UTfit Collaboration Research Articles

New UTfit analysis of the unitarity triangle in the Cabibbo–Kobayashi–Maskawa scheme

Flavour mixing and CP violation as measured in weak decays and mixing of neutral mesons are a fundamental tool to test the Standard Model and to search for new physics. New analyses performed at the LHC experiment open an unprecedented insight into the Cabibbo–Kobayashi–Maskawa metrology and new evidence for rare decays. Important progress has also been achieved in theoretical calculations of several hadronic quantities with a remarkable reduction of the uncertainties. This improvement is essential since previous studies of the Unitarity Triangle did show that possible contributions from new physics, if any, must be tiny and could easily be hidden by theoretical and experimental errors. Thanks to the experimental and theoretical advances, the Cabibbo–Kobayashi–Maskawa picture provides very precise Standard Model predictions through global analyses. We present here the results of the latest global Standard Model analysis performed by the UTfit collaboration including all the most updated inputs from experiments, lattice Quantum Chromo-Dynamics and phenomenological calculations.

Standard model evaluation ofϵKusing lattice QCD inputs forB^KandVcb

We report the Standard Model evaluation of the indirect CP violation parameter $\varepsilon_K$ using inputs determined from lattice QCD: the kaon bag parameter $\hat{B}_K$, $\xi_0$, $|V_{us}|$ from the $K_{\ell 3}$ and $K_{\mu 2}$ decays, and $|V_{cb}|$ from the axial current form factor for the exclusive decay $\bar{B} \to D^* \ell \bar{\nu}$ at zero-recoil. The theoretical expression for $\varepsilon_K$ is thoroughly reviewed to give an estimate of the size of the neglected corrections, including long distance effects. The Wolfenstein parametrization $(|V_{cb}|, \lambda, \bar{\rho}, \bar{\eta})$ is adopted for CKM matrix elements which enter through the short distance contribution of the box diagrams. For the central value, we take the Unitarity Triangle apex $(\bar{\rho}, \bar{\eta})$ from the angle-only fit of the UTfit collaboration and use $V_{us}$ as an independent input to fix $\lambda$. We find that the Standard Model prediction of $\varepsilon_K$ with exclusive $V_{cb}$ (lattice QCD results) is lower than the experimental value by $3.4\sigma$. However, with inclusive $V_{cb}$ (results of the heavy quark expansion), there is no gap between the Standard Model prediction of $\varepsilon_K$ and its experimental value. For the calculation of $\varepsilon_K$, we perform the renormalization group running to obtain $\eta_{cc}$ at next-to-next-to-leading-order; we find $\eta_{cc}^\mathrm{NNLO}=1.72(27)$.

The UTfit collaboration average of D meson mixing data: Winter 2014

We update the analysis of $D$ meson mixing including the latest experimental results as of January 2014. We derive constraints on the parameters $M_{12}$, $\Gamma_{12}$ and $\Phi_{12}$ that describe $D$ meson mixing using all available data, allowing for CP violation. We also provide posterior distributions for observable parameters appearing in $D$ physics.

Implication of nonuniversalZ′boson to the lepton polarization asymmetries in theB→K*ℓ+ℓ−decay

In this work we study the implication of the nonuniversal ${Z}^{\ensuremath{'}}$ model to the double lepton polarization asymmetries in the $B\ensuremath{\rightarrow}{K}^{*}{\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}}$, $(l=\ensuremath{\mu},\ensuremath{\tau})$ decay. To see the variation in the values of lepton polarization asymmetries from the standard model values, we have taken bounds of the UTfit collaboration, namely, ${S}_{1}$ and ${S}_{2}$ on the values of different parameters of the universal ${Z}^{\ensuremath{'}}$ model such as left-right couplings of the extra gauge boson with leptons and the new weak phase ${\ensuremath{\phi}}_{sb}$. It is found that double lepton polarization asymmetries are sensitive to the coupling parameters of ${Z}^{\ensuremath{'}}$ boson with fermions. Therefore, the measurements of these lepton polarization asymmetries for the above-mentioned decay at current colliders can be helpful to clarify the status of the existence of the extra gauge boson, i.e., ${Z}^{\ensuremath{'}}$.

Standard Model updates and new physics analysis with the Unitarity Triangle fit

We present the summer 2012 update of the Unitarity Triangle (UT) analysis performed by the UTfit Collaboration within the Standard Model (SM) and beyond. The increased accuracy on several of the fundamental constraints is now enhancing some of the tensions amongst and within the constraint themselves. In particular, the long standing tension between exclusive and inclusive determinations of the Vub and Vcb CKM matrix elements is now playing a major role. Then we present the generalisation the UT analysis to investigate new physics (NP) effects, updating the constraints on NP contributions to ΔF=2 processes. In the NP analysis, both CKM and NP parameters are fitted simultaneously to obtain the possible NP effects in any specific sector. Finally, based on the NP constraints, we derive upper bounds on the coefficients of the most general ΔF=2 effective Hamiltonian. These upper bounds can be translated into lower bounds on the scale of NP that contributes to these low-energy effective interactions.

The UTfit collaboration average of D meson mixing data: spring 2012

Abstract We derive constraints on the parameters M 12, Γ12 and Φ12 that describe D meson mixing using all available data, allowing for CP violation. We also provide posterior distributions and predictions for observable parameters appearing in D physics.

Unitarity Triangle Analysis: An Update

We present the update of the Unitarity Triangle analysis performed by the UTfit Collaboration within the Standard Model and beyond. Within the Standard Model, we find an overall consistency among the constraints, with some tension between the fit prediction and the experimental measurement of BR ( B → τ ν ) , sin 2 β and e K . Generalising the analysis beyond the Standard Model, we allow for New Physics effects in all Δ F = 2 processes simultanously. We obtain constraints on the parameters of the Cabibbo-Kobayashi-Maskawa matrix together with the New Physics ones. We find that a deviation from the Standard Model at the 3.1σ level in the B s - B ¯ s mixing phase is confirmed by the present update, which includes the new DO result on the dimuon charge asymmetry. However the new CDF measurement of ϕ s is not included yet as the experimental likelihood is not publicly available.

Formula omitted] from exclusive semileptonic [formula omitted] decays

We use Omnès representations of the form factors V, A1 and A2 for exclusive semileptonic B→ρ decays, and apply them to combine experimental partial branching fraction information with theoretical calculations of the three form factors to extract |Vub|. We find |Vub|=(2.8±0.2stat±0.5sys)×10−3, where we have conservatively assumed a 20% systematic error to account for the use of the quenched approximation in the lattice QCD calculations of the form factors. This value of |Vub| is slightly lower than the values extracted from exclusive semileptonic B→π decays, (3.47±0.29±0.03)×10−3 [J.M. Flynn, J. Nieves, Phys. Rev. D 76 (2007) 031302], (3.36±0.23)×10−3 [C. Bourrely, I. Caprini, L. Lellouch, Phys. Rev. D 79 (2009) 013008], (3.38±0.35)×10−3 [J. Bailey, et al., arXiv:0811.3640 [hep-lat]], and using all other inputs in CKM fits, (3.55±0.15)×10−3 [UTfit Collaboration M. Bona, et al., JHEP 0610 (2006) 081, hep-ph/0606167; UTfit Collaboration, http://utfit.roma1.infn.it/ckm-results/ckm-results.html]. The disagreement is greater when we compare to the result extracted from inclusive B→Xulν decays, |Vub|=(4.10±0.30exp±0.29th)×10−3 [M. Neubert, in: Proceedings of FPCP 2007: 5th Conference on Flavor Physics and CP Violation, Bled, Slovenia, 12–16 May 2007 (2007)].

First evidence of new physics in [formula omitted] mixing and its implications

We present an update of the analysis of B s mixing by the UTfit Collaboration, including the very recent tagged analyses of B s → J / Ψ ϕ by the CDF and DO collaborations. We find that the phase of the B s mixing amplitude deviates more than 2.9σ from the Standard Model prediction. This results points to extensions of the Standard Model with new sources of CP violation. We compare this result with the analysis of B d mixing and show that present data favour the presence of a new source of flavour violation. Finally, we consider the impact of this analysis for SUSY models and the possible implications for new physics effects in b → s hadronic penguin decays.

CP violation in [formula omitted] mixing in the SUSY SU(5) GUT with right-handed neutrinos

It is recently announced by the UTfit Collaboration that the CP phase of the Bs mixing amplitude, ϕBs, deviates more than 3σ from the Standard Model prediction. In this Letter we discuss how large correction to ϕBs is possible in the supersymmetric SU(5) ground unified model (SUSY SU(5) GUT) with right-handed neutrinos. Here, we assume the supergravity-like boundary condition for the SUSY-breaking terms. We found that the 95% probability region derived by the UTfit Collaboration is marginal in this model.

Lattice QCD confronts the Unitarity Triangle Fit

Before the starting of the B factories, the Unitarity Triangle (UT) analysis relied on the results of lattice QCD simulations to relate the experimental determinations of semileptonic B decays, K 0 − K ¯ 0 and B d , s 0 − B ¯ d , s 0 mixing to the CKM parameters. In the last years, much more information has been obtained from the direct determination of the UT angles from non-leptonic B decays. In this talk, we compare the results of the “classical” UT analysis (UTlattice) with the analysis based on the angles determinations (UTangles). We show that the recent measurement of Δ m s , combined with Δ m d and e K , allows from this comparison a quite accurate extraction of the values of the lattice parameters, B ˆ K , f B s B ˆ B s 1 / 2 , ξ and f B . These values, obtained “experimentally” by assuming the validity of the Standard Model, can be compared with the theoretical predictions from lattice QCD. We also discuss the different determinations of V u b and show that current data do not favor the value measured in inclusive decays. Finally, we present updated predictions for the leptonic branching fraction B R ( B → τ ν τ ) , and compare them with the recent experimental determination. We take the opportunity of this write up to update the results of ref. [M. Bona et al. [UTfit Collaboration], arXiv:hep-ph/0606167 ] with the most recent results presented at the ICHEP'06 conference.

The UTfit collaboration report on the status of the unitarity triangle beyond the Standard Model I. Model-independent analysis and minimal flavour violation

Starting from a (new physics independent) tree level determination of and , we perform the Unitarity Triangle analysis in general extensions of the Standard Model with arbitrary new physics contributions to loop-mediated processes. Using a simple parameterization, we determine the allowed ranges of non-standard contributions to |ΔF| = 2 processes. Remarkably, the recent measurements from B factories allow us to determine with good precision the shape of the Unitarity Triangle even in the presence of new physics, and to derive stringent constraints on non-standard contributions to |ΔF| = 2 processes. Since the present experimental constraints favour models with Minimal Flavour Violation, we present the determination of the Universal Unitarity Triangle that can be defined in this class of extensions of the Standard Model. Finally, we perform a combined fit of the Unitarity Triangle and of new physics contributions in Minimal Flavour Violation, reaching a sensitivity to a new physics scale of about 5 TeV. We also extrapolate all these analyses into a ``year 2010'' scenario for experimental and theoretical inputs in the flavour sector. All the results presented in this paper are also available at the URL http://www.utfit.org, where they are continuously updated.

The 2004 UTfit collaboration report on the status of the unitarity triangle in the standard model

Using the latest determinations of several theoretical and experimental parameters, we update the Unitarity Triangle analysis in the Standard Model. The basic experimental constraints come from the measurements of |V_ub/V_cb|, Delta M_d, the lower limit on Delta M_s, epsilon_k, and the measurement of the phase of the B_d - anti B_d mixing amplitude through the time-dependent CP asymmetry in B^0 to J/psi K^0 decays. In addition, we consider the direct determination of alpha, gamma, 2 beta + gamma and cos(2 beta) from the measurements of new CP-violating quantities, recently performed at the B factories. We also discuss the opportunities offered by improving the precision of the various physical quantities entering in the determination of the Unitarity Triangle parameters. The results and the plots presented in this paper can also be found at http://www.utfit.org, where they are continuously updated with the newest experimental and theoretical results.