Measurement of B0-B-0 flavor oscillations in hadronic B0 decays

Flavor oscillations of neutral B mesons have been studied in e+e- annihilation data collected with the BABAR detector at center-of-mass energies near the upsilon(4S) resonance. The data sample used for this purpose consists of events in which one B0 meson is reconstructed in a hadronic decay mode, while the flavor of the recoiling B0 is determined with a tagging algorithm that exploits the correlation between the flavor of the heavy quark and the charges of its decay products. From the time development of the observed mixed and unmixed final states, we determine the B0-B-0 oscillation frequency deltamd to be 0.516+/-0.016(stat)+/-0.010(syst) ps-1.     

Photon and light meson production in hadronic Z^0decays

The inclusive production rates and differential cross-sections of photons and mesons with a final state containing photons have been measured with the OPAL detector at LEP. The light mesons covered by the measurements are the , , , , and a. The particle multiplicities per hadronic Zdecay, extrapolated to the full energy range, are: where the first errors are statistical and the second systematic. In general, the results are in agreement with the predictions of the JETSET and HERWIG Monte Carlo models. Received: 9 April 1998 / Published online: 12 August 1998     

Strange baryon production in hadronic Z0 decays

The production of the $J^{P}={1?er 2}^{+}$ octet baryons Λ and Ξ^?, the $J^{P}={3?er 2}^{+}$ decuplet baryons Σ(1385)^±Ξ(1530)⁰, and Ω^?, and the $J^{P}={3?er 2}^{-}$ orbitally excited state Λ(1520) has been measured in a sample of approximately 3.65 million hadronic Z⁰ decays. The integrated rates and the differential cross-sections as a function of x _E, the scaled energy, are determined. The differential cross-sections of the Λ and Ξ^? baryons are found to be softer than those predicted by both the JETSET and HERWIG Monte Carlo generators. The measured baryon yields are found to disagree with the simple diquark picture where only one tuning parameter for spin 1 diquarks is allowed. The yields are further compared with a thermodynamic model of hadron production which includes the production of orbitally excited mesons and baryons. The momentum spectra of Λ, Ξ^?, Σ(1385)^±Ξ(1530)⁰, and Λ(1520) are also compared to the predictions of an analytical QCD formula.     

Measurement of charge asymmetries in charmless hadronic B meson decays

We search for CP-violating charge asymmetries (alpha(CP)) in the B meson decays to K(+/-)pi(-/+), K(+/-)pi(0), K(0)(S)pi(+/-), K(+/-)eta('), and omega pi(+/-). Using 9.66 million upsilon(4S) decays collected with the CLEO detector, the statistical precision on alpha(CP) is in the range of +/-0.12 to +/-0.25 depending on decay mode. While CP-violating asymmetries of up to +/-0.5 are possible within the standard model, the measured asymmetries are consistent with zero in all five decay modes studied.     

Measurement of inclusive π0 production in hadronic Z 0 decays

An analysis is presented of inclusive π⁰ production in Z ⁰ decays measured with the DELPHI detector. At low energies, π⁰ decays are reconstructed by using pairs of converted photons and combinations of converted photons and photons reconstructed in the barrel electromagnetic calorimeter (HPC). At high energies (up to $x_p={2cdot p?/{sqrt s}=0.75}$) the excellent granularity of the HPC is exploited to search for two-photon substructures in single showers. The inclusive differential cross section is measured as a function of energy for qq? and bb? events. The number of π⁰’s per hadronic Z ⁰ event is $N(?^0)/Z_{had} ^0=9.2pm 0.2({? stat})pm 1.0 ({? syst})$ and for bb? events the number of π⁰’s is ${? N}(?^0)/{? b?r b}=10.1pm 0.4({? stat})pm 1.1 ({? syst})$. The ratio of the number of π⁰’s in bb? events to hadronic Z ⁰ events is less affected by the systematic errors and is found to be 1.09 ±0.05 ±0.01. The measured π⁰ cross sections are compared with the predictions of different parton shower models. For hadronic events, the peak position in the $xi_{? p}={? ln}(1/{? x_p})$ distribution is $xi_p^{?ar}=3.90_{-0.14}^{+0.24}.$ The average number of π⁰’s from the decay of primary B hadrons is found to be N(B → π⁰ X)/B hadron = 2.78 ± 0.15(stat) ± 0.60(syst).     

Study of charmless hadronic B meson decays to pseudoscalar-vector final states

We report results of searches for charmless hadronic B meson decays to pseudoscalar( pi(+/-), K+/-, pi(0), or K(0)(S))-vector( rho, K(*), or omega) final states. By using 9.7x10(6) BB pairs collected with the CLEO detector, we report the first observation of B(-)--->pi(-)rho(0), B(0)-->pi(+/-)rho(-/+), and B(-)-->pi(-)omega, which are expected to be dominated by hadronic b-->u transitions. The measured branching fractions are (10.4(+3.3)(-3.4)+/-2.1)x10(-6), (27.6(+8.4)(-7.4)+/-4.2)x10(-6), and (11.3(+3.3)(-2.9)+/-1. 4)x10(-6), respectively. Branching fraction upper limits are set for all of the other decay modes investigated.     

Quark combinatorics and meson-production ratios in hadronic Z 0 decays

A vast body of experimental data accumulated in the past few years in hadronic Z ⁰ decays allows one to check quark-combinatorics relations for a new type of processes-namely, quark jets in the decays Z ⁰ → $q\bar q$ → hadrons. In this paper, we review quark-combinatorics rules for the yields of vector and pseudoscalar mesons, V/P, in the central and fragmentation regions of hadronic Z ⁰ decays. It is emphasized that, in the central region, a direct verification of quark-combinatorics rules is rather problematic because of a considerable background associated with the decay of highly excited resonances; however, such a verification is possible in the fragmentation region, at x _hadron～0.5–1, where the contribution of resonance decays is suppressed owing to a fast decrease of the spectra with increasing x _hadron. It is shown that, in the fragmentation region, experimental data on ρ⁰/π⁰ and p/π⁺ are in reasonable agreement with the predictions of quark combinatorics. The ratios of the heavy-meson yields, B*/B and D*/D, are also discussed: the data demonstrate good agreement with the quark combinatorial results. We analyze the structure of the suppression parameters for strange-and heavy-quark production in soft processes and estimate their orders of magnitude in multiperipheral processes; the ratio K ^±/π^± at x _hadron～0.5–0.8 and the production probabilities for $c\bar c$ and $b\bar b$ mesons are in good agreement with the estimates.     

Production of P-wave charm and charm-strange mesons in hadronic Z0 decays

Results are presented on the production of excited charm and excited charm-strange mesons in hadronic Z⁰ decays. The results are obtained from approximately 4.3 million hadronic Z⁰ decays, collected on or near the Z⁰ resonance using the OPAL detector at LEP. The D⁰ ₁(2420) and D^*0 ₂ (2460) mesons are reconstructed in the D^*+π^-. final state and their separate production rates in charm fragmentation and in weak decays of b-hadrons are determined. Assuming that the decay widths of these mesons are saturated by the allowed D*π and Dπ final states, the charm hadronization fractions and the inclusive branching ratios of b-hadrons to these neutral P-wave charm mesons are determined to be     

Charmless hadronic decays of B mesons to a pseudoscalar and a tensor meson

We study two-body charmless hadronic decays of B mesons to a pseudoscalar meson (P) and a tensor meson (T) in the frameworks of both flavor SU(3) symmetry and generalized factorization. Certain ways to test the validity of the generalized factorization are proposed, based on the flavor SU(3) analysis. We present a set of relations between a flavor SU(3) amplitude and the corresponding amplitude in the generalized factorization which bridge both approaches in decays. The branching ratios and CP asymmetries are calculated using the full effective Hamiltonian including all the penguin operators and the form factors obtained in the non-relativistic quark model of Isgur, Scora, Grinstein and Wise. We identify the decay modes in which the branching ratios and CP asymmetries are expected to be relatively large. Received: 6 July 2001 / Revised version: 8 October 2001 / Published online: 30 November 2001     

J/Ψ and Ψ′ production in hadronic Z0 decays

The production of Jψ mesons in Z⁰ decays is studied using 3.6 million hadronic events recorded by the OPAL detector at LEP. The inclusive Z⁰ to Jψ and b-quark to Jψ branching ratios are measured from the total yield of Jψ mesons, identified from their decays into lepton pairs. The Jψ momentum distribution is used to study the fragmentation of b-quarks. The production rate of ψ′ mesons, identified from their decays into a Jψ and a π⁺π^? pair, is measured as well. The following results are obtained: ${Br(Z^{0}?ghtarrow {? J}/?i X)=(3.9pm 0.2pm 0.3)cdot 10^{-3} {? and} ?op Br(Z^0?ghtarrow ?i ^?ime X)=(1.6pm 0.3pm 0.2)cdot 10^{-3}, }$ where the first error is statistical and the second systematic. Finally the Jψ sample is used to reconstruct exclusive b-hadron decays and calculate the corresponding b-hadron branching ratios and masses.     

B* production in Z0 decays

The process B*→Bγ has been observed in a sample of approximately 4.1 million hadronic Z⁰ decays collected by the OPAL detector at LEP in the years 1991–1995. Inclusively reconstructed B mesons have been combined with converted photons to reconstruct approximately 1900 B* mesons. The B*–B mass difference is found to be ΔM(B* ?B) = 46.2 ± 0.3 ± 0.8 MeV/c ², and the rate of B* meson production relative to that of B mesons is found to be σ _B*/σ _B = 0.760 ± 0.036 ± 0.083, where the first errors are statistical and the second systematic. The angular distribution of the transition photon in the B* rest frame has been measured and the relative contribution of longitudinal B* polarization states found to be σ _l/(σ _l + σ _t ) = 0.36 ± 0.06 ± 0.07, consistent with a simple spin counting picture. These results average over B⁰, B± and B _s ⁰ mesons.     

An updated study of B meson oscillations using dilepton events

This paper reports a study of B meson oscillations using hadronic Z⁰ decays with two identified leptons, and updates a previous publication by including data collected in 1994. Decay times are reconstructed for each of the semileptonic B decays by forming vertices which include the lepton and by estimating the B meson momentum. The mass difference, Δm _d, between the two mass eigenstates in the B0d system is measured to be 0.430 ± 0.043 ^+0.028 _?0.030 ps.1, where the first error is statistical and the second error is systematic. For the B⁰ _s system, a lower limit of Δms < 2.2 ps.1 is obtained at 95% C.L.     

Remarks on the charged multiplicity of hadronic Z0(91) decays

The charged multiplicity distribution of hadronic decays of Z ⁰ from LEP and those of inclusive $e^{+}+e^{-}?ghtarrow h{?erline h} at E_{? cm}=14 {? to} 60 {? GeV}$ at E _cm = 14 to 61 GeV are analyzed using a Poisson-type distribution for photon statistics, due to Scully-Lamb. Its two parameters are expressed in terms of 〈n〉 and f ₂ = 〈n(n ? 1)〉 ? 〈n〉² of the data in order to perform no-free-parameter fits. It is found that f₂ behaves like $E_{? cm}^{a}$ with a = 2.01 ± 0.11, whereas C ₂ = 〈n ²〉/〈n〉² ～ E _cm with ΔC ₂/ΔE _cm = (1.81 ± 0.14)·10^?3.     

Transverse momentum correlations in hadronic Z decays

Using data obtained with the ALEPH detector at the Z resonance, a measure based on transverse momentum is shown to exhibit a correlation between the two halves of a hadronic event which cannot be explained by energy-momentum conservation, flavour conservation, the imposition of an event axis or imperfect event reconstruction. Two possible interpretations based on existing Monte Carlo models are examined: a) ARIADNE, with the correlation forming early in the parton shower and with the transition from partons to hadrons playing only a minor part; b) JETSET, with the correlation forming at the fragmentation stage. A correlation technique based on a jet cluster analysis is used to make a comparison of the models with the data. It is concluded that both non-perturbative and perturbative effects make important contributions to the observed correlation.     

A measurement of the b-quark mass from hadronic Z decays

Hadronic Z decay data taken with the ALEPH detector at LEP1 are used to measure the three-jet rate as well as moments of various event-shape variables. The ratios of the observables obtained from b-tagged events and from an inclusive sample are determined. The mass of the b quark is extracted from a fit to the measured ratios using a next-to-leading order prediction including mass effects. Taking the first moment of the distribution, which is the observable with the smallest hadronization corrections and systematic uncertainties, the result is The measured ratio is alternatively employed to test the flavour independence of the strong coupling constant for b and light quarks. Received: 6 July 2000 / Published online: 13 November 2000     

Penguin decays of B meson

The theory of loop induced rare B decays is reviewed. Both electromagnetic penguin processes and gluon mediated penguin processes are discussed. After consideringb→sy andb→se ⁺ e ^? decays, purely hadronic modes likeB→K? are estimated. Constraints on the Higgs sector of SUSY theory fromb→sy is discussed. CP violation in charged B Decays is reviewed.