Particle Physics Phenomenology 9. Event generators and other software

(1)

Particle Physics Phenomenology

9. Event generators and other software

Torbj¨

orn Sj¨

ostrand

Department of Astronomy and Theoretical Physics

Lund University

S¨

olvegatan 14A, SE-223 62 Lund, Sweden

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Why generators? – 2

Allow theoretical and experimental studies of

complex

multiparticle physics

Large flexibility in physical quantities that can be addressed

Vehicle of ideology to disseminate ideas

from theorists to experimentalists

Can be used to

predict event rates and topologies

⇒

can estimate feasibility

simulate possible backgrounds

⇒

can devise analysis strategies

study detector requirements

⇒

can optimize detector/trigger design

study detector imperfections

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The generator landscape

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The bigger picture

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PDG Particle Codes – 1

A. Fundamental objects

1 d

11 e

−

21 g

2 u

12 νe

22 γ

32 Z

0

3 s

13 µ

−

23 Z

0

33 Z

00

0

4 c

14 ν

µ

24 W

+

34 W

0 +

5 b

15 τ

−

25 h

0

35 H

0

37 H

+

6 t

16 ν

τ

36 A

0

39 G

raviton

add

−

sign for antiparticle, where appropriate

+ a wide range of exotica, e.g.

SUSY

1000021

˜

g

Technicolor

3000113

ρ

TC

compositeness

4000005

b

∗

extra dimensions

5100039

G

∗

raviton

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PDG Particle Codes – 2

B. Mesons

100 |q

1 |

+ 10

|q

2 |

+ (2

s

+ 1) with

|q

1 | ≥ |q

2 |

particle if “heaviest” quark u,

s

, c,

b

; else antiparticle

111 π

0

311 K

0

130 K

0 _L

421 D

0

211 π

+

321 K

+

310 K

0 _S

431 D

+

_s

221 η

0 ₃₃₁

_η

0

0 ₄₁₁

_D

+

₄₄₃

_J

_/ψ

C. Baryons

1000

q

1 + 100

q

2 + 10

q

3 + (2s

+ 1)

with

q

1 ≥

q

2 ≥

q

3 , or Λ-like

q

1 ≥

q

3 ≥

q

2 2112

n

3122

Λ

0 2224

∆

++

3214

Σ

∗

0 2212

p

3212

Σ

0 1114

∆

−

3334

Ω

−

D. Diquarks

1000

q

1 + 100

q

2 + (2s

+ 1) with

q

1 ≥

q

2 1103

uu

1 2101

ud

0 2103

ud

3 2203

dd

3

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Les Houches Accord – overview

Context: ME generator

→

PS/UE/hadronization

Transfer info on processes, cross sections, parton-leven events, . . .

LHA

: Les Houches Accord (2001)

formulated in terms of two Fortran commonblocks

(+calling structure):

1) overall run information for initialization

2) parton configuration one event at a time

E Boos et al., hep-ph/0109068

LHEF

: Les Houches Event File(s) (2006)

same information, but stored as a single plaintext file.

+ language-independent, cleaner separation, reuse same file

−

large files if many events

J. Alwall et al., Computer Phys. Commun. 176 (2007) 300,

hep-ph/0609017

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SUSY Les Houches Accord

File with info on SUSY (or other BSM) model:

parameters, masses, mixing matrices, branching ratios, . . . .

Output from spectrum calculator, input to event generator.

Block SPINFO # Program information 1 SOFTSUSY # spectrum calculator 2 1.9.1 # version number Block MODSEL # Select model

1 1 # sugra

Block SMINPUTS # Standard Model inputs

1 1.27934000e+02 # alpha_em^(-1)(MZ) SM MSbar 2 1.16637000e-05 # G_Fermi 3 1.17200000e-01 # alpha_s(MZ)MSbar 4 9.11876000e+01 # MZ(pole) 5 4.25000000e+00 # Mb(mb) 6 1.74300000e+02 # Mtop(pole) 7 1.77700000e+00 # Mtau(pole) Block MINPAR # SUSY breaking input parameters

3 1.00000000e+01 # tanb 4 1.00000000e+00 # sign(mu) 1 1.00000000e+02 # m0 2 2.50000000e+02 # m12 5 -1.00000000e+02 # A0

# Low energy data in SOFTSUSY: MIXING=-1 TOLERANCE=1.00000000e-03 # mgut=2.45916471e+16 GeV

Block MASS # Mass spectrum

#PDG code mass particle 24 8.04191121e+01 # MW 25 1.10762378e+02 # h0 35 4.00599584e+02 # H0 36 4.00231463e+02 # A0

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Other interfaces

LHAPDF: uniform interface to PDF parametrizations,

see

http://projects.hepforge.org/lhapdf/

drawback: in Fortran; bloated!

HepMC: output of complete generated events

(intermediate stages and final state with hundreds of particles)

for subsequent detector simulation or analysis,

see

https://savannah.cern.ch/projects/hepmc/

Binoth LHA: provide one-loop virtual corrections

FeynRules: nascent standard for input of Lagrangian and

output of Feynman rules, to be used by matrix element

generators

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MCnet

?

“Trade Union” of (QCD) Event Generator developers

?

Collects HERWIG, SHERPA and PYTHIA.

Also ThePEG, ARIADNE, VINCIA, . . . ,

generator validation (RIVET) and tuning (PROFESSOR)

(CERN, Durham, Lund, Karlsruhe, UC London, + associated).

?

Funded by EU Marie Curie training network 2007–2010

?

Postdocs, graduate students, short-term visits: now done.

New applications for continued activities: no luck so far.

?

Annual Monte Carlo school:

?

Durham, UK, 2007; Debrecen, Hungary, 2008;

Lund, Sweden, 2009; Lauterbad, Germany, 2010;

Kyoto, Japan, 5 - 10 September 2011

? Manchester, UK, 2012 ?

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The workhorses: what are the differences?

HERWIG, PYTHIA and SHERPA offer convenient frameworks

for LHC physics studies, but with slightly different emphasis:

PYTHIA (successor to JETSET, begun in 1978):

• originated in hadronization studies: the Lund string

• leading in development of MPI for MB/UE

• pragmatic attitude to showers & matching

HERWIG (successor to EARWIG, begun in 1984):

• originated in coherent-shower studies (angular ordering)

• cluster hadronization & underlying event pragmatic add-on

• large process library with spin correlations in decays

SHERPA (APACIC++/AMEGIC++, begun in 2000):

• own matrix-element calculator/generator

• extensive machinery for CKKW ME/PS matching

• hadronization & min-bias physics under development

PYTHIA & HERWIG originally in Fortran, now all C++

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Who was Pythia?

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PYTHIA activities

Ambition

• Meet

experimental request

for C++ code.

• Housecleaning

⇒

more homogeneous.

• More

user-friendly

(e.g. names).

• Better match to software frameworks

• More space for growth.

• Better interfaces to standards.

Reality

• Work begun autumn 2004.

• 3 years at CERN

⇒

good progress.

• First release autumn 2007.

• Since then: slower progress,

requests lagging behind.

• Usage slowly taking off.

Team members

Stefan Ask

Richard Corke

Stephen Mrenna

Peter Skands

Contributors include

O. Alvestad, B. Bellenot,

R. Brun, L. Carloni,

N. Desai, N. Hod,

H. Hoeth, P. Ilten,

T. Kasemets, M. Kirsanov,

B. Lloyd, M. Montull,

A. Morsch, A. Naumann,

S. Navin, P. Newman,

S. Prestel, M. Sutton

MSTW, CTEQ, H1: PDFs

DELPHI, LHCb: D/B BRs

+ bug reports & fixes

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Event generation structure

1

_{Initialization step}

• select process(es) to study

• modify physics parameters:

m

t

,

m

h

, . . .

• set kinematics constraints

• modify generator performance

• initialize generator

• book histograms

2

Generation loop

• generate one event at a time

• analyze it (or store for later use)

• add results to histograms

• print a few events

3

Finishing step

• print deduced cross-sections

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PYTHIA Outlook

• PYTHIA 6 is winding down:

?

is supported but not developed;

?

still main option for current run (sigh),

?

but not after long shutdown 2013

!

• PYTHIA 8 is the natural successor,

?

is (sadly!) not yet quite up to speed in

all

respects,

?

but for much already better than PYTHIA6 ,

?

is starting to have competitive tunes,

?

and will continue to move ahead.

?

Currently version 8.150 with the features mentioned here.

• Advise to experimentalists:

?

step up PYTHIA 8 usage to gain experience;

?

if you want new features then be prepared to use PYTHIA 8;

?

provide feedback, both what works and what does not;

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HERWIG – 1

(Peter Richardson)

!"#$%&

!"#"$%&'()*$+,-.

/!!!0%12$)*3%4.'5"$,'#6

!'()*+,,

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HERWIG – 3

(Peter Richardson)

!"#$%&'()%*+#

! "#$%&$'%($)'+,,%-.)/0&%1#0'$)%1%1/*22%

.&+32.)%0)4$)$4%53/6

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:).+<$&/./0&%:3&9/0&1%

! =.>$1%<./9#&+%/#$%1#0'$)%/0%#.)4%<./)?%

$2$<$&/1%$.1*$)@

(29)

HERWIG – 4

(Peter Richardson)

!"#$%&#'()*+$$',%-.

! "#$%&'(')*$+,'-".$/0121$345$4$6789/$8#$

5:;/$<:=19$;:2$/01$7#=129>8#?$1@1#/$4#=$/01$

:A/8:#$:;$758#?$/01$B"CCD$<79/8A91$A42/:#$

8#/124E/8:#$<:=19F

! "#$+1238?GG$31$751$4$8<A2:@1=$@1258:#$:;$

/01$B"CCD$CH"$<:=19$8#E97=8#?$4$5:;/$

E:<A:#1#/F

(30)

HERWIG – 5

(Peter Richardson)

!"#$%&"$'"(')*

! "#$%&'(&)%&+,-+$%&./&"'/)&0-+1'&

,.2#1-).'/,&./&+$/)&3-+,&%-,&./4'145&

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2-)+.9&12*/),&-)&:')%;

! <%+&-+&2-/3&.27+'42/),&./&=+8.6>>&

)'&./$1#5&:')%&)37,&'(&-77+'-$%?

(31)

HERWIG – 6

(Peter Richardson)

!"#$%&'()**)*

! "#$%$&'%$&()*&'&%'(+$&),&-%).$//$/&'..0%'1$&

1)&234&5(&.0%%$(1&6$%/5)(&),&7$%*5+889

! :(&';;515)(&1#$&($<1&6$%/5)(&*5==&5(.=0;$9

(32)

HERWIG – 7

(Peter Richardson)

!"#$%&'(&)(*+

! "#$%$&'()$+,-(./.(012(3/456728(9:(

;7./72/10(<;14(=>7;?8.(68@2103

! ,4@1;2702(<1;(2>8(3/45672/10(1<(+(70.(A(

68@210/=(.8=7B3C

! ,0()8;D/?EE(D8(3/456728(2>/3(53/0?(2>8(

F"G(<1;476/34C

(33)

HERWIG – 8

(Peter Richardson)

!"#$%&'()*(

! "#$%&'()*++$,-&$.$/)00&'&#1$.22'3.45$-3$3#67$15&$

8&7#9.#$',6&-$03'$.$#&($93/&6$#&&/$13$:&$43/&/;

! <,139.1)4.667$4.64,6.1&-$15&$=

=$-4.11&')#*$

2'34&--&->$?

=$.#/$?

@$/&4.7-$.#/$*&#&'.1&-$

.66$15&$-2)#$43''&6.1)3#-;

! A,''&#167$)#$.//)1)3#$13$15&$BC$15&

.'&$.D.)6.:6&;

(34)

HERWIG – 9

(Peter Richardson)

!"#$%&'()*(

! "#$%&'(('%)+%),-).,/0%1)/1$%2,0,*%

3,/4.510%65..%2$%)7)5.)2.$%5%8#$%*$98%:$.$)0$;

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8,%>$?@/.$0%8,%-)A$%)++51%*$6%-,+$.0%

$7$*%$)05$:;

(35)

HERWIG – 10

(Peter Richardson)

!"#$%&'(")'%&

! "#$%&'()%(&*+,-$&$)./%()%.#$%#'0+,)(1'.(,)%

'+$%0$/(2)$0%.,%(&*+,-$%.#$%/(&34'.(,)%,5

! 6'()47%.#+,32#%.#$%().+,038.(,)%,5%54'-,3+%

/$8(5(8%'+'&$.$+/%()%.#$%#'0+,)(1'.(,)%

&,0$49

(36)

HERWIG – 11

(Peter Richardson)

!"#$%&'"&#'(")'*+,"-.

! "#$%&'(()&+,-.#/)0)/123&/4&+04#.)/&5-,04&1)

16)172#$4-$804&9#)30.$1)0.)40-).#+0:/;

! <0&)+1+#4$04&1)1*

! =+,-.#/)+1$$#,04&1/)0*.)0,,1%/)

+155-&+04&1)%&43)43#)2#$4-$804&9#)/40'#)16)

43#)#9#*4)61$)40-).#+0:/;

(37)

HERWIG – 12

(Peter Richardson)

!"#$%&''

! "#$%&$'%($)'+,,%-).+)/0%&.'%-).12$3%/%4566%

3056/7.&%.4%6$-7.&86$-7.&9%6$-7.&8#/2).&%/&2%

#/2).&8#/2).&%:.663.&3%'*7#%0/&;%

0-).1$0$&73%.1$)%73%<=>">?@%-)$2$:$33.)A

(38)

SHERPA – 1

(Frank Krauss)

Introduction Matrix elements Parton showers Merging Soft physics Forthcoming attractions

SHERPA

Status and prospects

Frank Krauss

1 IPPP Durham

CERN MC4LHC - Tools readiness workshop - 29.3.2010

1

_{for the Sherpas: J. Archibald, T. Gleisberg, S. H¨}

_{oche, H. Hoeth, F. Krauss,}

M. Sch¨

onherr, S. Schumann, F. Siegert, J. Winter, and K. Zapp

F. Krauss IPPP Durham

(39)

SHERPA – 2

(Frank Krauss)

A brief introduction

S

HERPA

has been under development since the late 1990’s

In the beginning, borrowed and re-implemented physics from others: virtuality-ordered parton shower - APACIC++, underlying event like PYTHIA6.2 Helicity amplitudes for matrix elements - AMEGIC++

Fragmentation/hadron decays through link to PYTHIAroutines

Constructed from scratch, in

C++

Mainly done by diploma and PhD students

Replaced physics modules one-by-one.

Status in S

HERPA

1.2: by now independent of other code

Virtuality-ordered shower replaced by dipole shower, Berends-Giele matrix elements,

Own version of cluster fragmentation AHADIC++, Huge own library of hadron andτ-decays, QED radiation through YFS formalism,

Only UE modelling still along the line of Sjostyrand-van der Zijl, PYTHIA6.2.

A full-fledged independent event generator

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SHERPA – 3

(Frank Krauss)

High multiplicity matrix elements

Matrix element generation in SHERPA

1.2 Provides three kinds of matrix elements:

Since 1.2.0:

C

OMIX- mainly SM, can handle up to 8-10 final state particles

(implementations for BSM-relevant methods have low priority inCOMIX.)

A

MEGIC++

- SM & BSM generator, up to 6 final state particles

(development stalled, will eventually move toCOMIX.)

specific, hard-coded ME’s

Using

C

O

M

I

X

makes S

HERPA

even easier to handle:

no more libraries written out to be compiled in intermediate step.

S

HERPA

/A

MEGIC++

support F

EYN

R

ULES

(a tool to generate Feynman rules directly from Lagrangians - a new standard to propagate BSM models?)

No support for LHA - considered pointless by S

HERPA

.

(41)

SHERPA – 4

(Frank Krauss)

SM matrix element generator COMIX

T.Gleisberg & S.Hoeche, JHEP0812(2008) 039

Colour-dressed Berends-Giele amplitudes in the SM

Fully recursive phase space generation

Example results (phase space performance):

(42)

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SHERPA – 6

(Frank Krauss)

BSM matrix element generator AMEGIC++

F.K., R.Kuhn, G.Soff, JHEP0202(2002) 044.

Uses helicity/recursion methods;

Helicity method supplemented with “factoring out”

(taming the factorial growth)

Phase space integration through multi-channeling

(i.e. one phasespace mapping/Feynman diagram)

Implemented & tested models: SM, SM+AGC, THDM, MSSM, ADD.

Tested in

>

1000 SM &

>

500 MSSM channels.

Recently: Automated dipole subtraction for NLO calculations

(Fully supports the NLO-LHA)

(44)

SHERPA – 7

(Frank Krauss)

Parton showering in Sherpa 1.2

Parton shower based on Catani-Seymour splitting kernels

First discussed in: Z.Nagy and D.E.Soper, JHEP0510(2005) 024 Implemented by M.Dinsdale, M.Ternick, S.Weinzierl Phys.Rev.D76(2007) 094003 and S.Schumann& F.K., JHEP0803(2008) 038

.

Explicit use of factorization formulae for real

emission process

←→

NLO dipole subtraction

Full phase space coverage

(invertible).

Typically good approximation to ME.

Project onto leading 1

/

N

c

&

employ spin-averaged dipole kernels.

four types of splittings: FF, IF, FI, II.

Recently: improved kinematics mappings to

account for exponentiation properties

(Work in progress.)

m-parton state splitting operator

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SHERPA – 10

(Frank Krauss)

Merging for Prompt-Photon Production

The perturbative QCD approach

Direct production

fixed-order calculations

-

γ

+jet @ NLO (JetPhox)

[Catani et. al]

-

γγ

@ NLO (DiPhox)

[Binoth et. al]

-

γγ

+jet @ NLO

[Del Duca et. al]

-

gg

→

γγ

g

[de Florian et. al]

Fragmentation component

QED

γ

−

q

collinear singularity

resummation to all orders

α

s

fragmentation function

D

γq,g

Apporach bases on IR safe xsec definition (photon isolation)

[cone, smooth isolation, democratic approach]

Assumption:

non-prompt

component, e.g.

π

0

_→

_γγ

_,

_η

_→

_γγ

_{, experimentally separable}

(48)

SHERPA – 11

(Frank Krauss)

A new model for Minimum Bias (and the underlying event)

Underlying ideas

Multi-channel eikonal approach

allows for natural description of low-mass diffraction

Rooted in unitarisation by exponentiating eikonals

BFKL-inspired interpretation: exchange of “ladders” (cut pomerons)

between hadrons

Naturally incorporates diffraction/diffractive parts in ladder dynamics

(49)

SHERPA – 12

(Frank Krauss)

Conclusions

SHERPA

v1.2 and beyond

S

HERPA

v1.2 added enhanced physics and usability:

higher multis, no more libraries, merging completely automatic

New merging algorithm with improved features:

less merging scale uncertainty (below 10% in most cases), smooth

transitions

has been extended to DIS (

→

VBF) and prompt photon production

Added dipole subtraction for NLO calculations (LH accord)

Will include new Minimum Bias model by summer

First steps towards NLO precision under way.

(50)

VINCIA

(Peter Skands)

VINCIA: towards NLO showers

Simple shower formalism based on

2 →

3 antenna factorization for

arbi-trary evolution variables, recoil maps, radiation kernels, etc.

Matching

= cancel dependence on free parameters to given order

+

Exponentiate matching

= Use subleading logs in ME to improve resummation

in-stead of destroying it

(currently no “matching scale” needed before

α

3

s

×

Born)

+

Improve Shower

=

No dead zones, Markov Ordering (+ partial NLL matching)

Tree-Level expansion vs MadGraph

(

fl

at phase-space scan,

full color

):

(Narrow distributions = good logarithmic precision)

&(# *, %(' (" $+! )! %'% *)$ &(# %'% *)$ &(# %'% *)$

Pure shower

<VINCIA>= |M4|2 ±8% |M5|2 ±20% |M6|2±25% (+ can do matching, up throughZ→6 is already in)

Current Version = 1.021: massless FSR (

fi

rst public release Sep 2009).

• Short Term: Long writeup

(shower + tree-matching + LEP Pheno study)

• This Summer: Massive quarks

(with M. Ritzmann, A. Gehrmann-de-Ridder)

• Long Term: Initial-State Radiation and multijet 1-loop matching.

(51)

ARIADNE

(Leif L¨

onnblad)

CKKW-Lˆ

Fortran vs. C++

Outlook

The old Fortran version

The new C++ version

DIPSY

Current status of A

RIADNE

!

Completely rewritten in

_C++

using T

_HE

PEG

(main work by Nils Lavesson)

!

Almost all components are in place

!

Simple

CKKW(L) matching

!

q

_→

g

splitting included

!

String fragmentation with P

_YTHIA

8 !

Validated for

e

+

e

−

!

Modi



ed model for initial-state radiation without recoil

gluons needed.

(52)

CASCADE – 1

(Hannes Jung)

"!

!*

!!*

#+#$$

%&

!!%&

%!##(

#,

&-%#!#! !!%

#.!#"/!

#.!#'#*

%)01

(53)

CASCADE – 2

(Hannes Jung)

& ""39#

"'" "!' +

7 "#" "

"##613$%

"")

"#" "

""#6666:4%

""&'" "

'' '

*"( "# +

"!' "#

0$2684 8

#" "!/""

# ".

(54)

",5-Other special-purpose programs

EVTGEN:

B

decays, with detailed handling of interference,

polarization and

CP

-violation effects.

TAUOLA,

τ

decays, with polarization effects (correlated in

pairs).

PHOTOS: photon emission in decays of (electroweak)

resonances or hadrons.

(55)

Existing parton-level tools: tree-level

(Frank Krauss)

(56)

(57)

(58)

MadGraph/MadEvent – 1

(Rikkert Frederix)

The most user-friendly package for automatic

ME generation/integration:

(59)

(60)

(61)

(62)

(63)

(64)

(65)

(66)

(67)

(68)

PROFESSOR – 3

(Hendrik Hoeth)

(69)

(70)

MCPLOTS

Repository of comparisons between various tunes and data,

mainly based on RIVET for data analysis,

see

http://mcplots.cern.ch/

.

Part of the LHC@home 2.0 platform for home computer

participation.

η -2 0 2 η /d ch dN ev 1/N 2 3 4 5 6 7 8 ATLAS Pythia 8 Pythia 8 (Tune 2C) Pythia 8 (Tune 2M) Pythia 8 (Tune 4C)

7000 GeV pp Minimum Bias

mcplots.cern.ch Pythia 8.153 ATLAS_2010_S8918562 > 0.1 GeV/c) T > 2, p ch Distribution (N η Charged Particle -2 0 2 0.5 1 1.5 Ratio to ATLAS η -2 0 2 η /d ch dN ev 1/N 1 1.5 2 2.5 3 3.5 ATLAS Pythia 8 Pythia 8 (Tune 2C) Pythia 8 (Tune 2M) Pythia 8 (Tune 4C)

7000 GeV pp Minimum Bias

mcplots.cern.ch Pythia 8.153 ATLAS_2010_S8918562 > 0.5 GeV/c) T > 1, p ch Distribution (N η Charged Particle -2 0 2 0.5 1 1.5 Ratio to ATLAS

(71)

Tuning

(Peter Skands)

3 Kinds of

Tuning

1. Fragmentation Tuning

Non-perturbative:

hadronization modeling & parameters

Perturbative:

jet radiation, jet broadening, jet structure

2. Initial-State Tuning

Non-perturbative:

PDFs, primordial k

T

Perturbative:

initial-state radiation, initial-



nal interference

3. Underlying-Event & Min-Bias Tuning

Non-perturbative:

Multi-parton PDFs, Color (re)connections,

collective effects, impact parameter dependence, …

Perturbative

:

Multi-parton interactions, rescattering

(72)

PYTHIA 8 tuning – 1

Tuning to

e

+

e

−

closely related to

p

⊥

-ordered PYTHIA 6.4;

Rivet+Professor (H. Hoeth)

⇒

FSR & hadronization OK (?)

First tuning to MB data by P. Skands:

⇒

(73)

PYTHIA 8 tuning – 2

But Rivet+Professor (H. Hoeth) shows it fails miserably for UE

(Rick Field’s transverse flow as function of jet

p

⊥

):

No universal tune MB + UE!

(74)

PYTHIA 8 tuning – 3

Final-state parton may have colour partner in the initial state.

How to subdivide FSR and ISR in this kind of dipole?

Large mass

→

large rapidity range for emission:

In dipole rest frame

(think rapidity space)

(75)

PYTHIA 8 tuning – 4

Is a simultaneous MB/UE Tevatron tune now possible?

Tunes 2C and 2M done “by hand” (using Rivet, but not Professor),

using the CTEQ6L1 and MRST LO** PDF sets, respectively,

to MB data (

n

ch

,

h

p

⊥

i

(

n

ch

), . . . .

Compare against Pro-Q20 and Perugia 0 (PYTHIA 6)

(76)

PYTHIA 8 tuning – 5

(77)

PYTHIA 8 tuning – 6

Rick Field: if

p

⊥

0 (

E

CM

)

∝

E

CM

tuned to LHC data,

then gives too much UE activity at Tevatron

(

⇒

need higher

p

⊥

0 to compensate)

MPI Cut-Off P

T0

(W

cm

)

1.0 1.5 2.0 2.5 3.0 3.5 0 2000 4000 6000 8000 10000 12000 Center-of-Mass Energy Wcm (GeV)

PT0 (G e V /c ) RDF Very Preliminary Tune Z1 CMS 900 GeV CMS 7 TeV CDF 1.96 TeV

Pick some key LHC data sets, use Tune 2C as starting point:

• slightly dampen diffractive cross section (ATLAS)

(78)

PYTHIA 8 tuning – 7

Tunes involving only some of the first LHC data (in Rivet).

Parameter

2C

2M

4C

4Cx

SigmaProcess:alphaSvalue

0.135 0.1265

0.135

0.135 SpaceShower:rapidityOrder

on

SpaceShower:alphaSvalue

0.137

0.130

0.137

0.137 SpaceShower:pT0Ref

2.0

2.0 MultipleInteractions:alphaSvalue

0.135

0.127

0.135

0.135 MultipleInteractions:pT0Ref

2.320

2.455

2.085

2.15 MultipleInteractions:ecmPow

0.21

0.26

0.19

0.19 MultipleInteractions:bProfile

3

4 MultipleInteractions:expPow

1.60

1.15

2.00 N/A

MultipleInteractions:a1

N/A

0.15 BeamRemnants:reconnectRange

3.0

1.5

1.5 SigmaDiffractive:dampen

off

on

SigmaDiffractive:maxXB

N/A

65

65 SigmaDiffractive:maxAX

N/A

65

65 SigmaDiffractive:maxXX

N/A

65

(79)

PYTHIA 8 tuning – 8

(80)

PYTHIA 8 tuning – 9

. . . but at the expense of Tevatron agreement:

Future:

• better understanding of data?

• official/validated inclusion in Rivet?

• combined tune Tevatron + LHC?

(81)

Tune comparison (MCPLOTS) – 1

ch N 50 100 150 200 ch /dN σ d σ 1/ -6 10 -5 10 -4 10 -3 10 -2 10 -1 10 1 ATLAS Herwig++ (UE7-2) Pythia 6 (350:P2011) Pythia 8 Sherpa

7000 GeV pp

Minimum Bias

mcplots.cern.ch

Herwig++ 2.5.1, Pythia 6.425, Pythia 8.153, Sherpa 1.3.0 ATLAS_2010_S8918562 > 0.1 GeV/c) T > 20, p ch (N 50 100 150 200 0.5 1 1.5 Ratio to ATLAS [GeV] T p 0 20 40 T dp η /d σ dT p π 1/2 ev 1/N -10 10 -9 10 -8 10 -7 10 -6 10 -5 10 -4 10 -3 10 -2 10 -1 10 1 10 2 10 3 10 4 10 ATLAS Herwig++ (UE7-2) Pythia 6 (350:P2011) Pythia 8 Sherpa

7000 GeV pp

Minimum Bias

mcplots.cern.ch

Herwig++ 2.5.1, Pythia 6.425, Pythia 8.153, Sherpa 1.3.0 ATLAS_2010_S8918562 > 0.1 GeV/c) T > 2, p ch Spectrum (N T Charged Particle p 0 20 40 0.5 1 1.5 Ratio to ATLAS

(82)

Tune comparison (MCPLOTS) – 2

[GeV] T p 100 200 300 400 dy [pb/GeV]T /dp σ 2 d 10 2 10 3 10 4 10 5 10 6 10 ATLAS Herwig++ (UE7-2) Pythia 6 (350:P2011) Pythia 8

7000 GeV pp

Jets mcplots.cern.ch

Herwig++ 2.5.1, Pythia 6.425, Pythia 8.153 ATLAS_2010_S8817804 Jet Transverse Momentum ()

100 200 300 400 0.5 1 1.5 Ratio to ATLAS [GeV] 12 m 600 800 1000 | [pb/GeV] max /dm d|y σ 2 d 1 10 2 10 ATLAS Herwig++ (UE7-2) Pythia 6 (350:P2011) Pythia 8 Sherpa

7000 GeV pp

Jets mcplots.cern.ch

Herwig++ 2.5.1, Pythia 6.425, Pythia 8.153, Sherpa 1.3.0 ATLAS_2010_S8817804 Di-jet mass () 600 800 1000 0.5 1 1.5 Ratio to ATLAS

(83)

Tune comparison (MCPLOTS) – 3

jet N 0 2 4 jets) [pb] jet N ≥ (W + σ 10 2 10 3 10 4 10 ATLAS Herwig++ (UE7-2) Pythia 6 (350:P2011) Pythia 8 Sherpa

7000 GeV pp

W+Jets mcplots.cern.ch

Herwig++ 2.5.1, Pythia 6.425, Pythia 8.153, Sherpa 1.3.0 ATLAS_2010_S8919674 Jets multiplicity () 0 2 4 0.5 1 1.5 Ratio to ATLAS chg N 10 20 30 [GeV] 〉 T p 〈 0.4 0.6 0.8 1 1.2 1.4 ATLAS Herwig++ (UE7-2) Pythia 6 (350:P2011) Pythia 8 Sherpa

7000 GeV pp

Underlying Event

mcplots.cern.ch

Herwig++ 2.5.1, Pythia 6.425, Pythia 8.153, Sherpa 1.3.0 ATLAS_2010_S8894728 > 0.5 GeV/c) T | < 2.5, p η (TRNS) (| ch vs N T Average p 10 20 30 0.5 1 1.5 Ratio to ATLAS