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At least 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
DOE OSTI2011

Vector Meson Photoproduction on Nuclei

Chiral symmetry, which is spontaneously broken in vacuum, is predicted to be partially restored in ordinary nuclear matter. The properties of vector mesons, such as their masses and/or widths are expected to change in the medium. The photoproduction reaction off nuclei is a very clean way of producing the {rho}, {omega} and {phi} mesons, and detect them via their hadronic or leptonic decays. The leptonic decay to e{sup +}e{sup -} has a small branching ratio but has the advantage of being free from final state interactions. One critical aspect in all these experiments is the correct determination of the shape and magnitude of the combinatorial background. The in-medium mass distributions and yields are compared to those measured in vacuum. No significant shift is observed in the masses of the mesons, however substantial increase in their widths is reported.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2013

Photoproduction of scalar mesons at medium energies

In this work we will focus on photoproduction of mesons states a{sub 0}(980), f{sub 0}(1500) and f{sub 0}(1710). The f{sub 0}(1500) and f{sub 0}(1710) mesons will be considered in distinct mixing possibilities and assuming that a{sub 0}(980) is member of the ground-state nonet. The theoretical formalism is the Regge approach with reggeized {rho} and {omega} exchange. The differential and integrated total cross section are computed for the cases of the mesons a{sub 0}(980), f{sub 0}(1500) and f{sub 0}(1710) focusing the GlueX energy regime with photon energy E = 9 GeV.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

Generalized Beth–Uhlenbeck approach to mesons and diquarks in hot, dense quark matter

An important first step in the program of hadronization of chiral quark models is the bosonization in meson and diquark channels. This procedure is presented at finite temperatures and chemical potentials for the SU(2) flavor case of the NJL model with special emphasis on the mixing between scalar meson and scalar diquark modes which occurs in the 2SC color superconducting phase. The thermodynamic potential is obtained in the Gaussian approximation for the meson and diquark fields and it is given in the Beth–Uhlenbeck form. This allows a detailed discussion of bound state dissociation in hot, dense matter (Mott effect) in terms of the in-medium scattering phase shift of two-particle correlations. It is shown for the case without meson–diquark mixing that the phase shift can be separated into a continuum and a resonance part. In the latter, the Mott transition manifests itself by a change of the phase shift at threshold by π in accordance with Levinson’s theorem, when a bound state transforms to a resonance in the scattering continuum. The consequences for the contribution of pionic correlations to the pressure are discussed by evaluating the Beth–Uhlenbeck equation of state in different approximations. A similar discussion is performed for the scalar diquark channel in the normal phase. Further developments and applications of the developed approach are outlined.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

Recent progress on light scalar mesons

This is a brief account of the recent developments on the determination of the mass and widths of the much debated scalar mesons, paying particular attention to the causes of major revision of the σ or f{sub 0}(500) meson in the last edition of the Review of Particle Physics, which has finally acknowledged that the situation concerning the mass and width of this controversial state has been settled, although this was already well-known to scalar meson practitioners for about a decade. I will briefly comment on the dispersive approach, followed by several groups, which seems to have been the most decisive in support of the existence and precise determinations of scalar meson properties.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2011

Attenuation of {omega} mesons in cold nuclear matter

The attenuation of {omega} mesons in cold nuclear matter has been investigated via the time-dependent multiple-scattering Monte Carlo multicollisional (MCMC) intranuclear cascade model. The inelastic {omega} width deduced from CBELSA/TAPS Collaboration data of meson transparency in complex nuclei ({Gamma}*{approx_equal}30 MeV/c{sup 2}) is approximately 5 times lower than the value obtained with recent theoretical models and consistent with an in-medium total {omega}N cross section within 25-30 mb for an average meson momentum of 1.1 GeV/c . The momentum-dependent transparency ratios suggest an elastic/total cross-section ratio around 40%. For the case of CLAS Collaboration data a much higher width is deduced ({Gamma}* > or approx. 120 MeV/c{sup 2}), with the MCMC model providing a consistent interpretation of the data, assuming a much higher meson absorption ({sigma}{sub {omega}N}* > or approx. 100 mb) for p{sub {omega}{approx}1}.7 GeV/c.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2015

Φ meson production in d+Au collisions at √s NN = 200 GeV

The PHENIX Collaboration has measured Φ meson production in d+Au collisions at √s NN =200 GeV using the dimuon and dielectron decay channels. The Φ meson is measured in the forward (backward) d-going (Au-going) direction, 1.2 < y < 2.2 (–2.2 < y < –1.2) in the transverse-momentum (p T ) range from 1–7 GeV/c and at midrapidity |y|<0.35 in the p T range below 7 GeV/c. The Φ meson invariant yields and nuclear-modification factors as a function of p T , rapidity, and centrality are reported. An enhancement of Φ meson production is observed in the Au-going direction, while suppression is seen in the d-going direction, and no modification is observed at midrapidity relative to the yield in p+p collisions scaled by the number of binary collisions. As a result, similar behavior was previously observed for inclusive charged hadrons and open heavy flavor, indicating similar cold-nuclear-matter effects.

200 GeV↗
DOE OSTI2011

Evolved QCD predictions for the meson-photon transition form factors: beyond the semiclassical AdS/QCD approximation

The QCD evolution of the pion distribution amplitude (DA) {phi}{sub {pi}} (x, Q{sup 2}) is computed for several commonly used models. Our analysis includes the nonperturbative form predicted by lightfront holographic QCD, thus combining the nonperturbative bound state dynamics of the pion with the perturbative ERBL evolution of the pion distribution amplitude. We calculate the meson-photon transition form factors for the {pi}{sup 0}, {eta} and {eta}' using the hard-scattering formalism. We point out that a widely-used approximation of replacing {phi} (x; (1 - x)Q) with {phi} (x;Q) in the calculations will unjustifiably reduce the predictions for the meson-photon transition form factors. It is found that the four models of the pion DA discussed give very different predictions for the Q{sup 2} dependence of the meson-photon transition form factors in the region of Q{sup 2} > 30 GeV{sup 2}. More accurate measurements of these transition form factors at the large Q{sup 2} region will be able to distinguish the four models of the pion DA. The rapid growth of the large Q{sup 2} data for the pion-photon transition form factor reported by the BABAR Collaboration is difficult to explain within the current framework of QCD. If the BABAR data for the meson-photon transition form factor for the {pi}{sup 0} is confirmed, it could indicate physics beyond-the-standard model, such as a weakly-coupled elementary C = + axial vector or pseudoscalar z{sup 0} in the few GeV domain, an elementary field which would provide the coupling {gamma}{sup *}{gamma} {yields} z{sup 0} {yields} {pi}{sup 0} at leading twist. Our analysis thus indicates the importance of additional measurements of the pion-photon transition form factor at large Q{sup 2}.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

K{sub e4} decay as a source of information about the σ-particle mass and about the nature of spin-1 mesons

Data on the form factors for K{sub e4} decay make it possible to fix the value of a parameter that is not determined by the theory itself and which is contained in the Lagrangian for the system formed by 0{sup +} and 0{sup −} mesons. This makes it possible to find the mass of the lightest σ meson: mσ = 663 MeV. As for the nature of spin-1 mesons, which also contribute to the form factors for K{sub e4} decay, data on them give no way to interpret spin-1 mesons as gauge bosons of chiral theory.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Effect of in-medium parameters of ρ meson in its photoproduction reactions on nuclei

There exist model calculations showing the modification of the hadronic parameters of ρ meson in the nuclear environment. From these parameters, we extract the ρ-meson-nucleus optical potential and show the medium effect due to this potential on the ρ-meson mass distribution spectra in the photonuclear reactions. The calculated results reproduced reasonably the measured e{sup +}e{sup −} invariant mass, i.e., ρ-meson mass, distribution spectra in γ, ρ{sup 0} → e{sup +}e{sup −} reactions on nuclei.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

37 Years with the light scalar mesons. The learned lessons

Attention is paid to the production mechanisms of light scalars that reveal their nature. We reveal the chiral shielding of the σ(600) meson. We show that the kaon loop mechanism of the ϕ radiative decays, ratified by experiment, is four-quark transition and points to the four-quark nature of light scalars. We show also that the light scalars are produced in the two photon collisions via four-quark transitions in contrast to the classic P wave tensor qq̅ mesons that are produced via two-quark transitions γγ → qq̅. We study the mechanism of production of the light scalar mesons in the D{sup +}{sub s }→ π{sup +}π{sup −} e {sup +}ν decays: D{sup +}{sub s }→ ss̅e {sup +}ν → [σ(600) + f {sub 0}(980)]e {sup +}ν → π{sup +}π{sup −} e {sup +}ν, and compare it with the mechanism of production of the light pseudoscalar mesons in the D{sup +}{sub s }→ (η/η′)e {sup +}ν decays: D{sup +}{sub s }→ ss̅e {sup +}ν → (η/η′)e {sup +}ν. As a result we find support to four-quark nature of light scalars. In the end, we outline the future research program.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Valence structures of light and strange mesons from the basis light-front quantization framework

In this work, we apply the basis light-front quantization (BLFQ) framework to solve for the structures of mesons with light and strange valence quarks. Our approach treats mesons as relativistic bound states with quarks confined in both the transverse direction and the light-front longitudinal direction. The spin-orbit interactions of these confined quarks are further specified by the Nambu–Jona-Lasinio model. We address the U(1)A axial anomaly by including the Kobayashi-Maskawa-’t Hooft interaction regularized by our basis. We present the structures of the pion, the kaon, the eta meson, and the eta-prime meson in terms of their valence light-front wave functions obtained from the eigenvalue problem of our light-front Hamiltonian.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2012

ISR Hadron Production in e+e- Annihilations and Meson-Photon Transition Form Factors

We present several recent results from the BaBar collaboration in the areas of initial state radiation physics and transition form factors. An updated study of the processes e{sup +}e{sup -} {yields} K{sup +}K{sup -}{pi}{sup +}{pi}{sup -} and e{sup +}e{sup -} {yields} K{sup +}K{sup -}{pi}{sup 0}{pi}{sup 0} provides an improved understanding of the Y (2175) meson. A very precise study of the process e{sup +}e{sup -} {yields} {pi}{sup +}{pi}{sup -} improves the precision on the calculated anomalous magnetic moment of the muon and provides by far the best information on excited {rho} states. Our previous measurements of the timelike transition form factors (TFF) of the {eta} and {eta}' mesons at Q{sup 2} = 112 GeV{sup 2}, combined with new measurements of the their spacelike TFFs and those of the {pi}{sup 0} and {eta}{sub c} mesons, provide powerful tests of QCD and models of the distribution amplitudes of quarks inside these mesons. The {eta}{sub c} TFF shows the expected behavior over the Q{sup 2} range 1-50 GeV{sup 2}, and we are sensitive to next-to-leading-order QCD corrections. The {eta} and {eta}' TFFs are consistent with expected behavior, but those for the {pi}{sup 0} are not. Extracting the strange and nonstrange components of the {eta} and {eta}' TFFs, we find the nonstrange component to be consistent with theoretical expectations and inconsistent with the measured {pi}{sup 0} TFF.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2012

Sigma meson and lowest possible glueball candidate in an extended linear {sigma} model

We formulate an extended linear {sigma} model of a quarkonia nonet and a tetraquark nonet as well as a complex iso-singlet (glueball) field to study the low-lying scalar meson. Chiral symmetry and U{sub A}(1) symmetry and their breaking play important role to shape the scalar meson spectrum in our work. Based on our study we will comment on what may be the mass of the lowest possible scalar and pseudoscalar glueball states. We will also discuss on what may be the nature of the sigma or f{sub 0}(600) meson.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2013

Meson production in two-photon interactions at LHC energies

The LHC opens a new kinematical regime at high energy, where several questions related to the description of the high-energy regime of the Quantum Chromodynamics (QCD) remain without satisfactory answers. Some open questions are the search for non-q-bar q resonances, the determination of the spectrum of q-bar q states and the identification of states with anomalous {gamma}{gamma} couplings. A possible way to study these problems is the study of meson production in two-photon interactions. In this contribution we calculate the meson production in two-photon interactions at LHC energies considering proton - proton collisions and estimate the total cross section for the production of the mesons {pi}, a, f, {eta} and {chi}.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Enhanced non-quark-antiquark and non-glueball N{sub c} behavior of light scalar mesons

We show that the latest and very precise dispersive data analyses require a large and very unnatural fine-tuning of the 1/N{sub c} expansion at N{sub c}=3 if the f{sub 0}(600) and K(800) light scalar mesons are to be considered predominantly qq states, which is not needed for light vector mesons. For this, we use scattering observables whose 1/N{sub c} corrections are suppressed further than one power of 1/N{sub c} for qq or glueball states, thus enhancing contributions of other nature. This is achieved without using unitarized ChPT, but if it is used we can also show that it is not just that the coefficients of the 1/N{sub c} expansion are unnatural, but that the expansion itself does not even follow the expected 1/N{sub c} scaling of a glueball or a qq meson.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

Event-Shape Engineering for the D-meson elliptic flow in mid-central Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV

The production yield of prompt D mesons and their elliptic flow coefficient $\nu$ 2 were measured with the Event-Shape Engineering (ESE) technique applied to mid-central (10–30% and 30–50% centrality classes) Pb-Pb collisions at the centre-of-mass energy per nucleon pair $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV, with the ALICE detector at the LHC. The ESE technique allows the classification of events, belonging to the same centrality, according to the azimuthal anisotropy of soft particle production in the collision. The reported measurements give the opportunity to investigate the dynamics of charm quarks in the Quark-Gluon Plasma and provide information on their participation in the collective expansion of the medium. D mesons were reconstructed via their hadronic decays at mid-rapidity, | η | < 0.8, in the transverse momentum interval 1 < p T < 24 GeV/ c . The $\nu$ 2 coefficient is found to be sensitive to the event-shape selection confirming a correlation between the D-meson azimuthal anisotropy and the collective expansion of the bulk matter, while the per-event D-meson yields do not show any significant modification within the current uncertainties.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

A supersymmetric theory of baryogenesis and sterile sneutrino dark matter from B mesons

Low-scale baryogenesis and dark matter generation can occur via the production of neutral B mesons at MeV temperatures in the early Universe, which undergo CP-violating oscillations and subsequently decay into a dark sector. In this work, we discuss the consequences of realizing this mechanism in a supersymmetric model with an unbroken U(1) R symmetry which is identified with baryon number. B mesons decay into a dark sector through a baryon number conserving operator mediated by TeV scale squarks and a GeV scale Dirac bino. The dark sector particles can be identified with sterile neutrinos and their superpartners in a type-I seesaw framework for neutrino masses. The sterile sneutrinos are sufficiently long lived and constitute the dark matter. The produced matter-antimatter asymmetry is directly related to observables measurable at B factories and hadron colliders, the most relevant of which are the semileptonic-leptonic asymmetries in neutral B meson systems and the inclusive branching fraction of B mesons into hadrons and missing energy. We discuss model independent constraints on these experimental observables before quoting predictions made in the supersymmetric context. Constraints from astrophysics, neutrino physics and flavor observables are studied, as are potential LHC signals with a focus on novel long lived particle searches which are directly linked to properties of the dark sector.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Measurement of the production of charm jets tagged with D0 mesons in pp collisions at $\sqrt{s}$ = 5.02 and 13 TeV

The measurement of the production of charm jets, identified by the presence of a D 0 meson in the jet constituents, is presented in proton–proton collisions at centre-of-mass energies of $\sqrt{s}$= 5.02 and 13 TeV with the ALICE detector at the CERN LHC. The D 0 mesons were reconstructed from their hadronic decay D 0 → K – π + and the respective charge conjugate. Jets were reconstructed from D 0 -meson candidates and charged particles using the anti-k T algorithm, in the jet transverse momentum range 5 < p T,chjet < 50 GeV/c, pseudorapidity |η jet | < 0.9 – R, and with the jet resolution parameters R = 0.2, 0.4, 0.6. The distribution of the jet momentum fraction carried by a D 0 meson along the jet axis $\left({z}_{\Big\Vert}^{\textrm{ch}}\right)$ was measured in the range 0.4 < ${z}_{\Big\Vert}^{\textrm{ch}}$ < 1.0 in four ranges of the jet transverse momentum. Comparisons of results for different collision energies and jet resolution parameters are also presented. The measurements are compared to predictions from Monte Carlo event generators based on leading-order and next-to-leading-order perturbative quantum chromodynamics calculations. A generally good description of the main features of the data is obtained in spite of a few discrepancies at low p T,chjet . Measurements were also done for R = 0.3 at $\sqrt{s}$= 5.02 and are shown along with their comparisons to theoretical predictions in an appendix to this paper.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗