963 research outputs found
Unbinned model-independent measurements with coherent admixtures of multibody neutral meson decays
Various studies of Standard Model parameters involve measuring the properties
of a coherent admixture of and states. A typical example
is the determination of the Unitarity Triangle angle in the decays
, . A model-independent approach to perform this
measurement is proposed that has superior statistical sensitivity than the
well-established method involving binning of the decay
phase space. The technique employs Fourier analysis of the complex phase
difference between and decay amplitudes and can be
easily generalised to other similar measurements, such as studies of charm
mixing or determination of the angle from decays.Comment: 24 pages, 6 figures; Updated with published versio
The teaching profession in Europe : historical and sociological analysis
A possible effect of direct CP violation in D -> K-S(0)pi(+)pi(-) decay on the gamma measurement from B-+/- -> DK +/-, D -> K-S(0)pi(+)pi(-) Dalitz plot analysis is considered. Systematic uncertainty of gamma coming from the current limits on direct CP violation in D -> K-S(0)pi(+)pi(-) is estimated, and a modified model-independent procedure of B-+/- -> DK +/-, D -> K-S(0)pi(+)pi(-) Dalitz plot analysis is proposed that gives an unbiased gamma measurement even in presence of direct CP violation in charm decays. The technique is applicable to other threebody D decays such as D-0 -> (KSK+K-)-K-0, D-0 -> pi(+)pi(-)pi(0), etc
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
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
First observation of the decay B0sâÏKâ0
The first observation of the decay B0sâÏKâ0 is reported. The analysis is based on a data sample corresponding to an integrated luminosity of 1.0 fbâ1 of pp collisions at sâ=7 TeV, collected with the LHCb detector. A yield of 30 ± 6 B0sâ(K+Kâ)(KâÏ+) decays is found in the mass windows 1012.5 < M (K + K â) < 1026.5 MeV/c 2 and 746 < M(K â Ï +) < 1046 MeV/c 2. The signal yield is found to be dominated by B0sâÏKâ0 decays, and the corresponding branching fraction is measured to be B(B0sâÏKâ0) = (1.10 ± 0.24 (stat) ± 0.14 (syst) ± 0.08 (f d /f s )) Ă 10â6, 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 B0sâÏKâ0 signal is 6.1 standard deviations. The fraction of longitudinal polarization in B0sâÏKâ0 decays is found to be f 0 = 0.51 ± 0.15 (stat) ± 0.07 (syst)
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