some validation of mc@nlo alpgen and toprex n.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
Some validation of MC@NLO, AlpGen and TopRex PowerPoint Presentation
Download Presentation
Some validation of MC@NLO, AlpGen and TopRex

Loading in 2 Seconds...

play fullscreen
1 / 19

Some validation of MC@NLO, AlpGen and TopRex - PowerPoint PPT Presentation


  • 130 Views
  • Uploaded on

Some validation of MC@NLO, AlpGen and TopRex. Stan Bentvelsen Feb 18 th , 2004. Resume of MC@NLO. MC@NLO: Matching NLO calculations of QCD process with parton shower MC simulation Fully exclusive events generated Hard emissions treated as in NLO Soft emissions handled by MC shower (Herwig)

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Some validation of MC@NLO, AlpGen and TopRex' - don


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
resume of mc@nlo
Resume of MC@NLO
  • MC@NLO:
    • Matching NLO calculations of QCD process with parton shower MC simulation
      • Fully exclusive events generated
        • Hard emissions treated as in NLO
        • Soft emissions handled by MC shower (Herwig)
        • No ‘double counting’ between these two
    • Running in ATLAS:
      • Create event file using ‘runNLO’ program (extern)
        • Contains kinematic of hard NLO process
      • Interface to Herwig via McAtNLO_i
release 7 6 0
Release 7.6.0
  • Herwig_i-00-01-29
    • Points to herwig6.504
      • Excellent – this is needed for heavy gauge boson production in McAtNlo
      • Bug: problem with ‘timel’ routine; herwig job cannot be longer than 1000 CPU seconds
  • McAtNlo_i-00-00-04
    • Interface outdated and buggy - need to be updated to comply to MCATNLO vsn 2.3 (or 2.2)
        • Inputini.F
        • Initmcatnlo.F
      • Works fine for top-production
      • Does not work for events with W,Z (JPR=13,14) and others?
      • Private version working against 6.5.0
resume weights

13.5%

86.5%

Resume: Weights

‘standard’ tt production

process -1706

  • Weights: ±w
    • ‘unweighted’ events, up to a sign!(practically weight ±1)
    • Efficient event generation possible
      • NLO distributions (without MC showering) are non-physical

tt production cross section

MCatNLO: 842 pb

HERWIG: 458 pb

PYTHIA: 490 pb

(nb: no consistent pdf’s!)

resume comparison to lo generators
Resume: Comparison to LO generators
  • Pt(tt system)
    • Herwig & MCatNLO agree at low Pt,
    • At large Pt MCatNLO ‘harder’
    • PYTHIA completely off

Same distribution on linear scale

All distributions normalised to 1

mcatnlo practicalities
MCATNLO practicalities
  • Event Weights
    • Stored in HepMC::GenEvent weight()
    • Not being picked up by Atlfast
      • My private AtlfastAlgs::StandardNtupleMaker is getting weights from herwig common (uh! Ugly!)
  • Event files
    • What is granularity of event files? How many events in one file?
    • Who is making these for DC2?
unit conversion
Unit conversion
  • External MCATNLO file
    • Units in GeV
  • Conversion
    • Conversion to MeV done in filling HepMC common block
  • Atlfast
    • Not updated to MeV yet
    • Not been able to fully check MCATNLO with Atlfast in 7.6.0
      • Jet-finding, thresholds, etc: need modification of StandardOptions values
alpgen multiparton generator
AlpGen ‘multiparton’ generator
  • Many hard processes – with extra n-jets (‘light jets’)
    • E.g.: tt+n-jets, W+n-jets
    • Exact (LO) matrix element
    • Alpgen generates file with hard scattering
      • External files
      • To be fed into Herwig/Pythia shower MC’s
    • GNU compiler bug, noticeable in optimized complex number arithmetic.
      • To be safe, use optimization flag, -O2 (default for AlpGen version v1.4)
        • Works fine under gcc 2.96
alpgen in 7 6 0
AlpGen in 7.6.0
  • Somewhat confusing structure:
    • Package AlpGen_i-00-00-04
      • Is not updated to Alpgen V1.3
      • What is the status of this package?
    • Package Herwig_i-00-01-29
      • Interface to AlpGen files in routine atoher_65.F
      • Called via UPINIT
      • Has been updated to Alpgen v 1.3 (excellent!)
  • Can the AlpGen_i package be deleted from release?
alpgen tt 1jet
Alpgen: tt+1jet
  • Inputs
      • Mtop=175
      • 1 extra light jet
      • Jet: Pt>10, ||<2.5, R>0.4
      • Initial grid 3 * 200000
      • Events: 40.106
      • Produced 60 samples
  • Production
    • Un-weighting to single lepton (e,,) decay
    • Effective : 293 pb
      • 1.9 106 events generated (8 10-4 generation efficiency)
      • 18.1% (351000) events pass first selection
        • ETmiss>20 GeV, lepton (e, ) Pt>20 and >=4 jets Pt>40

Example run in AlpGen

alpgen tt 1 jet production
tt-system alpgen affected by extra gluon

Previously problems, now solved!

Histograms normalized to unity

Extra jet:

Pt-min = 10 GeV

|η| < 2.5

R>0.4

AlpGen tt+1-jet production

Alpgen looks ok!

w jets background
W+jets background
  • Most important background for top: W+n jets
    • Leptonic decay of W, and n=4 extra jets
    • In Pythia only relevant process: qq’W (+q(g) )
      • No ‘hard’ matrix element for 4 extra jets
      • I.e.: 3 or 4 extra jets need to be generated by
        • Shower
        • Fragmentation+ Decays
        • Detector response+ Reconstruction
    • MC@NLO has NLO qq’ W+X
      • No ‘hard’ matrix element for 4 extra jets
      • Generated 350k events, only 1 event passed first selection
        • lepton (e, ) Pt>20 and >=4 jets Pt>40
    • Alpgen has ‘hard’ matrix element for 4 extra jets
nikhef data processing facility
Due to small generation efficiencies in Alpgen:

Use local NIKHEF LCG grid

Currently 30% of total LCG grid

This will change soon

Total 240 CPU’s

Mix of PIII: 0.8, 1.2, 2.0 and 2.6 GHz machines

NIKHEF data processing facility

AlpGen jobs take lot of CPU

  • Total submitted jobs: 2303
  • Total GHzHrs (equivalent hours on 1 GHz machine): 15469 (!)

AlpGen jobs running!

alpgen w 4jets
Alpgen: W+4jets
  • Un-weighting to W lepton (e,,) decay
    • Production 1
      • Effective : 4390 pb
        • 108401 unweighted events generated (3.6 10-6 efficiency)
        • 2.57% (2784) events pass first top selection
    • Production 2
      • Effective : 2430 pb
        • 380740 unweighted events generated (2.6 10-5 efficiency)
        • 3.41% (13002) events pass first selection
  • W+4 extra light jets
  • Jet: Pt>10, ||<3.0, R>0.3
  • No lepton cuts
  • Initial grid: 200000*3
  • Events: 150·106
  • Jobs: 198
  • W+4 extra light jets
  • Jet: Pt>10, ||<2.5, R>0.4
  • No lepton cuts
  • Initial grid: 200000*3
  • Events: 150·106
  • Jobs: 98
top signal background
Luminosity: 10 pb-1

MC@NLO signal

Alpgen1 sample

Luminosity: 150 pb-1

MC@NLO signal

Alpgen2 sample

Top signal + background
toprex generator
TopRex generator
  • Request from top-group to include TopRex
    • Relevant top physics:
      • Handling of spin-correlations in top-decays
      • Simulation of single-top processes
      • Rare top decays, processes, FCNC,…
    • Showering and decay handled by Pythia
    • Used in many (fortran based) Top analyses
    • Used by CMS
      • Slabospitsky,Sonnenschein
      • http://sirius.ihep.su/~spitsky/toprex/toprex.html
toprex generator1
TopRex generator
  • 2 packages:
    • External/TopRex
      • Pointer to toprex installation in/afs/cern.ch/atlas/offline/toprex
        • “out of the box” toprex installation
        • Perhaps need some cosmetic update (dir structure)
    • Generators/TopRex_i
      • Interface package ala Pythia_i
      • “toprex.dat” file to select process, switches, etc
  • All this is available and working and checked against release 6.5.0
    • Tbd: linking against GENSER version of Pythia

Can we have this available for DC2 ??

toprex
TopRex
  • Motivation:
    • Study top-spin correlations
    • Need detailed simulation to check these subtle effects

<CosΘ+ · CosΘ->

summary
Summary
  • MCATNLO
    • Update interface to vsn 2.2/2.3
    • Make sure weights are handled correctly
  • AlpGen
    • All in place – if AlpGen_i package removed
    • CPU demanding event generation
  • TopRex
    • All is there – need to be injected in Atlas software. Urgent requests from top-group

Logistics of externally generated event files