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