# The 35th International Symposium on Lattice Field Theory

18-24 June 2017
Palacio de Congresos
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# Weak Decays and Matrix Elements

## Place

Location: Palacio de Congresos
Date: from 19 Jun 14:30 to 23 Jun 19:10

## Conveners

• 19 Jun 14:30 - 16:10
• Dr. Lytle, Andrew (University of Glasgow)
• 19 Jun 16:40 - 18:00
• Dr. Kelly, Christopher (Columbia University)
• 20 Jun 15:00 - 16:40
• Dr. Koponen, Jonna (INFN Tor Vergata, Rome)
• 20 Jun 17:10 - 19:10
• Dr. Witzel, Oliver (University of Edinburgh)
• 21 Jun 09:00 - 11:00
• Mr. Garron, Nicolas (University of Liverpool)
• 21 Jun 11:30 - 13:30
• Kaneko, Takashi (KEK)
• 23 Jun 17:10 - 19:10
• Dr. Wingate, Matthew (University of Cambridge)

## Timetable | Contribution List

Displaying 38 contributions out of 38
Type: Parallel Session: Weak Decays and Matrix Elements
Track: Weak Decays and Matrix Elements
We report on the status of our calculation of the exclusive semileptonic decay, $B \rightarrow \pi\ell\nu$; a key process in the determination of the CKM matrix element $V_{ub}$. The M\"{o}bius domain wall action is used for both light and heavy quarks on gauge ensembles that include the effects of $2+1$ flavours of quarks in the sea at three values of the lattice spacing: $a\approx0.08~\mathrm{fm ... More Presented by Dr. Brian COLQUHOUN on 19/6/2017 at 14:50 Type: Parallel Session: Weak Decays and Matrix Elements Track: Weak Decays and Matrix Elements Using the MILC 2+1 flavor asqtad quark action ensembles, we are calculating the form factors$f_0$and$f_+$for the semileptonic$B_s \rightarrow K \ell\nu$decay. A total of six ensembles with lattice spacing from$\approx0.12$to 0.06 fm are being used. At the coarsest and finest lattice spacings, the light quark mass$m_l$is one-tenth the strange quark mass$m_s$. At the intermediate latti ... More Presented by Prof. Steven GOTTLIEB on 19/6/2017 at 15:10 Type: Parallel Session: Weak Decays and Matrix Elements Track: Weak Decays and Matrix Elements The quark flavor sector of the Standard Model is a fertile ground to test any new physics effect through the Unitarity test of the Cabbibo-Kobayashi-Maskawa (CKM) matrix. We present a lattice QCD calculation of the scalar and the vector form factors (over a large$q^2$region including$q^2=0$) associated with the$D\rightarrow Kl\nu$semi-leptonic decay. The central CKM matrix element,$V_{cs}$i ... More Presented by Dr. Bipasha CHAKRABORTY on 20/6/2017 at 18:30 Type: Parallel Session: Weak Decays and Matrix Elements Track: Weak Decays and Matrix Elements We present our calculation of$D \to \pi$and$D \to K$semileptonic form factors in 2+1 flavor lattice QCD. We simulate three lattice cutoffs$a^{-1} \sim $2.5, 3.6 and 4.5 GeV with pion masses as low as 230 MeV. The Moebius domain-wall action is employed for both light and charm quarks. We present our results for the vector and scalar form factors and discuss their dependence on the latt ... More Presented by Takashi KANEKO on 20/6/2017 at 17:10 Type: Parallel Session: Weak Decays and Matrix Elements Track: Weak Decays and Matrix Elements The decay$\Lambda_b \to \Lambda(1520)(\to p^+ K^-) \mu^+\mu^-$is a baryonic analogue of the mesonic process$\bar{B}^0 \to \bar{K}^{*0}(892)(\to \pi^+ K^-) \mu^+\mu^-$, in which tensions between theory and experiment have been observed. Here we give an update on our lattice calculations of$\Lambda_b \to \Lambda(1520)$form factors. To allow an exact projection to the$J^P=\frac32^-$quantum nu ... More Presented by Mr. Gumaro RENDON on 20/6/2017 at 13:20 Type: Parallel Session: Weak Decays and Matrix Elements Track: Weak Decays and Matrix Elements We present first results from our analysis of the form factors for$\bar{B}\rightarrow D^\star \ell \bar{\nu}$decay at non-zero recoil. Our analysis includes 15 MILC asqtad ensembles with$N_f=2+1$flavors of sea quarks and lattice spacings ranging from$a\approx0.15$~fm down to$0.045$~fm. The valence light quarks employ the asqtad action, whereas The$b$and$c$quarks are treated using the Fe ... More Presented by Dr. Alejandro VAQUERO AVILÉS-CASCO on 19/6/2017 at 15:00 Type: Parallel Session: Weak Decays and Matrix Elements Track: Weak Decays and Matrix Elements An update on the RBC-UKQCD measurement of BSM kaon mixing, simulated in nf=2+1 QCD with domain wall fermions at the physical quark masses. Presented by Ms. Julia KETTLE on 21/6/2017 at 9:30 Type: Parallel Session: Weak Decays and Matrix Elements Track: Weak Decays and Matrix Elements We present preliminary results of the calculation of$\bar{B} \rightarrow D^\ast \ell \bar{\nu}$form factor at zero recoil. We use$N_f=2+1+1$MILC HISQ ensembles. The charm and bottom quarks are implemented using the Oktay-Kronfeld (OK) action. For the light spectator quark, we use the HISQ action. We also report a recent progress in determining the critical hopping parameter$\kappa_\text{cri ... More
Presented by Mr. Sungwoo PARK on 19/6/2017 at 15:20
Type: Parallel Session: Weak Decays and Matrix Elements
Track: Weak Decays and Matrix Elements
I will review the domain wall charm physics program of the RBC and UKQCD collaborations using physical pion masses. After a brief recap of our previous results ($f_D$ and $f_{D_s}$), I will present our current set-up and present a status update of a number of observables.
Presented by Justus Tobias TSANG on 20/6/2017 at 18:50
Type: Parallel Session: Weak Decays and Matrix Elements
Track: Weak Decays and Matrix Elements
I present a high-precision lattice QCD calculation of $\Lambda_c\to\Lambda$ form factors and a determination of the CKM matrix element $|V_{cs}|$ from $\Lambda_c\to\Lambda \ell^+\nu_\ell$ decays. I will also show preliminary results for $\Lambda_c \to p$ form factors, which are relevant for the rare charm decays $\Lambda_c \to p \ell^+\ell^-$.
Presented by Prof. Stefan MEINEL on 20/6/2017 at 17:30
Type: Parallel Session: Weak Decays and Matrix Elements
Track: Weak Decays and Matrix Elements
We present results for the decay constants $f_B$ and $f_{B_s}$ and update our earlier determinations of $f_D$ and $f_{D_s}$. We employ HISQ ensembles with 2+1+1 flavors generated at six lattice spacings, including five with physical light-quark masses. Calculations are carried out with several heavy valence-quark masses ranging from near charm to bottom (at the finest lattice spacing). In additio ... More
Presented by Javad KOMIJANI on 20/6/2017 at 15:40
Type: Parallel Session: Weak Decays and Matrix Elements
Track: Weak Decays and Matrix Elements
We report preliminary results on semileptonic form factors of $B_c\rightarrow \eta_c l\nu$ and $B_c\rightarrow J/\psi l\nu$ decays as well as the decay constant of $B_c$ meson. For the charm quark we use overlap fermions whereas a non-relativistic formulation with improved coefficients is utilized for the bottom quark on a background of three 2+1+1 flavours HISQ lattice ensembles generated by the ... More
Presented by Prof. Nilmani MATHUR on 19/6/2017 at 15:40
Type: Parallel Session: Weak Decays and Matrix Elements
Track: Weak Decays and Matrix Elements
We investigate the dispersion relation of Mobius domain-wall fermions in free field theory at finite $L_s$. We find that the quark propagator constructed from the domain-wall fermion operator has $L_s-1$ extra poles as well as the pole which realizes the physical quark in the continuum limit. The unphysical contribution of these extra poles could be significant when we introduce heavy quarks. In t ... More
Presented by Dr. Masaaki TOMII on 23/6/2017 at 18:50
Type: Parallel Session: Weak Decays and Matrix Elements
Track: Weak Decays and Matrix Elements
We report on the status of our programme to develop a framework for the calculation of electromagnetic corrections to weak decay amplitudes. The $O(1\%)$ precision increasingly being reached in isospin-symmetric QCD calculations necessitates the inclusion of isospin-breaking effects, including electromagnetism, if continuing progress in the determination of the fundamental parameters of the Standa ... More
Presented by Prof. Guido MARTINELLI on 21/6/2017 at 10:40
Type: Parallel Session: Weak Decays and Matrix Elements
Track: Weak Decays and Matrix Elements
We compute semi-leptonic $B_s$ decay form factors using Heavy Quark Effective Theory on the lattice. To obtain good control of the $1/m_b$ expansion, one has to take into account not only the leading static order but also the terms arising at $O(1/m_b)$: kinetic, spin and current insertions. We show results for these terms calculated through the ratio method, using our prior results for the static ... More
Presented by Dr. Mateusz KOREN on 19/6/2017 at 15:50
Type: Parallel Session: Weak Decays and Matrix Elements
Track: Weak Decays and Matrix Elements
We present a lattice computation of pseudoscalar and vector heavy-light meson masses for heavy-quark masses ranging from the physical charm mass up to $\simeq 4$ times the physical b-quark mass. We employ the gauge configurations generated by the European Twisted Mass Collaboration (ETMC) with $N_f = 2+1+1$ dynamical quarks at three values of the lattice spacing ($a \simeq 0.062 - 0.089$ fm) with ... More
Presented by Aurora MELIS on 23/6/2017 at 16:30
Type: Parallel Session: Weak Decays and Matrix Elements
Track: Weak Decays and Matrix Elements
We present lattice QCD results for the matrix elements of $R_2$ and other dimension-7, $\Delta B = 2$ operators relevant for calculations of $\Delta \Gamma_s$, the $B_s-\bar{B}_s$ width difference. We have computed correlation functions using 5 ensembles of the MILC Collaboration's $2+1+1$-flavor gauge field configurations, spanning 3 lattice spacings and light sea quarks masses down to the ... More
Presented by Dr. Matthew WINGATE on 20/6/2017 at 16:00
Type: Parallel Session: Weak Decays and Matrix Elements
Track: Weak Decays and Matrix Elements
Because of the small size of the ratio $A_2/A_0$ of the $I=2$ to $I=0$ $K\to\pi\pi$ decay amplitudes (the $\Delta I=1/2$ rule) the effects of electromagnetism on $A_2$ may be a factor of 20 larger than given by a naive $O(\alpha)$ estimate. Thus, if future calculations of $A_2$ and $\varepsilon'/\varepsilon$ are to achieve 10% accuracy, these effects need to be included. Here we present the firs ... More
Presented by Prof. Norman CHRIST on 21/6/2017 at 12:10
Type: Parallel Session: Weak Decays and Matrix Elements
Track: Weak Decays and Matrix Elements
First-principle lattice calculation of inclusive B meson semileptonic decays is possible for a certain class of moments that is connected to the structure function at unphysical kinematics by analytic continuation. We present an exploratory lattice calculation and a comparison with the heavy quark expansion technique.
Presented by Dr. Shoji HASHIMOTO on 21/6/2017 at 10:20
Type: Parallel Session: Weak Decays and Matrix Elements
Track: Weak Decays and Matrix Elements
We report on the status of an ongoing effort by the RQCD and ALPHA Collaborations, aimed at determining leptonic decay constants of charmed mesons. Our analysis is based on large-volume ensembles generated within the CLS effort, employing $N_f=2+1$ non-perturbatively $\mathcal{O}(a)$ improved Wilson quarks, tree-level Symanzik-improved gauge action and open boundary conditions. The ensembles ... More
Presented by Mr. Kevin ECKERT on 21/6/2017 at 9:20
Type: Parallel Session: Weak Decays and Matrix Elements
Track: Weak Decays and Matrix Elements
We present our final results for the neutral $D$-meson mixing matrix elements of the complete set of dimension six $\Delta C=2$ local four-fermion operators from the first three-flavor lattice QCD calculation. We use a large subset of the MILC asqtad ensembles together with Fermilab charm and asqtad light valence quarks. We provide complete and detailed systematic error budgets which account for a ... More
Presented by Prof. Aida X. EL-KHADRA on 20/6/2017 at 16:20
Type: Parallel Session: Weak Decays and Matrix Elements
Track: Weak Decays and Matrix Elements
We study the scaling with the number of colors of the weak amplitudes mediating kaon mixing and decay, in the limit of light charm masses ($m_u = m_d = m_s = m_c$). The amplitudes are extracted directly on the lattice for $N_c = 3 - 8$ colors using twisted mass QCD. It is shown that the (subleading) $1/N_c$ corrections to $\hat B_K$ are small and that the naive $N_c \to \infty$ limit, $\hat B_ ... More Presented by Andrea DONINI on 21/6/2017 at 11:50 Type: Parallel Session: Weak Decays and Matrix Elements Track: Weak Decays and Matrix Elements Semileptonic decays of$B_s$mesons allow to explore new, independent channels to determine the CKM matrix elements$|V_{ub}|$and$|V_{cb}|$. In the past such determinations were hampered by the paucity of experimental data. In light of the large number of$B_s$mesons recorded by the LHCb experiment however such determinations are becoming feasible but require nonperturbative input in the form o ... More Presented by Dr. Oliver WITZEL on 19/6/2017 at 15:30 Type: Parallel Session: Weak Decays and Matrix Elements Track: Weak Decays and Matrix Elements Among the different scenarios of New Physics, those with an extended Higgs sector are examined with a lot of attention. Recent experimental observations of several anomalies in flavour physics with respect to expectations of the Standard Model further motivate the effort of phenomenologists. First, informations about the R_Ds* ratio, a test of lepton flavour universality equivalent to R_D*, al ... More Presented by Dr. Benoît BLOSSIER on 21/6/2017 at 9:00 Type: Parallel Session: Weak Decays and Matrix Elements Track: Weak Decays and Matrix Elements The leptonic decay of the charged pion in the presence of background magnetic fields is investigated using Wilson fermions. It is demonstrated that the magnetic field opens up a new channel for this decay. The magnetic field-dependence of the decay constants for both the ordinary and the new channel is determined. Using these inputs from QCD, we calculate the total decay rate perturbatively. Presented by Dr. Gergely ENDRODI on 23/6/2017 at 18:10 Type: Parallel Session: Weak Decays and Matrix Elements Track: Weak Decays and Matrix Elements We discuss the ongoing effort by the RBC & UKQCD collaborations to improve our lattice calculation of the measure of Standard Model direct CP violation, \epsilon', with physical kinematics. We present our progress in decreasing the (dominant) statistical error, which we aim to reduce by a factor of 2 within the next year, including a comparison of performance figures for our measurements on Intel ... More Presented by Dr. Christopher KELLY on 21/6/2017 at 13:10 Type: Parallel Session: Weak Decays and Matrix Elements Track: Weak Decays and Matrix Elements A physical point simulation of the rare kaon decays$K \to \pi \ell^+ \ell^-$with 4 active flavours is demanding for two reasons: first the simulation of a physical charm quark required for the GIM mechanism requires a fine lattice, and second a large volume is needed to suppress finite volume effects. A full lattice calculation of this decay is unfeasible with existing computational resources; a ... More Presented by Mr. Andrew LAWSON on 21/6/2017 at 12:50 Type: Parallel Session: Weak Decays and Matrix Elements Track: Weak Decays and Matrix Elements We present a lattice determination of the vector and scalar form factors of the$D \to \pi(K) \ell \nu$semileptonic decays, which are relevant for the extraction of the CKM matrix elements$|V_{cd}|$and$|V_{cs}|$from experimental data. Our analysis is based on the gauge configurations produced by the European Twisted Mass Collaboration with$N_f = 2 + 1 + 1$flavors of dynamical quarks. We sim ... More Presented by Mr. Giorgio SALERNO on 20/6/2017 at 17:50 Type: Parallel Session: Weak Decays and Matrix Elements Track: Weak Decays and Matrix Elements We report on a calculation of$B_c \to \eta_c l \nu$and$B_c \to J/\psi l \nu$semileptonic decays, using both NRQCD effective theory and a highly improved relativistic (HISQ) formalism at multiple lattice spacings down to$a = 0.045$fm to treat the$b$quark. In both formalisms we are able to obtain a signal across the full kinematic range, and good quantitative agreement is seen between the ... More Presented by Dr. Andrew LYTLE on 20/6/2017 at 13:00 Type: Parallel Session: Weak Decays and Matrix Elements Track: Weak Decays and Matrix Elements We present the status of an ongoing lattice-QCD calculation of form factors for exclusive semileptonic decays of$B$mesons with both charged currents ($B\to\pi\ell\nu$,$B_s\to K\ell\nu$) and neutral currents ($B\to\pi\ell^+\ell^-$,$B\to K\ell^+\ell^-$). The results are important for constraining or revealing physics beyond the Standard Model. This work uses MILC's (2+1+1)-flavor ensembles, with ... More Presented by Andreas KRONFELD on 19/6/2017 at 14:30 Type: Parallel Session: Weak Decays and Matrix Elements Track: Weak Decays and Matrix Elements We discuss a mixed-action approach in which sea quarks are regularized using non-perturbatively$O(a)$improved Wilson fermions, while an$N_f=2+1+1$fully-twisted tmQCD action is used for valence quarks. In this setup automatic O(a) improvement is preserved for valence observables, apart from small residual O(a) effects from the sea. An optimal strategy for matching sea and valence is set up, and ... More Presented by Mr. Jose Angel ROMERO JURADO on 23/6/2017 at 17:10 Type: Parallel Session: Weak Decays and Matrix Elements Track: Weak Decays and Matrix Elements We present a preliminary lattice calculation of the$D \to \pi$and$D \to K$tensor form factors$f_T$as a function of the 4-momentum transfer squared. ETMC recently computed the vector and scalar form factors$f_+(q^2)$and$f_0(q^2)$describing$D \to \pi(K) \ell \nu$semileptonic decays analyzing the vector current and the scalar density. The study of the weak tensor current, which is directl ... More Presented by Dr. Lorenzo RIGGIO on 20/6/2017 at 18:10 Type: Parallel Session: Weak Decays and Matrix Elements Track: Weak Decays and Matrix Elements A number of anomalies (apparent inconsistencies with the standard model (SM)) in semileptonic decays involving a$b \rightarrow c$transition, have surfaced over the years. For example there are persistent discrepancies between experimentally observed values and SM predictions for the ratios$\mathcal{B}(B \rightarrow D(*)\tau \nu)/\mathcal{B}(B->D(*) l \nu)$($l=e$or$\mu$). This implies lepton ... More Presented by Mr. Euan MCLEAN on 19/6/2017 at 14:40 Type: Parallel Session: Weak Decays and Matrix Elements Track: Weak Decays and Matrix Elements We report on the status and prospects of the RBC-UKQCD collaborations' computations of$\Delta m_K$, the$K_L$-$K_S$mass difference. This calculation is an important element of our wider programme of computations of the long-distance contributions to *flavour changing neutral current* processes in kaon physics, which also includes$\epsilon_K$and the amplitudes for$K\to\pi\ell^+\ell^-$and$K^ ... More
Presented by Prof. Christopher SACHRAJDA on 21/6/2017 at 12:30
Type: Parallel Session: Weak Decays and Matrix Elements
Track: Weak Decays and Matrix Elements
I present a new technique for extracting total transition rates into final states with any number of hadrons from lattice QCD. The method involves constructing a finite-volume Euclidean four-point function whose corresponding infinite-volume spectral function gives access to the decay and transition rates into all allowed out-states. The inverse problem of calculating the spectral function is solv ... More
Presented by Dr. Daniel ROBAINA on 21/6/2017 at 9:40
Type: Parallel Session: Weak Decays and Matrix Elements
Track: Weak Decays and Matrix Elements
I describe applications and extensions of a new technique for determining total transition rates into multi-hadron final states using lattice QCD. I will outline the connection of our new approach to the method of Lellouch and Lüscher, which gives decay amplitudes rather than total rates but is of limited utility when many decay channels are open. The Lellouch-Lüscher relation, together with oth ... More
Presented by Maxwell T. HANSEN on 21/6/2017 at 10:00
Type: Parallel Session: Weak Decays and Matrix Elements
Track: Weak Decays and Matrix Elements
In this work we present a new calculation of the Wilson Coefficients c1 and c2 of the Effective Weak Hamiltonian to all-orders in alpha_s, using lattice simulations. Given the current availability of lattice spacings we restrict our calculation to unphysically light W-bosons around 2 GeV and we demonstrate how both Wilson Coefficients can be obtained with controlled systematic uncertainties.
Presented by Dr. Mattia BRUNO on 23/6/2017 at 17:30
Type: Parallel Session: Weak Decays and Matrix Elements
Track: Weak Decays and Matrix Elements
We propose and apply a novel approach to determining |Vus| which uses inclusive strange hadronic tau decay data and hadronic vacuum polarization functions (HVPs) computed on the lattice. The experimental and lattice data are related through dispersion relations which employ a class of weight functions having poles at space-like momentum. Implementing this approach using lattice data generated by t ... More
Presented by Dr. Hiroshi OHKI on 23/6/2017 at 17:50
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