The Tevatron, with p p-bar collisions at sqrt(s)=1.96TeV can produce all
flavors of B hadrons and allows for unprecedented studies in the B physics
sector. The CDF and D0 collaborations have more than 5 fb-1 of data recorded. I
present here a selection of results on the masses, lifetimes and mixings of B
hadrons using between 1.0 and 2.8fb-1 of data.Comment: 5 pages, 3 figures. Proceedings for Recontres de Moriond QCD 2009,
  references adde

Malde, S.

English

arXiv

The Tevatron, with p{bar p} collisions at {radical}s = 1.96 TeV, can produce all flavors of B hadrons and allows for unprecedented studies in the B physics sector. The CDF and D0 collaborations have more than 5 fb{sup -1} of data recorded. I present here a selection of recent results on the masses, lifetimes and mixings of B hadrons using between 1.0 and 2.8 fb{sup -1} of data

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MEASUREMENTS OF THE MASSES, LIFETIMES AND MIXINGS OF BHADRONS AT THE TEVATRONS. MALDE on behalf of the CDF and D0 collaborationsDepartment of Physics, Denys Wilkinson Building, 1 Keble Road,Oxford OX1 3RH, United KingdomThe Tevatron, with pp collisions at√s =1.96 TeV, can produce all flavors of B hadrons andallows for unprecedented studies in the B physics sector. The CDF and D0 collaborationshave more than 5 fb−1 of data recorded. I present here a selection of recent results on themasses, lifetimes and mixings of B hadrons using between 1.0 and 2.8 fb−1 of data.1 Observation of the ΩbThe Tevatron has improved the understanding of B baryons through the observation of the Σ±b1,Ξ±b2,3 and, most recently, the Ω−b . These predicted baryons were not observed until Run II. D0observes the Ω−b in the decay channel Ω−b → J/Ψ[→ μ+μ−]Ω−[→ Λ0(→ pπ−)K−] using 1.3 fb−1of data. To increase the acceptance of the Ω−b the data is reprocessed with a modified trackingalgorithm that allows reconstruction of tracks with large impact parameters which occur in thisdecay channel, due to the long lifetime of the Ω and Λ baryon. A boosted decision tree is used toenhance the signal of the Ω over the combinatorial background, as shown in Fig. 1. D0 observes417.8±4.9(stat)±0.8(syst) Ω−b baryons and measures M(Ω−b ) = 6.165±0.010(stat)±0.013(syst)GeV/c2. The significance of the signal is greater than 5σ. The theoretical predictions of themass 5, 5.94< M(Ω−b ) <6.12 GeV/c2, are lower than the observed mass.2 B hadron lifetimesThe lifetimes of B hadron species test the Heavy Quark Expansion theory6. The predicted life-time ratios are7,8: τ(B+)/τ(B0)=1.053±0.016±0.017, τ(B0s )/τ(B0) = 1.00±0.01 and τ(Λb)/τ(B0)= 0.88±0.05. The experimental world averages for these ratios are τ(B+)/τ(B0) = 1.071±0.009,τ(B0s )/τ(B0) = 0.939±0.021 and τ(Λb)/τ(B0) = 0.904±0.032.K) (GeV)ΛM(1.6 1.65 1.7 1.75 1.8Events/(0.005 GeV)0100200300400500Right−signWrong−sign −1D0, 1.3 fb (a)K) (GeV)ΛM(1.6 1.65 1.7 1.75 1.8Events/(0.005 GeV)020406080100120140Right−signWrong−sign −1D0, 1.3 fb (b)) (GeV)b−ΩM(5.8 6 6.2 6.4 6.6 6.8 7Events/(0.04 GeV)02468101214D0 −11.3 fbDataFit(a)Figure 1: The left and center plots show Ω signal before and after the decision tree selection is applied. The righthand plot shows the mass distribution of the Ω−b candidates.) (GeV/c^2)-π c+Λm(5 5.5 6 6.5 72Candidates per 20 MeV/c0200400600800100012001400-1CDF II Preliminary, L = 1.1 fb Four-TrackbΛ Semi-leptonicbΛ OtherbΛB Four-TrackB Semi-leptonicB Other KcΛ → bΛρ cΛ → bΛπ cΣ → bΛ X*cΛ → bΛCombinatorial2Candidates per 20 MeV/c2) GeV/c-π +cΛm(5 5.5 6 6.5 7-3-2-10123ct (cm)0 0.05 0.1 0.15 0.2 0.25Candidates per 0.0025 cm110210-1CDF II Preliminary, L=1.1 fbB Four-Track KcΛ → bΛCombinatorial Four-TrackbΛ Semi-leptonicbΛ OtherbΛCandidates per 0.0025 cm) [cm]0bΛct(0 0.05 0.1 0.15 0.2 0.25-3-2-1012 lifetime [ps]bΛ0.5 1.0 1.5 2.0 (PRELIMINARY)π cΛCDF RunII 0.029±0.046 ±1.410 Λ ψCDF RunII J/ 0.033± -0.078+0.083 1.593 Λ ψD0 RunII J/ 0.042± -0.115+0.130 1.218  lcΛD0 RunII -0.091+0.0871-0.110+0.1201.290 0 lcΛCDF RunI  0.07± 0.15 ±  1.32  lcΛDELPHI  0.05± - 0.18+ 0.19  1.11  lcΛOPAL  0.06± - 0.22+ 0.24  1.29  ll0Λ l + cΛALEPH  0.11±  1.21 PDG 2008 -0.048+0.049 1.383 m]μ[100 200 300 400 500 600 Lifetime MeasurementsbΛFigure 2: The left hand plot shows the sample composition of the reconstructed Λb candidates. The decay timedistribution and fit projection is shown in the central plot. On the right is a comparison of τ (Λb) measurements.2.1 Λb lifetimeThe Λb lifetime has raised recent interest as the CDF measurement of τ(Λb) using Λb → J/ΨΛ 9was precise but larger than all previous measurements. CDF has also measured τ(Λb) usingfully reconstructed decays in the decay mode Λb → Λcπ, where the events are collected bythe displaced vertex trigger10. This trigger exploits the long lived nature of B hadrons andyields ∼3000 Λb events in 1.1 fb−1 of data after signal optimization. The sample compositionis shown in Fig. 2. The trigger acceptance biases the decay time distribution. This is correctedfor by modeling the trigger efficiency using Monte Carlo simulation. After the sample compo-sition is determined, an unbinned maximum likelihood fit is performed and measures cτ(Λb)=420.1±13.7(stat)±10.6(syst) μm. This is the world’s best determination of τ(Λb) and is con-sistent with all previous measurements as shown in Fig. 2. The lifetime ratio τ(Λb)/τ(B0) iscompatible with theoretical predictions. The systematic uncertainties in this measurement aredominated by uncertainties in the simulation of the trigger response and the decay kinematics.2.2 B0s lifetimePrevious measurements of τ(B0s ), which used semileptonic decay modes, were lower than τ(B0).CDF has measured the B0s flavor specific lifetime using the decay mode B0s → D−s π+ using 1.3fb−1 of data collected by the displaced vertex trigger11. As before, Monte Carlo simulation is usedto correct for the decay time bias of the trigger. The measurement uses 1100 fully reconstructeddecays and also 2000 partially reconstructed decays e.g. B0s → D−∗s π+, B0s → D−s ρ+ whichsignificantly improves the statistical precision of the result. The partially reconstructed decayshave missing particles which results in a incorrect measure of the mass and transverse momentumused to determine the decay time. This is corrected for statistically by introducing a K factor: t = LxymrecbcPT· K where the K factor distribution is determined from Monte Carlo and is theratio of the true lifetime and the lifetime measured using a partially reconstructed event. CDFmeasures cτ(B0s )= 455.0±12.2(stat)±8.2(syst)μm which is the most precise measurement of theflavor specific B0s lifetime and is compatible with the world average value12 of τ(B0).2.3 Simulation independent method of lifetime measurementThe use of Monte Carlo to model the trigger bias leads to large systematic uncertainties that willdominate measurements with more data. A simulation free method to correct the trigger biashas been developed13 at CDF to improve future measurements. This uses the decay kinematicsto determine a per event efficiency. The event efficiency is evaluated, as a function of decay time,by calculating the trigger acceptance at each possible decay time along the B meson momentumdirection. Using the decay mode B+ → D0π+, we measure τ(B+) = 498.6±6.9(stat)±4.5(syst)μm. This is consistent with the world average12, and the measurement is presented as a proof ofprinciple. Overall, the total systematic uncertainty is half the size of the typical error from thesimulation dependent method. The largest contributions to the systematic uncertainties for thesimulation free method come from assumptions on the track finding efficiencies of the trigger.2.4 Bc lifetimeThe lifetime of the Bc meson is expected to be much smaller than the other B mesons as eitherthe b or c quark can decay. CDF and D0 use the semileptonic decay channel Bc → J/ΨlX (wherel = μ, e). The neutrino is not reconstructed and the resulting mismeasurement of the mass andtransverse momentum of the Bc is statistically corrected for by determining K factors fromMonte Carlo. The decay time distributions of background events are modeled and calibratedusing Monte Carlo and data. CDF uses both the electron and muon channels in 1.0 fb−1 and thecombined measurement14 is cτ(Bc)=142±15(stat)±6(syst) μm. D0 analyzes the muon channelonly in 1.3 fb−1 and measures15 cτ(Bc)=134±11(stat)±10(syst) μm. Both measurements areconsistent with, and more precise than, theoretical predictions17.3 CP violation in B0s mixingThe study of CP violation in B0s mixing has been carried out by both experiments in thedecay B0s → J/Ψ[→ μ+μ−]φ[→ K+,K−]. The time evolution of a mixture of the B0s and itsantiparticle B0s is given by the Schrodinger equation iddt (ab ) =(M − iΓ2)( ab ), where M and Γ arethe 2 × 2 mass and decay matrices that relate the flavor eigenstates, B0s and B0s , with the masseigenstates, B0Hs and B0Ls . The difference in mass and width between B0Hs and B0Ls is related tothe off diagonal elements of the mass and decay matrices as follows: mHs −mLs = Δms ≈ 2|M12|,ΓL−ΓH = ΔΓ ≈ 2|Γ12|cos(φs) where φs = arg(−M12/Γ12) ≈ 0.04 in the Standard Model(SM)16.Any new particle participating in the mixing loop that carries a weak phase will be measurablegiven that the SM prediction is ∼0. This phase φNP is accessible through the measurementof βJ/Ψφs which is the relative phase between the direct decay amplitude and mixing followedby decay amplitude. In the SM βs = arg(−VtsV ∗tbVcsV ∗cb)≈ 0.02 where Vij are the elements of theCKM matrix. A large observed βs is a clear indication of new physics, and is related to the newphysics phase, φNP , through 2βJ/Ψφs = 2βSMs − φNPs .CDF and D0 reconstruct 3200 and 2000 signal events in 2.8 fb−1 of data respectively. Theangular distribution of the muons and kaons, (to disentangle the CP of final state), the tag-ging information, (to determine the initial flavor of the meson), mass, decay time and mixing (rad)     sβ-1 0 1)     -1 (psΓΔ-0.6-0.4-0.20.00.20.40.6-1CDF Run II Preliminary        L = 2.8 fb95% C.L.68% C.L.SM predictionNew Physics68% CL95% CL99% CL99.7% CLHFAG2008-3 -2 -1 0 1 2 3-0.6-0.4-0.20.00.20.40.6p-value = 0.0851.72σ from SMSMD     2.8 fb—1Figure 3: Confidence intervals on the ΔΓ − βs plane. Note that φs = −2βs and hence the shift with respect tothe SM expectation is in the same direction for each experiment.frequency are put together in an unbinned maximum likelihood fit to extract βs and ΔΓ. Theresults are presented in confidence intervals as the errors are non Gaussian in Fig. 3. CDFobserves a 1.8σ deviation18 from the expected SM values and D0 observes a 1.7σ deviation19.A combination of the D0 result and a previous CDF result20 using only 1.35 fb−1 of data givesa 2.2σ deviation from the SM. Although not statistically significant, it is interesting that bothexperiments observe similar shifts. The evolution of this measurement as more data and analysisimprovements are incorporated is awaited due to the potential to observe new physics.4 ConclusionsThe Tevatron continues to lead the way with B-baryon mass measurements and B hadron lifetimemeasurements. New and improved results can be expected with the data now available. CDFand D0 have made interesting measurements related to CP violation in B0s mixing and couldpotentially observe the signature of new physics in the future. These exciting results demonstratethe success of the B physics program at the Tevatron.References1. T. Aaltonen et al [CDF Collaboration], Phys. Rev. Lett. 99, 202001 (2007)2. V.M. Abazov et al [D0 Collaboration], Phys. Rev. Lett. 99, 052001 (2007)3. T. Aaltonen et al [CDF Collaboration], Phys. Rev. Lett. 99, 052002 (2007)4. V.M. Abazov et al [D0 Collaboration], Phys. Rev. Lett. 101, 232002 (2008)5. X. Liu et al, Phys. Rev. D 77, 014031 (2008)6. I.I.Y. Bigi, M.A. Schifman and N. Uraltsev, Ann. Rev. Nucl. Part. Sci 47 591 (1997)7. F. Gabbiani, A.I Onishchenko and A.A Petrov, Phys. Rev. D 70, 094031 (2004)8. M. Beneke et al, Nucl. Phys. B 639, 389 (2002)9. A. Abulencia et al [CDF Collaboration], Phys. Rev. Lett. 98, 122001 (2007)10. http://www-cdf.fnal.gov/physics/new/bottom/080703.blessed-lblcpi-ct/11. http://www-cdf.fnal.gov/physics/new/bottom/080207.blessed-bs-lifetime/12. C. Amsler et al, Phys. Lett. B 667, 1 (2008)13. http://www-cdf.fnal.gov/physics/new/bottom/080612.blessed-MCfree Blifetime/14. http://www-cdf.fnal.gov/physics/new/bottom/080327.blessed-BC LT SemiLeptonic/15. V.M. Abazov et al [D0 Collaboration], Phys. Rev. Lett. 102, 092001 (2009)16. A. Lenz and U. Nierste, JHEP 0706, 72 (2007) and references contained within.17. V.V. Kiselev hep-ph/0308214 (2008)18. http://www-cdf.fnal.gov/physics/new/bottom/080724.blessed-tagged BsJPsiPhi update prelim/19. V.M. Abazov et al [D0 Collaboration], Phys. Rev. Lett. 101, 241801 (2008)20. T. Aaltonen et al [CDF Collaboration], Phys. Rev. Lett. 100, 161802 (2008)

Measurements of the masses, lifetimes and mixings of B hadrons at the Tevatron

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