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| 3 | <title>A Second Hard Process</title> |
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| 28 | <form method='post' action='ASecondHardProcess.php'> |
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| 29 | |
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| 30 | <h2>A Second Hard Process</h2> |
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| 31 | |
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| 32 | When you have selected a set of hard processes for hadron beams, the |
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| 33 | <?php $filepath = $_GET["filepath"]; |
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| 34 | echo "<a href='MultipartonInteractions.php?filepath=".$filepath."' target='page'>";?>multiparton interactions</a> |
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| 35 | framework can add further interactions to build up a realistic |
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| 36 | underlying event. These further interactions can come from a wide |
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| 37 | variety of processes, and will occasionally be quite hard. They |
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| 38 | do represent a realistic random mix, however, which means one cannot |
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| 39 | predetermine what will happen. Occasionally there may be cases |
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| 40 | where one wants to specify also the second hard interaction rather |
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| 41 | precisely. The options on this page allow you to do precisely that. |
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| 42 | |
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| 43 | <br/><br/><strong>SecondHard:generate</strong> <input type="radio" name="1" value="on"><strong>On</strong> |
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| 44 | <input type="radio" name="1" value="off" checked="checked"><strong>Off</strong> |
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| 45 | (<code>default = <strong>off</strong></code>)<br/> |
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| 46 | Generate two hard scatterings in a collision between hadron beams. |
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| 47 | The hardest process can be any combination of internal processes, |
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| 48 | available in the normal <?php $filepath = $_GET["filepath"]; |
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| 49 | echo "<a href='ProcessSelection.php?filepath=".$filepath."' target='page'>";?>process |
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| 50 | selection</a> machinery, or external input. Here you must further |
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| 51 | specify which set of processes to allow for the second hard one, see |
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| 52 | the following. |
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| 53 | |
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| 54 | |
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| 55 | <h3>Process Selection</h3> |
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| 56 | |
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| 57 | In principle the whole <?php $filepath = $_GET["filepath"]; |
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| 58 | echo "<a href='ProcessSelection.php?filepath=".$filepath."' target='page'>";?>process |
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| 59 | selection</a> allowed for the first process could be repeated |
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| 60 | for the second one. However, this would probably be overkill. |
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| 61 | Therefore here a more limited set of prepackaged process collections |
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| 62 | are made available, that can then be further combined at will. |
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| 63 | Since the description is almost completely symmetric between the |
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| 64 | first and the second process, you always have the possibility |
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| 65 | to pick one of the two processes according to the complete list |
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| 66 | of possibilities. |
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| 67 | |
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| 68 | <p/> |
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| 69 | Here comes the list of allowed sets of processes, to combine at will: |
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| 70 | |
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| 71 | <br/><br/><strong>SecondHard:TwoJets</strong> <input type="radio" name="2" value="on"><strong>On</strong> |
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| 72 | <input type="radio" name="2" value="off" checked="checked"><strong>Off</strong> |
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| 73 | (<code>default = <strong>off</strong></code>)<br/> |
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| 74 | Standard QCD <i>2 -> 2</i> processes involving gluons and |
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| 75 | <i>d, u, s, c, b</i> quarks. |
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| 76 | |
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| 77 | |
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| 78 | <br/><br/><strong>SecondHard:PhotonAndJet</strong> <input type="radio" name="3" value="on"><strong>On</strong> |
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| 79 | <input type="radio" name="3" value="off" checked="checked"><strong>Off</strong> |
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| 80 | (<code>default = <strong>off</strong></code>)<br/> |
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| 81 | A prompt photon recoiling against a quark or gluon jet. |
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| 82 | |
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| 83 | <br/><br/><strong>SecondHard:TwoPhotons</strong> <input type="radio" name="4" value="on"><strong>On</strong> |
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| 84 | <input type="radio" name="4" value="off" checked="checked"><strong>Off</strong> |
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| 85 | (<code>default = <strong>off</strong></code>)<br/> |
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| 86 | Two prompt photons recoiling against each other. |
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| 87 | |
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| 88 | <br/><br/><strong>SecondHard:Charmonium</strong> <input type="radio" name="5" value="on"><strong>On</strong> |
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| 89 | <input type="radio" name="5" value="off" checked="checked"><strong>Off</strong> |
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| 90 | (<code>default = <strong>off</strong></code>)<br/> |
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| 91 | Production of charmonium via colour singlet and colour octet channels. |
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| 92 | |
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| 93 | <br/><br/><strong>SecondHard:Bottomonium</strong> <input type="radio" name="6" value="on"><strong>On</strong> |
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| 94 | <input type="radio" name="6" value="off" checked="checked"><strong>Off</strong> |
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| 95 | (<code>default = <strong>off</strong></code>)<br/> |
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| 96 | Production of bottomonium via colour singlet and colour octet channels. |
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| 97 | |
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| 98 | <br/><br/><strong>SecondHard:SingleGmZ</strong> <input type="radio" name="7" value="on"><strong>On</strong> |
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| 99 | <input type="radio" name="7" value="off" checked="checked"><strong>Off</strong> |
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| 100 | (<code>default = <strong>off</strong></code>)<br/> |
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| 101 | Scattering <i>q qbar -> gamma^*/Z^0</i>, with full interference |
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| 102 | between the <i>gamma^*</i> and <i>Z^0</i>. |
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| 103 | |
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| 104 | |
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| 105 | <br/><br/><strong>SecondHard:SingleW</strong> <input type="radio" name="8" value="on"><strong>On</strong> |
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| 106 | <input type="radio" name="8" value="off" checked="checked"><strong>Off</strong> |
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| 107 | (<code>default = <strong>off</strong></code>)<br/> |
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| 108 | Scattering <i>q qbar' -> W^+-</i>. |
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| 109 | |
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| 110 | |
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| 111 | <br/><br/><strong>SecondHard:GmZAndJet</strong> <input type="radio" name="9" value="on"><strong>On</strong> |
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| 112 | <input type="radio" name="9" value="off" checked="checked"><strong>Off</strong> |
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| 113 | (<code>default = <strong>off</strong></code>)<br/> |
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| 114 | Scattering <i>q qbar -> gamma^*/Z^0 g</i> and |
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| 115 | <i>q g -> gamma^*/Z^0 q</i>. |
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| 116 | |
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| 117 | |
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| 118 | <br/><br/><strong>SecondHard:WAndJet</strong> <input type="radio" name="10" value="on"><strong>On</strong> |
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| 119 | <input type="radio" name="10" value="off" checked="checked"><strong>Off</strong> |
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| 120 | (<code>default = <strong>off</strong></code>)<br/> |
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| 121 | Scattering <i>q qbar' -> W^+- g</i> and |
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| 122 | <i>q g -> W^+- q'</i>. |
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| 123 | |
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| 124 | |
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| 125 | <br/><br/><strong>SecondHard:TopPair</strong> <input type="radio" name="11" value="on"><strong>On</strong> |
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| 126 | <input type="radio" name="11" value="off" checked="checked"><strong>Off</strong> |
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| 127 | (<code>default = <strong>off</strong></code>)<br/> |
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| 128 | Production of a top pair, either via QCD processes or via an |
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| 129 | intermediate <i>gamma^*/Z^0</i> resonance. |
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| 130 | |
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| 131 | |
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| 132 | <br/><br/><strong>SecondHard:SingleTop</strong> <input type="radio" name="12" value="on"><strong>On</strong> |
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| 133 | <input type="radio" name="12" value="off" checked="checked"><strong>Off</strong> |
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| 134 | (<code>default = <strong>off</strong></code>)<br/> |
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| 135 | Production of a single top, either via a <i>t-</i> or |
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| 136 | an <i>s-</i>channel <i>W^+-</i> resonance. |
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| 137 | |
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| 138 | |
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| 139 | <p/> |
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| 140 | A further process collection comes with a warning flag: |
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| 141 | |
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| 142 | <br/><br/><strong>SecondHard:TwoBJets</strong> <input type="radio" name="13" value="on"><strong>On</strong> |
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| 143 | <input type="radio" name="13" value="off" checked="checked"><strong>Off</strong> |
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| 144 | (<code>default = <strong>off</strong></code>)<br/> |
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| 145 | The <i>q qbar -> b bbar</i> and <i>g g -> b bbar</i> processes. |
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| 146 | These are already included in the <code>TwoJets</code> sample above, |
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| 147 | so it would be doublecounting to include both, but we assume there |
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| 148 | may be cases where the <i>b</i> subsample will be of special interest. |
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| 149 | This subsample does not include flavour-excitation or gluon-splitting |
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| 150 | contributions to the <i>b</i> rate, however, so, depending |
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| 151 | on the topology if interest, it may or may not be a good approximation. |
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| 152 | |
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| 153 | |
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| 154 | <h3>Cuts and scales</h3> |
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| 155 | |
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| 156 | The second hard process obeys exactly the same selection rules for |
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| 157 | <?php $filepath = $_GET["filepath"]; |
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| 158 | echo "<a href='PhaseSpaceCuts.php?filepath=".$filepath."' target='page'>";?>phase space cuts</a> and |
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| 159 | <?php $filepath = $_GET["filepath"]; |
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| 160 | echo "<a href='CouplingsAndScales.php?filepath=".$filepath."' target='page'>";?>couplings and scales</a> |
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| 161 | as the first one does. Specifically, a <i>pTmin</i> cut for |
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| 162 | <i>2 -> 2</i> processes would apply to the first and the second hard |
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| 163 | process alike, and ballpark half of the time the second could be |
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| 164 | generated with a larger <i>pT</i> than the first. (Exact numbers |
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| 165 | depending on the relative shape of the two cross sections.) That is, |
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| 166 | first and second is only used as an administrative distinction between |
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| 167 | the two, not as a physics ordering one. |
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| 168 | |
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| 169 | <p/> |
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| 170 | Optionally it is possible to pick the mass and <i>pT</i> |
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| 171 | <?php $filepath = $_GET["filepath"]; |
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| 172 | echo "<a href='PhaseSpaceCuts.php?filepath=".$filepath."' target='page'>";?>phase space cuts</a> separately for |
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| 173 | the second hard interaction. The main application presumably would |
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| 174 | be to allow a second process that is softer than the first, but still |
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| 175 | hard. But one is also free to make the second process harder than the |
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| 176 | first, if desired. So long as the two <i>pT</i> (or mass) ranges |
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| 177 | overlap the ordering will not be the same in all events, however. |
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| 178 | |
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| 179 | <h3>Cross-section calculation</h3> |
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| 180 | |
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| 181 | As an introduction, a brief reminder of Poissonian statistics. |
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| 182 | Assume a stochastic process in time, for now not necessarily a |
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| 183 | high-energy physics one, where the probability for an event to occur |
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| 184 | at any given time is independent of what happens at other times. |
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| 185 | Then the probability for <i>n</i> events to occur in a finite |
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| 186 | time interval is |
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| 187 | <br/><i> |
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| 188 | P_n = <n>^n exp(-<n>) / n! |
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| 189 | </i><br/> |
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| 190 | where <i><n></i> is the average number of events. If this |
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| 191 | number is small we can approximate <i>exp(-<n>) = 1 </i>, |
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| 192 | so that <i>P_1 = <n></i> and |
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| 193 | <i>P_2 = <n>^2 / 2 = P_1^2 / 2</i>. |
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| 194 | |
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| 195 | <p/> |
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| 196 | Now further assume that the events actually are of two different |
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| 197 | kinds <i>a</i> and <i>b</i>, occuring independently of each |
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| 198 | other, such that <i><n> = <n_a> + <n_b></i>. |
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| 199 | It then follows that the probability of having one event of type |
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| 200 | <i>a</i> (or <i>b</i>) and nothing else is |
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| 201 | <i>P_1a = <n_a></i> (or <i>P_1b = <n_b></i>). |
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| 202 | From |
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| 203 | <br/><i> |
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| 204 | P_2 = (<n_a> + <n_b>)^2 / 2 = (P_1a + P_1b)^2 / 2 = |
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| 205 | (P_1a^2 + 2 P_1a P_1b + P_1b^2) / 2 |
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| 206 | </i><br/> |
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| 207 | it is easy to read off that the probability to have exactly two |
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| 208 | events of kind <i>a</i> and none of <i>b</i> is |
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| 209 | <i>P_2aa = P_1a^2 / 2</i> whereas that of having one <i>a</i> |
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| 210 | and one <i>b</i> is <i>P_2ab = P_1a P_1b</i>. Note that the |
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| 211 | former, with two identical events, contains a factor <i>1/2</i> |
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| 212 | while the latter, with two different ones, does not. If viewed |
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| 213 | in a time-ordered sense, the difference is that the latter can be |
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| 214 | obtained two ways, either first an <i>a</i> and then a <i>b</i> |
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| 215 | or else first a <i>b</i> and then an <i>a</i>. |
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| 216 | |
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| 217 | <p/> |
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| 218 | To translate this language into cross-sections for high-energy |
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| 219 | events, we assume that interactions can occur at different <i>pT</i> |
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| 220 | values independently of each other inside inelastic nondiffractive |
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| 221 | (= "minbias") events. Then the above probabilities translate into |
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| 222 | <i>P_n = sigma_n / sigma_ND</i> where <i>sigma_ND</i> is the |
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| 223 | total nondiffractive cross section. Again we want to assume that |
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| 224 | <i>exp(-<n>)</i> is close to unity, i.e. that the total |
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| 225 | hard cross section above <i>pTmin</i> is much smaller than |
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| 226 | <i>sigma_ND</i>. The hard cross section is dominated by QCD |
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| 227 | jet production, and a reasonable precaution is to require a |
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| 228 | <i>pTmin</i> of at least 20 GeV at LHC energies. |
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| 229 | (For <i>2 -> 1</i> processes such as |
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| 230 | <i>q qbar -> gamma^*/Z^0 (-> f fbar)</i> one can instead make a |
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| 231 | similar cut on mass.) Then the generic equation |
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| 232 | <i>P_2 = P_1^2 / 2</i> translates into |
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| 233 | <i>sigma_2/sigma_ND = (sigma_1 / sigma_ND)^2 / 2</i> or |
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| 234 | <i>sigma_2 = sigma_1^2 / (2 sigma_ND)</i>. |
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| 235 | |
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| 236 | <p/> |
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| 237 | Again different processes <i>a, b, c, ...</i> contribute, |
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| 238 | and by the same reasoning we obtain |
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| 239 | <i>sigma_2aa = sigma_1a^2 / (2 sigma_ND)</i>, |
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| 240 | <i>sigma_2ab = sigma_1a sigma_1b / sigma_ND</i>, |
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| 241 | and so on. |
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| 242 | |
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| 243 | <p/> |
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| 244 | There is one important correction to this picture: all collisions |
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| 245 | do no occur under equal conditions. Some are more central in impact |
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| 246 | parameter, others more peripheral. This leads to a further element of |
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| 247 | variability: central collisions are likely to have more activity |
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| 248 | than the average, peripheral less. Integrated over impact |
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| 249 | parameter standard cross sections are recovered, but correlations |
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| 250 | are affected by a "trigger bias" effect: if you select for events |
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| 251 | with a hard process you favour events at small impact parameter |
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| 252 | which have above-average activity, and therefore also increased |
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| 253 | chance for further interactions. (In PYTHIA this is the origin |
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| 254 | of the "pedestal effect", i.e. that events with a hard interaction |
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| 255 | have more underlying activity than the level found in minimum-bias |
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| 256 | events.) When you specify a matter overlap profile in the |
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| 257 | multiparton-interactions scenario, such an enhancement/depletion factor |
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| 258 | <i>f_impact</i> is chosen event-by-event and can be averaged |
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| 259 | during the course of the run. As an example, the double Gaussian |
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| 260 | form used in Tune A gives approximately |
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| 261 | <i><f_impact> = 2.5</i>. The above equations therefore |
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| 262 | have to be modified to |
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| 263 | <i>sigma_2aa = <f_impact> sigma_1a^2 / (2 sigma_ND)</i>, |
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| 264 | <i>sigma_2ab = <f_impact> sigma_1a sigma_1b / sigma_ND</i>. |
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| 265 | Experimentalists often instead use the notation |
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| 266 | <i>sigma_2ab = sigma_1a sigma_1b / sigma_eff</i>, |
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| 267 | from which we see that PYTHIA "predicts" |
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| 268 | <i>sigma_eff = sigma_ND / <f_impact></i>. |
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| 269 | When the generation of multiparton interactions is switched off it is |
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| 270 | not possible to calculate <i><f_impact></i> and therefore |
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| 271 | it is set to unity. |
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| 272 | |
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| 273 | <p/> |
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| 274 | When this recipe is to be applied to calculate |
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| 275 | actual cross sections, it is useful to distinguish three cases, |
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| 276 | depending on which set of processes are selected to study for |
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| 277 | the first and second interaction. |
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| 278 | |
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| 279 | <p/> |
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| 280 | (1) The processes <i>a</i> for the first interaction and |
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| 281 | <i>b</i> for the second one have no overlap at all. |
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| 282 | For instance, the first could be <code>TwoJets</code> and the |
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| 283 | second <code>TwoPhotons</code>. In that case, the two interactions |
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| 284 | can be selected independently, and cross sections tabulated |
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| 285 | for each separate subprocess in the two above classes. At the |
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| 286 | end of the run, the cross sections in <i>a</i> should be multiplied |
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| 287 | by <i><f_impact> sigma_1b / sigma_ND</i> to bring them to |
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| 288 | the correct overall level, and those in <i>b</i> by |
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| 289 | <i><f_impact> sigma_1a / sigma_ND</i>. |
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| 290 | |
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| 291 | <p/> |
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| 292 | (2) Exactly the same processes <i>a</i> are selected for the |
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| 293 | first and second interaction. In that case it works as above, |
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| 294 | with <i>a = b</i>, and it is only necessary to multiply by an |
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| 295 | additional factor <i>1/2</i>. A compensating factor of 2 |
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| 296 | is automatically obtained for picking two different subprocesses, |
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| 297 | e.g. if <code>TwoJets</code> is selected for both interactions, |
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| 298 | then the combination of the two subprocesses <i>q qbar -> g g</i> |
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| 299 | and <i>g g -> g g</i> can trivially be obtained two ways. |
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| 300 | |
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| 301 | <p/> |
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| 302 | (3) The list of subprocesses partly but not completely overlap. |
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| 303 | For instance, the first process is allowed to contain <i>a</i> |
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| 304 | or <i>c</i> and the second <i>b</i> or <i>c</i>, where |
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| 305 | there is no overlap between <i>a</i> and <i>b</i>. Then, |
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| 306 | when an independent selection for the first and second interaction |
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| 307 | both pick one of the subprocesses in <i>c</i>, half of those |
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| 308 | events have to be thrown, and the stored cross section reduced |
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| 309 | accordingly. Considering the four possible combinations of first |
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| 310 | and second process, this gives a |
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| 311 | <br/><i> |
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| 312 | sigma'_1 = sigma_1a + sigma_1c * (sigma_2b + sigma_2c/2) / |
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| 313 | (sigma_2b + sigma_2c) |
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| 314 | </i><br/> |
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| 315 | with the factor <i>1/2</i> for the <i>sigma_1c sigma_2c</i> term. |
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| 316 | At the end of the day, this <i>sigma'_1</i> should be multiplied |
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| 317 | by the normalization factor |
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| 318 | <br/><i> |
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| 319 | f_1norm = <f_impact> (sigma_2b + sigma_2c) / sigma_ND |
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| 320 | </i><br/> |
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| 321 | here without a factor <i>1/2</i> (or else it would have been |
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| 322 | doublecounted). This gives the correct |
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| 323 | <br/><i> |
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| 324 | (sigma_2b + sigma_2c) * sigma'_1 = sigma_1a * sigma_2b |
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| 325 | + sigma_1a * sigma_2c + sigma_1c * sigma_2b + sigma_1c * sigma_2c/2 |
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| 326 | </i><br/> |
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| 327 | The second interaction can be handled in exact analogy. |
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| 328 | |
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| 329 | <p/> |
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| 330 | For the considerations above it is assumed that the phase space cuts |
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| 331 | are the same for the two processes. It is possible to set the mass and |
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| 332 | transverse momentum cuts differently, however. This changes nothing |
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| 333 | for processes that already are different. For two collisions of the |
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| 334 | same type it is partly a matter of interpretation what is intended. |
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| 335 | If we consider the case of the same process in two non-overlapping |
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| 336 | phase space regions, most likely we want to consider them as |
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| 337 | separate processes, in the sense that we expect a factor 2 relative |
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| 338 | to Poissonian statistics from either of the two hardest processes |
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| 339 | populating either of the two phase space regions. In total we are |
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| 340 | therefore lead to adopt the same strategy as in case (3) above: |
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| 341 | only in the overlapping part of the two allowed phase space regions |
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| 342 | could two processes be identical and thus appear with a 1/2 factor, |
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| 343 | elsewhere the two processes are never identical and do not |
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| 344 | include the 1/2 factor. We reiterate, however, that the case of |
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| 345 | partly but not completely overlapping phase space regions for one and |
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| 346 | the same process is tricky, and not to be used without prior |
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| 347 | deliberation. |
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| 348 | |
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| 349 | <p/> |
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| 350 | The listing obtained with the <code>pythia.statistics()</code> |
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| 351 | already contain these corrections factors, i.e. cross sections |
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| 352 | are for the occurence of two interactions of the specified kinds. |
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| 353 | There is not a full tabulation of the matrix of all the possible |
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| 354 | combinations of a specific first process together with a specific |
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| 355 | second one (but the information is there for the user to do that, |
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| 356 | if desired). Instead <code>pythia.statistics()</code> shows this |
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| 357 | matrix projected onto the set of processes and associated cross |
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| 358 | sections for the first and the second interaction, respectively. |
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| 359 | Up to statistical fluctuations, these two sections of the |
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| 360 | <code>pythia.statistics()</code> listing both add up to the same |
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| 361 | total cross section for the event sample. |
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| 362 | |
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| 363 | <p/> |
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| 364 | There is a further special feature to be noted for this listing, |
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| 365 | and that is the difference between the number of "selected" events |
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| 366 | and the number of "accepted" ones. Here is how that comes about. |
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| 367 | Originally the first and second process are selected completely |
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| 368 | independently. The generation (in)efficiency is reflected in the |
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| 369 | different number of intially tried events for the first and second |
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| 370 | process, leading to the same number of selected events. While |
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| 371 | acceptable on their own, the combination of the two processes may |
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| 372 | be unacceptable, however. It may be that the two processes added |
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| 373 | together use more energy-momentum than kinematically allowed, or, |
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| 374 | even if not, are disfavoured when the PYTHIA approach to provide |
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| 375 | correlated parton densities is applied. Alternatively, referring |
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| 376 | to case (3) above, it may be because half of the events should |
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| 377 | be thrown for identical processes. Taken together, it is these |
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| 378 | effects that reduced the event number from "selected" to "accepted". |
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| 379 | (A further reduction may occur if a |
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| 380 | <?php $filepath = $_GET["filepath"]; |
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| 381 | echo "<a href='UserHooks.php?filepath=".$filepath."' target='page'>";?>user hook</a> rejects some events.) |
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| 382 | |
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| 383 | <p/> |
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| 384 | It is allowed to use external Les Houches Accord input for the |
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| 385 | hardest process, and then pick an internal one for the second hardest. |
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| 386 | In this case PYTHIA does not have access to your thinking concerning |
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| 387 | the external process, and cannot know whether it overlaps with the |
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| 388 | internal or not. (External events <i>q qbar' -> e+ nu_e</i> could |
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| 389 | agree with the internal <i>W</i> ones, or be a <i>W'</i> resonance |
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| 390 | in a BSM scenario, to give one example.) Therefore the combined cross |
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| 391 | section is always based on the scenario (1) above. Corrections for |
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| 392 | correlated parton densities are included also in this case, however. |
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| 393 | That is, an external event that takes a large fraction of the incoming |
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| 394 | beam momenta stands a fair chance of being rejected when it has to be |
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| 395 | combined with another hard process. For this reason the "selected" and |
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| 396 | "accepted" event numbers are likely to disagree. |
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| 397 | |
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| 398 | <p/> |
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| 399 | In the cross section calculation above, the <i>sigma'_1</i> |
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| 400 | cross sections are based on the number of accepted events, while |
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| 401 | the <i>f_1norm</i> factor is evaluated based on the cross sections |
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| 402 | for selected events. That way the suppression by correlations |
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| 403 | between the two processes does not get to be doublecounted. |
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| 404 | |
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| 405 | <p/> |
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| 406 | The <code>pythia.statistics()</code> listing contains two final |
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| 407 | lines, indicating the summed cross sections <i>sigma_1sum</i> and |
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| 408 | <i>sigma_2sum</i> for the first and second set of processes, at |
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| 409 | the "selected" stage above, plus information on the <i>sigma_ND</i> |
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| 410 | and <i><f_impact></i> used. The total cross section |
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| 411 | generated is related to this by |
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| 412 | <br/><i> |
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| 413 | <f_impact> * (sigma_1sum * sigma_2sum / sigma_ND) * |
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| 414 | (n_accepted / n_selected) |
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| 415 | </i><br/> |
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| 416 | with an additional factor of <i>1/2</i> for case 2 above. |
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| 417 | |
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| 418 | <p/> |
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| 419 | The error quoted for the cross section of a process is a combination |
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| 420 | in quadrature of the error on this process alone with the error on |
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| 421 | the normalization factor, including the error on |
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| 422 | <i><f_impact></i>. As always it is a purely statistical one |
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| 423 | and of course hides considerably bigger systematic uncertainties. |
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| 424 | |
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| 425 | <h3>Event information</h3> |
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| 426 | |
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| 427 | Normally the <code>process</code> event record only contains the |
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| 428 | hardest interaction, but in this case also the second hardest |
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| 429 | is stored there. If both of them are <i>2 -> 2</i> ones, the |
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| 430 | first would be stored in lines 3 - 6 and the second in 7 - 10. |
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| 431 | For both, status codes 21 - 29 would be used, as for a hardest |
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| 432 | process. Any resonance decay chains would occur after the two |
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| 433 | main processes, to allow normal parsing. The beams in 1 and 2 |
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| 434 | only appear in one copy. This structure is echoed in the |
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| 435 | full <code>event</code> event record. |
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| 436 | |
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| 437 | <p/> |
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| 438 | Most of the properties accessible by the |
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| 439 | <code><?php $filepath = $_GET["filepath"]; |
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| 440 | echo "<a href='EventInformation.php?filepath=".$filepath."' target='page'>";?>pythia.info</a></code> |
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| 441 | methods refer to the first process, whether that happens to be the |
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| 442 | hardest or not. The code and <i>pT</i> scale of the second process |
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| 443 | are accessible by the <code>info.codeMPI(1)</code> and |
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| 444 | <code>info.pTMPI(1)</code>, however. |
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| 445 | |
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| 446 | <p/> |
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| 447 | The <code>sigmaGen()</code> and <code>sigmaErr()</code> methods provide |
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| 448 | the cross section and its error for the event sample as a whole, |
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| 449 | combining the information from the two hard processes as described |
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| 450 | above. In particular, the former should be used to give the |
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| 451 | weight of the generated event sample. The statitical error estimate |
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| 452 | is somewhat cruder and gives a larger value than the |
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| 453 | subprocess-by-subprocess one employed in |
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| 454 | <code>pythia.statistics()</code>, but this number is |
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| 455 | anyway less relevant, since systematical errors are likely to dominate. |
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| 456 | |
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| 457 | <input type="hidden" name="saved" value="1"/> |
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| 458 | |
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| 459 | <?php |
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| 460 | echo "<input type='hidden' name='filepath' value='".$_GET["filepath"]."'/>"?> |
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| 461 | |
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| 462 | <table width="100%"><tr><td align="right"><input type="submit" value="Save Settings" /></td></tr></table> |
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| 463 | </form> |
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| 464 | |
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| 465 | <?php |
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| 466 | |
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| 467 | if($_POST["saved"] == 1) |
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| 468 | { |
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| 469 | $filepath = $_POST["filepath"]; |
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| 470 | $handle = fopen($filepath, 'a'); |
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| 471 | |
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| 472 | if($_POST["1"] != "off") |
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| 473 | { |
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| 474 | $data = "SecondHard:generate = ".$_POST["1"]."\n"; |
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| 475 | fwrite($handle,$data); |
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| 476 | } |
---|
| 477 | if($_POST["2"] != "off") |
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| 478 | { |
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| 479 | $data = "SecondHard:TwoJets = ".$_POST["2"]."\n"; |
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| 480 | fwrite($handle,$data); |
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| 481 | } |
---|
| 482 | if($_POST["3"] != "off") |
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| 483 | { |
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| 484 | $data = "SecondHard:PhotonAndJet = ".$_POST["3"]."\n"; |
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| 485 | fwrite($handle,$data); |
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| 486 | } |
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| 487 | if($_POST["4"] != "off") |
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| 488 | { |
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| 489 | $data = "SecondHard:TwoPhotons = ".$_POST["4"]."\n"; |
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| 490 | fwrite($handle,$data); |
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| 491 | } |
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| 492 | if($_POST["5"] != "off") |
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| 493 | { |
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| 494 | $data = "SecondHard:Charmonium = ".$_POST["5"]."\n"; |
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| 495 | fwrite($handle,$data); |
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| 496 | } |
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| 497 | if($_POST["6"] != "off") |
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| 498 | { |
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| 499 | $data = "SecondHard:Bottomonium = ".$_POST["6"]."\n"; |
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| 500 | fwrite($handle,$data); |
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| 501 | } |
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| 502 | if($_POST["7"] != "off") |
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| 503 | { |
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| 504 | $data = "SecondHard:SingleGmZ = ".$_POST["7"]."\n"; |
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| 505 | fwrite($handle,$data); |
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| 506 | } |
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| 507 | if($_POST["8"] != "off") |
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| 508 | { |
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| 509 | $data = "SecondHard:SingleW = ".$_POST["8"]."\n"; |
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| 510 | fwrite($handle,$data); |
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| 511 | } |
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| 512 | if($_POST["9"] != "off") |
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| 513 | { |
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| 514 | $data = "SecondHard:GmZAndJet = ".$_POST["9"]."\n"; |
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| 515 | fwrite($handle,$data); |
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| 516 | } |
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| 517 | if($_POST["10"] != "off") |
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| 518 | { |
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| 519 | $data = "SecondHard:WAndJet = ".$_POST["10"]."\n"; |
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| 520 | fwrite($handle,$data); |
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| 521 | } |
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| 522 | if($_POST["11"] != "off") |
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| 523 | { |
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| 524 | $data = "SecondHard:TopPair = ".$_POST["11"]."\n"; |
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| 525 | fwrite($handle,$data); |
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| 526 | } |
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| 527 | if($_POST["12"] != "off") |
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| 528 | { |
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| 529 | $data = "SecondHard:SingleTop = ".$_POST["12"]."\n"; |
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| 530 | fwrite($handle,$data); |
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| 531 | } |
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| 532 | if($_POST["13"] != "off") |
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| 533 | { |
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| 534 | $data = "SecondHard:TwoBJets = ".$_POST["13"]."\n"; |
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| 535 | fwrite($handle,$data); |
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| 536 | } |
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| 537 | fclose($handle); |
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| 538 | } |
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| 539 | |
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| 540 | ?> |
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| 541 | </body> |
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| 542 | </html> |
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| 543 | |
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| 544 | <!-- Copyright (C) 2012 Torbjorn Sjostrand --> |
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