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Attempting to generate the ALPGEN W + 2 photon event files for input to PYTHIA or HERWIG

W + 2 photon events in ALPGEN (P. Bell 4/8/2011). Attempting to generate the ALPGEN W + 2 photon event files for input to PYTHIA or HERWIG (for MC11 official production) ALPGEN can generate W + 2 photons + 0-4 jets

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Attempting to generate the ALPGEN W + 2 photon event files for input to PYTHIA or HERWIG

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  1. W + 2 photon events in ALPGEN (P. Bell 4/8/2011) • Attempting to generate the ALPGEN W + 2 photon event files for input to PYTHIA or HERWIG • (for MC11 official production) • ALPGEN can generate W + 2 photons + 0-4 jets • (weighted events in first step, unweighted in second, with some associated efficiency) • PYTHIA or HERWIG then does showering with “MLM parton matching” • (has a further associated efficiency) • Overall efficiency is low so need to run parallel jobs (have set up means to do this) • Some results/problems: • Wgg + 0J • 30M weighted events (3 hours) gives 36000 unweighted events =>25000 events to AOD • cross section = 0.013pb (Done) • Wgg + 1J • 300M weighted events (~24 hours) gives 50000 unweighted events => 25000 events to AOD • cross section = 0.013pb (Running) • Wgg + 2J • Estimation: will need 5000M weighted events => order 1000 hours (before MLM efficiency) • => Things get worse for 3J and 4J • (unweighting efficiency goes down and time per event goes up with more jets)

  2. ALPGEN generator settings 1 ! imode w2p0j_ele_v2 ! label for files 0 ! start with: 0=new grid, 1=previous warmup grid, 2=previous generation grid 10000 3 ! Nevents/iteration, N(warm-up iterations) 10000000 ! Nevents generated after warm-up *** The above 5 lines provide mandatory inputs for all processes *** The lines below modify existing defaults for the hard process under study ickkw 1 ebeam 3500.0 ndns 9 nph 2 njets 0 iwdecmod 1 metmin 0.0 ptjmin 15.0 ptphmin 10.0 ptlmin 20.0 etajmax 2.8 etaphmax 2.8 etalmax 2.8 drjmin 0.70 drphmin 0.30 drlmin 0.00 drphjmin 0.30 drphlmin 0.30 iqopt 1.0 qfac 1.0 ktfac 1.0 cluopt 1.0 iseed1 12345 iseed2 67890 ih2 1 Have tried to use tightest possible generator level cuts (highlight differences wrt defaults) Min charged lepton pT: ATLAS default = 0GeV ? Max charged lepton eta: ATLAS default = 10 Max photon eta: default: ATLAS default = 6 Max jet eta: default: ATLAS default = 6 jet-jet separation: ATLAS default = 0.7 photon-photon separation: ATLAS default = 0.1? photon-jet separation: ATLAS default = 0.1? photon-lepton separation: ATLAS default = 0.1?

  3. W + 2 photon events in ALPGEN • Summary • Question: Is such low efficiency expected? • (NB can reproduce results in ALPGEN manual) • Question: Do these input cuts look OK? • Event generation is very inefficient for > 1 jets: do we really need this? • (we know the +1 jet contribution is important - could run in “inclusive mode” for + >1 jets, • i.e. rely on showering) • Other MC news • Obtained a private (soon to be released) version of VBF@NLO • http://www-itp.particle.uni-karlsruhe.de/~vbfnloweb/wiki/doku.php • This has W + 2 photon at NLO, and the authors say they will “soon” implement the AQGCs

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