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At least 271 records · Page 15

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DOE OSTI2025

Observation of Coherent 𝜙⁡(1020) Meson Photoproduction in Ultraperipheral PbPb Collisions at $\sqrt{𝑠_{NN}}$ = 5.36 TeV

The first observation of coherent 𝜙⁡(1020) meson photoproduction off heavy nuclei is presented using ultraperipheral lead-lead collisions at a center-of-mass energy per nucleon pair of 5.36 TeV. The data were collected by the CMS experiment and correspond to an integrated luminosity of 1.62 μ⁢𝑏 −1 . The 𝜙⁡(1020) meson signals are reconstructed via the 𝐾 + ⁢𝐾 − decay channel. The production cross section is presented as a function of the 𝜙⁡(1020) meson rapidity in the range 0.3 < |𝑦| < 1.0, probing gluons that carry a fraction of the nucleon momentum (𝑥) around 10 −4 . The observed cross section exhibits little dependence on rapidity and is significantly suppressed, by a factor of ∼5, compared to a baseline model that treats a nucleus as a collection of free nucleons. Theoretical models that incorporate the nuclear shadowing effect generally provide a better description of the 𝜙⁡(1020) data than those incorporating gluon saturation. This study establishes a powerful new tool for exploring nuclear effects and nuclear gluonic structure in the small-𝑥 regime at a unique energy scale bridging the perturbative and nonperturbative quantum chromodynamics domains.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2020

Light mesons within the basis light-front quantization framework

In this work, we study the light-unflavored mesons as relativistic bound states in the nonperturbative Hamiltonian formalism of the basis light-front quantization approach. The dynamics for the valence quarks of these mesons is specified by an effective Hamiltonian containing the one-gluon exchange interaction and the confining potentials both introduced in our previous work on heavy quarkonia, supplemented additionally by a pseudoscalar contact interaction. We diagonalize this Hamiltonian in our basis function representation to obtain the mass spectrum and the light-front wave functions (LFWFs). Based on these LFWFs, we then study the structure of these mesons by computing the electromagnetic form factors, the decay constants, the parton distribution amplitudes, and the parton distribution functions. Our results are comparable to those from experiments and other theoretical models.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2020

Production of $π^0$ and $\eta$ mesons in $\mathrm{U+U}$ collisions at $\sqrt {s_{NN}} = 192$ $\mathrm {GeV}$

The PHENIX experiment at the Relativistic Heavy Ion Collider measured $π^0$ and $\eta$ mesons at midrapidity in $\mathrm{U+U}$ collisions at $\sqrt {s_{NN}} = 192$ $\mathrm {GeV}$ in a wide transverse momentum range. Measurements were performed in the $π^0(η) → γγ$ decay modes. A strong suppression of $π^0$ and $\eta$ meson production at high transverse momentum was observed in central $\mathrm{U+U}$ collisions relative to binary scaled p + p results. Yields of $π^0$ and $\eta$ mesons measured in $\mathrm{U+U}$ collisions show similar suppression pattern to those measured in Au + Au collisions at $\sqrt {s_{NN}} = 200$ $\mathrm {GeV}$ for similar numbers of participant nucleons. The $η/π^0$ ratios do not show dependence on centrality or transverse momentum and are consistent with previously measured values in hadron-hadron, hadron-nucleus, nucleus-nucleus, and $e^+e^-$ collisions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2022

φ meson production in ρ + Al, ρ + Au, d + Au , and 3 He + Au collisions at $\sqrt{s_{NN}}$ = 200 GeV

We report small nuclear collisions are mainly sensitive to cold-nuclear-matter effects; however, the collective behavior observed in these collisions shows a hint of hot-nuclear-matter effects. The identified-particle spectra, especially the φ mesons which contain strange and antistrange quarks and have a relatively small hadronic-interaction cross section, are a good tool to study these effects. The PHENIX experiment has measured φ mesons in a specific set of small collision systems p+Al, p+Au, and 3 He+Au, as well as d+Au at $\sqrt{s_{NN}}$=200 GeV. The transverse-momentum spectra and nuclear-modification factors are presented and compared to theoretical-model predictions. The comparisons with different calculations suggest that quark-gluon plasma may be formed in these small collision systems at $\sqrt{s_{NN}}$=200 GeV. However, the volume and the lifetime of the produced medium may be insufficient for observing strangeness-enhancement and jet-quenching effects. The comparison with calculations suggests that the main production mechanisms of φ mesons at midrapidity may be different in p+Al versus p/d/ 3 He+Au collisions at $\sqrt{s_{NN}}$=200 GeV. While thermal quark recombination seems to dominate in p/d/ 3 He+Au collisions, fragmentation seems to be the main production mechanism in p+Al collisions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2024

Studying the interaction between charm and light-flavor mesons

The two-particle momentum correlation functions between charm mesons ( D * ± and D ± ) and charged light-flavor mesons ( π ± and K ± ) in all charge combinations are measured for the first time by the ALICE Collaboration in high-multiplicity proton–proton collisions at a center-of-mass energy of s = 13 TeV . For DK and D * K pairs, the experimental results are in agreement with theoretical predictions of the residual strong interaction based on quantum chromodynamics calculations on the lattice and chiral effective field theory. In the case of D π and D * π pairs, tension between the calculations including strong interactions and the measurement is observed. For all particle pairs, the data can be adequately described by Coulomb interaction only, indicating a shallow interaction between charm and light-flavor mesons. Finally, the scattering lengths governing the residual strong interaction of the D π and D * π systems are determined by fitting the experimental correlation functions with a model that employs a Gaussian potential. The extracted values are small and compatible with zero. © 2024 CERN, for the ALICE Collaboration 2024 CERN

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2026

Cross sections of 𝜂 mesons in 𝑝 +𝑝 collisions at forward rapidity at $\sqrt{𝑠}$ = 500 GeV and central rapidity at $\sqrt{𝑠}$ = 510 GeV

We present the first measurements of the forward and midrapidity 𝜂-meson cross sections from 𝑝 + 𝑝 collisions at $\sqrt{𝑠}$ = 500 and 510 GeV, respectively. We also report the midrapidity 𝜂/𝜋 0 ratio at 510 GeV. The forward cross section is measured differentially in 𝜂-meson transverse momentum (𝑝 𝑇 ) from 1.0 to 6.5 GeV/𝑐 for pseudorapidity 3.0 < |𝜂| < 3.8. The midrapidity cross section is measured from 3.5 to 44 GeV/𝑐 for pseudorapidity |𝜂| < 0.35. Both cross sections serve as critical inputs to an updated global analysis of the 𝜂-meson fragmentation functions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2017

Production of φ Mesons on Nuclear Targets in the Quark–Gluon String Model

Experimental data on the production of φ mesons in proton–nucleus and nucleus–nucleus collisions are considered. These data show unusually small shadowing corrections to the inclusive density for φ-meson production in the midrapidity region. It is found that the results of calculations based on the quark–gluon string model are in qualitative agreement with experimental data on the density of produced φ mesons as a function of both the initial energy ranging from the Collaboration NA49 energy to the LHC high energies and the target atomic number A.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2015

Relativistic nuclear theory—nucleons and mesons: origin, current status, and trends

The nuclear shell model (NSM) is a fundamental model of nuclear theory. At the initial stage, the NSM was developed on the basis of the Schrödinger equation, in particular because it was not clear which Dirac matrices should be associated with various components of the (relativistic) shell model potential. In the early 1970s, the relativistic version of the NSM with meson fields as its main components was developed on the basis of the Dirac equation. The relativistic nuclear shell model (RNSM) includes meson fields with different space–time transformation properties (scalar, four-vector, etc.) that determine the behavior of the (corresponding) meson fields under Lorentz transformations. This fact directly indicates that nuclear theory should be relativistic and based on the Dirac equation.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2017

Charm meson production in Pb-Pb collisions at the LHC in HYDJET++ model

The phenomenological analysis of J /ψ and D meson production in Pb-Pb collisions at a center-of-mass energy of 2.76 TeV per nucleon pair is fulfilled in the framework of the two-component HYDJET++ model, which includes the thermal and nonthermal production mechanisms. A significant fraction of D -mesons is found to be in a kinetic equilibrium with the created matter, while J /ψ-mesons are characterized by earlier (as compared to light hadrons) freeze-out.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2017

Effects of the σ{sup ∗} and ϕ Mesons on the Properties of Massive Protoneutron Stars

The properties of massive neutron stars and protoneutron stars are studied in this work in the framework of relativistic mean-field theory. For certain choices of coupling parameters, a two-solar mass cold neutron star is obtained in the presence of hyperons, taking into account the influence of σ{sup ∗} and ϕ mesons. The model for the coupling parameters is then extrapolated to study the effects of σ{sup ∗} and ϕ mesons on the properties of massive protoneutron stars in different evolutionary stages. The coupling constants are determined by two different methods, and their corresponding influence on the equation of state, mass, radius, and temperature is studied. The effect of the strange mesons is different at different evolution stages of the neutron star. The properties of a protoneutron star corresponding to the mass of PSR J0348+0432 are also presented.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2012

Study of Bbar to Xu l nubar Decays in BBbar Events Tagged by a Fully Reconstructed B-meson Decay and Determination of |V_{ub}|

We report measurements of partial branching fractions for inclusive charmless semileptonic B decays {bar B} {yields} X{sub u}{ell}{bar {nu}}, and the determination of the CKM matrix element |V{sub ub}|. The analysis is based on a sample of 467 million {Upsilon}(4S) {yields} B{bar B} decays recorded with the BABAR detector at the PEP-II e{sup +}e{sup -} storage rings. We select events in which the decay of one of the B mesons is fully reconstructed and an electron or a muon signals the semileptonic decay of the other B meson. We measure partial branching fractions {Delta}{Beta} in several restricted regions of phase space and determine the CKM element |V{sub ub}| based on four different QCD predictions. For decays with a charged lepton momentum p*{sub {ell}} > 1.0 GeV in the B meson rest frame, we obtain {Delta}{Beta} = (1.80 {+-} 0.13{sub stat.} {+-} 0.15{sub sys.} {+-} 0.02{sub theo.}) x 10{sup -3} from a maximum likelihood fit to the two-dimensional M{sub X} - q{sup 2} distribution. Here, M{sub X} refers to the invariant mass of the final state hadron X and q{sup 2} is the invariant mass squared of the charged lepton and neutrino. From this measurement we extract |V{sub ub}| = (4.31 {+-} 0.25{sub exp.} {+-} 0.16{sub theo.}) x 10{sup -3} as the arithmetic average of four results obtained from four different QCD predictions of the partial rate. We separately determine partial branching fractions for {bar B}{sup 0} and B{sup -} decays and derive a limit on the isospin breaking in {bar B} {yields} X{sub u}{ell}{bar {nu}} decays.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2011

In-Medium QCD Sum Rules for {rho}-Meson and Chiral Scale

In this talk, chiral scale, 4{pi}f{sub {pi}{approx}1} GeV, was introduced as an indicator of partial restoration of chiral symmetry at finite density or temperature, rather than the argument between mass shift and collisional broadening. We use the finite energy sum rules to determine the chiral scale identified with the separation scale of the low-energy resonance part from the high-energy continuum part of {rho}-meson spectral function. In this framework, in-medium {rho}-meson mass should be discussed in terms of the first two moments of the spectral function.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2011

Measurement of the transition form factor of {eta} meson with WASA-at-COSY

Reaction {eta}{yields}e{sup +}e{sup -}{gamma} is used to investigate the transition form factor of {eta} meson with WASA detector at COSY. Where the {eta} meson is produced in pp collision at 1.4 GeV. We present the analysis techniques and preliminary results of {eta} Dalitz decays.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2012

Meson-photon transition form factors

We present the results of our recent analysis of the meson-photon transition form factors F{sub P{gamma}}(Q{sup 2}) for the pseudoscalar mesons P {pi}{sup 0},{eta},{eta} Prime ,{eta}{sub c}, using the local-duality version of QCD sum rules.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2013

Exclusive vector meson production at HERA

The exclusive photoproduction of {Upsilon} has been studied with the ZEUS detector in ep collisions at HERA. The exponential slope, b, of the |t|-dependence of the cross section, where t is the squared four-momentum transfer at the proton vertex, has been measured. This constitutes the first measurement of the |t|-dependence of the {gamma}p{yields}{Upsilon}p cross section. The differential crosssections as a function of t at lower energies of {gamma}p centre-of-mass has been studied in exclusive diffractive photoproduction of J/{psi} mesons with the H1 detector. The exclusive electroproduction of two pions has been measured by the ZEUS experiment. The two-pion invariant-mass distribution is interpreted in terms of the pion electromagnetic form factor, assuming that the studied mass range includes the contributions of the {rho}, {rho} Prime and . {rho}'' vector-meson states.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2013

Result and perspectives on meson spectroscopy with KLOE and KLOE-2

From 2000 to 2006 KLOE has collected 2.5 fb{sup −1} of e{sup +}e{sup −} collisions at the peak of the φ(1020) and 250 pb{sup −1} off-peak. In this paper the most recent results on meson spectroscopy are presented, with emphasis on rare eta meson decays, the search for the U boson, and γγ collisions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2015

Photoproduction of vector mesons in ultra-peripheral p–Pb and Pb–Pb collisions at the LHC with the ALICE experiment

Vector mesons are copiously produced in ultra-peripheral collisions. In these collisions, the impact parameter is larger than the sum of the radii of the two projectiles, implying that electromagnetic processes become dominant. The cross section of production of vector mesons is expected to be sensitive to the gluon distribution and can therefore probe nuclear gluon shadowing (Pb–Pb) and the gluon structure function in the nucleon (p-Pb). The ALICE Collaboration has performed the first measurements of the production of ρ{sup 0}, J/ψ and ψ/(2S) in Pb–Pb ultra-peripheral collision as well as the cross section for exclusive J/ψ photoproduction off protons in ultra-peripheral proton-lead collisions at the LHC. The results are compared to the STARLIGHT Monte Carlo and to QCD based models.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2016

B-meson production at Tevatron and the LHC in the Regge limit of quantum chromodynamics

We study the inclusive hadroproduction of B{sup 0}, B{sup +}, and B{sub s}{sup 0} mesons in the leading order in the parton Reggeization approach. We have described B-meson transverse momentumdistributionsmeasured in the central region of rapidity by the CDF Collaboration at Fermilab Tevatron and CMS Collaboration at LHC within uncertainties and without free parameters, applying Kimber–Martin–Ryskin unintegrated gluon distribution function in a proton.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗