We report measurements of single- and double- spin asymmetries for $W^{\pm}$ and $Z/\gamma^*$ boson production in longitudinally polarized $p+p$ collisions at $\sqrt{s} = 510$ GeV by the STAR experiment at RHIC. The asymmetries for $W^{\pm}$ were measured as a function of the decay lepton pseudorapidity, which provides a theoretically clean probe of the proton's polarized quark distributions at the scale of the $W$ mass. The results are compared to theoretical predictions, constrained by recent polarized deep inelastic scattering measurements, and show a preference for a sizable, positive up antiquark polarization in the range $0.05<x<0.2$.
We report on the $W$ and $Z/\gamma^*$ differential and total cross sections as well as the $W^+$/$W^-$ and $(W^+ + W^-)$/$(Z/\gamma^*)$ cross-section ratios measured by the STAR experiment at RHIC in $p+p$ collisions at $\sqrt{s} = 500$ GeV and $510$ GeV. The cross sections and their ratios are sensitive to quark and antiquark parton distribution functions. In particular, at leading order, the $W$ cross-section ratio is sensitive to the $\bar{d}/\bar{u}$ ratio. These measurements were taken at high $Q^2 \sim M_W^2,M_Z^2$ and can serve as input into global analyses to provide constraints on the sea quark distributions. The results presented here combine three STAR data sets from 2011, 2012, and 2013, accumulating an integrated luminosity of 350 pb$^{-1}$. We also assess the expected impact that our $W^+/W^-$ cross-section ratios will have on various quark distributions, and find sensitivity to the $\bar{u}-\bar{d}$ and $\bar{d}/\bar{u}$ distributions.
A search for excited states of the standard model fermions was performed using the ZEUS detector at the HERA electron-proton collider, operating at a centre of mass energy of 296 GeV. In a sample corresponding to an integrated luminosity of 0.55 pb−1, no evidence was found for any resonant state decaying into final states composed of a fermion and a gauge boson. Limits on the coupling strength times branching ratio of excited fermions are presented for masses between 50 GeV and 250 GeV, extending previous search regions significantly.
The production of 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 BR (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).
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 σ WW = 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: m W = 80.14 ± 0.34 (stat.) ± 0.09 (syst.) ± 0.03 (LEP energy) GeV/ c 2
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 |Vcs|= 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.
The e + e − → W + W − cross section is measured in a data sample collected by ALEPH at a mean centre-of-mass energy of 172.09 GeV, corresponding to an integrated luminosity of 10.65 pb −1 . Cross sections are given for the three topologies, fully leptonic, semi-leptonic and hadronic of a W-pair decay. Under the assumption that no other decay modes are present, the W-pair cross section is measured to be 11.7±1.2 (stat.) ±0.3 (syst.) pb . The existence of the triple gauge boson vertex of the Standard Model is clearly preferred by the data. The decay branching ratio of the W boson into hadrons is measured to be B(W→hadrons) =67.7±3.1 (stat.) ±0.7 (syst.) % , allowing a determination of the CKM matrix element | V cs |=0.98±0.14(stat.)±0.03(syst.).
The cross sections for single vector boson production in the We ν and Zee channels are measured from the data collected by the ALEPH detector at LEP for centre-of-mass energies between 183 and 209 GeV. These data correspond to a total integratedluminosity of 683 pb −1 . Single-W production is studied in both hadronic and leptonic decay channels. Hadronic and dimuon decays are used for single-Z production. The measured cross sections agree with the Standard Model predictions.
Single W production is studied in the data recorded with the ALEPH detector at LEP at centre-of-mass energies between 161 and 183 GeV. The cross section is measured to be σ W =0.41±0.17(stat.)±0.04(syst.) pb at 183 GeV, consistent with the Standard Model expectation. Limits on non-standard WW γ couplings are deduced as −1.6<κ γ <1.5 (λ γ =0) and −1.6<λ γ <1.6 (κ γ =1) at 95% C.L. A search for effectively invisible decays of the W boson in W pair production is performed, leading to an upper limit on the branching ratio of 1.3% ( Γ inv =27 MeV ) at 95% C.L.
The W + W- production cross section is measured from a data sample corresponding to a total integrated luminosity of 683 pb-1, collected by the ALEPH experiment at LEP at centre-of-mass energies from
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