arXiv subjects

K. Abe

Publications and source records attributed to K. Abe.

At least 451 records · Page 25Linked to original sources

arXiv1999

Symmetry Tests in Polarized Z0 Decays to bbg

Angular asymmetries have been measured in polarized Z0 decays to bbg collected by the SLD experiment at the SLC. A high purity bbg event sample is selected by utilizing B lifetime information given by the SLD CCD pixel vertex detector and the stable micron-size SLC beams, and the b- and bbar-jets are identified using lifetime information and momentum-weighted track charge. The forward-backward asymmetry is observed in the b-quark polar angle distribution, and the parity-violation parameter is measured to test the Standard Model. Two angular correlations between the three-jet plane and the Z0 polarization are studied. The CP-even and T-odd, and the CP-odd and T-odd, angular asymmetries are sensitive to physics beyond the Standard Model. The latter requires tagging both the b- and bbar-jet. We measure the expectation values of these quantities to be consistent with zero and set limits on the correlations at the 5% level.

hep-ex↗

arXiv1999

An Improved Direct Measurement of Leptonic Coupling Asymmetries with Polarized $Z^0$'s

We report new direct measurements of the $Z^0$-lepton coupling asymmetry parameters $A_e$, $A_μ$ and $A_τ$, with polarized $Z^0$'s collected by the SLD detector at the SLAC Linear Collider. The parameters are extracted from the measurement of the left-right-forward-backward asymmetries for each lepton species. The 1996, 1997 and 1998 SLD runs are included in this analysis and combined with published data from the 1993-95 runs. Preliminary results are $A_e = 0.1558 \pm 0.0064$, $A_μ=0.137 \pm 0.016 $ and $A_τ=0.142 \pm 0.016$. If lepton universality is assumed, a combined asymmetry parameter $A_{l} = 0.1523 \pm 0.0057$ results. This translates into an effective weak mixing angle $\sin^2θ^{eff}_W = 0.23085 \pm 0.00073$ at the $Z^0$ resonance.

hep-ex↗

arXiv1999

Direct Measurement of A_c using Inclusive Charm Tagging at the SLD Detector

We report a new measurement of A_c using data obtained by SLD in 1993-98. This measurement uses a vertex tag technique, where the selection of a c hemisphere is based on the reconstructed mass of the charm hadron decay vertex. The method uses the 3D vertexing capabilities of SLD's CCD vertex detector and the small and stable SLC beams to obtain a high c-event tagging efficiency and purity of 28% and 82%, respectively. Charged kaons identified by the CRID detector and the charge of the reconstructed vertex provide an efficient quark-antiquark tag, with the analyzing power calibrated from the data. We obtain a preliminary result of A_c = 0.603 \pm 0.028 \pm 0.023

hep-ex↗

arXiv1999

Direct Measurement of A_b using Charged Kaons at the SLD Detector

We report a new measurement of A_b using data obtained by SLD in 1997-98. This measurement uses a vertex tag technique, where the selection of a b hemisphere is based on the reconstructed mass of the bottom hadron decay vertex. The method uses the 3D vertexing capabilities of SLD's CCD vertex detector and the small and stable SLC beams to obtain a high b-event tagging efficiency and purity of 78% and 97%, respectively. Charged kaons identified by the CRID detector provide an efficient quark-antiquark tag, with the analyzing power calibrated from the data. We obtain a preliminary result of A_b = 0.997 \pm 0.044 \pm 0.067

hep-ex↗

arXiv1999

Combined SLD Measurement of Ab at the Z Resonance using Various Techniques

We present a new preliminary combination of measurements of the parity-violation parameter Ab made by the SLD collaboration using various experimental techniques. The techniques differ in detail, but in general a sample of bb events is selected or enhanced by using the topologically reconstructed mass of the separated vertices formed by decaying B hadrons. The direction of the b(bbar) quark is signed by one of four final state tags: jet charge, vertex charge, leptons, or identified K+- from the b vertex. We account for statistical and systematic correlations between the four analyses to arrive at our combined result: Ab=0.905 +/- 0.017 {stat} +/- 0.020 (syst).

hep-ex↗

arXiv1999

New Measurement of Ab at the Z Resonance using a Vertex-Charge Technique

We present a new preliminary measurement of the parity-violation parameter Ab using a self-calibrating vertex-charge technique. In the SLD experiment we observe hadronic decays of polarized Z bosons produced in collisions between longitudinally polarized electrons and unpolarized positrons at the SLAC Linear Collider. A sample of bb events is selected using the topologically reconstructed mass of B hadrons. From out 1996-8 data sample of approximately 400,000 hadronic Z decays, we obtain Ab = 0.897 +/- 0.027 (stat) +0.036/-0.034 (syst).

hep-ex↗

arXiv1999

Measurement of the B+ and B0 Lifetimes using Topological Vertexing at SLD

The lifetimes of B+ and B0 mesons have been measured using the entire sample of 550,000 hadronic Z0 decays collected by the SLD experiment at the SLC between 1993 and 1998. In this paper, we describe the inclusive analysis of the 350,000 hadronic Z0 decays collected in 1997-98 with the upgraded SLD vertex detector. In this data period, a high statistics sample of 30903 (20731) charged (neutral) vertices with good charge purity is obtained. The charge purity is enhanced by using the vertex mass, the SLC electron beam polarization (73% for 1997-8) and an opposite hemisphere jet charge technique. Combining the results of this data sample with the results from the earlier data yield the following preliminary values: $τ_{B^+}=1.623\pm0.020($stat$)\pm0.034$(syst) ps, $τ_{B^0}=1.589\pm0.021($stat$)\pm0.043$(syst) ps, $τ_{B^+}/τ_{B^0} = 1.037\pm^{0.025}_{0.024}($stat$) \pm0.024$(syst).

hep-ex↗

arXiv1999

Measurement of $A_c$ with charmed mesons at SLD

We present a direct measurement of the parity-violation parameter A_c. The measurement is based on 550k Z^0 decays collected by the SLD detector. The mean electron-beam polarization is |P_e| = 73 %. The tagging of c-quark events was performed using two methods: The exclusive reconstruction of D^*+, D^+, and D^0 mesons, and the inclusive P_T spectrum of soft-pions (pi_s) in the decay of D^*+ -> D^0 pi_s^+. The results of these two methods are combined to give A_c = 0.688 +- 0.035(stat.) +- 0.025(sys.) (preliminary).

hep-ex↗

arXiv1999

Precision Measurement of Cosmic-Ray Antiproton Spectrum

The energy spectrum of cosmic-ray antiprotons has been measured in the range 0.18 to 3.56 GeV, based on 458 antiprotons collected by BESS in recent solar-minimum period. We have detected for the first time a distinctive peak at 2 GeV of antiprotons originating from cosmic-ray interactions with the interstellar gas. The peak spectrum is reproduced by theoretical calculations, implying that the propagation models are basically correct and that different cosmic-ray species undergo a universal propagation. Future BESS flights toward the solar maximum will help us to study the solar modulation and the propagation in detail and to search for primary antiproton components.

astro-ph↗

arXiv1998

Production of pi+, K+, K0, K*0, phi, p and Lambda-0 in Hadronic Z0 Decays

We have measured the differential production cross sections as a function of scaled momentum x_p=2p/E_cm of the identified hadron species pi+, K+, K0, K*0, phi, p, Lambda0, and of the corresponding antihadron species in inclusive hadronic Z0 decays, as well as separately for Z0 decays into light (u, d, s), c and b flavors. Clear flavor dependences are observed, consistent with expectations based upon previously measured production and decay properties of heavy hadrons. These results were used to test the QCD predictions of Gribov and Lipatov, the predictions of QCD in the Modified Leading Logarithm Approximation with the ansatz of Local Parton-Hadron Duality, and the predictions of three fragmentation models. Ratios of production of different hadron species were also measured as a function of x_p and were used to study the suppression of strange meson, strange and non-strange baryon, and vector meson production in the jet fragmentation process. The light-flavor results provide improved tests of the above predictions, as they remove the contribution of heavy hadron production and decay from that of the rest of the fragmentation process. In addition we have compared hadron and antihadron production as a function of x_p in light quark (as opposed to antiquark) jets. Differences are observed at high x_p, providing direct evidence that higher-momentum hadrons are more likely to contain a primary quark or antiquark. The differences for pseudoscalar and vector kaons provide new measurements of strangeness suppression for high-x_p fragmentation products.

hep-ex↗

arXiv1998

Development of a Large-Area Aerogel Cherenkov Counter Onboard BESS

This paper describes the development of a threshold type aerogel Cherenkov counter with a large sensitive area of 0.6 m$^2$ to be carried onboard the BESS rigidity spectrometer to detect cosmic-ray antiprotons. The design incorporates a large diffusion box containing 46 finemesh photomultipliers, with special attention being paid to achieving good performance under a magnetic field and providing sufficient endurance while minimizing material usage. The refractive index of the aerogel was chosen to be 1.03. By utilizing the muons and protons accumulated during the cosmic-ray measurements at sea level, a rejection factor of 10$^4$ was obtained against muons with $β\approx 1$, while keeping 97% efficiency for protons below the threshold.

hep-ex↗

arXiv1997

Measurement of alpha_s(M_Z^2) from Hadronic Event Observables at the Z^0 Resonance

The strong coupling alpha_s(M_Z^2) has been measured using hadronic decays of Z^0 bosons collected by the SLD experiment at SLAC. The data were compared with QCD predictions both at fixed order, O(alpha_s^2), and including resummed analytic formulae based on the next-to-leading logarithm approximation. In this comprehensive analysis we studied event shapes, jet rates, particle correlations, and angular energy flow, and checked the consistency between alpha_s(M_Z^2) values extracted from these different measures. Combining all results we obtain alpha_s(M_Z^2) = 0.1200 \pm 0.0025(exp.) \pm 0.0078(theor.), where the dominant uncertainty is from uncalculated higher order contributions.

hep-ex↗

arXiv1997

Next-to-Leading Order QCD Analysis of Polarized Deep Inelastic Scattering Data

We present a Next-to-Leading order perturbative QCD analysis of world data on the spin dependent structure functions $g_1^p, g_1^n$, and $g_1^d$, including the new experimental information on the $Q^2$ dependence of $g_1^n$. Careful attention is paid to the experimental and theoretical uncertainties. The data constrain the first moments of the polarized valence quark distributions, but only qualitatively constrain the polarized sea quark and gluon distributions. The NLO results are used to determine the $Q^2$ dependence of the ratio $g_1/F_1$ and evolve the experimental data to a constant $Q^2 = 5 GeV^2$. We determine the first moments of the polarized structure functions of the proton and neutron and find agreement with the Bjorken sum rule.

hep-ph↗

arXiv1997

Measurement of the Neutron Spin Structure Function g2n and Asymmetry A2n

We have measured the neutron structure function g$_{2}^{n}$ and the virtual photon-nucleon asymmetry A$_{2}^{n}$ over the kinematic range $0.014\leq x \leq 0.7$ and $1.0 \leq Q^{2} \leq 17.0$ by scattering 48.3 GeV longitudinally polarized electrons from polarized $^{3}$He. Results for A$_{2}^{n}$ are significantly smaller than the $\sqrt{R}$ positivity limit over most of the measured range and data for g$_2^{n}$ are generally consistent with the twist-2 Wandzura-Wilczek prediction. Using our measured g$_{2}^{n}$ we obtain results for the twist-3 reduced matrix element $d_{2}^{n}$, and the integral $\int$g$_{2}^{n}(x)dx$ in the range $0.014\leq x \leq 1.0$. Data from this experiment are combined with existing data for g$_{2}^{n}$ to obtain an average for $d_{2}^{n}$ and the integral $\int$g$_{2}^{n}(x)dx$.

hep-ex↗

arXiv1997

Precision Determination of the Neutron Spin Structure Function g1n

We report on a precision measurement of the neutron spin structure function $g^n_1$ using deep inelastic scattering of polarized electrons by polarized ^3He. For the kinematic range 0.014<x<0.7 and 1 (GeV/c)^2< Q^2< 17 (GeV/c)^2, we obtain $\int^{0.7}_{0.014} g^n_1(x)dx = -0.036 \pm 0.004 (stat) \pm 0.005 (syst)$ at an average $Q^2=5 (GeV/c)^2$. We find relatively large negative values for $g^n_1$ at low $x$. The results call into question the usual Regge theory method for extrapolating to x=0 to find the full neutron integral $\int^1_0 g^n_1(x)dx$, needed for testing quark-parton model and QCD sum rules.

hep-ex↗

arXiv1997

First Measurement of Leptonic Coupling Asymmetries with Polarized Z bosons

We present direct measurements of the $Z^0$-lepton coupling asymmetry parameters, $A_e$, $A_μ$, and $A_τ$, based on a data sample of 12,063 leptonic $Z^0$ decays collected by the SLD detector. The $Z$ bosons are produced in collisions of beams of polarized $e^-$ with unpolarized $e^+$ at the SLAC Linear Collider. The couplings are extracted from the measurement of the left-right and forward-backward asymmetries for each lepton species. The results are: $A_e=0.152 \pm 0.012 {(stat)} \pm 0.001 {(syst)}$, $A_μ=0.102 \pm 0.034 \pm 0.002$, and $A_τ=0.195 \pm 0.034 \pm 0.003$.

hep-ex↗

arXiv1997

Measurement of the B+ and B0 Lifetimes from 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 SLC between 1993 and 1995. The analysis identifies the semileptonic decays of B mesons and reconstructs the B meson decay length and charge by vertexing the lepton with a partially reconstructed D meson. This new method results in a sample of 634 (584) charged (neutral) decays with high charge purity. The ratio of B+ : B0 decays in the charged (neutral) sample is 3:1 (1:3). A maximum likelihood fit yields t(B+) = 1.61 +0.13 -0.12(stat) +/- 0.07(syst) ps, t(B0) = 1.56 +0.14 -0.13(stat) +/- 0.10(syst) ps, and t(B+)/t(B0) = 1.03 +0.16 -0.14(stat) +/- 0.09(syst).

hep-ex↗

arXiv1997

Measurement of the B+ and B0 Lifetimes using Topological Vertexing

The lifetimes of B+ and B0 mesons have been measured using a sample of 150,000 hadronic Z0 decays collected by the SLD experiment at the SLC between 1993 and 1995. The analysis reconstructs the decay length and charge of the B meson using a novel topological vertexing technique. This method results in a high statistics sample of 6033 (3665) charged (neutral) vertices with good charge purity. A maximum likelihood fit procedure finds: t(B+) = 1.67 +/- 0.07(stat) +/- 0.06(syst) ps, t(B0) = 1.66 +/- 0.08(stat) +/- 0.08(syst) ps, t(B+)/t(B0) = 1.01 +0.09-0.08(stat) +/- 0.05(syst).

hep-ex↗