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MC in UK
Review of Monte Carlo Event Generators in the
UK
Peter Richardson
CERN TH & IPPP Durham
RAL: 21st July, 2017
Peter Richardson MC in UK
MC in UK
Outline
Motivation, projects and history
Current Status
Recent Highlights
The Future
Peter Richardson MC in UK
MC in UK
Motivation and History
Basics of Event Generation
Monte Carlo event generators combine:
hard perturbative QCD calculations;approximate QCD evolution from high to low energy scalesusing the parton shower;perturbative multiple parton scattering models of theunderlying event;non-perturbative models of the hadronization process;simulations of hadron decays;
to provide simulations of complete events.
They are essential tools that both encapsulate the currenttheoretical understanding of hadronic collisions and producesimulated events which can be compared with data.
Peter Richardson MC in UK
MC in UK
Motivation and History
A Monte Carlo Event
t
t
Hard Process, nowcalculated at (N)NLO
Peter Richardson MC in UK
MC in UK
Motivation and History
A Monte Carlo Event
t
t
Initial- and final-state parton showerp, p
p, p
Peter Richardson MC in UK
MC in UK
Motivation and History
A Monte Carlo Event
t
t b
W−
bW+
νℓℓ+
Perturbative decaysof heavy particles
p, p
p, p
Peter Richardson MC in UK
MC in UK
Motivation and History
A Monte Carlo Event
t
t b
W−
bW+
νℓℓ+
Secondary hardprocesses
p, p
p, p
Peter Richardson MC in UK
MC in UK
Motivation and History
A Monte Carlo Event
t
t b
W−
bW+
νℓℓ+
Hadrons
Hadrons
Hadrons
Hadrons
Hadrons
Hadronizationp, p
p, p
Peter Richardson MC in UK
MC in UK
Motivation and History
A Monte Carlo Event
t
t b
W−
bW+
νℓℓ+
Hadrons
Hadrons
Hadrons
Hadrons
Hadrons
Hadron Decaysp, p
p, p
Peter Richardson MC in UK
MC in UK
Motivation and History
Projects with U.K. Involvement and Leadership
Currently three major Monte Carlo event generators, U.K.leadership in two of them
Herwig (Richardson, IPPP & Seymour, Manchester)SHERPA (Krauss, IPPP)
Other projects
Leadership of High Energy Jets (HEJ) (Andersen, IPPP &Smillie, Edinburgh)Involvement with MinLO and POWHEGBox (Hamilton, UCLZanderighi, Oxford)
Leadership in HepData project for data preservation (IPPP)and Rivet and Professor programs for data comparison/tuning(Glasgow,IPPP)
Leadership of E.U. network MCnet.
Peter Richardson MC in UK
MC in UK
Motivation and History
History
The U.K. has been a leader in MC development since thebirth of the field. Webber, Cambridge HERWIG 1984→,Sakurai Prize 2012
Significant investment in early-mid 2000s
2 PRDAs to develop new program based on HERWIG in C++(PPARC responsive RAs)e-Science money to redevelop HepData and develop Rivet.Additional permanent appointments Seymour, Richardson,Krauss.Significant investment from the IPPP.More recent appointments of Zanderighi, Hamilton,Zanderighi,Andersen, Smillie
Peter Richardson MC in UK
MC in UK
Current Status
Last 15 years in Monte Carlo
The last fifteen years have seen significant changes in theMonte Carlo generator field.
At the end of LEP
Main programs were FORTRAN HERWIG6 and PYTHIA6.Parton showers with matching to the first hard emission forsimple processes such as e+e− → qq and Drell-Yan.
Developments since LEP
Multiple emissions at LO, CKKWMatching to NLO (1st approach Frixione and Webber)Merging at NLO (NLO normalisation for multiple emissions)MINLO, Sherpa, Herwig 7.1First NNLO Hamilton, Nason, Oleari, Zanderighi
Peter Richardson MC in UK
MC in UK
Current Status
New Programs
At the end of LEP the existingFORTRAN generators needed tobe rewritten to allow physicsimprovements and long termdevelopment:
HERWIG redeveloped asHerwig++ and then Herwig7;PYTHIA → Pythia 8;Sherpa developed from scratch;
all in C++.
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New generation of event generators which are the workhorsesat the LHC, together with specialised programs for thecalculation of hard processes in the various merging schemes.
Peter Richardson MC in UK
MC in UK
Current Status
New Programs
At the end of LEP the existingFORTRAN generators needed tobe rewritten to allow physicsimprovements and long termdevelopment:
HERWIG redeveloped asHerwig++ and then Herwig7;PYTHIA → Pythia 8;Sherpa developed from scratch;
all in C++.
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New generation of event generators which are the workhorsesat the LHC, together with specialised programs for thecalculation of hard processes in the various merging schemes.
Peter Richardson MC in UK
MC in UK
Recent Results
At the LHC: ATLAS Z+jets
) [p
b]je
ts*+
Nγ
(Z/
σ
-210
-110
1
10
210
310
410
510
610ATLAS Preliminary
1−13 TeV, 3.16 fb
jets, R = 0.4tanti-k
< 2.5jet
y > 30 GeV, jet
Tp
) + jets−l+ l→*(γZ/
Data
HERPAS + ATHLACK B
2.2HERPA S
6YP + LPGEN A
8 CKKWLYP + MG5_aMC
8 FxFxYP + MG5_aMC
0≥ 1≥ 2≥ 3≥ 4≥ 5≥ 6≥ 7≥
Pre
d./D
ata
0.5
1
1.5
0≥ 1≥ 2≥ 3≥ 4≥ 5≥ 6≥ 7≥
Pre
d./D
ata
0.5
1
1.5
jetsN
0≥ 1≥ 2≥ 3≥ 4≥ 5≥ 6≥ 7≥
Pre
d./D
ata
0.5
1
1.5
100 200 300 400 500 600 700
[pb/
GeV
]je
t
T/d
pσd
-410
-310
-210
-110
1
10
210
310 ATLAS Preliminary1−13 TeV, 3.16 fb
jets, R = 0.4tanti-k
< 2.5jet
y > 30 GeV, jet
Tp
1 jet≥) + −l+ l→*(γZ/ Data
NNLOjetti
1 jet N≥ Z + HERPAS + ATHLACK B
2.2HERPA S6YP + LPGEN A
8 CKKWLYP + MG5_aMC8 FxFxYP + MG5_aMC
100 200 300 400 500 600 700
Pre
d./D
ata
0.5
1
1.5
100 200 300 400 500 600 700
Pre
d./D
ata
0.5
1
1.5
(leading jet) [GeV]jet
Tp
100 200 300 400 500 600 700
Pre
d./D
ata
0.5
1
1.5
ATLAS-CONF-2016-046
Peter Richardson MC in UK
MC in UK
Recent Results
At the LHC: ATLAS W+jets
(4th leading jet) [GeV]j
Tp
40 60 80 100 120 140 160 180 200
[1/
GeV
]j T
/dp
4j≥W
+σd
-410
-310
-210
-110
1
10ATLAS
jets, R=0.4,tanti-k
| < 4.4j
> 30 GeV, |yj
Tp
Scaled Predictions
4 jet≥) + ν l→W(Data,
-1 = 7 TeV, 4.6 fbs+SHERPAATHLACKB
HEJALPGENSHERPAMEPS@NLO
40 60 80 100 120 140 160 180 200
Pre
d. /
Dat
a
0.6
0.8
1
1.2
1.4 +SHERPAATHLACKB
ATLAS
40 60 80 100 120 140 160 180 200
Pre
d. /
Dat
a
0.6
0.8
1
1.2
1.4 HEJ
40 60 80 100 120 140 160 180 200P
red.
/ D
ata
0.6
0.8
1
1.2
1.4 ALPGEN
(4th leading jet) [GeV]j
Tp
40 60 80 100 120 140 160 180 200
Pre
d. /
Dat
a
0.6
0.8
1
1.2
1.4
SHERPA
MEPS@NLO
Peter Richardson MC in UK
MC in UK
Recent Results
Effect of Jet Veto in Gluon Fusion with HEJ
MCFMHEJSherpa
| > 4ab
y∆|
> 40 GeVT,j
p
| > 4ab
y∆|
> 40 GeVT,j
p
| > 4ab
y∆|
> 40 GeVT,j
p
| > 4ab
y∆|
> 40 GeVT,j
p
| > 4ab
y∆|
> 40 GeVT,j
p
| > 4ab
y∆|
> 40 GeVT,j
p
| > 4ab
y∆|
> 40 GeVT,j
p
| > 4ab
y∆|
> 40 GeVT,j
p
| > 4ab
y∆|
> 40 GeVT,j
p
| > 4ab
y∆|
> 40 GeVT,j
p
(0)
σ)
/ c
(yσ0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
cy
0 0.5 1 1.5 2 2.5 3 3.5 4
from 1706.01002, Andersen, et.al
Peter Richardson MC in UK
MC in UK
Recent Results
Merging with bottom quarks
from 1612.04640 Krauss, Napoletano, Schumann
Peter Richardson MC in UK
MC in UK
Recent Results
Merging W+W
− and W+W
−+jet with MINLO
10−5
10−4
10−3
10−2
10−1
dσ/d
pT,j 1[pb/G
eV]
Ratio
Njets≥1
dσ/d
pT,j 1[pb/G
eV]
Ratio
Njets≥1
WWJ−MiNLO
WWJ[NLO]
pT,j1[GeV]
0.5
1.0
1.5
0 100 200 300 400 500
10−6
10−5
10−4
10−3
10−2
10−1
dσ/d
pT,j 2[pb/G
eV]
Ratio
Njets≥2
dσ/d
pT,j 2[pb/G
eV]
Ratio
Njets≥2
WWJ−MiNLO
WWJ[NLO]
pT,j2[GeV]
0.5
1.0
1.5
0 100 200 300 400 500
JHEP 1609 (2016) 057 Hamilton et.al.
Peter Richardson MC in UK
MC in UK
Recent Results
Extending MINLO
10−3
10−2
10−1
100
101
102
≥ 0 ≥ 1 ≥ 2 ≥ 3 ≥ 4
Njets
σ[pb]
#/H
JJ
#/H
JJ⋆
#/N
NLOPS
Anti−kT
R=0.4
pT > 100 GeV
Njets
σ[pb]
#/H
JJ
#/H
JJ⋆
#/N
NLOPS
Anti−kT
R=0.4
pT > 100 GeV
σ[pb]
#/H
JJ
#/H
JJ⋆
#/N
NLOPS
Anti−kT
R=0.4
pT > 100 GeV
σ[pb]
#/H
JJ
#/H
JJ⋆
#/N
NLOPS
Anti−kT
R=0.4
pT > 100 GeV
HJJ⋆
NNLOPS
HJJ 0.7
1.0
1.3
≥ 0 ≥ 1 ≥ 2 ≥ 3 ≥ 4
0.7
1.0
1.3
0.7
1.0
1.3
JHEP 1605 (2016) 042 Frederix and Hamilton
Peter Richardson MC in UK
MC in UK
Recent Results
Herwig 7.1
b
bb
bbb
bbb b
b b b b b b b b b b b b b b b b b b b b b b b b b bbbbbb
b
❍❡r✇✐❣ ✼✳✶▼❛❞●�❛♣❤✴❖♣✁♥▲♦♦♣s✴❈♦❧♦�❋✉❧❧
❆✂❊P❍ ❉✄t✄b
❡❡✭✵✱✶✱✷✮
♠☎✆ ❂ ✝♠✆♠☎✆ ❂ ♠✆✞✝
♠☎❙ ❂ ✝♠❙♠☎❙ ❂ ♠❙✞✝
✶✵✟✸
✶✵✟✠
✶✵✟✡
✶
✶✵ ✡
❚☛r☞✌t ✭✍✎✏✑ ❂ ✾✒✳✝ ✓❡❱✮
✔✕✖✗✖✕✗✘
✵✳✻ ✵✳✻✺ ✵✳✼ ✵✳✼✺ ✵✳✽ ✵✳✽✺ ✵✳✙ ✵✳✙✺
✵✳✻✵✳✼✵✳✽✵✳✙✶✳✵✶✳✶✶✳✷✶✳✚✶✳✹
✛
✜✢✕✣✤✥✤
Bellm et.al. arXiv:1705.06919. Main new feature multi-jet NLO merging (Bellm,
Gieseke, Plater arXiv:1705.06700).
Peter Richardson MC in UK
MC in UK
Recent Results
Herwig 7.1
b bb b b b b b
bb
bb
bb
b b
❍❡r✇✐❣ ✼✳✶▼❛❞●�❛♣❤✴❖♣✁♥▲♦♦♣s✴❈♦❧♦�❋✉❧❧
❆❚✂❆❙ ❉✄t✄b
❲✭✵✮ ❢☎✆✆
❲✭✵✱✶✱✷✮ ❢☎✆✆
❲✭✵✯✱✶✯✱✷✮✱ ✝✞ ✟P■✱ ✝✞ ✠✄✡✳
❲✭✵✯✱✶✯✱✷✮✱ ✝✞ ✠✄✡✳
❲✭✵✯✱✶✯✱✷✮ ❢☎✆✆
✶
✶✵ ☛
✶✵ ☞
✶✵ ✸♠☎✞✝ ❝✠✄✝✝❡✆✱ ✡r❡✌✌❡✡ ✆❡✈❡✆
✍✎✏✰✕✑❥✒✍✓✔❥✖✗❥✑
✵ ✵✳✺ ✶ ✶✳✺ ✷ ✷✳✺ ✘
✵✳✷✵✳✹✵✳✻✵✳✽✶
✶✳✷✶✳✹✶✳✻✶✳✽
✙✚✛✜✢✛✣
✤✥✒✦✧★✧
Bellm et.al. arXiv:1705.06919. Main new feature multi-jet NLO merging (Bellm,
Gieseke, Plater arXiv:1705.06700).
Peter Richardson MC in UK
MC in UK
Recent Results
Subleading-Logs
from Hoche, Krauss, Prestel arXiv:1705.00982
Peter Richardson MC in UK
MC in UK
The Future
The Future
U.K continues to be the world-leader in MC development.
Important synergy between:
event generator projects Herwig & Sherpa;data preservation Rivet & HepDatahigher order/multiplicity calculations HEJ, MINLO,POWHEGBox, BLACKHAT,. . .experimental community
Can lead to new developments e.g. Contour.
Peter Richardson MC in UK