Nucleon Structure Research Articles

Jet-induced enhancement of deuteron production in pp and p-Pb collisions at the LHC

Jet-associated deuteron production in pp collisions at s=13 TeV and p-Pb collisions at sNN=5.02 TeV is studied in the coalescence model by using the phase-space information of proton and neutron pairs from a multiphase transport (AMPT) model at the kinetic freezeout. In the low transverse momentum (pT) region pT/A<1.5 GeV/c, where A is the mass number of a nucleus, the in-jet coalescence factor B2In-jet for deuteron production, given by the ratio of the in-jet deuteron number to the square of the in-jet proton number, is found to be larger than the coalescence factor B2 in the medium perpendicular to the jet by a factor of about 10 in pp collisions and of 25 in p−Pb collisions, which are consistent with the ALICE measurements at the LHC. Such large low-momentum enhancements mainly come from coalescence of nucleons inside the jet with the medium nucleons. Coalescence of nucleons inside the jet dominates deuteron production only at the higher pT region of pT/A≳4 GeV/c, where both the yield ratio d/p of deuteron to proton numbers and the B2 are also significantly larger in the jet direction than in the direction perpendicular to the jet due to the strong collinear correlation among particles produced from jet fragmentation. Studying jet-associated deuteron production in relativistic nuclear collisions thus opens up a new window to probe the phase-space structure of nucleons inside jets.

Extracting the femtometer structure of strange baryons using the vacuum polarization effect

One of the fundamental goals of particle physics is to gain a microscopic understanding of the strong interaction. Electromagnetic form factors quantify the structure of hadrons in terms of charge and magnetization distributions. While the nucleon structure has been investigated extensively, data on hyperons are still scarce. It has recently been demonstrated that electron-positron annihilations into hyperon-antihyperon pairs provide a powerful tool to investigate their inner structure. We present a method useful for hyperon-antihyperon pairs of different types which exploits the cross section enhancement due to the effect of vacuum polarization at the J/ψ resonance. Using the 10 billion J/ψ events collected with the BESIII detector, this allows a precise determination of the hyperon structure function. The result is essentially a precise snapshot of the Λ¯Σ0(ΛΣ¯0)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\bar{\\Lambda }{\\Sigma }^{0}\\,(\\Lambda {\\bar{\\Sigma }}^{0})$$\\end{document} transition process, encoded in the transition form factor ratio and phase. Their values are measured to be R = 0.860 ± 0.029(stat.) ± 0.015(syst.), ΔΦΛ¯Σ0=(1.011±0.094(stat.)±0.010(syst.))rad\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Delta {\\Phi }_{\\bar{\\Lambda }{\\Sigma }^{0}}=(1.011\\pm 0.094({{\\rm{stat.}}})\\pm 0.010({{\\rm{syst.}}}))\\,{{\\rm{r}}}ad$$\\end{document} and ΔΦΛΣ¯0=(2.128±0.094(stat.)±0.010(syst.))rad\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Delta {\\Phi }_{\\Lambda {\\bar{\\Sigma }}^{0}}=(2.128\\pm 0.094({{\\rm{stat.}}})\\pm 0.010({{\\rm{syst.}}}))\\,{{\\rm{r}}}ad$$\\end{document}. Furthermore, charge-parity (CP) breaking is investigated in this reaction and found to be consistent with CP symmetry.

Spin-orbit correlations in the nucleon in the large- Nc limit

We study the twist-3 spin-orbit correlations of quarks described by the nucleon matrix elements of the parity-odd rank-2 tensor QCD operator (the parity-odd partner of the QCD energy-momentum tensor). Our treatment is based on the effective dynamics emerging from the spontaneous breaking of chiral symmetry and the mean-field picture of the nucleon in the large-Nc limit. The twist-3 QCD operators are converted to effective operators, in which the QCD interactions are replaced by spin-flavor-dependent chiral interactions of the quarks with the pion field. We compute the nucleon matrix elements of the twist-3 effective operators and discuss the role of the chiral interactions in the spin-orbit correlations. We derive the first-quantized representation in the mean-field picture and develop a quantum-mechanical interpretation. The chiral interactions give rise to new spin-orbit couplings and qualitatively change the correlations compared to the quark model picture. We also derive the twist-3 matrix elements in the topological soliton picture where the quarks are integrated out (skyrmion). The methods used here can be extended to other QCD operators describing higher-twist nucleon structure and generalized parton distributions. Published by the American Physical Society 2024

The EMC effect for few-nucleon bound systems in light-front Hamiltonian dynamics

The light-front formalism for a covariant description of the European Muon Collaboration (EMC) effect, already applied to He3, is formally extended to any nucleus, and used for actually calculating the 3H and He4 cases. The realistic and accurate nuclear description of few-nucleon bound systems, obtained with both phenomenological and chiral potentials, has been properly combined with the Poincaré covariance and macroscopic locality, automatically satisfying both number of particles and momentum sum rule. While retaining the on-mass-shell nucleon structure functions, one is then able to predict a sizable EMC effect for He4, as already observed for He3. Moreover, the impact on the EMC effect of both i) the short-range correlations, such as those generated by modern nuclear interactions, and ii) the ratio between the neutron and proton structure functions has been studied. The short-range correlations generated by retaining only the standard nuclear degrees of freedom act on the depth of the minimum in the EMC ratio, while the uncertainties linked to the ratio of neutron to proton structure functions are found to be very small. These light-front results facilitate ascribing deviations from experimental data due to genuine QCD effects, not included in a standard nuclear description, and initiating unbiased investigations.

Algebraic cluster model calculations for shape phase transitions of boson-fermion systems

The Algebraic Cluster Model (ACM) is an interacting boson model that gives the relative motion of the cluster configurations in which all vibrational and rotational degrees of freedom are present from the outset. We schemed a solvable extended transitional Hamiltonian based on affine [Formula: see text] Lie algebra within the framework for two-, three- and four-body algebraic cluster models that explains both regions [Formula: see text], [Formula: see text] and [Formula: see text], respectively. We offer that this method can be used to study [Formula: see text] nucleon structures with [Formula: see text] and [Formula: see text] in specific [Formula: see text] such as structures [Formula: see text], [Formula: see text], [Formula: see text]; [Formula: see text], [Formula: see text], [Formula: see text]; [Formula: see text], [Formula: see text]. Numerical extraction to the energy levels, the expectation value of the boson number operator, and the behavior of the overlap of the ground state wave function within the control parameters of this evaluated Hamiltonian are presented. The effect of the coupling of the odd particle to an even–even boson core is discussed along the shape transition and, in particular, at the critical point.

Inside the Nucleon: Tomographic Interpretations and Universality of GPDs with DDVCS

The goal of Double Deeply Virtual Compton Scattering (DDVCS) experiments is to better understand the internal structure of the nucleon. Previous attempts to resolve the internal structure of nucleons have resulted in electromagnetic form factors and parton distribution functions for elastic scattering and deep inelastic scattering processes, respectively. Generalized Parton Distributions (GPDs) are the latest attempt to unify these models of nucleon structure. The GPDs of DDVCS give us ability to investigate off of the diagonal where x ̸= ±ξ. The main goal of our analysis is to determine the best experimental setup in order to deduce the kinematic variables on which GPDs depend from the lab observables. The effectiveness of our data collection in the laboratory is by determined the physical kinematics, Q2, Q′2,t, xi,ϕLM, ϕCMV , and θCMV . We can then run DDVCS experiments and collect data on observables to improve upon the current models for GPDs of the nucleon.

Scalar field, nucleon structure and relativistic chiral theory for nuclear matter

Scalar field, nucleon structure and relativistic chiral theory for nuclear matter

Studying the impact of virtuality-dependent nucleon structure modification on spectator-tagged deep inelastic scattering

Studying the impact of virtuality-dependent nucleon structure modification on spectator-tagged deep inelastic scattering

Constraining the low-x structure of nuclei with LHCb

The LHCb detector’s forward geometry provides unprecedented access to the very low regions of Bjorken x inside the nucleon. With full particle ID and a fast DAQ, LHCb is able to fully reconstruct plentiful charged particles and neutral mesons, as well as relatively rare probes such as heavy quarks, providing a unique set of constraints on nucleon structure functions. This contribution will discuss recent LHCb measurements sensitive to the low-x structure of nucleons, and discuss the impact of recent LHCb measurements that dramatically reduce nPDF uncertainties.

Study of nucleon structure using hadron beam at J-PARC

Recently, 30-GeV proton beam became available at the high momentum beamline of the J-PARC Hadron Experimental Facility. A following project of beamline upgrade will make available negative and positive secondary π/K/p beam up to 20 GeV/c. We will study the nucleon partonic structure utilizing the high-momentum hadron beams. The generalized parton distributions (GPDs) of nucleon can be accessed by various single diffractive hard exclusive processes (SDHEPs): a pure hadronic process (p + p → p + π + B), a diphoton production process (π− + p → γ + γ + n), and an exclusive Drell-Yan process (π− + p → μ+ + μ− + n). Measurements of these reactions give complementary information of nucleon GPDs to one from lepton-induced exclusive reactions.

Solution of the Nucleon Structure Problem from a Field Theory of Fermions and Bosons and the Origin of the Proton Stability

Solution of the Nucleon Structure Problem from a Field Theory of Fermions and Bosons and the Origin of the Proton Stability

The large-area hybrid-optics CLAS12 RICH: First years of data-taking

The CLAS12 deep-inelastic scattering experiment at the upgraded 12 GeV continuous electron beam accelerator facility of Jefferson Lab conjugates luminosity and wide acceptance to study the 3D nucleon structure in the yet poorly explored valence region, and to perform precision measurements in hadron spectroscopy. A large area ring-imaging Cherenkov detector has been designed to achieve the required hadron identification in the momentum range from 3 GeV/c to 8 GeV/c, with the kaon rate about one order of magnitude lower than the rate of pions and protons. The adopted solution comprises aerogel radiator and composite mirrors in a novel hybrid optics design, where either direct or reflected light could be imaged in a high-packed and high-segmented photon detector. The first RICH module was assembled during the second half of 2017 and installed at the beginning of January 2018, in time for the start of the experiment. The second RICH module, planned with the goal to be ready for the beginning of the operation with polarized targets, has been timely built despite the complications caused by the pandemic crisis and successfully installed in June 2022. The detector performance is here discussed with emphasis on the operation and stability during the data-taking, calibration and alignment procedures, reconstruction and pattern recognition algorithms, and particle identification.

Electromagnetic form factors for nucleons in short-range correlations

Recent experimental studies have led to the suggestion that short-range correlations may be a major contributor to the nuclear EMC effect. This hypothesis requires that the structure function for nucleons involved in short-range correlations should be heavily suppressed compared to that of a free nucleon. Based on calculations performed within an AdS/QCD motivated, light-front quark-diquark model, we find that this large suppression of the nucleon structure function leads to a strong suppression of the nucleon elastic form factors.

Effect of symmetry breaking of polarized light sea quarks on the nucleon and nuclear structure functions, and sum rules

Effect of symmetry breaking of polarized light sea quarks on the nucleon and nuclear structure functions, and sum rules

The Jefferson Lab tritium program of nucleon and nuclear structure measurements

The Jefferson Lab tritium program of nucleon and nuclear structure measurements

Azimuthal Correlations within Exclusive Dijets with Large Momentum Transfer in Photon-Lead Collisions.

The structure of nucleons is multidimensional and depends on the transverse momenta, spatial geometry, and polarization of the constituent partons. Such a structure can be studied using high-energy photons produced in ultraperipheral heavy-ion collisions. The first measurement of the azimuthal angular correlations of exclusively produced events with two jets in photon-lead interactions at large momentum transfer is presented, a process that is considered to be sensitive to the underlying nuclear gluon polarization. This study uses a data sample of ultraperipheral lead-lead collisions at sqrt[s_{NN}]=5.02 TeV, corresponding to an integrated luminosity of 0.38 nb^{-1}, collected with the CMS experiment at the LHC. The measured second harmonic of the correlation between the sum and difference of the two jet transverse momentum vectors is found to be positive, and rising, as the dijet transverse momentum increases. A well-tuned model that has been successful at describing a wide range of proton scattering data from the HERA experiments fails to describe the observed correlations, suggesting the presence of gluon polarization effects.

Pseudoscalar Meson Dominance and Nucleon Structure

Pseudoscalar Meson Dominance and Nucleon Structure

Physical implications of the extrapolation and statistical bootstrap of nucleon structure function ratios F2nF2p for mirror nuclei He3 and H3

A nuclear physics example of statistical bootstrap is used on the MARATHON nucleon structure function ratio data in the quark momentum fraction regions ${x}_{B}\ensuremath{\rightarrow}0$ and ${x}_{B}\ensuremath{\rightarrow}1$. The extrapolated ${F}_{2}$ ratio as quark momentum fraction ${x}_{B}\ensuremath{\rightarrow}1$ is $\frac{{F}_{2}^{n}}{{F}_{2}^{p}}\ensuremath{\rightarrow}0.4\ifmmode\pm\else\textpm\fi{}0.05$ and this value is compared to theoretical predictions. The extrapolated ratio when ${x}_{B}\ensuremath{\rightarrow}0$ favors the simple model of isospin symmetry with the complete dominance of sea quarks at low momentum fraction. At high-${x}_{B}$, the proton quark distribution function ratio $d/u$ is derived from the ${F}_{2}$ ratio and found to be $d/u\ensuremath{\rightarrow}1/6$. Our extrapolated values for both the $\frac{{F}_{2}^{n}}{{F}_{2}^{p}}$ ratio and the $d/u$ parton distribution function ratio are within uncertainties of perturbative QCD values from quark counting, helicity conservation arguments, and a Dyson-Schwinger equation with a contact interaction model. In addition, it is possible to match the statistical bootstrap value to theoretical predictions by allowing two compatible models to act simultaneously in the nucleon wave function. One such example is nucleon wave functions composed of a linear combination of a quark-diquark state and a three-valence quark correlated state with coefficients that combine to give the extrapolated ${F}_{2}$ ratio at ${x}_{B}=1$.

Hot spot model of nucleon and double parton scattering

We calculate the rate of double parton scattering (DPS) in proton-proton collisions in the framework of the recently proposed hot spot model of the nucleon structure. The resulting rate, especially for the case of three hot spots, is compared with the current experimental data on DPS at the LHC.

Recent data analysis to revisit the spin structure function of the nucleon in Laplace space

Considering a fixed-flavor number scheme and based on Laplace transformation, we perform leading-order and next-to-leading-order QCD analyses that include world data on polarized structure functions ${g}_{1}$ and ${g}_{2}$. During our analysis, taking the DGLAP evolution equations, we employ the Jacobi polynomials expansion technique. In our recent analysis we utilize the recent available data and consequently include more data than what we did in our previous analysis. We obtain good agreements between our results for the polarized parton densities and nucleon structure functions with all available experimental data and some common parametrization models.