The value of |V{sub cb}| has been measured recently from a simultaneous fit to moments of the hadronic-mass and lepton-energy distributions in inclusive semileptonic B-mesons decays with a precision of 2%. Both exclusive and inclusive measurements of |V{sub ub}| have also been carried out in B {yields} X{sub u}{ell}{nu} decays. Precision measurements of the mixing parameter, {Delta}m{sub d}, have been obtained. In addition, direct limits on the total decay-rate difference {Delta}{Lambda} between the two B{sup 0} mass eigenstates and on CP, T and CPT violation due exclusively to oscillations have recently been provided by BaBar

Cote, D.

U., /Montreal

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Work supported  in part by Department of Energy contract DE-AC02-76SF00515SEMILEPTONIC B DECAYS, B MIXING AND MAGNITUDESOF CKM ELEMENTS AT BABARDavid Coˆte´ ∗Universite´ de Montre´alABSTRACTThe value of |Vcb| has been measured recently from a simultaneous ﬁt tomoments of the hadronic-mass and lepton-energy distributions in inclusivesemileptonic B-mesons decays with a precision of 2%. Both exclusive and in-clusive measurements of |Vub| have also been carried out in B → Xuν decays.Precision measurements of the mixing parameter, ∆md, have been obtained.In addition, direct limits on the total decay-rate diﬀerence ∆Γ between thetwo B0 mass eigenstates and on CP, T and CPT violation due exclusively tooscillations have recently been provided by BaBar.1 IntroductionThere are strong motivations for studying semileptonic B decays and B0B¯0mixing. First of all, these processes are related to some of the fundamental∗ cote@slac.stanford.eduSLAC-PUB-11519SLAC, Stanford University, Stanford, CA  94309Contributed to DAFNE 2004: Workshop on Physics at Meson Factories, 06/07/2004--6/11/2004, Rome, Frascati, Italyparameters of the Standard Model. With input from theory, it is then possibleto determine the values of |Vub| and |Vcb| from measurements of inclusive and/orexclusive branching fractions of B → Xuν and B → Xcν, respectively. Themeasurement of the B0B¯0 oscillation frequency, ∆md, constrains the value of|Vtd|. From a ﬁt of heavy quark expansion (HQE) relations to the data, theinclusive study of B → Xcν also yields a relatively precise determination ofthe b and c quark masses. Secondly, the B0B¯0 mixing and semileptonic Bdecay branching fractions have large eﬀects on other measurements and thusneed to be measured precisely. Indeed, ∆md is used in all the time-dependentCP measurements while the semileptonic decays are an important source ofbackground for many measurements. Finally, the semileptonic B decays areuseful to test various QCD eﬀective theories.2 Inclusive |Vcb| measurement 5)The ﬁrst attempts to determine |Vcb| suﬀered from large uncertainties due topoorly known theoretical parameters. For BaBar’s latest inclusive |Vcb| mea-surement, we aimed to measure simultaneously these parameters, Br(B →Xcν) and |Vcb|, by using HQE relations calculated in the kinetic mass schemeto order 1/m3b and αS1). These HQE relations depend on the mb and mc quarkmasses and on the non-perturbative QCD parameters µG, µπ, ρLS and ρD. Allare poorly known but constraints on a large number of measurable quantitiesallow their experimental determination as well as Br(B → Xcν) and |Vcb|.This was achieved with a global HQE ﬁt to the measured ﬁrst moments of thelepton energy and hadronic mass distribution as a function of diﬀerent leptonenergy cuts.2.1 Electron energy moments 3)Taking Ri(E0, µ) =∫∞E0(Ee − µ)i( dΓdEe )dEe, the electron energy moments arethen deﬁned as: partial branching fraction (0th moment): Br(E0) = τB ·R0(E0, 0); ﬁrst moment: M1(E0) =R1(E0,0)R0(E0,0); central moments: Mn(E0) =Rn(E0,M1(E0))R0(E0,0), n = 2, 3. These moments were extracted from B → Xceν de-cays tagged with di-electron events containing one high momentum electronand one opposite charge electron as well as requiring a typical B-B event topol-ogy. The remaining backgrounds, determined mostly from data control sam-ples, were then subtracted. Various corrections were applied to correct for theeﬀect of Bremsstrahlung, electron ID eﬃciency, etc... Four hundred thousandsignal events were kept from a sample of 47.4 fb−1. The 0th to 3rd electron en-ergy moments were then computed for various minimum electron energy cuts,varying from 0.6 GeV to 1.5 GeV in the Υ(4S) frame.2.2 Hadronic mass moments 4)This measurement used events consisting of a fully reconstructed B meson -Breco (via its hadronic decays). The other B meson decaying semileptonicallywas required to have exactly one energetic lepton and a missing energy, mo-mentum and total charge consistent with a single neutrino. The hadronic mass,MXc, was then reconstructed with a kinematic ﬁt to all the remaining particlesof the event. The ﬁrst four hadronic mass moments (as deﬁned in Sect. 2.1)were then computed for minimun electron energy cuts varying between 0.9 GeVand 1.5 GeV in the Υ(4S) frame.2.3 Fit results and comparison with other measurementsThe global ﬁt (Sect. 2) to the measured moments (Sect. 2.1 and 2.2) shows animpressive agreement between HQE predictions and experimental data. Theresults of ﬁts to electron energy moments alone are consistent with those tohadronic mass moments alone. The results are:|Vcb| = (41.4± 0.4exp ± 0.4HQE ± 0.2αS ± 0.6ΓSL)× 10−3;Br(B → Xceν) = (10.61± 0.16exp ± 0.06HQE) %;mb(1GeV ) = (4.61± 0.05exp ± 0.04HQE ± 0.02αS) GeV ;mc(1GeV ) = (1.18± 0.07exp ± 0.06HQE ± 0.02αS) GeV .These values represent the best measurements to date of these parameters.It is interesting to note that the b and c quark masses are in excellent agreementwith theoretical expectations. Results for the HQE parameters: µ2π, µ2G, ρ3Dand ρ3LS are also presented in5).3 Inclusive |Vub| measurement 7)The semileptonic B decays investigated for the inclusive measurement of |Vub|were identiﬁed by the same method as described in Sect.2.2. To isolate the rela-tively rare B → Xuν decays out of the very abundant B → Xcν, we requireda small reconstructed mX and no kaon on the semileptonic side of the events.Br(B → Xuν) is determined from the measured ratio Ru = Br(B→Xuν)Br(B→Xν) ,where Br(B → Xν) is taken from a previous BaBar measurement 2). Thismethod allows a cancellation of systematic errors due to Breco on the tag sideand lepton ID on the semileptonic side. Using 6):|Vub| = 0.0045·(Br(B → Xuν)0.0021.55psτB)1/2×(1.0±0.020pert±0.0521/m3b) (1), we obtained: |Vub| = (4.62± 0.28(stat)± 0.27(syst)± 0.48(theo))× 10−3 andBr(B → Xuν) = (2.24± 0.27(stat)± 0.26(syst)± 0.39(theo))× 10−3.4 Exclusive |Vub| measurement 8)BaBar’s ﬁrst attempt to measure |Vub| from an exclusive channel used a tech-nique which consisted of selecting B → ρeν events containing a very energeticelectron and having missing energy and momentum consistent with a singleneutrino. The exclusive reconstruction of the B → ρeν decay is achieved byreconstructing a ρ and requiring ∆E = Ebeam − Eρ − E − Emiss to be com-patible with zero. This analysis led to:Br(B → ρeν) = (3.29± 0.42(stat)± 0.47(syst)± 0.60(theo))× 10−4and |Vub| = (3.64± 0.22(stat)± 0.25(syst)+0.390.56 (theo))× 10−3.5 B0B¯0 mixingBaBar had previously 9) performed several precision measurements of the B0B¯0oscillation frequency, ∆md, and of the B0 lifetime, τB. In those analyses, thetotal decay-rate diﬀerence between B0 and B¯0, CP violation in mixing andCPT violation were assumed to be negligible. Recently, a generalized B0B¯0mixing analysis was performed 10) which didn’t made these assumptions. Inall analyses, the experimental technique consisted of ﬁrst fully reconstructinga B (as in Sect. 2.2) and of measuring the vertex position of this “Breco”. Thevertex of the second “Btag” was determined using the remaining charged tracksof the event. Its ﬂavor was determined from the charge of lepton(s) and/orkaon(s) and/or soft pion(s) among the remaining tracks. The distance alongthe beam axis between the Breco and Btag vertices was then used to estimatethe lifetime diﬀerence ∆t between the two B mesons. The reconstructed Bpairs were classiﬁed in categories which depended on the ﬂavor of Breco andBtag. A ﬁt to the measured ∆t distributions in the diﬀerent categories wasperformed to extract the B0B¯0 mixing parameters.5.1 Previous B0B¯0 mixing analysesIn these measurements, the B0B¯0 pairs are classiﬁed as ”mixed” or “unmixed”,where the unmixed events correspond to B0B¯0 → B0B¯0 events and the mixedones to B0B¯0 → B0B0/B¯0B¯0 events. The mixed and unmixed samples aredescribed by two diﬀerent probability density functions (PDF):N±(∆t,∆md) =e−|∆t|/τ4τ·(1±cos(∆t∆md))⊗(Reconstruction effects). (2)The parameter ∆md is then extracted from the asymmetry A:A(∆t) =N+(∆t)−N−(∆t)N+(∆t) + N−(∆t)= cos(∆md∆t). (3)From a sample of 23 millions B pairs, we obtained:∆md = 0.500± 0.008± 0.006ps−1 and τB0 = 1.529± 0.012± 0.029ps.5.2 “Generalized” B0B¯0 mixing analysisIn this analysis, the B0B¯0 pairs are classiﬁed in 6 diﬀerent categories: B0B0,B0B¯0, B¯0B0, B¯0B¯0, B0BCP , B¯0BCP , where the two Bs are Btag and Breco,respectively. Unlike the previous mixing analysis, the Breco which are CPeigenstates are also used in this analysis leading to a more complex ﬁt formula.From a sample of 82 fb−1, we obtained:sgn(ReλCP )∆Γd/Γd = −0.008± 0.037(stat)± 0.018(syst);|q/p| = 1.029± 0.013(stat)± 0.011(syst);(ReλCP /|λCP |)Rez = 0.014± 0.035(stat)± 0.034(syst);Imz = 0.038± 0.029(stat)± 0.025(syst).where λCP ≡ (q/p)( ¯ACP /ACP ), ACP ( ¯ACP ) is the amplitude for B0 → fCP(B¯0 → fCP ), and z ≡ δmd−(i/2)δΓd∆md−(i/2)∆Γd . Here, δ (∆) means the diﬀerence betweenthe B0 ﬂavor (mass) eigenstates and sgn(ReλCP ) indicate that the sign ofReλCP is undetermined. More detailed explanations are given in Ref. 10)but we note here that ∆Γd/Γd is the lifetime diﬀerence between the Bheavyand Blight mass eigenstates, z = (0, 0) imply CPT violation and |q/p| = 1imply P (B0 → B¯0) = P (B¯0 → B0). All our present results conﬁrmed theassumptions previously made in the B0B¯0 mixing and CP analyses.6 SummaryNew BaBar precision measurements of |Vcb|, Br(B → Xceν), mb, mc and4 HQE parameters were obtained, improving signiﬁcantly our knowledge ofthese quantities. Inclusive (exclusive) |Vub| measurements with a precision of13% (18%) were also carried out at BaBar using B → Xuν decays. Theseare currently dominated by theoretical errors, but much progress is expectedsoon. Finally, a new analysis with variable ∆Γd/Γd, |q/p| and z mixing pa-rameters validate the assumptions made in previous BaBars mixing and CPmeasurements.References1. P. Gambino, N. Uraltsev, Eur. Phys. J. C34, 181-189 (2004),N. Uraltsev, hep-ph/04031662. BaBar Collaboration (B. Aubert et al.), Phys. Rev. D67, 031101 (2003)3. BaBar Collaboration (B. Aubert et al.), Phys. Rev.D69, 111104 (2004)4. BaBar Collaboration (B. Aubert et al.), Phys. Rev. D69, 111103 (2004)5. BaBar Collaboration (B. Aubert et al.), Phys. Rev. Lett. 93, 011803 (2004)6. M. Battaglia et al, The CKM matrix and the unitarity triangle (2002),e-print archive: hep-ph/03041327. BaBar Collaboration (B. Aubert et al.), Phys. Rev. Lett. 92, 071802 (2004)8. BaBar Collaboration (B. Aubert et al.), Phys. Rev. Lett. 90, 181801 (2003)9. BaBar Collaboration (B. Aubert et al.), Phys. Rev. Lett. 88, 221802 (2002),BaBar Collaboration (B. Aubert et al.), Phys. Rev. Lett. 88, 221803 (2002),BaBar Collaboration (B. Aubert et al.), Phys. Rev. Lett. 89, 011802 (2002),BaBar Collaboration (B. Aubert et al.), Phys. Rev. D66, 032003 (2002),BaBar Collaboration (B. Aubert et al.), Phys. Rev. D67, 072002 (2003)10. BaBar Collaboration (B. Aubert et al.), Phys. Rev. Lett. 92, 181801 (2004),BaBar Collaboration (B. Aubert et al.), Phys. Rev. D70, 012007 (2004)

Semileptonic B Decays, B Mixing And Magnitudes of CKM Elements at BaBar

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Semileptonic B Decays, B Mixing And Magnitudes of CKM Elements at BaBar

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