The BaBar detector: Upgrades, operation and performance Couderc, F.; Prudent, X.; Groysman, Y. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
11/2013, Volume:
729, Issue:
C
Journal Article
Peer reviewed
Open access
The BaBar detector operated successfully at the PEP-II asymmetric e+e− collider at the SLAC National Accelerator Laboratory from 1999 to 2008. This report covers upgrades, operation, and performance ...of the collider and the detector systems, as well as the trigger, online and offline computing, and aspects of event reconstruction since the beginning of data taking.
We report on a precision measurement of the ratio R_{τμ}^{ϒ(3S)}=B(ϒ(3S)→τ^{+}τ^{-})/B(ϒ(3S)→μ^{+}μ^{-}) using data collected with the BABAR detector at the SLAC PEP-II e^{+}e^{-} collider. The ...measurement is based on a 28 fb^{-1} data sample collected at a center-of-mass energy of 10.355 GeV corresponding to a sample of 122 million ϒ(3S) mesons. The ratio is measured to be R_{τμ}^{ϒ(3S)}=0.966±0.008_{stat}±0.014_{syst} and is in agreement with the standard model prediction of 0.9948 within 2 standard deviations. The uncertainty in R_{τμ}^{ϒ(3S)} is almost an order of magnitude smaller than the only previous measurement.
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We present a search for nine lepton-number-violating and three lepton-flavor-violating neutral charm decays of the type D0→h′−h−ℓ′+ℓ+ and D0→h′−h+ℓ′±ℓ∓, where h and h′ represent a K or π meson and ℓ ...and ℓ′ an electron or muon. The analysis is based on 468 fb−1 of e+e− annihilation data collected at or close to the ϒ(4S) resonance with the BABAR detector at the SLAC National Accelerator Laboratory. No significant signal is observed for any of the twelve modes, and we establish 90% confidence level upper limits on the branching fractions in the range (1.0–30.6)×10−7. The limits are between 1 and 3 orders of magnitude more stringent than previous measurements.
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We report the observation of the rare charm decay D0→K−π+e+e−, based on 468 fb−1 of e+e− annihilation data collected at or close to the center-of-mass energy of the ϒ(4S) resonance with the BABAR ...detector at the SLAC National Accelerator Laboratory. We find the branching fraction in the invariant mass range 0.675<m(e+e−)<0.875 GeV/c2 of the electron-positron pair to be B(D0→K−π+e+e−)=(4.0±0.5±0.2±0.1)×10−6, where the first uncertainty is statistical, the second systematic, and the third due to the uncertainty in the branching fraction of the decay D0→K−π+π+π− used as a normalization mode. The significance of the observation corresponds to 9.7 standard deviations including systematic uncertainties. This result is consistent with the recently reported D0→K−π+μ+μ− branching fraction, measured in the same invariant mass range, and with the value expected in the standard model. In a set of regions of m(e+e−), where long-distance effects are potentially small, we determine a 90% confidence level upper limit on the branching fraction B(D0→K−π+e+e−)<3.1×10−6.
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We present first evidence that the cosine of the CP-violating weak phase 2β is positive, and hence exclude trigonometric multifold solutions of the Cabibbo-Kobayashi-Maskawa (CKM) Unitarity Triangle ...using a time-dependent Dalitz plot analysis of B^{0}→D^{(*)}h^{0} with D→K_{S}^{0}π^{+}π^{-} decays, where h^{0}∈{π^{0},η,ω} denotes a light unflavored and neutral hadron. The measurement is performed combining the final data sets of the BABAR and Belle experiments collected at the ϒ(4S) resonance at the asymmetric-energy B factories PEP-II at SLAC and KEKB at KEK, respectively. The data samples contain (471±3)×10^{6}BBover ¯ pairs recorded by the BABAR detector and (772±11)×10^{6}BBover ¯ pairs recorded by the Belle detector. The results of the measurement are sin2β=0.80±0.14(stat)±0.06(syst)±0.03(model) and cos2β=0.91±0.22(stat)±0.09(syst)±0.07(model). The result for the direct measurement of the angle β of the CKM Unitarity Triangle is β=22.5±4.4(stat)±1.2(syst)±0.6(model)°. The measurement assumes no direct CP violation in B^{0}→D^{(*)}h^{0} decays. The quoted model uncertainties are due to the composition of the D^{0}→K_{S}^{0}π^{+}π^{-} decay amplitude model, which is newly established by performing a Dalitz plot amplitude analysis using a high-statistics e^{+}e^{-}→ccover ¯ data sample. CP violation is observed in B^{0}→D^{(*)}h^{0} decays at the level of 5.1 standard deviations. The significance for cos2β>0 is 3.7 standard deviations. The trigonometric multifold solution π/2-β=(68.1±0.7)° is excluded at the level of 7.3 standard deviations. The measurement resolves an ambiguity in the determination of the apex of the CKM Unitarity Triangle.
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