R. Field Talks

PYTHIA Tunes Rick Field University of Florida

R. Field Publications

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PYTHIA 6.206 (CTEQ5L)
Tune	Matter Distribution	PARP(67)	Comments
A	Double Gaussian	4.0 (old PYTHIA default)	Describes fairly well both "min-bias" interactions and the "underlying event" in hard scattering processes at 630 GeV and 1.8 TeV.
B	Double Gaussian	1.0 (new PYTHIA default)	Similar to Set A but with less initial-state radiation. Set A is slightly favored. Comparing Set B and Set A shows how sensitive a given analysis is to the initial-state radiation.
C	Single Gaussian	4.0 (old PYTHIA default)	Similar to Set A, but does not describe "min-bias" interactions as well.
D	Single Gaussian	1.0 (new PYTHIA default)	Similar to Set B, but does not describe "min-bias" interactions as well.
Click on tune A, B, C, or D for the parameters and details.

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Comments

• At version 6.138 PYTHIA changed its default value of PARP(67) from 4.0 to 1.0. The larger the value of PARP(67) the more initial-state radiation. All of CDF Run I had PARP(67) = 4.0, but if you run with PYTHIA 6.2 defaults you get PARP(67) = 1.0. The CDF "underlying event" studies (and b-correlations) favor the old value of PARP(67) (i.e. Set A and Set C), but it is interesting to see how sensitive a given analysis is to the initial-state radiation. Also, PARP(67) = 4.0 might be a bit high. I am working on a tune in between 1.0 and 4.0.
• At present Set A seems to be the best tune since it does a good job on both the "underlying event" in hard scattering processes and on "min-bias" (same program).
• For more details see my talk "Min-Bias and the Underlying Event at the Tevatron and the LHC" (56 page, Acrobat PDF file).

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Rick Field
Last modified: November 1, 2002