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M.Smizanska 18.2.2009

Few comments on B-production sensitivity to (some) PDFs at LHC energy within ATLAS sensitive volume. M.Smizanska 18.2.2009. LHC experiments, p-p collisions: parton kinematics for b-events.

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M.Smizanska 18.2.2009

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  1. Few comments on B-production sensitivity to (some) PDFs at LHC energy within ATLAS sensitive volume M.Smizanska 18.2.2009

  2. LHC experiments, p-p collisions: parton kinematics for b-events • Bjorken x1 vs x2 plots for events that passed trigger&offline selections for one of B hadrons and no constraints for anti B in the same event. • ATLAS/CMS needs down to 10-4Starts from 10GeV – the picture shows also lines for lower pT just to demonstrate that minimal x doesn’t change below 10GeV. • LHCb most sensitive to knowledge of structure functions at xas low as 10-5 • CDF x-range for b-production within 10-3 LHC 1-2 orders lower although not all the LHC statistics at the limiting x ATLAS/CMS LHCb ATLAS x-range for b-events after trigger - well covered by HERA measurements, so all modern PDFS should be able correctly predict! B-production measurements at LHC

  3. with mb = 4.75 GeV and mR = mF =m 0 MRST HO   0.43 mbCTEQ5M1   0.55 mb Calculated by A.Dainese, using NLQCD MNR code Uncertaintes in b-cross section at NLQCD • P.Nason, CERN 2000-004 • Large uncertaintes for LHC predicitons – dominantly due to higher order effects • (mRand mFscale factors in the running coupling constant as(mR2/L2) and the PDF functions Fi(x, mF2) • Sensitivity to variations of gluon density is small - constraints form HERA DATA are strong enough in the region where most of B-production takes place B-production measurements at LHC

  4. Example of Pythia small sensitivity to PDFs for b-production in phase space covered by L1 muon trigger ATLAS muon rates with PYTHIA5: ratio for CTEQ3L/EHLQ • The ratio of the integrated muon pT spectra for CTEQ3 and EHLQ • all Pythia ‘production mechanisms’ summed together • Pythia ‘production mechanisms’ shown separately: • full line flavour excitation g+b→ g+b • dashed gluon gluon fusion g+g →bb • dotted gluon gluon scattering followed by gluon splitting g+g →g+g, g →bb • The most sensitive is b-flavour excitation mechanism Pythia at LHC energy and ATLAS – weak dependence of muon rates on PDFs, even very old ones as EHQL. B-production measurements at LHC

  5. Dependency on PDF may appear in PY despite QCD stable vrt PDF change. “Unstability” of Pythia to PDF may be a consequence of other PY parameters, not properly understood.. B-production measurements at LHC

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