Production of antihydrogen Baur, G.; Boero, G.; Brauksiepe, A. ...
Physics letters. B,
02/1996, Letnik:
368, Številka:
3
Journal Article
Recenzirano
Odprti dostop
Results are presented for a measurement for the production of the antihydrogen atom
H
0 ≡
p
e
+
, the simplest atomic bound state of antimatter.
A method has been used by the PS210 collaboration at ...LEAR which assumes that the production of
H
0
is predominantly mediated by the e
+e
−-pair creation via the two-photon mechanism in the antiproton-nucleus interaction. Neutral
H
0
atoms are identified by a unique sequence of characteristics. In principle
H
0
is well suited for investigations of fundamental CPT violation studies under different forces, however, in our investigations we concentrate on the production of this antimatter object, since so far it has never been observed before.
The production of 11 antihydrogen atoms is reported including possibly 2±1 background signals, the observed yield agrees with theoretical predictions.
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.
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.
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.
Evidence of B + → τ + ν decays with hadronic B tags Grauges, E.; Palano, A.; Eigen, G. ...
Physical review. D, Particles, fields, gravitation, and cosmology,
08/2013, Letnik:
88, Številka:
3
Journal Article
Recenzirano
Odprti dostop
We present a search for the decay B + → τ + ν using 467.8 × 10 6 B ¯¯¯ B pairs collected at the Υ ( 4 S ) resonance with the BABAR detector at the SLAC PEP-II B -Factory. We select a sample of events ...with one completely reconstructed B − in the hadronic decay mode ( B − → D ( * ) 0 X − and B − → J / ψ X − ). We examine the rest of the event to search for a B + → τ + ν decay. We identify the τ + lepton in the following modes: τ + → e + ν ¯ ν , τ + → μ + ν ¯ ν , τ + → π + ¯ ν and τ + → ρ + ¯ ν . We find an excess of events with respect to the expected background, which excludes the null signal hypothesis at the level of 3.8 σ (including systematic uncertainties) and corresponds to a branching fraction value of B ( B + → τ + ν ) = ( 1.83 + 0.53 − 0.49 ( stat ) ± 0.24 ( syst ) ) × 10 − 4 .
We describe a measurement of the time-integrated luminosity of the data collected by the BABAR experiment at the PEP-II asymmetric-energy e+e- collider at the Upsilon(4S), Upsilon(3S), and ...Upsilon(2S) resonances and in a continuum region below each resonance. We measure the time-integrated luminosity by counting e+e- --> e+e- and (for the Upsilon(4S) only) e+e- --> mu+mu- candidate events, allowing additional photons in the final state. We use data-corrected simulation to determine the cross sections and reconstruction efficiencies for these processes, as well as the major backgrounds. Due to the large cross sections of e+e- --> e+e- and +e- --> mu+mu-, the statistical uncertainties of the measurement are substantially smaller than the systematic uncertainties. The dominant systematic uncertainties are due to observed differences between data and simulation, as well as uncertainties on the cross sections. For data collected on the Upsilon(3S) and Upsilon(2S) resonances, an additional uncertainty arises due to Upsilon --> e+e- background. For data collected off the Upsilon resonances, we estimate an additional uncertainty due to the time-dependent efficiency variations, which can affect the short off-resonance runs.
Based on the full BABAR data sample of 466.5 million BB¯ pairs, we present measurements of the electron spectrum from semileptonic B meson decays. We fit the inclusive electron spectrum to ...distinguish Cabibbo-Kobayashi-Maskawa (CKM) suppressed B→Xueν decays from the CKM-favored B→Xceν decays, and from various other backgrounds, and determine the total semileptonic branching fraction B(B→Xeν)=(10.34±0.04stat±0.26syst)%, averaged over B± and B0 mesons. We determine the spectrum and branching fraction for charmless B→Xueν decays and extract the CKM element |Vub|, by relying on four different QCD calculations based on the heavy quark expansion. While experimentally, the electron momentum region above 2.1 GeV/c is favored, because the background is relatively low, the uncertainties for the theoretical predictions are largest in the region near the kinematic endpoint. Detailed studies to assess the impact of these four predictions on the measurements of the electron spectrum, the branching fraction, and the extraction of the CKM matrix element |Vub| are presented, with the lower limit on the electron momentum varied from 0.8 GeV/c to the kinematic endpoint. We determine |Vub| using each of these different calculations and find, |Vub|=(3.794±0.107exp −0.219 SF+0.292 −0.068 theory+0.078)×10−3 (De Fazio and Neubert), (4.563±0.126exp −0.208 SF+0.230 −0.163 theory+0.162)×10−3 (Bosch, Lange, Neubert, and Paz), (3.959±0.104exp −0.154 SF+0.164 −0.079 theory+0.042)×10−3 (Gambino, Giordano, Ossola, and Uraltsev), (3.848±0.108exp −0.070 theory+0.084)×10−3 (dressed gluon exponentiation), where the stated uncertainties refer to the experimental uncertainties of the partial branching fraction measurement, the shape function parameters, and the theoretical calculations.
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