EvtGen in ATLASEvtGen in ATLAS

James R Catmore, University of Lancaster, UKJames R Catmore, University of Lancaster, UK

MMáária Smiria Smižžanskanskáá, University of Lancaster, UK, University of Lancaster, UK

Malte Muller, now at University College London, UKMalte Muller, now at University College London, UK

ContentsContents

About EvtGenAbout EvtGen Why are ATLAS B-physics people interested in it? Why should other people be interested in it?

Overview of ATLAS EvtGen ActivitiesOverview of ATLAS EvtGen Activities Technical work Physics validation

Progress Progress

Further workFurther work

About EvtGenAbout EvtGen

Decay model packageDecay model package Originated in BaBar; authors Anders Ryd, David Lange et al Tuned against new data from BaBar, Belle, CLEO Valuable validation work performed by B-factories Large collaboration of experiments has accepted EvtGen as

their principal B-decay package – LHCb, ATLAS, CMS, CDF, D0, BaBar, Belle

Agreement achieved on development and alteration of code by laboratories other than BaBar

BaBar incorporates changes to code on request

About EvtGen IIAbout EvtGen II

EvtGen has several highly desirable technical features for EvtGen has several highly desirable technical features for B-physics simulationsB-physics simulations

Works with complex amplitudes Interference effects CP-violation

Uses spinor algebra Polarizations Helicity states

Correct angular distributions Novel and highly efficient algorithm for handling cascade

decays

Correct generation of B-events is extremely important for the Correct generation of B-events is extremely important for the triggering and selection of physics processes decaying to B-triggering and selection of physics processes decaying to B-hadrons (Higgs, SUSY, exotics….)hadrons (Higgs, SUSY, exotics….)

About EvtGen IIIAbout EvtGen III

EvtGen provides a rich selection of decay EvtGen provides a rich selection of decay modelsmodels A A modelmodel in EvtGen is a in EvtGen is a classclass which provides a which provides a recipe for a recipe for a

complex amplitudecomplex amplitude Each spin configuration has its Each spin configuration has its own modelown model

e.g., SVV, SSS, STS, SVS, TSS, VSS etc

A calculation is performed using A calculation is performed using complex amplitudes complex amplitudes and and spinor algebra.spinor algebra.

Cascade decays are handled “node-wise” with a Cascade decays are handled “node-wise” with a spin spin density matrixdensity matrix for each node for generating the angular for each node for generating the angular distributiondistribution

Nodes are Nodes are independentindependent, hence a different model can be , hence a different model can be applied to each nodeapplied to each node

EvtGen AlgorithmEvtGen Algorithm

−+μμ−+πK

0dB ψJ *0K

−+→ μμψλ ψ

J

JA

−+→ πλ

KK

K

A*0

*0

*00

*0

KJBd

KJA ψ

λλ ψ

→

EvtGen Algorithm IIEvtGen Algorithm II

−+μμ−+πK

0dB ψJ *0K

∑ →=*0

*00

*00

2

KJ

d

KJd

KJB

BAP

λλ

ψλλ

ψ

ψ

EvtGen Algorithm IIIEvtGen Algorithm III

−+μμ−+πK

0dB ψJ *0K

∑=′*0K

JJ

J

λ

ψλλ ψψ

ρ*00

*0

KJBd

KJA ψ

λλ ψ

→ [ ]**00

*0

KJBd

KJA ψ

λλ ψ

→′′

∑′

=ψψ λλ

ψJJ

SFPJψ

λλ ψψρ J

JJ ′−+→ μμψ

λ ψ

J

JA [ ]*−+→

′μμψ

λ ψ

J

JA

EvtGen Algorithm IVEvtGen Algorithm IV

−+μμ−+πK

0dB ψJ *0K

∑′

′ =ψψ λλ

λλρJJ

KK

K *0

*0*0

−+→ μμψλ ψ

J

JA [ ]*−+→

′μμψ

λ ψ

J

JA

*00

*0

KJBd

KJA ψ

λλ ψ

→ [ ]**00

*0

KJBd

KJA ψ

λλ ψ

→′′

∑′

=*0*0

*0

KK

SFPK

λλ

*0

*0*0

K

KKλλρ ′

−+→ πλ

KK

K

A*0

*0[ ]**0

*0

−+→′

πλ

KK

K

A

ATLAS EvtGen Activities IATLAS EvtGen Activities I

Wholly UK (Lancaster) activityWholly UK (Lancaster) activity Mária Smižanská [research officer] – software development James Catmore [PhD student] – software development and

physics validation Malte Muller [CERN summer student] – initial technical work Collaboration with LHCb, CDF, D0

Software developmentSoftware development Adapting to CMT context Development of interface between ATHENA and EvtGen,

made according to requirements for Dedicated B-physics studies General B-decay facility to be used by top, SUSY, Higgs,

exotics groups

ATLAS EvtGen Activities IIATLAS EvtGen Activities II

Physics validationPhysics validation Lancaster team is participating in EvtGen validation as part

of a world-wide collaboration Significant work performed by CLEO, BaBar, Belle,

teams tuning EvtGen to their data EvtGen will be a valuable source of new data from the

labs involved in its development Often new data will reach the EvtGen data files

before it is published in the literature New theory implemented in EvtGen decay models

Current Lancaster validation work involves the testing of EvtGen models against data from dedicated Monte Carlo generators

EvtGen in ATHENAEvtGen in ATHENA

Event Generator (PYTHIA)

Conversion to HepMC

B-mesons

HepMC B-mesons

PDG

Decay files

HepMC Event Record

HepMC decay products

User inputEvtGen

Technical DevelopmentTechnical Development

ATHENA release 7.3.0 ATHENA release 7.3.0 copy of latest (July 2003) Babar release LHCb incoherent oscillations CDF Bs & B-baryons

StructureStructure atlas/offline/external/EvtGen/ source code …libEvtGen.a Externals/EvtGen/…/requirements

points to libEvtGen.a

Generators/EvtGen_i/…/EvtDecay Generators/EvtGen_i/…/EvtDecay EvtDecay top algorithm, interface to EvtGen. EvtDecay top algorithm, interface to EvtGen.

Can be combined with algorithms Pythia, PythiaB, SingleParticleGun

Technical Development IITechnical Development II

Generators/EvtGen_i/share/PythiaEvtGen.txt Generators/EvtGen_i/share/PythiaEvtGen.txt Concatenate algorithms Pythia + EvtDecay includes ‘StopBweakDecays.txt’ datacards to stop all weak

Pythia B-decays Pythia:

produce event (81,82) but user can have any Pythia production

strong B-decays store HepMC event in transient store

EvtDecay: reads HepMC from transient store pass all B to decay in EvtGen add the decay into HepMC

Technical Development IIITechnical Development III

Generators/EvtGen_i/share/PythiaBEvtGen.txtGenerators/EvtGen_i/share/PythiaBEvtGen.txt Concatenates algorithms PythiaB+EvtDecay 2.-4. same as previous

PythiaB provides in addition:PythiaB provides in addition: Pre-selection of Pythia events with b-quark in fiducial

volume repeated hadronization to speed-up production

Physics ValidationPhysics Validation

EvtGenEvtGen We have validated the

base helicity model for SVV, SVV_HELAMP

Strong sector only (no mixing, CP-violation)

Used it to generate angular distributions for the decay

BdJ/ψ(μ+μ) K0*(K+π-)

Tested against dedicated Monte Carlo

Dedicated Monte Dedicated Monte CarloCarlo

Uses probability density function calculated directly using Helicity Formalism

Implemented in accept-reject Monte Carlo program (M.Smižanská)

The DecayThe Decay

B0d

K0*J/ψμ+

μ-K+

π-

Decay AnglesDecay Angles

J/ψ

K*

Angular DistributionAngular Distribution

Derived directly from the Helicity FormalismDerived directly from the Helicity Formalism which is the normal method of calculating angular

distributions of decays

For our S For our S V (l V (l++ll--) V (S) V (S11SS22) decay the probability density ) decay the probability density function for decay angles (function for decay angles (1,1, 2,2, ) is) is

( )

( )∑=

±

±

=

Γ=

8

121

21

3

21

,,64

9

coscos,,

i

ii Ff

ddd

dW

φθθπ

φθθφθθ

±if iF

( )2

0 0A

LΓ1

22

12 cossin

( )20cA

LΓ1 ( ) 2

21

2 sincos1 θθ+

( )20⊥A

HΓ1 ( ) 2

21

2 sincos1 θθ+

2 ( )0cA( )00A

LΓ1

φ cos2sin2sin 21

i

1 4

2 1

3 -1

4

5

6

1

1

( )20cA

LΓ1

( )20⊥A

HΓ1

φ 2cossinsin 22

12

φ 2cossinsin 22

12

SVV_HELAMPSVV_HELAMP

( )pM ijjsisssA*22

*1121 εε=

jikijkijij pcppba ++= εδM

( )

( )

( )⎥⎦⎤

⎢⎣

⎡ ++=

−=

+−=

−+

−+

−+

HHHc

HHi

b

HHa

2

1

4

3

4

3

2

4

3

2

1

0π

π

π

721.000 ==HA

566.02

117.0683.0

2=

+=

+= −+ HH

Ac

400.02

117.0683.0

2=

−=

−= −+

⊥HH

A

ResultsResults

Further work for Lancaster teamFurther work for Lancaster team

The requirement: prepare first production release of EvtDecay for The requirement: prepare first production release of EvtDecay for use in Release 8.0.0use in Release 8.0.0

Successful start of a Successful start of a longlong program, a lot to do….. program, a lot to do….. Technical Development

User interfaces Event selection Kinematic cuts

Physics Validation Exclusive b-decays

Strong sector helicity model Incoherent mixing models CP violation, effects on angular distributions for B and anti-B

decays b-jets

No work done (except Bd X tests made by BaBar)· Needed for top, Higgs, SUSY groups

Assessment of HLT performance in light of the above

ConclusionsConclusions

Software development now at an advanced stageSoftware development now at an advanced stage

Physics validation underwayPhysics validation underway

A useful and successful beginning – but much work A useful and successful beginning – but much work remains to be doneremains to be done