SEARCH · Engineering Papers

Results for “PION”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,675 records · Page 93

All sources NASA NTRS DOE OSTI

DOE OSTI2016

B*Bπ coupling using relativistic heavy quarks

We report on a calculation of the B*Bπ coupling in lattice QCD. The strong matrix element (Bπ|B*) is directly related to the leading order low-energy constant in heavy meson chiral perturbation theory (HM Χ PT) for B mesons. We carry out our calculation directly at the b-quark mass using a non-perturbatively tuned clover action that controls discretization effects of order |p → a| and (ma) n for all n. Our analysis is performed on RBC/UKQCD gauge configurations using domain-wall fermions and the Iwasaki gauge action at two lattice spacings of a –1 = 1.729(25) GeV, a –1 = 2.281 (28) GeV, and unitary pion masses down to 290 MeV. We achieve good statistical precision and control all systematic uncertainties, giving a final result for the HM Χ PT coupling g b = 0.56(3) stat (7) sys in the continuum and at the physical light-quark masses. Furthermore, this is the first calculation performed directly at the physical b-quark mass and lies in the region one would expect from carrying out an interpolation between previous results at the charm mass and at the static point.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2016

Study of π 0 pair production in single-tag two-photon collisions

We report a measurement of the differential cross section of π 0 pair production in single-tag two-photon collisions, γ*γ→π 0 π 0 , in e + e - scattering. The cross section is measured for Q 2 up to 30 GeV 2 , where Q 2 is the negative of the invariant mass squared of the tagged photon, in the kinematic range 0.5 GeV < W < 2.1 GeV and |cosθ*| < 1.0 for the total energy and pion scattering angle, respectively, in the γ*γ center-of-mass system. The results are based on a data sample of 759 fb -1 collected with the Belle detector at the KEKB asymmetric-energy e + e - collider. The transition form factor of the f 0 (980) and that of the f 2 (1270) with the helicity-0, -1, and -2 components separately are measured for the first time and are compared with theoretical calculations.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2016

nCTEQ15 - Global analysis of nuclear parton distributions with uncertainties in the CTEQ framework

We present the new nCTEQ15 set of nuclear parton distribution functions with uncertainties. This fit extends the CTEQ proton PDFs to include the nuclear dependence using data on nuclei all the way up to 208 Pb. The uncertainties are determined using the Hessian method with an optimal rescaling of the eigenvectors to accurately represent the uncertainties for the chosen tolerance criteria. In addition to the Deep Inelastic Scattering (DIS) and Drell-Yan (DY) processes, we also include inclusive pion production data from RHIC to help constrain the nuclear gluon PDF. Here, we investigate the correlation of the data sets with specific nPDF flavor components, and asses the impact of individual experiments. We also provide comparisons of the nCTEQ15 set with recent fits from other groups.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2016

Measurement of the neutral D meson mixing parameters in a time-dependent amplitude analysis of the D 0 → π + π - π 0 decay

Here we perform the first measurement on the D 0 -D 0 mixing parameters using a time-dependent amplitude analysis of the decay D 0 →π + π - π 0 . The data were recorded with the BABAR detector at center-of-mass energies at and near the $Y$(4S) resonance, and correspond to an integrated luminosity of approximately 468.1 fb -1 . The neutral D meson candidates are selected from D*(2010) + →D 0 π$+\atop{s}$ decays where the flavor at the production is identified by the charge of the low-momentum pion, π$+\atop{s}$. The measured mixing parameters are x=(1.5±1.2±0.6)% and y=(0.2±0.9±0.5)%, where the quoted uncertainties are statistical and systematic, respectively.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2016

$B^0_{(s)}$-mixing matrix elements from lattice QCD for the Standard Model and beyond

We calculate—for the first time in three-flavor lattice QCD—the hadronic matrix elements of all five local operators that contribute to neutral B 0 - and B s -meson mixing in and beyond the Standard Model. 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 |V td | = 8.00(34)(8)×10 -3 , |V ts | = 39.0(1.2)(0.4)×10 -3 , and |V td /V ts | = 0.2052(31)(10), which differ from CKM-unitarity expectations by about 2σ. In addition, 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.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2016

Low energy scattering phase shifts for meson-baryon systems

Here, in this work, we calculate meson-baryon scattering phase shifts in four channels using lattice QCD methods. From a set of calculations at four volumes, corresponding to spatial sizes of 2, 2.5, 3, and 4 fm, and a pion mass of 𝑚 𝜋 ∼ 390 MeV, we determine the scattering lengths and effective ranges for these systems at the corresponding quark masses. We also perform the calculation at a lighter quark mass, 𝑚 𝜋 ∼ 230 MeV, on the largest volume. Using these determinations, along with those in previous work, we perform a chiral extrapolation of the scattering lengths to the physical point after correcting for the effective range contributions using the multivolume calculations performed at 𝑚 𝜋 ∼ 390 MeV.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2016

Study of excited Ξ c states decaying into Ξ c 0 and Ξ c + baryons

Here, with a data sample of 980 fb - 1 of e + e - annihilation data taken with the Belle detector operating at the KEKB asymmetric-energy e + e - collider, we discuss the results of a study of excited Ξ c states that decay, via the emission of photons and/or charged pions, into Ξ c 0 or Ξ c + ground state charmed-strange baryons. We present new measurements of the masses of all members of the Ξ c ' , Ξ c ( 2645 ) , Ξ c ( 2790 ) , Ξ c ( 2815 ) , and Ξ c ( 2980 ) isodoublets, measurements of the intrinsic widths of those that decay strongly, and evidence of previously unknown transitions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2016

Axial, scalar, and tensor charges of the nucleon from 2+1+1-flavor Lattice QCD

We present results for the isovector axial, scalar, and tensor charges 𝑔$^{𝑢−𝑑}_{𝐴}$, 𝑔$^{𝑢−𝑑}_{𝑆}$, and 𝑔$^{𝑢−𝑑}_{𝑇}$ of the nucleon needed to probe the Standard Model and novel physics. The axial charge is a fundamental parameter describing the weak interactions of nucleons. The scalar and tensor charges probe novel interactions at the TeV scale in neutron and nuclear 𝛽-decays, and the flavor-diagonal tensor charges 𝑔$^{𝑢}_{𝑇}$, 𝑔$^{𝑑}_{𝑇}$, and 𝑔$^{𝑠}_{𝑇}$ are needed to quantify the contribution of the quark electric dipole moment (EDM) to the neutron EDM. The lattice-QCD calculations were done using nine ensembles of gauge configurations generated by the MILC Collaboration using the highly improved staggered quarks action with 2+1+1 dynamical flavors. These ensembles span three lattice spacings 𝑎 ≈0.06,0.09, and 0.12 fm and light-quark masses corresponding to the pion masses 𝑀 𝜋 ≈ 135,225, and 315 MeV. High-statistics estimates on five ensembles using the all-mode-averaging method allow us to quantify all systematic uncertainties and perform a simultaneous extrapolation in the lattice spacing, lattice volume, and light-quark masses for the connected contributions. Our final estimates, in the $\overline{MS}$ scheme at 2 GeV, of the isovector charges are 𝑔$^{𝑢−𝑑}_{𝐴}$ = 1.195⁢(33)⁢(20), 𝑔$^{𝑢−𝑑}_{𝑆}$ = 0.97⁢(12)⁢(6), and 𝑔$^{𝑢−𝑑}_{𝑇}$ = 0.987⁢(51)⁢(20). The first error includes statistical and all systematic uncertainties except that due to the extrapolation Ansatz, which is given by the second error estimate. Combining our estimate for 𝑔$^{𝑢−𝑑}_{𝑆}$ with the difference of light quarks masses (𝑚 𝑑 − 𝑚 𝑢 ) QCD = 2.67⁢(35) MeV given by the Flavor Lattice Average Group, we obtain (𝑀 𝑁 − 𝑀 𝑃 ) QCD = 2.59⁢(49) MeV.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2016

Nonperturbative solution of scalar Yukawa model in two- and three-body Fock space truncations

The light-front Tamm-Dancoff method of finding the nonperturbative solutions in field theory is based on the Fock decomposition of the state vector, complemented by the sector-dependent nonperturbative renormalization scheme. We show in detail how to implement the renormalization procedure and to solve the simplest nontrivial example of the scalar Yukawa model in the two- and three-body Fock space truncations incorporating scalar “nucleon” and one or two scalar “pions”.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2016

First Monte Carlo analysis of fragmentation functions from single-inclusive e + e - annihilation

Here, we perform the first iterative Monte Carlo (IMC) analysis of fragmentation functions constrained by all available data from single-inclusive $e^+ e^-$ annihilation into pions and kaons. The IMC method eliminates potential bias in traditional analyses based on single fits introduced by fixing parameters not well contrained by the data, and provides a statistically rigorous determination of uncertainties. Our analysis reveals specific features of fragmentation functions using the new IMC methodology and those obtained from previous analyses, especially for light quarks and for strange quark fragmentation to kaons.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2017

Fragmentation functions beyond fixed order accuracy

Here, we give a detailed account of the phenomenology of all-order resummations of logarithmically enhanced contributions at small momentum fraction of the observed hadron in semi-inclusive electron-positron annihilation and the timelike scale evolution of parton-to-hadron fragmentation functions. The formalism to perform resummations in Mellin moment space is briefly reviewed, and all relevant expressions up to next-to-next-to-leading logarithmic order are derived, including their explicit dependence on the factorization and renormalization scales. We discuss the details pertinent to a proper numerical implementation of the resummed results comprising an iterative solution to the timelike evolution equations, the matching to known fixed-order expressions, and the choice of the contour in the Mellin inverse transformation. First extractions of parton-to-pion fragmentation functions from semi-inclusive annihilation data are performed at different logarithmic orders of the resummations in order to estimate their phenomenological relevance. To this end, we compare our results to corresponding fits up to fixed, next-to-next-to-leading order accuracy and study the residual dependence on the factorization scale in each case.

74 ATOMIC AND MOLECULAR PHYSICS↗

DOE OSTI2017

QCD equation of state to O ( μ B 6 ) from lattice QCD

We calculated the QCD equation of state using Taylor expansions that include contributions from up to sixth order in the baryon, strangeness and electric charge chemical potentials. Calculations have been performed with the Highly Improved Staggered Quark action in the temperature range T ϵ [135 MeV , 330 MeV] using up to four different sets of lattice cutoffs corresponding to lattices of size N$3\atop{σ}$ × N τ with aspect ratio N σ /N τ = 4 and N τ = 6-16 . The strange quark mass is tuned to its physical value, and we use two strange to light quark mass ratios m s /m l = 20 and 27, which in the continuum limit correspond to a pion mass of about 160 and 140 MeV, respectively. Sixth-order results for Taylor expansion coefficients are used to estimate truncation errors of the fourth-order expansion. We show that truncation errors are small for baryon chemical potentials less then twice the temperature (μ B ≤ 2T). The fourth-order equation of state thus is suitable for the modeling of dense matter created in heavy ion collisions with center-of-mass energies down to √sNN ~ 12 GeV . We provide a parametrization of basic thermodynamic quantities that can be readily used in hydrodynamic simulation codes. The results on up to sixth-order expansion coefficients of bulk thermodynamics are used for the calculation of lines of constant pressure, energy and entropy densities in the T - μ B plane and are compared with the crossover line for the QCD chiral transition as well as with experimental results on freeze-out parameters in heavy ion collisions. These coefficients also provide estimates for the location of a possible critical point. We argue that results on sixth-order expansion coefficients disfavor the existence of a critical point in the QCD phase diagram for μ B /T≤2 and T/T c (μ B = 0) > 0.9 .

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2017

Pascalutsa-Vanderhaeghen light-by-light sum rule from photon-photon collisions

Light-by-light scattering sumrules based on general field theory principles relate cross-sections with different helicities. In this paper the simplest sumrule is tested for the $I=0$ and $2$ channels for \lq\lq real'' photon-photon collisions. Important contributions come from the long-lived pseudoscalar mesons and from di-meson intermediate states. The latest Amplitude Analysis of $\gamma\gamma\to\pi\pi, \overline{K}K$ allows this contribution to be evaluated. Furthermore, we find that other multi-meson contributions up to 2.5~GeV are required to satisfy the sumrules. While data on three and four pion cross-sections exist, there is no information about their isospin and helicity decomposition. Nevertheless, we show the measured cross-sections are sufficiently large to ensure the sumrules for the helicity differences are likely fulfilled.

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 OSTI2017

Light-front holographic distribution amplitudes of pseudoscalar mesons and their application to B -meson decays

In this article the dynamical spin effects of the light-front holographic wave functions for light pseudoscalar mesons are studied. These improved wave functions are then confronted with a number of hadronic observables: the decay constants of π and K mesons, their ξ -moments, the pion-to-photon transition form factor, and the pure annihilation $\bar{B}_s$ → π + π - and $\bar{B}_d$ → K + K - decays. Taking f π , fK , and their ratio fK / f π as constraints, we perform a χ 2 analysis for the holographic parameters, including the mass scale parameter $\sqrtλ$ and the effective quark masses, and find that the fitted results are quite consistent with the ones obtained from the light-quark hadronic Regge trajectories. In addition, we also show that the end point divergence appearing in the pure annihilation $\bar{B}_s$ → π + π - and $\bar{B}_d$ → K + K - decays can be controlled well by using these improved light-front holographic distribution amplitudes.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2017

Strange and charm quark spins from the anomalous Ward identity

In this article, we present a calculation of the strange and charm quark contributions to the nucleon spin from the anomalous Ward identity (AWI). This is performed with overlap valence quarks on 2 + 1 -flavor domain-wall fermion gauge configurations on a 2 4 3 × 64 lattice with lattice spacing a - 1 = 1.73 GeV and the light sea mass at m π = 330 MeV . To satisfy the AWI, the overlap fermion for the pseudoscalar density and the overlap Dirac operator for the topological density, which do not have multiplicative renormalization, are used to normalize the form factor of the local axial-vector current at finite q 2 . For the charm quark, we find that the negative pseudoscalar term almost cancels the positive topological term. For the strange quark, the pseudoscalar term is less negative than that of the charm. By imposing the AWI, the strange g A ( q 2 ) at q 2 = 0 is obtained by a global fit of the pseudoscalar and the topological form factors, together with g A ( q 2 ) and the induced pseudoscalar form factor h A ( q 2 ) at finite q 2 . The chiral extrapolation to the physical pion mass gives Δ s + Δ s ¯ = - 0.0403 ( 44 ) ( 78 ) .

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2017

Off-forward gluonic structure of vector mesons

Here, the spin-independent and transversity generalized form factors (GFFs) of the Φmeson are studied using lattice QCD calculations with light quark masses corresponding to a pion mass m π ~ 450(5) MeV . One transversity and three spin-independent GFFs related to the lowest moments of leading-twist spin-independent and transversity gluon distributions are obtained at six nonzero values of the momentum transfer up to 1.2 Ge V 2 . These quantities are compared with the analogous spin-independent quark GFFs and the electromagnetic form factors determined on the same lattice ensemble. In conclusion, the results show quantitative distinction between the spatial distribution of transversely polarized gluons, unpolarized gluons, and quarks and point the way towards further investigations of the gluon structure of nucleons and nuclei.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2017

On the Feynman-Hellmann theorem in quantum field theory and the calculation of matrix elements

In this paper, the Feynman-Hellmann theorem can be derived from the long Euclidean-time limit of correlation functions determined with functional derivatives of the partition function. Using this insight, we fully develop an improved method for computing matrix elements of external currents utilizing only two-point correlation functions. Our method applies to matrix elements of any external bilinear current, including nonzero momentum transfer, flavor-changing, and two or more current insertion matrix elements. The ability to identify and control all the systematic uncertainties in the analysis of the correlation functions stems from the unique time dependence of the ground-state matrix elements and the fact that all excited states and contact terms are Euclidean-time dependent. We demonstrate the utility of our method with a calculation of the nucleon axial charge using gradient-flowed domain-wall valence quarks on the $N_f=2+1+1$ MILC highly improved staggered quark ensemble with lattice spacing and pion mass of approximately 0.15 fm and 310 MeV respectively. We show full control over excited-state systematics with the new method and obtain a value of $g_A = 1.213(26)$ with a quark-mass-dependent renormalization coefficient.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗