We report on a precision measurement of the neutron spin structure function g1ng^n_1g1n 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 ∫0.0140.7g1n(x)dx=−0.036±0.004(stat)±0.005(syst)\int^{0.7}_{0.014} g^n_1(x)dx = -0.036 \pm 0.004 (stat) \pm 0.005 (syst)∫0.0140.7g1n(x)dx=−0.036±0.004(stat)±0.005(syst) at an average Q2=5(GeV/c)2Q^2=5 (GeV/c)^2Q2=5(GeV/c)2. We find relatively large negative values for g1ng^n_1g1n at low xxx. The results call into question the usual Regge theory method for extrapolating to x=0 to find the full neutron integral ∫01g1n(x)dx\int^1_0 g^n_1(x)dx∫01g1n(x)dx, needed for testing quark-parton model and QCD sum rules. (arXiv)
Based on the full BABAR data sample, we report improved measurements of the ratios R(D(*))=B(B̄→D(*)τ⁻ν¯τ)/B(B̄→D(*)ll¯ν¯l), where l is either e or μ. These ratios are sensitive to new physics ...contributions in the form of a charged Higgs boson. We measure R(D)=0.440±0.058±0.042 and R(D*)=0.332±0.024±0.018, which exceed the standard model expectations by 2.0σ and 2.7σ, respectively. Taken together, our results disagree with these expectations at the 3.4σ level. This excess cannot be explained by a charged Higgs boson in the type II two-Higgs-doublet model.
A high-gradient-doping technique is applied to strained polarized photocathodes. A 5.0–
7.5
nm
p-type surface layer doped to
5×10
19
cm
−3
is found sufficient to overcome the surface charge limit ...while maintaining high beam polarization. This technique can be employed to meet the charge requirements of the Next Linear Collider with a polarization approaching 80%.
The spin structure function of the neutron ital gsub 1sup ital n has been determined over the range 0.03ltital xlt0.6 at an average ital Qsup 2 of 2 (GeV/ital c)sup 2 by measuring the asymmetry in ...deep inelastic scattering of polarized electrons from a polarized sup 3He target at energies between 19 and 26 GeV. The integral of the neutron spin structure function is found to be integralsub 0sup 1ital gsub 1sup ital n(ital x)ital dx=minus0.022plus minus0.011. Earlier reported proton results together with the Bjorken sum rule predict integralsub 0sup 1ital gsub 1sup ital n(ital x)ital dx=minus0.059plus minus0.019.
The process e+e−→π+π−2π0γ is investigated by means of the initial-state radiation technique, where a photon is emitted from the incoming electron or positron. Using 454.3 fb−1 of data collected ...around a center-of-mass energy of s=10.58 GeV by the BABAR experiment at SLAC, approximately 150000 signal events are obtained. The corresponding nonradiative cross section is measured with a relative uncertainty of 3.6% in the energy region around 1.5 GeV, surpassing all existing measurements in precision. Using this new result, the channel’s contribution to the leading order hadronic vacuum polarization contribution to the anomalous magnetic moment of the muon is calculated as (gμπ+π−2π0−2)/2=(17.9±0.1stat±0.6syst)×10−10 in the energy range 0.85 GeV<ECM<1.8 GeV. In the same energy range, the impact on the running of the fine-structure constant at the Z0-pole is determined as Δαπ+π−2π0(MZ2)=(4.44±0.02stat±0.14syst)×10−4. Furthermore, intermediate resonances are studied and especially the cross section of the process e+e−→ωπ0→π+π−2π0 is measured.
A precise measurement of the cross section of the process $e^+e^-\to\pi^+\pi^-(\gamma)$ from threshold to an energy of 3GeV is obtained with the initial-state radiation (ISR) method using $232\invfb$ ...of data collected with the BaBar detector at $e^+e^-$ center-of-mass energies near 10.6GeV. The ISR luminosity is determined from a study of the leptonic process $e^+e^-\to\mu^+\mu^-(\gamma)\gamma_{\rm ISR}$, which is found to agree with the next-to-leading-order QED prediction to within 1.1%. The cross section for the process $e^+e^-\to\pi^+\pi^-(\gamma)$ is obtained with a systematic uncertainty of 0.5% in the dominant $\rho$ resonance region. The leading-order hadronic contribution to the muon magnetic anomaly calculated using the measured $\pi\pi$ cross section from threshold to 1.8GeV is $(514.1 \pm 2.2({\rm stat}) \pm 3.1({\rm syst}))\times 10^{-10}$.
A set of thin GaAs
p-type negative electron affinity (NEA) photocathodes have been used to measure the yield of photoemitted electrons at high intensity excitation. The active layer thickness is 100 ...nm and the
p-type doping ranges from 5×10
18 to 5×10
19 cm
−3 for a set of four samples. The results show that the surface escape probability is a linear function of the NEA energy. The surface photovoltage effect on photoemission is found to diminish to zero at a doping level of 5×10
19 cm
−3. The experimental results are shown to be in good agreement with calculations using a charge limit model based on surface photovoltage kinetics that assume a constant electron energy relaxation rate in the band bending region.
The decay τ−→K−KSντ has been studied using 430×106 e+e−→τ+τ− events produced at a center-of-mass energy around 10.6 GeV at the PEP-II collider and studied with the BABAR detector. The mass spectrum ...of the K−KS system has been measured and the spectral function has been obtained. The measured branching fraction B(τ−→K−KSντ)=(0.739±0.011(stat)±0.020(syst))×10−3 is found to be in agreement with earlier measurements.
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