D→K,lνD \rightarrow K, l \nu Semileptonic Decay Scalar Form Factor and ∣Vcs∣|V_{cs}| from Lattice QCD

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 $N_f = 2 + 1$ lattices and determine the scalar form factor $f_0(q^2)$ for $D \rightarrow K, l \nu$ 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 $f_0(q^2)$. The method uses the kinematic "$z$" variable instead of $q^2$ or the kaon energy $E_K$ and is applicable over the entire physical $q^2$ range. We find $f^{D \rightarrow K}_0(0) \equiv f^{D \rightarrow K}_+(0) = 0.747(19)$ in the chiral plus continuum limit and hereby improve the theory error on this quantity by a factor of $\sim$4 compared to previous lattice determinations. Combining the new theory result with recent experimental measurements of the product $f^{D \rightarrow K}_+(0) * |V_{cs}|$ from BaBar and CLEO-c leads to the most precise direct determination of the CKM matrix element $|V_{cs}|$ to date, $|V_{cs}| = 0.961(11)(24)$, where the first error comes from experiment and the second is the lattice QCD theory error. We calculate the ratio $f^{D \rightarrow K}_+(0)/f_{D_s}$ and find $2.986 \pm 0.087$ GeV$^{-1}$ 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

D→π,lνD \rightarrow \pi, l \nu Semileptonic Decays, ∣Vcd∣|V_{cd}| and 2nd^{nd} Row Unitarity from Lattice QCD

We present a new calculation of the $D \rightarrow \pi, l \nu$ semileptonic form factor $f^{D \rightarrow \pi}_+(q^2)$ at $q^2 = 0$ based on HISQ charm and light valence quarks on MILC $N_f = 2 +1$ lattices. Using methods developed recently for HPQCD's study of $D \rightarrow K, l \nu$ decays, we find $f^{D \rightarrow \pi}_+(0) = 0.666(29)$. 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 $|V_{cd}| = 0.225(6)_{exp.}(10)_{lat.}$, where the first error comes from experiment and the second from theory. With a total error of $\sim5.3$\% the accuracy of direct determination of $|V_{cd}|$ from $D$ 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 $|V_{cd}|$, HPQCD's earlier $|V_{cs}|$ and $|V_{cb}|$ from the Fermilab Lattice \& MILC collaborations. We find $|V_{cd}|^2 + |V_{cs}|^2 + |V_{cb}|^2 = 0.976(50)$, improving on the current PDG2010 value.Comment: 7 pages, 7 figures, and 4 table

S = 3 Ground State for a Tetranuclear Mn^(IV)₄O₄ Complex Mimicking the S₃ State of the Oxygen Evolving Complex

The S₃ state is currently the last observable intermediate prior to O–O bond formation at the oxygen-evolving complex (OEC) of Photosystem II, and its electronic structure has been assigned to a homovalent Mn^(IV)₄ core with an S = 3 ground state. While structural interpretations based on the EPR spectroscopic features of the S₃ state provide valuable mechanistic insight, corresponding synthetic and spectroscopic studies on tetranuclear complexes mirroring the Mn oxidation states of the S₃ state remain rare. Herein, we report the synthesis and characterization by XAS and multifrequency EPR spectroscopy of a Mn^(IV)₄O₄ cuboidal complex as a spectroscopic model of the S₃ state. Results show that this Mn^(IV)₄O₄ complex has an S = 3 ground state with isotropic ⁵⁵Mn hyperfine coupling constants of −75, −88, −91, and 66 MHz. These parameters are consistent with an αααβ spin topology approaching the trimer–monomer magnetic coupling model of pseudo-octahedral Mn^(IV) centers. Importantly, the spin ground state changes from S = 1/2 to S = 3 as the OEC is oxidized from the S₂ state to the S₃ state. This same spin state change is observed following oxidation of the previously reported Mn^(III)Mn^(IV)₃O₄ cuboidal complex to the Mn^(IV)₄O₄ complex described here. This sets a synthetic precedent for the observed low-spin to high-spin conversion in the OEC

The D to K and D to pi semileptonic decay form factors from Lattice QCD

We present a new and very high statistics study of D and D_s semileptonic decay form factors on the lattice. We work with MILC N_f=2+1 lattices and use the Highly Improved Staggered Action (HISQ) for both the charm and the light valence quarks. We use both scalar and vector currents to determine the form factors f_0(q^2) and f_+(q^2) for a range of D and D_s form factors including those for D to pi and D to K semileptonic decays. By using a phased boundary condition we are able to tune accurately to q^2=0. We also compare the shape in q^2 to that from experiment. We show that the form factors are very insensitive to the spectator quark: D to K and D_s to eta_s form factors are essentially the same, and the same is true for D to pi and D_s to K. This has important implications when considering the corresponding B/B_s processes.Comment: 7 pages, 9 figures, talk given at the XXIX International Symposium on Lattice Field Theory, July 10-16, 2011, Squaw Valley, Lake Tahoe, C

Heavy-light current-current correlators

The current-current correlator method has been used successfully to obtain very accurate results for quark masses and the coupling alpha_s. The calculations were done using Highly Improved Staggered Quarks (HISQ) and heavy-heavy meson correlators. We now extend this work to the significantly more challenging heavy-light case, reporting the first results here. The aim is to determine nonperturbative Z factors for NRQCD heavy-light currents, but first we test the method in the HISQ case where Z=1.Comment: 7 pages. Presented at the XXVIII International Symposium on Lattice Field Theory (Lattice 2010), June 14-19 2010, Villasimius, Ital

Chandra Observations of A Galactic Supernova Remnant Vela Jr.: A New Sample of Thin Filaments Emitting Synchrotron X-Rays

A galactic supernova remnant (SNR) Vela Jr. (RX J0852.0$-$4622, G266.6$-$1.2) shows sharp filamentary structure on the north-western edge of the remnant in the hard X-ray band. The filaments are so smooth and located on the most outer side of the remnant. We measured the averaged scale width of the filaments ($w_u$ and $w_d$) with excellent spatial resolution of {\it Chandra}, which are in the order of the size of the point spread function of {\it Chandra} on the upstream side and 49.5 (36.0--88.8) arcsec on the downstream side, respectively. The spectra of the filaments are very hard and have no line-like structure, and were well reproduced with an absorbed power-law model with $\Gamma =$2.67 (2.55--2.77), or a {\tt SRCUT} model with $\nu_{rolloff}$ = 4.3 (3.4--5.3)$\times 10^{16}$ Hz under the assumption of $p=0.3$. These results imply that the hard X-rays are synchrotron radiation emitted by accelerated electrons, as mentioned previously. Using a correlation between a function ${\cal B} \equiv \nu_{rolloff}/w_d^2$ and the SNR age, we estimated the distance and the age of Vela Jr.: the estimated distance and age are 0.33 (0.26--0.50) kpc and 660 (420--1400) years, respectively. These results are consistent with previous reports, implying that ${\cal B}$--age relation may be a useful tool to estimate the distance and the age of synchrotron X-ray emitting SNRs.Comment: 19 pages, 8 figures, ApJ, in pres

Precise B, B_s and B_c meson spectroscopy from full lattice QCD

We give the first accurate results for $B$ and $B_s$ meson masses from lattice QCD including the effect of $u$, $d$ and $s$ sea quarks, and we improve an earlier value for the $B_c$ meson mass. By using the Highly Improved Staggered Quark action for $u/d$, $s$ and $c$ quarks and NRQCD for the $b$ quarks, we are able to achieve an accuracy in the masses of around 10 MeV. Our results are: $m_B$ = 5.291(18) GeV, $m_{B_s}$ = 5.363(11) GeV and $m_{B_c}$ = 6.280(10) GeV. Note that all QCD parameters here are tuned from other calculations, so these are parameter free tests of QCD against experiment. We also give scalar, $B_{s0}^*$, and axial vector, $B_{s1}$, meson masses. We find these to be slightly below threshold for decay to $BK$ and $B^*K$ respectively.Comment: 22 pages, 19 figure

Recent topics of mesic atoms and mesic nuclei -- ϕ\phi mesic nuclei exist ?--

We study $\phi$-meson production in nuclei to investigate the in-medium modification of the $\phi$-meson spectral function at finite density. We consider (${\bar p},\phi$), ($\gamma,p$) and ($\pi^-,n$) reactions to produce a $\phi$-meson inside the nucleus and evaluate the effects of the medium modifications to reaction cross sections. The structures of the bound states, $\phi$-mesic nuclei, are also studied. For strong absorptive interaction cases, we need to know the spectrum shape in a wide energy region to deduce the properties of $\phi$.Comment: Talk given at EXA08, Vienna, September 2008. To be published in the Proceedings, Hyperfine Interactions. 6 pages, 6 figure

B and B-s meson decay constants from lattice QCD

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