Fragmentation Functions Research Articles

Transverse polarization of hyperons produced in semi-inclusive deep inelastic scattering

We study the transverse polarization of hyperons produced in semi-inclusive deep inelastic scattering, $ep\to e\Lambda^\uparrow X$, in the framework of the collinear twist-3 factorization. The cross section from the twist-3 distribution functions and the twist-3 quark fragmentation functions is computed in the leading order with respect to the QCD coupling constant. The constraint relations among the twist-3 FFs are taken into account to simplify the formula. The formula is relevant to large-$P_T$ hyperon production in the future Electron-Ion-Collider experiment.

Using Z Boson Events to Study Parton-Medium Interactions in Pb-Pb Collisions.

The spectra measurements of charged hadrons produced in the shower of a parton originating in the same hard scattering with a leptonically decaying Z boson are reported in lead-lead nuclei (Pb-Pb) and proton-proton (pp) collisions at a nucleon-nucleon center-of-mass energy of 5.02TeV. Both Pb-Pb and pp data sets are recorded by the CMS experiment at the LHC and correspond to an integrated luminosity of 1.7 nb^{-1} and 320 pb^{-1}, respectively. Hadronic collision data with one reconstructed Z boson candidate with the transverse momentum p_{T}>30 GeV/c are analyzed. The Z boson constrains the initial energy and direction of the associated parton. In heavy ion events, azimuthal angular distributions of charged hadrons with respect to the direction of a Z boson are sensitive to modifications of the in-medium parton shower and medium response. compared to reference data from pp interactions, the results for central Pb-Pb collisions indicate a modification of the angular correlations. The measurements of the fragmentation functions and p_{T} spectra of charged particles in Z boson events, which are sensitive to medium modifications of the parton shower longitudinal structure, are also reported. Significant modifications in central Pb-Pb events compared to the pp reference data are also found for these observables.

Polarized vector meson production in semi-inclusive DIS

We make a systematic calculation for polarized vector meson production in semi-inclusive lepton-nucleon deep inelastic scattering ${e}^{\ensuremath{-}}N\ensuremath{\rightarrow}{e}^{\ensuremath{-}}VX$. We consider the general case of neutral current electroweak interactions at high energies which give rise to parity-violating effects. We present a general kinematic analysis for the process and show that the cross sections are expressed by 81 structure functions. We further give a parton model calculation for the process and show the results for the structure functions in terms of the transverse momentum dependent parton distribution functions and fragmentation functions at the leading order and leading twist of perturbative quantum chromodynamics. The results show that there are 27 nonzero structure functions at this order, among which 15 are related to the tensor polarization of the vector meson. Thirteen structure functions are generated by parity-violating effects. We also present the result and a rough numerical estimate for the spin alignment of the vector meson.

Longitudinal and transverse polarizations of Λ hyperon in unpolarized SIDIS and e+e− annihilation

We make a systematic study of $\mathrm{\ensuremath{\Lambda}}$ hyperon polarizations in unpolarized lepton induced semi-inclusive reactions such as ${e}^{\ensuremath{-}}N\ensuremath{\rightarrow}{e}^{\ensuremath{-}}\mathrm{\ensuremath{\Lambda}}X$ and ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}\mathrm{\ensuremath{\Lambda}}hX$. We present the general form of cross sections in terms of structure functions obtained from a general kinematic analysis. This already shows that the produced hyperons can be polarized in three orthogonal directions, i.e., the longitudinal direction along the hyperon momentum, the normal direction of the production plane, and the transverse direction in the production plane. We present the parton model results at the leading twist and leading order in perturbative QCD using transverse momentum dependent factorization and provide the expressions for these structure functions and polarizations in terms of three-dimensional parton distribution functions and fragmentation functions. We emphasize in particular that by studying the longitudinal polarization and the transverse polarization in the production plane, we can extract the corresponding chiral-odd fragmentation functions ${H}_{1Lq}^{\ensuremath{\perp}\mathrm{\ensuremath{\Lambda}}}$, ${H}_{1Tq}^{\mathrm{\ensuremath{\Lambda}}}$, and ${H}_{1Tq}^{\ensuremath{\perp}\mathrm{\ensuremath{\Lambda}}}$. We also present numerical results of rough estimates utilizing available parametrizations of fragmentation functions and approximations. We discuss how to measure these polarizations and point out in particular that they can be carried out in future EIC and/or ${e}^{+}{e}^{\ensuremath{-}}$ annihilation experiments such as Belle.

Pion fragmentation functions at high energy colliders

We revisit the description of pion production in proton-proton collisions in the light of the very precise data taken at the Large Hadron Collider (LHC) over the past decade. First attempts to include LHC results in next-to-leading order global QCD analyses of parton-to-pion fragmentation functions insinuated some conflict between data sets at different center-of-mass system energies. We show that the data can be well described within their uncertainties by a consistent set of pion fragmentation functions once the theoretical scale dependence is taken into account in the global QCD analysis.

Nuclear modification factor of light neutral-meson spectra up to high transverse momentum in p–Pb collisions at [formula omitted] TeV

Neutral pion (π0) and η meson production cross sections were measured up to unprecedentedly high transverse momenta (pT) in p–Pb collisions at sNN=8.16TeV. The mesons were reconstructed via their two-photon decay channel in the rapidity interval −1.3<y<0.3 in the ranges of 0.4<pT<200 GeV/c and 1.0<pT<50 GeV/c, respectively. The respective nuclear modification factor (RpPb) is presented for pT up to of 200 and 30 GeV/c, where the former was achieved by extending the π0 measurement in pp collisions at s=8TeV using the merged cluster technique. The values of RpPb are below unity for pT<10 GeV/c, while they are consistent with unity for pT>10 GeV/c, leaving essentially no room for final state energy loss. The new data provide strong constraints for nuclear parton distribution and fragmentation functions over a broad kinematic range and are compared to model predictions as well as previous results at sNN=5.02TeV.

Formation of energy spectra of electrons in a dense weakly ionized plasma generated by fission fragments

AbstractFor a weakly ionized dense plasma irradiated by fission fragments, the coupled self‐consistent Boltzmann equations for fission fragments and electrons are defined. The evolution of the energy spectra of fast particles in a plasma is investigated on the basis of these equations. Studies of the energy distribution function of fission fragments and primary electrons for a helium‐3 plasma irradiated by neutron flux, as well as their non‐stationary and stationary analytical solutions, are found and analysed.

Measurement of charged-pion production in deep-inelastic scattering off nuclei with the CLAS detector

Background: Energetic quarks in nuclear deep-inelastic scattering propagate through the nuclear medium. Processes that are believed to occur inside nuclei include quark energy loss through medium-stimulated gluon bremsstrahlung and intranuclear interactions of forming hadrons. More data are required to gain a more complete understanding of these effects. Purpose: To test the theoretical models of parton transport and hadron formation, we compared their predictions for the nuclear and kinematic dependence of pion production in nuclei. Methods: We have measured charged-pion production in semi-inclusive deep-inelastic scattering off D, C, Fe, and Pb using the CLAS detector and the CEBAF 5.014-GeV electron beam. We report results on the nuclear-to-deuterium multiplicity ratio for π+ and π− as a function of energy transfer, four-momentum transfer, and pion energy fraction or transverse momentum—the first three-dimensional study of its kind. Results: The π+ multiplicity ratio is found to depend strongly on the pion fractional energy z and reaches minimum values of 0.67±0.03, 0.43±0.02, and 0.27±0.01 for the C, Fe, and Pb targets, respectively. The z dependencies of the multiplicity ratios for π+ and π− are equal within uncertainties for C and Fe targets but show differences at the level of 10% for the Pb-target data. The results are qualitatively described by the GiBUU transport model, as well as with a model based on hadron absorption, but are in tension with calculations based on nuclear fragmentation functions. Conclusions: These precise results will strongly constrain the kinematic and flavor dependence of nuclear effects in hadron production, probing an unexplored kinematic region. They will help to reveal how the nucleus reacts to a fast quark, thereby shedding light on its color structure and transport properties and on the mechanisms of the hadronization process.Received 25 September 2021Accepted 23 December 2021DOI:https://doi.org/10.1103/PhysRevC.105.015201©2022 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasColor confinementDeep inelastic scatteringLepton induced nuclear reactionsParticle interactionsParticle productionQuantum chromodynamicsStrong interactionNuclear PhysicsParticles & Fields

Impact of the LHCb p+He4 fixed-target D0/D¯0 data on the intrinisic cc¯ component in the nucleon

We discuss the impact of the new LHCb fixed-target $p\!+\!^{4}\!He$ data for $D^0/{\bar D}^0$ production on the intrinsic $c \bar c$ component in the nucleon wave function. Within the scenario presented here neither the traditional gluon-gluon fusion or quark-antiquark annihilation mechanisms calculated in the $k_T$-factorization approach nor their counterparts from the collinear next-to-leading order collinear framework are sufficient to describe the transverse momentum and rapidity distributions of $D^0/{\bar D}^0$ mesons. First the $c{\bar c}$-pair production within the standard frameworks is considered. Here a crucial role of the $c \to D$ hadronization effects at low energies and low transverse momenta is found and discussed, which was not analyzed in previous studies. A contribution related to intrinsic $c \bar c$ component in the nucleon wave function is included in addition. Two models of the symmetric ($c(x) = \bar c(x)$) intrinsic charm (IC) component are considered. The intrinsic charm $g^* c \to g c$ (or $g^* {\bar c} \to g {\bar c}$) contribution needs to be regularized in order to obtain a suppression of the minijet $p_{T}$ spectrum present in the phenomenological minijet model, commonly used in Monte Carlo generators. We show that in our model the regularization parameter can be obtained from the fit to the LHCb fixed-target data under consideration here. We discuss uncertainties of our calculations (scale, charm quark mass, fragmentation function) as well as set limits on the IC probability. According to our model the intrinsic charm probability $P_{IC} = 1.65\%$ allows to significantly improve description of the LHCb data but the number is rather uncertain.

The high-energy limit of perturbative QCD: Theory and phenomenology

After a brief introduction of formal and phenomenological progresses in the study of the high-energy limit of perturbative QCD, we present arguments supporting the statement that the inclusive emission of Higgs bosons or heavy-flavored hadrons acts as fair stabilizer of high-energy resummed differential distributions. We come out with the message that the hybrid high-energy and collinear factorization, built in term of the next-to-leading logarithmic resummation à la BFKL and supplemented by collinear parton distributions and fragmentation functions, is a valid and powerful tool to gauge the feasibility of precision analyses of QCD in its high-energy limit.

Shannon entropy of fragmentation functions and their Kullback-Leibler divergence to parton pdfs

The flow of information in high-energy collisions has been recently investigated by various groups: this includes the entanglement entropy of the proton becoming classical information entropy of pdfs, jet splitting affecting entropy, or the entropy distribution in hadron decays. Here we examine fragmentation functions in this context, including their entropy as probability distributions, and propose it as one convenient number to characterize progress in their extraction. We also use the Kullback-Leibler divergence to examine relations between FFs and pdfs such as that of Barone, Drago and Ma.

The Functions of the Cryptography in the Olonets Codex of Incantations of 17th Сentury. 1. Systematization of Data

The article presents the first part of a study devoted to the analysis of the functions of cryptographic fragments in the Olonets Codex of Incantations of the 17th century. The paper defines a corpus of cryptographic fragments in the Olonets Codex (55 fragments in Russian in 9 records, as well as the cryptography of the word &amp;quot;amen&amp;quot; in another 18 texts). It has been established that cryptography in the Olonets Codex gravitates towards texts of verbal magic, and among them - to incantations of social and interpersonal themes and &amp;quot;forbidden&amp;quot;. The positions of the encrypted fragments in the structure of individual records (headers, instructions, incantations themselves) and within the incantations are revealed, fragments of texts with cryptograms are given, and a cryptographic vocabulary is compiled.

Cytoplasmically localized tRNA-derived fragments inhibit translation in Drosophila S2 cells.

Transfer ribonucleic acids (tRNAs) serve not only as amino acid carriers during translation but also as a template for the biogenesis of short fragments that can regulate gene expression. Despite recent progress in the function of tRNA-derived fragments (tRFs), their intracellular localization, protein partners, and role in regulating translation are not well understood. We used synthetic tRFs to investigate their localization and function in Drosophila S2 cells. Under our experimental setting, all synthetic tRFs tested were localized at distinct sites within the cytoplasm in a similar manner in Drosophila S2 cells. Cytoplasmically-localized tRFs were positioned in close proximity to GW182 and XRN1 proteins. Functionally, tRFs, which slightly suppressed proliferation in S2 cells, inhibited translation without any major shift in the polysome profile. These results suggest that 5'-tRFs are cytoplasmically-localized and regulate gene expression through inhibition of translation in Drosophila.

In Vitro Visualization of Cell-to-Cell Interactions Between Natural Killer Cells and Sensory Neurons.

Cell-to-cell interactions between the immune and nervous systems are increasingly recognized for their importance in health and disease. Assessment of cellular neuro-immune interactions can be aided by co-culture of two (or more) cells in an in vitro model system that preserves the morphology of neuronal cells. Here we describe methods to investigate the cytotoxic effector functions of natural killer cells on sensory neurons isolated from syngeneic embryonic and adult mice. We present methods for the morphological analysis of axon fragmentation (pruning) and dynamic cell function via live confocal calcium imaging. These techniques can easily be adapted to study interactions between other combinations of immune cell subsets and neuronal populations.

Charm hadronisation measurements with the ALICE experiment

Charm quarks are produced in hard scatterings at the early stages of the hadronic collisions due to the heavy mass of the quark. The production cross section of charm can be described by pQCD calculations based on the factorisation approach. This description traditionally assumes universal fragmentation functions of charm into hadrons among different collision systems. The ALICE experiment measured charmed-baryon production in pp collisions for different baryon species, observing a significant enhancement of the charm baryon-to-meson yield ratios, for pT &lt; 10–12 GeV/c, with respect to measurements performed at e+e− and ep colliders. Measurements of charmed baryon production in pp collisions also provide a fundamental reference for heavy-ion collisions, in which an enhancement of the baryon-to-meson ratio could be due to an additional hadronisation mechanism via coalescence of charm quarks with lighter quarks in a deconfined medium. This contribution discusses the latest measurements of charm production performed by the ALICE Collaboration in pp collisions at the LHC via D mesons, Λc+, Σc0,+,++, Ξc0,+, and Ωc0 baryons at midrapidity at √s = 5.02 and 13 TeV. The most recent measurements of the Λc+/D0 ratio in Pb–Pb collisions at √sNN = 5.02 are also presented, together with the first measurement of the charm fragmentation fraction into hadrons in pp and p–Pb collisions at the same energy.

Applying different angular ordering constraints and kt -factorization approaches to the single inclusive hadron production in the e+e− annihilation processes

We study the differential cross section of the single inclusive ${e}^{+}{e}^{\ensuremath{-}}$ annihilation to the hadrons via $\ensuremath{\gamma}$-production, in the different ${k}_{t}$-factorization frameworks. In order to take into account the transverse momenta of the incoming partons, for the first time, we apply the Kimber et al. (KMR) method to calculate the unintegrated parton fragmentation functions (UFFs) from the ordinary integrated one, i.e., the parton fragmentation functions (FFs), which satisfy the similar Dokshitzer-Gribov-Lipatov-Altarelli-Parisi (DGLAP) evolution equations, such as those of parton distribution functions (PDFs). Also, by utilizing the different angular ordering constraints the results corresponding to the Martin et al. (MRW) in the leading order (LO) and the next-to-leading-order (NLO) are obtained. The LO sets of DSS library for the input FFs is used. The numerical results are compared with the experimental data in the different energies which are reported by the different collaborations, such as TASSO, AMY, MARK II, CELLO, DELPHI, SLD, ALEPH and Belle with the other $\mathrm{QCD}+\mathrm{fragmentation}$ models such as pythia6.4 and 8.2 parton showers. The behaviors of the normalized differential cross sections and the multiplicity versus the ``transverse momentum'' (${p}_{\ensuremath{\perp}}$) are discussed. The final results demonstrate that the KMR and MRW UFFs give a good description of data and there is not much significant difference between the above three schemes. On the other hand, our results become closer to the data for the lower values of ${p}_{\ensuremath{\perp}}$ and the higher values of center of mass energies.

Studying QCD modeling of uncertainties in particle spectra from dark-matter annihilation into jets

Motivated by various excesses observed by the Fermi-LAT and AMS collaborations, we perform a detailed analysis of QCD uncertainties on particle spectra from dark-matter annihilation (or decay) into jets. When annihilated to SM particles, the final-state annihilation products undergo various complicated processes such as QED and QCD bremsstrahlung, hadronisation, and hadron decays. These processes contain some intrinsic uncertainties which are usually difficult to model and which are neglected in physical analyses. First, we perform several re-tunings of the fragmentation function parameters. Then, we estimate two kinds of uncertainties: (i) perturbative from QCD showers and (ii) non-perturbative from hadronisation function. The results are tabulated for a wide range of dark matter masses, mχ ∈ [5,105] GeV, and annihilation channels. They can be found on Zenodo: https://doi.org/10.5281/zenodo.3764809.

Kotzinian-Mulders effect in semi-inclusive DIS within TMD factorization * *Supported by the National Natural Science Foundation of China (12075043)

In this study, we investigate the Kotzinian-Mulders effect under semi-inclusive deep inelastic scattering (SIDIS) within the framework of transverse momentum dependent (TMD) factorization. The asymmetry is contributed by the convolution of the Kotzinian-Mulders function and the unpolarized fragmentation function . As a TMD distribution, the Kotzinian-Mulders function in the coordinate space in the perturbative region can be represented as the convolution of the C-coefficients and the corresponding collinear correlation function. The Wandzura-Wilczek approximation is used to obtain this correlation function. We perform a detailed phenomenological numerical analysis of the Kotzinian-Mulders effect in the SIDIS process within TMD factorization at the kinematics of the HERMES and COMPASS experiments. We observe that the obtained -, -, and -dependent Kotzinian-Mulders effects are basically consistent with the HERMES and COMPASS measurements. We also make predictions at EIC and EicC kinematics.

Factorized approach to radiative corrections for inelastic lepton-hadron collisions

We propose a factorized approach to QED radiative corrections for inclusive and semi-inclusive deep-inelastic scattering to systematically account for QED and QCD radiation contributions to both processes on equal footing. This is achieved by utilizing factorization to resum logarithmically enhanced QED radiation into universal lepton distribution and fragmentation (or jet) functions. Numerical simulations suggest that the QED effects induced by the rotational distortion of the hadron transverse momentum, arising from the mismatch between the experimental Breit frame and the true photon-hadron frame, can be as large as 50\% for moderate $Q$, and become increasingly important for large transverse momenta. Our framework provides a uniform treatment of radiative effects for extracting three-dimensional hadron structure from high-energy lepton-hadron scattering at current and future facilities, such as the Electron-Ion Collider.

GT(x) contribution to single spin asymmetries in SIDIS

Motivated by a novel origin of transverse single spin asymmetry (SSA) in semi-inclusive Deep Inelastic Scattering (SIDIS) uncovered by some of us, we quantitatively investigate its impact on the theoretical understanding of the mechanism responsible for SSA. This new contribution from the quark-initiated channel first appears in two-loop perturbation theory and involves the $g_T(x)$ distribution. We point out another entirely analogous piece from the gluon-initiated channel proportional to the gluon helicity distribution $\Delta G(x)$. Both contributions are solely expressed in terms of twist-two polarized parton distribution functions and twist-two fragmentation functions in the Wandzura-Wilczek approximation, such that they can be unambiguously evaluated without introducing free parameters. We make predictions for measurements of the asymmetries $A_{UT}$ at the future Electron-Ion Collider (EIC), and find that $A_{UT}$ associated with the $\sin (\phi_h-\phi_S)$, $\sin \phi_S$ and $\sin (2\phi_h-\phi_S)$ harmonics can reach up to 1-2\% even at the top EIC energy.