2,826 research outputs found

    The Search for Beauty-fully Bound Tetraquarks Using Lattice Non-Relativistic QCD

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    Motivated by multiple phenomenological considerations, we perform the first search for the existence of a bΛ‰bΛ‰bb\bar{b}\bar{b}bb tetraquark bound state with a mass below the lowest non-interacting bottomonium-pair threshold using the first-principles lattice non-relativistic QCD methodology. We use a full SS-wave colour/spin basis for the bΛ‰bΛ‰bb\bar{b}\bar{b}bb operators in the three 0++0^{++}, 1+βˆ’1^{+-} and 2++2^{++} channels. We employ four gluon field ensembles at multiple lattice spacing values ranging from a=0.06βˆ’0.12a = 0.06 - 0.12 fm, all of which include uu, dd, ss and cc quarks in the sea, and one ensemble which has physical light-quark masses. Additionally, we perform novel exploratory work with the objective of highlighting any signal of a near threshold tetraquark, if it existed, by adding an auxiliary potential into the QCD interactions. With our results we find no evidence of a QCD bound tetraquark below the lowest non-interacting thresholds in the channels studied.Comment: 24 Pages; 19 Figures; Accepted By PRD; Unaveraged Correlator Data Publicly Available in SQLite Databas

    The B(s)β†’D(s)lΞ½B_{(s)} \to D_{(s)}l\nu Decay with Highly Improved Staggered Quarks and NRQCD

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    We report on progress of a lattice QCD calculation of the B→DlνB\to Dl\nu and Bs→DslνB_s\to D_s l\nu semileptonic form factors. We use a relativistic staggered action (HISQ) for light and charm quarks, and an improved non-relativistic (NRQCD) action for bottom, on the second generation MILC ensembles.Comment: Presented at Lattice 2017, the 35th International Symposium on Lattice Field Theory at Granada, Spain (18-24 June 2017

    Bβ†’Dβˆ—B \rightarrow D^* vector, axial-vector and tensor form factors for the full q2q^2 range from lattice QCD

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    We compute the complete set of SM and tensor B(s)β†’D(s)βˆ—β„“Ξ½Λ‰B_{(s)}\to D_{(s)}^*\ell\bar{\nu} semileptonic form factors across the full kinematic range of the decay using second generation MILC nf=2+1+1n_f=2+1+1 HISQ gluon field configurations and HISQ valence quarks, with the heavy-HISQ method. Lattice spacings range from 0.09fm0.09\mathrm{fm} to 0.044fm0.044\mathrm{fm} with pion masses from β‰ˆ300MeV\approx 300\mathrm{MeV} down to the physical value and heavy quark masses ranging between β‰ˆ1.5mc\approx 1.5 m_c and 4.1mcβ‰ˆ0.9mb4.1 m_c \approx 0.9 m_b; currents are normalised nonperturbatively. Using the recent B(s)β†’D(s)βˆ—β„“Ξ½Λ‰β„“B_{(s)}\to D^*_{(s)}\ell\bar{\nu}_\ell data from Belle and LHCb together with our form factors we determine a model independent value of Vcb=39.03(56)exp(67)lattΓ—10βˆ’3V_{cb}=39.03(56)_\mathrm{exp}(67)_\mathrm{latt}\times 10^{-3}, in agreement with previous exclusive determinations and in tension with the inclusive result at the level of 3.6Οƒ3.6\sigma. We observe a β‰ˆ1Οƒ\approx 1\sigma tension between the shape of the differential decay rates computed using our form factors and those measured by Belle. We compute a lattice-only SM value for the ratio of semitauonic and semimuonic decay rates, R(Dβˆ—)=0.273(15)R(D^*)=0.273(15), which we find to be closer to the recent Belle measurement and HFLAV average than theory predictions using fits to experimental differential rate data for Bβ†’Dβˆ—β„“Ξ½Λ‰β„“B\to D^*\ell\bar{\nu}_\ell. Determining VcbV_{cb} using the total rate for Bβ†’Dβˆ—β„“Ξ½B\to D^*\ell\nu gives a value in agreement with inclusive results. We compute the longitudinal polarisation fraction for the semitauonic mode, FLDβˆ—=0.395(24)F_L^{D^*}=0.395(24), which is in tension at the level of 2.2Οƒ2.2\sigma with the recent Belle measurement. Our calculation combines Bβ†’Dβˆ—B\to D^* and Bsβ†’Dsβˆ—B_s\to D_s^* lattice results, and we provide an update which supersedes our previous lattice computation of the Bsβ†’Dsβˆ—B_s\to D_s^* form factors. We also give the chiral perturbation theory needed to analyse the tensor form factors.Comment: 49 pages, 27 figure

    Bcβ†’J/ψB_c \rightarrow J/\psi Form Factors for the full q2q^2 range from Lattice QCD

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    We present the first lattice QCD determination of the Bcβ†’J/ψB_c \rightarrow J/\psi vector and axial-vector form factors. These will enable experimental information on the rate for BcB_c semileptonic decays to J/ψJ/\psi to be converted into a value for VcbV_{cb}. Our calculation covers the full physical q2q^2 range of the decay and uses non-perturbatively renormalised lattice currents. We use the Highly Improved Staggered Quark (HISQ) action for all valence quarks on the second generation MILC ensembles of gluon field configurations including uu, dd, ss and cc HISQ sea quarks. Our HISQ heavy quarks have masses ranging upwards from that of cc; we are able to reach that of the bb on our finest lattices. This enables us to map out the dependence on heavy quark mass and determine results in the continuum limit at the bb. We use our form factors to construct the differential rates for Bcβˆ’β†’J/ΟˆΞΌβˆ’Ξ½Λ‰ΞΌB_c^- \rightarrow J/\psi \mu^- \bar{\nu}_\mu and obtain a total rate with 7%7\% uncertainty: Ξ“(Bcβˆ’β†’J/ΟˆΞΌβˆ’Ξ½Λ‰ΞΌ)/∣ηEWVcb∣2=1.73(12)Γ—1013Β sβˆ’1\Gamma(B_c^-\rightarrow J/\psi \mu^-\bar{\nu}_{\mu})/|\eta_{\mathrm{EW}}V_{cb}|^2 = 1.73(12)\times 10^{13} ~\mathrm{s}^{-1}. Including values for VcbV_{cb}, Ξ·EW\eta_{\mathrm{EW}} and Ο„Bc\tau_{B_c} yields a branching fraction for this decay mode of 0.0150(11)(10)(3) ~with uncertainties from lattice QCD, Ξ·EWVcb\eta_\mathrm{EW}V_{cb} and Ο„Bc\tau_{B_c} respectively.Comment: 23 pages, 14 Figures, Version accepted for publication in Phys. Rev.

    Dβ†’K,lΞ½D \rightarrow K, l \nu Semileptonic Decay Scalar Form Factor and ∣Vcs∣|V_{cs}| from Lattice QCD

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    We present a new study of D semileptonic decays on the lattice which employs the Highly Improved Staggered Quark (HISQ) action for both the charm and the light valence quarks. We work with MILC unquenched Nf=2+1N_f = 2 + 1 lattices and determine the scalar form factor f0(q2)f_0(q^2) for Dβ†’K,lΞ½D \rightarrow K, l \nu semileptonic decays. The form factor is obtained from a scalar current matrix element that does not require any operator matching. We develop a new approach to carrying out chiral/continuum extrapolations of f0(q2)f_0(q^2). The method uses the kinematic "zz" variable instead of q2q^2 or the kaon energy EKE_K and is applicable over the entire physical q2q^2 range. We find f0Dβ†’K(0)≑f+Dβ†’K(0)=0.747(19)f^{D \rightarrow K}_0(0) \equiv f^{D \rightarrow K}_+(0) = 0.747(19) in the chiral plus continuum limit and hereby improve the theory error on this quantity by a factor of ∼\sim4 compared to previous lattice determinations. Combining the new theory result with recent experimental measurements of the product f+Dβ†’K(0)βˆ—βˆ£Vcs∣f^{D \rightarrow K}_+(0) * |V_{cs}| from BaBar and CLEO-c leads to the most precise direct determination of the CKM matrix element ∣Vcs∣|V_{cs}| to date, ∣Vcs∣=0.961(11)(24)|V_{cs}| = 0.961(11)(24), where the first error comes from experiment and the second is the lattice QCD theory error. We calculate the ratio f+Dβ†’K(0)/fDsf^{D \rightarrow K}_+(0)/f_{D_s} and find 2.986Β±0.0872.986 \pm 0.087 GeVβˆ’1^{-1} and show that this agrees with experiment.Comment: 23 pages, 31 figures, 11 tables. Added a paragraph in sction VII, and updated with PDG 2010 instead of PDG 200

    Dβ†’Ο€,lΞ½D \rightarrow \pi, l \nu Semileptonic Decays, ∣Vcd∣|V_{cd}| and 2nd^{nd} Row Unitarity from Lattice QCD

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    We present a new calculation of the Dβ†’Ο€,lΞ½D \rightarrow \pi, l \nu semileptonic form factor f+Dβ†’Ο€(q2)f^{D \rightarrow \pi}_+(q^2) at q2=0q^2 = 0 based on HISQ charm and light valence quarks on MILC Nf=2+1N_f = 2 +1 lattices. Using methods developed recently for HPQCD's study of Dβ†’K,lΞ½D \rightarrow K, l \nu decays, we find f+Dβ†’Ο€(0)=0.666(29)f^{D \rightarrow \pi}_+(0) = 0.666(29). This signifies a better than factor of two improvement in errors for this quantity compared to previous calculations. Combining the new result with CLEO-c branching fraction data, we extract the CKM matrix element ∣Vcd∣=0.225(6)exp.(10)lat.|V_{cd}| = 0.225(6)_{exp.}(10)_{lat.}, where the first error comes from experiment and the second from theory. With a total error of ∼5.3\sim5.3\% the accuracy of direct determination of ∣Vcd∣|V_{cd}| from DD semileptonic decays has become comparable to (and in good agreement with) that from neutrino scattering. We also check for second row unitarity using this new ∣Vcd∣|V_{cd}|, HPQCD's earlier ∣Vcs∣|V_{cs}| and ∣Vcb∣|V_{cb}| from the Fermilab Lattice \& MILC collaborations. We find ∣Vcd∣2+∣Vcs∣2+∣Vcb∣2=0.976(50)|V_{cd}|^2 + |V_{cs}|^2 + |V_{cb}|^2 = 0.976(50), improving on the current PDG2010 value.Comment: 7 pages, 7 figures, and 4 table

    B and B-s meson decay constants from lattice QCD

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    We present a new determination of the B and B-s meson decay constants using nonrelativistic quantum chromodynamics (NRQCD) b-quarks, highly improved staggered quark (HISQ) light and strange valence quarks and the MILC collaboration N-f = 2 + 1 lattices. The new calculations improve on HPQCD\u27s earlier work with NRQCD b-quarks by replacing AsqTad with HISQ valence quarks, by including a more chiral MILC fine ensemble in the analysis, and by employing better tuned quark masses and overall scale. We find f (B) = 0.191(9) GeV, f (Bs) = 0.228(10) GeV and f (Bs)/f (B) = 1.188(18). Combining the new value for f (Bs)/f (B) with a recent very precise determination of the B-s meson decay constant based on HISQ b-quarks, f (Bs) = 0.225(4) GeV, leads to f (B) = 0.189(4) GeV. With errors of just 2.1% this represents the most precise f (B) available today
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