Zvv bkg, how to get an estimate with first data ?

1. Zvv bkg, how to get an estimate with first data ? • Time schedule is tight. Goal : get an estimate by may/june if we get data from end february • Need to organize ourselves to make sure all topics are covered R. Brunelière

2. Zvv signal • MC samples: • alpgen full simulation samples at 10 TeV are existing : http://www-f9.ijs.si/atlpy/atlprod/prodtask/?q=10771&tatype__exact=G • alpgen samples at 7 TeV being generated at freiburg => then official mc request • alpgen matching uncertainties samples have been generated at freiburg at 10 TeV • NLO MCFM production can be done for 1,2jets with new MCFM version 5.7 • Objet and event selection cuts are defined by etmiss group • Our data-driven methods should work for any set of cut, but need starting point for studies. Propose to concentrate : • On 2-jets channel checking it works on the different discriminating variables (,,MT2,MCT,HTmiss). Also because 2jets channel is only one where theory uncertainties can be fully studied and Wlv bkg is less sensitive to ttbar contribution. • Same exercise on 4jets channel

3. The different control samples • List of possible control samples : • Zmumu • Zee • Wlv (l=mu,e) • Gamma (both prompt unconverted and converted photons) • Any other ? CS Statistics Difficulty

4. Zll control sample • Basic idea : • 2 methods : • So-called “replace” method means N(Zll;data) applies same cuts as N(Zvv;data) including Meff cut • So-called “MC” method means N(Zll;data) applies only preselection cuts. N(Zvv;data) predicted assuming MC is predicting correct Meff shape • If Meff cut is too high, only “MC” method is possible with first data but requires good understanding of theory uncertainties (in particular NLO/LO Meff shape)

5. Z control sample (1/2) • MC samples: • alpgen full simulation samples at 10 TeV are existing : http://www-f9.ijs.si/atlpy/atlprod/prodtask/?q=AlpgenJimmyZmumuNp&tatype__exact=K • alpgen samples at 7 TeV already generated and requested by SM and top wg • alpgen matching uncertainties samples have been generated at 10 TeV. Request for Atlfast1 being done now. • NLO MCFM production done by James Buchanan at 10 TeV. Will probably redo later at 7 TeV. • Objet and event selection cuts are defined by etmiss group, but can also start with Z/W+jets strawman selection for leptons : https://twiki.cern.ch/twiki/bin/view/AtlasProtected/WZJetsCOM09#Strawman_selection • Trigger : mu10 + susy trigger to check trigger efficiency

6. Z control sample (2/2) • Theory uncertainties on acceptance corrections: • NLO/LO using MCFM for 1,2 jets • Matching uncertainties using the different alpgen samples • Pdf using pdf reweighting tool from Yusuke • Turn on/off jimmy UE • Are FSR introducing any bias ? • Detector uncertainties : JES, soft MET, muon id efficiency uncertainties • Is it enough to take lepton id corrections from Z/W+jets wg ? • How much is QCD background ? How to estimate it ? • How do we compute “MET” ? Pt(1+2) or neutronification ? • How much statistics+systematics uncertainties do we get after all preselection cuts ? After different Meff cut ? • Suffers from statistics but benchmark channel for other control samples which can be cross-checked wrt Zmumu

7. Zee control sample • Same as Z, but electrons are also reconstructed as jets : • => • Bias “other” jets reconstructed like when R(jet,elec) < 0.6. How big is this effect ? Can we remove the two electron clusters and redo jets (and MET) ? Can we use existing tools : embedding, jet/met, redecay, simpler method ? On AODs ? • Cannot directly check susy trigger. Need looking at trigger objects, remove objects associated to offline electrons, check trigger chain again • Not so easy to do. • Can benefit again of work done in Z/W+jets wg (e.g. by Hugo and Caterina)

8. Wlv control sample (1/2) • Method : • Good points: • Wlv has ~ same statistics as Zvv • W/Z ratio very stable and hopefully well known (up to 2 jets) • W/Z ratio is among first SM W/Z+jets paper => lot of work being done there • Reversing method + using Zll can be used to predict Wlv background • Bad points: • For 3,4 jets, ttbar background very difficult to estimate (except via using b-tagging) • For 3,4 jets, W/Z ratio no more predicted at NLO. Can we still trust it ?

9. Wlv control sample (2/2) • MC samples: • alpgen full simulation samples at 10 TeV are existing : http://www-f9.ijs.si/atlpy/atlprod/prodtask/?q=AlpgenJimmyW&tatype__exact=K • alpgen samples at 7 TeV already generated and requested by SM and top wg • alpgen matching uncertainties samples have been generated at 10 TeV. Request for Atlfast1 being done now. • NLO MCFM production done by myself at 10 TeV. Soon available on grid. Redo later at 7 TeV. • Wev sample has same trouble as Zee. Easier to start with W • Background rejection for 2jets ? How ? • Who is already working on this topic ? Yusuke ?

10. Prompt photon control sample • Used by CMS for Zvv estimation. Statistics ~ Zvv. But tricky. • MC samples: • alpgen full simulation samples at 10 TeV are existing : http://www-f9.ijs.si/atlpy/atlprod/prodtask/?q=AlpgenJimmyGamNp&tatype__exact=K but too small ! • I have started generating alpgen samples at 7 TeV up to 5 jets. Already nearly done. • In order to study theory uncertainty properly, photon fragmentation correction has to be included => use recent Sherpa : http://arxiv.org/abs/0912.3501 • Amir proposal concerning background rejection + obj selection efficiency : make use of converted/unconverted rate not affecting final distributions. • +jets/Zll+jets measurement and comparison with MC should be used as proof of feasibility

11. Summary • Proposal : start with 2jets analysis as proof of feasibility for the various methods • Should quickly setup who is working on what to avoid duplicated effort • Examples few topic uncovered till now : • Theory systematics • Background rejection (specially for Wlv) • Prompt photon whole method • Trigger emulation • Concentrate myself to work on few topics : • MC samples production/study • Theory uncertainties (with MCFM/Alpgen/Sherpa)