Collider Physics and QCD PhenomenologyMike Seymour (based at CERN)

• HERWIG Monte Carlo event generator– Current version ~ frozen (bug fixes and minor new features only)– HERWIG++

• completely new framework (integrated with PYTHIA7)• completely new parton shower algorithms (initial-state and final-state)• revised hadronization model• available now for e+e– annihilation and “real soon now” for hadron–hadron

• NLO calculations and NLO MCs– Higgs + 2 jets at NLO

• Collider phenomenology– W/Z production and mass measurement ! Emily Nurse– jet algorithms and top mass measurement ! Chris Tevlin– underlying event effects at Tevatron and LHC

• Resummation of large logarithms– ‘gaps between jets’ ! Albrecht Kyrieleis and JRF

• matching with BFKL • a new source of ‘non-global’ logarithms?

Hadron Emission Reactions With Interfering Gluons

• Physics overview– Angular ordered parton

showers

– Cluster hadronization model

HERWIG – Hadron Emission Reactions With Interfering Gluons

• Physics overview– Angular ordered parton

showers

– Cluster hadronization model

– Soft underlying event

• Current development– Parton shower/matrix element

matching• Hardest emission• Multijet matching• MC@NLO

– Multiple scattering model• Jimmy

– HERWIG++

• HERWIG++– Class structure– New parton shower algorithm– Improved cluster fragmentation model– New underlying event model “Jimmy+Ivan”

– e+e– version available now– Basic hadronic processes (Drell–Yan, QCD 2!2) “this year”– Full HERWIG functionality “next year”

– Work on Fortran HERWIG rapidly ramping down

HERWIG-related phenomenology

• Underlying events: HERA ! Tevatron ! LHC ?– Four new models!

• W/Z pt distributions and the W mass measurement– Emily Nurse (DØ student)

Tuning HERWIG on W/Z pt distributionsE.Nurse, MHS

PTRMS QCDLAM VQCUT

DEFAULT 0.0 0.18 0.48

HERWIG TUNE

1.6 0.14 0.19

MC@NLO TUNE

1.35 0.19 0.50

NLO Jet Calculations

• S.Catani, MHS: Nucl.Phys.B485(1997)291; SC, S.Dittmaier, MHS & Z.Trocsanyi NPB627(2002)189

– Subtraction method, based on– Universal (dipole) factorization theorem

• Implemented in– EVENT2, DISENT, ORIENT (MHS)– NLOJET++ (Zoltan Nagy)– MCFM (John Campbell and Keith Ellis)

• Single framework for NLO implementations of all ‘femtobarn’ processes at Tevatron

• Ideal starting point for universal implementation of MC@NLO?

Jet Algorithms

• Cone vs cluster algorithm MHS, Z.Phys.C62(1994)127

• Top mass reconstruction as a test case

• Update in progress (Chris Tevlin, ATLAS student)

ClusterCone

Resummation of Large Logarithms

• Event shape cross sections » sn log2n

• Non-global event shapes and non-global logs(Dasgupta and Salam, Phys.Lett.B512(2001)323; JHEP0203(2002)017)

• Interjet observables, rapidity gaps(R.B.Appleby and MHS, JHEP0309(2003)056)

• Work in progress– More non-global contributions?– Resummation of non-global logs?– Application to exclusive diffractive Higgs production…