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ATLAS B-Physics Reach

ATLAS B-Physics Reach. M.Smizanska, Lancaster University, UK maria.smizanska@cern.ch. ATLAS: b-events from central pp LHC collisions. 100 m b. 230 m b. B-physics strategy with tight funding constraints.

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ATLAS B-Physics Reach

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  1. ATLAS B-Physics Reach M.Smizanska, Lancaster University, UK maria.smizanska@cern.ch

  2. ATLAS: b-events from central pp LHC collisions 100mb 230mb M.Smizanska: ATLAS B-physics reach

  3. B-physics strategy with tight funding constraints • Recent work has addressed the issue of maximizing B-physics capabilities in context of reduced initial Trigger/DAQ system (funding limitations) • Extend Region-of-Interest mechanism of level-2 trigger to reconstruction of B decays: • Level-1 muon was always used to provide region of interest • Now, level-1 jet to guide reconstruction of hadronic modes, e.g. Bs  Dsp, and electrons, e.g. J/y e+e- • Use result of level-2 trigger to seed reconstruction in the Event Filter • Only reconstruct limited region of Inner Detector containing B candidate • Strong reduction in processing requirements compared to previous strategy that involved full scan of Inner Detector at level-2 • Nevertheless, with presently assured funding, the initial Trigger/DAQ system will be almost saturated by the priority “discovery physics” programme when the luminosity is at the target of L = 2  1033 cm-2s-1 • At this luminosity, B-physics would be based on dimuon trigger only which has very low rate but nevertheless covers many interesting channels • At lower luminosities, e.g. towards end of LHC coast, spare Trigger/DAQ capacity can be used to extend the B physics potential M.Smizanska: ATLAS B-physics reach

  4. single-muon all h b c all b h di-muon J/y c @1033cm-2s-1 B – physics trigger strategies, cont. Level-1: single-muon or di-muon Efficient down to pT 5GeV ( lower still in endcap). Different scenarios according to luminosity conditions & rates 1. Di-muon trigger: L1 2m + L2 precision m tracking in muon spectrometer and Inner detector. Bd J/y (mm) + Ks0 , Bs J/y (mm),f, etc Lb  J/y (mm)L, rare decays B  mm,Bd K0* mm, Bd rmm, etc 2. Muon-electron(g) trigger: L1 m + L1 e/g cluster (ET>2GeV)+ L2 tracking in region Bd J/y (ee) + Ks0 + Bm, Lb J/y (ee) L + B m, Bd K0* g + B  m, etc 3. Muon-hadron trigger: L1 m + L1 Jet (ET>5GeV) + L2 tracking in region B pp+ Bm, Bs Dsp +Bm, etc M.Smizanska: ATLAS B-physics reach

  5. ATLAS performance parameters principal for B-physics Low pT electron identification Combined EM calorimeter-TRT electron identification TRT electron identification Rejection of bb m6X events without electron vs efficiency of events bb m6e5X. Eff=70%,R=570, level-2 rate of signal is 40Hz, fake rate 10Hz due to hadrons misidentified as electrons. Invariant mass for all track pairs in bb J/y (ee)K0 events before and after TRT selection cuts. Electrons have pT>1GeV. M.Smizanska: ATLAS B-physics reach

  6. ATLAS performance parameters principal for B-physics, cont. Low and medium-pT muon performance Lowest pT muon identification & reconstruction efficiency J/y(mm) reconstruction in the environment of b-jet with pT~(50-80) GeV (for QCD b-production studies) Inner detector + Muon spectrometer the same in log scale muons Inner detector + Muon spectrometer + Hadron calorimeter pions Even in high pT jet, a mass reconstruction is negligibly affected by fake pairs when a muon identified in Muon spectrometer match to the wrong track in the Inner Detector. M.Smizanska: ATLAS B-physics reach

  7. Precise measurementsofBd J/yKs0decay Method: maximum likelihood fit, using experimental inputs: proper time resolution, tag probability, wrong tag fraction, background composition. Direct CP violation term neglected here. M.Smizanska: ATLAS B-physics reach

  8. sensitivity in a-sensitivity as a function of a and theoretical uncertainty of |P/T| using full LHC potential The current theoretical uncertainty |P/T|~30% dominates other systematical and statistical errors of full LHC potential. M.Smizanska: ATLAS B-physics reach

  9. f q1 q2 Bs Physics of Bs meson Program for precise measurements of Bs-anti-Bs system parameters : DGs, Dms and probing Bs mixing phase fs= -2l2hallowing to investigate new physics. Dms from Bs Ds p and Bs Ds a1already after 1 year sensitivity up Dms - 36 ps-1 fully explore SM allowed range Dms (14.3 - 26) ps-1 DGs and fs= -2l2h from Bs J/yf or BsJ/yh both sensitive, but precision sufficient only in Bs J/yf Angular analyses of cascade decay Bs J/y (mm)f(KK) determine DGs, Gs and fs simultaneously with parameters of helicity amplitudes A||(t=0), AT(t=0), A0(t=0), d1, d2. Parameter Dms will be measured by decays to flavor specific final states Bs Ds p and Bs Ds a1 . M.Smizanska: ATLAS B-physics reach

  10. CP - violation weak phase in BsJ/y f Standard Model region-updated 2003 New physics Left-right symmetric model (NP-LR) - version used here last updated in 2000. ATLAS (3years): 1st level trigger 1m only. Extension by 2m trigger under investiga- tion, not included. TDR Detector. ATLAS - same – as above with Final Detector Layout– Preliminary LHCb(5years): full 1st Level trigger, performance parameters as given in 2000 Experimental potential of both experiments not yet fully exploited: more studies on additional triggers, tagging. M.Smizanska: ATLAS B-physics reach

  11. Potential for Rare decays Bmm Will measure branching ration of Bsmm which is in SM of order Br<(10-9) Perform high sensitivity search on Bdmm Before LHC BK*mm will be measured however mass and angular distributions detailed enough to show New Physics only at LHC. Bmm can be seen before LHC only if drastically enhanced. A study proved good performance at nominal LHC luminosity. After 1 year 1034cm-2 s-1 3 years at luminosity 1033cm-2 s-1 M.Smizanska: ATLAS B-physics reach

  12. Exclusive Rare decays of B mesons ATLAS statistics will allow angular analyses that can carry evidence for new physics. E.g. forward-backward asymmetry: Three points: mean values of AFB in three q2/MB2 experimental regions with error bars Lowest mass region: sufficient accuracy to separate SM and MSSM if Wilson coefficient C7g <0 SM MSSM C7g >0 MSSM C7g <0 M.Smizanska: ATLAS B-physics reach

  13. other studies of ATLAS b-physics group • Studies not mentioned here: • Double heavy flavor mesons. • QCD tests of beauty production at LHC central region. Correlations bb. • Physics of Beauty baryons, production polarizations, decays. M.Smizanska: ATLAS B-physics reach

  14. B-physics prospects with ATLAS - conclusions • ATLAS is preparing a multi thematic B-physics program - including B-decays and B-production. • ATLAS B-physics trigger strategy revised to maximize physics potential within tight funding constraints - rely on dimuon trigger for initial luminosity 2  1033 cm-2s-1- extend selection at lower luminosities when there is spare processing capacity. • In CP violation the main emphasis will be on underlying mechanisms and evidence of New physics. ATLAS is especially precise in measurement of b. In BsJ/y f large CP violation would indicate new physics. • Bs mixing studies make clear that there is sensitivity to Dms beyond SM expectations. The width difference DGs can be measured best in BsJ/y f with relative precision 8%. • Rare decays B mm have favorable experimental signature allowing to measure also at nominal LHC luminosity 1034cm-2 s-1. Will measure branching ration of Bs mm which is in SM of order Br<(10-9) Precision measurements will be done for B K*mm. • Beauty production and bb correlations in central LHC collisions will be measured for QCD tests. M.Smizanska: ATLAS B-physics reach

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