864 research outputs found
Observation of the decay B0 -> D0K+K- with the LHCb detector at CERN
The first observation of the decay mode B0 -> D0K+K- is presented using
0.62 fb-1 of data collected by the LHCb detector in 2011. The branching fraction
is measured with respect to the topologically similar decay mode, B0 -> D0Ļ+Ļ-. The ratio of branching fractions is measured to be
B(B0 -> D0K+K-) / B(B0 -> D0Ļ+Ļ-) = 0.056 Ā± 0.011 Ā± 0.007,
where the first uncertainty is statistical and the second is systematic. Using the
world average value for the denominator yields
B(B0 -> D0K+K-) = (4.7 Ā± 0.9 Ā± 0.6 Ā± 0.5) x 10-5,
where the third uncertainty is from B(B0 -> D0Ļ+Ļ-). Secondly, evidence for the B0s -> D0K+K- decay mode is presented. The branching fraction ratio with respect to B0 -> D0K+K- is found to be
B(B0s -> D0K+K-) / B(B0 -> D0K+K-) = 0.90 Ā± 0.27 Ā± 0.20,
where the first uncertainty is statistical and the second is systematic
First observation of Bs0 ā D*s2+XĪ¼-Ī½ decays
Using data collected with the LHCb detector in protonāproton collisions at a centre-of-mass energy of 7 TeV, the semileptonic decays B0sāD+sXĪ¼āĪ½ and B0sāD0K+XĪ¼āĪ½ are detected. Two structures are observed in the D0K+ mass spectrum at masses consistent with the known Ds1(2536)+ and Dās22573)+ mesons. The measured branching fractions relative to the total B0s semileptonic rate are B(B0sāDā+s2XĪ¼āĪ½)/B(B0sāXĪ¼āĪ½) = (3.3Ā±1.0Ā±0.4)%, and B(B0sāD+s1XĪ¼āĪ½)/B(B0sāXĪ¼āĪ½) = (5.4Ā±1.2Ā±0.5)%, where the ļ¬rst uncertainty is statistical and the second is systematic. This is the ļ¬rst observation of the Dā+s2 state in B0s decays; we also measure its mass and width
Measurement of the Bs0-Bs0 oscillation frequency Ī“ms in Bs0āDs-(3)Ļ decays
The Bs0-Bs0 oscillation frequency Ī“ms is measured with 36 pb-1 of data collected in pp collisions at s=7TeV by the LHCb experiment at the Large Hadron Collider. A total of 1381 Bs0āDs-Ļ+ and Bs0āDs-Ļ+Ļ-Ļ + signal decays are reconstructed, with average decay time resolutions of 44 fs and 36 fs, respectively. An oscillation signal with a statistical significance of 4.6Ļ is observed. The measured oscillation frequency is Ī“m s=17.63Ā±0.11(stat)Ā±0.02(syst)ps -1
Absolute luminosity measurements with the LHCb detector at the LHC
Absolute luminosity measurements are of general interest for colliding-beam experiments at storage rings. These measurements are necessary to determine the absolute cross-sections of reaction processes and are valuable to quantify the performance of the accelerator. Using data taken in 2010, LHCb has applied two methods to determine the absolute scale of its luminosity measurements for proton-proton collisions at the LHC with a centre-of-mass energy of 7 TeV. In addition to the classic ''van der Meer scan'' method a novel technique has been developed which makes use of direct imaging of the individual beams using beam-gas and beam-beam interactions. This beam imaging method is made possible by the high resolution of the LHCb vertex detector and the close proximity of the detector to the beams, and allows beam parameters such as positions, angles and widths to be determined. The results of the two methods have comparable precision and are in good agreement. Combining the two methods, an overal precision of 3.5% in the absolute luminosity determination is reached. The techniques used to transport the absolute luminosity calibration to the full 2010 data-taking period are presented
First observation of the decay B0sāĻKā0
The first observation of the decay B0sāĻKā0 is reported. The analysis is based on a data sample corresponding to an integrated luminosity of 1.0 fbā1 of pp collisions at sā=7 TeV, collected with the LHCb detector. A yield of 30 Ā± 6 B0sā(K+Kā)(KāĻ+) decays is found in the mass windows 1012.5 < M (K + K ā) < 1026.5 MeV/c 2 and 746 < M(K ā Ļ +) < 1046 MeV/c 2. The signal yield is found to be dominated by B0sāĻKā0 decays, and the corresponding branching fraction is measured to be B(B0sāĻKā0) = (1.10 Ā± 0.24 (stat) Ā± 0.14 (syst) Ā± 0.08 (f d /f s )) Ć 10ā6, where the uncertainties are statistical, systematic and from the ratio of fragmentation fractions f d /f s which accounts for the different production rate of B 0 and B0s mesons. The significance of B0sāĻKā0 signal is 6.1 standard deviations. The fraction of longitudinal polarization in B0sāĻKā0 decays is found to be f 0 = 0.51 Ā± 0.15 (stat) Ā± 0.07 (syst)
Observation of the suppressed ADS modes BĀ± ā [ĻĀ±K-/+ Ļ+Ļ-]D KĀ± and BĀ± ā [ĻĀ± K-/+Ļ+Ļ-]DĻĀ±
An analysis of and BĀ± ā DKĀ± and BĀ± ā DĻĀ±
decays is presented where the D meson is reconstructed in the four-body final state KĀ± Ļ-/+Ļ+Ļ-. Using LHCb data corresponding to an integrated luminosity of 1.0 fb-1, first observations are made of the suppressed ADS modes BĀ± ā[ĻĀ± K-/+Ļ+Ļ-]DKĀ± and BĀ± ā [ĻĀ± K-/+Ļ+Ļ-]DĻĀ± with a significance of 5.1 sigma and greater than 10 sigma, respectively. Measurements of CP asymmetries and CP-conserving ratios of partial widths from this family of decays are also performed. The magnitude of the ratio between the suppressed and favoured BĀ± ā DK Ā± amplitudes is determined to be rKB = 0.097 Ā± 0.011
First evidence of direct CP violation in charmless two-body decays of Bs0 mesons
Using a data sample corresponding to an integrated luminosity of 0.35āāfb-1 collected by LHCb in 2011, we report the first evidence of CP violation in the decays of Bs0 mesons to KĀ±Ļā pairs, ACP(Bs0āKĻ)= 0.27Ā±0.08(stat)Ā±0.02(syst), with a significance of 3.3Ļ. Furthermore, we report the most precise measurement of CP violation in the decays of B0 mesons to KĀ±Ļā pairs, ACP(B0āKĻ)=-0.088Ā±0.011(stat)Ā±0.008(syst), with a significance exceeding 6Ļ
When evolution is the solution to pollution : key principles, and lessons from rapid repeated adaptation of killifish (Fundulus heteroclitus) populations
Ā© The Author(s), 2017. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Evolutionary Applications 10 (2017): 762ā783, doi:10.1111/eva.12470.For most species, evolutionary adaptation is not expected to be sufficiently rapid to buffer the effects of human-mediated environmental changes, including environmental pollution. Here we review how key features of populations, the characteristics of environmental pollution, and the genetic architecture underlying adaptive traits, may interact to shape the likelihood of evolutionary rescue from pollution. Large populations of Atlantic killifish (Fundulus heteroclitus) persist in some of the most contaminated estuaries of the United States, and killifish studies have provided some of the first insights into the types of genomic changes that enable rapid evolutionary rescue from complexly degraded environments. We describe how selection by industrial pollutants and other stressors has acted on multiple populations of killifish and posit that extreme nucleotide diversity uniquely positions this species for successful evolutionary adaptation. Mechanistic studies have identified some of the genetic underpinnings of adaptation to a well-studied class of toxic pollutants; however, multiple genetic regions under selection in wild populations seem to reflect more complex responses to diverse native stressors and/or compensatory responses to primary adaptation. The discovery of these pollution-adapted killifish populations suggests that the evolutionary influence of anthropogenic stressors as selective agents occurs widely. Yet adaptation to chemical pollution in terrestrial and aquatic vertebrate wildlife may rarely be a successful āsolution to pollutionā because potentially adaptive phenotypes may be complex and incur fitness costs, and therefore be unlikely to evolve quickly enough, especially in species with small population sizes.National Science Foundation Grant Numbers: DEB-1265282, OCE-1314567, DEB-1120263;
National Institutes of Environmental Health Sciences Grant Numbers: R01ES021934-01, P42ES007381;
Postdoctoral Research Program at the US Environmental Protection (US EPA);
Office of Research and Development;
Oak Ridge Institute for Science and Education (ORISE) Grant Number: DW92429801;
US Department of Energ
Strong constraints on the rare decays Bs0 -> Ī¼+Ī¼- and B0 -> Ī¼+Ī¼-
A search for Bs0āĪ¼+Ī¼- and B0āĪ¼+Ī¼- decays is performed using 1.0āāfb-1 of pp collision data collected at ās=7āāTeV with the LHCb experiment at the Large Hadron Collider. For both decays, the number of observed events is consistent with expectation from background and standard model signal predictions. Upper limits on the branching fractions are determined to be B(Bs0āĪ¼+Ī¼-)<4.5(3.8)Ć10-9 and B(B0āĪ¼+Ī¼-)<1.0(0.81)Ć10-9 at 95% (90%) confidence level
- ā¦