Home OALib Journal OALib PrePrints Submit Ranking News My Lib FAQ About Us Follow Us+
 Title Keywords Abstract Author All
Search Results: 1 - 10 of 100 matches for " "
 Physics , 2012, DOI: 10.1007/JHEP02(2013)010 Abstract: We predict the amplitude of the $B\to K \ell^+\ell^-$ decay in the region of the dilepton invariant mass squared $0  Robert Knegjens Physics , 2014, Abstract: In light of recent LHC results for the extraction of the$B_s$mixing phase$\phi_s$, we can already conclude that if New Physics (NP) is present in this observable, it is hiding pretty well. Thus, as our hunt continues, we must be weary not to confuse NP for penguin effects, or vice versa. In this talk the progress made towards addressing hadronic uncertainties in extractions of$\phi_s$from$B_s\to J/\psi \phi$is reviewed, and the nature of the scalar$f_0(980)$state, which plays a dominant role in the extraction of$\phi_s$from the$B_s\to J/\psi \pi^+\pi^-$decay, is discussed.  Physics , 2015, DOI: 10.1103/PhysRevD.92.034503 Abstract: Measurements of the$\Lambda_b \to p \ell^- \bar{\nu}_\ell$and$\Lambda_b \to \Lambda_c \ell^- \bar{\nu}_\ell$decay rates can be used to determine the magnitudes of the CKM matrix elements$V_{ub}$and$V_{cb}$, provided that the relevant hadronic form factors are known. Here we present a precise calculation of these form factors using lattice QCD with 2+1 flavors of dynamical domain-wall fermions. The$b$and$c$quarks are implemented with relativistic heavy-quark actions, allowing us to work directly at the physical heavy-quark masses. The lattice computation is performed for six different pion masses and two different lattice spacings, using gauge-field configurations generated by the RBC and UKQCD collaborations. The$b \to u$and$b \to c$currents are renormalized with a mostly nonperturbative method. We extrapolate the form factor results to the physical pion mass and the continuum limit, parametrizing the$q^2$-dependence using$z$-expansions. The form factors are presented in such a way as to enable the correlated propagation of both statistical and systematic uncertainties into derived quantities such as differential decay rates and asymmetries. Using these form factors, we present predictions for the$\Lambda_b \to p \ell^- \bar{\nu}_\ell$and$\Lambda_b \to \Lambda_c \ell^- \bar{\nu}_\ell$differential and integrated decay rates. Combined with experimental data, our results enable determinations of$|V_{ub}|$,$|V_{cb}|$, and$|V_{ub}/V_{cb}|$with theory uncertainties of 4.4%, 2.2%, and 4.9%, respectively.  Damir Becirevic Physics , 1996, DOI: 10.1103/PhysRevD.54.6842 Abstract: The bounds on the form factors for$B \to \rho \ell \nu_\ell$decay are studied. Constrained by lattice data and a constrained conformal mapping, the more informations can be obtained for$A_1(q^2)$form-factor which dominates the decay rate at large$q^2$. Specifically, we confirm a moderately increasing behavior of this form factor.  Matthias Neubert Physics , 1994, Abstract: I discuss the theoretical uncertainties in the extraction of$|\,V_{cb}|$from a measurement of the$\bar B\to D^*\ell\,\bar\nu$decay rate close to zero recoil. In particular, I combine previous estimates of the$1/m_Q^2$corrections to the normalization of the hadronic form factor at zero recoil with sum rules derived by Shifman {\it et al}.\ to obtain a new prediction with less uncertainty. I also give a prediction for the slope of the form factor$\widehat\xi(w)$at zero recoil:$\widehat\varrho^2=0.7\pm 0.2$. Using the most recent experimental results, I obtain the model-independent value$|\,V_{cb}|=0.0395\pm 0.0030$.  Physics , 2008, DOI: 10.1103/PhysRevD.77.065026 Abstract: We review the uncertainties in the spin-independent and -dependent elastic scattering cross sections of supersymmetric dark matter particles on protons and neutrons. We propagate the uncertainties in quark masses and hadronic matrix elements that are related to the$\pi$-nucleon$\sigma$term and the spin content of the nucleon. By far the largest single uncertainty is that in spin-independent scattering induced by our ignorance of the$$matrix elements linked to the$\pi$-nucleon$\sigma$term, which affects the ratio of cross sections on proton and neutron targets as well as their absolute values. This uncertainty is already impacting the interpretations of experimental searches for cold dark matter. {\it We plead for an experimental campaign to determine better the$\pi$-nucleon$\sigma$term.} Uncertainties in the spin content of the proton affect significantly, but less strongly, the calculation of rates used in indirect searches.  Physics , 2015, DOI: 10.1103/PhysRevLett.115.152002 Abstract: The rare decay$B\to\pi\ell^+\ell^-$arises from$b\to d$flavor-changing neutral currents and could be sensitive to physics beyond the Standard Model. Here, we present the first$ab$-$initio$QCD calculation of the$B\to\pi$tensor form factor$f_T$. Together with the vector and scalar form factors$f_+$and$f_0$from our companion work [J. A. Bailey$et~al.$, Phys. Rev. D 92, 014024 (2015)], these parameterize the hadronic contribution to$B\to\pi$semileptonic decays in any extension of the Standard Model. We obtain the total branching ratio${\text{BR}}(B^+\to\pi^+\mu^+\mu^-)=20.4(2.1)\times10^{-9}$in the Standard Model, which is the most precise theoretical determination to date, and agrees with the recent measurement from the LHCb experiment [R. Aaij$et~al.$, JHEP 1212, 125 (2012)]. Note added: after this paper was submitted for publication, LHCb announced a new measurement of the differential decay rate for this process [T. Tekampe, talk at DPF 2015], which we now compare to the shape and normalization of the Standard-Model prediction.  Gustavo Burdman Physics , 1995, DOI: 10.1103/PhysRevD.52.6400 Abstract: We study the potential of$B\to K^{(*)} \ell^+\ell^-\$ decays as tests of the standard model. After discussing the reliability of theoretical predictions for the hadronic matrix elements involved, we examine the impact of different new physics scenarios on various observables. We show that the angular information in \bks together with the dilepton mass distribution can highly constrain new physics. This is particularly true in the large dilepton mass region, where reliable predictions for the hadronic matrix elements can be made with presently available data. We compare the Standard Model predictions with those of a Two-Higgs doublet model as well as TopColor models, all of which give distinct signals in this region.