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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An x-dependent prot<strong>on</strong> size – 1<br />
Normally assume that PDFs factorize in l<strong>on</strong>gitudinal and<br />
transverse space:<br />
f (x, r) = f (x) ρ(r)<br />
In c<strong>on</strong>tradicti<strong>on</strong> with<br />
• intuitive picture of part<strong>on</strong>s spreading out by cascade to lower x<br />
• Mueller’s dipole cascade<br />
• formally BFKL, Balitsky-JIMWLK, Colour Glass C<strong>on</strong>densate, . . .<br />
• Froissart-Martin σ tot ∝ ln 2 s<br />
by Gribov <strong>the</strong>ory related to r p ∝ ln(1/x)<br />
• generalized part<strong>on</strong> distributi<strong>on</strong>s, . . .<br />
For now address inelastic n<strong>on</strong>diffrative <strong>event</strong>s with ansatz:<br />
ρ(r, x) ∝ 1 (<br />
a 3 (x) exp − r 2 )<br />
(<br />
a 2 with a(x) = a 0 1 + a 1 ln 1 )<br />
(x)<br />
x<br />
a 1 ≈ 0.15 tuned to rise of σ ND<br />
a 0 tuned to value of σ ND , given PDF, p ⊥0 , . . . ]<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 19/46
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