V+jets and V+hf in HERWIG

Mike Seymour

CERN/University of ManchesterBerkeley Workshop March 27th 2008

V+jets and V+hf in HERWIG

• V+jets and V+hf in HERWIG– some musings on Andy’s Z+bjet HERWIG results

• V+jets and V+hf in Herwig++• Status reports

– HERWIG– Herwig++– Rivet/CEDAR

V+jet studies in HERWIG

• See talks of:– Andrea Messina– Andy Mehta– Jason Nielsen– Michelangelo Mangano (?)– Nils Lavesson– etc (?)

Z/γ+bjet from Tevatron

• First a consistency check:– HERWIG6.510, CTEQ6L, inclusive Z (on shell)

– parton level: apply +10% correction to σ(Z+b)/σ(Z)– inclusive kt algorithm, R=0.7, massive jets 1 jet containing b quark with pt>20, |y|<1.5

– and the answer is…

Z/γ+bjet from Tevatron

• First a consistency check:– HERWIG6.510, CTEQ6L, inclusive Z (on shell)

– parton level: apply +10% correction to σ(Z+b)/σ(Z)– inclusive kt algorithm, R=0.7, massive jets 1 jet containing b quark with pt>20, |y|<1.5

– and the answer is…

0.20% GOOD !

• Where do these b’s come from?

• 0.07% from gluon splitting• ~0.01% from backward evolution to a b!• 0.12% from bb->Z

– this is 0.69% of qq->Z, but only 18% of these have a b jet

Z/γ+bjet from Tevatron

Z/γ+bjet from Tevatron

• Where do the rest of the b’s disappear to?

• 60% of b’s do not backward evolve to a gluon: forced (non-perturbative evolution)

Z/γ+bjet from Tevatron

• but the other 40% look reasonable:

Z/γ+bjet from Tevatron

• Suppose we artificially force b quarks to be evolved back to a gluon perturbatively– i.e. replace forced emission by “abort and

reshower” exception

HERWIG would give 0.38%

Z/γ+bjet from Tevatron

• Aside 1: MLM mentioned distortion from ‘abort and reshower’ exceptions:– I find 2.8% of bb->Z events have one

• small• acts in opposite direction

Z/γ+bjet from Tevatron

• Aside 2: gluon splitting contribution:– LEP measures ~0.3% Z->qq+(g->bb)– PYTHIA predicts ~0.16%– HERWIG predicts ~0.26%

• (v. old numbers - need to be checked)

Z/γ+bjet from Tevatron

• Conclusion:• More to be understood in backward evolution

of b partons, interplay between– modern pdfs: VFNS, current mass– parton showers: massless evolution with

constituent mass as infrared cut-off

V+jets and V+hf in Herwig++

HERWIG status

• Version 6.510 released October 31st 2005– Not tuned to data (like all versions 6.1 onwards) !– Steadily growing list of bugs:

• VBF -> Higgs forward-backward asymmetry• B baryon decays• …

– Very few promised new features• gg->Higgs ME corrections• W/Z spin correlations in HW/Z production

– New release promised “real soon now”

Herwig++ status• Version 2.1.4 released March 3rd 2008

– Version 2.2 coming soon• third digit ~ monthly, second digit ~ twice yearly

• Similar quality physics in most areas– Hadronization– Underlying event (Jimmy)

• Better in some– Parton shower mass effects (quasi-collinear)– Secondary hadron decays– BSM Simulation (Feynman rules input, spin corr.)

• Full tune to e+e- data and Tevatron U.E

Herwig++ status• Complete Physics and Manual

– arXiv:0803.0883 [hep-ph]

• Hooks for generalized CKKW/MLM matching built in (but nothing hangs from them yet…)

• Version 3.0 foreseen for this Fall: complete replacement for HERWIG

CEDAR/Rivet

• Combined E-Data Analysis Resource for high-energy physics– HEPdata (database of experimental results)– HEPForge

• development environment used by ~ general purpose MCs

– LHAPDF– HEPML, RivetGun, AGiLe, … (utilities/interfaces)– JetWeb (web front end for Rivet)– Rivet (object oriented replacement for HZtool)

• Experiment-independent implementation of hadron-level analysis for MC standardized comparison

MCnet opportunities 2008:• CTEQ-MCnet school• Short-term studentships: for th. and exptl. students to spend 3-6 months with MC authors in:

- CERN- Durham/Cambridge- Karlsruhe- Lund- UCL

on a project of their choice- Next closing date:

- March 31st