We calculate—for the first time in three-flavor lattice QCD—the hadronic matrix elements of all five local operators that contribute to neutral B0- and Bs-meson mixing in and beyond the Standard ...Model. In this paper, we present a complete error budget for each matrix element and also provide the full set of correlations among the matrix elements. We also present the corresponding bag parameters and their correlations, as well as specific combinations of the mixing matrix elements that enter the expression for the neutral B-meson width difference. We obtain the most precise determination to date of the SU(3)-breaking ratio ξ=1.206(18)(6), where the second error stems from the omission of charm-sea quarks, while the first encompasses all other uncertainties. The threefold reduction in total uncertainty, relative to the 2013 Flavor Lattice Averaging Group results, tightens the constraint from B mixing on the Cabibbo-Kobayashi-Maskawa (CKM) unitarity triangle. Our calculation employs gauge-field ensembles generated by the MILC Collaboration with four lattice spacings and pion masses close to the physical value. We use the asqtad-improved staggered action for the light-valence quarks and the Fermilab method for the bottom quark. We use heavy-light meson chiral perturbation theory modified to include lattice-spacing effects to extrapolate the five matrix elements to the physical point. We combine our results with experimental measurements of the neutral B-meson oscillation frequencies to determine the CKM matrix elements |Vtd|=8.00(34)(8)×10-3, |Vts|=39.0(1.2)(0.4)×10-3, and |Vtd/Vts|=0.2052(31)(10), which differ from CKM-unitarity expectations by about 2σ. Lastly, these results and others from flavor-changing-neutral currents point towards an emerging tension between weak processes that are mediated at the loop and tree levels.
We compute the form factors for the B → Kl+l- semileptonic decay process in lattice QCD using gauge-field ensembles with 2+1 flavors of sea quark, generated by the MILC Collaboration. The ensembles ...span lattice spacings from 0.12 to 0.045 fm and have multiple sea-quark masses to help control the chiral extrapolation. The asqtad improved staggered action is used for the light valence and sea quarks, and the clover action with the Fermilab interpretation is used for the heavy b quark. We present results for the form factors f+(q2), f0(q2), and fT(q2), where q2 is the momentum transfer, together with a comprehensive examination of systematic errors. Lattice QCD determines the form factors for a limited range of q2, and we use the model-independent z expansion to cover the whole kinematically allowed range. We present our final form-factor results as coefficients of the z expansion and the correlations between them, where the errors on the coefficients include statistical and all systematic uncertainties. Lastly, we use this complete description of the form factors to test QCD predictions of the form factors at high and low q2.
We compute the leptonic decay constants functionofD+, functionof sub(Ds), and functionof sub(K+) and the quark-mass ratios m sub(c)/m sub(s) and m sub(s)/m sub(l) in unquenched lattice QCD using the ...experimentally determined value of functionof sub(pi+) for normalization. We use the MILC highly improved staggered quark ensembles with four dynamical quark flavors-up, down, strange, and charm-and with both physical and unphysical values of the light sea-quark masses. The use of physical pions removes the need for a chiral extrapolation, thereby eliminating a significant source of uncertainty in previous calculations. Four different lattice spacings ranging from a asymptotically = 0.06 to 0.15 fm are included in the analysis to control the extrapolation to the continuum limit. Our primary results are ... MeV, ... MeV, and ..., where the errors are statistical and total systematic, respectively. The errors on our results for the charm decay constants and their ratio are approximately 2-4 times smaller than those of the most precise previous lattice calculations. We also obtain ..., updating our previous result, and determine the quark-mass ratios ... and ... When combined with experimental measurements of the decay rates, our results lead to precise determinations of the Cabibbo-Kobayashi-Maskawa matrix elements V sub(us) = 0.22487(51)(29)(20)(5), V sub(cd) = 0.217(1)(5)(1) and V sub(cs) = 1.010(5)(18)(6), where the errors are from this calculation of the decay constants, the uncertainty in the experimental decay rates, structure-dependent electromagnetic corrections, and, in the case of V sub(us), the uncertainty in V sub(ud), respectively.
The aim of this paper is to evaluate experimentally the relationships between cross-polarization discrimination (XPD), signal cross correlation, and polarization diversity gain with ...horizontally/vertically (HV) polarized reception at the base-station (BS) end at 1800 MHz. The performance of the horizontal/vertical polarization diversity scheme was also compared with a diversity scheme with /spl plusmn/45/spl deg/ slanted polarizations and horizontal space diversity at 1800 MHz in a personal communication system (PCS) mobile network. A measurement campaign was conducted in small/micro cells in different types of areas, taking into account the influence of mobile antenna inclination. According to the measurements, XPD values for horizontal/vertical polarizations vary between 5-15 dB, depending on the environment. Furthermore, XPD values depend highly on the radio propagation path between the BS and mobile station (MS) due to line-of-sight (LOS) and nonline-of-sight (NLOS) situations. Signal cross correlations of horizontal and vertical polarizations in both LOS and NLOS situations were clearly below 0.7, which is the generally accepted value to have a reasonable improvement at the receiving end with diversity. Finally, the results showed that almost equal diversity gain and system performance in a PCS network at 1800 MHz can be achieved in small/micro cells in different environments with /spl plusmn/45/spl deg/ slanted polarizations at the BS end when comparing results with horizontal space diversity. The performance of horizontal/vertical polarization diversity scheme was approximately 1 dB worse than horizontal space diversity.
Bs → Kℓv form factors with 2+1 flavors Liu, Yuzhi; Bailey, Jon A; Bazavov, A ...
EPJ Web of Conferences,
01/2018, Letnik:
175
Conference Proceeding, Journal Article
Recenzirano
Odprti dostop
Using the MILC 2+1 flavor asqtad quark action ensembles, we are calculating the form factors f0 and f+ for the semileptonic Bs → Kℓv decay. A total of six ensembles with lattice spacing from ≈ 0.12 ...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 lattice spacing, the ratio m’l/m’s ranges from 0.05 to 0.2. The valence b quark is treated using the Sheikholeslami-Wohlert Wilson-clover action with the Fermilab interpretation. The other valence quarks use the asqtad action. When combined with (future) measurements from the LHCb and Belle II experiments, these calculations will provide an alternate determination of the CKM matrix element |Vub|.
Dramatic progress has been made over the last decade in the numerical study of quantum chromodynamics (QCD) through the use of improved formulations of QCD on the lattice (improved actions), the ...development of new algorithms, and the rapid increase in computing power available to lattice gauge theorists. In this article simulations of full QCD are described using the improved staggered quark formalism, ''asqtad'' fermions. These simulations were carried out with two degenerate flavors of light quarks (up and down) and with one heavier flavor, the strange quark. Several light quark masses, down to about three times the physical light quark mass, and six lattice spacings have been used. These enable controlled continuum and chiral extrapolations of many low energy QCD observables. The improved staggered formalism is reviewed, emphasizing both advantages and drawbacks. In particular, the procedure for removing unwanted staggered species in the continuum limit is reviewed. Then the asqtad lattice ensembles created by the MILC Collaboration are described. All MILC lattice ensembles are publicly available, and they have been used extensively by a number of lattice gauge theory groups. The physics results obtained with them are reviewed, and the impact of these results on phenomenology is discussed. Topics include the heavy quark potential, spectrum of light hadrons, quark masses, decay constants of light and heavy-light pseudoscalar mesons, semileptonic form factors, nucleon structure, scattering lengths, and more.
We calculate in three-flavor lattice QCD the short-distance hadronic matrix elements of all five ΔC=2 four-fermion operators that contribute to neutral D-meson mixing both in and beyond the Standard ...Model. We use the MILC Collaboration’s Nf=2+1 lattice gauge-field configurations generated with asqtad-improved staggered sea quarks. We also employ the asqtad action for the valence light quarks and use the clover action with the Fermilab interpretation for the charm quark. We analyze a large set of ensembles with pions as light as Mπ≈180 MeV and lattice spacings as fine as a≈0.045 fm, thereby enabling good control over the extrapolation to the physical pion mass and continuum limit. We obtain for the matrix elements in the $\overline{MS}$-NDR scheme using the choice of evanescent operators proposed by Beneke et al., evaluated at 3 GeV, $\langle$D0|Oi|$\bar{D}$0 $\rangle$={0.0805(55)(16),-0.1561(70)(31),0.0464(31)(9),0.2747(129)(55),0.1035(71)(21)} GeV4 (i=1–5). The errors shown are from statistics and lattice systematics, and the omission of charmed sea quarks, respectively. To illustrate the utility of our matrix-element results, we place bounds on the scale of CP-violating new physics in D0 mixing, finding lower limits of about 10–50×103 TeV for couplings of O(1). To enable our results to be employed in more sophisticated or model-specific phenomenological studies, we provide the correlations among our matrix-element results. For convenience, we also present numerical results in the other commonly used scheme of Buras, Misiak, and Urban.
Abstract
We present the first unquenched lattice-QCD calculation of the form factors for the decay
$$B\rightarrow D^*\ell \nu $$
B
→
D
∗
ℓ
ν
at nonzero recoil. Our analysis includes 15 MILC ensembles ...with
$$N_f=2+1$$
N
f
=
2
+
1
flavors of asqtad sea quarks, with a strange quark mass close to its physical mass. The lattice spacings range from
$$a\approx 0.15$$
a
≈
0.15
fm down to 0.045 fm, while the ratio between the light- and the strange-quark masses ranges from 0.05 to 0.4. The valence
b
and
c
quarks are treated using the Wilson-clover action with the Fermilab interpretation, whereas the light sector employs asqtad staggered fermions. We extrapolate our results to the physical point in the continuum limit using rooted staggered heavy-light meson chiral perturbation theory. Then we apply a model-independent parametrization to extend the form factors to the full kinematic range. With this parametrization we perform a joint lattice-QCD/experiment fit using several experimental datasets to determine the CKM matrix element
$$|V_{cb}|$$
|
V
cb
|
. We obtain
$$\left| V_{cb}\right| = (38.40 \pm 0.68_{\text {th}} \pm 0.34_{\text {exp}} \pm 0.18_{\text {EM}})\times 10^{-3}$$
V
cb
=
(
38.40
±
0
.
68
th
±
0
.
34
exp
±
0
.
18
EM
)
×
10
-
3
. The first error is theoretical, the second comes from experiment and the last one includes electromagnetic and electroweak uncertainties, with an overall
$$\chi ^2\text {/dof} = 126/84$$
χ
2
/dof
=
126
/
84
, which illustrates the tensions between the experimental data sets, and between theory and experiment. This result is in agreement with previous exclusive determinations, but the tension with the inclusive determination remains. Finally, we integrate the differential decay rate obtained solely from lattice data to predict
$$R(D^*) = 0.265 \pm 0.013$$
R
(
D
∗
)
=
0.265
±
0.013
, which confirms the current tension between theory and experiment.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
We present the first unquenched lattice-QCD calculation of the form factors for the decay B→D∗ℓν at nonzero recoil. Our analysis includes 15 MILC ensembles with Nf=2+1 flavors of asqtad sea quarks, ...with a strange quark mass close to its physical mass. The lattice spacings range from a≈0.15 fm down to 0.045 fm, while the ratio between the light- and the strange-quark masses ranges from 0.05 to 0.4. The valence b and c quarks are treated using the Wilson-clover action with the Fermilab interpretation, whereas the light sector employs asqtad staggered fermions. We extrapolate our results to the physical point in the continuum limit using rooted staggered heavy-light meson chiral perturbation theory. Then we apply a model-independent parametrization to extend the form factors to the full kinematic range. With this parametrization we perform a joint lattice-QCD/experiment fit using several experimental datasets to determine the CKM matrix element |Vcb|. We obtain Vcb=(38.40±0.68th±0.34exp±0.18EM)×10-3. The first error is theoretical, the second comes from experiment and the last one includes electromagnetic and electroweak uncertainties, with an overall χ2/dof=126/84, which illustrates the tensions between the experimental data sets, and between theory and experiment. This result is in agreement with previous exclusive determinations, but the tension with the inclusive determination remains. Finally, we integrate the differential decay rate obtained solely from lattice data to predict R(D∗)=0.265±0.013, which confirms the current tension between theory and experiment.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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