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2 | <head> |
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3 | <title>Leptoquark Processes</title> |
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29 | |
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30 | <h2>Leptoquark Processes</h2> |
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31 | |
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32 | Leptoquarks arise in many scenarios, and can have widely different |
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33 | characteristics, with respect to spin, isospin amd flavour. |
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34 | The current implentation in no sense attempts to exhaust these |
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35 | possibilities, but only to encode one of the simplest possibilities, |
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36 | with a single scalar leptoquark, denoted <i>LQ</i> and assigned PDG |
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37 | code 42. The leptoquark is assumed to carry specific quark |
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38 | and lepton quantum numbers, by default <i>u</i> quark plus electron. |
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39 | These flavour numbers are conserved, i.e. a process such as |
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40 | <i>u e^- -> LQ -> d nu_e</i> is not allowed. |
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41 | |
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42 | <p/> |
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43 | Although only one leptoquark is implemented, its flavours may be |
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44 | changed arbitrarily to study the different possibilities. The |
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45 | flavours of the leptoquark are defined by the quark and lepton |
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46 | flavours in the decay mode list. Therefore, to change from the |
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47 | current <i>u e^-</i> to <i>c mu^+</i>, say, you only need |
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48 | a line |
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49 | <br/><code>pythia.readString("42:0:products = 4 -13");</code> |
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50 | <br/>in your main program, or the equivalent in a command file. |
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51 | The former must always be a quark, while the latter could be a lepton |
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52 | or an antilepton; a charge-conjugate partner is automatically defined |
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53 | by the program. At initialization, the charge is recalculated as a |
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54 | function of the flavours defined; also the leptoquark name is redefined |
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55 | to be of the type <code>LQ_q,l</code>, where actual quark and lepton |
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56 | flavours are displayed. |
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57 | |
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58 | <p/> |
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59 | The leptoquark is likely to be fairly long-lived, in which case it |
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60 | could have time to fragment into a mesonic- or baryonic-type state, which |
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61 | would decay later on. Currently this posibility is not handled; therefore |
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62 | the leptoquark is always assumed to decay before fragmentation. |
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63 | For that reason the leptoquark can also not be put stable. |
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64 | |
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65 | <h3>Production processes</h3> |
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66 | |
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67 | Four production processes have been implemented, which normally would |
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68 | not overlap and therefore could be run together. |
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69 | |
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70 | <br/><br/><strong>LeptoQuark:all</strong> <input type="radio" name="1" value="on"><strong>On</strong> |
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71 | <input type="radio" name="1" value="off" checked="checked"><strong>Off</strong> |
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72 | (<code>default = <strong>off</strong></code>)<br/> |
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73 | Common switch for the group of lowest-order <i>LQ</i> production |
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74 | processes, i.e. the four ones below. |
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75 | |
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76 | |
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77 | <br/><br/><strong>LeptoQuark:ql2LQ</strong> <input type="radio" name="2" value="on"><strong>On</strong> |
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78 | <input type="radio" name="2" value="off" checked="checked"><strong>Off</strong> |
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79 | (<code>default = <strong>off</strong></code>)<br/> |
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80 | Scatterings <i>q l -> LQ</i>. |
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81 | Code 3201. |
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82 | |
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83 | |
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84 | <br/><br/><strong>LeptoQuark:qg2LQl</strong> <input type="radio" name="3" value="on"><strong>On</strong> |
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85 | <input type="radio" name="3" value="off" checked="checked"><strong>Off</strong> |
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86 | (<code>default = <strong>off</strong></code>)<br/> |
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87 | Scatterings <i>q g -> LQ l</i>. |
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88 | Code 3202. |
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89 | |
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90 | |
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91 | <br/><br/><strong>LeptoQuark:gg2LQLQbar</strong> <input type="radio" name="4" value="on"><strong>On</strong> |
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92 | <input type="radio" name="4" value="off" checked="checked"><strong>Off</strong> |
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93 | (<code>default = <strong>off</strong></code>)<br/> |
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94 | Scatterings <i>g g -> LQ LQbar</i>. |
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95 | Code 3203. |
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96 | |
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97 | |
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98 | <br/><br/><strong>LeptoQuark:qqbar2LQLQbar</strong> <input type="radio" name="5" value="on"><strong>On</strong> |
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99 | <input type="radio" name="5" value="off" checked="checked"><strong>Off</strong> |
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100 | (<code>default = <strong>off</strong></code>)<br/> |
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101 | Scatterings <i>q qbar -> LQ LQbar</i>. |
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102 | Code 3204. |
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103 | |
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104 | |
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105 | <h3>Parameters</h3> |
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106 | |
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107 | In the above scenario the main free parameters are the leptoquark flavour |
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108 | content, set as already described, and the <i>LQ</i> mass, set as usual. |
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109 | In addition there is one further parameter. |
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110 | |
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111 | <br/><br/><table><tr><td><strong>LeptoQuark:kCoup </td><td></td><td> <input type="text" name="6" value="1.0" size="20"/> (<code>default = <strong>1.0</strong></code>; <code>minimum = 0.0</code>)</td></tr></table> |
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112 | multiplicative factor in the <i>LQ -> q l</i> squared Yukawa coupling, |
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113 | and thereby in the <i>LQ</i> width and the <i>q l -> LQ</i> and |
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114 | other cross sections. Specifically, <i>lambda^2/(4 pi) = k alpha_em</i>, |
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115 | i.e. it corresponds to the $k$ factor of [<a href="Bibliography.php" target="page">Hew88</a>]. |
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116 | |
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117 | |
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120 | <?php |
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124 | </form> |
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125 | |
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126 | <?php |
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127 | |
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128 | if($_POST["saved"] == 1) |
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129 | { |
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130 | $filepath = $_POST["filepath"]; |
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131 | $handle = fopen($filepath, 'a'); |
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132 | |
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133 | if($_POST["1"] != "off") |
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134 | { |
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135 | $data = "LeptoQuark:all = ".$_POST["1"]."\n"; |
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136 | fwrite($handle,$data); |
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137 | } |
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138 | if($_POST["2"] != "off") |
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139 | { |
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140 | $data = "LeptoQuark:ql2LQ = ".$_POST["2"]."\n"; |
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141 | fwrite($handle,$data); |
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142 | } |
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143 | if($_POST["3"] != "off") |
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144 | { |
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145 | $data = "LeptoQuark:qg2LQl = ".$_POST["3"]."\n"; |
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146 | fwrite($handle,$data); |
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147 | } |
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148 | if($_POST["4"] != "off") |
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149 | { |
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150 | $data = "LeptoQuark:gg2LQLQbar = ".$_POST["4"]."\n"; |
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151 | fwrite($handle,$data); |
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152 | } |
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153 | if($_POST["5"] != "off") |
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154 | { |
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155 | $data = "LeptoQuark:qqbar2LQLQbar = ".$_POST["5"]."\n"; |
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156 | fwrite($handle,$data); |
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157 | } |
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158 | if($_POST["6"] != "1.0") |
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159 | { |
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160 | $data = "LeptoQuark:kCoup = ".$_POST["6"]."\n"; |
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161 | fwrite($handle,$data); |
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162 | } |
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163 | fclose($handle); |
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164 | } |
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165 | |
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166 | ?> |
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168 | </html> |
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169 | |
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170 | <!-- Copyright (C) 2012 Torbjorn Sjostrand --> |
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171 | |
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