New Review of Monte Carlo Event Generators in the UK · 2017. 7. 21. · Review of Monte Carlo...

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


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.


MC in UK


A Monte Carlo Event

t

t

Hard Process, nowcalculated at (N)NLO


MC in UK


A Monte Carlo Event

t

t

Initial- and final-state parton showerp, p

p, p


MC in UK


A Monte Carlo Event

t

t b

W−

bW+

νℓℓ+

Perturbative decaysof heavy particles

p, p

p, p


MC in UK


A Monte Carlo Event

t

t b

W−

bW+

νℓℓ+

Secondary hardprocesses

p, p

p, p


MC in UK


A Monte Carlo Event

t

t b

W−

bW+

νℓℓ+

Hadrons

Hadrons

Hadrons

Hadrons

Hadrons

Hadronizationp, p

p, p


MC in UK


A Monte Carlo Event

t

t b

W−

bW+

νℓℓ+

Hadrons

Hadrons

Hadrons

Hadrons

Hadrons

Hadron Decaysp, p

p, p


MC in UK


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.


MC in UK


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


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


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++.

1990 1995 2000 2005 2010 2015Date

0

100000

200000

300000

400000

500000

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s

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0

2

4

6

8

10

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14

16

Authors

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.


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++.

1990 1995 2000 2005 2010 2015Date

0

100000

200000

300000

400000

500000

Line

s

Lines Hw++Lines HwAuthors Hw++Authors Hw

0

2

4

6

8

10

12

14

16

Authors

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.


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


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


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


MC in UK

Recent Results

Merging with bottom quarks

from 1612.04640 Krauss, Napoletano, Schumann


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.


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


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).


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).


MC in UK

Recent Results

Subleading-Logs

from Hoche, Krauss, Prestel arXiv:1705.00982


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.


New Review of Monte Carlo Event Generators in the UK · 2017. 7. 21. · Review of Monte Carlo...

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