Sherpa An event generator for LHC · R. Kuhn, F . Krauss, G. Sof f JHEP 0202:044, 2002 AMEGIC++ is...

for the Sherpa collaboration: Timo Fischer, Tanju Gleisberg, SH, Frank Krauss, Thomas Laubrich,

Radoslaw Matyszkiewicz, Steffen Schumann, Frank Siegert & Jan Winter

SherpaAn event generator for LHC

Stefan HöcheUniversität Dortmund

Université Catholique de Louvain

1

1

combinationn of the above: CKKWParton shower generation

Outline

Stefan Höche, WG Seminar Dortmund, 22.8.2006

This talk is meant to be a quick guided tour through Sherpa ...

Multiple parton interactions

Matrix element generation

Cluster fragmentationHadron decays

Perturbative physics

Semihard / nonperturbative physics

The Sherpa Framework


Scope of the Sherpa project:Provide a multi-purpose Monte Carlo event generator for

new physics searches at future colliders

Provide framework for implementation of new models

Account for multijet production through multi-partontree-level matrix elements merged with the parton shower

SM background simulation (bread- & butter physics)

new interaction modelsnew hadronisation & hadron decay models...

Special emphasis:

Current status:Full MC simulation of e e , γγ and hadron collisions possible+ -

Work on DIS-like situations and new models in progress

2

The Sherpa Framework

Key features:Automatic ME generationvia AMEGIC++Generation of QCD/QED radiationvia APACIC++ ( PYTHIA-like PS )Merging of ME and PS according to CKKW S. Catani, F. Krauss, R. Kuhn, B. Webber JHEP 0111:063, 2001 & F.Krauss JHEP 0208:015, 2002

Simulation of multiple interactions acc. to T. Sjöstrand, M. van Zijl Phys. Rev. D36 (1987) ( own model in preparation )Cluster fragmentation in preparation( currently string fragmentation via PYTHIA )Own hadron decay framework including a τ decay library

Sherpa is the framework, responsible for steering the generatorStefan Höche, WG Seminar Dortmund, 22.8.2006

R. Kuhn, F. Krauss, G. Soff JHEP 0202:044, 2002

Sherpas built-in ME generator AMEGIC++ providesFully automated calculation of (polarized) cross sectionsin the SM, MSSM and ADD modelPerformance comparable to that of dedicated codesExpandability (users can implement new models)

Extensively tested, e.g.

Comparison of arbitrary 2 2 MSSMprocesses vs. WHIZARD/O’Mega &SMadGraph K. Hagiwara, W. Kilian, F. Krauss, T.Ohl, T. Plehn, D. Rainwater, J. Reuter, S.Schumann hep-ph/0512260

+ -e e 6f comparison vs. HELAC/PHEGASmutual deviations in ~100 processes

Matrix Elements: AMEGIC++


R. Kuhn, F. Krauss, G. Soff JHEP 0202:044, 2002

AMEGIC++ is an ME-generator-generator:Given initial and final state, AMEGIC++ constructs all diagrams

Corresponding phase space mappings are generated

C++ code, representing all the above is stored to diskmust be compiled and becomes part of the generator

Diagrams are translated into C++ code employing the helicity formalism hep-ph/9403244

1

2

0

3 54

a

t

b

cz

c

b

CF1 + z2

1 ! zCF

1 + (1 ! z)2

z

TR

!z2 + (1 ! z)2" 2CA

(1 ! z + z2)2

z(1 ! z)

1

Diso(23, 45) ! P0(23) ! P0(45)

! Diso(2, 3) ! Diso(4, 5)

( allows efficient mapping of potentially complicated peak structure in subsequent PS integration )



2.2 Results 21

In the phase-space integration cuts on transverse momentum pT , pseudo-rapidity ! and thecone distance !R have been applied on all final state particles with the exception of massiveparticles with mi > 3 GeV and neutrinos, whose phase space remains unconstrained. Thecuts read, in particular:

pTi > 20 GeV,

|!i| < 2.5

!Rij =!

!"2 + !!2 > 0.4 , (2.13)

Statistical errors of the Monte Carlo integrations, i.e. one standard deviation, are given inparentheses.

Numerical results

X-sects (pb) e!!e + n QCD jetsNumber of jets 0 1 2 3 4 5 6

ALPGEN 3904(6) 1013(2) 364(2) 136(1) 53.6(6) 21.6(2) 8.7(1)AMEGIC++ 3908(3) 1011(2) 362.3(9) 137.5(5) 54(1)CompHEP 3947.4(3) 1022.4(5) 364.4(4)GR@PPA 3905(5) 1013(1) 361.0(7) 133.8(3) 53.8(1)JetI 3786(81) 1021(8) 361(4) 157(1) 46(1)

MadEvent 3902(5) 1012(2) 361(1) 135.5(3) 53.6(2)

Table 2.8: Cross sections for the process e!!e + n jets at the LHC. All results are in pb.

X-sects (pb) e+!e + n QCD jetsNumber of jets 0 1 2 3 4 5 6

ALPGEN 5423(9) 1291(13) 465(2) 182.8(8) 75.7(8) 32.5(2) 13.9(2)AMEGIC++ 5432(5) 1277(2) 466(2) 184(1) 77.3(4)CompHEP 5485.8(6) 1287.5(7) 467.3(8)GR@PPA 5434(7) 1273 (2) 467.7(9) 181.8(5) 76.6(3)JetI 5349(143) 1275(12) 487(3) 212(2)

MadEvent 5433(8) 1277(2) 464(1) 182(1) 75.9(3)

Table 2.9: Cross sections for the process e+!e + n jets at the LHC. All results are in pb.

The first processes considered here are the production of electroweak gauge bosons. InTables 2.9 and 2.8 the cross sections for the production of positively and negatively chargedW bosons accompanied by the production of up to 6 jets are presented1. The achievedprecision of AMEGIC++ and the other codes is on the sub-per cent level. Note that the crosssections for pp ! W+ + X are approximately 35% larger than the corresponding crosssections for pp ! W! + X. This is in contrast to the Tevatron, where proton anti-protoncollisions are performed, such that the charge does not matter for the production cross

1AMEGIC++ is able to calculate the cross section for the production of gauge bosons with up to four extrajets.

2.2 Results 21

In the phase-space integration cuts on transverse momentum pT , pseudo-rapidity ! and thecone distance !R have been applied on all final state particles with the exception of massiveparticles with mi > 3 GeV and neutrinos, whose phase space remains unconstrained. Thecuts read, in particular:

pTi > 20 GeV,

|!i| < 2.5

!Rij =!

!"2 + !!2 > 0.4 , (2.13)

Statistical errors of the Monte Carlo integrations, i.e. one standard deviation, are given inparentheses.

Numerical results

X-sects (pb) e!!e + n QCD jetsNumber of jets 0 1 2 3 4 5 6

ALPGEN 3904(6) 1013(2) 364(2) 136(1) 53.6(6) 21.6(2) 8.7(1)AMEGIC++ 3908(3) 1011(2) 362.3(9) 137.5(5) 54(1)CompHEP 3947.4(3) 1022.4(5) 364.4(4)GR@PPA 3905(5) 1013(1) 361.0(7) 133.8(3) 53.8(1)JetI 3786(81) 1021(8) 361(4) 157(1) 46(1)

MadEvent 3902(5) 1012(2) 361(1) 135.5(3) 53.6(2)

Table 2.8: Cross sections for the process e!!e + n jets at the LHC. All results are in pb.

X-sects (pb) e+!e + n QCD jetsNumber of jets 0 1 2 3 4 5 6

ALPGEN 5423(9) 1291(13) 465(2) 182.8(8) 75.7(8) 32.5(2) 13.9(2)AMEGIC++ 5432(5) 1277(2) 466(2) 184(1) 77.3(4)CompHEP 5485.8(6) 1287.5(7) 467.3(8)GR@PPA 5434(7) 1273 (2) 467.7(9) 181.8(5) 76.6(3)JetI 5349(143) 1275(12) 487(3) 212(2)

MadEvent 5433(8) 1277(2) 464(1) 182(1) 75.9(3)

Table 2.9: Cross sections for the process e+!e + n jets at the LHC. All results are in pb.

The first processes considered here are the production of electroweak gauge bosons. InTables 2.9 and 2.8 the cross sections for the production of positively and negatively chargedW bosons accompanied by the production of up to 6 jets are presented1. The achievedprecision of AMEGIC++ and the other codes is on the sub-per cent level. Note that the crosssections for pp ! W+ + X are approximately 35% larger than the corresponding crosssections for pp ! W! + X. This is in contrast to the Tevatron, where proton anti-protoncollisions are performed, such that the charge does not matter for the production cross

1AMEGIC++ is able to calculate the cross section for the production of gauge bosons with up to four extrajets.

Comparison of ME-generators in the context of MC4LHC( http://indico.cern.ch/categoryDisplay.py?categId=152 )



Parton Showers: APACIC++

a

t

b

cz

c

b

CF1 + z2

1 ! zCF

1 + (1 ! z)2

z

TR

!z2 + (1 ! z)2" 2CA

(1 ! z + z2)2

z(1 ! z)

1

R. Kuhn, F. Krauss, G. Ivanyi, G. Soff CPC 134 (2001) 223F. Krauss, A. Schälicke, G. Soff, hep-ph/0503087

Features of Sherpas parton shower, APACIC++ :Virtuality ordered parton cascade,colour coherence imposed by angular vetoFinal & initial state showering ine e & hadron collisions ( no DIS-like situations )+ -

Algorithm similar to virtuality ordered PYTHIA parton shower

Extensively tested ( see next slides )

2nd key ingredient to the CKKW ME-PS mergingimplemented in Sherpa ( 1st is AMEGIC++ )


Event shapes in e e -annihilation at E = 91 GeV (LEP I)

SHERPASHERPA

DELPHI 91 GeVAPACIC++ 2.0

/dT

! d

!1/

-310

-210

-110

1

10

1-ThrustTheory/Data - 1Theory/Data - 1Theory/Data - 1

-0.2-0.1

00.10.2

1-Thrust0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5

SHERPASHERPA

DELPHI 91 GeVAPACIC++ 2.0

/dM

! d

!1/

-110

1

10

MajorTheory/Data - 1Theory/Data - 1Theory/Data - 1

-0.2-0.1

00.10.2

Major0 0.1 0.2 0.3 0.4 0.5 0.6

+ -cms




SHERPASHERPA

JADE & OPAL 91 GeVAPACIC++ 2.0

)34

(Y10

/dlo

g!

d!

1/0.2

0.4

0.6

0.8

1

1.2

)34(Y10logTheory/Data - 1Theory/Data - 1Theory/Data - 1

-0.2-0.1

00.10.2

)34(Y10log-4.5 -4 -3.5 -3 -2.5 -2 -1.5 -1

SHERPASHERPA

JADE & OPAL 91 GeVAPACIC++ 2.0

)23

(Y10

/dlo

g!

d!

1/

0.1

0.2

0.3

0.4

0.5

0.6

0.7

)23(Y10logTheory/Data - 1Theory/Data - 1Theory/Data - 1

-0.2-0.1

00.10.2

)23(Y10log-4 -3.5 -3 -2.5 -2 -1.5 -1 -0.5

Differential jet rates in e e -annihilation at E = 91 GeV (LEP I)+ -cms




Exact to fixed order inthe running coupling

Basic idea of CKKW: Combine both approaches to have

+ ut

2

u+t

2 2

3

Matrix Elements

Include all quantuminterferencesCalculable only for lowFS multiplicity (n≤6-8)

Resum all (next-to) leadinglogarithms to all orders Interference effects only through angular ordering

Good description of hard/wide angle radiation (ME)Correct intrajet evolution (PS)

! Must prevent double-counting

+ ut

2

u+t

2 2

3

Parton Showers

d!n+1 = d!n !

!

a!q,g

dt

tdz

"s(t, z)

2#Pa"bc(z)

THE CKKW Procedure


Qcut

ME Domain

µH

!s(Q1)!s(Qcut)

Qcut

ME Domain

µH

!q(Qcut,µH )!q(Qcut,Q1)

!q(Qcut,Q1)

!q(Qcut,µH)

!g(Qcut,Q1)

!s(Q1)!s(Qcut)

Qcut

ME Domain

µH

!q(Qcut,µH )!q(Qcut,Q1)

!q(Qcut,Q1)

!q(Qcut,µH)

!g(Qcut,Q1)

!s(Q1)!s(Qcut)

PS Domain

Qcut (6)

µH (7)!q(Qcut,µH)!q(Qcut,Q1) (8)

!q(Qcut,Q1) (9)

!q(Qcut,µH) (10)

!g(Qcut,Q1) (11)!s(Q1)

!s(Qcut)(12)

1

2

0

3 54

2

This yields the correct jet rates !

CKKW Cooking Recipe

Define jet resolution parameter Q (Q-jet measure) divide phase space into regions of jet production (ME) and jet evolution (PS)

Simple example: 2-jet rate in ee qq

R2(q) =

!

!(Qcut, µhard)!(q, µhard)

!(Qcut, µhard)

"2

cut

Select final state multiplicity and kinematicsaccording to σ ‘above’ Q cutKT-cluster backwards (construct PS-tree) and identify core processReweight ME to obtain exclusive samples at QStart the parton shower at the hard scaleveto all emissions harder than Q

cut

cut

4


0 50 100 150 200 250

1

10

210

310

410

0 50 100 150 200 250

1

10

210

310

410dataSherpa range

D0 RunII Preliminary

(Z) [GeV]Tp

Nr. o

f Eve

nts

0 50 100 150 200 2500.2

1

234

(Z) [GeV]Tp

Data

/ SH

ERPA

Z-p measured at D0/T

The D0 collaboration, D0 note 5066-CONF/ /

THE CKKW Procedure


0 0.5 1 1.5 2 2.5 30

50

100

150

200

250

0 0.5 1 1.5 2 2.5 30

50

100

150

200

250data w/stat errordata w/stat & sys errorSherpa range statSherpa range stat & sys

D0 RunII Preliminary

(jet,jet)! "

Nr. o

f Eve

nts

0 0.5 1 1.5 2 2.5 30.2

1

234

(jet,jet)! "

Data

/ SH

ERPA

Δϕ measured at D0/12

The D0 collaboration, D0 note 5066-CONF/ /

THE CKKW Procedure


hep-ex/0602019

SHERPASHERPASHERPASHERPASHERPASHERPASHERPASHERPA

Sherpa

/2! !3/4 !/2! !3/4 !/2! !3/4 !/2! !3/4 !/2! !3/4 !/2! !3/4 !/2! !3/4 !/2! !3/4 !

> 180 GeV (x8000)maxTp

< 180 GeV (x400)max

T130 < p

< 130 GeV (x20)max

T100 < p

< 100 GeVmax

T75 < p

dij

et

"#

/dd

ijet

$ d

dij

et

$1/

-310

-210

-110

1

10

210

310

410

510

dijet"#

Δϕ in p bins12

Azimuthal dijet decorrelationT, max

THE CKKW Procedure


Multiple Parton Interactions

Ongoing dedicated CDF analysis to validate the existence of multiple parton scatterings

defines leading charged particle jet

Event generation w/o multiple scatterings

too few charged particles in low-p regiontoo steep dN /dp spectra


!"#$%&'()&*(+,-.$&/*.01

!"!"!"!"

23$#145&$4&6 23$#145&$4&6

2307#$'6

287#96

2307#$':;.'&6()&*

287#9:;.'&6()&*

!"#$#% &%$'!"#$#%

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

!234."56

7)$8#'%8-!."$#%

7)$8#'%8-!."$#%

9%5,"*:'%8-;<,%$9%5,"*:'%8-;<,%$

examines charged multiplicity in differentazimuthal regions w.r.t. leading jet

T,jet1

charged T

!"#$%&'(#&(!)*+,-)'(#&.&)/"0+,$#-(1)2(3456

7

5

8

9

:

7 ; 57 5; 87 8; 97 9; :7 :; ;7

/")0+,$#-(1)2(3456))0<(=>+6

!"#$%&'(#&(!)?*+,-@)A%)5)<

(=>+)BA%

5CD)"(=)E!!!!E?5C7)/"@7C;)<(=>+) F($GHF($G)I(G%$%3&

J$#1)KLGML%(%3

KNO1$3$).%+L##(+3(1

3,(L#P)+L##(+3(1

J(#QA-)"L3$R

MultiplE Parton Interactions

Built according to PYTHIA modelT. Sjöstrand & M. van Zijl, Phys. Rev. D36 (1987)

Hard processes with final state multiplicity different from tworequire unique definition of starting scale for MI evolution

employ K -algorithm to define 2 2 core processset starting scale to p of final state QCD parton(s) from this process


!"#$#% &%$'!"#$#%

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

!234."56

7)$8#'%8-!."$#%

7)$8#'%8-!."$#%

9%5,"*:'%8-;<,%$9%5,"*:'%8-;<,%$

T

T

Features of Sherpas multiple interaction module:

Parton showers attached to secondary interactions

Set up to work with the CKKW matching

µMI

Sherpa algorithm (works for arbitrary n-jet ME ):

1

µMI

Preliminary Results

SHERPASHERPASHERPASHERPASHERPA

Min Bias Run IJet20 Run I

Sherpa w/o MIPYTHIA w/ MI

Sherpa w/ MI

in 1

GeV

bin

Cha

rged

N

5

10

15

20

25

Track Finding Efficiency: 0.92

>0.5Tp |<1.0!|Theory / Data - 1


>0.5Tp |<1.0!|Theory / Data - 1


>0.5Tp |<1.0!|Theory / Data - 1


>0.5Tp |<1.0!|Theory / Data - 1


>0.5Tp |<1.0!|Theory / Data - 1


>0.5Tp |<1.0!|Theory / Data - 1


>0.5Tp |<1.0!|Theory / Data - 1


>0.5Tp |<1.0!|Theory / Data - 1

-0.2-0.1

00.10.2

GeV T, jet1P0 5 10 15 20 25 30 35 40 45 50

1

Charged multiplicity vs. PT

of the leading charged particle jet 1

MC results correctedfor track finding efficiency

Sherpa producescorrect shape

Total charged multiplicityagrees

TeV4LHC, CERN, April 29. 2005 – p.9

N vs. p in CTCCharged T,jet1



1

Preliminary Results




Sherpa w/ MI

in 1

GeV

bin

Cha

rged

N

0.5

1

1.5

2

2.5

3

3.5

4


>0.5Tp |<1.0!|Theory / Data - 1


>0.5Tp |<1.0!|Theory / Data - 1


>0.5Tp |<1.0!|Theory / Data - 1


>0.5Tp |<1.0!|Theory / Data - 1


>0.5Tp |<1.0!|Theory / Data - 1


>0.5Tp |<1.0!|Theory / Data - 1


>0.5Tp |<1.0!|Theory / Data - 1


>0.5Tp |<1.0!|Theory / Data - 1

-0.2-0.1

00.10.2

GeV T, jet1P0 5 10 15 20 25 30 35 40 45 50




Sherpa w/ MI

in 1

GeV

bin

Cha

rged

N

123456789

10


>0.5Tp |<1.0!|Theory / Data - 1


>0.5Tp |<1.0!|Theory / Data - 1


>0.5Tp |<1.0!|Theory / Data - 1


>0.5Tp |<1.0!|Theory / Data - 1


>0.5Tp |<1.0!|Theory / Data - 1


>0.5Tp |<1.0!|Theory / Data - 1


>0.5Tp |<1.0!|Theory / Data - 1


>0.5Tp |<1.0!|Theory / Data - 1

-0.2-0.1

00.10.2

GeV T, jet1P0 5 10 15 20 25 30 35 40 45 50




Sherpa w/ MI

in 1

GeV

bin

Cha

rged

N

2

4

6

8

10

12


>0.5Tp |<1.0!|Theory / Data - 1


>0.5Tp |<1.0!|Theory / Data - 1


>0.5Tp |<1.0!|Theory / Data - 1


>0.5Tp |<1.0!|Theory / Data - 1


>0.5Tp |<1.0!|Theory / Data - 1


>0.5Tp |<1.0!|Theory / Data - 1


>0.5Tp |<1.0!|Theory / Data - 1


>0.5Tp |<1.0!|Theory / Data - 1

-0.2-0.1

00.10.2

GeV T, jet1P0 5 10 15 20 25 30 35 40 45 50

1

Charged multiplicity vs. PT

of leading charged particle jetin !!!jet1regions 1


N vs. p in CTCin different regions w.r.t. leading charged particle jet

Charged T,jet1



1

Preliminary Results

SHERPASHERPASHERPASHERPA ! "Transverse" "! "Toward" " ! "Away" "

> 30 GeV Jet20 Run IT, jet1P

! "Transverse" "! "Toward" " ! "Away" "! "Transverse" "! "Toward" " ! "Away" "

> 30 GeV Sherpa w/o MIT, jet1P

! "Transverse" "! "Toward" " ! "Away" "

> 30 GeV PYTHIA w/ MIT, jet1P

> 30 GeV Sherpa w/ MIT, jet1P

° in

3.6

Cha

rged

N

-110

1

10


>0.5Tp |<1.0#|Theory / Data - 1


>0.5Tp |<1.0#|Theory / Data - 1


>0.5Tp |<1.0#|Theory / Data - 1


>0.5Tp |<1.0#|Theory / Data - 1

-0.2-0.1

00.10.2

° jet1!$%0 20 40 60 80 100 120 140 160 180

pT,jet1 > 30GeV








° in

3.6

Cha

rged

N

-110

1

10


>0.5Tp |<1.0#|Theory / Data - 1


>0.5Tp |<1.0#|Theory / Data - 1


>0.5Tp |<1.0#|Theory / Data - 1


>0.5Tp |<1.0#|Theory / Data - 1

-0.2-0.1

00.10.2

° jet1!$%0 20 40 60 80 100 120 140 160 180

pT,jet1 > 5GeV








° in

3.6

Cha

rged

N

-110

1

10


>0.5Tp |<1.0#|Theory / Data - 1


>0.5Tp |<1.0#|Theory / Data - 1


>0.5Tp |<1.0#|Theory / Data - 1


>0.5Tp |<1.0#|Theory / Data - 1

-0.2-0.1

00.10.2

° jet1!$%0 20 40 60 80 100 120 140 160 180

pT,jet1 > 2GeV

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

-.$&/*.01(

!"!"!"!"

2304#$'5(

23$#167&$6&5( 23$#167&$6&5(

284#95(

2304#$'5(:!"!"!"!":(;(<=0(:####:(;(,(23$#167&$6&5(<=0(;(:!"!"!"!":(;(,>=0(:####:(;(,(

284#95(:!"!"!"!":(?(,>=0(:####:(;(,(!

1

Charged multiplicity vs. !!!jet1

relative to leading charged particle jetfor different pT,jet1

1


N vs. Δφ in CTCfor different p of leading charged particle jet

Charged jet1T



1

Cluster Fragmentation

!!

!"

#

$$

"!

!

#

!

!!

!"

#

$$

"!

!

#

! 1

N2

C

f!f

!

f

C

X

Y

!

"C

Y

f

X"

!

f!f

!

f

C

X

Y

!

"C

Y

f

X"

!

1

N2

C

Sherpas cluster fragementation model:J. Winter, F. Krauss, G. Soff Eur. Phys. J. C36: 381-395, 2004

Colour ordered partons transformed into primary clustersaccording to combination of

kinematical weight

Wij, kl =t0

t0 + 4(wij + wkl)2

colour weight

Clusters decayed according to overlap between cluster mass and hadron mass spectrum

cluster mass in hadron regime transition to hadronelse 2-body decayC HH, C CH or C CCcombined weight applied again1

1with t replaced by Q (hadronic scale)0 0 Stefan Höche, WG Seminar Dortmund, 22.8.2006

Results for e+e! !H

chhem,udsN

0 5 10 15 20 25 30 35 40

)c

hh

em

,ud

s)

(dn

/dN

ev

en

t(1

/n

0

0.02

0.04

0.06

0.08

0.1

0.12

Charged particle hemisphere multiplicity distribution

MC simulation

SHERPA preliminary

mean: 10.0722

Experimental data

OPAL

cm energy = 91.2 GeV

uds only

0 5 10 15 20 25 30 35 40-1

-0.8

-0.6

-0.4

-0.2

-0

0.2

0.4

0.6

0.8

1

0

5

10

15

20

25

30

1 10 100

Ecm /GeV

!Nch"

SHERPA preliminary

e+e# data

$$2, MARK I

LENA

CL

EO

HR

S, T

PC

JADE, TASSO

AMY

TO

PA

Z, V

EN

US

MA

RK

II

ALEPH, DELPHIL3, OPAL

Correction for heavy quarks

"Nch# = "N udsch # + fc!c + fb!b

DPG-Tagung Mainz, 30. Marz 2004 – p.5

N vs. E charged cms


J. Winter, F. Krauss, G. Soff Eur. Phys. J. C36: 381-395, 2004




Results for e+e! !H

pudsx

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

)pu

ds

) (d

n/d

x0

(1/n

10-2

10-1

1

10

102

Charged particle scaled momentum distribution

MC simulations

PYTHIA-6.1

HERWIG-6.1

SHERPA preliminary

Experimental data:

SLD


uds only

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-0.6

-0.4

-0.2

0

0.2

0.4

0.6puds!

0 1 2 3 4 5 6 7 8 9 10

)pu

ds

!)

(dn

/d0

(1/n

0

1

2

3

4

5

6

7

) distributionpCharged particle log( 1 / x

MC simulations

PYTHIA-6.1

HERWIG-6.1

SHERPA preliminary

Experimental data:

OPAL


uds only

0 1 2 3 4 5 6 7 8 9 10-0.5

-0.4

-0.3

-0.2

-0.1

-0

0.1

0.2

0.3

0.4

0.5

DPG-Tagung Mainz, 30. Marz 2004 – p.6

log charged scaled momentum


pudsx

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

)pu

ds

) (d

n/d

xeven

t(1

/n

10-5

10-4

10-3

10-2

10-1

1

10

102

Charged particle scaled momentum distribution

MC simulations

PYTHIA-6.1

HERWIG-6.1

SHERPA preliminary

mean: 0.0616581 mean: 0.0637626 mean: 0.0605735

Experimental data

OPAL

DELPHI

SLD


uds only

Charged particle scaled momentum




Hadron & T Decays

Sherpas hadron decay package:Full flexibility, all information is read from parameter files( branching ratios, decay channels, form factors, integrators )

So far not too many hadron decays ( PYTHIA for the rest ... )

Frank Siegert at TU Dresden

Easy to extend with specific decay modes / models( feel free to add your favourite decay ... )

Extensively tested in τ decays

Jan Stieglitz & SH at Uni Dortmund

Full spin information from matrix element, if needed

This is being worked on:(special emphasis on Bs)


Hadron & T Decays

Example: parameter files for τ decaysHadronDecays.dat :#-------------------------------------------------------

#-- Files for hadron decay tables ----------------------

#-------------------------------------------------------

# particle -> directory/ name.dat do not forget the / and space

# Taus

15 -> tau-/ Decays.dat;

# Pseudoscalars

111 -> pi/ Decays.dat;

211 -> pi+/ Decays.dat;

...


tau-/Decays.dat :# outgoing part. | BR | DC-file

# leptonic

{16,11,-12} | 0.1784 | Tau_Electron.dat;

{16,13,-14} | 0.1736 | Tau_Muon.dat;

# modes with 1 pseudoscalar

{16,-211} | 0.1106 | Tau_Pion.dat;

{16,-321} | 0.00686 | Tau_Kaon.dat;

...

Hadron & T Decays

Example: parameter files for τ decays


# Decay: tau- --> nu_tau nu_eb e-

# 0 --> 1 2 3

Channels {

AlwaysIntegrate = 0; ! 0...read results and skip integration

! 1...don't read results and integrate

Isotropic 1;

}

Parameters {

v = 1. ! V-A structure of tau-nutau

a = 1.

v2 = 1. ! V-A structure of elec-nuelec

a2 = 1.

}

Result {

3.83691e-13 8.60159e-16 2.04794e-12;

}

tau-/Tau_Electron.dat :

Hadron & T Decays

Example: parameter files for τ decays


T Decays

Decay kinematics in hadronic τ decays

Breit-Wigner form factor parametrisationin particular: Kühn-Santamaria model J. H. Kühn, A. Santamaria, Z. Phys. C48 (1990) 445

Resonance chiral theoryG. Ecker et al., Nucl. Phys. B321 (1989), 311 parameters: chiral couplings of meson resonances

Decay kinematics in leptonicτ decays

where Lµ

l= !!l|"

µ(a " b"5)|l#M =

GF!2

L!

µLµ

l

left handed currents: a=b=1 ( EW Lagrangian )


5 Results and Discussion

This chapter is dedicated to the presentation of some results which were obtained by em-ploying the new HADRONS++ module.

5.1 Leptonic Channels

The leptonic channels can be treated analytically. So comparing the analytical solution of adistribution with the simulation provides an excellent sanity check if the implementation iscorrect. Setting a2 = b2 = 1 in Eq. (4.4), it can be shown that the energy spectrum [25] ofthe outgoing lepton is

d!(!! ! l!"l"! )

dE=

a21 + b2

1

2

G2F |#p|E

3(2$)3"

!

12"

M2! + m2

l # 2M!E#

+(a1 + b1)2

a21 + b2

1

$

8M!E # 3M2! # m2

l

%

3 +2M!

E

&' (

(5.1)

Figure 5.1: Energy spectrum of the outgoing electron in the ! rest frame.

sanity check: test of V-A structure energy in decay! ! "! e

!

"ee!

T Decays


Invariant mass spectrum in ! ! K

!

"+"!

#!

T Decays


CLEO-CONF-94-23

Eur. Phys. J. C4 (1998) 409HADRONIC DECAYS

COMPARISON

0.001

0.01

0.1

1

0 0.5 1 1.5 2 2.5 3 3.5

1/N

dN

/dm

2 [

GeV

-2]

m23! [GeV

2]

invariant mass distribution

"# --> !

#!#!+$"

Resonance Chiral TheoryKuehn Santamaria Model

ALEPH 98

THOMAS LAUBRICH (TU DRESDEN) TAU DECAYS WITH SHERPA SEPTEMBER 2ND, 2005 12 / 15

Invariant mass spectrum in ! ! "! #

!

#!

#+

T Decays


proof-of-concept: -correlations in

!!e+e!

1 !

d!

d!

"e+e!

e+e!

! tt ! e+!ebe

!

!eb

!

sPin Correlations


sPin Correlations

PYTHIA+TAUOLA: hep-ph/01013115.3 Spin Correlations 67

Figure 5.14: Energy distribution of the outgoing !! in the rest frame of the W!-boson. Theblack line corresponds to a simulation with PYTHIA [5] and TAUOLA [6] published in Ref. [46].

The " polarisation is then P! = !1 [46] so that the distribution slope is maximally negativeand touches zero at z = 1. The respective distribution is shown in Fig. 5.14.

-energy distribution inW

!

! !!

"! ! "!#"!

! Z ! W+W

!


Sherpa has proven to be a powerful toolto describe LEP and Tevatron dataLHC predictions are in excellent agreement with other codes ( e.g. hep-ph/0602031 )The new hadron decay package is well under way

Future plans

Tuning of cluster fragmentation modelImprovement of multi-jet ME calculation

Extension of hadron decay package ...

summary / Outlook

for further information on Sherpaplease visit our web site

WWW.sherpa-mc.de

[email protected]

or send us an E-mail

Sherpa An event generator for LHC · R. Kuhn, F . Krauss, G. Sof f JHEP 0202:044, 2002 AMEGIC++ is...

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