109927315
Measurement of W pair production in e+ e- collisions at 189-GeV
Abstract The production of W + W − pairs is analysed in a data sample collected by ALEPH at a mean centre-of-mass energy of 188.6 GeV, corresponding to an integrated luminosity of 174.2 pb −1 . Cross sections are given for different topologies of W decays into leptons or hadrons. Combining all final states and assuming Standard Model branching fractions, the total W-pair cross section is measured to be 15.71±0.34 (stat.) ±0.18 (syst.) pb . Using also the W-pair data samples collected by ALEPH at lower centre-of-mass energies, the decay branching fraction of the W boson into hadrons is measured to be B(W→hadrons)=66.97±0.65(stat.)±0.32(syst.)%, allowing a determination of the CKM matrix element | V cs |=0.951±0.030(stat.)±0.015(syst.).
53511895
Measurement of the W mass in $e^+e^-$ collisions at production threshold
In June 1996, the LEP centre-of-mass energy was raised to 161 GeV. Pair production of W bosons in e+e− collisions was observed for the first time by the LEP experiments. An integrated luminosity of 11 pb−1 was recorded in the ALEPH detector, in which WW candidate events were observed. In 6 events both Ws decay leptonically. In 16 events, one W decays leptonically, the other into hadrons. In the channel where both Ws decay into hadrons, a signal was separated from the large background by means of several multi-variate analyses. The W pair cross-section is measured to be σWW = 4.23 ± 0.73 (stat.) ± 0.19 (syst.) pb. From this cross-section, the W mass is derived within the framework of the Standard Model: mW = 80.14 ± 0.34 (stat.) ± 0.09 (syst.) ± 0.03 (LEP energy) GeV/c2
144007210
A precise determination of the number of families with light neutrinos and of the Z boson partial widths
More extensive and precise results are reported on the parameters of Z decay. On the basis of 20 000 Z decays collected with the ALEPH detector at LEP we find Mz=91.182±0.026 (exp.) ±0.030 (beam) GeV, Γz=2.541±0.056 GeV and σhad0=41.4±0.8 nb. The partial widths for the hadronic and leptonic channels are Γhad=1804±44 MeV, Γe+e−=82.1±3.4 MeV, Γμ+μ−=87.9±6.0 MeV and Γτ+τ−=86.1±5.6 MeV, in good agreement with the standard model. On the basis of the average leptonic width Γl+l−=83.9±2.2 MeV, the effective weak mixing angle is found to be sin2θw(Mz)=0.231±0.008. Usin g the partial widths calculated in the standard model, the number of light neutrino families is Nν=3.01±0.15 (exp.)±0.05 (theor.).
123148086
Charm counting in b decays
The inclusive production of charmed particles in decays has been measured from the yield of D0, D+, Ds+ and Λc+ decays in a sample of events with high b purity collected with the ALEPH detector from 1992 to 1995. From these measurements, adding the charmonia production rate and an estimate of the charmed strange baryon contribution, the average number of charm quarks per b decay is determined to be nc = 1.230 ± 0.036 ± 0.038 ± 0.053, where the uncertainties are due to statistics, systematic effects and branching ratios, respectively.
122002257
Production of D**s mesons in hadronic Z decays
The production rates of the orbitally excited Ds** mesons, Ds1 and Ds2*, are measured with the 4.1 million hadronic Z decays recorded by the ALEPH detector during 1991--1995. The Ds** mesons are reconstructed in the decay modes Ds1+ -> D*+ K0, Ds1+ -> D*0 K+ and Ds2*+ -> D0 K+. The production rate of the Ds1 is measured to be n(Z->Ds1+-)=(0.52+-0.09+-0.06)%, under the assumption that the two considered decay modes of the Ds1 saturate the branching ratio. The production rate of the Ds2* is determined to be n(Z->Ds2*+-)=(0.83+-0.29+0.07-0.13)%, assuming that the branching fraction of the decay Ds2*+ -> D0 K+ is 45%. The production rates in Z->cc and Z->bbar decays are measured separately.
15227858
Measurement of W pair production in e+ e- collisions at 183-GeV
Abstract The production of W + W − pairs is analysed in a data sample collected by ALEPH at a mean centre-of-mass energy of 182.7 GeV, corresponding to an integrated luminosity of 57 pb −1 . Cross sections are given for different topologies of W decays into leptons or hadrons. Under Standard Model assumptions for the W-pair production and decay, the W-pair cross section is measured to be 15.57±0.62 (stat.) ±0.29 (syst.) pb . Using also the W-pair data samples collected by ALEPH at lower centre-of-mass energies, the decay branching ratio of the W boson into hadrons is measured to be B(W→hadrons) =68.93±1.21 (stat.) ±0.51 (syst.) % , allowing a determination of the CKM matrix element |V cs |=1.043±0.058 (stat.) ±0.026 (syst.) . The agreement of the cross sections with the Standard Model prediction allows a limit to be set on the W decay rate to undetectable final states.
107065256
Networking with China
This paper presents the history and current status Of computer networking between IHEP in Beijing, China and the rest of the world, starting with no links at the beginning of 1987 thru X.25 public networks and dial up links, to the installing, in March 1993, of one of the first dedicated 64 kbps satellite computer links between China and the outside world. In May 1994, IHEP became the first Chinese institution to have a fully operational world-wide Internet connection. Experience with this dedicated link between SLAC and IHEP will be presented together with future plans to add a land line between KEK and IHEP and to extend the links within China.
119256974
CAN COLD QUARK MATTER BE SOLID
The state of cold quark matter challenges both astrophysicists and particle physicists, and even many-body physicists. It is conventionally suggested that BCS-like color superconductivity occurs in cold quark matter; however, other scenarios with a ground state rather than of Fermi gas could still be possible. It is addressed that quarks are dressed and clustered in cold quark matter at realistic baryon densities of compact stars, since a weakly coupling treatment of the interaction between constituent quarks would not be reliable. Cold quark matter is conjectured to be in a solid state if thermal kinematic energy is much lower than the interaction energy of quark clusters, and such a state could be relevant to different manifestations of pulsar-like compact stars.
9662073
Effect of asymmetric strange–antistrange sea to the NuTeV anomaly
Abstract We calculate the strange quark and antiquark distributions of the nucleon by using the effective chiral quark model, and find that the strange–antistrange asymmetry can bring a contribution of about 60–100% to the NuTeV deviation of sin 2 θ w from the standard value measured in other electroweak processes. The results are insensitive to different inputs. The light-flavor quark asymmetry of d ¯ – u ¯ is also investigated and found to be consistent with the experimental measurements. Therefore the chiral quark model provides a successful picture to understand the NuTeV anomaly, as well as the light-flavor quark asymmetry and the proton spin problem in previous studies.
14113874
Sigma meson cloud and proton's light flavor sea quarks
Abstract We take into account the sigma meson cloud effect in the meson cloud model to calculate the distributions of light flavor sea quarks in the proton. Our calculation gives a better description of the data for d ¯ ( x ) / u ¯ ( x ) . We also provide a picture that the probability of finding a physical proton in a Fock state | N ω 〉 is reasonable small with a smaller cutoff Λ ω .
119279262
PSR B1257+12: a quark star with planets?
A recent observation has shown that PSR B1257+12 could have quite small X‐ray emitting area, only about 2000 m2, which is more than three orders smaller than the canonical polar cap size. We suggest here that PSR B1257+12 could be a low‐mass quark star with radius of R≃0.6 km and mass of M≃3×10−4 M⊙. Such a low‐mass quark star system may form in an accretion induced collapse process or a collision process of two quark stars.