1. Overview of IPPP Monte Carlo Tools
Peter Richardson
IPPP, Durham University
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2. Summary Introduction Basics of Event Generation
Matrix Elements and Perturbative Decays
Parton Shower and Matching
Hadronization and Tuning
Underlying Event
Summary
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3. Introduction
Monte Carlo event generators are essential both experimental analyses of real data and studies and predictions for future experiments.
As such the programs and their authors are a vital interface between experimental and theoretical communities.
Often they are the only theoretical calculations used in an experimental analyse and it is therefore vital that they are as accurate as possible and include the latest theoretical advances.
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4. A Monte Carlo Event Hard Perturbative scattering:
Usually calculated at leading order in QCD, electroweak theory or some BSM model.
Modelling of the soft underlying event
Multiple perturbative scattering.
Perturbative Decays calculated in QCD, EW or some BSM theory.
Initial and Final State parton showers resum the large QCD logs.
Finally the unstable hadrons are decayed.
Non-perturbative modelling of the hadronization process.
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5. Monte Carlo Projects
At the IPPP we are involved with two of the major simulation packages
HERWIG Richardson, Grellscheid, Hamilton, Gigg, Tully.
SHERPA Krauss, Hoeche
We play a major part in both projects and are involved in many different aspects of the physics.
We are also involved in the CEDAR project (Buckley, Whalley)
and the EU MCnet network.
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6. COMIX, a new Matrix element generator
Several independent analyses show clear advantages of Berends-Giele type recursive relations for numerical evaluation of tree-level Matrix Elements
Can be generalised to the full Standard Model, not just QCD.
Employed in new Matrix Element generator Comix, together with a new approach for combined colour sampling.
Current checks in randomly selected QED processes.
Shows clear advantages over commonly used helicity methods (AMEGIC++, MadGraph)
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7. BSM physics in Herwig++
New method of including new physics in Herwig++, including spin correlations,
M. Gigg, P. Richardson
hep-ph/
e- near
e- far
q*L
e*R Z* g* q
e- near
e+ far
e+ near
e+ far
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8. Herwig++ Shower
Following the initial release for e+e- collisions most work has been on
Initial-state shower in hadron collisions
Radiation in the decays of unstable particles
Various matching approaches.
Herwig++ with intrinsic pT compared to CDF data
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9. Top Shower and Matrix Element Correction in tgbW+g
JHEP 0702:069, 2007, Keith Hamilton, Peter Richardson.
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10. Nason Approach
One recent idea is an approach to NLO Monte Carlo simulations with only positive weights events, P. Nason JHEP 0411:040, 2004.
We (K. Hamilton, J. Tully, PR) are looking at this approach.
In particular the treatment of soft radiation (truncated shower) for both NLO simulations and its application in other situations.
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11. SHERPA Shower and CKKW
The main SHERPA shower, APACIC++, has been available for some time.
Recently most work has been on
CKKW matching
Catani-Seymour Shower
Colour Dipole Shower
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12. SHERPA Colour Dipole Shower
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13. SHERPA Colour Dipole Shower
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14. SHERPA Catani-Seymour Shower
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15. SHERPA Colour Dipole Shower
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16. Tuning of Event Generators
Historically the event generators were tuned to LEP data by the LEP collaborations, obviously isn’t going to happen for the new generation of programs.
However it is vital that the new programs are tuned to both LEP, HERA and Tevatron data.
We are involved with this both as part of CEDAR and MCnet and with a new SPG.
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17. SHERPA kT based UE Model
Recently method proposed to describe high-energy jet production in kT-factorization (IPPP/07/20)
LO BFKL kernel matched to unintegrated parton distributions
Quark production modelled by including LO DGLAP kernels in the soft limit.
Encouraging results for jet production at the Tevatron.
Will be employed for ME-generation of hard secondary interactions in new Multiple Interaction model for Sherpa.
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18. Hadron Decays and QED Radiation
Traditionally the general purpose event generators have relied on external packages for the simulation of
Tau Decays (TAUOLA)
Hadron Decays (QQ, EvtGen)
QED Radiation (PHOTOS)
However this can cause problems with interfaces.
Both Herwig++ and SHERPA are moving to sophisticated simulations for all of these.
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19. Tau Decays, tgrnt
Herwig++
SHERPA
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20. Bgpen
SHERPA
Herwig++
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21. B mixing in SHERPA
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22. bgsg in HERWIG
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23. YFS
Both HERWIG and SHERPA have moved to an approach based on the YFS formalism for the simulation of QED radiation in particle decays.
This has the advantage that it is systematically improvable by adding the higher order corrections and has proved highly successful in, for example e+e- collisions.
In both cases any number of soft photons are described together with a correction for the hardest emission.
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24. YFS Herwig++ K. Hamilton and P. Richardson JHEP 0607:010, 2006.
SHERPA M. Schoenherr
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25. Herwig++ Support and Maintenance
On the Herwig++ side we have one long term (core) post, D. Grellscheid, to provide
Core user support
Technical C++ and software expertise to support the design, code management and testing
This will give improved support to the experiments for the LHC and allow other members of the collaboration to concentrate on physics issues.
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26. Workshops and Schools
We have had many Monte Carlo related workshops and schools since the start of the IPPP
Physics and Techniques of Event Generators: 1st MCnet school. (2007)
YETI 06 SM and BSM
C++ Monte Carlo Developers Forum (2005)
YETI 05
Monte Carlos at Hadron Colliders (2003)
Matrix Elements and Parton Showers (2000)
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27. Future Things are moving fast on both Herwig++ and SHERPA.
For Herwig++
JIMMY underlying event model (Aug)
BSM physics (Aug)
Hadron decays, tau/mesons (Aug), baryons (Dec)
For SHERPA
2 new shower models (Oct)
MHV techniques, Berends-Giele subtraction terms (Oct)
Cluster Hadronization (Dec)
kT underlying event model (Dec)
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28. Summary Since 2003 we have built a world-leading Monte Carlo group.
The IPPP’s Monte Carlo activities are a vital part of the IPPP programme and provide an essential link to the experimental community.
We are involved in a wide range of event simulation physics and projects using our simulation expertise for physics studies.
In the past few years most of the work has concentrated on C++ and the development of the core physics modules.
Work is now progressing on the physics developments and studies.
Our strength in this area will help us to support the U.K. experimentalists during the LHC.
IPPP 26th July