SLD Experiment Research Articles

Bs MIXING AT SLD

We set a preliminary 95% C.L. exclusion on the oscillation frequency of [Formula: see text] mixing using a sample of 400,000 hadronic Z0 decays collected by the SLD experiment at the SLC during the 1996-98 run. Three analyses are presented in this paper. The first analysis partially reconstructs the [Formula: see text] by combining a fully reconstructed Ds with the remaining charged B decay tracks. The second analysis selects a sample of events with a partially reconstructed charm vertex and a lepton track. The third naalysis reconstructs b-hadrons topologically and exploits the b→c cascade charge structure to determine the flavor of the b-hadron at decay. All three analyses take advantage of the large forward-backward asymmetry of the polarized [Formula: see text] decays and information in the hemisphere opposite to the reconstructed B vertex to determine the b-hadron flavor at production. The results of the three analyses are combined to exclude the following values of the [Formula: see text] oscillation frequency: Δms<7.6 ps-1 and 11.8<Δms<14.8 ps-1 at the 95% confidence level.

Comparing fragmentation of strange quark in Z0 decays and K+p reactions

The ratios of the production rates K∗0(892)/K, φ/K, ρ0/π, ω/π, Δ++(1232)/p, Σ∗+(1385)/Λ, Ξ−/Λ and their xp-dependence obtained from results of the LEP and SLD experiments in Z0 hadronic decays are analyzed. The corresponding ratios for promptly produced mesons are estimated at xp→1. A comparison of the LEP results with those from the Mirabelle and BEBC K+p experiments at 32 and 70 GeV/c shows striking similarity in fragmentation of the s̄ valence quark of the incident K+ and strange quarks produced in Z0 decays. The JETSET model describes the LEP, Mirabelle and BEBC results. The model of Pei is consistent with the data for mesons, but presumably underestimates the fractions of primary octet baryons. The quark combinatorics model of Anisovich et al. is incompatible with the data.

The search for B s0 oscillations at SLD

The SLD experiment at the SLAC Linear Collider has updated three searches for the time dependence of B s 0 oscillations. One search uses events with a reconstructed D s meson ; a second search uses events with a lepton and a topologically identified charmed meson; and the third uses events in which both a secondary and tertiary vertex are distinguished. The combined analyses are sensitive to values of Δ m s , the oscillation frequency, up to 13.0 ps −1 . A preliminary maximum likelihood analysis excludes Δ m s <7.6 ps −1 and 11.8< Δ m s <14.8 ps −1 at 95% CL. Including this data, the combined world data now imply Δ m s >15.0 ps −1 at 95% CL, and are not incompatible with a signal near the expected value, Δ m s ∼15 ps −1 .

Light quark fragmentation in polarized Z0 decays at SLD

We report results on two physics topics from the SLD experiment at the SLAC Linear Collider, using our full sample of 550,000 events of the type e + e − → Z 0 → q q . The electron beam was polarized, enabling the quark and antiquark hemispheres to be tagged in each event. One physics topic is the first study of rapidities signed such that positive rapidity is along the quark rather than antiquark direction. Distributions of ordered differences in signed rapidity between pairs of particles are analyzed, providing the first direct observation of baryon number ordering along the q q axis. The other topic is the first direct measurement of A s , the parity-violating coupling of the Z 0 to strange quarks, by measuring the left-right forward-backward production asymmetry in polar angle of the tagged s quark. We obtain A s = 0.895 ± 0.066( stat. ) ± 0.062( syst. ), which is consistent with the Standard Model and is currently the most precise measurement of this quantity.

Review on B oscillations

Abstract Measurements of Bd oscillations from CDF, LEP and SLD experiments are reviewed and their world averages are presented. Time-dependent and time-integrated mixing measurements are combined with direct reconstruction of specific final states to obtain the best estimate of the B species production fractions from b-quark hadronization. Finally, searches for Bs oscillations at CDF, LEP and SLD are reviewed, presenting the combined result. An emphasis is put on recent results, as well as perspectives for the near future.

First Symmetry Tests in PolarizedZ0Decays tobb¯g

We have made the first direct symmetry tests in the decays of polarized Z0 bosons into fully identified bbg states, collected in the SLD experiment at SLAC. We searched for evidence of parity violation at the bbg vertex by studying the asymmetries in the b-quark polar- and azimuthal-angle distributions, and for evidence of T-odd, CP-even or CP-odd, final-state interactions by measuring angular correlations between the three-jet plane and the Z0 polarization. We found results consistent with standard model expectations and set 95% C. limits on anomalous contributions.

Search for charmless hadronic decays of B mesons with the SLAC SLD detector

Based on a sample of approximately 500,000 hadronic Z0 decays accumulated between 1993 and 1998, the SLD experiment has set limits on 24 fully charged two-body and quasi two-body exclusive charmless hadronic decays of B+, B0, and B0_s mesons. The precise tracking capabilities of the SLD detector provided for the efficient reduction of combinatoric backgrounds, yielding the most precise available limits for ten of these modes.

A CCD vertex detector for a high-energy linear e +e − Collider

I present a summary of the experience with CCD-based vertex detectors at the SLD experiment at SLAC, and discuss their advantages for use at a future high-energy e+e- collider. The extensive R+D programme to improve further the vertexing capabilities of CCD detectors is also outlined.

Recent tests of QCD at SLD

We present selected results on strong interaction physics from the SLD experiment at the SLAC Linear Collider. We report on several new studies of 3- and 4-jet hadronic Z{sup 0} decays, in which jets are identified as quark, antiquark or gluon. The gluon energy spectrum is measured over the full kinematic range, providing an improved test of QCD and limits on anomalous bbg and bbg couplings. The parity violation in Z{sup 0} {yields} b{bar b}g decays is consistent with electroweak theory plus QCD. New tests of T- and CP-conservation at the bbg vertex are performed. An improved measurement of the rate of gluon splitting into b{bar b} pairs yields g{sub b{bar b}} = 0.00244 {+-} 0.00059(stat.) {+-} 0.00034(syst.). We also present a number of new results on jet fragmentation into identified hadrons. The B hadron energy spectrum is measured over the full kinematic range using a new, inclusive technique, allowing stringent tests of predictions for its shape and a precise measurement of 0 corresponds to the quark direction provides additional new insights into fragmentation, including the first direct observation of baryon number ordering along the q{bar q} axis.« less

Time-dependent B s0– [formula omitted] mixing using inclusive and semileptonic B decays at SLD

Abstract We have searched for time-dependent B s 0 – B s 0 mixing using a sample of 400 000 hadronic Z 0 decays collected by the SLD experiment at the SLC. The analyses take advantage of the excellent vertexing efficiency and resolution of the pixel-based CCD Vertex Detector which provides a B decay length resolution of approximately 100 μm . All analyses determine the B hadron flavor at production by exploiting the large forward–backward asymmetry of polarized Z 0 → b b decays. This flavor tag is enhanced by incorporating additional information from the hemisphere opposite that of the reconstructed B decay. In one analysis, B decay vertices are reconstructed inclusively with a topological technique, and separation between B s 0 and B s 0 decays is based on the reconstruction of a “charge dipole” of the topological vertices to exploit the B s 0 →D s − cascade charge structure. The other two analyses select semileptonic decays to tag the B flavor at decay and reconstruct the B decay vertex by intersecting the lepton with either all tracks in the nearest jet or the trajectory of a topologically reconstructed D vertex. The three analyses are combined to exclude the following values of the oscillation frequency: Δ m s 6.0 ps −1 Δ m s ps −1 . Future prospects are outlined.

Precise measurement of the weak mixing angle from leptonic polarization asymmetries at the SLD experiment

This paper presents measurements of the leptonic asymmetries in Z{sup 0} decays measured with the SLD detector at the SLAC Linear Collider. A data sample of approximately 500,000 Z{sup 0} boson decays has been used. These measurements lead to a precise determination of the effective weak mixing angle sin{sup 2} {theta}{sub w}{sup eff}. The combined preliminary result is sin{sup 2} {theta}{sub w}{sup eff} = 0.23110 {+-} 0.00029.

New results in B physics at SLD

Analysis of B decays recorded by the SLD experiment at the SLC e + e − collider is presented. The results are based on a sample of 150,000 hadronic Z 0 decays collected between 1993 and 1995 together with 250,000 hadronic Z 0 decays collected from 1996 to 1998 with an upgraded vertex detector. The large longitudinal polarization of the SLC e − beam (average « P e ∼ 73%) was utilised by some of the measurements. The precise CCD pixel vertex detector allows efficient and pure identification of the B decay tracks. Measurements of the B + and B 0 lifetimes, the B energy and a search for b → sg are presented. The B o s - ¯B o s mixing analyses and the excluded values of the oscillation frequency Δ m s will be discussed.

QCD tests using bb̄g events and a new measurement of the B-hadron energy spectrum

We present new studies of 3-jet final states from hadronic Z0 decays recorded by the SLD experiment, in which jets are identified as quark, antiquark or gluon. Our gluon energy spectrum, measured over the full kinematic range, is consistent with the predictions of QCD, and we derive a limit on an anomalous chromomagetic bbg coupling. We measure the parity violation in Z0 decays into bb̄g to be consistent with the predictions of electroweak theory and QCD, and perform new tests of T- and CP-conservation at the bbg vertex. We also present a new technique for reconstructing the energy of a B hadron using the set of charged tracks attached to a secondary vertex. The B hadron energy spectrum is measured over the full kinematic range, allowing improved tests of predictions for the shape of the spectrum. The average scaled energy is measured to be 〈 χB 〉 = 0.719 ± 0.005(stat.) (Preliminary).

Effective weak mixing angle in the MSSM

The predictions of the MSSM are discussed in the light of recent LEP and SLD precision data. The full supersymmetric one loop corrections to the effective weak mixing angle, experimentally determined in LEP and SLD experiments, are considered. It is demonstrated, both analytically and numerically, that, potentially dangerous, large logarithmic sparticle corrections are cancelled. The relative difference factor \Delta k between the mixing angle defined as a ratio of couplings and the experimentally obtained angle is discussed. It is found that \Delta k is dominated by the oblique corrections, while the non-oblique overall supersymmetric EW and SQCD corrections are negligible. The comparison of the MSSM with radiative electroweak symmetry breaking to the LEP+SLD precision data indicates that rather large values of the soft breaking parameter M_{1/2} in the region greater than 500 GeV are preferred.

B physics at SLD

We review recent B physics results obtained in polarized e + e − interactions at the SLC by the SLD experiment. The excellent 3-D vertexing capabilities of SLD are exploited to extract precise B + and B d 0 lifetimes, as well as measurements of the time evolution of B d 0 − B d 0 mixing.

Measurement of theBhadron energy distribution inZ0decays

We have measured the B hadron energy distribution in Z0 decays using a sample of semi-leptonic B decays recorded in the SLD experiment at SLAC. The energy of each tagged B hadron was reconstructed using information from the lepton and a partially reconstructed charm-decay vertex. We compared the scaled energy distribution with several models of heavy quark fragmentation. The average scaled energy of primary B hadrons was found to be <x_E_B> = 0.716 +- 0.011 (stat.) +0.022 -0.021 (syst.).

Measurement of theB+andB0Lifetimes Using Topological Reconstruction of Inclusive and Semileptonic Decays

The lifetimes of B+ and B0 mesons are measured using a sample of 150 000 hadronic Z0 decays collected by the SLD experiment at the SLAC Linear Collider between 1993 and 1995. Two analyses are presented in which the decay length and charge of the B meson are reconstructed. The first method uses a novel topological vertexing technique while the second uses semi-inclusively reconstructed semileptonic decays. The topological analysis yields a sample of 6033 (3665) charged (neutral) vertices with good charge purity, whereas the semileptonic analysis yields a smaller sample of 634 (584) charged (neutral) decays with excellent charge purity. Combining the results from both analyses, we find τB+=1.66±0.06(stat)±0.05(syst)ps, τB0=1.64±0.08(stat)±0.08(syst)ps, and τB+/τB0=1.01±0.07(stat)±0.06(syst).Received 14 January 1997DOI:https://doi.org/10.1103/PhysRevLett.79.590©1997 American Physical Society

Neutral current couplings of leptons to polarized Z0's in the SLD experiment

We study neutral current couplings of leptons to polarized Z0's in the SLD experiment in terms of the leptonic asymmetry parameters Ae, Aμ and Aτ. We discuss in detail eL, R− + e+ → Z0 → μ− μ+ and τ− τ+, with left(L)- or right(R)-handed polarized electron beams. SLD's most precise measurement of Ae is shown to result from the left-right cross section asymmetry, ALR, where the dependence on initial state electronic couplings enable use of essentially all of the data. Comparing Aμ and Aτ, with Ae tests the universality of leptonic couplings. Aμ = 0.102 ± 0.033 ± 0.001, Aτ = 0.190 ± 0.034 ± 0.001, and Ae = 0.148 ± 0.016 ± 0.002 from these two leptonic channels. If lepton universality is assumed, a combined asymmetry parameter Aeμτ = 0.147 ± 0.013 results, which directly corresponds to an effective value of the weak mixing angle sin2 θWeff = 0.2315 ± 0.0017.

Formula omitted] mixing measurements at SLD

The time dependence of B d 0 − B d 0 ¯ mixing has been measured using a sample of 150,000 hadronic Z 0 decays collected by the SLD experiment at the SLC between 1993 and 1995. Four different analyses have been performed. All analyses tag the B candidate at production with a combined tag that exploits the large polarized b forward-backward asymmetry together with the opposite hemisphere b jet charge. Two of the analyses exploit 3D topological vertexing to determine the B meson decay length, in conjunction with either a charged kaon or charge dipole final state tag. The other two analyses use identified high ( p, p t ) leptons intersected with either a partially reconstructed D meson, or the weighted average of tracks in the b jet. Taking into account correlated statistical and systematic errors, the preliminary SLD average for the mass difference between the two B d 0 mass eigenstates is: Δ m d = 0.525 ± 0.043( stat ) ± 0.037( syst ) ps −1 .

Progress on R b and R c measurements

A review on Rb and Rc, measurements is given at the light of the recent developments and findings of the LEP and SLD experiments.