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Strange Goings On in B Physics Simulations - And Other Stories

Strange Goings On in B Physics Simulations - And Other Stories. Laura Gilbert - Oxford Atlas Physics meeting 6th March 2006. Strange sea asymmetries – background studies . Signal: . Tag with: -electron -missing Et -K π ( ππ )( π 0 ) + bachelor pion. e -. s. ν. c. g. d. D *+. π +.

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Strange Goings On in B Physics Simulations - And Other Stories

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  1. Strange Goings On in B Physics Simulations - And Other Stories Laura Gilbert - Oxford Atlas Physics meeting 6th March 2006

  2. Strange sea asymmetries – background studies Signal: Tag with: -electron -missing Et -Kπ(ππ)(π0) + bachelor pion e- s ν c g d D*+ π+ Sample: W→enu at NLO. Previously re-run DC2 sample and searched for signal in ATLFAST. Now waiting for DC3 full sim sample prepared in December. (Chris: virtual Ws and ATLFAST) d D0 Kπ(ππ)(π0) jet

  3. DC3 Sample Status Useful Wiki Pages: https://uimon.cern.ch/twiki/bin/view/Atlas/WZMcAtNloSample https://uimon.cern.ch/twiki/bin/view/Atlas/NewsforPhysicsUsers • Oxford responsible for W->enu, munu. Should end up with 1 million of each fully generated. • Confusing. 11.0.3 test versions for We-nu (inc. CBNT) allegedly available on OSG (Don Quixote) but fetch commands failing – error reported and not fixed. • 11.0.3 test versions available for Wmu-nu on LCG. Need grid cert, 2M space/file, and altered script “./downloadLFC.sh” then it’s quite simple. First glance: AODs, ESDs ok, CBNTs dodgy.**NEED TO VALIDATE THIS SAMPLE WITHIN THE WEEK**/afs/cern.ch/user/l/lgilbert/DC3/LAURA/mc11.005251.McAtNloWmunu.recon.v11000305/mc11.005251.McAtNloWmunu.recon.CBNT.v11000305/mc11.005251.McAtNloWmunu.recon.*.v11000305._*.root • 11.0.41 now ongoing, mysteriously running on Nordugrid. Some recent failures, jobs resubmitted. Investigating how to get them back!

  4. s e- c π+ ν g D*+ D0 Kπ(ππ)(π0) c jet Strange sea asymmetries – background studies Background: Ccbar sample: signal + irreducible background + reducible background. Signal from ccbar: Irreducible background→ if this is d

  5. e- ν D K c jet g π+ D*+ D0 Kπ(ππ)(π0) c jet Strange sea asymmetries – background studies Background: Remove reducible background with electron exclusion cuts? Close tracks from D. Similarly for Bbbar where B Decays to D and ttbar where ts decay to Bs. Lifetime cuts should remove these.

  6. Creating background samples • Ideally: Use PythiaB with EVTGEN to create QQbar pairs. Method to get b/c quark sample: • Run Pythia(B) with MSEL=1 (qqbar/gg pairs) • Turn off all weak C/B hadron decays in Pythia. • EvtGen will take undecayed heavy hadrons and decay them (weak only) according to specified branching fractions to give required decay chains. • Filter out all undecayed hadrons (BR=0) so that only the required decays remain. • Tried many variations on this theme. All crash identically.

  7. Unexpected issues! • Very strange crashes when EvtGen combines with Pythia(B). • Runs fine for ~100 events • Starts to create events with undecayed quarks, undecayed “string” particles, undecayed excited hadrons. • Frequency of crashes increases through run. Various filters added but cannot increase total no. viable events. • Suggests serious problems!! B Physics group now confirms that no B jobs can be run at all. • Handed to B physics people to fix: Rolf Seuster now.

  8. Alternative generation? • Herwig: cannot be tied into EvtGen in Athena, no interface • Generate specifically bbbar/ccbar decay using process number 1705/4. • Filter events so: eta<2.7; lepton pT>10GeV; MpT>10GeV; B/no B hadrons required. • Filter efficiency: 0.5% for bbar backround. not ideal!! • Can’t see a better way to boost sample on first glance. Needs more work. • Find Pythia/Herwig alone tend to generate leptons with low energy from qqbar production. Definitely need to be able to boost signal. • Suspect easiest to wait for fix to EvtGen interface but continuing just incase!

  9. What now? • Working with EvtGen people to try to solve interfacing issues. Have another go at backgrounds when tools available. • Some small DC3 samples should be available within the week allegedly. Provide feedback and hopefully analyse CBNTs. Try with muons now if possible - ind CBNT error. • Trigger studies on same sample if recon works. • Making a new VM with 11.0.41 once I’ve tested it.

  10. Conclusions • Everything’s broken • DC3 is doomed • I’ll never graduate

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