1 | <chapter name="Hadron Scattering"> |
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2 | |
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3 | <h2>Hadron Scattering</h2> |
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4 | |
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5 | A simple hadron scattering model. It is intended to take into account |
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6 | that the overlap of multiple strings at low transverse dimensions |
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7 | is likely to lead to some collective effects, not unlike those |
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8 | observed in heavy-ion collisions, even if not quite as pronounced. |
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9 | Specifically, it is assumed that the hadrons produced can scatter |
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10 | against each other on the way out, before the fragmenting system |
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11 | has had time to expand enough that the hadrons get free. Thereby |
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12 | heavier particles are shifted to higher transverse momenta, at the |
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13 | expense of the lighter ones. |
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14 | |
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15 | <note>Warning:</note> This is still at an experimental level, |
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16 | and should not be used unless you know what you are doing. |
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17 | |
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18 | <flag name="HadronScatter:scatter" default="off"> |
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19 | Master flag for hadron scattering. |
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20 | </flag> |
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21 | |
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22 | <flag name="HadronScatter:afterDecay" default="off"> |
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23 | Perform hadron scattering before or after first round of decays, |
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24 | involving very short-lived particles like the <ei>rho</ei>. |
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25 | The default is to perform scattering directly after the |
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26 | string fragmentation, before any decays. |
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27 | </flag> |
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28 | |
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29 | <flag name="HadronScatter:allowDecayProd" default="off"> |
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30 | Allow two hadrons with same parent hadron to scatter. |
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31 | </flag> |
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32 | |
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33 | <flag name="HadronScatter:scatterRepeat" default="off"> |
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34 | Allow hadrons which have already scattered to scatter again. |
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35 | Even if switched on, the same pair can not scatter off each |
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36 | other twice. |
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37 | </flag> |
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38 | |
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39 | <h3>Hadron selection</h3> |
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40 | |
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41 | <modepick name="HadronScatter:hadronSelect" default="0" |
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42 | min="0" max="0"> |
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43 | Probability that a hadron is soft enough to scatter. |
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44 | (A high-<ei>pT</ei> hadron presumably being part of a jet, |
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45 | and thus produced away from the high-particle-density region |
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46 | at small transverse dimensions.) |
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47 | <option value="0"> |
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48 | <ei>P = N exp(-pT^2 / 2 / sigma^2) / |
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49 | ( (1 - k) exp(-pT^2 / 2 / sigma^2) + k pT0^p / (pT0^2 + pT^2)^(p/2), </ei> |
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50 | with <ei>sigma = 2 StringPT:sigma</ei> and <ei>pT0</ei> the same as that |
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51 | used in <ei>MultipartonInteractions</ei>. |
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52 | </option> |
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53 | </modepick> |
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54 | |
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55 | <parm name="HadronScatter:N" default="1.0" min="0.01" max="1.0"> |
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56 | <ei>N</ei> parameter as above. |
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57 | </parm> |
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58 | <parm name="HadronScatter:k" default="1.0" min="0.01" max="1.0"> |
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59 | <ei>k</ei> parameter as above. |
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60 | </parm> |
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61 | <parm name="HadronScatter:p" default="6" min="2" max="30"> |
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62 | <ei>p</ei> parameter as above. |
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63 | </parm> |
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64 | |
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65 | <h3>Scattering probability</h3> |
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66 | |
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67 | <modepick name="HadronScatter:scatterProb" default="0" |
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68 | min="0" max="2"> |
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69 | Probability for a pair of hadrons to scatter. |
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70 | <option value="0">All hadrons scatter with probability |
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71 | <ei>j max(0, 1 - dR^2 / rMax^2)</ei>. Angular distribution |
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72 | is picked flat in <ei>cos(theta).</ei></option> |
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73 | <option value="1">As option 0, above, but only <ei>pi-pi</ei>, |
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74 | <ei>pi-K</ei> and <ei>pi-p</ei> scatterings are considered. |
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75 | </option> |
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76 | <option value="2">Only <ei>pi-pi</ei>, <ei>pi-K</ei> and |
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77 | <ei>pi-p</ei> scatterings are considered, with probability |
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78 | given by <ei>(1 - exp(-j sigEl)) max(0, 1 - dR^2 / rMax^2)</ei>. |
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79 | The elastic cross sections and angular distributions are taken |
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80 | from the partial-wave distributions. |
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81 | </option> |
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82 | </modepick> |
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83 | |
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84 | <parm name="HadronScatter:j" default="0.5" min="0.0", max="10.0"> |
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85 | <ei>j</ei> parameter as above. |
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86 | </parm> |
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87 | <parm name="HadronScatter:rMax" default="0.5" min="0.1" max="2.0"> |
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88 | <ei>rMax</ei> parameter as above. |
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89 | </parm> |
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90 | |
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91 | <flag name="HadronScatter:tile" default="off"> |
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92 | Use tiling in <ei>(eta, phi)</ei> to reduce number of pairwise tests. |
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93 | </flag> |
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94 | |
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95 | </chapter> |
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96 | |
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97 | <!-- Copyright (C) 2012 Torbjorn Sjostrand --> |
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98 | |
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