# Weak Decays and Matrix Elements

Chiral and continuum extrapolation of B-meson decay constants computed using domain-wall light quarks and nonperturbatively tuned relativistic b-quarks
Oliver Witzel
Tue, 14:00, Seminar Room C -- Parallels 3C (Slides)

We report on our progress to obtain the decay constants $$f_B$$ and $$f_{B_s}$$ from lattice-QCD simulations on the RBC and UKQCD Collaborations 2+1 flavor domain-wall-Iwasaki lattices. Using domain-wall light quarks and relativistic b-quarks we analyze data with several partially quenched light-quark masses at two lattice spacings of a ~ 0.11 fm and a ~ 0.08 fm. We perform combined chiral and continuum extrapolations using chiral perturbation theory.

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The form factor for $$B$$ to $$\pi$$ semileptonic decay from 2+1 flavors of domain-wall fermions
Taichi Kawanai
Tue, 14:20, Seminar Room C -- Parallels 3C (Slides)

We study the $$B\to\pi$$ semileptonic decay process using lattice QCD with domain-wall light quarks and relativistic b-quarks. The lattice calculation of the $$B\to\pi$$ form factor is needed to extract the CKM matrix element $$|V_{ub}|$$ from experimental measurements of the branching fraction. We use the 2+1 flavor domain-wall Iwasaki gauge configurations generated by the RBC and UKQCD collaborations at two lattice spacings (a~0.08fm and 0.11fm) and several sea-quark masses, and compute the form factors $$f_0(q^2)$$ and $$f_+(q^2)$$ with several partially-quenched valence quark masses. Our lightest pion mass is about 290MeV. For the bottom quark, we use the relativistic heavy-quark action and tune the parameters of the anistotropic clover action nonperturbatively. We present preliminary results for the chiral and continuum extrapolations of the $$B\to\pi$$ form factor using SU(2) Chiral perturbation theory.

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A new computer algebra system for (lattice) perturbation theory and the RBC/UKQCD heavy quark physics program
Christoph Lehner
Tue, 14:40, Seminar Room C -- Parallels 3C (Slides)

I discuss a new computer algebra system optimized for automated perturbation theory for a wide range of regulators both in the continuum and using a lattice. The current implementation includes support for Wilson-type fermions, DWF, and the Schroedinger Functional. I will present details of applications within the heavy quark physics program of the RBC and UKQCD collaborations.

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On one-loop corrections to the matching conditions of Lattice HQET including $$1/m_b$$ terms
Piotr Korcyl
Tue, 15:00, Seminar Room C -- Parallels 3C (Slides)

HQET is an effective theory for QCD with $$N_f\ge 1$$ light quarks and a single massive quark if the mass of the latter is bigger than $$\Lambda_QCD$$. As any effective theory, HQET is predictive only when a set of parameters have been determined through a process called matching. The non-perturbative matching procedure including 1/mb terms, applied by the ALPHA col- laboration, consists of 19 carefully chosen observables which are precisely computable in lattice QCD as well as in lattice HQET. The matching con- ditions are then a set of 19 equalities which relate the QCD and HQET values of these observables. We present a study of one-loop corrections to the matching conditions used to fix the renormalization constants of axial and vector currents. Our results enable us to quantify the quality of the relevant observables, also in view of the envisaged non-perturbative implementation of this matching procedure.

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B-physics with $$N_f=2$$ Wilson fermions
Fabio Bernardoni, Patrick Fritzsch, Georg von Hippel, Michele Della Morte, Jochen Heitger, John Bulava, Nicolas Garron, Rainer Sommer, Hubert Simma, Antoine Gerardin, Benoit Blossier
Tue, 15:20, Seminar Room C -- Parallels 3C (Slides)

We report the final results of the ALPHA collaboration for some B-physics observables: fB, fBs and mb. We employ CLS configurations with 2 flavors of O(a) improved Wilson fermions in the sea and pion masses ranging down to 190 MeV. The b-quark is simulated in HQET to order 1/mb. The renormalization the matching and the improvement were performed non-perturbatively, and three lattice spacings reaching a=0.048fm are used in the continuum extrapolation.

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B-physics computations from $$N_f=2$$ tmQCD
Petros Dimopoulos, Nuria Carrasco Vela, Roberto Frezzotti, Vicent Gimenez Gomez, Gregorio Herdoiza, Vittorio Lubicz, Eleonora Picca [for the ETM Collaboration], Giancarlo Rossi, Francesco Sanfilippo, Silvano Simula, Andrea Shindler, Cecilia Tarantino
Tue, 15:40, Seminar Room C -- Parallels 3C (Slides)

We present a lattice QCD computation of the $$b$$-quark mass, the $$B$$ and $$B_s$$ decay constants, the $$B$$-mixing bag parameters for the full four-fermion operator basis as well as estimates for $$\xi$$ and $$f_{Bq}\sqrt{B_q}$$ extrapolated to the continuum limit and the physical pion mass. We have used $$N_f = 2$$ dynamical quark gauge configurations at four values of the lattice spacing generated by ETMC. Extrapolation in the heavy quark mass from the charm to the bottom quark region has been carried out on ratios of physical quantities computed at nearby quark masses, as they have an exactly known infinite mass limit.

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$$B$$ decay to radially excited $$D$$
Benoit Blossier, Damir Becirevic, Antoine Gerardin, Francesco Sanfilippo, Alain Le Yaouanc
Tue, 16:20, Seminar Room C -- Parallels 4C (Slides)

There is a strong conjecture that radial excitations of $$D$$ mesons are a significant component of the hadronic final state in $$B$$ decay. Still, their properties need to be examined with some care: indeed a comparison of experimental data with a valuable class of quark models results in a quite larger width of the $$D'$$ $$2S$$ state than expected. The hypothesis of a large form factor in $$B \to D'$$ semileptonic decay can be tested on the hadronic decay $$B \to D' \pi$$. Indeed, the same form factor enters the so-called class I process, with the pion emission, assuming the validity of the factorization approximation. However, in the case of $$B^- \to D'^0 \pi^-$$, it is necessary to evaluate the so-called class III process, with the $$D'$$ emission, that is parametrized by the decay constant $$f_{D'}$$. We present an estimate of this constant on $${N_f}=2$$ lattice simulations and discuss the phenomenological consequences of our findings on $$B \to D'$$ semileptonic decay.

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The $$B^*B\pi$$ coupling with relativistic heavy quarks
Ben Samways
Tue, 16:40, Seminar Room C -- Parallels 4C (Slides)

We report on a calculation of the $$B^*B\pi$$ coupling in Lattice QCD. This involves determining the strong matrix element $$\langle B \pi | B^*\rangle$$, which is directly related to the leading order LEC in Heavy Meson Chiral Perturbation Theory (HM$$\chi$$PT) for B-mesons. We carry out our calculation directly at the b-quark mass using an improved relativistic heavy quark action and domain wall light quarks. We use 2+1 flavour RBC/UKQCD gauge ensembles at two lattice spacings of $$a^{-1}=1.73(3)$$ GeV and $$a^{-1}=2.28(3)$$ GeV with unitary pions masses down to 290 MeV.

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Probing TeV scale physics in precision UCN decays
Rajan Gupta
Tue, 17:00, Seminar Room C -- Parallels 4C (Slides)

I will describe calculations of matrix elements of quark bilinear operators in nucleon states being done by the PNDME collaboration to probe physics beyond the standard model. Results on iso-vector and iso-scalar charges, electric and magnetic form-factors and charge radii will be presented. These calculations are being done using clover valence fermions on 2+1+1 HISQ ensembles generated by the MILC collaboration at two values of light quark masses corresponding to pion masses of 310 and 220 MeV and at two values of the lattice spacing of 0.12 and 0.09 fm. We demonstrate control over systematic errors due to excited state contamination and renormalization constants and preliminary estimates of discretization errors.

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Neutral B meson mixing with static heavy and domain-wall light quarks
Tomomi Ishikawa, Yasumichi Aoki, Taku Izubuchi, Christoph Lehner, Amarjit Soni
Tue, 17:20, Seminar Room C -- Parallels 4C (Slides)

Neutral B meson mixing matrix elements and B meson decay constants are calculated. Static approximation is used for b quark and domain-wall fermion formalism is employed for light quarks. The calculations are made on 2+1 flavor dynamical ensembles generated by RBC-UKQCD Collaborations, whose lattice spacings are 0.086fm and 0.11fm with a fixed physical spatial volume of about (2.7fm)$$^3$$. In the static quark action, link-smearings are used to improve the signal-to-noise ratio. We employ two kinds of the link-smearing and their results are combined in taking a continuum limit. For the matching between the lattice and the continuum theory, one-loop perturbative O(a) improvements are made to reduce discretization errors. We also show statistical improvements by the all-mode-averaging method.

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$$D$$ and $$D_s$$ decay constants from a chiral analysis on HISQ ensembles
Claude Bernard, Jongjeong Kim, Javad Komijani, Doug Toussaint
Wed, 11:00, Seminar Room C -- Parallels 6C (Slides)

We present a determination of the decay constants of charmed pseudoscalar mesons on the ensembles with four dynamical quarks that have been generated by the MILC collaboration. The HISQ action is used for both the valence and sea quarks. The lattice data is fit to chiral expressions that have been recently derived in staggered chiral perturbation theory for heavy-light mesons composed of two staggered quarks. Since a subset of our data is at physical values of the light quark masses, it is possible to make an alternative, more straightforward, analysis (to be presented by D. Toussaint) that focuses on the physical-mass data and does not require chiral fitting. However, the chiral analysis allows us to use all our data, thereby reducing statistical errors and allowing better control of some of the systematic errors.

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$$D_s$$ to $$\phi$$ and other transitions from lattice QCD
Gordon Donald, Christine Davies, Jonna Koponen
Wed, 11:20, Seminar Room C -- Parallels 6C (Slides)

The weak semileptonic Ds to phi decay is a pseudoscalar to vector meson transition and the decay rate contains vector and axial vector form factors. We calculate these form factors using lattice QCD with HISQ valence quarks on MILC gauge configurations containing 2+1 flavours of asqtad sea quarks. We discuss how to normalise the various discretisations used for vector and axial vector currents with staggered quarks. The form factors are calculated over the physical range of q2 and we compare our results for the decay rate to experiment to extract the CKM element Vcs. We use the same normalisation techniques to calculate the rate for $$J/\psi \to \eta_c \gamma$$ as a test of lattice QCD.

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Semileptonic D-decays with twisted mass QCD on the lattice
Francesco Sanfilippo, Vittorio Lubicz, Damir Becirevic
Wed, 11:40, Seminar Room C -- Parallels 6C (Slides)

We compute the hadronic matrix elements relevant to the semileptonic $$D\to\pi/K$$ and $$D_s\to K$$ decays. Besides the usual vector and scalar form factors, we also present the first lattice results for the penguin induced form factor. Our results are obtained from the simulations of twisted mass QCD with $$N_f=2$$ dynamical quarks and at several lattice spacings allowing us to make the smooth extrapolation to the continuum limit.

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$$D_s \to \eta(')$$ semi-leptonic decay form factors
Issaku Kanamori
Wed, 12:00, Seminar Room C -- Parallels 6C (Slides)

We report on our on-going study of the $$D_s \to \eta(')$$ semi-leptonic decay form factors with $$n_f=2+1$$ configurations. We include disconnected fermion loop diagrams, which give large contributions to the $$D_s \to \eta'$$ form factor.

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$$K$$ and $$D$$ oscillations in the Standard Model and its extensions from $$N_f=2+1+1$$ Twisted Mass LQCD
Nuria Carrasco Vela, Petros Dimopoulos, Roberto Frezzotti, Vicent Gimenez Gomez, Vittorio Lubicz, David Palao, Giancarlo Rossi, Francesco Sanfilippo, Silvano Simula, Cecilia Tarantino
Wed, 12:20, Seminar Room C -- Parallels 6C (Slides)

We present results for the B-parameters of the complete basis of four-fermion operators needed to study the neutral K and D meson oscillations within the Standard Model and its extensions. We perform numerical simulations using Nf=2+1+1 maximally twisted sea quarks generated by the ETMC and Osterwalder-Seiler valence quarks. With this setup we achieve both O(a) improvement and continuum-like renormalization pattern for the relevant four-fermion operators. The analysis includes data at three values of the lattice spacing and pion masses as low as ~230 MeV, allowing for accurate continuum limit and chiral extrapolation. The computation of the renormalization constants of the complete operator basis is performed non perturbatively in the RI-MOM scheme using dedicated simulations with Nf=4 degenerate sea quark flavours.

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The $$D_s$$,$$D$$, $$B_s$$ and $$B$$ decay constants from 2+1 flavor lattice QCD
James Simone
Wed, 12:40, Seminar Room C -- Parallels 6C (Slides)

We present an update of our study of the D and B leptonic decay constants on the MILC Nf=2+1 asqtad gauge ensembles using asqtad-improved staggered light valence quarks and clover heavy quarks in the Fermilab interpretation. Our previous analysis [Phys.Rev. D85 (2012) 114506] computed the decay constants at lattice spacings a ~= 0.15, 0.12 and 0.09 fm. Our current analysis addresses many important sources of uncertainty in our first analysis by: extending the simulations to more ensembles including finer a ~= 0.06 and 0.045 fm lattice spacings, increasing statistics, better tuning of the quark masses and better determinations of the axial-vector current matching.

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Kaon semileptonic form factors with $$N_f=2+1+1$$ HISQ fermions and physical light quark masses
Elvira Gamiz
Thu, 14:00, Seminar Room C -- Parallels 7C (Slides)

We present results for the form factor $$f_+^{K \pi}(0)$$, needed to extract the CKM matrix element $$|V_{us}|$$ from experimental data on semileptonic K decays, on the HISQ $$N_f=2+1+1$$ MILC configurations. In this calculation the HISQ action is also used for the valence sector. The set of data presented includes three different values of the lattice spacing and data at the physical light quark masses. We discuss the different approaches for the chiral and continuum extrapolation, a preliminary error budget, and how this calculation improves over our previous determination of $$f_+^{K \pi}(0)$$ on the asqtad $$N_f=2+1$$ MILC configurations.

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Kaon semileptonic decay from the SU(3)-symmetric point down to physical quark masses
Andreas Juettner
Thu, 14:20, Seminar Room C -- Parallels 7C (Slides)

We present the RBC/UKQCD collaboration's results for the $$K\to\pi$$ semileptonic vector form factor. We are simulating chiral fermions from close to the SU(3)-symmetric point down to physical parameters for three lattice spacings in large volume. Using partially twisted boundary conditions we calculate the form factor directly at zero momentum transfer. The comprehensive set of data points allows for turning the extrapolation in the quark mass into an interpolation around the physical point thereby removing the dominant systematic uncertainty in previous results. We discuss our prediction in view of Standard Model phenomenology.

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Calculating the $$K_L-K_S$$ mass difference and $$\epsilon_K$$ to sub-percent accuracy
Norman Christ
Thu, 14:40, Seminar Room C -- Parallels 7C (Slides)

The real and imaginary parts of the KL-KS mixing matrix receive contributions from all three charge-2/3 quarks: up, charm and top. These give both short- and long-distance contributions which are accessible through a combination of perturbative and lattice methods. We will discuss a strategy to compute both the mass difference, $$\Delta M_K$$, and $$\epsilon_K$$ to sub-percent accuracy, looking in detail at the contributions from each of the three CKM matrix element products $$V_{id}^* V_{is}$$ for i=u, c and t as described in arXiv:1212.5931 [hep-lat].

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$$K_L$$-$$K_S$$ mass difference from Lattice QCD
Jianglei Yu
Thu, 15:00, Seminar Room C -- Parallels 7C (Slides)

We will report on the first full calculation of the $$K_L$$-$$K_S$$ mass difference in lattice QCD. The calculation is performed on a 2+1 flavor, domain wall fermion, $$24^3 \times 64$$ ensemble with a 329 MeV pion mass and a 575 MeV kaon mass. Both double penguin diagrams and disconnected diagrams are included in this calculation. The calculation is made finite through the GIM mechanism by introducing a 949 MeV valence charm quark. While the double penguin diagrams contribute a very small fraction to the mass difference, there is a large cancellation between disconnected diagrams and other types of digrams. We obatain the mass difference $$\Delta M_K=3.24(29)\times 10^{-12}$$ MeV for these unphysical kinematics.

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Finite-volume effects in the evaluation of the $$K_L$$-$$K_S$$ mass difference
Christopher Sachrajda, Norman Christ, Guido Martinelli
Thu, 15:20, Seminar Room C -- Parallels 7C (Slides)

The flavour physics programme of the RBC-UKQCD collaboration includes the evaluation of the long-distance contributions to the $$K_L$$-$$K_S$$ mass difference, $$\Delta M_K$$. The long-distance contributions lead to the presence of finite-volume corrections which generally do not decrease exponentially with the volume of the lattice, but as inverse powers. The evaluation of these corrections for the case when the masses and volume are tuned so that $$M_K$$ is equal to the energy of one of the discrete two-pion states was presented at Lattice 2010. In this talk I discuss the finite-volume corrections in the general case, where there is no such degeneracy and suggest an optimal choice of volumes such that the corrections are exponentially small.

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Kaon Mixing Beyond the Standard Model
Andrew Lytle, Nicolas Garron, Renwick Hudspith, Peter Boyle, Christopher Sachrajda
Thu, 15:40, Seminar Room C -- Parallels 7C (Slides)

We report on the calculation of hadronic matrix elements needed to parameterize $$K-\bar{K}$$ mixing in generic BSM scenarios, using domain wall fermions (DWF) at two lattice spacings. We use Nf=2+1 DWF with Iwasaki gauge action at inverse lattice spacings of 2.28 and 1.73 GeV, with multiple unitary pions on each ensemble, the lightest being 290 and 330 MeV on the finer and coarser of the two ensembles respectively. Results on each ensemble are extrapolated to the physical pion mass, and the continuum limit is taken. Renormalization is carried out in the RI/MOM scheme and then converted perturbatively to MSbar. This extends previous work by the addition of a second lattice spacing ($$a^{-1} \approx 1.73$$ GeV), allowing the determination in the continuum limit.

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Progress Towards an ab Initio, Standard Model Calculation of Direct CP-Violation in K decay
Christopher Kelly, (RBC \& UKQCD Collaboration)
Thu, 16:30, Seminar Room C -- Parallels 8C (Slides)

The RBC \& UKQCD collaborations recently published the first direct lattice calculation of the $$K\to\pi \pi$$ decay amplitude in the I=2 channel. In order to compare the parameter epsilon', the measure of direct CP-violation in $$K\to\pi \pi$$ decays, with the prediction of the Standard Model, a calculation must also be performed in the I=0 channel. To obtain physical kinematics in this channel without the need for multi-exponential fits or a moving initial kaon state, we will use G-parity boundary conditions on the quarks to remove the state with stationary pions and to tune the two pion energy to equal the kaon mass. I will describe our implementation and understanding of this choice of boundary conditions, and describe the status of the project.

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Determination of the $$A_2$$ amplitude of $$K\to\pi\pi$$ decays
Thu, 16:50, Seminar Room C -- Parallels 8C (Slides)

I review the status of recent calculations by the RBC-UKQCD of the complex amplitude $$A_2$$, corresponding to the decay of a kaon to a two pion state with total isospin 2. In particular, I present the preliminary results from two new ensembles: $$48^3$$ with $$a^{-1}=1.73$$ GeV and $$64^3$$ with $$a^{-1}=2.3$$ GeV, both at physical kinematics. These results, combined with our earlier ones on a $$32^3$$ lattice with $$a^{-1}=1.36$$ GeV, enable us to significantly reduce the discretization errors. The partial cancellation between the two dominant contractions contributing to Re($$A_2$$) has been confirmed and we propose that this cancellation is a major contribution to $$\Delta I=1/2$$ rule.

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Using all-to-all propagators for $$K\rightarrow\pi\pi$$ decays
Daiqian Zhang
Thu, 17:10, Seminar Room C -- Parallels 8C (Slides)

In order to determine the direct CP-violation parameter $$\epsilon^\prime$$ from first principles, the decay amplitude for $$K \to \pi\pi(\Delta I = 1/2)$$ must be calculated on the lattice, where the main difficulty is the disconnected diagrams appearing in the correlation function. In order to control the statistical fluctuations in these disconnected diagrams, we will use all-to-all propagators, which allow the construction of $$\pi\pi$$ operators with reduced coupling to the vacuum. The resulting I=0 $$\pi\pi$$ scattering phase shift obtained using this methods shows that it works as we expected. We will also describe the current progress in implementing this method for $$K\to\pi\pi$$ decays.

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Weak Decay Measurements from 2+1 flavor DWF Ensembles
Robert Mawhinney
Thu, 17:30, Seminar Room C -- Parallels 8C (Slides)

The RBC and UKQCD Collaborations have generated 2+1 flavor DWF ensembles, with physical quark masses and spatial volumes of $$(5.5 fm)^3$$, at two lattice spacings, $$1/a = 1.7$$ and 2.3 GeV. Measurements of light hadron masses and decay constants, as well as $$B_K$$, $$f^+_{K \pi}(0)$$ for $$K\ell 3$$ decays and Re($$A_2$$) and Im($$A_2$$) amplitudes for $$K \to \pi \pi$$ decays are being done using the EigCG algorithm and all-mode-averaging. These techniques have sped the measuremnts up by a factor of $$\approx 10$$. Details of the measurement strategy will be discussed, along with some preliminary results. Further details about indiviudal observables will be presented in other talks by the RBC and UKQCD collaboration.

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Strange and charmed pseudoscalar meson decay constants from simulations at physical quark masses
Doug Toussaint, Claude Bernard, Jongjeong Kim, Javad Komijani, Ruth van de Water
Thu, 17:50, Seminar Room C -- Parallels 8C (Slides)

We update our determinations of $$f_K$$, $$f_D$$, $$f_{D_s}$$ and quark mass ratios from simulations with four flavors of dynamical quarks at the physical quark masses. The availability of ensembles with light quarks near their physical mass means that instead of a chiral extrapolation to the physical light quark mass, we only need small corrections for sea quark mass mistuning. This analysis is complementary to an analysis of $$f_D$$ and $$f_{D_s}$$ using partially-quenched staggered chiral perturbation theory (to be presented by C. Bernard). While the ChiPT analysis allows us to use data at unphysical quark masses where statistical errors are often smaller, the analysis presented here allows us to combine all of the scale setting, quark mass tuning and decay constant determinations into a unified analysis, which simplifies the handling of many of the systematic errors.

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$$B$$, $$B_s$$, $$K$$ and $$\pi$$ weak matrix elements with physical light quarks
Rachel Dowdall, Christine Davies, Ronald Horgan, G. Peter Lepage, Craig McNeile, Christopher Monahan, Junko Shigemitsu
Thu, 18:10, Seminar Room C -- Parallels 8C (Slides)

I report on HPQCD calculations of meson decay constants and bag parameters using NRQCD heavy and HISQ light quarks on MILC Nf=2+1+1 gauge ensembles that include physical light quark masses.

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$$B\to\pi$$ semileptonic form factors from unquenched lattice QCD
Daping Du, Jon Bailey, Alexei Bazavov, Aida El-Khadra, Steven Gottlieb, Rajendra Jain, Andreas Kronfeld, Yuzhi Liu, Yannick Meurice , Ruth van de Water, Ran Zhou
Fri, 16:30, Seminar Room D -- Parallels 10D (Slides)

We update the lattice calculation of the $$B\to\pi$$ semileptonic form factors which are important for determining the CKM matrix element $$|V_{ub}|$$ and using the $$B\to\pi \ell^+\ell^-$$ decay mode to constrain new physics. We use the MILC asqtad 2+1 flavor lattice ensembles, with four lattice spacings (about 0.12, 0.09, 0.06 and 0.045 fm) and up/down quark over strange quark mass ratios as low as 0.05. We extrapolate the lattice data using staggered chiral perturbation theory in the hard pion and SU(2) limits. To extend the result to the full kinematic range, we introduce a new functional method to reparameterize the extrapolation in $$q^2$$ using the model-independent $$z$$ expansion. We also present a preliminary error budget for the calculation.

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$$B_s\to D_s \ell \nu_\ell$$ near zero recoil from tmQCD
Mariam Atoui, Damir Becirevic, Vincent Morénas, Francesco Sanfilippo
Fri, 16:50, Seminar Room D -- Parallels 10D (Slides)

We study the form factors relevant to the theoretical description of the semileptonic decays $$B_s \to D_s \mu \nu_\mu$$ and $$B_s \to D_s \tau \nu_\tau$$, in and beyond the Standard Model. We focus to the region near the zero-recoil and evaluate the form factors without recourse to heavy quark effective theory. The quark action used in this work is twisted mass QCD and the configurations are those with $$N_f=2$$ dynamical quark flavors.

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Semileptonic decays $$B\to D \ell \nu$$ at nonzero recoil
Siwei Qiu, Carleton DeTar, Laiho Jack, Ruth van de Water, Andreas Kronfeld (Fermilab Lattice and MILC Collaborations)
Fri, 17:10, Seminar Room D -- Parallels 10D (Slides)

The Fermilab Lattice-MILC collaboration has completed its analysis of the semileptonic decays $$B \to D^{(*)} \ell \nu$$ using the MILC (2+1)-flavor asqtad ensembles with lattice spacings as small as 0.045 fm and light-to-strange-quark mass ratios as low as 1/20. We use the Fermilab interpretation of the clover action for heavy valence quarks and the asqtad action for light valence quarks. We compute the hadronic form factors for $$B \to D$$ at both zero and nonzero recoil and for $$B \to D^*$$ at zero recoil. We report our result for $$|V_{cb}|$$.

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Heavy-meson semileptonic decays for the Standard Model and beyond
Andreas Kronfeld, Yuzhi Liu, Ran Zhou
Fri, 17:30, Seminar Room D -- Parallels 10D (Slides)

We calculate with lattice QCD the form factors for the semileptonic decays $$B_s\to K\ell\nu$$ and $$B\to K\ell\ell$$. The first calculation, when combined with potential measurements at Belle II or LHCb, would provide a new way to determine the CKM matrix element $$|V_{ub}|$$. The second process arises at the one-loop level in the Standard Model and is, thus, a probe of new physics. We work at several lattice spacings and a range of light quark masses, using the MILC $$2+1$$-flavor asqtad ensembles. We use the Fermilab method for the $$b$$ quark. We obtain chiral-continuum extrapolations for $$E_K$$ up to $$\sim 1.2$$~GeV and then extend to the kinematic range with the model-independent $$z$$~expansion.

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$$B$$ and $$B_s$$ semileptonic decay form factors with NRQCD/HISQ quarks
Chris Bouchard, Peter Lepage, Christopher Monahan, Heechang Na, Junko Shigemitsu
Fri, 17:50, Seminar Room D -- Parallels 10D (Slides)

We discuss our ongoing effort to calculate form factors for several $$B$$ and $$B_s$$ semileptonic decays. We have recently completed the first unquenched calculation of the form factors for the rare decay $$B \to K \ell^+ \ell^-$$. Extrapolated over the full kinematic range of $$q^2$$ via model-independent $$z$$ expansion, these form factor results allow us to calculate several Standard Model observables. We compare with experiment (Babar, Belle, CDF, and LHCb) where possible and make predictions elsewhere. We discuss preliminary results for $$B_s \to K \ell \nu$$ which, when combined with anticipated experimental results, will provide an alternative exclusive determination of $$|V_{ub}|$$. We are exploring the possibility of using ratios of form factors for this decay with those for the unphysical decay $$B_s \to \eta_s$$ as a means of significantly reducing form factor errors. We are also studying $$B \to \pi \ell \nu$$, form factors for which are combined with experiment in the standard exclusive determination of $$|V_{ub}|$$. Our simulations use NRQCD heavy and HISQ light valence quarks on the MILC 2+1 dynamical asqtad configurations.

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Status of Semileptonic Hyperon Decays from Lattice QCD using 2+1 flavor Domain Wall Fermions
Shoichi Sasaki
Fri, 18:10, Seminar Room D -- Parallels 10D (Slides)

We report the current status of hyperon semileptonic decays from fully dynamical lattice QCD. The calculations are carried out with gauge configurations generated by the RBC and UKQCD collaborations with (2+1)-flavors of dynamical domain-wall fermions and the Iwasaki gauge action at two couplings, $$\beta$$ = 2.13 and 2.25. Our results show that a sign of the second-order correction of SU(3) breaking on the hyperon vector coupling $$f_1(0)$$ is negative at simulated pion masses of $$M_\pi$$=330-558 MeV. The size of the second-order corrections observed here is also comparable to what is observed in lattice calculations of kaon semileptonic decays. We also evaluate the systematic uncertainty on $$f_1(0)$$ due to the lattice discretization error.

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Lattice calculation of BSM B-parameters using improved staggered fermions in $$N_f = 2+1$$ unquenched QCD
Boram Yoon, Taegil Bae, Yong-Chull Jang, Chulwoo Jung, Hwancheol Jeong, Hyung-Jin Kim, Jangho Kim, Jongjeong Kim, Kwangwoo Kim, Sunghee Kim, Jaehoon Leem, Jeounghwan Pak, Stephen Sharpe, Weonjong Lee
Poster Session

We present the beyond the Standard Model (BSM) B-parameters calculated using improved staggered fermions in $$N_f = 2+1$$ flavors. The matching factors are perturbatively calculated at the one-loop level, and the valence quark masses are extrapolated to the physical values using SU(2) staggered chiral perturbation theory. The continuum and sea quark mass extrapolations are performed using four lattice spacings (a=0.12, 0.09, 0.06 and 0.045 fm) and several different light sea quark masses. We present the B-parameters at 2GeV and 3GeV in the MS-bar scheme with naive dimensional regularization. By combining with experimental value of $$\epsilon_K$$, the results can put strong constraints on the BSM physics.

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Calculations of $$K \to \pi\pi$$ decay amplitude with improved Wilson fermion
Naruhito Ishizuka, Ken-Ichi Ishikawa, Akira Ukawa, Tomoteru Yoshie
Poster Session

We present results of our trial calculations of the $$K \to \pi\pi$$ decay amplitude. Calculations are carried out with $$N_f=2+1$$ gauge configurations previously generated by the PACS-CS Collaboration with the Iwasaki gauge action and nonperturbatively $$O(a)$$-improved Wilson fermion on $$La=2.9 fm$$ at $$m_\pi=300,{rm MeV}$$.

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Charm quark mass and D-meson decay constants from two-flavour lattice QCD
Jochen Heitger, Georg von Hippel, Stefan Schaefer, Francesco Virotta
Poster Session

We present a computation of the charm quark's mass and the leptonic D-meson decay constants $$f_{{\rm D}}$$ and $$f_{{\rm D}_{\rm s}}$$ in two-flavour lattice QCD with non-perturbatively O($$a$$) improved Wilson quarks. Our analysis is based on large-volume CLS configurations at two lattice spacings ($$a=0.066,0.049$$ fm, where the lattice scale is set by $$f_{{\rm K}}$$) and pion masses ranging down to $$\sim 190$$ MeV at $$Lm_{\pi}\ge 4$$, in order to perform controlled continuum and chiral extrapolations with small systematic uncertainties.

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Recent update on $$B_K$$ and $$\varepsilon_K$$ with staggered quarks
Weonjong Lee, Taegil Bae, Yong-Chull Jang, Hwancheol Jeong, Chulwoo Jung, Hyung-Jin Kim, Jangho Kim, Jongjeong Kim, Kwangwoo Kim, Sunghee Kim, Jaehoon Leem, Jeonghwan Pak, Stephen Sharpe, Boram Yoon
Poster Session

We present results of $$B_K$$ and $$\varepsilon_K$$ calculated using improved staggered quarks on the MILC asqtad lattices. Since Lattice 2012, we have added a number of new measurements on the fine ($$a\approx 0.09$$ fm) ensembles and superfine ($$a\approx 0.06$$ fm) ensembles. This allows us to perform a new simutaneous analysis on the dependence on light sea quark masses and on scaling violation (i.e. discretization error of $$\mathcal{O}(a^2)$$). We report an updated version of the error budget of this analysis.

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Matrix elements for D- and B-Mixing from 2+1 flavor lattice QCD
Chia Cheng Chang, Claude Bernard, Chris Bouchard, Aida El-Khadra, Elizabeth Freeland, Elvira Gamiz, Andreas Kronfeld, Laiho Jack, Ruth van de Water
Poster Session

We present the status of the Fermilab Lattice and MILC collaboration's calculation of hadronic matrix elements for D- and B-mixing. We use the asqtad staggered action for light valence quarks in combination with the Fermilab interpretation of the Sheikoleslami-Wohlert action for heavy quarks. The calculations use MILC's 2+1 flavor asqtad ensembles. Ensembles include four lattice spacings from 0.125 -- 0.045 fm and up/down to strange quark mass ratios as low as 0.05. Our calculations cover the complete set of five local operators needed to describe B meson mixing in the Standard Model and Beyond. In the charm sector, our calculation of local mixing matrix elements may be used to constrain new physics models. We will present final B-mixing correlator fit results for the full data set and preliminaries for the D-mixing calculation.

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Radiative Decays in Non-Relativistic QCD
Ciaran Hughes, Rachel Dowdall, Ronald Horgan, Matthew Wingate
Poster Session

Radiative transitions between bottomonium states offer an insight into the internal structure of heavy-quark bound states within QCD. Babar has evaluated the branching fraction of $$\Upsilon(2s) , \Upsilon(3s) \rightarrow \gamma \eta_b(1s)$$. The measured hyperfine splittings also provide a better understanding of the non-relativistic bound states and the role of spin-spin interactions in quarkonium models. I report progress of an exploratory calculation that studies radiative decays in the bottomonium system, where we use non-relativistic QCD including $$u,d,s$$ and $$c$$ HISQ quarks in the sea.

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Flavour Symmetry Breaking in Octet Hyperon Matrix Elements
Ashley Cooke
Poster Session

We investigate the effects of SU(3) flavour symmetry breaking on octet baryon diagonal and transition matrix elements. Results from 2+1 flavours of dynamical O(a)-improved Wilson (clover fermions) for hyperon form factors will be discussed and our simulation techniques outlined. SU(3) flavour symmetry breaking is explored by keeping the singlet quark mass fixed. We use 5 individual choice of quark masses on $$24^3\times 48$$ lattices with a lattice spacing of ~0.078fm.

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