1,723,625 research outputs found
Observation of CP Violation in Charm Decays
Full text linkA search for charge-parity (CP) violation in D0→K-K+ and D0→π-π+ decays is reported, using pp collision data corresponding to an integrated luminosity of 5.9 fb-1 collected at a center-of-mass energy of 13 TeV with the LHCb detector. The flavor of the charm meson is inferred from the charge of the pion in D∗(2010)+→D0π+ decays or from the charge of the muon in B̄→D0μ-ν̄μX decays. The difference between the CP asymmetries in D0→K-K+ and D0→π-π+ decays is measured to be ΔACP=[-18.2±3.2(stat)±0.9(syst)]×10-4 for π-tagged and ΔACP=[-9±8(stat)±5(syst)]×10-4 for μ-tagged D0 mesons. Combining these with previous LHCb results leads to ΔACP=(-15.4±2.9)×10-4, where the uncertainty includes both statistical and systematic contributions. The measured value differs from zero by more than 5 standard deviations. This is the first observation of CP violation in the decay of charm hadrons
Precision measurements of ππ scattering lengths at NA48/2
No full textLow energy ππ scattering has been studied with high precision by the NA48/2 experiment at the CERN SPS using large data samples of K ±→π±π0π 0 and K±→π+π -e±ν(Ke4) decays. The π0π0 invariant mass distribution in the K ±→π±π0π 0 decay exhibits a Wigner cusp at the π+π - threshold, from which the scattering lengths a0 and a2 are extracted. The measurement of a0 and a2 is also performed from Ke4 decay, with similar precision. The combination of these measurement provides a stringent test of Chiral Perturbation Theory. © 2011 American Institute of Physics
Observation of the B0 → D ̄ ∗0K+π- and Bs0 → D ̄ ∗0K-π+ decays
No full textThe first observations of B0→D ̄∗(2007)0K+π- and Bs0→D ̄∗(2007)0K-π+ decays are presented, and their branching fractions relative to that of the B0→D ̄∗(2007)0π+π- decay are reported. These modes can potentially be used to investigate the spectroscopy of charm and charm-strange resonances and to determine the angle γ of the Cabibbo-Kobayashi-Maskawa unitarity triangle. It is also important to understand them as a source of potential background in determinations of γ from B+→DK+ and B0→DK+π- decays. The analysis is based on a sample corresponding to an integrated luminosity of 5.4 fb-1 of proton-proton collision data at 13 TeV center-of-mass energy recorded with the LHCb detector. The D ̄∗(2007)0 mesons are fully reconstructed in the D ̄0π0 and D ̄0γ channels with the D ̄0→K+π- decay. A novel weighting method is used to subtract background while simultaneously applying an event-by-event efficiency correction to account for resonant structures in the decays
Precision measurements of K±→π ±π0γ decay at NA48/2 and search for CP violation
No full textThe direct emission (DE) and interference (INT) terms of the radiative decay K±→π±π0γ have been measured by the NA48/2 experiment at CERN SPS. About 6•10 5 K±→π±π 0γ decays have been selected from data collected during 2003 and 2004. The relative amounts of DE and INT with respect to the dominant Inner Bremsstrahlung (IB) contribution have been measured in the range
Model independent measurement of the leptonic kaon decay K± → μ±νμe+e- and study of the K± →π±π0e+e- decay by the NA48/2 experiment
No full textTwo recent results on rare kaon decays are presented, based on ∼ 2×1011 K± decays recorded by the NA48/2 experiment at CERN SPS in 2003 and 2004. The branching ratio of the rare leptonic decay K± → μ±νμ e+e- has been measured in the region of large e+e- invariant mass Mee ≥140 MeV/c2, where low energy QCD contributions become important and can be calculated in the framework of Chiral Perturbation Theory (ChPT). This branching ratio is measured to be BR(K± → μ±νμ e+e-| Mee ≥ 140 MeV/c2 ) = (7.8±0.2)×10-8. The K± → π±π0e+e- rare decay has been observed for the first time, with about 5000 candidates and a 5% background. The branching ratio in the full kinematic region is measured to be BR(K± → π ±π0e+e-) = (4.22×0.15)×10-6, in good agreement with ChPT-based theoretical predictions
Measurement of Antiproton Production in p-He Collisions at sNN =110 GeV
No full textThe cross section for prompt antiproton production in collisions of protons with an energy of 6.5 TeV incident on helium nuclei at rest is measured with the LHCb experiment from a data set corresponding to an integrated luminosity of 0.5 nb-1. The target is provided by injecting helium gas into the LHC beam line at the LHCb interaction point. The reported results, covering antiproton momenta between 12 and 110 GeV/c, represent the first direct determination of the antiproton production cross section in p-He collisions, and impact the interpretation of recent results on antiproton cosmic rays from space-borne experiments
Recent results from the NA62 and NA48/2 experiments at CERN
No full textA measurement of the K+→π0e+νγ radiative decay and a search for the K+→π−(π0)e+e+ lepton number violating decays by the NA62 experiment are presented, together with the first observation and branching fraction measurement of the rare decay K+→π0π0μ+ν by the NA48/2 experiment
Kaon decays at NA48: Recent results and perspectives
No full textWe report recent results on charged kaon rare decays obtained by the NA48/2 collaboration. The Ke4 decays K± →p+p-e±n(Ke4(+-)) and K± →p0p0e±n(Ke4(00)) have been studied extensively, providing measurements of the branching ratios, together with the Ke4(+-) form factors and a precise determination of pp scattering lengths. Prospects for a study of Kμ4 decays are discussed. A new measurement of the branching ratio and gg invariant mass spectrum of K± → p±gg decays has been obtained from a combined analysis of NA48/2 and NA62 minimum-bias data. The analysis of a high statistics and low background sample of K± →p±p0g decays provided the first evidence of a non-zero interference between Inner Bremsstrahlung and Direct Emission amplitudes. The K± →p±p0e+e- decay has been observed for the first time, with a statistics of about 4500 events. The branching ratios of K± →p±e+e- and K± →p±μ+μ- decays have been measured with a few percent precision. Improved upper limits are given for CP-violating asymmetries in these decays, and for the branching fraction of the Lepton Number violating decay K± →πμ±μ±
The NA62 RICH detector
No full textThe RICH detector of the NA62 experiment at CERN SPS is required to suppress contamination in candidate events by a factor at least 100 between 15 and 35 GeV/c momentum, to measure the pion arrival time with ps resolution and to produce a trigger for a charged track. It consists of a 17 m long tank filled with Neon gas at atmospheric pressure. \v{C}erenkov light is reflected by a mosaic of 20 spherical mirrors placed at the downstream end of the vessel and is collected by 1952 photomultipliers placed at the upstream end. The construction of the detector will be described and the performance reached during first runs will be discussed.The RICH detector of the NA62 experiment at CERN SPS is required to suppress contamination in candidate events by a factor at least 100 between 15 and 35 GeV/c momentum, to measure the pion arrival time with ps resolution and to produce a trigger for a charged track. It consists of a 17 m long tank filled with Neon gas at atmospheric pressure. Čerenkov light is reflected by a mosaic of 20 spherical mirrors placed at the downstream end of the vessel and is collected by 1952 photomultipliers placed at the upstream end. The construction of the detector will be described and the performance reached during first runs will be discussed
Precision measurement of the form factors of the charged kaon semileptonic decays by the NA48/2 experiment at CERN
Full text linkThe final result on the charged kaon semileptonic form factors from the NA48/2 experiment is presented. The measurement is based on 4.28 million and 2.91 million events collected in 2004 with very low background ( and , respectively). The joint analysis of these samples provides the most precise combined measurement of form factors
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