R. Field Talks

PYTHIA Tune Set A Rick Field University of Florida

R. Field Publications

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PYTHIA 6.206 Tune Set A (CTEQ5L)
Parameter	Default	Tune	Description
PARP(67)	1.0	4.0	Scale factor that governs the amount of initial-state radiation.
MSTP(81)	1	1	Turns on multiple parton interactions (MPI).
MSTP(82)	1	4	Double Gaussian matter distribution.
PARP(82)	1.9	2.0	Cut-off for multiple parton interactions, PT0.
PARP(83)	0.5	0.5	Warm Core: 50% of matter in radius 0.4.
PARP(84)	0.2	0.4	Warm Core: 50% of matter in radius 0.4.
PARP(85)	0.33	0.9	Probability that the MPI produces two gluons with color connections to the "nearest neighbors".
PARP(86)	0.66	0.95	Probability that the MPI produces two gluons either as described by PARP(85) or as a closed gluon loop. The remaining fraction consists of quark-antiquark pairs.
PARP(89)	1,000.0	1,800.0	Determines the reference energy E0.
PARP(90)	0.16	0.25	Determines the energy dependence of the cut-off PT0 as follows PT0(Ecm) = PT0(Ecm/E0)PARP(90).
Click here for the tcl file.

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Comments

• To model HC+DD+SD+EL run MSEL=2. To model the HC inelastic cross section run MSEL=1.
• For "min-bias" and low PT jet production run PT(hard) > CKIN(3)=0.0. To get more statistice on high PT jets run CKIN(3) > 5.0 (do not run in the range 0 < CKIN(3) < 5).
• Below are some plots and numbers (at the generator level with no PT cut) for PYTHIA 6.206 tune Set A. Since the MPI cross section (given below) depends sensitively on the parameters, it serves as an important check.
• Click on the plot to get an enlarged version and a table of the numbers.

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500,000 Generated PYTHIA (Set A) Events (1.96 TeV, CTEQ5L, MSEL=1, PT(hard) > CKIN(3) = 0 GeV/c)
Observable	Value	Comments
sigma	39.5 mb	Overall cross section (can be scaled if desired).
sigma MPI	310 mb	The MPI cross section is independent of PT(hard), but depends sensitively to the tuned parameters. It is printed out by PYTHIA and is stored in VINT(145).
<Nchg> (|eta|<1)	8.8	Includes all PT. Note that dNchg/deta at eta=0 is about 4.3.

Generated PTYHIA (Set A) Events (1.96 TeV, CTEQ5L, MSEL=1)
Minimum PT(hard) CKIN(3)	Sigma	<Nchg> (|eta|<1)
0.0	39.5 mb	8.8
10.0	0.570 mb	19.4
20.0	0.0316 mb	23.1

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Rick Field
Last modified: November 1, 2002