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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Interleaved evoluti<strong>on</strong><br />
• Transverse-momentum-ordered part<strong>on</strong> showers for ISR and FSR<br />
• MPI also ordered in p ⊥<br />
⇒ Allows interleaved evoluti<strong>on</strong> for ISR, FSR and MPI:<br />
(<br />
dPMPI<br />
dP<br />
=<br />
dp ⊥ dp ⊥<br />
(<br />
× exp −<br />
+ ∑ dP ISR<br />
dp ⊥<br />
∫ p⊥max<br />
(<br />
dPMPI<br />
p ⊥<br />
dp ′ ⊥<br />
+ ∑ )<br />
dP FSR<br />
dp ⊥<br />
+ ∑ dP ISR<br />
dp ′ ⊥<br />
Ordered in decreasing p ⊥ using “Sudakov” trick.<br />
Corresp<strong>on</strong>ds to increasing “resoluti<strong>on</strong>”:<br />
smaller p ⊥ fill in details of basic picture set at larger p ⊥ .<br />
Start from fixed hard interacti<strong>on</strong> ⇒ underlying <strong>event</strong><br />
No separate hard interacti<strong>on</strong> ⇒ minbias <strong>event</strong>s<br />
Possible to choose two hard interacti<strong>on</strong>s, e.g. W − W −<br />
+ ∑ ) )<br />
dP FSR<br />
dp<br />
⊥<br />
′ dp ⊥<br />
′<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 17/46
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