V+jets and V+hf in HERWIG
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Transcript of V+jets and V+hf in HERWIG
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