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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Three pseudoscalar meson production in e+e- annihilation

We study, at leading order in the large number of colours expansion and within the Resonance Chiral Theory framework, the odd-intrinsic-parity $e^+ e^- \rightarrow \pi^+ \pi^- (\pi^0 , \eta)$ cross-sections in the energy regime populated by hadron resonances, namely $9 \, m_{\pi}^2 \lsim E \lsim 2 \, \mbox{GeV}$. In addition we implement our results in the Monte Carlo generator PHOKHARA 7.0 and we simulate hadron production through the radiative return method.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

Charmed and light pseudoscalar meson decay constants from four-flavor lattice QCD with physical light quarks

We compute the leptonic decay constants f D+ , f Ds , and f K+ , and the quark-mass ratios m c =m s and m s =m l in unquenched lattice QCD using the experimentally determined value of f π+ for normalization. We use the MILC Highly Improved Staggered Quark (HISQ) 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 spacing ranging from a ≈ 0:06 fm to 0:15 fm are included in the analysis to control the extrapolation to the continuum limit. Our primary results are f D+ = 212:6(0:4)$(^{+1.0}_{-1.2})$ MeV, f Ds = 249:0(0:3)$(^{+1.1}_{-1.5})$ MeV, and f Ds /f D+ = 1:1712(10)$(^{+29}_{-32})$, where the errors are statistical and total systematic, respectively. The errors on our results for the charm decay constants and their ratio are approximately two to four times smaller than those of the most precise previous lattice calculations. We also obtain f K+ / f π+ = 1:1956(10)$(^{+26}_{-18})$, updating our previous result, and determine the quark-mass ratios m s /m l = 27:35(5)$(^{+10}_{-7})$ and m c /m s = 11:747(19)$(^{+59}_{-43})$. When combined with experimental measurements of the decay rates, our results lead to precise determinations of the CKM matrix elements !Vus! = 0:22487(51)(29)(20)(5), !Vcd! = 0:217(1)(5)(1) and !Vcs! = 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 !Vus!, the uncertainty in |Vud|, respectively.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Partonic structure of neutral pseudoscalars via two photon transition form factors

Here, the γγ* → η c,b transition form factors are computed using a continuum approach to the two valence-body bound-state problem in relativistic quantum field theory, and thereby unified with equivalent calculations of electromagnetic pion elastic and transition form factors. The resulting γγ* → η c form factor, G ηc (Q 2 ), is consistent with available data; significantly, at accessible momentum transfers, Q 2 G ηc (Q 2 ) lies well below its conformal limit. These observations confirm that the leading-twist parton distribution amplitudes of heavy-heavy bound states are compressed relative to the conformal limit. A clear understanding of the distribution of valence quarks within mesons thus emerges, a picture which connects Goldstone modes, built from the lightest quarks in nature, with systems containing the heaviest valence quarks that can now be studied experimentally, and highlights basic facts about manifestations of mass within the Standard Model.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Mass dependence of pseudoscalar meson elastic form factors

A continuum approach to quark-antiquark bound-states is used to determine the electromagnetic form factors of pion-like mesons with masses m 0- /GeV = 0.14, 0.47, 0.69, 0.83 on a spacelike domain that extends to Q 2 ≲ 10 GeV 2 . The results enable direct comparisons with contemporary lattice-QCD calculations of heavy-pion form factors at large values of momentum transfer and aid in understanding them. Finally, they also reveal, inter alia, that the form factor of the physical pion provides the best opportunity for verification of the factorised hard-scattering formula relevant to this class of exclusive processes and that this capacity diminishes steadily as the meson mass becomes heavier.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗