2,816 research outputs found
First observation of Bs0 â D*s2+XÎŒ-Îœ decays
Using data collected with the LHCb detector in protonâproton collisions at a centre-of-mass energy of 7 TeV, the semileptonic decays B0sâD+sXÎŒâÎœ and B0sâD0K+XÎŒâÎœ are detected. Two structures are observed in the D0K+ mass spectrum at masses consistent with the known Ds1(2536)+ and Dâs22573)+ mesons. The measured branching fractions relative to the total B0s semileptonic rate are B(B0sâDâ+s2XÎŒâÎœ)/B(B0sâXÎŒâÎœ) = (3.3±1.0±0.4)%, and B(B0sâD+s1XÎŒâÎœ)/B(B0sâXÎŒâÎœ) = (5.4±1.2±0.5)%, where the ïŹrst uncertainty is statistical and the second is systematic. This is the ïŹrst observation of the Dâ+s2 state in B0s decays; we also measure its mass and width
Measurement of the Bs0-Bs0 oscillation frequency ÎŽms in Bs0âDs-(3)Ï decays
The Bs0-Bs0 oscillation frequency ÎŽms 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 Bs0âDs-Ï+ and Bs0âDs-Ï+Ï-Ï + signal decays are reconstructed, with average decay time resolutions of 44 fs and 36 fs, respectively. An oscillation signal with a statistical significance of 4.6Ï is observed. The measured oscillation frequency is ÎŽm s=17.63±0.11(stat)±0.02(syst)ps -1
The gamma-ray telescope Gamma-1
French and Soviet specialists have designed and built the gamma-ray telescope GAMMA-1 to detect cosmic gamma rays above 50 MeV. The sensitive area of the detector is 1400 sq cm, energy resolution is 30% at 300 MeV, and angular resolution 1.2 deg at 300 MeV (and less than 20' arc when a coded aperture mask is used). Results on calibration of the qualification model and Monte-Carlo calculations are presented
The use of quantum-correlated D^0 decays for phi3 measurement
We report the results of the Monte-Carlo study of the method to determine the
CKM angle phi3 using Dalitz plot analysis of D0 decay from B->DK process. Our
main goal is to find the optimal strategy for a model-independent phi3
extraction. We find that the analysis using decays of CP-tagged D mesons only
cannot provide a completely model-independent measurement in the case of
limited data sample. The procedure involving binned analysis of B->DK and
psi(3770)->(K0 pi+ pi-)_D (K0 pi+ pi-)_D decays is proposed, that allows to
reach the phi3 precision comparable to unbinned model-dependent fit.Comment: Replaced by journal versio
A model-independent Dalitz plot analysis of B±âDK± with DâK0Sh+hâ (h=Ï,K) decays and constraints on the CKM angle Îł
A binned Dalitz plot analysis of B ±âDK ± decays, with DâKS0Ï+Ï- and DâKS0K+K-, is performed to measure the CP-violating observables x ± and y ± which are sensitive to the CKM angle Îł. 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 -=(0.0±4.3±1.5±0.6)Ă10 -2, y -=(2.7±5.2±0.8±2.3)Ă10 -2, x +=(-10.3±4.5±1.8±1.4)Ă10 -2 and y +=(-0.9±3.7±0.8±3.0)Ă10 -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 Îł=(44-38+43)°, with a second solution at ÎłâÎł+180°, and r B=0.07±0.04, where r B is the ratio between the suppressed and favoured B decay amplitudes
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
Strong constraints on the rare decays Bs0 -> Ό+Ό- and B0 -> Ό+Ό-
A search for Bs0âÎŒ+ÎŒ- and B0âÎŒ+ÎŒ- decays is performed using 1.0ââfb-1 of pp collision data collected at âs=7ââTeV 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(Bs0âÎŒ+ÎŒ-)<4.5(3.8)Ă10-9 and B(B0âÎŒ+ÎŒ-)<1.0(0.81)Ă10-9 at 95% (90%) confidence level
First evidence of direct CP violation in charmless two-body decays of Bs0 mesons
Using a data sample corresponding to an integrated luminosity of 0.35ââfb-1 collected by LHCb in 2011, we report the first evidence of CP violation in the decays of Bs0 mesons to K±Ïâ pairs, ACP(Bs0âKÏ)= 0.27±0.08(stat)±0.02(syst), with a significance of 3.3Ï. Furthermore, we report the most precise measurement of CP violation in the decays of B0 mesons to K±Ïâ pairs, ACP(B0âKÏ)=-0.088±0.011(stat)±0.008(syst), with a significance exceeding 6Ï
Search for the rare decays B0sâÎŒ+ÎŒâ and B0âÎŒ+ÎŒâ
A search for the decays and B0âÎŒ+ÎŒâ is performed with 0.37 fbâ1 of pp collisions at collected by the LHCb experiment in 2011. The upper limits on the branching fractions are and B(B0âÎŒ+ÎŒâ)<3.6Ă10â9 at 95% confidence level. A combination of these results with the LHCb limits obtained with the 2010 dataset leads to and B(B0âÎŒ+ÎŒâ)<3.2Ă10â9 at 95% confidence level
Highlights from Five Years at the B Factories
The highlights and conflicts at the B Factories are briefly reviewed.
violation was established in 2001 in and related modes,
which has now become a precision measurement of CP violation in - mixing. However, the situation for the and charmless
modes, which probe also CP violation in the {\it decay} amplitude, are
not quite settled yet. They could be hinting at presence of both strong (CP
conserving) and new physics (CP violating) phases. We critically assess the
developments and discuss some related discrepancies and highlights, such as
observation of direct CP violation, and make a projection towards the next few
years.Comment: 16 pages, 5 figures, to appear as Brief Review in Mod. Phys. Lett.
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