1,343 research outputs found
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
A model-independent Dalitz plot analysis of BĀ±āDKĀ± with DāK0Sh+hā (h=Ļ,K) decays and constraints on the CKM angle Ī³
A binned Dalitz plot analysis of B Ā±āDK Ā± decays, with DāKS0Ļ+Ļ- and DāKS0K+K-, is performed to measure the CP-violating observables x Ā± and y Ā± which are sensitive to the CKM angle Ī³. The analysis exploits 1.0 fb -1 of data collected by the LHCb experiment. The study makes no model-based assumption on the variation of the strong phase of the D decay amplitude over the Dalitz plot, but uses measurements of this quantity from CLEO-c as input. The values of the parameters are found to be x -=(0.0Ā±4.3Ā±1.5Ā±0.6)Ć10 -2, y -=(2.7Ā±5.2Ā±0.8Ā±2.3)Ć10 -2, x +=(-10.3Ā±4.5Ā±1.8Ā±1.4)Ć10 -2 and y +=(-0.9Ā±3.7Ā±0.8Ā±3.0)Ć10 -2. The first, second, and third uncertainties are the statistical, the experimental systematic, and the error associated with the precision of the strong-phase parameters measured at CLEO-c, respectively. These results correspond to Ī³=(44-38+43)Ā°, with a second solution at Ī³āĪ³+180Ā°, and r B=0.07Ā±0.04, where r B is the ratio between the suppressed and favoured B decay amplitudes
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)
Measurement of the resonant and CP components in BĀÆ 0 ā J=ĻĻĆ¾Ļā decays
The resonant structure of the reaction BĀÆ0āJ/ĻĻ+Ļā is studied using data from 3āāfbā1 of integrated luminosity collected by the LHCb experiment, one third at 7 TeV center-of-mass energy and the remainder at 8 TeV. The invariant mass of the Ļ+Ļā pair and three decay angular distributions are used to determine the fractions of the resonant and nonresonant components. Six interfering Ļ+Ļā states, Ļ(770), f0(500), f2(1270), Ļ(1450), Ļ(782) and Ļ(1700), are required to give a good description of invariant mass spectra and decay angular distributions. The positive and negative charge parity fractions of each of the resonant final states are determined. The f0(980) meson is not seen and the upper limit on its presence, compared with the observed f0(500) rate, is inconsistent with a model where these scalar mesons are formed from two quarks and two antiquarks (tetraquarks) at the eight standard deviation level. In the qqĀÆ model, the absolute value of the mixing angle between the f0(980) and the f0(500) scalar mesons is limited to be less than 17Ā° at 90% confidence level
Search for the rare decays B0sāĪ¼+Ī¼ā and B0āĪ¼+Ī¼ā
A search for the decays and B0āĪ¼+Ī¼ā is performed with 0.37 fbā1 of pp collisions at collected by the LHCb experiment in 2011. The upper limits on the branching fractions are and B(B0āĪ¼+Ī¼ā)<3.6Ć10ā9 at 95% confidence level. A combination of these results with the LHCb limits obtained with the 2010 dataset leads to and B(B0āĪ¼+Ī¼ā)<3.2Ć10ā9 at 95% confidence level
Study of beauty hadron decays into pairs of charm hadrons
First observations of the decays Īb 0 ā Īc +D(s) - are reported using data corresponding to an integrated luminosity of 3fb-1 collected at 7 and 8 TeV center-of-mass energies in proton-proton collisions with the LHCb detector. In addition, the most precise measurement of the branching fraction B(Bs 0āD+Ds -) is made and a search is performed for the decays B(s) 0āĪc +Īc -. The results obtained are B(Īb 0āĪc +D-)/ B(Īb 0āĪc +D s -)=0.042Ā±0.003(stat)Ā±0.003(syst), [B(Īb 0āĪc +D s -)/B(BĢ0āD+D s -)]/[B(Īb 0āĪ c +Ļ-)/B(BĢ0āD +Ļ-)]=0.96Ā±0.02(stat)Ā±0.06(syst),B(B s 0āD+Ds -)/ B(BĢ0āD+Ds -)=0. 038Ā±0.004(stat)Ā±0.003(syst),B(BĢ0āĪ c +Īc -)/B(BĢ 0āD+Ds -)<0.0022[95%C.L.], B(Bs 0āĪc +Ī c -)/B(Bs 0āD+D s -)<0.30[95%C.L.]. Measurement of the mass of the Īb 0 baryon relative to the BĢ0 meson gives M(Īb 0)-M(BĢ0)=339. 72Ā±0.24(stat)Ā±0.18(syst)MeV/c2. This result provides the most precise measurement of the mass of the Īb 0 baryon to date
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
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