 32 | For an explicit illustration of how this works, see the example.cc
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| 33 | file which can be built using
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| 34 |
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| 35 | make example
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| 36 |
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| 37 | and should be run with
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| 38 |
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| 39 | ./example < ../data/Pythia-Zp2jets-lhc-pileup-1ev.dat
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| 40 |
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| 41 | The expected output can be found in example.ref
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| 42 |
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| 43 | ----------------------------------------------------------------------
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| 44 | More advanced usage
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| 45 | ===================
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| 46 |
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| 47 | If you have FastJet 3.1, then you can use its RectangularGrid to have
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| 48 | obtain control over the grid; for example to apply a soft killer
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| 49 | separately to central and forward particles you might have:
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| 50 |
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| 51 | double central_rapmax = 2.5, forward_rapmax = 5.0, tile_size = 0.5;
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| 52 |
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| 53 | // the central SK runs from -central_rapmax to central_rapmax; we
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| 54 | // can have separate rapidity and phi tile sizes, but here keep
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| 55 | // them the same
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| 56 | RectangularGrid central_grid(-central_rapmax, central_rapmax, tile_size, tile_size);
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| 57 | SoftKiller central_killer(central_grid);
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| 58 | Selector central_selector = SelectorAbsRapMax(central_rapmax); // for later use
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| 59 |
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| 60 | // for the forward SK, we have a grid from -5.0 to 5.0 but then use
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| 61 | // only grid tiles whose central point passes the forward selector
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| 62 | Selector forward_selector = SelectorAbsRapRange(central_rapmax, forward_rapmax);
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| 63 | RectangularGrid forward_grid(-forward_rapma, forward_rapmax, tile_size, tile_size, forward_selector);
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| 64 | SoftKiller central_killer(forward_grid);
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| 65 |
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| 66 | // now process central and forward particles separately
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| 67 | vector<PseudoJet> central_kept_particles = central_killer(central_selector(particles));
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| 68 | vector<PseudoJet> forward_kept_particles = forward_killer(forward_selector(particles));
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| 69 |
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| 70 |
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