Unquenched Lattice QCD Calculations Research Articles

Study of dynamics ofD0→K−e+νeandD0→π−e+νedecays

In an analysis of a 2.92 fb(-1) data sample taken at 3.773 GeV with the BESIII detector operated at the BEPCII collider, we measure the absolute decay branching fractions B(D-0 -> K(-)e(+)nu(e)) = (3.505 +/- 0.014 +/- 0.033)% and B(D-0 -> pi(-)e(+)nu(e)) = (0.295 +/- 0.004 +/- 0.003)%. From a study of the differential decay rates we obtain the products of hadronic form factor and the magnitude of the Cabibbo-Kobayashi-Maskawa (CKM) matrix element f(+)(K)(0)vertical bar V-cs vertical bar = 0.7172 +/- 0.0025 +/- 0.0035 and f(+)(pi)(0)vertical bar V-cd vertical bar = 0.1435 +/- 0.0018 +/- 0.0009. Combining these products with the values of vertical bar V-cs(d)vertical bar from the SM constraint fit, we extract the hadronic form factors f(+)(K)(0) = 0.7368 +/- 0.0026 +/- 0.0036 and f(+)(pi)(0) = 0.6372 +/- 0.0080 +/- 0.0044, and their ratio f(+)(pi)(0)/f(+)(K)(0) = 0.8649 +/- 0.0112 +/- 0.0073. These form factors and their ratio are used to test unquenched lattice QCD calculations of the form factors and a light cone sum rule (LCSR) calculation of their ratio. The measured value of f(+)(K(pi))(0)vertical bar V-cs(d)vertical bar and the lattice QCD value for f(+)(K(pi))(0) are used to extract values of the CKM matrix elements of vertical bar V-cs vertical bar = 0.9601 +/- 0.0033 +/- 0.0047 +/- 0.0239 and vertical bar V-cd vertical bar = 0.2155 +/- 0.0027 +/- 0.0014 +/- 0.0094, where the third errors are due to the uncertainties in lattice QCD calculations of the form factors. Using the LCSR value for f(+)(pi)(0)/f(+)(K)(0), we determine the ratio vertical bar V-cd vertical bar/vertical bar V-cs vertical bar = 0.238 +/- 0.004 +/- 0.002 +/- 0.011, where the third error is from the uncertainty in the LCSR normalization. In addition, we measure form factor parameters for three different theoretical models that describe the weak hadronic charged currents for these two semileptonic decays. All of these measurements are the most precise to date.

Towards the glueball spectrum from unquenched lattice QCD

We use a variational technique to study heavy glueballs on gauge configurations generated with 2+1 flavours of ASQTAD improved staggered fermions. The variational technique includes glueball scattering states. The measurements were made using 2150 configurations at 0.092 fm with a pion mass of 360 MeV. We report masses for 10 glueball states. We discuss the prospects for unquenched lattice QCD calculations of the oddballs.

A possible signature of new physics at BES-III

The recent observations of the purely leptonic decay D+s → μ+ νμ and τ+ ντ at CLEO-c and B factory may allow a possible contribution from a charged Higgs boson. One such measurement of the decay constant fDS differs from the most precise unquenched lattice QCD calculation by a level of 4 σ. Meanwhile, the measured ratio, , is larger than the standard model prediction at a 2.0σ level. We discuss that the precise measurement of the ratio ) at BES-III will shed light on the presence of new intermediate particles by comparing the data with the theoretical predictions, especially, the predictions of high precise unquenched lattice QCD calculations.

Charm Physics at CLEO-c

The latest results are presented from CLEO-c on W annihilation decays of the D + and D s + mesons. This includes the decay constants and the first observation of the decay D s + → p n ¯ . Presented here is the final result for the D + from the complete data set of 818 pb−1 and an updated result for the D s + from 400 pb−1 of the total data set of 600 pb−1 The final result is f D + = ( 205.8 ± 8.5 ± 2.5 ) MeV , and the preliminary value for the D s + is f D s + = ( 267.9 ± 8.2 ± 3.9 ) MeV , where both results are radiatively corrected. The recent most precise unquenched Lattice-QCD calculation for the D + agree with this result but are in disagreement with the D s + . Using almost identical analysis techniques the decay D s + → p n ¯ has been observed with a branching fraction B ( D s + → p n ¯ ) = ( 1.30 ± 0.36 −0.16 +0.12 ) × 10 −3 .

Measurements of branching fractions and q2 distributions for B→πℓν and B→ρℓν decays with B→D(∗)ℓν decay tagging

We report measurements of the charmless semileptonic decays $B^0 \to \pi^- / \rho^- \ell^{+} \nu$ and $B^+ \to \pi^0 / \rho^0 \ell^{+} \nu$, based on a sample of $2.75 \times 10^8$ $B \bar{B}$ events collected at the $\Upsilon(4S)$ resonance with the Belle detector at the KEKB $e^+e^-$ asymmetric collider. In this analysis, the accompanying $B$ meson is reconstructed in the semileptonic mode $B \to D^{(*)} \ell \nu$, enabling detection of the signal modes with high purity. We measure the branching fractions ${\mathcal B}(B^0 \to \pi^- \ell^+ \nu) = (1.38\pm 0.19\pm 0.14\pm 0.03) \times 10^{-4}$, ${\mathcal B}(B^0 \to \rho^- \ell^+ \nu) = (2.17\pm 0.54\pm 0.31\pm 0.08) \times 10^{-4}$, ${\mathcal B}(B^+ \to \pi^0 \ell^+ \nu) = (0.77\pm 0.14\pm 0.08\pm 0.00) \times 10^{-4}$ and ${\mathcal B}(B^+ \to \rho^0 \ell^+ \nu) = (1.33\pm 0.23\pm 0.17\pm 0.05) \times 10^{-4}$, where the errors are statistical, experimental systematic, and systematic due to form-factor uncertainties, respectively. For each mode we also present the partial branching fractions in three $q^2$ intervals: $q^2 < 8$, $8 \leq q^2 < 16$, and $q^2 \geq 16$ GeV$^2/c^2$. From our partial branching fractions for $B \to \pi \ell \nu$ and recent results for the form factor from unquenched Lattice QCD calculations, we obtain values of the CKM matrix element $|V_{ub}|$.

Measurement of theB0→π−l+νForm-Factor Shape and Branching Fraction, and Determination of|Vub|with a Loose Neutrino Reconstruction Technique

We report the results of a study of the exclusive charmless semileptonic decay, B0-->pi(-l)(+nu), undertaken with approximately 227 x 10(6) BB pairs collected at the Upsilon(4S) resonance with the BABAR detector. The analysis uses events in which the signal B decays are reconstructed with an innovative loose neutrino reconstruction technique. We obtain partial branching fractions in 12 bins of q2, the momentum transfer squared, from which we extract the f + (q2) form-factor shape and the total branching fraction B(B0-->pi(-l)(+nu))=(1.46+/-0.07stat+/-0.08syst) x 10(-4). Based on a recent unquenched lattice QCD calculation of the form factor in the range q2>16 GeV2, we find the magnitude of the Cabibbo-Kobayashi-Maskawa matrix element /Vub/ to be (4.1+/-0.2stat +/- 0.2syst(+0.6)-0.4_{FF}) x 10(-3), where the last uncertainty is due to the normalization of the form factor.

An estimate of the chiral condensate from unquenched lattice QCD

Using the parameters in the chiral Lagrangian obtained by MILC from their unquenched lattice QCD calculations with 2+1 flavours of sea quarks, I estimate the chiral condensate. I obtain the result 〈ψ¯ψ〉(2 GeV)/nf = −(259±27 MeV)3 in the MS¯ scheme. I compare this value to other determinations.

Phenomenology of static-light mesons from unquenched lattice QCD calculations

We present results for the static-light meson from unquenched lattice QCD. The unquenched gauge configurations were generated using the non-perturbatively improved clover action. At the fixed lattice spacing of 0.1 fm the lightest sea quark mass used is a third of the strange quark mass. A comparison is made between heavy-light chiral perturbation theory and the fstaticB B decay constant. The mass of the bottom quark is also reported: mb¯(mb¯)=4.25(2)(11) GeV, where the first error is statistical and the last error is the systematic uncertainty.

Measurements of the [formula omitted] dependence of the [formula omitted] and [formula omitted] form factors

Using a large sample of D 0 → K − μ + ν and D 0 → π − μ + ν decays collected by the FOCUS photoproduction experiment at Fermilab, we present new measurements of the q 2 dependence for the f + ( q 2 ) form factor. These measured f + ( q 2 ) form factors are fit to common parameterizations such as the pole dominance form and compared to recent unquenched Lattice QCD calculations. We find m pole = 1.93 ± 0.05 ± 0.03 GeV / c 2 for D 0 → K − μ + ν and m pole = 1.91 −0.15 +0.30 ± 0.07 GeV / c 2 for D 0 → π − μ + ν and f − ( K ) ( 0 ) / f + ( K ) ( 0 ) = − 1.7 −1.4 +1.5 ± 0.3 .

An unquenched lattice QCD calculation of the mass of the bottom quark

We compute the b quark mass from dynamical lattice QCD with clover quarks. The calculation is done at a fixed lattice spacing with sea quark masses as low as half the strange quark mass. Our final result is mb¯(mb¯)=4.25(2)(11) GeV, where the first error is statistical and the last error is the systematic uncertainty.