Semi-inclusive Electroproduction Research Articles

Semi-inclusive electroproduction of hidden-charm and double-charm hadronic molecules

The semi-inclusive electroproduction of exotic hadrons, including the $T_{cc}$, $P_{cs}$, and hidden-charm baryon-antibaryon states, is explored under the assumption that they are $S$-wave hadronic molecules of a pair of charmed hadrons. We employ the Monte Carlo event generator Pythia to produce the hadron pairs and then bind them together to form hadronic molecules. With the use of such a production mechanism, the semi-inclusive electroproduction rates are estimated at the order-of-magnitude level. Our results indicate that a larger number of $P_{cs}$ states and $\Lambda_c\bar{\Lambda}_c$ molecules can be produced at the proposed electron-ion colliders in China (EicC) and in the US (EIC). The results also suggest that the $T_{cc}$ states and other hidden-charm baryon-antibaryon states can be searched for at EIC. Besides, the potential 24-GeV upgrade of the Continuous Beam Accelerator Facility at the Thomas Jefferson National Accelerator Facility can play an important role in the search for the hidden-charm tetraquark and pentaquark states due to its high luminosity.

Beam Spin Asymmetry in Semi-Inclusive Electroproduction of Hadron Pairs.

A first measurement of the longitudinal beam spin asymmetry A_{LU} in the semi-inclusive electroproduction of pairs of charged pions is reported. A_{LU} is a higher-twist observable and offers the cleanest access to the nucleon twist-3 parton distribution function e(x). Data have been collected in the Hall-B at Jefferson Lab by impinging a 5.498-GeV electron beam on a liquid-hydrogen target, and reconstructing the scattered electron and the pion pair with the CLAS detector. One-dimensional projections of the A_{LU}^{sinϕ_{R}} moments are extracted for the kinematic variables of interest in the valence quark region. The understanding of dihadron production is essential for the interpretation of observables in single-hadron production in semi-inclusive DIS, and pioneering measurements of single-spin asymmetries in dihadron production open a new avenue in studies of QCD dynamics.

Dihadron fragmentation functions in the quark-jet model: Transversely polarized quarks

Within the most recent extension of the quark-jet hadronization framework, we explore the transverse-polarization-dependent dihadron fragmentation functions (DiFFs) $H_1^\sphericalangle$ and $H_1^\perp$ of a quark into $\pi^+\pi^-$ pairs. Monte Carlo (MC) simulations are employed to model polarized quark hadronization and calculate the corresponding number densities. These, in turn, are used to extract the Fourier cosine moments of the DiFFs $H_1^\sphericalangle$ and $H_1^\perp$. A notable finding is that there are previously unnoticed apparent discrepancies between the definitions of the so-called interference DiFF (IFF) $H_1^\sphericalangle$, entering the cross sections for two-hadron semi-inclusive electroproduction, and those involved in the production of two pairs of hadrons from back-to-back jets in electron-positron annihilation. This manuscript completes the studies of all four leading twist DiFFs for unpolarized hadron pairs within the quark-jet framework, following our previous work on the helicity-dependent DiFF $G_1^\perp$.

Semi-inclusive charged-pion electroproduction off protons and deuterons: Cross sections, ratios, and access to the quark-parton model at low energies

A large set of cross sections for semi-inclusive electroproduction of charged pions (π±) from both proton and deuteron targets was measured. The data are in the deep-inelastic scattering region with invariant mass squared W2>4 GeV2 (up to ≈7 GeV2) and range in four-momentum transfer squared 2<Q2<4 (GeV/c)2, and cover a range in the Bjorken scaling variable 0.2<x<0.6. The fractional energy of the pions spans a range 0.3<z<1, with small transverse momenta with respect to the virtual-photon direction, Pt2<0.2 (GeV/c)2. The invariant mass that goes undetected, Mx or W′, is in the nucleon resonance region, W′<2 GeV. The new data conclusively show the onset of quark-hadron duality in this process, and the relation of this phenomenon to the high-energy factorization ansatz of electron-quark scattering and subsequent quark→pion production mechanisms. The x, z, and Pt2 dependences of several ratios (the ratios of favored-unfavored fragmentation functions, charged pion ratios, deuteron-hydrogen and aluminum-deuteron ratios for π+ and π−) have been studied. The ratios are found to be in good agreement with expectations based upon a high-energy quark-parton model description. We find the azimuthal dependences to be small, as compared to exclusive pion electroproduction, and consistent with theoretical expectations based on tree-level factorization in terms of transverse-momentum-dependent parton distribution and fragmentation functions. In the context of a simple model, the initial transverse momenta of d quarks are found to be slightly smaller than for u quarks, while the transverse momentum width of the favored fragmentation function is about the same as for the unfavored one, and both fragmentation widths are larger than the quark widths.19 MoreReceived 7 March 2011DOI:https://doi.org/10.1103/PhysRevC.85.015202©2012 American Physical Society

Transverse spin structure of the nucleon through target single-spin asymmetry in semi-inclusive deep-inelastic (e, e’ $ \pi^{\pm}_{}$ ) reaction at Jefferson Lab

Jefferson Lab (JLab) 12 GeV energy upgrade provides a golden opportunity to perform precision studies of the transverse spin and transverse-momentum-dependent structure in the valence quark region for both the proton and the neutron. In this paper, we focus our discussion on a recently approved experiment on the neutron as an example of the precision studies planned at JLab. The new experiment will perform precision measurements of target Single Spin Asymmetries (SSA) from semi-inclusive electro-production of charged pions from a 40-cm long transversely polarized $^3$He target in Deep-Inelastic-Scattering kinematics using 11 and 8.8 GeV electron beams. This new coincidence experiment in Hall A will employ a newly proposed solenoid spectrometer (SoLID). The large acceptance spectrometer and the high polarized luminosity will provide precise 4-D ($x$, $z$, $P_T$ and $Q^2$) data on the Collins, Sivers, and pretzelocity asymmetries for the neutron through the azimuthal angular dependence. The full 2$\pi$ azimuthal angular coverage in the lab is essential in controlling the systematic uncertainties. The results from this experiment, when combined with the proton Collins asymmetry measurement and the Collins fragmentation function determined from the e$^+$e$^-$ collision data, will allow for a quark flavor separation in order to achieve a determination of the tensor charge of the d quark to a 10% accuracy. The extracted Sivers and pretzelocity asymmetries will provide important information to understand the correlations between the quark orbital angular momentum and the nucleon spin and between the quark spin and nucleon spin.

Nucleon transversity study using a polarized 3He target in Hall A at JLab

A first measurement of Single target Spin Asymmetry (SSA) from semi-inclusive electro-production of charged pions from a transversely polarized 3He target in Deep-Inelastic-Scattering kinematics was completed in Hall A at Jefferson Lab in early 2009. Such SSA will allow for an extraction of the much desired information on the Collins and Sivers asymmetry from the “neutron” in order to probe the quark transversity distributions. Future 11 GeV measurements at Jefferson Lab in Hall A using a solenoid magnetic detector system is being planned.

Kinematic correction to the cross-section of semi-inclusive π-meson electroproduction in the low-energy range

The Q2 -dependence of the cross-section of semi-inclusive π-meson electroproduction has been studied in the low-energy range covering the nucleonic resonances. It has been found that the Q2 -dependence of these data differs from the behavior of the factorized cross-section for high energies. The analysis of ratios of measured to model-calculated cross-sections renders a simple polynomial function for introducing the Q2 -correction into the cross-section. This additional correction provides much better agreement between the experimental and calculated data.

Transverse momentum dependence of semi-inclusive pion production

Cross sections for semi-inclusive electroproduction of charged pions (π±) from both proton and deuteron targets were measured for 0.2<x<0.5, 2<Q2<4 GeV2, 0.3<z<1, and Pt2<0.2 GeV2. For Pt<0.1 GeV, we find the azimuthal dependence to be small, as expected theoretically. For both π+ and π−, the Pt dependence from the deuteron is found to be slightly weaker than from the proton. In the context of a simple model, this implies that the initial transverse momenta width of d quarks is larger than for u quarks and, contrary to expectations, the transverse momentum width of the favored fragmentation function is larger than the unfavored one.

Latest HERMES results on transverse spin effects in hadron structure and formation⋆

Transverse target single-spin asymmetries in semi-inclusive deep inelastic scattering allow to study the so-called Collins and Sivers mechanisms. The first one connects the poorly known fundamental transversity distribution function, describing the transverse spin-polarization of quarks in a transversely polarized proton, to the Collins fragmentation function, describing spin-orbit correlations in the hadron formation process. The second one is sensitive to the Sivers function, which correlates the intrinsic transverse momentum of quarks with the proton’s spin orientation and is related to the orbital angular momentum of quarks. Preliminary results on azimuthal single target-spin asymmetries in semi-inclusive electro-production of pions and kaons at the HERMES experiment are presented. The full data set collected with a transversely polarized hydrogen target was analyzed providing the HERMES most precise results on the Collins and Sivers azimuthal moments.

Neutron transversity measurement at Jefferson Lab with a polarized 3He target

A first measurement of single target spin asymmetry (SSA) from semi-inclusive electroproduction of charged pions from a transversely polarized 3He target in deep-inelastic-scattering kinematics will take data in Hall A at Jefferson Lab in 2008. Such SSA will allow for an extraction of the much desired information on the Collins and Sivers asymmetry from the “neutron” in order to probe the quark transversity distributions. The experiment will be a coincidence measurement with the BigBite spectrometer detecting the scattered electrons and the left-arm HRS spectrometer detecting the charged pions. The prospect of future 11 GeV measurements at Jefferson Lab in Hall A using a solenoid magnetic detector system is also discussed in this talk.

From Inclusive Scattering to Exclusive Reactions – recent results from HERMES

Single-spin asymmetries for semi-inclusive electroproduction of charged pions in deep-inelastic scattering of positrons are measured for the first time with transverse target polarization. They provide access to the transversity distribution via the Collins mechanism and the previously unmeasured Sivers function. The comparison of this data to similar data taken with longitudinally polarized protons provides insight into subleading-twist contributions. A second class of reaction promising new insights into the structure of the nucleon, hard exclusive electroproduction of real photons (named Deeply Virtual Compton Scattering) or mesons closely linked to the novel formalism of Generalized Parton Distributions is studied. The data were accumulated by the HERMES experiment at DESY scattering the HERA 27.6 GeV electron or positron beam off longitudinally or transversely polarized hydrogen targets.

Publisher’s Note: Exclusive channels in semi-inclusive production of pions and kaons [Phys. Rev. D72, 034034 (2005)

We investigate the role of exclusive channels in semi-inclusive electroproduction of pions and kaons. Using the QCD factorization theorem for hard exclusive processes we evaluate the cross sections for exclusive pseudoscalar and vector meson production in terms of generalized parton distributions and meson distribution amplitudes. We investigate the uncertainties arising from the modeling of the nonperturbative input quantities. Combining these results with available experimental data, we compare the cross sections for exclusive channels to that obtained from quark fragmentation in semi-inclusive deep inelastic scattering. We find that rho^0 production is the only exclusive channel with significant contributions to semi-inclusive pion production at large z and moderate Q^2. The corresponding contribution to kaon production from the decay of exclusively produced phi and K^* is rather small.

Exclusive channels in semi-inclusive production of pions and kaons

We investigate the role of exclusive channels in semi-inclusive electroproduction of pions and kaons. Using the QCD factorization theorem for hard exclusive processes we evaluate the cross sections for exclusive pseudoscalar and vector meson production in terms of generalized parton distributions and meson distribution amplitudes. We investigate the uncertainties arising from the modeling of the nonperturbative input quantities. Combining these results with available experimental data, we compare the cross sections for exclusive channels to that obtained from quark fragmentation in semi-inclusive deep inelastic scattering. We find that ${\ensuremath{\rho}}^{0}$ production is the only exclusive channel with significant contributions to semi-inclusive pion production at large $z$ and moderate ${Q}^{2}$. The corresponding contribution to kaon production from the decay of exclusively produced $\ensuremath{\phi}$ and ${K}^{*}$ is rather small.

Measurement of Transverse Target-spin Asymmetries at Hermes

Azimuthal asymmetries are observed in the cross section of semi-inclusive charged pion electroproduction from a transversely polarized hydrogen target at Hermes. Their si- multaneous dependence on the azimuthal angles of both the pion and the target spin axis allows the extraction of two Fourier components that are interpreted in terms of Collins and Sivers effects. For π + -production both components are found to be positive, while for π − -production the Sivers asymmetry vanishes and the Collins asymmetry is found to be negative and surprisingly large in magnitude.

Single-Spin Asymmetries in Semi-Inclusive Deep-Inelastic Scattering on a Transversely Polarized Hydrogen Target

Single-spin asymmetries for semi-inclusive electroproduction of charged pions in deep-inelastic scattering of positrons are measured for the first time with transverse target polarization. The asymmetry depends on the azimuthal angles of both the pion (phi) and the target spin axis (phi(S)) about the virtual-photon direction and relative to the lepton scattering plane. The extracted Fourier component sin((phi+phi(S))(pi)(UT) is a signal of the previously unmeasured quark transversity distribution, in conjunction with the Collins fragmentation function, also unknown. The component sin((phi-phi(S)(pi)(UT) arises from a correlation between the transverse polarization of the target nucleon and the intrinsic transverse momentum of quarks, as represented by the previously unmeasured Sivers distribution function. Evidence for both signals is observed, but the Sivers asymmetry may be affected by exclusive vector meson production.

Chiral-odd fragmentation functions in single pion inclusive electroproduction

We consider a sub-leading twist chiral-odd pion fragmentation function and explore its contribution in single pion semi-inclusive electroproduction. We evaluate the single beam-spin azimuthal asymmetry ALU and the double spin asymmetry ALT in polarized electroproduction of pions from an unpolarized and transversely polarized nucleon, respectively. The beam asymmetry is expressed as the product of chiral-odd, and T-odd and even distribution and fragmentation functions. The double spin asymmetry contains information on the quark's transversity distribution. In a quark–diquark–spectator framework we estimate these asymmetries at 6 GeV, 12 GeV, and 27.5 GeV energies.

Ratio of [formula omitted] in semi-inclusive electroproduction

It is shown that the Λ/Λ cross section ratio in semi-inclusive electroproduction of Λ and Λ hyperons in deep inelastic scattering of charged lepton on a nucleon target, can provide useful information on the quark to Λ fragmentation functions. This ratio is calculated explicitly in a quark–diquark model, a pQCD based analysis, and an SU(3) symmetry model, with three different options for the contribution from the unfavored fragmentation functions. The x-dependence of this ratio is sensitive to the ratio of unfavored fragmentation functions over favored fragmentation functions, DūΛ(z)/DuΛ(z), whereas the z-dependence is sensitive to the flavor structure of the fragmentation functions, i.e., the ratio DuΛ(z)/DsΛ(z). Future measurements by the HERMES Collaboration at DESY can discriminate between various cases.

Measurement of single-spin azimuthal asymmetries in semi-inclusive electroproduction of pions and kaons on a longitudinally polarised deuterium target

Single-spin asymmetries have been measured for semi-inclusive electroproduction of π+, π−, π0 and K+ mesons in deep-inelastic scattering off a longitudinally polarised deuterium target. The asymmetries appear in the distribution of the hadrons in the azimuthal angle φ around the virtual photon direction, relative to the lepton scattering plane. The corresponding analysing powers in the sinφ moment of the cross section are 0.012±0.002(stat.)±0.002(syst.) for π+, 0.006±0.003(stat.)±0.002(syst.) for π−, 0.021±0.005(stat.)±0.003(syst.) for π0 and 0.013±0.006(stat.)±0.003(syst.) for K+. The sin2φ moments are compatible with zero for all particles.

Drell-Yan representation for vector-meson spin-density matrix elements in semi-inclusive electroproduction

Polarized vector-meson production in semi-inclusive electron-nucleon scattering with longitudinally polarized electron beam has been investigated. A Drell-Yan-like representation for the spin-density matrix elements of a vector meson that takes into account the leading radiative corrections is derived. The calculations have been performed for two widely used reference systems, the Gottfried-Jackson and the helicity systems.

Double-spin cosφ asymmetry in semi-inclusive electroproduction

We consider the double-spin cos(phi) asymmetry for pion electroproduction in semi-inclusive deep inelastic scattering of longitudinally polarized leptons off longitudinally polarized protons. We estimate the size of the asymmetry in the approximation where all twist-3 interaction-dependent distribution and fragmentation functions are set to zero. In that approximation at HERMES kinematics a sizable negative cos(phi) double-spin asymmetry for pi+ electroproduction is predicted.