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This thesis presents first measurements of moments of the hadronic nX2 distribution measured in inclusive semileptonic decays of B mesons to final states containing a charm quark, B 2!Xcl[nu]. The variable nX2 is a combination of the invariant mass of the charmed meson mX, its energy in the B-meson rest-frame EX;BRF, and a constant ~[Lambda] = 0.65 GeV, nX2 = mX2c4-2~[Lambda]EX, BRF + ~[Lambda]2. The moments nXk with k = 2,4,6 are measured as proposed by theory to constrain assumptions made in the theoretical description of inclusive observables in semileptonic B-meson decays. This description uses Heavy Quark Expansion (HQE), an effective QCD combined with an Operator Product Expansion. The measurement is based on a sample of 231.6 million e+e- 2![Upsilon](4S) 2!B$\bar{B}$ events recorded with the BABAR experiment at the PEP-II e+e--storage rings at SLAC. We reconstruct the semileptonic decay by identifying a charged lepton in events tagged by a fully reconstructed hadronic decay of the second B meson. Correction procedures are derived from Monte Carlo simulations to ensure an unbiased measurement of the moments of the nX2 distribution. All moments are measured requiring minimum lepton momenta between 0.8 GeV/c and 1.9 GeV/c in the rest frame of the B meson. Performing a simultaneous fit to the measured moments nXk up to order k = 6 combined with other measurements of moments of the lepton-energy spectrum in decays B 2!Xcl[nu] and moments of the photon-energy spectrum in decays B 2!Xs[gamma], we determine the quark-mixing parameter.
A largely model-independent measurement of the inclusive electron momentum spectrum and branching fraction for semileptonic decays of B mesons is presented based on data recorded at the[Upsilon](4S) resonance with the BABAR detector. Backgrounds from secondary charm decays are separated from prompt B decays using charge and angular correlations between the electron from one B meson and a high momentum electron tag from the second B meson. The resulting branching fraction is[Beta](B[yields] Xe[nu])= (10.87[+-] 0.18(stat)[+-] 0.30(syst))%. Based on this measurement we determine the CKM matrix elementV[sub cb].
This important book covers topics that are of major interest to the high energy physics community, including the most recent results from flavour factories, dark matter and neutrino physics. In addition, it considers future high energy machines.
This important book covers topics that are of major interest to the high energy physics community, including the most recent results from flavour factories, dark matter and neutrino physics. In addition, it considers future high energy machines.
The BABAR experiment at SLAC provides an opportunity for measurement of the Standard Model parameters describing CP violation. A method of measuring the CKM matrix element V[sub cb] using Inclusive Semileptonic B decays in events tagged by a fully reconstructed decay of one of the B mesons is presented here. This mode is considered to be one of the most powerful approaches due to its large branching fraction, simplicity of the theoretical description and very clean experimental signatures. Using fully reconstructed B mesons to flag B[bar B] event we were able to produce the spectrum and branching fraction for electron momenta P[sub C.M.S.]> 0.5 GeV/c. Extrapolation to the lower momenta has been carried out with Heavy Quark Effective Theory. The branching fractions are measured separately for charged and neutral B mesons. For 82 fb[sup -1] of data collected at BABAR we obtain: BR(B[sup [+-]] [yields] X e[bar [nu]]) = 10.63 [+-] 0.24 [+-] 0.29%, BR(B[sup 0] [yields] X e[bar [nu]]) = 10.68 [+-] 0.34 [+-] 0.31%, averaged BR(B [yields] X e[bar [nu]]) = 10.65 [+-] 0.19 [+-] 0.27%, ratio of Branching fractions BR(B[sup [+-]])/BR(B[sup 0]) = 0.996 [+-] 0.039 [+-] 0.015 (errors are statistical and systematic, respectively). They also obtain V[sub cb] = 0.0409 [+-] 0.00074 [+-] 0.0010 [+-] 0.000858 (errors are: statistical, systematic and theoretical).