Progress on the Pythia 8 event generator
Progress on the Pythia 8 event generator
Progress on the Pythia 8 event generator
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Matrix Elements vs. Part<strong>on</strong> Showers<br />
Matrix Elements vs. Part<strong>on</strong> Showers<br />
ME ME : : Matrix Elements<br />
+ + systematic expansi<strong>on</strong> in αα s (‘exact’) s + + powerful for multipart<strong>on</strong> Born Born level level<br />
+ + flexible phase space cuts<br />
− −loop loop calculati<strong>on</strong>s very tough<br />
−<br />
−<br />
negative cross secti<strong>on</strong> in<br />
incollinear regi<strong>on</strong>s<br />
regi<strong>on</strong>s<br />
⇒ unpredictive jet/<strong>event</strong> structure<br />
⇒ structure<br />
− no easy match to hadr<strong>on</strong>izati<strong>on</strong><br />
− no easy match to hadr<strong>on</strong>izati<strong>on</strong> p 2 ⊥ ,θ2 ,m<br />
virtual<br />
2<br />
PS PS : : Part<strong>on</strong> Showers<br />
−<br />
−<br />
approximate, to LL (or<br />
(or<br />
NLL)<br />
NLL)<br />
− main topology not predetermined<br />
− main ⇒ inefficient for exclusive states<br />
⇒ inefficient for exclusive states<br />
+ process-generic ⇒ simple multipart<strong>on</strong><br />
+ process-generic simple multipart<strong>on</strong><br />
+ Sudakov form factors/resummati<strong>on</strong><br />
+ Sudakov<br />
⇒ sensible<br />
formjet/<strong>event</strong> factors/resummati<strong>on</strong><br />
structure<br />
⇒ sensible structure<br />
+ easy to match to hadr<strong>on</strong>izati<strong>on</strong><br />
dσ<br />
dp 2 , dσ<br />
dθ 2, dσ<br />
dm<br />
⊥<br />
2<br />
real<br />
dσ<br />
dp 2 , dσ<br />
dθ 2, dσ<br />
dm<br />
⊥<br />
2<br />
real×Sudakov<br />
+ easy to match to hadr<strong>on</strong>izati<strong>on</strong> p 2 ⊥ ,θ2 ,m 2<br />
Torbjörn Sjöstrand <str<strong>on</strong>g>Progress</str<strong>on</strong>g> <strong>on</strong> <strong>the</strong> <strong>Pythia</strong> 8 <strong>event</strong> <strong>generator</strong> slide 10/46
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