Monte Carlo Generators for HERA Physics

DESY Workshop 1998/99

http://www.desy.de/~heramc latest update June 18, 2002

Background and aim / Topics to be studied / Time plan and organization / Presentation of results

Working groups Monte Carlo programs
Proceedings
Meetings - agenda and presentations:
Start-up meeting April 27-30 1998
Working group meetings June 8-12 / July 8-9 and September 1-4 1998
Mid-term review meeting October 5-9 1998
Working group meetings: December 7-11 1998
Final meeting February 1-5 1999
How to get to DESY Housing at DESY Hotels
Organizing Committee: heramc@desy.de

Günter Grindhammer, MPI (chair)

Gunnar Ingelman, Uppsala/DESY (co-chair)

Tony Doyle, Glasgow

Hannes Jung, Lund

WG10
QCD Cascades

WG20
F.H.O. prog. DIS & gp

WG30
Transition gp to DIS

WG40
Non-perturbative QCD

WG50
Diffraction

WG60
Heavy flavors

WG70
QED radiative effects

WG80
Exotics

Background and Aim:

The increasing statistics in the HERA experiments provides an improved basis for detailed physics studies. Monte Carlo (MC) generators for different processes play an important, sometimes crucial, role in these analyses. Although many observed phenomena can be well described by existing generators, there are also severe discrepancies that demonstrate problems in generators or underlying models. The problems are both of technical and conceptual nature and their resolution will improve our understanding of the physics involved. This will require improvements in existing MC's or development of new ones. There are always some developments of the MC's, but a major coordinated effort has not been made since the HERA 1991 workshop (e.g. not within the 95/96 workshop on 'Future physics at HERA'). The coming luminosity upgrade of HERA will lead to even higher precision which calls for refinements of the Monte Carlo generators. In view of the interesting present and future analyses of HERA data, the time is now right to make an effort on Monte Carlo generators for HERA physics.

Topics to be studied:

The interest will be focused on various hard and soft QCD processes/issues, but other topics in and beyond the Standard Model are also of interest. A first discussion has given the following list of topics:

the transition from DIS to photoproduction
2+1-jet rate: problems in next-to-leading order (NLO) calculations, resolved photons
NLO matrix element (ME) programs and their possible transformation to complete generators with parton showers (PS) and hadronization
small-x parton dynamics; parton emission a la DGLAP, BFKL, CCFM, LDC
linked dipole chain (LDC) model and MC
MC event generators for CCFM, forward/backward evolution, hadronisation
MC for processes described by 'semihard' theory
matching of matrix elements with parton showers
parameterisation of parton densities and their use in MC's
PS generator with splitting functions in NLO
soft gluon treatment in PS, cutoff, coherence, angular ordering
ordering variable and evolution scale in DGLAP PS
diffraction/rapidity gaps: pomeron models, 2 gluon exchange (+ higher orders), soft colour interactions, proton dissociation
multiple parton interactions
hadronization issues: proton and photon remnant, soft color interactions, clusters, strings etc.
higher order QED radiative effects
MC's for special processes: W-production, lepton pair production, etc.
MC's for new physics processes: SUSY, leptoquark, instantons, etc.
upgrade of tools for comparison with data, e.g. HZTOOL

Time plan and organization:

Real progress in terms of improved or new programs cannot be achieved in a single meeting, but require substantial work and thereby time. Therefore, we plan a plenary starting meeting April 27-30, 1998 to discuss the problems, set priorities and form study groups. These groups will then have informal meetings as necessary over a rather long period. We will avoid having a big organization with many formal groups and conveners, but some coordination will be needed for different topics. A mid-term plenary meeting is planned for late September or early October -98 and the final meeting at DESY in January -99. Those interested are welcome to spend some time at DESY, not only for these meetings, but also for more extensive collaborative work.

Presentation of results:

Final meeting at DESY with presentation of results for the HERA community. The main outcome should be improved and easily accessible generators together with associated manuals, studies and physics papers. These will be collected in proceedings on the www. In particular, all generators should be briefly described and have links to their home pages, where code, manual, sample programs and news/updates can be obtained. Also a collection of relevant papers, in particular resulting from the workshop will be collected on www.