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Sinéad Farrington University of Glasgow for the CDF Collaboration European Physical Society Aachen, 17 th -23 rd July 2003 B Lifetimes and Flavour Tagging at CDF Run II
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Sinead Farrington EPS Aachen 17th-23rd July 2003 2 Outline Overview of B Physics at CDF B lifetimes: –Exclusively reconstructed B’s decaying via J/ –Semileptonically decaying B’s Flavour Tagging
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Sinead Farrington EPS Aachen 17th-23rd July 2003 3 B Physics at CDF Run II pp collisions produce a wide spectrum of B hadrons in a challenging environment Tevatron upgrade to 1.96 TeV CoM energy larger b production cross section -
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Sinead Farrington EPS Aachen 17th-23rd July 2003 4 B Triggers at CDF Run II Di-Muon (J/ ) p T ( )>1.5 GeV/c J/ modes at low (conventional) p T ( J/ ) 0 GeV/c Measure x-section (See talk by Tara Shears) J/ Yield=2x Run I l + displaced track p T (e/ )>4 GeV/c Semileptonic modes p T (trk)>2 GeV/c Lifetimes,flavour tagging 120 m<d 0 (trk)<1mm B Yields 3x Run I Two displaced tracks p T (trk)>2 GeV/c Hadronic modes 120 m<d 0 (trk)<1mm Charm Physics, B 0 s mixing NEW! (bb) << (pp) B events are selected with specialised triggers: Indivdual data samples of about 140pb -1 accumulated - -
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Sinead Farrington EPS Aachen 17th-23rd July 2003 5 B Hadron Lifetimes According to the spectator model all B mesons would have the same lifetime… but that is not the whole story! The HQE predicts by how much the lifetimes differ. Objective 1: Measure lifetimes accurately to form input to theories Objective 2: Prove the detector and triggers are working Objective 3: Measure s / s B 0 s l D s is an admixture of CP even and CP odd states Pair it with fully CP even or CP odd state (or use polarisation analysis) and measure s / s PDG Values
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Sinead Farrington EPS Aachen 17th-23rd July 2003 6 B Hadron Lifetimes EXCLUSIVE J/ trigger clean fully reconstructed lifetime unbiased low statistics J/ K+K+ B+B+ SEMILEPTONIC lepton+displaced track trigger clean partially reconstructed - need MC to unfold ct lifetime biased good statistics Reconstruct decay length by vertexing Measure p T of decay products B 0 J/ K 0* B + J/ K + b J/ B 0 s J/ B 0 l D ( * )- b l c B 0 s l D s
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Sinead Farrington EPS Aachen 17th-23rd July 2003 7 Fit Methodology: Simultaneous fit of M(B) signal fraction, define sidebands c (B) lifetime Background Parameterisation: Signal Contribution: Exclusive B J/ X Lifetimes
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Sinead Farrington EPS Aachen 17th-23rd July 2003 8 b J/ Lifetime and Crosscheck CONTROL SAMPLE
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Sinead Farrington EPS Aachen 17th-23rd July 2003 9 Exclusive B J/ X Lifetimes: B 0 s Meson CDF Run II Preliminary B+B+ 1.63 0.05 0.04 ps B0dB0d 1.51 0.06 0.02 ps B0sB0s 1.33 0.14 0.02 ps bb 1.25 0.26 0.10 ps B 0 s J/ is mostly CP even measures mostly L component Access s / s via angular analysis – coming soon World’s largest sample of fully reconstructed B s mesons
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Sinead Farrington EPS Aachen 17th-23rd July 2003 10 Extraction of Semileptonic Lifetimes Lepton+ displaced track trigger implemented successfully for the first time! samples rich in B hadron semileptonic decays Follow the standard methodology: reconstruct the D decay near to lepton B decay not fully reconstructed extract the factor from Monte Carlo: extract lifetime from decay length: but with one crucial complication: lifetime bias from the displaced vertex trigger: 4 GeV lepton + 2 GeV track with 120 m<d 0 <1mm Emulate trigger with Monte Carlo and model the lifetime bias which is factored into the fit function.
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Sinead Farrington EPS Aachen 17th-23rd July 2003 11 K Factor and Bias from MC K Factor Distribution P(K) Reconstruction efficiency including trigger bias, as a function of proper lifetime Normalised to unit area Arbitrary vertical scale
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Sinead Farrington EPS Aachen 17th-23rd July 2003 12 B Semileptonic Channels M(pK ) (GeV/c 2 ) apply PID CDF Run II Preliminary 70pb -1 b l c l DsDs DD
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Sinead Farrington EPS Aachen 17th-23rd July 2003 13 Semileptonic Decay Fit Model Unbinned maximum likelihood fit to c (B) –Background is parameterised by delta function and positive exp convoluted with Gaussian resolution: Free parameters: D E + f + G –Signal: exp convoluted with Gaussian resolution, K factor distribution, P(K), and bias function, –Maximum likelihood function:
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Sinead Farrington EPS Aachen 17th-23rd July 2003 14 Semileptonic Lifetime Fits b c Lifetime statistical error projections B+B+ 0.04 ps B0dB0d 0.06 ps B0sB0s 0.07 ps bb 0.09 ps Highest statistical accuracy lifetime fits in B 0 s and b : Control Samples Fit results show discrepancy with world average Many crosschecks Currently working to understand all effects of trigger bias etc. CDF Run II Preliminary 70pb -1 B 0 s D s ct(B)(mm)
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Sinead Farrington EPS Aachen 17th-23rd July 2003 15 Flavour Tagging Development OPPOSITE SIDE Soft Lepton Tag* Opposite side K Tag Jet charge tag OPPOSITE SAME SAME SIDE Same side K/ Tag* Determine B flavour at production and decay to measure –B 0 mixing, B 0 s mixing, CP violation Figure of merit: D 2 – : tag efficiency –D: Right-Wrong/Right+Wrong CDF has a battery of tags which are being developed further
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Sinead Farrington EPS Aachen 17th-23rd July 2003 16 Same Side Tag Asymmetry Identify fragmentation pion Measure raw asymmetry: Test tagger on B + should see NO oscillations! B l D 0 B + J/ K + For B 0 s mixing apply same side K tag: very powerful
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Sinead Farrington EPS Aachen 17th-23rd July 2003 17 Tagger Studies in Semileptonic Sample lepton + displaced track trigger provides high statistics sample of ~150000 B (and D) semileptonic decays Strategy: trigger lepton estimate of B flavour at production count numbers of opposite side tags can subdivide sample by muon system and p T rel parameterise relative dilution for use in likelihood fit cross check consistency with partially reconstructed lepton+D +,0 consistent results believe dilution in lepton+D s This number is UNBIASED since we’re using an independent (and high statistics) control sample track p(e/ +D) P.V. Detailed sample composition studies: –Mass cut removes D decays: 2<M(l+track)<4GeV/c 2 –Background subtraction variable separates B’s from background: signed IP of displaced track
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Sinead Farrington EPS Aachen 17th-23rd July 2003 18 Soft Muon Tag D 2 Soft Muon Tagger D 2 =0.660 0.093 % CDF Run I: D 2 =0.584 0.082 % Identify charge on opposite side Sufficient statistics to examine parameterisation of dilution as function of p T rel Method will be used to evaluate, optimise and compare all taggers Unbiased way of optimising taggers Next step: measure D 2 for a reconstructed channel Background subtraction has been used to obtain measurement of D 2
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Sinead Farrington EPS Aachen 17th-23rd July 2003 19 Summary Lifetime measurements made in clean B J/ channels: Lepton + displaced vertex trigger has been implemented at CDF for the first time –lifetime measurements ongoing: will give best statistical accuracy in B 0 s and b –Flavour Tagging procedure has been established and two taggers have been optimised and evaluated in a non-biased way Measurements of s / s coming soon and first steps towards B 0 s mixing are happening! CDF Run II Preliminary B+B+ 1.63 0.05 0.04 ps B0dB0d 1.51 0.06 0.02 ps B0sB0s 1.33 0.14 0.02 ps bb 1.25 0.26 0.10 ps
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Sinead Farrington EPS Aachen 17th-23rd July 2003 20 K Factor and Bias from MC ELECTRONS:
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Sinead Farrington EPS Aachen 17th-23rd July 2003 21 Major upgrades at CDF provide Increased geometric coverage Extended muon system new 3D silicon tracker faster response drift chamber Triggers: large bandwidth, background reduction, displaced vertex triggering
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Sinead Farrington EPS Aachen 17th-23rd July 2003 22 Determine B flavour at production and decay to measure –B 0 mixing, B 0 s mixing, CP violation Figure of merit: D 2 – : tag efficiency –D: Right-Wrong/Right+Wrong CDF has a battery of tags which are being developed further Run II’s lepton+displaced vertex trigger large sample of semileptonic decays allows us to measure , D and D 2 in data and optimise the taggers can then apply them in any sample without bias
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Sinead Farrington EPS Aachen 17th-23rd July 2003 23
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