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Measurement of B Oscillations and CP Violation s 9 Results from DØ 0 0 J. Ellison, for the DØ Collaboration 2 University of California, Riverside, CA 92521, USA n a J 0 2 Abstract ] We present a measurement of the B0 −B¯0 oscillation frequency, ∆m , using a combination x s s s of semi-leptonic and hadronic B decay candidates selected from data collected by the DØ e s ExperimentattheFermilabTevatron.WealsopresentseveralresultsonCPviolation,including - p an improved measurement of the B CP-violating phase from a flavor-tagged analysis of B0 → s s e J/ψ+φ decays. h [ 2 Key words: v PACS: 5 3 1 1. Introduction 2 . 1 Among the primary goals of the Tevatron is the observation of B oscillations and the s 0 searchforCPviolationinB-mesondecays.Inthispaperwedescribesomerecentresults 9 in these areas. The data used for the results described here are based on approximately 0 : 1.2−2.8 fb−1 of data collected by the DØ Experiment at the Fermilab Tevatron. The v DØ detector consists of a central tracking system surrounded by a uranium liquid-argon i X calorimeter and an outer muon detection system and is described in [1]. r a 2. Measurement of B Oscillations s InthispaperwereportapreliminarymeasurementoftheB0−B¯0 oscillationfrequency s s ∆m based on the analysis of five decay channels: (1) B0 → D−µ+νX,D− → φπ−; s s s s (2) B0 → D−e + νX,D− → φπ−; (3) B0 → D−µ+νX,D− → K∗0K−; (4) B0 → s s s s s s s D−µ+νX,D− →K0K−;(5)B0 →D−π+,D →φπ−.Thedatasetswereapproximatley s s s s s s 2.4 fb−1 for all channels except (4) whihc used a dataset of 1.2 fb−1. DØ has previously reporteddirectlimitsonB oscillationsusing1fb−1 ofdatainthefirstdecaychannel[2]. s PreprintsubmittedtoElsevier January21,2009 After selection and reconstruction of the B0 decays, the flavor of the B0 at decay is s s determined from the charge of the muon, electron, or pion in the final state. The flavor at production is determined using a combined flavor tagger based on opposite-side and same-side tagging [3]. The effectiveness of the tagging algorithm is characterized by the tagging efficiency (cid:15) and the dilution D defined by D = (N −N )/(N +N ), RS WR RS WR where N and N are the number of right-sign and wrong-sign tags, respectively. RS WR The overall effectiveness of the combined tagger, obtained using B → µνD∗− data and B →J/ψφ data and Monte Carlo, is (cid:15)D2 =4.49±0.88%. s The determination of the proper decay length takes into account possible missing momentum, e.g. due to the presence of a neutrino in the semileptonic decay modes. The properdecaylengthisgivenbycτ =xMK,wherexM isthemeasuredorvisibleproper B0 s decay length, given by (cid:34)d(cid:126)Bs0 ·p(cid:126) (cid:96)Ds−(cid:35) pµDs− xM = T T cM with K = T (p(cid:96)Ds−)2 Bs0 pBs0 T T The K-factor, K, is determined from Monte Carlo. Themeasurementof∆m isaccomplishedusinganunbinnedlikelihhodfittothedata. s The likelihood function is constructed using the probabilities for mixed and unmixed decays, (cid:18) (cid:19) 1 K Kx P (t)= exp − (1−Dcos∆m Kx/c) mix 2cτ cτ s Bs Bs (cid:18) (cid:19) 1 K Kx P (t)= exp − (1+Dcos∆m Kx/c) nomix 2cτ cτ s Bs Bs and accounting for detector resolutions and background contributions. The combined amplitude scan, where the likelihood is modified to include an amplitude term, L ∝ 1±ADcos(∆m Kx/c), is shown in Fig. 1(a). The likelihood as a function of ∆m is s s shown in Fig. 1(b). The measured value of ∆m is obtained from a fit to the likelihood s vs. ∆m in the region of the minimum shown in Fig. 1(b), and yields ∆m = 18.53± s s 0.93(stat.)±0.30(syst.) ps−1. The significance of this result is 2.9 σ. The∆m measurementcanbetranslatedintoaconstrainton|V /V |,andweobtain s td ts (cid:12) (cid:12) (cid:12)(cid:12)Vtd(cid:12)(cid:12)=0.2018±0.005(exp.)+0.0081(theor.) (cid:12)V (cid:12) −0.0060 ts 3. Analysis of B0 → J/ψ+K∗0 and B0 → J/ψ+φ Decays d s Before discussing CP Violation in B0 →J/ψ+φ, we present results of an analysis of s B0 →J/ψ+K∗0 andB0 →J/ψ+φdecays,inwhichCPviolationisneglected.Theaim d s istomeasuretheparameterswhichdescribethetime-dependentangulardistributionsof thesedecayswheretheinitialB mesonflavorisnotdetermined.Therelevantparameters are the linear polarization amplitudes, the strong phases, and the lifetimes. This allows ustoobtainthelifetimeratio,andtestSU(3)flavorsymmetryandfactorization.Thisis achievedbyfittingtothemass,lifetime,andangulardistributionsofthedecayproducts. For details of the analysis see [4]. 2 Fig.1.(a)Bs0 oscillationamplitudeasafunctionof∆ms and(b)Bs0 oscillationlikelihoodasafunction of∆ms. The preliminary results are shown in Table 1. The B results are competitive and d consistentwithpreviousmeasurementsbyCDF,BaBar,andBelle.Themeasurementsof the strong phases indicate the presence of final-state interactions for B0 → J/ψ+K∗0, d since δ is 3.5 σ away from zero. Also, comparison of the polarization amplitudes and 1 strong phases shows no evidence for violation of SU(3) flavor symmetry. Table1 Preliminaryresultsforthelinearpolarizationamplitudes,strongphases,lifetimeandwidthdifference forBd0→J/ψ+K∗0 andBs0→J/ψ+φ.A0 andA(cid:107) arethelinearpolarizationamplitudes,δ1,δ2,and δ(cid:107) are the strong phases, τ is the lifetime, and for the Bs decay, ∆Γs is the width difference between thelightandheavymasseigenstates. 4. Flavor-Tagged Analysis of B0 → J/ψ+φ Decays s The B0 → J/ψ φ decay involves a final state that is a mixture of CP-even and CP- s oddstates.InordertoseparatetheCP-evenandCP-oddstates,weperformamaximum likelihoodfittothemass,lifetime,andtime-dependentangulardistributionsoftheB0 → s J/ψ(→µ+µ−)φ(K+K−) decay. The fit yields the CP-violating phase φ and the width s difference∆Γ ≡Γ −Γ .Thedecaycanbedescribedbythreedecayanglesθ,φ,andψ s L H definedin[5].Weemployinitialstateflavortaggingwhichimprovesthesensitivitytothe 3 Fig.2.(a)Resultsofthefitsintheφs−∆Γs planefortheDØBs→J/ψφanalysisbasedon2.8fb−1 ofdata.(b)FitresultsfromthecombinationoftheDØresultswithCDFresultsbasedon1.35fb−1 of data. CP-violating phase and removes a sign ambiguity on φ for a given ∆Γ present in our s s previous analysis [6]. In the fit, ∆M is constrained to its measured value (from CDF) s and the strong phases are constrained to values measured for B at the B-factories, d allowing some degree of violation of SU(3) symmetry. The B flavor at production is s determined using a combined opposite-side plus sameside tagging algorithm. Confidence level contours in the φ −∆Γ plane are shown in Fig. 2(a). s s The fit yields a likelihood maximum at φ =−0.57+0.24 and ∆Γ =0.19±0.07 ps−1, s −0.30 s where the errors are statistical only. As a result of the constraints on the strong phases, the second maximum, at φ = 2.92+0.30, ∆Γ = −0.19±0.07 ps−1, is disfavored by a s −0.24 s likelihood ratio of 1:29. Fromthefitresultsandstudiesofthesystematicerrorsweobtainthewidthdifference ∆Γ ≡ Γ −Γ = 0.19±0.07(stat)+0.02(syst) ps−1 and the CP-violating phase, φ = s L H −0.01 s −0.57+0.24(stat)+0.07(syst). The allowed 90% C.L. intervals of ∆Γ and φ are 0.06 < −0.30 −0.02 s s ∆Γ <0.30 ps−1 and −1.20<φ <0.06, respectively. The probability to obtain a fitted s s value of φ lower than -0.57 given SM contributions only is 6.6%, which corresponds to s approximately 1.8 σ from the SM prediction. The results have been combined with CDF results by the Heavy Flavor Averaging Group. The CDF results are based on a data set of 1.35 fb−1 and the combination was performed with no constraints on the strong phases. The results are shown in Fig. 2(b). The fit yields two solutions as follows: φ =−2.37+0.38 rad, ∆Γ =−0.15+0.066 ps−1 s −0.27 s −0.059 φ =−0.75+0.27 rad, ∆Γ =0.15+0.059 ps−1 s −0.38 s −0.066 The p-value assuming only SM contributions is 3.1%, corresponding to 2.2 σ from the SM prediction. 4 5. Search for Direct CP Violation in B± → J/ψ K±(π±) Decays DØ has performed a search for direct CP violation by measurement of the charge asymmetry in B± →J/ψ K±(π±) decays [7]. The charge asymmetry is defined by N(B− →J/ψ K−(π−))−N(B+ →J/ψ K+(π+)) A (B+ →J/ψ K+(π+))= CP N(B− →J/ψ K−(π−))+N(B+ →J/ψ K+(π+)) Direct CP violation in these decays leads to a non-zero charge asymmetry. In the SM there is a small level of CP violation: A (B+ →J/ψ K+)≈0.003 [8] and A (B+ → CP CP J/ψ π+)≈0.01 [9]. New physics may significantly enhance A . CP After selection of B± → J/ψ K±(π±) candidates, the invariant mass of the J/ψK is constructed and fit to the sum of contributions from B± → J/ψ K±, B± → J/ψ π±, B± →J/ψ K∗,andcombinatorialbackground.Fromthefitwefindapproximately40,000 B± → J/ψ K± candidates and about 1,600 B± → J/ψ π± candidates. To extract the charge asymmetry the sample is divided into 8 subsamples according to the solenoid polarity, the sign of the pseudorapidity of the J/ψK system, and the charge of the K candidate. A χ2 fit to the number of events in each subsample yields the integrated raw chargeasymmetry.Thisisthencorrectedfortheasymmetryofthekaoninteractionrate on nucleons to obtain the final results: A (B+ →J/ψ K+)=+0.0075±0.0061(stat.)±0.0027(syst.) CP A (B+ →J/ψ π+)=−0.09±0.08(stat.)±0.03(syst.) CP Theresultsareconsistentwiththeworldaverageresults[10].TheprecisionforA (B+ → CP J/ψ π+) is comparable with the current world average, while for A (B+ → J/ψ K+) CP the precision is a significant (factor of 2.5) improvement over the current world average. 6. Search for Direct CP Violation in Semileptonic B Decays s InthissectionwereportanewsearchforCPviolationinthedecayB0 →D−µ+νX, (D− → s s s φπ−, φ → K+K−) by measurement of the charge asymmetry using a time-dependent analysis with flavor tagging. The technique used is similar to that used in the DØ B s oscillation analysis (see Section 2). A fit to the invariant KKπ mass of the selected data is shown in Fig. 3. The sample is divided into 8 subsamples according to solenoid polarity, the sign of the pseudorapidity of the D µ system, and the muon charge. An unbinned likelihood s fit is used to extract the asymmetry. The systematic uncertainties are mainly due to uncertaintiesinthecc¯contribution,uncertaintiesintheefficiencyvsvisibleproperdecay length, and uncertainties in the B →D(∗)µν branching fractions. Accounting for these s s yields the final result: as =−0.0024±0.0117(stat.)+0.0015(syst.) sl −0.0024 This result is consistent with the SM prediction and is the most precise measurement to date. 5 Fig.3.TheKKπ invariantmassdistributionshowingtheµ+D− andµ+D− signalstogetherwiththe s fitresults. 7. Measurement of Br(B0 → D(∗)D(∗)) s s s FortheB0 system,thewidthdifferencebetween∆Γ ≡Γ −Γ isrelatedtothewidth s s L H difference between the CP eigenstates, ∆ΓCP ≡ Γeven −Γodd, by ∆Γ = ∆ΓCP cosφ . s s s s s s The quantity ∆ΓCP can be estimated from the branching fraction Br(B0 →D(∗)D(∗)). s s s s DØhasperformedapreliminarymeasurementofBr(B0 →D(∗)D(∗))basedon2.8fb−1 s s s ofdatausingeventswhichcontaindecaysD+ →φπ+ andD− →φµ−ν (andtheircharge s s conjugates).Thesignalisextractedfroma2-dimensionallikelihoodfittothedatainthe m(D φπ)−m(φµ) plane. The results are [12]: s Br(B0 →D(∗)D(∗))=0.035±0.010(stat.)±0.011(syst.) s s s ∆ΓCP s =0.072±0.021(stat.)±0.022(syst.) Γ s Assuming CP violation in the SM is small, the results are in good agreement with the SM prediction. References [1] V.M. Abazov et al., (The DØ Collaboration), “The Upgraded D0 Detector,” Nucl. Instr. and MethodsA565,463(2006). [2] V.M.Abazovetal.,(TheDØCollaboration),Phys.Rev.Lett.97,021802(2006). [3] V. M. Abazov et al., (The DØ Collaboration), Phys. Rev. D 74, 112002 (2006); V. M. Abazov et al.,(TheDØCollaboration),DØConferenceNote5210. [4] V.M.Abazovetal.,(TheDØCollaboration),arXiv:0810.0037,submittedtoPhys.Rev.Lett. [5] V.M.Abazovetal.,(TheDØCollaboration),arXiv:0802.2255,submittedtoPhys,Rev.Lett. [6] V.M.Abazovetal.,(TheDØCollaboration),Phys.Rev.Lett.98,121801(2007). [7] V.M.Abazovetal.,(TheDØCollaboration),Phys.Rev.Lett.100,211802(2008). [8] W.-S.Hou,M.Nagashima,A.Soddu,arXiv:hep-ph/0605080. [9] I.Dunietz,Phys.Lett.BB316,561(1993);W.-S.Hou,arXiv:hep-ph/9905541(1999). [10]C.Amsleretal.,PhysicsLettersB667,1(2008). [11]V.M.Abazovetal.,(TheDØCollaboration),Phys.Rev.Lett.97,021802,(2006). [12]V.M.Abazovetal.,(TheDØCollaboration),arXiv:0811.2173,submittedtoPhys.Rev.Lett. 6