The Underlying-Event Model in PYTHIA (6&8) - Peter Skands - Cern

PARP(78)
PARP(82)
0.5
0.4
0.3
0.2
0.1
0
3
2.5
2
1.5
1
0.5
0
P. Skands
Evolution of PARP(78) with √ s
PARP(83)
Tuning vs Testing Models
10 3
PARP(78)
Evolution of PARP(83) with √ s
TEST models
Tune parameters in several
complementary regions
Consistent model → same
parameters
10
Model breakdown → nonuniversal
parameters
3
10 3
(b) PARP(78) vs √ s, Nch ≥ 6
Evolution of PARP(82) with √ Evolution of PARP(78) with s
√ s
PARP(78)
0.5
0.7
0.6
0.5
Multiparton interactions
PARP(82) PARP(78)
Exp=0.25
630 GeV
900 GeV
10 3
IR Regularization
(d) PARP(82) vs √ (a) PARP(78) vs s, Nch ≥ 6
√ s, Nch ≥ 1
√
1800 &
1960 GeV
Regularise cross section with p⊥0 as free parameter
dˆσ
dp2 ∝
⊥
α2s (p2 ⊥ )
p4 →
⊥
α2s (p2 ⊥0 + p2 ⊥ )
(p2 ⊥0 + p2 ⊥ )2
with energy dependence
p⊥0(ECM) =p ref
ECM
Eref ɛ 0.4
0.3
0.2
0.1
⊥0 ×
CM
Perugia 0
√ s /GeV
Pythia 6
7 TeV
Matter profile in impact-parameter space
gives time-integrated overlap which determines level of activity:
simple Gaussian or more peaked variants
0
0
2
1.5
1
0.5
0
(c) PARP(82) vs √ s, Nch ≥ 1
PARP(83)
(e) PARP(83) vs √ s, Nch ≥ 1
10 3
√ s /GeV
√ s /GeV
0.5
PARP(78)
Figure 1: Evolution of parameters with energy. .
√ √
s /GeVs
/GeV
“Energy Scaling of MB Tunes”, H. Schulz + PS, in preparation
ISR and MPI compete for beam momentum → PDF rescaling
+ flavour effects (valence, qq pair companions, . . . )
rrelated primordial k⊥ and colour in beam remnant
ced close in space–time ⇒ colour rearrangement;
⇒ steeper 〈p⊥〉(nch) 10
PARP(78)
0.4
0.3
0.2
0.1
0
630 GeV
Evolution of PARP(78) with √ s
630 GeV
900 GeV
900 GeV
Color Reconnection
Strength
10 3
1800 &
1960 GeV
(b) PARP(78) vs √ s, Nch ≥ 6
√ √
PARP(83)
0.5
0
2
1.5
1
0.5
0
10 3
(d) PARP(82) vs √ s, Nch ≥ 6
Evolution of PARP(83) with √ s
PARP(83)
Transverse Mass
Distribution
10 3
1800 &
1960 GeV
(f) PARP(83) vs √ s, Nch ≥ 6
Gauss
Perugia 0
Exponential
√ s /GeV
Pythia 6
7 TeV
√ s /GeV
Pythia 6
Perugia 0
7 TeV
√ s /GeV
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