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1 Summar y of 3 P3 "Simulations and Computations in Theoretical Physics and Phenomenology":

-- Automated Calculation and Simulation Systems --

Thorsten Ohl
è -- Universitat Wurzburg -- è
ohl@physik.uni-wuerzburg.de

ACAT 2002, Moscow State University, June 28, 2002

Th. Ohl

Automatic Calculation Systems

ACAT 2002


Contents

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1 Introduction . . . . . . . . . . . . . . . . . . . . .
Mission Schema Dramatis Personae Status and Trends at ACAT 2002

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2 Trends . . . . . . . . . . . . . . . . . . . . . . . . 3 Outlook

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More General Models Component Architecture & Persistency Loops

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Automatic Calculation Systems

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Introduction

1

1 Introduction . . . . . . . . . . . . . . . . . . . . .
Mission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Schema . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Dramatis Personae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Status and Trends at ACAT 2002 . . . . . . . . . . . . . . . . . . . . . .

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2 5 6 7

2 Trends . . . . . . . . . . . . . . . . . . . . . . . . 3 Outlook

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. . . . . . . . . . . . . . . . . . . . . . . 18

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Mission
Future (Linear) Colliders as New Frontier in Energy and Precision: § final states with many tagged weakly interacting par ticles accessible

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§ (in the absence of low energy SUSY:) physics beyond the standard model may only be accessible in precision tests of standard model processes § e. g.: ïï í W /Z couplings in e+ e- f1 f2 f3 f4 (already at LEP2) ïï í W W scattering in e+ e- e e f1 f2 f3 f4 ï ïïï ï í tt production in e+ e- f1 f2 f3 f4 f5 f6 ïïï ï í W W /tt scattering in e+ e- e e f1 f2 f3 f4 f5 f6 ï we will need reliable predictions and simulation tools to unleash the full potential of the Future Colliders í studying EWSB requires complete (gauge invariant!) calculations í polarization must be included

Th. Ohl

Automatic Calculation Systems

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Mission
qualitatively more complicated than, say, LEP1 í the number of Feynman diagrams explodes combinatorially

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í the algebraic expressions grow much more complicated with the growing number of building blocks (independent momenta and polarizations) í the gauge cancellations become extremely hazardous í the phase space also becomes much more intricate even if we had enough graduate students and postdocs, we should not waste them on repetitive "assembly line" calculations formalize the calculations so that the repetitive par t can be delegated to patient computers. loops for many par ticles will need a lot more work one-loop calculations for 2 4 remain the limit of our capabilities

Th. Ohl

Automatic Calculation Systems

ACAT 2002


Mission
Fully automated calculation and simulation systems in par ticle physics aim to produce model parameters process e. g. cuts L m, g, . . . = e+ e- e e ²+ ² du ï ï pT ,min , Emin , . . .

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event samples

without (or with as little as possible) exper t human inter vention. NB: these systems do typically produce par tonic final states and leave fragmentation and hadronization to Pythia, HERWIG et al. The job of automated calculation and simulation systems can be divided in two steps 1. calculate matrixelement T (i. e. generate Feynman diagrams, derive arithmetical expression and generate executable code) 2. integrate |T |2 d² or generate events according to |T |2 d², usually with a little help from the structure of T .

Th. Ohl

Automatic Calculation Systems

ACAT 2002


Schema
Feynman rules MADGRAPH CompHEP O'Mega matrix elements cuts parameters

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WHIZARD phase space & steering unweighted events (STDHEP) hadronization & detector

VAMP sampling



histograms

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Automatic Calculation Systems

ACAT 2002


Dramatis Personae
Some systems are complete, some provide components of complete systems: § CompHEP: complete system (2 talks, 2 posters) § CalcHEP: CompHEP clone (1 talk) § GRACE: complete system (1 talk and additional talks on sampling!) § O'Mega: matrix elements § WHIZARD: phase space § HELAC/PHEGAS: standard model matrix elements and phase space § Madgraph: standard model matrix elements § Alpha: standard model matrix elements § FeynArts/FeynCalc: loop diagrams § CalcPHEP: standard model 2 2 processes @ 1-loop (2 talks, 2 posters)

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Automatic Calculation Systems

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Status and Trends at ACAT 2002
tree-level standard model for 2 4 and e+ e- 6par ticles is well under control for some time now and can readily be used by non-exper ts § suppor t for general 2 6 and 2 8 processes is not completely usable for production yet í systems with already complete physics suppor t do not scale optimally í optimally scaling systems not completely implemented yet but is coming along fast Challenges § `Beyond The Standard Model' (MSSM in par ticular) í progress repor ted at ACAT 2002 (see below) § loops growing evidence, concern and consensus that the classic analytical approach "does not scale" projects have star ted working on (semi-)numerical approaches
Th. Ohl Automatic Calculation Systems

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ACAT 2002


Trends

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1 Introduction . . . . . . . . . . . . . . . . . . . . . 2 Trends . . . . . . . . . . . . . . . . . . . . . . . .
More General Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . Component Architecture & Persistency . . . . . . . . . . . . . . . . . . . Loops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2 9
9 12 15

3 Outlook

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ACAT 2002


More General Models
Currently, all automated systems use a set of Feynman rules (propagators and ver tices) as input mathematically equivalent to the lagrangian describing the model derivation from lagrangian extremely tedious and error-prone, e. g.: many thousand different ver tices in the MSSM Talks § T. Kaneko: A Package for Generating Feynman Rules in the GRACE System § A. Semenov: The CompHEP/SUSY Package Posters § A. Kryukov, V. Bunichev, A. Vologdin: Using form fir Symbolic Evaluation of Feynman Diagrams in the CompHEP Package § A. Belyaev: Study of Viable SUSY GUTs with Non-Universal Gaugino Mediation: CompHEP and ISAJET Application
Th. Ohl Automatic Calculation Systems

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ACAT 2002


More General Models
Tools for the derivation of Feynman rules for complicated models (MSSM, in par ticular) need to § expand lagrangians in component fields and momenta § handle mixing from non-diagonal mass matrices using a ver y natural notation in order to avoid errors.

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such tools turn quickly into fully developed symbolic manipulation languages with special features, e. g.: í objects from mutually commutative, but non-commutative algebras (e. g. for non-simple gauge groups) are not described transparently by general purpose computer algebra systems í covariant derivatives play a dual role as operators and field components we will soon have several independently derived `model files' for the MSSM

Th. Ohl

Automatic Calculation Systems

ACAT 2002


More General Models
Moving `Beyond The Standard Model' requires `first generation' systems to relax some assumptions, e. g.: § Dirac spinors Majorana spinors § quar tic ver tices ver tices of higher degree § dimension-4 operators higher dimension operators (more complicated momentum depenence) § non-commutative field theories (really strange ver tices . . . ) § non Feynman diagram contributions, like K-matrix unitarization

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One solution is to replace hard-coded subsystems making special assumptions by general purpose components, e. g.: § CompHEP repor ted in a poster how the special pur pose C-routines for symbolic squared diagram evaluation are being replaced by calls to the general purpose form system
Th. Ohl Automatic Calculation Systems ACAT 2002


Component Architecture & Persistency
Question: § how can components communicate . . . § . . . across abstraction layers? (subroutines, objects, modules, etc.) § . . . across adress spaces? (processes, networks, etc.) § . . . across time? (data storage, persistency) Talks è § L. Lonnblad: Status of the Pythia7 Project

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§ A. Cherstnev: Toolkit for Par tonic Events Data Bases in the CompHEP Package

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Automatic Calculation Systems

ACAT 2002


Component Architecture & Persistency

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Pythia7 is not an automated system in the the strict sense (all physics knowledge is hardcoded), but all automated systems have to talk to Pythia for fragmentation and hadronization of hard events. . . § A project to completely rewrite the Lund event generators in C++. Pythia7 can be used for simulation of any high-energy par ticle collision, but the main target is LHC physics. It will provide a general structure for implementing models for event generation, only the Lund Model (HERWIG++ has joined the effor t). § Pythia7 exists today as a proof-of-concept version (some basic 2 2 matrix elements, remnant handling and Lund string fragmentation. § Plans í A new pre-release in 2002 with the first HERWIG stuff. í A usable generator in 2003 í The Standard Generator at the star t-up of LHC § NB: Help is appreciated.
Th. Ohl Automatic Calculation Systems ACAT 2002


Component Architecture & Persistency
External representations of event samples useful for

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§ communicating from par tonic event generators to soft QCD Monte Carlos to detector simulations § saving intermediate and/or final results í reading stored events faster than regeneration for complicated par tonic states í there will always be a gain for reweighting processed data never underestimate the value of external representations for debugging A. Cherstnev proposed a text based Data Description Language for event samples and implemented the necessar y toolkit for manipulating it § merging of data sets, etc. Discussion: § abstract syntax very useful, but the concrete syntax could be replaced with XML for even easier interfacing.
Th. Ohl Automatic Calculation Systems ACAT 2002


Loops
Talks § D. Bardin: Project CalcPHEP, Calculus for Precision High Energy Physics § P. Christova: QED Radiative Corrections within the CalcPHEP Project Posters ï § L. Kalinovskaya: About the Implementation of e+ e- ff Processes in the Framework of the CalcPHEP Project

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§ G. Nanava: A Monte Carlo Simulation of Decays Within the CalcPHEP Project Reimplementation of the complete standard model 1-loop radiative corrections ï (incl. soft bremsstrahlung) for e+ e- ff from scratch

Th. Ohl

Automatic Calculation Systems

ACAT 2002


Loops
Motivation § preserving the body of knowledge for future generations by providing a consistent and systematic option for redoing the calculations § application to off-resonance physics at JLC/NLC/Tesla Procedure § decomposition into form factors § calculation of form factors

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í collection of form3 procedures for symbolic calculation, renormalization and creating For tran code for numerics Status § t-channel NC and s-channel done § s-channel/t-channel interferences and decays in progress ver y good agreement with existing codes
Th. Ohl Automatic Calculation Systems ACAT 2002


Outlook

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1 Introduction . . . . . . . . . . . . . . . . . . . . . 2 Trends . . . . . . . . . . . . . . . . . . . . . . . . 3 Outlook

2 9

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Automatic Calculation Systems

ACAT 2002


Outlook

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If we ever manage to produce a fully general and efficient automated calculation and simulation system, that is even easy to use for experimentalists . . . . . . we risk to make ourselves obsolete as phenomenological theorists. For tunately . . . . . . we will never get there because § smar t theoretical theorists will always come up with new theories with new features that we have not anticipated § smar t experimentalists will always push the frontiers in energy and precision, calling for ever more precise calculations of ever more complicated processes

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Automatic Calculation Systems

ACAT 2002


Outlook

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#loops Mincer

terra incognita
CompHEP/Grace Alpha/HELAC O'Mega #legs

FeynAr ts/FeynCalc

unchar ted territor y: í the only complete 1-loop calculations of 2 4 processes in the minimal standard model remains "almost completed" systematically char ting model landscapes will remain practically impossible unless we develop new methods
Th. Ohl Automatic Calculation Systems ACAT 2002


Outlook
Final word: § variety is good, we need to be able to cross check our results § communication is even better í among developers (ACAT 200x) í among programs using pluggable components

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Th. Ohl

Automatic Calculation Systems

ACAT 2002