Spin Asymmetries Research Articles

Next-to-Next-to-Leading Order Global Analysis of Polarized Parton Distribution Functions.

We present a next-to-next-to-leading order (NNLO) global QCD analysis of the proton's helicity parton distribution functions, the first of its kind. To obtain the distributions, we use data for longitudinal spin asymmetries in inclusive and semi-inclusive lepton-nucleon scattering as well as in weak-boson and hadron or jet production in proton-proton scattering. We analyze the data using QCD perturbation theory at NNLO accuracy, employing approximations provided by the threshold resummation formalism in cases where full NNLO results for partonic hard-scattering functions are not readily available. Our numerical results suggest a remarkable perturbative stability of the extracted helicity parton distribution functions.

Spin effect induced momentum spiral and asymmetry degree in pair production

Spin effect on the pair production under circularly polarized fields is investigated. Significantly different from what momentum spirals caused by two counterrotating fields with a time delay, we find for the first time that the spirals can also be induced due to the particle spin effect even if in a single field. We further examine the bichromatic combinational fields. The inhomogeneous spiral structures can be observed in the momentum spectrum; in particular, the spiral not only does exist in two cases of spin, but also is about 2 orders of magnitude amplified compared with that in the single field. Meanwhile, the spin asymmetry degree on the momentum distributions is investigated, and it was found that the effect of spin flip exists with an increased time delay between two fields. The spin asymmetry degree on the number density can reach to 98% in certain conditions. These results indicate that the signatures of created particles, especially the spiral structures, are strongly associated with information pertaining to the laser field as well as the created particle spin, which can deepen the understanding of vacuum pair production. Published by the American Physical Society 2024

Spin asymmetry of O 2p –related states in SrTiO3(001)

Atomically clean SrTiO3(001) is characterized by low energy electron diffraction, core level and valence band photoelectron spectroscopy, the latter also with spin resolution. Samples prepared by a sputtering-annealing procedure exhibited in-gap states in the valence band spectra, Ti3+ components in Ti 2p core level spectra and a noticeable spin asymmetry in the 3–9 eV binding energy range, which corresponds to valence states of mainly O 2p character. Upon annealing in oxygen, the spin asymmetry vanishes, accompanied by the intensity decrease of the contribution of titanium low ionization states and of in-gap states, indicating that these three phenomena are mutually connected. The observed spin asymmetry may be generated by indirect exchange mediated by the in-gap states between O 2p orbitals, or by the partial Ti 3d character of these states, which acquire non-zero spin in case of incomplete oxygen coordination.

Spin asymmetries for C -even quarkonium production as a probe of gluon distributions

Within the framework of transverse momentum dependent factorization in combination with nonrelativistic quantum chromodynamics (QCD), we study charmonium and bottomonium production in hadronic collisions. We focus on quarkonium states with even charge conjugation, for which the color-singlet production mechanism is expected to be also dominant in the small transverse momentum region, qT2≪4Mc,b2. It is shown that the distributions of linearly polarized gluons inside unpolarized, longitudinally, and transversely polarized protons contribute to the cross sections for scalar and pseudoscalar quarkonia in a very distinctive, parity-dependent way, whereas their effects on higher angular momentum states are strongly suppressed. We derive analytical expressions for single and double spin asymmetries, which would allow for the direct extraction of the gluon transverse momentum dependent distributions, mirroring the phenomenological studies of the Drell-Yan processes aimed at the extraction of their quark counterparts. By adopting Gaussian models for the gluon transverse momentum dependent distributions, which fulfill without saturating everywhere their positivity bounds, we provide numerical predictions for the transverse single-spin asymmetries. These observables could be measured at LHCSpin, the fixed target experiment planned at the LHC. Published by the American Physical Society 2024

The connection between nucleon energy correlators and fracture functions

We establish a sum rule that connects fracture functions to nucleon energy-energy correlators (NEECs) in a one-to-one correspondence. Using this sum rule, we study the energy pattern in the target fragmentation region of deep inelastic scatterings. Through investigations up to twist-3, we express all eighteen energy-pattern structure functions in terms of associated NEECs, elucidating various azimuthal and spin asymmetries critical for nucleon tomography. Additionally, we investigate the perturbative matching of the twist-2 quark NEECs. We demonstrate that the Sivers-type and worm-gear-type quark NEECs match onto twist-3 multi-parton distributions. Our work provides a framework for examining energy-weighted observables through hadron production processes in the target fragmentation region, offering new insights into nucleon tomography.

Spin asymmetry and dipole moments in τ-pair production with ultraperipheral heavy ion collisions

Spin asymmetry and dipole moments in τ-pair production with ultraperipheral heavy ion collisions

Single spin asymmetry AULsin(2ϕh) in dihadron production in SIDIS

The paper calculates the helicity-dependent dihadron fragmentation function by extending the dihadron spectator model and examine the single longitudinal spin asymmetry AULsin(2ϕh) from dihadron in semi-inclusive inelastic scattering. This function elucidates the relationship between the longitudinal polarization of the fragmented quark and the transverse momentum of the resulting hadron pairs. A study by the COMPASS collaboration detected a minimal signal in their experimental search for this azimuthal asymmetry in semi-inclusive inelastic scattering. Here, we use the spectator model to calculate the unknown T-odd dihadron fragmentation function H1⊥. Adopting collinear factorization to describe the data, avoiding the transverse momentum dependent factorization and the associated resummation effects, helping us understand the asymmetry and explaining why the signal is so weak. We involve the approach of transverse momentum dependence in the model calculations, in order to formulate the differential cross sections and the spin asymmetries in terms of the collinear parton distributions and the collinear dihadron fragmentation functions. A transverse momentum factor analysis method was used, in which the transverse momentum of the final hadron pairs was not integrated. The asymmetry of sin(2ϕh) in COMPASS kinematics was calculated and compared with experimental data. In addition, predictions for the same asymmetry are also presented for HERMES and the Electron Ion Collider. Published by the American Physical Society 2024

Accessing the gluon GTMD F1,4 in exclusive π0 production in ep collisions

We demonstrate that the longitudinal single target-spin asymmetry in exclusive π0 production in ep collisions can give access to the imaginary part of the gluon generalized transverse momentum distribution (GTMD) F1,4. Such a longitudinal spin asymmetry that results from the Coulomb-nuclear interference effect, leads to a characteristic azimuthal angular correlation of sin2ϕ, where ϕ is the azimuthal angle between the scattered lepton transverse momentum and the recoil proton’s transverse momentum. We also present a numerical estimate of the asymmetry for the kinematics accessible at EIC and EicC. Published by the American Physical Society 2024

Measurements of the Z0/γ⁎ cross section and transverse single spin asymmetry in 510 GeV p + p collisions

The differential cross section for Z0 production, measured as a function of the boson's transverse momentum (pT), provides important constraints on the evolution of the transverse momentum dependent parton distribution functions (TMDs). The transverse single spin asymmetry (TSSA) of the Z0 is sensitive to one of the polarized TMDs, the Sivers function, which is predicted to have the opposite sign in p+p→W/Z+X from that which enters in semi-inclusive deep inelastic scattering. In this Letter, the STAR Collaboration reports the first measurement of the Z0/γ⁎ differential cross section as a function of its pT in p+p collisions at a center-of-mass energy of 510 GeV, together with the Z0/γ⁎ total cross section. We also report the measurement of Z0/γ⁎ TSSA in transversely polarized p+p collisions at 510 GeV.

Probing the four-fermion operators via the transverse double spin asymmetry at the Electron-Ion Collider

The chirality-flipping operators of light fermions are currently poorly constrained by experimental analyses due to the lack of interference with standard model (SM) amplitudes in traditional observables. In this work, we propose to investigate the semileptonic scalar and tensor four-fermion operators of electron and quarks through the transverse double spin asymmetry (DSA) at Electron-Ion Collider, where both the electron and proton beams could be highly transversely polarized. Due to the chirality-flipping nature of these operators, we demonstrate that their interference with the SM results in an unsuppressed contribution to the DSA, and could lead to nontrivial azimuthal cos2ϕ and sin2ϕ distributions that are linearly dependent on their Wilson coefficients. This new method has the potential to significantly improve the current constraints on these scalar and tensor four-fermion operators without relying on theoretical assumptions about other types of new physics effects, particularly for the tensor-type operator of the u quark. Additionally, our findings indicate that both the real and imaginary parts of these operators can be simultaneously constrained and offer a new opportunity for probing potential CP-violation effects. However, it is important to note that these results would be sensitive to the quark transversity distributions, which are currently poorly constrained by the experimental data, but could be significantly improved at the upcoming Electron-Ion Collider. Therefore, our work opens up a new avenue to utilize this new spin asymmetry for exploring the new physics effects from the scalar/tensor four-fermion operators. Published by the American Physical Society 2024

Simultaneous reweighting of Transverse Momentum Dependent distributions

The Bayesian reweighting procedure is extended to the case of multiple independent extractions of transverse momentum dependent parton distributions (TMDs). By exploiting the data on transverse single spin asymmetries, AN, for inclusive pion production in polarized proton-proton collisions measured at RHIC, we perform a simultaneous reweighting of the quark Sivers, transversity and Collins TMD functions extracted from semi-inclusive deep inelastic scattering (SIDIS) and e+e− annihilation into hadron pairs. The impact of the implementation of the Soffer bound, as well as the differences between older and newer AN data, are investigated. The agreement with AN data at large-xF values, a kinematical region complementary to those explored in SIDIS measurements, is enhanced, improving the knowledge of the polarized quark TMDs in the large-x region.

Perturbative QCD contribution to transverse single spin asymmetries in the Drell-Yan process and SIDIS

Perturbative QCD contribution to transverse single spin asymmetries in the Drell-Yan process and SIDIS

Relaxation time for the alignment between quark spin and angular velocity in a rotating QCD medium

We compute the relaxation times for massive quarks and antiquarks to align their spins with the angular velocity in a rigidly rotating medium at finite temperature and baryon density. The rotation effects are implemented using a fermion propagator immersed in a cylindrical rotating environment. The relaxation time is computed as the inverse of the interaction rate to produce an asymmetry between the quark (antiquark) spin components along and opposite to the angular velocity. For conditions resembling heavy-ion collisions, the relaxation times for quarks are smaller than for antiquarks. For semicentral collisions, the relaxation time for quarks is within the possible lifetime of the QGP for all collision energies. However, for antiquarks, this happens only for collision energies sNN≳50 GeV. The results are quantified in terms of the intrinsic quark and antiquark polarizations, namely, the probability to build the spin asymmetry as a function of time. Our results show that these intrinsic polarizations tend to 1 with time at different rates given by the relaxation times with quarks reaching a sizable asymmetry at a faster pace. These are key results to further elucidate the mechanisms of hyperon polarization in relativistic heavy-ion collisions. Published by the American Physical Society 2024

Nonperturbative theory for the QED corrections to elastic electron-nucleus scattering

A potential for the vertex and self-energy correction is derived from the first-order Born theory. The inclusion of this potential in the Dirac equation, together with the Uehling potential for vacuum polarization, allows for a nonperturbative treatment of these quantum electrodynamical effects within the phase-shift analysis. Investigating the 12C and 208Pb targets, a considerable deviation of the respective cross section change from the Born results is found for the heavier target. It is shown that at low impact energies the dispersion effects play no role. Estimates for the correction to the beam-normal spin asymmetry and its accuracy at 5 MeV (for 208Pb and 197Au) are also provided.

Beam spin asymmetry measurements of deeply virtual π0 production with CLAS12

The new experimental measurements of beam spin asymmetry were performed for the deeply virtual exclusive π0 production in a wide kinematic region with the photon virtualities Q2 up to 6.6 GeV2 and the Bjorken scaling variable xB in the valence regime. The data were collected by the CEBAF Large Acceptance Spectrometer (CLAS12) at Jefferson Lab with longitudinally polarized 10.6 GeV electrons scattered on an unpolarized liquid-hydrogen target. Sizable asymmetry values indicate a substantial contribution from transverse virtual photon amplitudes to the polarized structure functions. The interpretation of these measurements in terms of the Generalized Parton Distributions (GPDs) demonstrates their sensitivity to the chiral-odd GPD E¯T, which contains information on quark transverse spin densities in unpolarized and polarized nucleons and provides access to the nucleon's transverse anomalous magnetic moment. Additionally, the data were compared to a theoretical model based on a Regge formalism that was extended to the high photon virtualities.

Gluon TMDs from J/ψ production in longitudinally polarized deeply inelastic scattering

We investigate the feasibility of exploring the gluon transverse-momentum-dependent distribution functions (TMDs) inside a longitudinally polarized nucleon. We utilize quarkonium production via the color-octet mechanism combined with TMD formalism in semi-inclusive deeply inelastic scattering (SIDIS) at low transverse momentum as a tool to access polarized gluon TMDs. The corresponding cross-section of the process is expressed in terms of gluon TMDs and non-relativistic QCD matrix elements. We provide the expressions for the sin⁡2ϕ azimuthal asymmetries of J/ψ production in SIDIS with an unpolarized beam colliding on longitudinally polarized nucleon. The asymmetry receives a contribution from the time-reversal-odd gluon TMD h1L⊥g(x,pT2). The maximum possible asymmetry deduced from the positivity bound is sizable and could be measured. We also estimate the double longitudinal spin asymmetry ALL of J/ψ production using a spectator model result for g1Lg(x,pT2).

(Invited) Direct Bonding and Its Interface for High-Density Integration of Superconducting Qubits

Superconducting qubits are one of the intensive approaches to fabricate quantum computing (QC). Qubits can be manufactured by the current Si-based semiconductor manufacturing processes. However, circuits should be superconducting material such as Nb (Tc=9.29 K), Al (Tc=1.18 K), Pb (Tc=7.2 K), In (Tc=3.4 K) , etc. In current technology, qubits are arranged in planar geometry in a chip, and each qubit should wire to control and read signal lines in the same plane. When a large number of qubits are integrated, these wires would be too constrained, and several problems would be actualized, such as wiring for qubits located at the chip center, crosstalk among wiring, and so on. The signal integrity for the QC devices is much better to have qubits at short distances from the control circuitry. Therefore, 3D wiring is required for a large-scale qubit integration. 3D integration of qubits with interposer chips by flip-chip bonding is the proof-of-concept of the large-scale qubit integration. The 3D integration approaches for qubit- based devices are the same as conventional electronic devices, including the through silicon via (TSV) process for interposers and micro bump flip-chip bonding. However, they use superconducting metals instead of copper and other non-superconducting materials. Most flip-chip microbump bonding processes require thermal compression at over 170 °C. Superconducting elements are easily degraded by heat. Consequently, we apply surface activated bonding (SAB) to a superconducting metal as a low-temperature bonding process for superconducting circuits.The test element group (TEG) for the current-voltage (I-V) measurement of the bonded interface was bonded by SAB method, and at the Nb SAB interface layer is a 2- to 3-nm-thick amorphous layer and the layer consist of Si-rich interfacial layer compared to the Nb bulk area. The bonding specimens were activated on jigs made of Si during the bonding process; then the Si sputtered by FAB was redeposited on the bonding surfaces. Furthermore, the bonded specimen was wired using Al wire to a chip carrier with a stage installed into a 0.3-K cryostat. As a result, the Tc of this path is 9.3 K, which is very similar to that of Nb bulk (9.2 K). However, a small step of the Tc at 9.1-9.4 K was also observed. (Fig.1) [1]In this study, we discuss the superconducting interface of direct bonded Nb-Nb by Tc, and also the interfacial structure measured by polarized neutron reflectometry (PNR). The results show clear spin asymmetry in the superconducting state, as splitting is observed in the fringes of the parallel neutron (neutron spins parallel to the external magnetic field 0.1 T) reflection R+ and the antiparallel (neutron spins antiparallel to it) reflection R−, where the latter has become larger. This well-known effect is related to the flux penetration in the superconducting state. Therefore, unique information about the superconducting state of the buried thin film can be measured by using the polarized neutron beam. For this project the major advantage of PNR will be to characterize the superconducting state at the deeply buried Nb interfaces, sandwiched between the two substrate wafers, which would be infeasible using alternate techniques.[1] M. Fujino, et. al., J. Appl. Phys., 133, 015301, 2023 Figure 1

Ferromagnetic insulator induced inverse proximity effect in superconducting DoS

A ferromagnetic insulator proximate with a superconductor induces some spin asymmetry in superconducting correlations. Density of states (DoS) changes as a result of the induction of magnetization in superconductor (S) under the influence of the inverse proximity effect with the ferromagnetic insulator (FI). The study solves the Usadel equations numerically and calculates characteristic features of the density of states at the interface boundary and at the boundary with vacuum, caused by FI. The electron density of states was analyzed, showing significant singlet-to-triplet conversion, even for small values of the interface parameter (φ). In DoS, the zero bias peak tends to play a larger role than the spin-splitting of the BCS peaks. The features of the density of state obtained in this work can be measured experimentally.

Single Transverse Spin Asymmetry as a New Probe of Standard-Model-Effective-Field-Theory Dipole Operators.

Electroweak dipole operators in the standard-model-effective-field theory (SMEFT) are important indirect probes of quantum effects of new physics beyond the standard model (SM), yet they remain poorly constrained by current experimental analyses for lack of interference with the SM amplitudes in constructing cross section observables. In this Letter, we point out that dipole operators flip fermion helicities and so are ideally studied through single transverse spin asymmetries. We illustrate this at a future electron-positron collider with transversely polarized beams, where such an effect exhibits as azimuthal cosϕ and sinϕ distributions which originate from the interference of the electron dipole operators with the SM and are linearly dependent on their Wilson coefficients. This new method can improve the current constraints on the electron dipole couplings by 1-2 orders of magnitude, without depending on other new physics operators, and can also simultaneously constrain both their real and imaginary parts, offering a new opportunity for probing potential CP-violating effects.

Spin- and angle-resolved photoemission spectroscopy study of heptahelicene layers on Cu(111) surfaces.

It has been demonstrated previously that electrons interact differently with chiral molecules depending on their polarization. For enantiomeric pure monolayers of heptahelicene, opposite asymmetries in spin polarization were reported and attributed to the so-called chirality-induced spin selectivity effect. However, these promising proof-of-concept photoemission experiments lack the angular and energy resolution that could provide the necessary insights into the mechanism of this phenomenon. In order to fill in the missing gaps, we provide a detailed spin- and angle-resolved photoemission spectroscopy study of heptahelicene layers on a Cu(111) substrate. Throughout the large accessible energy and angle range, no chirality induced spin asymmetry in photoemission could be observed. Possible reasons for the absence of signatures of the spin-dependent electron transmission through the chiral molecular layer are briefly discussed.