Hadronic B decays at BABAR

We present preliminary results on hadronic decays of B mesons, based on data recorded at the Υ (4S) resonance with the BABAR detector at the PEP-IIB-factory at SLAC. We measure branching fractions of many B decay modes, including decays to J/ψφK, J/ψπ+π− and ηcK final states. We report the observation of the decay B → D+ s π − and the first measurement of the flavor-tagged D meson production in B0 decays. Since their preliminary nature, the results presented in this paper are based on different data samples. Invited talk presented at the XXXVIIth Rencontres de Moriond on QCD and Hadronic Interactions, 3/16/2002—3/23/2002, Les Arcs, France Stanford Linear Accelerator Center, Stanford University, Stanford, CA 94309 Work supported in part by Department of Energy contract DE-AC03-76SF00515. 1 The BABAR detector The BABAR detector [1] at the PEP-II asymmetric-energy B-factory [2] at SLAC consists of a silicon vertex tracker (SVT) for precise decay vertex determination, a 40-layer drift chamber (DCH) for momentum and track angles measurement, a detector of internally reflected Cherenkov radiation (DIRC) for charged hadron identification, and a CsI(Tl) electromagnetic calorimeter (EMC) for photon reconstruction and electron identification. A superconducting solenoid provides a magnetic field of 1.5 T, and the iron of the flux return is instrumented with resistive plate chambers (IFR) to provide muon identification and neutral hadron reconstruction. 2 Hadronic B decays to charmonium Color suppressed transitions b → cc̄s(d) are responsible for hadronic B decays to final states containing a charmonium. Theoretical predictions are based on the factorization hypothesis, that can be accurately tested with extensive and precise branching fraction determinations [3]. 2.1 Rare B decays to states with a J/ψ The Cabibbo-suppressed decays B → J/ψη(η) are described by a b → cc̄d transition, as the observed decay B → J/ψπ. An upper limit on the decay B → J/ψη has been set by the L3 Collaboration [4], while there is no published result for the B → J/ψη channel. The decay B → J/ψφK is described by a bq̄ → cc̄ss̄sq̄ transition, in which the ss̄ pair is produced from sea quarks or via gluon emission. This mode has been observed by the CLEO Collaboration [5] with a branching fraction of B(B → J/ψφK) = (8.8 −3.0 ± 1.3) × 10 −5. The decay B → J/ψφ, which has not yet been observed, is explained with the occurrence of cc̄dd̄ rescattering into a cc̄ss̄ state. The above decay modes have been studied at BABAR. The η is reconstructed in γγ or π+π−π0 final states and the η in the η(→ γγ)π+π− channel. The φ is reconstructed in the K+K− final state. Table 1 shows the preliminary results 1 obtained from the analysis of 50.9 fb−1 of data recorded at the Υ (4S) resonance [6]. 2.2 Measurement of B → J/ψππ In the decay B → J/ψπ+π−, the π+π− pair comes from the B0 → J/ψρ0(→ π+π−) channel or can be produced in a non-resonant state. The B0 → J/ψρ0 mode is useful for the measurement of sin 2β and possible interference with higher order diagrams could produce a sizeble deviation of the branching fraction from the tree level expectation. An upper limit on this decay has been set by the CLEO Collaboration [7]. At BABAR, the decay B0 → J/ψπ+π− is exclusively reconstructed and the signal yield is extracted from an unbinned maximum likelihood fit to the π+π− invariant mass of the selected candidates [8]. The preliminary result obtained from a sample of 51.7 fb−1 of data recorded at the Υ (4S) resonance is B(B → J/ψπ+π−) = (5.0 ± 0.7 ± 0.6)× 10−5. Unless otherwise stated, charged conjugate modes are implied throughout the paper Table 1: Preliminary branching fraction determinations for rare B decays to final states with a J/ψ . When the signal yield is not statistically significant, a 90% C.L. upper limit is reported. Decay Mode Branching Fraction B0 → J/ψη(→ γγ) < 3.0× 10−5 B0 → J/ψη(→ π+π−π0) < 5.2× 10−5 B0 → J/ψη(combined) < 2.7× 10−5 B0 → J/ψη(→ η(γγ)π+π−) < 6.4× 10−5 B+ → J/ψφK+ (4.4 ± 1.4± 0.7) × 10−5 B0 → J/ψφK0 (10.2 ± 3.8± 1.8) × 10−5 B → J/ψφK (combined) (5.0 ± 1.3± 0.7) × 10−5 B0 → J/ψφ < 0.95 × 10−5 2.3 Measurement of B → ηcK The decay B0 → ηcKS can be used for a theoretically clean determination of sin 2β, in the same way as the “golden” mode B0 → J/ψKS . Previous studies of the neutral and charged decay modes were performed by the CLEO Collaboration [9]. At BABAR, the decay B → ηcK is exclusively reconstructed, with the ηc decaying in KSK π, K+K−π0 or K+K−K+K− final states [10]. The preliminary results obtained from a data sample of 20.7 fb−1 recorded at the Υ (4S) resonance are B(B+ → ηcK +) = (1.50±0.19±0.15±0.46)×10−3 and B(B0 → ηcK 0) = (1.06± 0.28± 0.11± 0.33)× 10−3, where the third error contribution is due to the uncertainty on the value of B(ηc → KKπ), as reported in the PDG [11]. 3 Observation of B → D s π − One of the methods to determine the angle γ of the unitarity triangle [12] is the measurement of sin(2β + γ) from the time dependent CP -asymmetry of the decay B0 → D+π− [13]. The asymmetry evolution depends on the parameter λDπ ≡ A(B 0 → D+π−)/A(B0 → D−π+) which can be determined from the branching fraction measurement of B0 → D+ s π − through the relation: B(B → D s π ) ≈ B(B0 → D−π+) tan2 θC ( f2 Ds f2 D )