Lifetime difference in B_s mixing: Standard Model and beyond
Andriy Badin, Fabrizio Gabbiani, Alexey A. Petrov
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7 pages, 5 figures. To be published in the proceedings of DPF-2009, Detroit, MI, July 2009, eConf C090726. Presented by Andriy Badin at APS DPF 2009 meeting
We present a calculation of $1/m_b^2$ corrections to the lifetime differences of $B_s$ mesons in the heavy-quark expansion. We find that they are small to significantly affect $ΔΓ$ $(B_s)$ and present the result for lifetime difference including non-perturbative $1/m_b$ and $1/m_b^2$ corrections. We also analyze the generic $ΔB$ = 1 New Physics contributions to the lifetime difference of $B_s$ mesons and provide several examples
The investigation of mixing phenomena and lifetime in neutral B meson systems provides an important testing ground for standard model flavour dynamics. Spectroscopic parameters has been used to calculate the pseudoscalar decay constant and predictions of mixing mass parameters and lifetimes of the B$_{d}$ and B$_{s}$ mesons.
A review of the results on B^0- \bar {\rm B^0} mixing and b-lifetimes obtained by CDF, LEP and SLD collaborations is presented with special emphasis on B^0_s- \bar {{\rm B}^0_s} mixing.
We re-examine constraints from the evidence for observation of the lifetime difference in $D^0$-${\bar D}^0$ mixing on the parameters of supersymmetric models with R-parity violation (RPV). We find that RPV SUSY can give large negative contribution to the lifetime difference. We also discuss the importance of the choice of weak or mass basis when placing the constraints on RPV-violating couplings from flavor mixing experiments.
We re-examine constraints from the recent evidence for observation of the lifetime difference in D^0 - \bar{D}^0 mixing on the parameters of supersymmetric models with R-parity violation (RPV). We find that RPV SUSY can give large negative contribution to the lifetime difference. We also discuss the importance of the choice of weak or mass basis when placing the constraints on RPV-violating couplings from flavor mixing experiments.
We present the summary of the Working Group on lifetimes, mixing and weak mixing phases in charm and beauty mesons at the CKM 2010 workshop. In the past year or so good progress was achieved on both experimental and theoretical sides. While this yields improvement in our understanding of neutral meson mixing, further work is necessary to achieve the highest possible precision in order to investigate current hints for deviations between experiment and standard model predictions. With the recent LHC startup we see bright prospects for the near term future for huge improvements.
We find that in the nonmanifest left-right (LR) model, an important LR mixing effect was not considered in the paper by E. Golowich, S. Pakvasa, and A. Petrov, Phys. Rev. Lett. 98, 181801 (2007).
New physics contribution to the lifetime difference in $D^0 - \bar{D}^0$ mixing is re-examined within the non-manifest Left-Right Symmetric Model. Diagrams with one of $ΔC = 1$ transitions, mediated by a propagator with $W_L - W_R$ mixing, are revisited. While these diagrams are believed to give the dominant contribution, compatible with the experimental data, it is shown that due to GIM cancelation, such diagrams are negligible in sum. Thus, Left-Right Symmetric Model contribution to the lifetime difference in $D^0 - \bar{D}^0$ mixing is about two orders of magnitude less than actual experime…
We present a calculation of 1/m^2_b corrections to the lifetime differences of B_s mesons ΔΓ_s in the heavy-quark expansion. We find that they are small to significantly affect ΔΓ_s and present the result for lifetime difference including non-perturbative 1/m_b and 1/m_b^2 corrections. We also analyze the generic ΔB = 1 New Physics contributions to ΔΓ_s and provide several examples.
We review the status of mixing and lifetimes of $b$-hadrons. We will show that $ΔΓ/ ΔM$, $a_{sl}$ and $ϕ$ are better suited to search for new physics effects than $ΔM$ alone, because of our poor knowledge of the decay constants. The theoretical precision in the determination of $Γ_{12} / M_{12}$ - which contains all information on $ΔΓ/ ΔM$, $a_{sl}$ and $ϕ$ - can be tested directly by investigating the lifetimes of $b$-hadrons, because both quantities rely on the same theoretical footing. In particular we will also present a numerical estimate for the lifetime of the $Ξ_b$-baryon.
In this talk we review the theoretical status of the lifetime ratios of heavy hadrons and of the B-mixing quantities $ΔM_s$, $ΔΓ_s$ and $ϕ_s$. While $ΔM_s$ and $ΔΓ_s$ suffer from large uncertainties due to the badly known decay constants, the ratio $ΔΓ_s / ΔM_s$ can be determined with almost no non-perturbative uncertainties, therefore it can be used to look for possible new physics effects.
The first general analysis of New Physics contributions to the D0-anti-D0 lifetime difference (equivalently Delta Gamma_D} is presented. The extent to which New Physics (NP) contributions to |Delta C|=1 processes can produce effects in Delta Gamma_D, even if such NP contributions are undetectable in the current round of D0 decay experiments, is studied. New Physics models which do and do not dominate the lifetime difference in the flavor SU(3) limit are identified. Specific examples are provided.
We update the Standard-Model predictions for several quantities related to $B_s - \bar B_s$ and $B_d - \bar B_d$ mixing. The mass and width differences in the $B_s$ system read $ ΔM_s^{\rm SM} = (17.3 \pm 2.6) ps^{-1}$ and $ΔΓ_s^{\rm SM}= (0.087 \pm 0.021) ps^{-1}$, respectively. The CP asymmetries in flavour-specific decays are $a_{\rm fs}^{s,\rm SM} = (1.9 \pm 0.3) \cdot 10^{-5}$ and $a_{\rm fs}^{d,\rm SM} = - (4.1 \pm 0.6) \cdot 10^{-4}$. We further critically discuss the sensitivity of $ΔΓ_d$ to new physics and the uncertainties in the relation between $ΔΓ_s$ and the branching fraction of …
We discuss neutral B_{s,d} meson mixing and b-hadron lifetimes from the perspective of recent lattice calculations. In particular, we consider matrix elements which can be combined with measured ΔM_{s,d} to constrain |V_{td}|, the lifetime ratios τ(Λ_b)/τ(B_d) and τ(B^-)/τ(B_d) and the lifetime difference, ΔΓ_s/Γ_s, in the neutral B_s meson system.
Measurements of the effective lifetimes of $B_s$-meson decays, which only require untagged rate analyses, allow us to probe the width difference $ΔΓ_s$ and the CP-violating phase $ϕ_s$ of $B^0_s$-$\bar B^0_s$ mixing. We point out that the dependence of the effective lifetime on non-linear terms in $ΔΓ_s$ allows for a determination of $ϕ_s$ and $ΔΓ_s$ given a pair of $B_s$ decays into CP-even and CP-odd final states. Using recent lifetime measurements of $B^0_s\to K^+K^-$ and $B^0_s\to J/ψf_0(980)$ decays, we illustrate this method and show how it complements the constraints in the $ϕ_s$-$ΔΓ_s$…
$B_d$ and $B_s$ meson systems play a fundamental role to test and improve our understanding of Standard Model flavor dynamics. The mixing parameters $Δm_{d,s}$ represent important constraints in the unitarity triangle analysis. Their theoretical estimates require non-perturbative calculations of B-meson decay constants and B-parameters; accurate results, recently obtained from the lattice, are reviewed. Other phenomenologically interesting quantities are the beauty hadron lifetime ratios and, the width differences and CP-violation parameters in $B_d$ and $B_s$ systems. We discuss their theoret…
The lifetime splitting between the B^+ and B_d^0 mesons has recently been calculated in the next-to-leading order of QCD. These corrections are necessary for a reliable theoretical prediction, in particular for the meaningful use of hadronic matrix elements computed with lattice QCD. Using results from quenched lattice QCD we find tau(B^+)/tau(B^0_d)=1.053 +/- 0.016 +/- 0.017, where the uncertainties from unquenching and 1/m_b corrections are not included. The lifetime difference of heavy baryons Xi_b^0 and Ξ_b^- is also discussed.
We review the status of bottom quark physics at the CDF experiment. The measurements reported are based on about 110 pb-1 of data collected at the Fermilab Tevatron pp= Collider operating at sqrt{s} = 1.8 TeV. In particular, we review results on B hadron lifetimes, measurements of the time dependence of B0 B0= oscillations, and a search for CP violation in B0 --> J/Psi K0s decays. Prospects for future B physics at CDF in the next run of the Tevatron Collider starting in the year 2000 are also given.
We show that in a confining hidden valley model where the lightest hidden particles are dark hadrons that have mass splittings larger than $\mathcal{O}(0.1)$ GeV, if the lightest dark hadron is either stable or decays into Standard Model (SM) hadrons/charged leptons during the big-bang nucleosynthesis (BBN), at least one of the heavier dark hadrons needs to decay into SM particles within $\mathcal{O}(10)$ nanosec. Once being produced at collider experiments, this heavier dark hadron is likely to decay within $\mathcal{O}(1)$ meter distance, which strengthens the motivation of searching for lon…
The hadronic matrix elements of dimension-six $ΔF=0,2$ operators are crucial inputs for the theory predictions of mixing observables and lifetime ratios in the $B$ and $D$ system. We determine them using HQET sum rules for three-point correlators. The results of the required three-loop computation of the correlators and the one-loop computation of the QCD-HQET matching are given in analytic form. For mixing matrix elements we find very good agreement with recent lattice results and comparable theoretical uncertainties. For lifetime matrix elements we present the first ever determination in the…
Sterile neutrinos can be a possible candidate for dark matter. Sterile neutrinos are radiatively unstable and can inject photon energy into the intergalactic medium (IGM). The injection of photon energy into IGM can modify the temperature and ionization history of IGM gas during cosmic dawn. Theoretical models based on the ΛCDM framework predict an absorption profile in the 21 cm line during the cosmic dawn era. Recently, the Experiment to Detect the Global Epoch of Reionization Signature (EDGES) collaboration confirmed such an adsorption signal. Injection of energy into IGM can modify the abs…
We review the theoretical status of the lifetime ratios $τ_{B^+} / τ_{B_d}$, $τ_{B_s} / τ_{B_d}$, $τ_{Λ_b} / τ_{B_d}$ and $τ_{B_c}$ and of the mixing quantities $ΔM_s$, $ΔΓ_s$ and $ϕ_s$. $ΔM_s$ and $ΔΓ_s$ suffer from large uncertainties due to the badly known decay constants, while the ratio $ΔΓ_s / ΔM_s$ can be determined with almost no non-perturbative uncertainties, therefore it can be used perfectly to find possible new physics contributions in the mixing parameters. We suggest a very clear method of visualizing the bounds on new physics and demonstrate this by combining the latest experim…
We compute perturbative QCD corrections to the lifetime splitting between the charged and neutral $B$ meson in the framework of the heavy quark expansion. These next-to-leading logarithmic corrections are necessary for a meaningful use of hadronic matrix elements of local operators from lattice gauge theory. We find the uncertainties associated with the choices of renormalization scale and scheme significantly reduced compared to the leading-order result. We include the full dependence on the charm-quark mass $m_c$ without any approximations. Using hadronic matrix elements estimated in the lit…
The Standard Model contribution to D0-anti-D0 mixing is dominated by the contributions of light s and d quarks. Neglecting the tiny effects due to b quark, both mass and lifetime differences vanish in the limit of SU(3) symmetry. Thus, the main challenge in the Standard Model calculation of the mass and width difference in the D0-anti-D0 system is to estimate the size of SU(3) breaking effects. We prove that D meson mixing occurs in the Standard Model only at second order in SU(3) violation. We consider the possibility that phase space effects may be the dominant source of SU(3) breaking. We f…
The Standard Model contribution to D0-anti-D0 mixing is dominated by the contributions of light s and d quarks. Neglecting the tiny effects due to b quark, both mass and lifetime differences vanish in the limit of SU(3)_F symmetry. Thus, the main challenge in the Standard Model calculation of the mass and width difference in the D0-anti-D0 system is to estimate the size of SU(3) breaking effects. We prove that D meson mixing occurs in the Standard Model only at second order in SU(3) violation. We consider the possibility that phase space effects may be the dominant source of SU(3) breaking. We…
The talk reviews the status of Standard Model predictions for lifetimes and mixing rates of charmed mesons. I discuss sources of SU(3) breaking in the hadron state affecting the Delta C = 2 Hamiltonian and argue that they are the dominant effect generating a D0 decay width splitting.
In this talk electroweak corrections related to the finite top quark lifetime to the total top pair threshold e+e- cross section at NNLL order are discussed. We include the absorptive parts in electroweak matching conditions of the NRQCD operators related to the top decay and use the optical theorem. Gauge invariance is maintained. The corrections lead to ultraviolet phase space divergences and NLL mixing effects. The corrections can amount to several percent and are phenomenologically relevant.
The motivation most often cited in searches for D0-anti-D0 mixing and CP-violation in charm system lies with the possibility of observing a signal from New Physics which dominates that from the Standard Model. We review recent theoretical predictions and experimental constraints on D0-anti-D0 mixing parameters, concentrating on possible effects of New Physics.
We study the the electroweak symmetry breaking induced by the interaction of unparticles and the SM Higgs with an additional complex scalar. Furthermore, we estimate the contribution of the mixing scalars on the muon anomalous magnetic moment. We observe that this contribution is at least two order less than the discrepancy between the experimental and the SM results of the muon anomalous magnetic moment.
We conduct a systematic study of the impact of new physics in quark-level $b \to c \bar{c} s$ transitions on $B$-physics, in particular rare $B$-decays and $B$-meson lifetime observables. We find viable scenarios where a sizable effect in rare semileptonic $B$-decays can be generated, compatible with experimental indications and with a possible dependence on the dilepton invariant mass, while being consistent with constraints from radiative $B$-decay and the measured $B_s$ width difference. We show how, if the effect is generated at the weak scale or beyond, strong renormalisation-group effect…
In this work we discuss the theoretical status for the study of the lifetime of heavy hadrons. After presenting some introductory topics like the effective weak Hamiltonian and the heavy quark effective theory (HQET), we describe the construction of the heavy quark expansion (HQE), which constitutes the theoretical framework to systematically compute the total decay width of heavy hadrons, in terms of an expansion in inverse powers of the heavy quark mass. The structure of the HQE is discussed in detail, and the computation of the lowest dimensional contributions, explicitly outlined. Particul…
The interpretation of the existing experimental evidences for oscillations of neutrinos in schemes with three and four neutrino mixing is reviewed. Forms of the lepton mixing matrix allowed by the neutrino oscillation data are considered. The possible neutrino mass spectra compatible with the observations are analyzed. The possibility to obtain information about the neutrino mass spectrum from the future $^{3}$H $β-$decay and $(ββ)_{0ν}-$decay experiments is also considered.
We present a calculation of the B0 - anti-B0 mixing matrix element in the framework of QCD sum rules for three-point functions. We compute alpha_s corrections to a three-point function at the three-loop level in QCD perturbation theory, which allows one to extract the matrix element with next-to-leading order (NLO) accuracy. This calculation is imperative for a consistent evaluation of experimentally-measured mixing parameters since the coefficient functions of the effective Hamiltonian for B0 - anti-B0 mixing are known at NLO. We find that radiative corrections violate factorization at NLO; t…
We investigate the pair production of right-handed neutrinos from the decay of an additional neutral $Z^{\prime}$ boson in the gauged $B-L$ model. Taking into account current constraints on the $Z^{\prime}$ mass and the associated gauge coupling $g_{1}^{\prime}$, we analyse the sensitivity of proposed experiments at the lifetime frontier, FASER 2, CODEX-b, MATHUSLA as well as a hypothetical version of the MAPP detector to a long lived heavy neutrino $N$ originating in the decays of the $Z^{\prime}$. We further complement this study with determining the reach of LHCb and a CMS-type detector for…
We review the theoretical status of the lifetime ratios $τ_{B^+} / τ_{B_d}$ and $τ_{B_s} / τ_{B_d}$ and of the mixing quantities $ΔM_s$, $ΔΓ_s$ and $ϕ_s$. We show that the ratio $ΔΓ_s / ΔM_s$ can be determined with almost no non-perturbative uncertainties. Finally we explain how this precise determination of the standard model values can be used to find possible new physics contributions in $ΔM_s $, $ΔΓ_s$, $ΔΓ_s / ΔM_s$ and $a_{fs}^s$. Combining the latest experimental bounds on these quantities one already gets some hints for new physics contributions.
We review the current status of theoretical predictions for mixing quantities and lifetimes in the $B$-sector. In particular, due to the first non-zero measurement of the decay rate difference in the neutral $B_s$-system, $ΔΓ_s/ Γ_s = 17.6 % \pm 2.9 %$ by the LHCb collaboration and very precise data for $τ_{B_s}$ from TeVatron and LHCb our theoretical tools can now be rigorously tested and it turns out that the Heavy Quark Expansion works in the $B$-system to an accuracy of at least 30% for quantities like $Γ_{12}$, which is most sensitive to hypothetical violations of quark hadron duality. Th…
Inclusive bottom hadron decays are analyzed based on the heavy quark effective field theory (HQEFT). Special attentions in this paper are paid to the b\to u transitions and nonspectator effects. As a consequence, the CKM quark mixing matrix elements |V_ub| and |V_cb| are reliably extracted from the inclusive semileptonic decays B\to X_u e νand B\to X_c e ν. Various observables, such as the semileptonic branch ratio B_SL, the lifetime differences among B^-, B^0, B_s and Λ_b hadrons, the charm counting n_c, are predicted and found to be consistent with the present experimental data.
We compute and compare the baryon asymmetry of the universe in thermal leptogenesis scenario with and without flavour effects for different neutrino mass models namely degenerate, inverted hierarchical and normal hierarchical models, with tribimaximal mixings and beyond. Considering three possible diagonal forms of Dirac neutrino mass matrices $m_{LR}$, the right-handed Majorana mass matrices $M_{RR}$ are constructed from the light neutrino mass matrices $m_{LL}$ through the inverse seesaw formula. The normal hierarchical model is found to give the best predictions of the baryon asymmetry for …
We investigate the prospects to extract supersymmetric couplings from a decay length measurement at the LHC. Specifically, we exploit the opportunity of a light and long-lived stop which is pair-produced through gluinos in association with like-sign top quarks. Any observed finite value of the stop decay length strongly supports models in which flavor is broken in a minimal way solely by the Standard Model Yukawa couplings. We find that a 1 picosecond stop lifetime, dominated by t~ -> c chi^0 decays, yields macroscopic transverse impact parameters of about 180 microns. If the lightest neutrali…
Heavy meson pairs produced in the decays of heavy quarkonium resonances at e+ e- machines (beauty and tau-charm factories) have the useful property that the two mesons are in the CP-correlated states. By tagging one of the mesons as a CP eigenstate, a lifetime difference of heavy neutral meson mass eigenstates width difference may be determined by measuring the leptonic branching ratio of the other meson. We discuss the use of this and related methods both in the case where time dependent mixing is small and when it is significant. We consider the impact of possible CP-violating effects and pr…
The possibility of additional quarks and leptons beyond the three generations already established is discussed. The make-up of this Report is (I) Introduction: the motivations for believing that the present litany of elementary fermions is not complete; (II) Quantum Numbers: possible assignments for additional fermions; (III) Masses and Mixing Angles: mass limits from precision electroweak data, vacuum stability and perturbative gauge unification; empirical constraints on mixing angles; (IV) Lifetimes and Decay Modes: their dependence on the mass spectrum and mixing angles of the additional qu…
The {\it theory unifying spin and charges and predicting families}, proposed by N.S.M.B., predicts at the low energy regime two (in the mixing matrix elements decoupled) groups of four families. There are two kinds of contributions to mass matrices in this theory. One kind distinguishes on the tree level only among the members of one family, that is among the $u$-quark, $d$-quark, neutrino and electron, the left and right handed, while the other kind distinguishes only among the families. Mass matrices for $d$-quarks and electrons are on the tree level correspondingly strongly correlated and s…
We report a set of exact formulae for computing Dirac masses, mixings, and CP-violation parameter(s) from 3$\times$3 Yukawa matrices $Y$ valid when $Y Y^\dagger \rightarrow U^\dagger \,Y Y^\dagger \, U$ under global $U(3)_{Q_L}$ flavour symmetry transformations $U$. The results apply to the Standard Model Effective Field Theory (SMEFT) and its `geometric' realization (geoSMEFT). We thereby complete, in the Dirac flavour sector, the catalogue of geoSMEFT parameters derived at all orders in the $\sqrt{2 \langle H^\dagger H \rangle} / Λ$ expansion. The formalism is basis-independent, and can be a…
The idea, following Michel and O'Raifeartaigh, of assigning meaning to the (gauge) \underline{group} and not only the Lie algebra for a Yang Mills theory is reviewed. Hints from the group and the fermion spectrum of the Standard Model are used to suggest the putting forward of our AGUT-model, which gives a very good fit to the orders of magnitudes of the quark and lepton masses and the mixing angles including the CP-breaking phase. But for neutrino oscillations modifications of the model are needed. Baryogenesis is not in conflict with the model.
In the Standard Model (SM) the photon in radiative $\bar B^0$ and $\bar B_s$ decays is predominantly left-handed. Thus, mixing induced CP asymmetries in $b\to sγ$ and $b\to dγ$ are suppressed by $m_s/m_b$ and $m_d/m_b$, respectively, and are very small. In many extensions of the SM, such as the left-right symmetric model (LRSM), SU(2)xU(1) models with exotic fermions and SUSY, the amplitude of right-handed photons grows proportional to the virtual heavy fermion mass, which can lead to large asymmetries. As an example, in the LRSM, asymmetries larger than 50% are possible even when radiative de…
B-hadron physics plays a fundamental role to test and improve our understanding of flavor dynamics within and beyond the Standard Model. Of particular phenomenological interest are beauty hadron lifetime ratios and, width differences and semileptonic CP-asymmetries in B_d and B_s systems. We discuss their theoretical predictions which, in the last years, have been improved thanks to accurate lattice calculations of operator matrix elements and perturbative computations of Wilson coefficients.
We review the status of mixing of neutral $B$-mesons, including a discussion of the current precision of Standard Model (SM) predictions as well as the space that is left for effects of new physics. In that respect we present several observables, which are particularly sensitive to the remaining new physics (NP) parameter space. $B$-mixing can also be used to test the fundaments of quantum mechanics, here we suggest a new measurement of the ratio of like-sign dilepton events to opposite-sign dilepton events. Finally we summarise briefly the status of lifetimes of heavy hadrons. The correspondi…
I present numerical updates of the Standard-Model predictions for the mass and width differences and the CP asymmetries in flavor-specific decays in Bs-Bs-bar and Bd-Bd-bar mixing. Then I discuss the current status of new physics in these mixing amplitudes.
We use lattice QCD to calculate the B-mixing hadronic matrix elements for a basis of effective four-quark operators that spans the space of all possible contributions in, and beyond, the Standard Model. We present results for the SU(3)-breaking ratio and discuss our ongoing calculation of the mixing matrix elements, including the first calculation of the beyond the Standard Model matrix elements from unquenched lattice QCD.
We study the Standard Model short-distance prediction for the mass and lifetime differences between the two neutral D meson mass eigenstates. We find that, despite α_s/4πsuppression, next-to-leading order (NLO) short-distance QCD corrections exceed the corresponding leading order (LO) amplitudes. For the lifetime difference, this stems from the lifting of helicity suppression of a light-quark intermediate state. We find y_D is given by y_NLO to a reasonable approximation but x_D is greatly affected by destructive interference between x_LO and x_NLO. The net effect is to render y_D ~ x_D ~ 6 x …
We give a brief overview and progress report on our lattice QCD calculation of neutral B mixing hadronic matrix elements needed for Standard Model and Beyond the Standard Model physics. Reference [1] contains more details and results.
The current status of the phenomenology of short-baseline neutrino oscillations induced by light sterile neutrinos in the framework of 3+1 mixing is reviewed.
New physics models that increase the decay rate of $B_s \to τ^+ τ^-$ contribute to the absorptive part of $B_s$--$\bar{B}_s$ mixing, and may enhance $ΔΓ_s$ all the way up to its current experimental bound. In particular, the model with a scalar leptoquark can lead to a significant violation of the expectation $ΔΓ_s \leq ΔΓ_s$ (SM). It can even allow regions in the $ΔΓ_s$-$β_s$ parameter space that are close to the best fit obtained by CDF and D\{O} through $B_s \to J/ψϕ$. In addition, it can help explain the anomalous like-sign dimuon charge asymmetry observed recently by DØ. A measurement of …
I present here the HFAG averages for the parameters that regulate flavor mixing and \CP violation in the neutral $D$ meson system. I also discuss recent results from the $B$ factories for the measurements of the mixing parameter \yCP and the \CP violation parameter \deltaY (\AGamma) in the lifetime ratio analysis of the transitions to the \CP-even eigenstates $\Dz\to K^+K^-,π^+π^-$, relative to the transitions to the \CP-mixed state $\Dz \to K^-π^+$.
We give a progress report on the calculation of B meson mixing matrix elements, focusing on contributions that could arise beyond the Standard Model. The calculation uses asqtad (light quark) and Fermilab (heavy quark) valence actions and MILC ensembles with 2+1 flavors of asqtad sea quarks. We report preliminary B^0_s fit results, at a lattice spacing of 0.12 fm, for the SUSY basis of effective four-quark mixing operators and include an estimate for the final error budget.
