MPI in Pythia 8
MPI in Pythia 8 MPI in Pythia 8
MPI in PYTHIA 8 Richard Corke Department of Astronomy and Theoretical Physics Lund University September 2010 Richard Corke (Lund University) MPI10@DESY September 2010 1 / 25
- Page 2 and 3: Overview 1 MPI in PYTHIA 8 2 Enhanc
- Page 4 and 5: MI MPI in inPYTHIA PYTHIA8 8 p⊥Or
- Page 6 and 7: MPI in PYTHIA 8 Impact parameter
- Page 8 and 9: MPI I in PYTHIA in PYTHIA 8 8 olour
- Page 10 and 11: nhanced Enhanced Screening screenin
- Page 12 and 13: Enhanced Enhancedscreening Screenin
- Page 14 and 15: Rescattering ◮ Typical case of sm
- Page 16 and 17: Rescattering ◮ In general not pos
- Page 18 and 19: Rescattering Rescattering Status
- Page 20 and 21: Rescattering ◮ Hadron level ◮ F
- Page 22 and 23: Tuning prospects ◮ FSR and hadron
- Page 24 and 25: Tuning prospects ◮ Also study how
- Page 26 and 27: Tuning prospects ◮ More plots: ht
- Page 28: Summary ◮ PYTHIA 8 MPI model ◮
<strong>MPI</strong> <strong>in</strong> PYTHIA 8<br />
Richard Corke<br />
Department of Astronomy and Theoretical Physics<br />
Lund University<br />
September 2010<br />
Richard Corke (Lund University) <strong>MPI</strong>10@DESY September 2010 1 / 25
Overview<br />
1 <strong>MPI</strong> <strong>in</strong> PYTHIA 8<br />
2 Enhanced screen<strong>in</strong>g<br />
3 Rescatter<strong>in</strong>g<br />
4 Tun<strong>in</strong>g prospects<br />
5 Summary<br />
Richard Corke (Lund University) <strong>MPI</strong>10@DESY September 2010 2 / 25
<strong>MPI</strong> <strong>in</strong> PYTHIA 8<br />
Interleaved evolution<br />
◮ Note: what follows covers the current <strong>MPI</strong> framework of PYTHIA 8<br />
◮ Transverse-momentum-ordered parton showers<br />
◮ <strong>MPI</strong> also ordered <strong>in</strong> p⊥<br />
◮ Mix of possible underly<strong>in</strong>g event processes, <strong>in</strong>clud<strong>in</strong>g jets, γ, J/ψ, DY, ...<br />
◮ Radiation from all <strong>in</strong>teractions<br />
◮ Interleaved evolution for ISR, FSR and <strong>MPI</strong><br />
dP<br />
dp⊥<br />
dP<strong>MPI</strong><br />
=<br />
dp⊥<br />
+ <br />
dPISR<br />
dp⊥<br />
p⊥max<br />
× exp −<br />
p⊥<br />
dP<strong>MPI</strong><br />
dp ′ ⊥<br />
+ <br />
dPFSR<br />
dp⊥<br />
+ dPISR<br />
dp ′ ⊥<br />
+ dPFSR<br />
dp ′ <br />
dp<br />
⊥<br />
′ <br />
⊥<br />
Richard Corke (Lund University) <strong>MPI</strong>10@DESY September 2010 3 / 25
MI <strong>MPI</strong> <strong>in</strong> <strong>in</strong>PYTHIA PYTHIA8 8<br />
p⊥Order<strong>in</strong>g<br />
<strong>MPI</strong> overview<br />
Other half of solution:<br />
perturbative QCD not valid at small p⊥ s<strong>in</strong>ce q, g not asymptotic states<br />
(conf<strong>in</strong>ement!).<br />
◮ Model for non-diffractive events, σnd ∼ (2/3)σtot<br />
◮ Ordered <strong>in</strong> decreas<strong>in</strong>g p⊥us<strong>in</strong>g “Sudakov” trick<br />
◮ Ordered <strong>in</strong> decreas<strong>in</strong>g p⊥ us<strong>in</strong>g “Sudakov” trick<br />
dP<strong>MPI</strong><br />
=<br />
dp⊥<br />
1<br />
p⊥i−1<br />
dσ<br />
1 dσ<br />
exp −<br />
σnd dp⊥<br />
p⊥<br />
σnd dp ′ dp<br />
⊥<br />
′ <br />
dP<br />
= ⊥<br />
dp⊥i<br />
1<br />
p⊥i−1<br />
dσ<br />
1 dσ<br />
exp −<br />
σnd dp⊥<br />
p⊥<br />
σnd dp ′ dp<br />
⊥<br />
′ Naively breakdown at<br />
<br />
p⊥m<strong>in</strong> ⊥<br />
¯h 0.2 GeV · fm<br />
≈<br />
rp 0.7 fm<br />
≈ 0.3 GeV ΛQCD ◮ QCD 2 → 2 cross-section cross sectionis divergent divergent, <strong>in</strong> p⊥ but→not0 valid limit, at small p⊥<br />
as but q, q/g g not asymptotic states<br />
. . . but better replace rp by (unknown) colour screen<strong>in</strong>g length d <strong>in</strong> hadron<br />
r r<br />
d<br />
resolved<br />
λ ∼ 1/p ⊥<br />
r r<br />
d<br />
screened<br />
◮ Regularise cross-section, <strong>in</strong>troduc<strong>in</strong>g p⊥0 as a free parameter<br />
◮ Regularise cross section, p⊥0 is now a free parameter<br />
dˆσ<br />
dp2 ∝<br />
⊥<br />
α2 S (p2 ⊥ )<br />
p4 →<br />
⊥<br />
α2 S (p2 ⊥0 + p2 ⊥ )<br />
(p2 ⊥0 + p2 ⊥ )2<br />
dˆσ<br />
dp2 ∝<br />
⊥<br />
α2 s(p2 ⊥ )<br />
p4 →<br />
⊥<br />
α2 s(p2 ⊥0 + p2 ⊥ )<br />
(p2 ⊥0 + p2 ⊥ )2<br />
Richard Corke (Lund University) Multiple Interactions <strong>in</strong> PYTHIA 8 October 2008 5 / 24<br />
Richard Corke (Lund University) <strong>MPI</strong>10@DESY September 2010 4 / 25
<strong>MPI</strong> <strong>in</strong> PYTHIA 8<br />
p⊥0 and energy scal<strong>in</strong>g<br />
◮ p⊥0 depends on energy<br />
◮ Ansatz: scales <strong>in</strong> a similar manner to the total cross section<br />
(effective power related to the Pomeron <strong>in</strong>tercept)<br />
p⊥0(ECM) = p ref<br />
⊥0 ×<br />
<br />
ECM<br />
E ref<br />
pow<br />
ECM CM<br />
PYTHIA Tune Z1<br />
◮ Need many measurements at different energies<br />
◮ Rick Field, MB & UE Work<strong>in</strong>g Group, Tune Z1 (PYTHIA 6)<br />
P T0 (GeV/c)<br />
3.5<br />
3.0<br />
2.5<br />
2.0<br />
1.5<br />
RDF Very Prelim<strong>in</strong>ary<br />
<strong>MPI</strong> Cut-Off P T0(W cm)<br />
CDF 1.96 TeV<br />
CMS 900 GeV<br />
1.0<br />
0 2000 4000 6000 8000 10000 12000<br />
Center-of-Mass Energy W cm (GeV)<br />
<strong>MPI</strong> Cut-Off versus the Center-of Mass Energy W cm: PYTHIA Tune Z1 was determ<strong>in</strong>ed<br />
Tune Z1<br />
CMS 7 TeV<br />
p T0(W)=p T0(W/W0) e<br />
Richard Corke (Lund University) <strong>MPI</strong>10@DESY September 2010 5 / 25
<strong>MPI</strong> <strong>in</strong> PYTHIA 8<br />
Impact parameter<br />
◮ Require one <strong>in</strong>teraction for a physical event<br />
◮ Introduce impact parameter, b, with matter profile<br />
◮ S<strong>in</strong>gle Gaussian; no free parameters<br />
◮ Overlap function<br />
<br />
exp<br />
◮ Double Gaussian<br />
ρ(r) ∝<br />
1 − β<br />
a 3 1<br />
<br />
exp −<br />
−b Epow exp<br />
2<br />
r<br />
a2 1<br />
<br />
<br />
+ β<br />
a3 <br />
exp −<br />
2<br />
◮ Time-<strong>in</strong>tegrated overlap of hadrons dur<strong>in</strong>g collision<br />
2<br />
r<br />
a2 2<br />
◮ Average activity at b ∝ O(b)<br />
<br />
O(b) = dt d 3 xρ(x, y, z) ρ(x + b, y, z + t)<br />
◮ Central collisions usually more active<br />
◮ Probability distribution broader than Poissonian<br />
Richard Corke (Lund University) <strong>MPI</strong>10@DESY September 2010 6 / 25
<strong>MPI</strong> <strong>in</strong> PYTHIA 8<br />
PDF rescal<strong>in</strong>g and primordial k⊥<br />
◮ ISR and <strong>MPI</strong> compete for beam momentum → PDF rescal<strong>in</strong>g<br />
◮ Squeeze orig<strong>in</strong>al x range<br />
◮ Flavour effects<br />
0 < x < 1 → 0 < x <<br />
<br />
1 − <br />
xi<br />
◮ Sea quark <strong>in</strong>itiator (qs) leaves beh<strong>in</strong>d an anti-sea companion (qc)<br />
◮ qc distribution from g → qs + qc perturbative ansatz<br />
◮ Normalisation of sea + gluon distributions fluctuate<br />
for total momentum conservation<br />
◮ Primordial k⊥<br />
◮ Needed for agreement with e.g. p⊥(Z 0 ) distributions<br />
◮ Give all <strong>in</strong>itiator partons Gaussian k⊥, width<br />
σ(Q, m) = Q 1 σsoft + Q σhard<br />
2<br />
+ Q<br />
Q 1 2<br />
◮ Rotate/boost systems to new frame<br />
m 1 2<br />
m<br />
+ m<br />
Richard Corke (Lund University) <strong>MPI</strong>10@DESY September 2010 7 / 25
<strong>MPI</strong> I <strong>in</strong> PYTHIA <strong>in</strong> PYTHIA 8 8<br />
olour Colour Reconnection<br />
reconnection<br />
0.7<br />
◮<br />
◮ Rearrangement<br />
Rearrangement<br />
of<br />
of<br />
f<strong>in</strong>al-state<br />
f<strong>in</strong>al-state<br />
colour<br />
colour<br />
connections,<br />
connections such that overall str<strong>in</strong>g<br />
6 such that overall str<strong>in</strong>g<br />
Total uncerta<strong>in</strong>ty<br />
length<br />
length<br />
is reduced<br />
is reduced<br />
4<br />
Systematic uncerta<strong>in</strong>ty<br />
FIG. 7: The dependence of the average track pT on the event multiplicity. A comparison with the Run I<br />
shown. The error bars <strong>in</strong> the upper plot describe the uncerta<strong>in</strong>ty on the data po<strong>in</strong>ts. This uncerta<strong>in</strong>ty <strong>in</strong>clud<br />
uncerta<strong>in</strong>ty on the data and the statistical uncerta<strong>in</strong>ty on the total correction. In the lower plot the system<br />
(solid yellow band) and the total uncerta<strong>in</strong>ty are shown. The total uncerta<strong>in</strong>ty is the quadratic sum of the unc<br />
1.5<br />
on the data po<strong>in</strong>ts and the systematic uncerta<strong>in</strong>ty.<br />
<strong>Pythia</strong> hadron level : CDF RunII Prelim<strong>in</strong>ary<br />
◮ Large amount of reconnection required for agreement with data<br />
> [GeV/c]<br />
< p > [GeV/c]<br />
T<br />
◮ Large amount of reconnection<br />
◮needed Probability to match for adata system to<br />
TuneA p =0<br />
1.3<br />
T<br />
Atlas Tune<br />
1.2<br />
◮ Start reconnect with NC<br />
with → ∞a harder limit, but system<br />
real-world has NC = 3<br />
p<br />
◮ Chang<strong>in</strong>g the P = colour structure of an<br />
event can lead to (dis)agreement<br />
1.1<br />
1<br />
0.9<br />
0.8<br />
0.7<br />
Data Run II<br />
| η|<br />
≤ 1 and p ≥ 0.4 GeV/c<br />
T<br />
with data multiplicity<br />
2 ⊥R<br />
(p2 ⊥R + p2 ,<br />
⊥ )<br />
p⊥R = R ∗ p MI<br />
1.4<br />
1.3<br />
Data Run II | η|<br />
≤1<br />
and p ≥0.4<br />
GeV/c<br />
T<br />
1.2<br />
1.1<br />
1<br />
0.9<br />
0.8<br />
<strong>Pythia</strong> hadron level :<br />
⊥0<br />
< p<br />
T<br />
0.7<br />
Uncerta<strong>in</strong>ty %<br />
1.4<br />
0.9<br />
0.8<br />
2<br />
TuneA no <strong>MPI</strong><br />
TuneA p =1.5<br />
T<br />
| η|<br />
≤1<br />
and p ≥0.4<br />
GeV/c<br />
T<br />
Data Run II<br />
Data Run I<br />
0<br />
0 5 10 15 20 25 30 35 40 45 50<br />
charged particle multiplicity<br />
0 5 10 15 20 25 30 35 40 45 50<br />
TuneA no <strong>MPI</strong><br />
TuneA p =1.5<br />
TuneA p =0<br />
T<br />
ATLAS tune<br />
Mean p⊥as a function of multiplicity, CDF, Run II<br />
Measurement of Inelastic P ¯ P Inclusive Cross Sections at √ T<br />
0.6<br />
0 5 10 15 20 25 30 35 40 45 50 s=1.96<br />
TeV, The CDF Collaboration, charged particle Prelim<strong>in</strong>ary multiplicity<br />
Richard Corke (Lund University) <strong>MPI</strong>10@DESY September 2010 8 / 25<br />
FERMILAB-PUB-09-098-E
nhanced<br />
Enhanced<br />
Screen<strong>in</strong>g<br />
screen<strong>in</strong>g<br />
troduction<br />
◮ Idea of Gösta Gustafson from work on model<strong>in</strong>g <strong>in</strong>itial states<br />
with an extended Mueller dipole formalism<br />
◮ “Elastic and quasi-elastic pp and γ ∗ ◮ Idea of Gösta Gustafson from work on modell<strong>in</strong>g <strong>in</strong>itial states<br />
with an extended Mueller dipole formalism<br />
◮ “Elastic and quasi-elastic pp and γ p scatter<strong>in</strong>g <strong>in</strong> the Dipole Model,”<br />
C. Flensburg, G. Gustafson and L. Lönnblad, Eur. Phys. J. C 60 (2009) 233<br />
⋆ p scatter<strong>in</strong>g <strong>in</strong> the Dipole Model,”<br />
C. Flensburg, G. Gustafson and L. Lonnblad, arXiv:0807.0325 [hep-ph].<br />
1<br />
0.8<br />
0.6<br />
0.4<br />
0.2<br />
0<br />
-0.2<br />
-0.4<br />
rapidity 0<br />
-0.6 -0.4 -0.2 0 0.2 0.4 0.6<br />
◮ Even at a fixed impact parameter, <strong>in</strong>itial state will conta<strong>in</strong><br />
◮ Even at fixed impact parameter, <strong>in</strong>itial state will conta<strong>in</strong><br />
more/less fluctuations on an event-by-event basis<br />
more/less fluctuations on an event-by-event basis<br />
◮ More activity → more screen<strong>in</strong>g<br />
◮ More activity → more screen<strong>in</strong>g<br />
Richard Corke (Lund University) Multiple Interactions <strong>in</strong> PYTHIA 8 October 2008 20 / 24<br />
Richard Corke (Lund University) <strong>MPI</strong>10@DESY September 2010 9 / 25
nhanced<br />
Enhanced<br />
Screen<strong>in</strong>g<br />
screen<strong>in</strong>g<br />
troduction<br />
◮ Idea of Gösta Gustafson from work on model<strong>in</strong>g <strong>in</strong>itial states<br />
with an extended Mueller dipole formalism<br />
◮ “Elastic and quasi-elastic pp and γ ∗ ◮ Idea of Gösta Gustafson from work on modell<strong>in</strong>g <strong>in</strong>itial states<br />
with an extended Mueller dipole formalism<br />
◮ “Elastic and quasi-elastic pp and γ p scatter<strong>in</strong>g <strong>in</strong> the Dipole Model,”<br />
C. Flensburg, G. Gustafson and L. Lönnblad, Eur. Phys. J. C 60 (2009) 233<br />
⋆ p scatter<strong>in</strong>g <strong>in</strong> the Dipole Model,”<br />
C. Flensburg, G. Gustafson and L. Lonnblad, arXiv:0807.0325 [hep-ph].<br />
1<br />
0.8<br />
0.6<br />
0.4<br />
0.2<br />
0<br />
-0.2<br />
-0.4<br />
rapidity 16<br />
-0.6 -0.4 -0.2 0 0.2 0.4 0.6<br />
◮ Even at a fixed impact parameter, <strong>in</strong>itial state will conta<strong>in</strong><br />
◮ Even at fixed impact parameter, <strong>in</strong>itial state will conta<strong>in</strong><br />
more/less fluctuations on an event-by-event basis<br />
more/less fluctuations on an event-by-event basis<br />
◮ More activity → more screen<strong>in</strong>g<br />
◮ More activity → more screen<strong>in</strong>g<br />
Richard Corke (Lund University) Multiple Interactions <strong>in</strong> PYTHIA 8 October 2008 20 / 24<br />
Richard Corke (Lund University) <strong>MPI</strong>10@DESY September 2010 9 / 25
Enhanced Enhancedscreen<strong>in</strong>g Screen<strong>in</strong>g<br />
Enhanced Screen<strong>in</strong>g <strong>in</strong> PYTHIA<br />
dˆσ<br />
dp 2 ⊥<br />
∝ α2 S (p2 ⊥0 + p2 ⊥ )<br />
(p2 ⊥0 + p2 ⊥ )2 → α2 S (p2 ⊥0 + p2 ⊥ )<br />
(n p2 ⊥0 + p2 ⊥ )2<br />
[GeV/c]<br />
1.3<br />
1.2<br />
1.1<br />
1<br />
0.9<br />
0.8<br />
0.7<br />
CDF Run II<br />
<strong>Pythia</strong> 8.114 No reconnection<br />
<strong>Pythia</strong> 8.114 No reconnection + ES1<br />
<strong>Pythia</strong> 8.114 No reconnection + ES2<br />
ES1: n = no. of MI<br />
ES2: n = no. of MI + ISR<br />
0.6<br />
0 5 10 15 20 25 30 35<br />
Charged particle multiplicity<br />
Richard Corke (Lund University) Multiple Interactions <strong>in</strong> PYTHIA 8 October 2008 21 / 24<br />
Richard Corke (Lund University) <strong>MPI</strong>10@DESY September 2010 10 / 25
Enhanced Enhancedscreen<strong>in</strong>g Screen<strong>in</strong>g<br />
Enhanced Screen<strong>in</strong>g <strong>in</strong> PYTHIA<br />
dˆσ<br />
dp 2 ⊥<br />
∝ α2 S (p2 ⊥0 + p2 ⊥ )<br />
(p2 ⊥0 + p2 ⊥ )2 → α2 S (p2 ⊥0 + p2 ⊥ )<br />
(n p2 ⊥0 + p2 ⊥ )2<br />
[GeV/c]<br />
1.3<br />
1.2<br />
1.1<br />
1<br />
0.9<br />
0.8<br />
0.7<br />
CDF Run II<br />
<strong>Pythia</strong> 8.114 No reconnection<br />
<strong>Pythia</strong> 8.114 No reconnection + ES1<br />
<strong>Pythia</strong> 8.114 No reconnection + ES2<br />
<strong>Pythia</strong> 8.114, RR * p ⊥0 = 5.56<br />
<strong>Pythia</strong> 8.114 ES1, RR * p ⊥0 = 4.35<br />
<strong>Pythia</strong> 8.114 ES2, RR * p ⊥0 = 3.08<br />
ES1: n = no. of MI<br />
ES2: n = no. of MI + ISR<br />
0.6<br />
0 5 10 15 20 25 30 35<br />
Charged particle multiplicity<br />
Richard Corke (Lund University) Multiple Interactions <strong>in</strong> PYTHIA 8 October 2008 21 / 24<br />
Richard Corke (Lund University) <strong>MPI</strong>10@DESY September 2010 10 / 25
Rescatter<strong>in</strong>g<br />
lt. <strong>in</strong>t.<br />
R<br />
Rescatter<strong>in</strong>g<br />
dP<br />
= +<br />
◮ <strong>MPI</strong> Introduction traditionally disjo<strong>in</strong>t 2 → 2 <strong>in</strong>teractions<br />
<br />
dP p⊥i−1<br />
ISR<br />
exp −<br />
◮ Rescatter<strong>in</strong>g: ◮with Consider<br />
ISR sum<br />
aallow over<br />
4 →<br />
all<br />
4an previous<br />
andalready a 3 →<br />
MI<br />
3 scattered process parton to <strong>in</strong>teract aga<strong>in</strong><br />
mult. <strong>in</strong>t. p⊥max<br />
ISR<br />
p⊥1<br />
3<br />
(4) Evolution <strong>in</strong>terleaved with ISR (2004)<br />
• Transverse-momentum-ordered showers<br />
<br />
dPMI<br />
dp ⊥<br />
p ⊥<br />
dp ⊥<br />
is 3 → 3 <strong>in</strong>stead of 4 → 4:<br />
hard <strong>in</strong>t.<br />
<strong>in</strong>teraction ISR<br />
p number<br />
′ ⊥1<br />
dp ⊥<br />
p ⊥<br />
dPMI<br />
dp ′ ⊥<br />
+ dPISR dp ′ <br />
dp<br />
⊥<br />
′ <br />
⊥<br />
(5) Rescatter<strong>in</strong>g (<strong>in</strong> progress)<br />
◮ mult. <strong>in</strong>t.<br />
p⊥2Interaction<br />
cross-section<br />
is 3 → 3 <strong>in</strong>stead of 4 → 4:<br />
ISR<br />
dσ<strong>in</strong>t<br />
dp mult. <strong>in</strong>t.<br />
p⊥3<br />
ISR<br />
p⊥m<strong>in</strong><br />
<strong>in</strong>teraction<br />
1 2 3 number<br />
2 =<br />
⊥<br />
<br />
dx1 dx2 f1(x1, Q 2 ) f2(x2, Q 2 ) dˆσ<br />
dp2 ⊥<br />
◮ Paver and Treleani (1984)<br />
dσ<strong>in</strong>t<br />
dp2 ∼ N1N2 ˆσ<br />
⊥<br />
σ4→4 ∼ (N1N2 ˆσ)(N ′<br />
1N ′<br />
2 ˆσ) σ3→3 ∼ (N1N2 ˆσ)(N ′<br />
1 ˆσ)<br />
σ3→3<br />
∼<br />
σ4→4<br />
1<br />
N ′<br />
◮ Investigated by Paver and Treleani (1984), size of effect<br />
dσ<strong>in</strong>t<br />
dp<br />
→ small<br />
2<br />
2 =<br />
⊥<br />
<br />
dx1 dx2 f1(x1, Q 2 ) f2(x2, Q 2 ) dˆσ<br />
dp2 ∼ N1N2ˆσ<br />
⊥<br />
σ4→4 ∼ (N1N2ˆσ)(N ′ 1N ′ 2ˆσ) σ3→3 ∼ (N1N2ˆσ)(N ′ 1ˆσ)<br />
σ3→3<br />
∼<br />
σ4→4<br />
1<br />
N ′ → small<br />
2<br />
◮ But should be there!<br />
Richard Corke (Lund University) Multiple Interactions <strong>in</strong> PYTHIA 8 October 2008 13 / 24<br />
◮ Plays a role <strong>in</strong> the collective effects of <strong>MPI</strong><br />
◮ Possible colour connection effects<br />
Richard Corke (Lund University) <strong>MPI</strong>10@DESY September 2010 11 / 25
Rescatter<strong>in</strong>g<br />
◮ Typical case of small angle scatter<strong>in</strong>gs between partons from 2 <strong>in</strong>com<strong>in</strong>g<br />
hadrons, such that they are still associated with their orig<strong>in</strong>al hadrons<br />
f (x, Q 2 ) → frescaled(x, Q 2 ) + <br />
δ(x − xn)<br />
◮ In this limit, momentum sum rule holds<br />
1<br />
0<br />
x frescaled(x, Q 2 ) dx + <br />
xn = 1<br />
◮ Orig<strong>in</strong>al <strong>MPI</strong> <strong>in</strong>teractions supplemented by:<br />
◮ S<strong>in</strong>gle rescatter<strong>in</strong>gs: one parton from the rescaled PDF, one delta function<br />
◮ Double rescatter<strong>in</strong>gs: both partons are delta functions<br />
◮ One simplification: rescatter<strong>in</strong>gs<br />
always occur at “later times”<br />
◮ Z 0 preceeded by rescatter<strong>in</strong>g not<br />
possible<br />
Richard Corke (Lund University) <strong>MPI</strong>10@DESY September 2010 12 / 25<br />
n<br />
n
Rescatter<strong>in</strong>g<br />
◮ In general not possible to uniquely identify a scattered parton with an<br />
<strong>in</strong>com<strong>in</strong>g hadron, so use approximate rapidity based prescription<br />
2 2<br />
p⊥ dN / dp⊥<br />
0.5<br />
0.4<br />
0.3<br />
0.2<br />
0.1<br />
Step: Step function at y = 0<br />
Simultaneous: Partons belong to both beams simultaneously<br />
Tanh/l<strong>in</strong>ear: In between<br />
(a)<br />
Step<br />
L<strong>in</strong>ear<br />
Tanh<br />
Simultaneous<br />
0<br />
0.1 1 10<br />
2 2<br />
p⊥ (GeV )<br />
100<br />
◮ Little sensitivity to choice<br />
2 2<br />
p⊥ dN / dp⊥<br />
0.05<br />
0.04<br />
0.03<br />
0.02<br />
0.01<br />
(b)<br />
Step<br />
L<strong>in</strong>ear<br />
Tanh<br />
Simultaneous<br />
0<br />
0.1 1 10<br />
2 2<br />
p⊥ (GeV )<br />
100<br />
Figure 5: p⊥ distributions of (a) s<strong>in</strong>gle rescatter<strong>in</strong>gs and (b) double rescatter<strong>in</strong>gs <strong>in</strong> LHC<br />
m<strong>in</strong>imum bias events (pp, √ ◮ Natural suppression for s<strong>in</strong>gle rescatter<strong>in</strong>g<br />
◮ No suppression for s double = 14 TeV, rescatter<strong>in</strong>g, old tune). but Parameters still smallfor effect the different options<br />
are the same as the previous figure. Note the difference <strong>in</strong> vertical scale between (a) and<br />
(b), and that the step, l<strong>in</strong>ear and tanh curves are so close that they may be difficult to<br />
dist<strong>in</strong>guish<br />
Richard Corke (Lund University) <strong>MPI</strong>10@DESY September 2010 13 / 25
Rescatter<strong>in</strong>g<br />
◮ In general not possible to uniquely identify a scattered parton with an<br />
<strong>in</strong>com<strong>in</strong>g hadron, so use approximate rapidity based prescription<br />
Step: Step function at y = 0<br />
Simultaneous: Partons belong to both beams simultaneously<br />
Tanh/l<strong>in</strong>ear: In between<br />
p ⊥ 2 dN / dp⊥ 2<br />
Ratio<br />
1.6<br />
1.4<br />
1.2<br />
1<br />
0.8<br />
0.6<br />
0.4<br />
0.2<br />
0<br />
0.6<br />
0.5<br />
0.4<br />
0.3<br />
0.2<br />
0.1<br />
0<br />
(a)<br />
Old Tune - Normal<br />
New Tune - Normal<br />
Old Tune - S<strong>in</strong>gle<br />
New Tune - S<strong>in</strong>gle<br />
Old Tune - S<strong>in</strong>gle / Normal (Step)<br />
New Tune - S<strong>in</strong>gle / Normal (Step)<br />
Old Tune - Double / Normal (Sim)<br />
0.1 1 10<br />
2 2<br />
p⊥ (GeV )<br />
100 1000<br />
Probability<br />
0.2<br />
0.15<br />
0.1<br />
0.05<br />
Old Tune<br />
New Tune<br />
(b)<br />
0<br />
0.1 1 10<br />
2 2<br />
p⊥ (GeV )<br />
Figure 6: Rescatter<strong>in</strong>g <strong>in</strong> LHC m<strong>in</strong>imum bias events (pp, √ ◮ Little sensitivity to choice<br />
s = 14TeV, old<br />
◮ Natural suppression (a) shows for thes<strong>in</strong>gle p⊥ distribution rescatter<strong>in</strong>g of scatter<strong>in</strong>gs and s<strong>in</strong>gle rescatter<strong>in</strong>gs per eve<br />
◮ No suppression the ratio for double plot is double rescatter<strong>in</strong>g, rescatter<strong>in</strong>g but still withsmall the simultaneous effect beam prescriptio<br />
tune, where its effect is maximal. (b) shows the probability for a parton<br />
hard process of an event, to rescatter as a function of its <strong>in</strong>itial p⊥<br />
Richard Corke (Lund University) <strong>MPI</strong>10@DESY September 2010 13 / 25
0.4<br />
0.2<br />
Rescatter<strong>in</strong>g<br />
0<br />
Ratio<br />
0.6<br />
0.6<br />
0.5<br />
0.4<br />
0.3<br />
0.2<br />
0.1<br />
0<br />
◮ Use step prescription<br />
Old Tune - S<strong>in</strong>gle / Normal (Step)<br />
New Tune - S<strong>in</strong>gle / Normal (Step)<br />
Old Tune - Double / Normal (Sim)<br />
0.1 1 10<br />
2 2<br />
p⊥ (GeV )<br />
100 1000<br />
0<br />
0.1 1 10<br />
2 2<br />
p⊥ (GeV )<br />
100 1000<br />
◮ Amount of rescatter<strong>in</strong>g sensitive to amount of underly<strong>in</strong>g activity<br />
◮ Default tune change start<strong>in</strong>g with PYTHIA 8.127<br />
◮ <strong>MPI</strong>: p ref<br />
⊥0 = 2.15 → 2.25, E pow<br />
Figure 6: Rescatter<strong>in</strong>g <strong>in</strong> LHC m<strong>in</strong>imum bias events (pp,<br />
CM = 0.16 → 0.24<br />
◮ Matter profile from double to s<strong>in</strong>gle Gaussian<br />
◮ ISR activity <strong>in</strong>creased<br />
√ s = 14TeV, old and new tunes).<br />
(a) shows the p⊥ distribution of scatter<strong>in</strong>gs and s<strong>in</strong>gle rescatter<strong>in</strong>gs per event. Included <strong>in</strong><br />
the ratio plot is double rescatter<strong>in</strong>g with the simultaneous beam prescription us<strong>in</strong>g the old<br />
tune, where its effect is maximal. (b) shows the probability for a parton, created <strong>in</strong> the<br />
hard process of an event, to rescatter as a function of its <strong>in</strong>itial p⊥<br />
Old<br />
New<br />
Probabili<br />
Tevatron LHC<br />
M<strong>in</strong> Bias QCD Jets M<strong>in</strong> Bias QCD Jets<br />
Scatter<strong>in</strong>gs 2.81 5.09 5.19 12.19<br />
S<strong>in</strong>gle rescatter<strong>in</strong>gs 0.41 1.32 1.03 4.10<br />
Double rescatter<strong>in</strong>gs 0.01 0.04 0.03 0.15<br />
Scatter<strong>in</strong>gs 2.50 3.79 3.40 5.68<br />
S<strong>in</strong>gle rescatter<strong>in</strong>gs 0.24 0.60 0.25 0.66<br />
Double rescatter<strong>in</strong>gs 0.00 0.01 0.00 0.01<br />
Tevatron: p¯p, √ s = 1.96 TeV, QCD jet ˆp ⊥m<strong>in</strong> = 20 GeV LHC: pp, √ s = 14 TeV, QCD jet ˆp ⊥m<strong>in</strong> = 50 GeV<br />
Table 1: Average number of scatter<strong>in</strong>gs, s<strong>in</strong>gle rescatter<strong>in</strong>gs and double rescatter<strong>in</strong>gs <strong>in</strong><br />
m<strong>in</strong>imum bias and QCD jet events at Tevatron (pp, √ s = 1.96 TeV, QCD jet ˆp⊥m<strong>in</strong> =<br />
20 GeV) and LHC (pp, √ ◮ Double rescatter<strong>in</strong>g always small, so ignored <strong>in</strong> what follows<br />
s = 14.0 TeV, QCD jet ˆp⊥m<strong>in</strong> = 50 GeV) energies for both the old<br />
and new tunes<br />
Richard Corke (Lund University) <strong>MPI</strong>10@DESY September 2010 14 / 25<br />
0.1<br />
0.05
Rescatter<strong>in</strong>g<br />
Rescatter<strong>in</strong>g<br />
Status<br />
◮ So far nice and simple, but want fully hadronic events<br />
◮ Prelim<strong>in</strong>ary framework <strong>in</strong> place to get hadronic f<strong>in</strong>al states<br />
◮ Integration with showers needed<br />
◮ Keep system mass/rapidity unchanged where possible<br />
◮ Non-trivial k<strong>in</strong>ematics with rescatter<strong>in</strong>g, FSR and primordial k⊥<br />
◮ A radiat<strong>in</strong>g parton will shuffle momentum with a recoiler parton<br />
◮ Colour effects<br />
◮ FSR: usually nearest colour neighbour<br />
◮ ◮ Parton Primordial showers k⊥given use dipole by boost<strong>in</strong>g picture scatter<strong>in</strong>g for recoil sub-systems<br />
◮ With rescatter<strong>in</strong>g, colour can flow between systems<br />
◮ Rescatter<strong>in</strong>g: colour dipoles can span between scatter<strong>in</strong>g sub-systems<br />
◮ Momentum shuffled between systems is given a different primordial k⊥boost<br />
◮ Temporary solution of deferr<strong>in</strong>g FSR until after primordial k⊥is added<br />
◮ Full event generation, <strong>in</strong>clud<strong>in</strong>g showers, primordial k⊥ and<br />
colour reconnections<br />
Richard Corke (Lund University) Multiple Interactions <strong>in</strong> PYTHIA 8 October 2008 17 / 24<br />
Richard Corke (Lund University) <strong>MPI</strong>10@DESY September 2010 15 / 25
Rescatter<strong>in</strong>g<br />
10 6<br />
dσ / dp ⊥ (nb / GeV)<br />
10 5<br />
(a)<br />
2 -> 3<br />
3 -> 3<br />
◮ Compare sources of 3- and 4-jets at the parton level<br />
◮ Contributions to 3-jet rate<br />
◮ 2 → 3 from s<strong>in</strong>gle radiation<br />
◮ 3 → 3 from s<strong>in</strong>gle rescatter<strong>in</strong>g<br />
◮ 4 → 3 double parton scatter<strong>in</strong>g with one jet lost<br />
◮ Contributions to 4-jet rate<br />
◮ 2 → 4 from double radiation<br />
◮ 3 → 4 from s<strong>in</strong>gle radiation + s<strong>in</strong>gle rescatter<strong>in</strong>g<br />
◮ 4 → 4 from DPS<br />
◮ 4 → 4 ′ 10<br />
from two s<strong>in</strong>gle rescatter<strong>in</strong>gs<br />
0<br />
10 1<br />
10 2<br />
10 3<br />
10 4<br />
0<br />
10<br />
20 40 60 80 100<br />
p⊥ (GeV)<br />
0<br />
10 1<br />
10 2<br />
10 3<br />
10 4<br />
0 20 40 60 80 100<br />
p⊥ (GeV)<br />
Figure 13: Breakdown of contributions to the (a) three-jet and (b) four-jet cross sections<br />
(see text) for LHC m<strong>in</strong>imum bias events (pp, √ s = 14 TeV, new tune) when no p⊥ or<br />
rapidity cuts are applied<br />
dσ / dp ⊥ (nb / GeV)<br />
10 4<br />
10 3<br />
10 2<br />
10 1<br />
10 0<br />
10 -1<br />
10 -2<br />
(a)<br />
2 -> 3<br />
3 -> 3<br />
4 -> 3<br />
30 40 50 60 70 80 90 100<br />
p⊥ (GeV)<br />
dσ / dp ⊥ (nb / GeV)<br />
10 6<br />
10 5<br />
10 4<br />
10 3<br />
10 2<br />
10 1<br />
10 0<br />
10 -1<br />
10 -2<br />
pp, √ s = 14 TeV, new tune, p ⊥ > 10 GeV, |η| < 1.0<br />
dσ / dp ⊥ (nb / GeV)<br />
(b)<br />
(b)<br />
2 -> 4<br />
3 -> 4<br />
4 -> 4<br />
4 -> 4’<br />
2 -> 4<br />
3 -> 4<br />
4 -> 4<br />
30 40 50 60 70 80 90 100<br />
p⊥ (GeV)<br />
Figure 14: Breakdown of contributions to the<br />
√<br />
(a) three-jet and (b) four-jet cross sections<br />
Richard Corke (Lund University) <strong>MPI</strong>10@DESY September 2010 16 / 25
Rescatter<strong>in</strong>g<br />
◮ Hadron level<br />
◮ Feed results <strong>in</strong>to FastJet,<br />
anti-k⊥ algorithm, R = 0.4<br />
◮ 2-, 3- and 4-jet exclusive cross<br />
sections<br />
◮ Some <strong>in</strong>crease <strong>in</strong> jet rates, but<br />
contributions can be<br />
“compensated” by changes <strong>in</strong><br />
parameters elsewhere<br />
◮ Also studied<br />
dσ / dp ⊥ (nb / GeV)<br />
Ratio<br />
10 5<br />
10 4<br />
10 3<br />
10 2<br />
10<br />
2.2<br />
1.8<br />
1.4<br />
1<br />
0.6<br />
1<br />
2-jet Normal<br />
3-jet Normal<br />
4-jet Normal<br />
2-jet Rescatter<br />
3-jet Rescatter<br />
4-jet Rescatter<br />
2-jet 3-jet 4-jet<br />
20 30 40 50 60 70 80 90<br />
p⊥ (GeV)<br />
pp, √ s = 14 TeV, old tune, p ⊥ > 12.5 GeV, |η| < 1.0<br />
Figure 19: Two-, three- and four-jet exclusive cross sections for LHC m<strong>in</strong>imu<br />
(pp, √ s = 14 TeV, p⊥jet > 12.5 GeV, |η| < 1.0, old tune)<br />
◮ Colour reconnections<br />
◮ “Cron<strong>in</strong>” effect are very deeply entangled <strong>in</strong> the downward evolution of the f<strong>in</strong>al state, so it<br />
any such signatures may exist. For the three-jet sample of Fig. 19, we stud<br />
◮ ∆R & ∆φ distributions<br />
∆R value between the different pairs of jets per event. One could hope that th<br />
of ∆R values from three-jet events where rescatter<strong>in</strong>g is <strong>in</strong>volved is somehow<br />
the background events (e.g. three-jet events from radiation which may be cha<br />
peaked <strong>in</strong> the small ∆R region). For the four-jet sample, we <strong>in</strong>stead stud<br />
and largest ∆φ values between the jets per event. It is known that DPS<br />
characteristic ∆φ peak at π, but there are also radiative contributions wh<br />
rescatter<strong>in</strong>g. Unfortunately, for both samples, the results with and withou<br />
are essentially <strong>in</strong>dist<strong>in</strong>guishable.<br />
◮ No “smok<strong>in</strong>g-gun” signatures for rescatter<strong>in</strong>g<br />
◮ Would any effects be visible <strong>in</strong> a full tune?<br />
Richard Corke (Lund University) <strong>MPI</strong>10@DESY September 2010 17 / 25
References<br />
◮ PYTHIA references<br />
◮ “PYTHIA 6.4 Physics and Manual,”<br />
T. Sjöstrand, S. Mrenna and P. Z. Skands, JHEP 0605 (2006) 026<br />
◮ “A Brief Introduction to PYTHIA 8.1,”<br />
T. Sjöstrand, S. Mrenna and P. Z. Skands,<br />
Comput. Phys. Commun. 178 (2008) 852<br />
◮ Model references<br />
◮ “A Multiple Interaction Model for the Event Structure<br />
<strong>in</strong> Hadron Collisions,”<br />
T. Sjöstrand and M. van Zijl, Phys. Rev. D 36 (1987) 2019<br />
◮ “Multiple <strong>in</strong>teractions and the structure of beam remnants,”<br />
T. Sjöstrand and P. Z. Skands, JHEP 0403 (2004) 053<br />
◮ “Transverse-momentum-ordered showers and <strong>in</strong>terleaved<br />
multiple <strong>in</strong>teractions,”<br />
T. Sjöstrand and P. Z. Skands, Eur. Phys. J. C 39 (2005) 129<br />
◮ “Multiparton Interactions and Rescatter<strong>in</strong>g,”<br />
R. Corke and T. Sjöstrand, JHEP 1001 (2010) 035<br />
Richard Corke (Lund University) <strong>MPI</strong>10@DESY September 2010 18 / 25
Tun<strong>in</strong>g prospects<br />
◮ FSR and hadronisation tuned to LEP data (H. Hoeth)<br />
◮ Already default for PYTHIA 8.125 and later<br />
◮ Problems with simultaneous tun<strong>in</strong>g of MB and UE<br />
〈N ch〉/dη dφ<br />
MC/data<br />
1.2<br />
1<br />
0.8<br />
0.6<br />
<br />
0.4<br />
0.2<br />
0<br />
1.4<br />
1.2<br />
1<br />
0.8<br />
0.6<br />
Transverse region charged particle density<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
CDF data<br />
PYTHIA 8.135<br />
0 50 100 150 200 250 300 350 400<br />
pT(lead<strong>in</strong>g jet) / GeV<br />
◮ MB well described, but UE rises too fast!<br />
<br />
<br />
<br />
〈∑ ptrack T 〉/dη dφ / GeV<br />
2<br />
1.5<br />
1<br />
0.5<br />
0<br />
1.4<br />
Transverse region charged ∑ p ⊥ density<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
CDF data<br />
PYTHIA 8.135<br />
0 50 100 150 200 250 300 350 400<br />
pT(lead<strong>in</strong>g jet) / GeV<br />
Richard Corke (Lund University) <strong>MPI</strong>10@DESY September 2010 19 / 25<br />
MC/data<br />
1.2<br />
1<br />
0.8<br />
0.6
Tun<strong>in</strong>g prospects<br />
◮ New <strong>in</strong> PYTHIA 8: FSR <strong>in</strong>terleav<strong>in</strong>g<br />
◮ F<strong>in</strong>al-state dipoles can stretch to the <strong>in</strong>itial state (FI dipole)<br />
◮ How to subdivide FSR and ISR <strong>in</strong> an FI dipole?<br />
◮ Large mass → large rapidity range for emission<br />
◮ In dipole rest frame<br />
m >> p⊥<br />
Double<br />
counted<br />
m/2<br />
p⊥<br />
m ∼ p⊥<br />
◮ Suppress f<strong>in</strong>al-state radiation <strong>in</strong> double-counted region<br />
Richard Corke (Lund University) <strong>MPI</strong>10@DESY September 2010 20 / 25
Tun<strong>in</strong>g prospects<br />
◮ Also study how well the parton shower fills the phase space<br />
◮ Compare aga<strong>in</strong>st 2 → 3 real matrix elements<br />
◮ Would chang<strong>in</strong>g the shower start<strong>in</strong>g scale give better agreement?<br />
◮ Qualitatively, PS do<strong>in</strong>g a good job<br />
dσ / dp ⊥ [nb / GeV]<br />
0.1<br />
0.01<br />
0.001<br />
0.0001<br />
p⊥3 PS<br />
p⊥3 ME<br />
1e-05<br />
0 10 20 30 40 50<br />
p⊥ [GeV]<br />
dσ / dp ⊥ [nb / GeV]<br />
1<br />
0.1<br />
0.01<br />
0.001<br />
0.0001<br />
1e-05<br />
dσ / dp ⊥ [nb / GeV]<br />
0.1<br />
0.01<br />
0.001<br />
0.0001<br />
1e-06<br />
0 10 20 30 40 50<br />
p⊥ [GeV]<br />
p⊥4 PS<br />
p⊥4 ME<br />
1e-05<br />
0 10 20 30 40 50<br />
p⊥ [GeV]<br />
p⊥5 PS<br />
p⊥5 ME<br />
p ⊥ m<strong>in</strong><br />
3<br />
p ⊥ m<strong>in</strong><br />
5<br />
= 5.0 GeV<br />
= 5.0 GeV<br />
Rsep = 0.25<br />
Richard Corke (Lund University) <strong>MPI</strong>10@DESY September 2010 21 / 25
Tun<strong>in</strong>g prospects<br />
◮ Is a simultaneous MB/UE Tevatron tune now possible?<br />
◮ Tunes 2C and 2M<br />
◮ CTEQ6L1 and MRST LO** PDF tunes to Tevatron data<br />
◮ Start with by-hand tune<br />
◮ Compare aga<strong>in</strong>st Pro-Q20 and Perugia 0<br />
◮ Underly<strong>in</strong>g event description improved!<br />
〈N ch〉/dη dφ<br />
MC/data<br />
1<br />
0.8<br />
0.6<br />
<br />
0.4<br />
0.2<br />
0<br />
1.4<br />
1.2<br />
1<br />
0.8<br />
0.6<br />
Transverse region charged particle density<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
CDF data<br />
PYTHIA 6.422 Pro-Q20<br />
PYTHIA 6.422 Perugia 0<br />
PYTHIA 8.142 Tune 2C<br />
PYTHIA 8.142 Tune 2M<br />
0 50 100 150 200 250 300 350 400<br />
pT(lead<strong>in</strong>g jet) / GeV<br />
<br />
<br />
<br />
〈∑ ptrack T 〉/dη dφ / GeV<br />
MC/data<br />
2<br />
1.5<br />
1<br />
<br />
0.5<br />
<br />
0<br />
1.4<br />
Transverse region charged ∑ p ⊥ density<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
CDF data<br />
PYTHIA 6.422 Pro-Q20<br />
PYTHIA 6.422 Perugia 0<br />
PYTHIA 8.142 Tune 2C<br />
PYTHIA 8.142 Tune 2M<br />
0 50 100 150 200 250 300 350 400<br />
pT(lead<strong>in</strong>g jet) / GeV<br />
Richard Corke (Lund University) <strong>MPI</strong>10@DESY September 2010 22 / 25<br />
1.2<br />
1<br />
0.8<br />
0.6
Tun<strong>in</strong>g prospects<br />
◮ More plots: http://www.thep.lu.se/˜richard/pythia81<br />
〈pT〉 / GeV<br />
MC/data<br />
Mean track pT vs multiplicity, |η| < 1, p⊥ > 0.4 GeV<br />
2.4<br />
2.2<br />
2<br />
1.8<br />
1.6<br />
1.4<br />
1.2<br />
1<br />
0.8<br />
0.6<br />
1.4<br />
1.2<br />
1<br />
0.8<br />
0.6<br />
CDF data<br />
PYTHIA 6.422 Pro-Q20<br />
PYTHIA 6.422 Perugia 0<br />
PYTHIA 8.142 Tune 2C<br />
PYTHIA 8.142 Tune 2M<br />
<br />
<br />
5 10 15 20 25 30 35 40 45<br />
Nch <br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
<br />
CDF data<br />
PYTHIA 6.422 Pro-Q20<br />
PYTHIA 6.422 Perugia 0<br />
PYTHIA 8.142 Tune 2C<br />
10<br />
PYTHIA 8.142 Tune 2M<br />
−5<br />
10−4 10−3 10−2 10−1 Charged multiplicity at<br />
1<br />
√ s = 1800 GeV, |η| < 1, pT > 0.4 GeV<br />
dσ/dn ch<br />
MC/data<br />
1.4<br />
1.2<br />
1<br />
0.8<br />
0.6<br />
0 5 10 15 20 25 30 35 40<br />
Nch ◮ Broadly <strong>in</strong> l<strong>in</strong>e with previous tunes<br />
◮ MRST LO** has more momentum<br />
◮ Lower αs and higher p ref<br />
⊥0<br />
◮ Use overlap function for matter profile<br />
◮ Parameter gives handle on width of multiplicity distributions<br />
◮ Suggests slightly wider than s<strong>in</strong>gle Gaussian<br />
◮ Reduced colour reconnection<br />
Richard Corke (Lund University) <strong>MPI</strong>10@DESY September 2010 23 / 25
Tun<strong>in</strong>g prospects<br />
◮ New LHC data<br />
◮ Measurements of MB/UE at new energies!<br />
◮ Experiments appear consistent with themselves<br />
◮ But tension with older data?<br />
◮ Move from NSD/INEL to INEL>0<br />
◮ Reproducible def<strong>in</strong>itions!<br />
◮ Diffractive description more important?<br />
◮ New framework <strong>in</strong> PYTHIA 8 for high-mass diffraction<br />
◮ “Diffraction <strong>in</strong> <strong>Pythia</strong>,” S. Nav<strong>in</strong>, arXiv:1005.3894 [hep-ph]<br />
◮ Based on Ingelman–Schle<strong>in</strong> picture<br />
◮ S<strong>in</strong>gle diffraction: Pomeron emitted from one <strong>in</strong>com<strong>in</strong>g hadron<br />
<strong>in</strong>teracts with <strong>in</strong>com<strong>in</strong>g hadron on the other side<br />
◮ Total cross sections<br />
◮ Early look at MB numbers suggest dampen<strong>in</strong>g diffractive cross sections?<br />
◮ New possibility to dampen rise available<br />
◮ ATLAS-CONF-2010-048: “Both PYTHIA8 and PHOJET would do slightly<br />
better <strong>in</strong> describ<strong>in</strong>g the data if there was an <strong>in</strong>crease <strong>in</strong> the ND component”<br />
Richard Corke (Lund University) <strong>MPI</strong>10@DESY September 2010 24 / 25
Summary<br />
◮ PYTHIA 8 <strong>MPI</strong> model<br />
◮ Well established model that has evolved over time<br />
◮ Fully <strong>in</strong>terleaved with parton showers<br />
◮ Rich mix of possible underly<strong>in</strong>g event processes<br />
◮ Still under development<br />
◮ Enhanced screen<strong>in</strong>g<br />
◮ Perhaps part of a solution towards lower<strong>in</strong>g colour reconnections<br />
◮ More evidence to come from DIPSY?<br />
◮ Rescatter<strong>in</strong>g<br />
◮ First model to <strong>in</strong>clude such effects<br />
◮ No dist<strong>in</strong>ctive signatures; perhaps full tune would reveal more<br />
◮ Future project: x-dependent proton profile<br />
◮ Tun<strong>in</strong>g prospects<br />
◮ Simultaneous MB/UE tun<strong>in</strong>g with<strong>in</strong> reach<br />
◮ Initial tunes to Tevatron data<br />
◮ Impact of LHC data still uncerta<strong>in</strong><br />
◮ Article <strong>in</strong> preparation<br />
Richard Corke (Lund University) <strong>MPI</strong>10@DESY September 2010 25 / 25