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Isolating New Physics Effects from Hadronic Form Factor Uncertainties in B\to K^* \ell^+\ell^-  [PDF]
Diganta Das,Rahul Sinha
Physics , 2012,
Abstract: The discovery of New Physics, using weak decays of mesons is difficult due to intractable strong interaction effects needed to describe it. We show how the multitude of "related observables" obtained from B\to K^* \ell^+\ell^-, can provide many new "clean tests" of the Standard Model. The hallmark of these tests is that several of them are independent of the unknown form factors required to describe the decay using heavy quark effective theory. We derive a relation between observables that is free of form factors and Wilson coefficients, the violation of which will be an unambiguous signal of New Physics. We also derive other relations between observables and form factors that are independent of Wilson coefficients and enable verification of hadronic estimates. We find that the allowed parameter space for observables is very tightly constrained in Standard Model, thereby providing clean signals of New Physics. The relations derived will provide unambiguous signals of New Physics if it contributes to these decays.
New Physics Effects and Hadronic Form Factor Uncertainties in B -> K^* l^+ l^-  [PDF]
Diganta Das,Rahul Sinha
Physics , 2012, DOI: 10.1103/PhysRevD.86.056006
Abstract: It is well known that New Physics can contribute to weak decays of heavy mesons via virtual processes during its decays. The discovery of New Physics, using such decays is made difficult due to intractable strong interaction effects needed to describe it. Modes such as B -> K^* l^+ l^- offer an advantage as they provide a multitude of observables via angular analysis. We show how the multitude of "related observables" obtained from B -> K^* l^+ l^-, can provide many new "clean tests" of the Standard Model. The hallmark of these tests is that several of them are independent of the unknown universal form factors in heavy quark effective theory. We derive a relation between observables that is free of form factors and Wilson coefficients, the violation of which will be an unambiguous signal of New Physics. We also derive relations between observables and form factors that are independent of Wilson coefficients and enable verification of hadronic estimates. We show how form factor ratios can be measured directly from helicity fraction with out any assumptions what so ever. We find that the allowed parameter space for observables is very tightly constrained in Standard Model, thereby providing clean signals of New Physics. We examine both the large-recoil and low-recoil regions of the K^* meson and point out special features and derive relations between observables valid in the two limits. In the large-recoil regions several of the relations are unaffected by corrections to all orders in \alpha_s. We present yet another new relation involving only observables that would verify the validity of the relations between form-factors assumed in the low-recoil region. The several relations and constraints derived will provide unambiguous signals of New Physics if it contributes to these decays.
$B \to K \ell^{+}\ell^{-}$ decay at large hadronic recoil  [PDF]
A. Khodjamirian,Th. Mannel,Y. -M. Wang
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
Addressing Hadronic Uncertainties in Extractions of $φ_s$  [PDF]
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.
$Λ_b \to p \ell^- \barν_\ell$ and $Λ_b \to Λ_c \ell^- \barν_\ell$ form factors from lattice QCD with relativistic heavy quarks  [PDF]
William Detmold,Christoph Lehner,Stefan Meinel
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.
$B \to ρ\ell ν_\ell$ Form Factors  [PDF]
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.
Theoretical Uncertainties in the Extraction of $|V_{cb}|$ from $\bar B\to D^*\ell\,\barν$ Decays near Zero Recoil  [PDF]
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 $|\,V_{cb}|=0.0395\pm 0.0030$.
Hadronic Uncertainties in the Elastic Scattering of Supersymmetric Dark Matter  [PDF]
John Ellis,Keith A. Olive,Christopher Savage
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.
$B\toπ\ell\ell$ form factors for new-physics searches from lattice QCD  [PDF]
Jon A. Bailey,A. Bazavov,C. Bernard,C. M. Bouchard,C. DeTar,Daping Du,A. X. El-Khadra,E. D. Freeland,E. Gamiz,Steven Gottlieb,U. M. Heller,A. S. Kronfeld,J. Laiho,L. Levkova,Yuzhi Liu,E. Lunghi,P. B. Mackenzie,Y. Meurice,E. Neil,Si-Wei Qiu,J. N. Simone,R. Sugar,D. Toussaint,R. S. Van de Water,Ran Zhou
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.
Testing the Standard Model in $B\to K^{(*)} \ell^+\ell^-$  [PDF]
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.
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