Several models for minimum-bias and the underlying event are going to be investigated in this project. Examples of these, are the models implemented in PYTHIA, HERWIG, JIMMY and PHOJET MC event generators. The comparison of MC tunings to experimental data is the main focus of this project. We plan to check how reliable the different tunings are by comparing their predictions to a wide range of observables. We also plan to compare the LHC predictions generated by the different tunings.

Arthur Moraes (Glasgow) and Craig Buttar (Glasgow)

Experimental collaborators from HERA could help by advising us on what HERA data sets are more sensitive to the underlying event and should, therefore, be used to tune the MC models.

• Describing minimum bias and the underlying event at the LHC, A. Moraes, C. Buttar and I. Dawson. In: 'Physics at Tev Colliders 2003' QCD/SM Working Group: Summary Report. Contributed to 3rd Les Houches Workshop: Physics at TeV Colliders, Les Houches, France, 26 May - 6 Jun 2003. e-Print Archive: hep-ph/0403100 .
• Simulations of minimum bias events and the underlying event, MC tuning and predictions for the LHC, C. M. Buttar, D. Clements, I. Dawson and A. Moraes. Acta Physica Polonica B 35(1) (2004) 433.
• Minimum bias and the underlying event: towards the LHC, I. Dawson, A. Moraes and C. Buttar. Czechoslovak Journal of Physics 54 (2004), Suppl. A, 221.
• Charged Jet Evolution and the Underlying Event in Proton-Antiproton Collisions at 1.8 TeV, T. Affolder et al., The CDF Collaboration, Phys. Rev. D65, (2002) 092002.
• PYTHIA Web Page
• HERWIG Web Page
• JIMMY Web Page

• Comparison of predictions for the underlying event and minimum-bias interactions generated by several PYTHIA tunings and PHOJET were presented at the working group meeting in March 2004.
  
• First distributions for the underlying event generated by JIMMY were presented at the working group meeting in October 2004.
  

(2004.10.13) Planning to compare the MC tunings to pT distributions from the UE in jet events and also try to generate < pT > vs. < Nchg > again for UE particles.
Medium term project: get a tuning for PYTHIA6.3 .