High Precision Measurements of Bs Parameters in BsJ/ Roger Jones University o

High Precision Measurements of Bs Parameters in BsJ/ Roger Jones University o www.phwiki.com

High Precision Measurements of Bs Parameters in BsJ/ Roger Jones University o

Ventrelle, Chrissa, Food Columnist has reference to this Academic Journal, PHwiki organized this Journal High Precision Measurements of Bs Parameters in BsJ/ Roger Jones University of Lancaster United Kingdom as long as the ATLAS B-physics Group Beauty 2005, Assisi, Italy Overview of ATLAS Weight: 7000 tonnes Radius: 11m Length: 46m Muon chambers Barrel toroid Inner detector EM calorimeter Forward calorimeter Hadronic calorimeter End-cap toroid The LHC Environment pp collisions: 14 TeV centre of mass energy Luminosity: 2007: 50 days @ 0.5 x 1033 cm-2s-1 Tuning 2008-2009: 200 days @ 2 x 1033 cm-2s-1 “Low” 2010+: 1034 cm-2s-1 “High” Drops by factor ~2 during 10 hour run 1 proton bunch crossing every 25ns 4.6/23 pp collisions/crossing @ low/high luminosity ~1% of pp collisions produce a bb pair At luminosity 2 x 1033 cm-2s-1 bb events produced with rate of 106 Hz 10Hz output to permanent storage as long as B-physics so highly selective in addition to adaptable B-physics trigger required

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B-physics trigger strategies (see Natalia Panikashvili) As luminosity drops during the fill, more triggers are turned on Bs-Bs mixing S : mixing phase = 2 sin c sin Vub / Vcb Arises through the interference of mixing in addition to decay Highly sensitive to SUSY contributions Parameter is small in the St in addition to ard Model (~0.02) so challenging measurement General box diagrams as long as Bs-Bs mixing: s = ½ ( H + L ) s = L – H Ms = MH – ML Xs = Ms / s BSJ/ Extracting mixing parameters requires separation of CP eigenstate amplitudes Scalar Vector + Vector decay: final state described by three helicity amplitudes Determined by the angular distribution of the decay, in addition to also proper times in addition to tag 1 2 3 Transversity basis: linear combinations of helicity amplitudes which are CP-eigenstates. Complete determination yields mixing parameters 4

Decay parameterization 3 transversity amplitudes 2 independent magnitudes in addition to 2 independent phases: A A 1 2 3 mixing parameters, 1 weak phase s s Ms S 8 parameters to be extracted from the data Theoretical distribution + h.c. Distribution is model-independent – new physics enters through the modification of existing values Accurately modelled by EvtGen Is it a B or a B (Tagging) b/b b/b Signal B/B-meson Jet charge tag b/b b/b Lepton tag from semi-leptonic decay For Bd(s) J/(63)K0S Tagging efficiency tag = 0.64 (0.62) Wrong-tag fraction Wtag = 0.42 (0.39) tag(electron) = 0.012 tag(muon) = 0.025 Wtag(electron) = 0.27 Wtag(muon) = 0.24 Signal B/B-meson

The workflow 1 2 EVENT GENERATION: PythiaB, EvtGen SIMULATION/DIGITIZATION/RECONSTRUCTION 3 ‘AS REAL’ ANALYSIS 4 PARAMETER EXTRACTION: maximum likelihood using detector per as long as mance parameters derived from full simulation. Details of Analysis All studies based on fully simulated ATLAS events in addition to using the current reconstruction software 1 000 000 Bs decays produced with PythiaB in addition to EvtGen to generate the correct angular distribution in addition to mixing (model input: A,A, 1,2,s,s, s,Ms) Cuts: 1 muon > 6 GeV; 1 muon > 3 GeV; kaons > 0.5 GeV BSJ/()(KK) All computations per as long as med in addition to all results stored on the Grid (LCG) ‘As real’ Analysis Fit track pairs to J/ hypothesis: pT(1) > 3GeV && pT(2) > 3GeV () < 2.4 2/DoF < 6 && m(J/) (-3,3) = 38MeV Fit track pairs to hypothesis pT(K) > 0.5GeV (K) < 2.4 2/DoF < 6 && m() (1009.2, 1029.6) GeV J/ invariant mass invariant mass ‘As real’ Analysis BS fit Four-track fit to single vertex; 2/DoF < 10 must point at primary vertex Bs proper decay time > 0.5ps pT(Bs) > 10 GeV m(Bs) (-3,3); = 17MeV Bs invariant mass Bs proper decay time Analysis Results in addition to projections Total number of signal events within kinematic cuts after 30 fb-1: 810 000 LVL1/LVL2 trigger di-muon efficiency: 77% Number of signal events after trigger: 623 700 Background analysis Background 1: Identical spin structure in addition to topology to signal S/B ~ 15.1 Background 2: Angular structure assumed to be isotropic S/B ~ 6.8 BdJ/()K0(K+-) (background 1) bbJ/()X (background 2) Simulation/digitization/reconstruction: Identical to signal Analysis Same analysis code run over background to calculate acceptance

Normalised Maximum Likelihood Estimator Tagging efficiency. B-tag: tag1 = 1 – w; tag2 = w (Anti B)-tag: tag1 = w; tag2 = 1 – w No tag: tag1 = tag2 = 0.5 Convolution with Gaussian to account as long as proper decay time resolution Reconstruction efficiency in addition to acceptance corrections: determined from simulation Background (level determined from simulation) Theoretical PDF: W+ as long as B0 at production W- as long as anti-B0 at production Maximum Likelihood test results XS fixed: can be determined with BsDs Uncertainties on s are a function of Xs (Bs)=85fs s/=0.1 Uncertainties: Correlations: Conclusion: Estimated reach of ATLAS No sensitivity to St in addition to ard Model values (nor have LHCb or CMS) CDF recently made a unexpectedly large measurement of s/s Study of this “Golden Channel” in ATLAS should provide a rich yield of interesting data

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Ventrelle, Chrissa Food Columnist

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