Proton Structure Research Articles

Unsymmetric Protonation Driven Highly Efficient H2O2 Photosynthesis in Supramolecular Photocatalysts via One-Step Two-Electron Oxygen Reduction.

Photocatalytic hydrogen peroxide (H2O2) production has emerged as an attractive alternative to the traditional anthraquinone process. However, its performance is often hindered by low selectivity and sluggish kinetics of oxygen reduction reaction (ORR). Herein, we report an anthrazoline-based supramolecular photocatalyst, SA-SADF-H+, featuring an unsymmetric protonation structure for H2O2 photosynthesis from water and air.The introduction of unsymmetric protonation disrupts the initial mirror symmetry of SADF, significantly enhancing the molecular dipole and facilitating efficient charge separation and electron transfer. Additionally, this modification increases the hydrophilicity of SA-SADF-H+, enabling the interaction of water and dissolved oxygen with the catalytic sites. The altered electron density distribution creates numerous dual active sites for Yeager-type O2 adsorption, facilitating an efficient ORR towards H2O2 via a direct one-step two-electron pathway. Notably, SA-SADF-H+ achieves an outstanding photocatalytic H2O2 production at a rate of 4667 μmol L-1 h-1, with a remarkable solar-to-chemical conversion (SCC) of 1.35%, surpassing most organic photocatalytic systems. Furthermore, SA-SADF-H+ demonstrates remarkable photocatalytic antibacterial activity, achieving 100% antibacterial efficiency against Staphylococcus aureus within 60 min.

Cascade CO2 Insertion in Carbanion Ionic Liquids Driven by Structure Rearrangement.

The CO2 chemisorption in state-of-the-art sorbents based on oxide/hydroxide/amine moieties is driven by strong chemical bonding formation in the carbonate/bicarbonate/carbamate products, which in turn leads to high energy input in sorbent regeneration. In addition, the CO2 uptake capacity was limited by the active sites' utilization efficiency, with each active site incorporating one CO2 molecule or less. In this work, a new concept and generation of sorbent was developed to achieve cascade insertion of multiple CO2 molecules by leveraging structure rearrangement as the driving force, leading to in situ generation of extra CO2-binding sites and significantly reduced energy input for CO2 release. The designed ionic liquids (ILs) containing carbanions with conjugated and asymmetric structure, deprotonated (methylsulfonyl)acetonitrile ([MSA]) anion, allowed the cascade insertion of two CO2 molecules via consecutive C-C and O-C bond formations. The proton transfer and structure rearrangement of the carboxylic acid intermediates played critical roles in stabilizing the first integrated CO2 and generating extra electron-rich oxygen sites for the insertion of the second CO2. The structure variation and reaction pathway were confirmed by operando spectroscopy, magnetic resonance spectroscopy (NMR), mass spectroscopy, and computational chemistry. The energy input in sorbent regeneration could be further reduced by harnessing the phase-changing behavior of the carbanion salts in ether solutions upon reacting with CO2, avoiding the energy consumption in heating the solvent. The fundamental insights obtained herein provide a promising approach to greatly improve the CO2 sorption performance via sophisticated molecular-scale structural engineering of the sorbents.

Finite Nuclear Size Effect on the Relativistic Hyperfine Splittings of 2s and 2p Excited States of Hydrogen-like Atoms

Hyperfine splittings play an important role in quantum information and spintronics applications. They allow for the readout of the spin qubits, while at the same time providing the dominant mechanism for the detrimental spin decoherence. Their exact knowledge is thus of prior relevance. In this work, we analytically investigate the relativistic effects on the hyperfine splittings of hydrogen-like atoms, including finite-size effects of the nucleis’ structure. We start from exact solutions of Dirac’s equation using different nuclear models, where the nucleus is approximated by (i) a point charge (Coulomb potential), (ii) a homogeneously charged full sphere, and (iii) a homogeneously charged spherical shell. Equivalent modelling has been done for the distribution of the nuclear magnetic moment. For the 1s ground state and 2s excited state of the one-electron systems H1, H2, H3, and He+3, the calculated finite-size related hyperfine shifts are quite similar for the different structure models and in excellent agreement with those estimated by comparing QED and experiment. This holds also in a simplified approach where relativistic wave functions from a Coulomb potential combined with spherical-shell distributed nuclear magnetic moments promises an improved treatment without the need for an explicit solution of Dirac’s equation within the nuclear core. Larger differences between different nuclear structure models are found in the case of the anisotropic 2p3/2 orbitals of hydrogen, rendering these excited states as promising reference systems for exploring the proton structure.

Phenomenological investigation of the beauty content of a proton in the framework of kt -factorization using Kimber-Martin-Ryskin and Martin-Ryskin-Watt unintegrated parton distributions

In this paper, we address the reduced beauty cross section [σredbb¯(x,Q2)] and the beauty structure function [F2bb¯(x,Q2)], to study the beauty content of a proton. We calculate σredbb¯ and F2bb¯ in the kt-factorization formalism by using the integral form of the Kimber-Martin-Ryskin and Martin-Ryskin-Watt unintegrated parton distribution function (KMR and MRW-UPDF) with the angular ordering constraint (AOC) and the MMHT2014 PDF set as the input. Recently Guiot and van Hameren demonstrated that the upper limit, kmax, of the transverse-momentum integration performed in the kt-factorization formalism should be almost equal to Q, where Q is the hard scale, otherwise it leads to an overestimation of the proton structure function [F2(x,Q2)]. In the present work, we show that kmax cannot be equal to Q at low and moderate energy region, and also by considering the gluon and quark contributions to the same perturbative order and a physical gauge for the gluon, i.e., Aμqμ′=0 in the calculation of F2bb¯ in the kt-factorization formalism, we do not encounter any overestimation of the theoretical predictions due to different choices of kmax>Q. Finally, the resulted σredbb¯ and F2bb¯ are compared to the experimental data and the theoretical predictions. In general, the extracted σredbb¯ and F2bb¯ based on the KMR and MRW approaches are in perfect agreement with the experimental data and theoretical predictions at high energies, but at low and moderate energies, the one developed from the KMR approach has better consistency than that of the MRW approach. Published by the American Physical Society 2024

Contact interaction study of proton parton distributions

Using a symmetry-preserving formulation of a vector×\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\,\ imes \\,$$\\end{document}vector contact interaction (SCI) and treating the proton as a quark + interacting-diquark bound state, whose structure is obtained by solving a Poincaré-covariant Faddeev equation, we provide a comprehensive, coherent set of predictions for unpolarised and polarised proton parton distribution functions (DFs): valence, glue, and four-flavour separated sea. The results enable many themes to be addressed, including: the asymmetry of antimatter in the proton; the neutron:proton structure function ratio; helicity retention in hard scattering processes; the charm quark momentum fraction; the sign and size of the polarised gluon DF; and the origin of the proton spin. In all cases where sound analyses of data are available, SCI predictions are semiquantitatively in agreement with the results. Those mismatches which exist are typically attributable to the momentum-independence of the underlying interaction. Judiciously interpreted, the SCI delivers a sound and insightful explanation of proton structure as expressed in DFs.

Gravitational Form Factors of the Proton from Lattice QCD.

The gravitational form factors (GFFs) of a hadron encode fundamental aspects of its structure, including its shape and size as defined from, e.g., its energy density. This Letter presents a determination of the flavor decomposition of the GFFs of the proton from lattice QCD, in the kinematic region 0≤-t≤2 GeV^{2}. The decomposition into up-, down-, strange-quark, and gluon contributions provides first-principles constraints on the role of each constituent in generating key proton structure observables, such as its mechanical radius, mass radius, and D term.

Direct Evidence of Drift‐Compressional Wave Generation in the Earth's Magnetosphere Detected by Arase

AbstractWe present the first direct evidence of an in situ excitation of drift‐compressional waves driven by drift resonance with ring current protons in the magnetosphere. Compressional Pc4–5 waves with frequencies of 4–12 mHz were observed by the Arase satellite near the magnetic equator at L ∼ 6 in the evening sector on 19 November 2018. Estimated azimuthal wave numbers (m) ranged from −100 to −130. The observed frequency was consistent with that calculated using the drift‐compressional mode theory, whereas the plasma anisotropy was too small to excite the drift‐mirror mode. We discovered that the energy source of the wave was a drift resonance instability, which was generated by the negative radial gradient in a proton phase space density at 20–25 keV. This proton distribution is attributed to a temporal variation of the electric field, which formed the observed multiple‐nose structures of ring current protons.

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.

Analysis of the gluon distribution with next-to-leading order splitting function at small-x* *Supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (XDB34030301), the National Natural Science Foundation of China (12375073), the Major Project of Basic and Applied Basic Research in Guangdong Province (2020B0301030008), the Basic Research Program (Natural Science) of Guizhou Province, China(QKHJC-ZK[2023]YB027), and the Education

An approximated solution for the gluon distribution from DGLAP evolution equations with the NLO splitting function in the small-x limit is presented. We first obtain simplified forms of the LO and NLO splitting functions in the small-x limit. With these approximated splitting functions, we obtain the analytical gluon distribution using the Mellin transform. The free parameters in the boundary conditions are obtained by fitting the CJ15 gluon distribution data. We find that the asymptotic behavior of the gluon distribution is consistent with the CJ15 data; however, the NLO results considering the "ladder" structure of gluon emission are slightly better than the LO results. These results indicate that the corrections from NLO have a significant influence on the behavior of the gluon distribution in the small-x region. In addition, we investigate the DGLAP evolution of the proton structure function using the analytical solution of the gluon distribution. The differential structure function reveals that our results have a similar tendency to the CJ15 data at small-x.

Nucleon axial-vector form factor and radius from future neutrino experiments

Precision measurements of antineutrino elastic scattering on hydrogen from future neutrino experiments offer a unique opportunity to access the low-energy structure of protons and neutrons. We discuss the determination of the nucleon axial-vector form factor and radius from antineutrino interactions on hydrogen that can be collected at the future Long-Baseline Neutrino Facility and study the sources of theoretical and experimental uncertainties. The projected accuracy would improve existing measurements by 1 order of magnitude and be competitive with contemporary lattice-QCD determinations, potentially helping to resolve the corresponding tension with measurements from (anti)neutrino elastic scattering on deuterium. We find that the current knowledge of the nucleon vector form factors could be one of the dominant sources of uncertainty. We also evaluate the constraints that can be simultaneously obtained on the absolute ν¯μ flux normalization. Published by the American Physical Society 2024

Investigation of proton structure function F2p at HERA in light of an analytical solution to the Balitsky–Kovchegov equation

In this paper, the proton structure function F2p(x,Q2) at small-x is investigated using an analytical solution to the Balitsky–Kovchegov (BK) equation. In the context of the color dipole description of deep inelastic scattering (DIS), the structure function F2p(x,Q2) is computed by applying the analytical expression for the scattering amplitude N(k, Y) derived from the BK solution. At transverse momentum k and total rapidity Y, the scattering amplitude N(k, Y) represents the propagation of the quark-antiquark dipole in the color dipole description of DIS. Using the BK solution we extracted the integrated gluon density xg(x, Q 2) and then compared our theoretical estimation with the LHAPDF global data fits, NNPDF3.1sx and CT18. Finally, we have investigated the behavior of F2p(x,Q2) in the kinematic region of 10−5 ≤ x ≤ 10−2 and 2.5 GeV2 ≤ Q 2 ≤ 60 GeV2. Our predicted results for F2p(x,Q2) within the specified kinematic region are in good agreement with the recent high-precision data for F2p(x,Q2) from HERA (H1 Collaboration) and the LHAPDF global parametrization group NNPDF3.1sx.

Complete next-to-leading order calculation of single inclusive π0 production in forward proton-nucleus collisions

We present the first fully consistent calculation of inclusive π0 production at forward rapidities at next-to-leading order (NLO) accuracy in proton-lead collisions at s=8.16 TeV within the color glass condensate approach. The center-of-mass energy dependence is determined by the Balitsky-Kovchegov equation with the initial condition constrained at NLO accuracy by the proton structure function measurements. We find that the LHCb data further constrain this nonperturbative input, and that both the NLO corrections to the evolution equation and to the impact factor have significant effects on the nuclear modification factor RpPb. The complete NLO calculation is shown to be in qualitative agreement with the LHCb data, and the predictions are found to be sensitive to the details of the applied deep inelastic scattering (DIS) fit. These results demonstrate the need to perform global analyses of DIS and LHC data in order to probe gluon saturation phenomena at precision level at very small momentum fraction x. Published by the American Physical Society 2024

Probing the Structure of the 1:1 Hydrogen-Bonded Complexes of Metallocenes with HCl.

Matrix isolation infrared spectroscopy combined with density functional calculations has been used to form, isolate, and characterize the 1:1 hydrogen-bonded complexes of HCl with ferrocene and ruthenocene. Two unique structures were calculated for each complex, analogous to the two binding sites proposed for the attachment of proton to these metallocenes. The spectra, combined with calculated shifts of the H-Cl stretching mode, support the formation of a complex with the HCl hydrogen bonding to one of the cyclopentadienyl rings, exo to the plane of the ring. Evidence also was obtained for a second structure with the hydrogen of the HCl subunit directed toward the Fe or Ru center between the two cyclopentadienyl rings. This structure is similar to the proposed metal-bound proton structure based on earlier mass spectrometric and computational studies. Importantly, these results were supported by parallel experiments with DCl and the two metallocenes.

Direct Detection of Cosmic Rays with the Dark Matter Particle Explorer

The origin, acceleration, and propagation of high-energy cosmic rays is one of the most important questions in modern physics and astronomy. To fully uncover such a mystery, precise measurements of the energy spectra and anisotropies of cosmic rays, as well as multi-wavelength electromagnetic radiation from various types of energetic objects are required. The direct measurements of energy spectra of different species via particle detectors in space are an essential way to study cosmic ray physics. China launched the first space astronomical satellite, the Dark Matter Particle Explorer (DAMPE) in the end of 2015, which keeps operation in space for more than 7 years. The DAMPE has a relatively large acceptance and a high energy resolution, and has made important progresses in measuring the spectral structures of cosmic ray protons, helium nuclei, and boron-to-carbon and boron-to-oxygen ratios. These new measurements bring new insights in understanding the origin and propagation of cosmic rays. This paper reviews the instrumentation and operation of DAMPE, with an emphasis on its scientific results and physical implications in cosmic ray studies.

NLO corrections to the deeply virtual meson production revisited: impact on the extraction of generalized parton distributions

We revisit the next-to-leading order (NLO) perturbative QCD corrections for the deeply virtual meson production (DVMP) process, exploring its phenomenology both in isolation and in a multichannel fit combined with deeply virtual Compton scattering (DVCS). Our approach involves the conformal partial wave (CPaW) formalism, which allows for the straightforward inclusion of higher-order contributions and evolutionary effects. Our findings indicate that a description of the longitudinal component of the vector meson DVMP cross-section at high energies is achievable only at NLO within the standard collinear approach. Furthermore, we demonstrate a simultaneous description of DIS, DVCS, and DVMP processes, providing insights into the proton structure described at NLO by unique universal generalized parton distribution (GPD) functions.

Self-consistent description of HERA data at low Q2 and soft hadron production at LHC

Using the analytical expression for transverse momentum dependent (TMD) gluon density in a proton, a self-consistent simultaneous description of low Q2 data on proton structure function F2(x,Q2), reduced cross section for the electron-proton deep inelastic scattering at HERA and soft hadron production in pp collisions at the LHC is achieved in the framework of color dipole approach and modified quark-gluon string model.

Transient photocatalytic oxidation of toluene vapor via nanostructured layers prepared by sol-gel on anatase particles

Gas-phase photocatalytic degradation of toluene mixed with wet oxygen was performed in a continuous reactor using anatase nanoparticles, home-prepared by the sol-gel method combined with peptization treatments. Titanium (IV) isopropoxide was used to synthesize amorphous titania precursor, partially transformed into crystalline nanoparticles by hydrothermal or thermal treatments. The main oxidation product was carbon dioxide, but traces of benzene and benzoic acid were also detected. In order to characterize the catalysts, the evolution of titanium (IV) alkoxide to form anatase nanoparticles was studied using 1H-MAS NMR, EPR, TPD, and FTIR techniques. The results indicate that the four coordinated Ti4+ cations of the alkoxide induce the formation of amorphous aggregates of polymeric layers. The organics removal by peptization originates thin nanostructured titania layers that cover anatase particles, forming TiO2 homojunction. Photoactivity runs showed that both toluene retention and mineralization occurred at the start of irradiation, both processes exhibiting a long transient. After different times, retention stopped while mineralization reached steady-state conditions. Hydrated proton structures are considered to be the origin of both processes. Under irradiation, water photodesorption from these structures favors both the interaction of nanostructured layers with anatase particles, determining hole transfer to external surfaces and the generation of hydrated hydronium cations which, depending on the water loss, are centers able to carry out toluene mineralization or retention. After the mineralization step, photocatalytic centers must be reconstituted by recovering water, a process whose rate becomes the rate-determining one.

Twist decomposition of non-linear effects in Balitsky–Kovchegov evolution of proton structure functions

Effects of non-linear small-x evolution of the gluon distribution given by the Balitsky–Kovchegov equation are analyzed within the collinear approximation framework. We perform a twist decomposition of the proton structure functions F2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$F_2$$\\end{document} and FL\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$F_{\ extrm{L}}$$\\end{document} obtained from the Balitsky–Kovchegov equation using the Mellin representation of the scattering cross-sections at high energies. In both the structure functions we find strong corrections coming from the non-linear effects in the gluon evolution at twist 2, and strongly suppressed higher twist effects. This implies that unitarization effects of high energy scattering amplitudes are mostly the leading twist effect. Furthermore we consider the double logarithmic limit of the Balitsky–Kovchegov equation for the collinear gluon distribution, and compare the result to the Gribov–Levin–Ryskin equation. We find that these two equations differ by two powers of the hard scale logarithm for the large scales.

Hide and seek: how PDFs can conceal new physics

The interpretation of LHC data, and the assessment of possible hints of new physics, require the precise knowledge of the proton structure in terms of parton distribution functions (PDFs). We present a systematic methodology designed to determine whether and how global PDF fits might inadvertently ‘fit away’ signs of new physics in the high-energy tails of the distributions. We showcase a scenario for the High-Luminosity LHC, in which the PDFs may completely absorb such signs of new physics, thus biasing theoretical predictions and interpretations. We discuss strategies to single out the effects in this scenario, and disentangle the inconsistencies that stem from them. Our study brings to light the synergy between the high luminosity programme at the LHC and future low-energy non-LHC measurements of large-x sea quark distributions. The analysis code used in this work is made public so that any users can test the robustness of the signal associated to a given BSM model against absorption by the PDFs.

Impact of NNLO QED corrections on lepton-proton scattering at MUSE

We present the complete next-to-next-to-leading order (NNLO) pure pointlike QED corrections to lepton-proton scattering, including three-photon-exchange contributions, and investigate their impact in the case of the MUSE experiment. These corrections are computed with no approximation regarding the energy of the emitted photons and taking into account lepton-mass effects. We contrast the NNLO QED corrections to known next-to-leading order corrections, where we include the elastic two-photon exchange (TPE) through a simple hadronic model calculation with a dipole ansatz for the proton electromagnetic form factors. We show that, in the low-momentum-transfer region accessed by the MUSE experiment, the improvement due to more sophisticated treatments of the TPE, including inelastic TPE, is of similar if not smaller size than some of the NNLO QED corrections. Hence, the latter have to be included in a precision determination of the low-energy proton structure from scattering data, in particular for electron-proton scattering. For muon-proton scattering, the NNLO QED corrections are considerably smaller.