Momentum Dependence Research Articles

First study of the initial gluonic fluctuations using UPCs with ALICE

Incoherent and dissociative J/ψ photoproduction is sensitive to fluctuations of the gluonic structure of the target. Thus, the measurement of Jψ photoproduction of the colliding hadron sheds light on the initial state of QCD and provides important constraints on the initial conditions used in hydrodynamical models of heavy-ion collisions. The first measurement of the transverse momentum dependence of both coherent and incoherent Jψ photoproduction in ultraperipheral Pb–Pb collisions at midrapidity is presented. These new results provide, a clear indication of subnucleonic fluctuations of the lead target. We also present the new measurement of dissociative Jψ photoproduction cross section as a function of energy, in p–Pb collisions at forward rapidity. Dissociative results do not show any indication of saturation and agree with previous data.

A novel solution to the hyperon-puzzle in neutron stars

Hyperons are baryons with strangeness content and heavier than nucleons. Due to the high densities in the neutron star interior, they are energetically allowed to appear. The strangeness baryons can thus co-exist together with nucleons and leptons in β-equilibrium. However, as a generic feature, the neutron star equation of state softens largely when hyperons are present in neutron star matter. This is the so-called hyperon-puzzle: many state-of-the-art nuclear models cannot describe the precise observations of neutron star masses, when hyperons are included in their descriptions. We propose a new solution to this persisting hyperon-puzzle issue. It is based on the explicit momentum dependence of the hyperon potentials. They modify the strangeness thresholds and forbid or strongly suppress their population in neutron stars.

Elliptic flow in Pb+Pb Collision at (s_NN )=5.02 TeV

Elliptic flow signal, v_2, is widely studied in heavy ion collisions. Researches have been done to obtain the pseudorapidity dependence of v_2, while the measurement of transverse momentum dependence is relatively few. This paper presents the transverse momentum dependence of v_2 in Pb+Pb collision at(s_NN )=5.02 TeV. The measurement is performed in the region with pseudorapidity ||<2.8 and transverse momentum 0.2 < p_T<6.0GeV. In this work, we use sub-event method to measure elliptic flow for the collisions in different ranges of transverse momentum. The result shows a polynomial relation between elliptic flow signal and transverse momentum. In Section 4, the limitation of our measurement is also discussed.

Evolution of midrapidity average transverse momentum of pions, kaons, protons and antiprotons in Au+Au collisions in (snn)1∕2= 7–39-GeV energy range from the beam energy scan program

The [Formula: see text] dependencies of the experimental average transverse momentum, [Formula: see text], of the charged pions, charged kaons, protons and antiprotons produced at midrapidity ([Formula: see text]) in [Formula: see text] collisions from the Beam Energy Scan (BES) program at the RHIC (Relativistic Heavy Ion Collider), measured by STAR Collaboration in the [Formula: see text]–39-GeV energy range, have been described quite well with the power-law model function. We have obtained [Formula: see text] inequality at all BES energies, indicating the clear mass ordering (dependence) of the power parameter [Formula: see text]. On the whole, the exponent parameter [Formula: see text] for the charged kaons as well as (anti)protons decreases noticeably with increasing [Formula: see text] collision energy from [Formula: see text][Formula: see text]GeV to [Formula: see text][Formula: see text]GeV. Drastic change observed in the energy ([Formula: see text]) dependence of the parameter [Formula: see text] for the charged kaons at [Formula: see text][Formula: see text]GeV could possibly indicate a significant change in the mechanism(s) of the charged kaon production in [Formula: see text] collisions at around [Formula: see text][Formula: see text]GeV. Significant change in the [Formula: see text] dependence of the parameter [Formula: see text] for the charged pions observed at around [Formula: see text][Formula: see text]GeV is consistent with a possible change in the mechanism(s) of the particle production in [Formula: see text] collisions at around [Formula: see text][Formula: see text]GeV, reported earlier by STAR Collaboration. Significant gaps between [Formula: see text] (protons) and [Formula: see text] (antiprotons) as well as between ([Formula: see text]) and [Formula: see text] have been seen in the region [Formula: see text]–20[Formula: see text]GeV. These gaps diminish and practically disappear with [Formula: see text] and [Formula: see text] (protons) [Formula: see text] (antiprotons) in the region [Formula: see text][Formula: see text]GeV. Altogether, the findings, regarding collision energy dependencies of the parameter [Formula: see text] for the studied particle species, could indicate the probable phase transition of a nuclear matter to the mixed phase of QGP and hadrons taking place in [Formula: see text] collisions at around [Formula: see text][Formula: see text]GeV. The differences found between parameter [Formula: see text] versus [Formula: see text] dependencies of the particles and antiparticles have been connected with the ratios of antiparticle and particle yields and differences in the mechanisms of production of particles and antiparticles. It is deduced that the exponent parameter [Formula: see text] should be sensitive to the degree of particle (system) thermalization and particle production mechanisms, and its drastic change could be related to the change in the mechanisms of particle production or/and phase transitions in the nuclear/hadronic matter.

Double-copying self-dual Yang-Mills theory to self-dual gravity on twistor space

We construct a simple Lorentz-invariant action for maximally supersymmetric self-dual Yang-Mills theory that manifests colour-kinematics duality. We also show that this action double-copies to a known action for maximally supersymmetric self-dual gravity. Both actions live on twistor space and illustrate nicely the homotopy algebraic perspective on the double copy presented in [1]. This example is particularly interesting as the involved Hopf algebra controlling the momentum dependence is non-commutative and suggests a generalisation to gauged maximally supersymmetric self-dual gravity.

Machine Learning Approach to Analyze the Heavy Quark Diffusion Coefficient in Relativistic Heavy Ion Collisions.

The diffusion coefficient of heavy quarks in a deconfined medium is examined in this research using a deep convolutional neural network (CNN) that is trained with data from relativistic heavy ion collisions involving heavy flavor hadrons. The CNN is trained using observables such as the nuclear modification factor RAA and the elliptic flow v2 of non-prompt J/ψ from the B-hadron decay in different centralities, where B meson evolutions are calculated using the Langevin equation and the instantaneous coalescence model. The CNN outputs the parameters, thereby characterizing the temperature and momentum dependence of the heavy quark diffusion coefficient. By inputting the experimental data of the non-prompt J/ψ(RAA,v2) from various collision centralities into multiple channels of a well-trained network, we derive the values of the diffusion coefficient parameters. Additionally, we evaluate the uncertainty in determining the diffusion coefficient by taking into account the uncertainties present in the experimental data (RAA,v2), which serve as inputs to the deep neural network.

Phi meson in nuclear medium

I will report on the progress in theoretical studies of the ϕ meson mass shift in a nuclear medium and provide an overview of the current experimental status for observing such an effect. Additionally, I will discuss how the distinct momentum dependencies of the transverse and longitudinal modes can be experimentally distinguished, particularly through the e+e− and K+K− decay modes of the ϕ meson as it decays within the medium.

Center-of-mass momentum dependence of short-range correlations with the coarse-grained Granada potential

Center-of-mass momentum dependence of short-range correlations with the coarse-grained Granada potential

On the existence of a tight planar relation between stellar specific angular momentum, mass, and effective surface brightness for ALFALFA galaxies

ABSTRACT Measurements of the dependence of stellar specific angular momentum (j*) on stellar mass (M*) are presented for large samples of galaxies from the Arecibo Legacy Fast ALFA (ALFALFA) survey, spanning the stellar mass range ∼108–1011 M⊙. Accurate estimates of j* are generated using measurements of I-band effective radius and velocity width of the H i line profile. While the full sample (N = 3607) of galaxies yields a j*–M* relation with power-law index α = 0.404 ± 0.03, it is shown that various subsamples have indices that are very similar to the best literature results, yet with comparatively lower intrinsic scatters. A galaxy’s mean I-band surface brightness within its effective radius (<μeff>) is shown to significantly correlate with j*–M* scatter. A 3D plane fit to all N = 3607 galaxies in log10j*–log10M*–<μeff> space yields j* ∝ M0.589 ± 0.002 <μeff>0.193 ± 0.002 with scatter σ = 0.089 dex. <μeff>-selected subsamples of size up to N = 1450 yield power-law j*–M* relations mostly consistent with α = 0.55 ± 0.02 from the literature and with intrinsic scatter ranging from 0.083 to 0.129 dex. Thus, this paper presents new, highly accurate measurements of the j*–M* relation that can be used to better understand the important roles played by angular momentum in the formation and evolution of galaxies.

Antiparallel Spin Polarization Induced by Current in a Bilayer

The antiparallel current‐induced spin polarization (CISP) in an inversion‐symmetric double‐quantum‐well structure with the antiparallel Rashba effective magnetic field is calculated by solving the Boltzmann equation which is derived for the distribution operator in layer‐pseudospin space in the relaxation‐time approximation. The antiparallel CISP in an analytical form, obtained for constant momentum relaxation time in the limit of large Fermi energy, exhibits factor‐two increase with increasing the interlayer‐tunneling strength. This increase originates from the correction (to the semiclassical CISP) created by the subband mixing due to the momentum dependence of the Rashba effective magnetic field. The present interlayer‐coupling dependence of the antiparallel CISP is successfully explained as the layer‐pseudospin Hanle effect in which the spin in the original Hanle effect is replaced by the layer pseudospin. The present finding suggests that the correction by band mixing can be significant in the transport properties of various systems with the momentum‐dependent effective magnetic field.

Momentum Dependence of the Electronic Excitations in Polyfluorinated Metal Phthalocyanines

Momentum Dependence of the Electronic Excitations in Polyfluorinated Metal Phthalocyanines

Dynamical Chiral Symmetry Breaking in Quantum Chromo Dynamics: Delicate and Intricate

Dynamical chiral symmetry breaking (DχSB) in quantum chromo dynamics (QCD) for light quarks is an indispensable concept for understanding hadron physics, i.e., the spectrum and the structure of hadrons. In functional approaches to QCD, the respective role of the quark propagator has been evident since the seminal work of Nambu and Jona-Lasinio has been recast in terms of QCD. It not only highlights one of the most important aspects of DχSB, the dynamical generation of constituent quark masses, but also makes plausible that DχSB is a robustly occurring phenomenon in QCD. The latter impression, however, changes when higher n-point functions are taken into account. In particular, the quark–gluon vertex, i.e., the most elementary n-point function describing the full, non-perturbative quark–gluon interaction, plays a dichotomous role: It is subject to DχSB as signalled by its scalar and tensor components but it is also a driver of DχSB due to the infrared enhancement of most of its components. Herein, the relevant self-consistent mechanism is elucidated. It is pointed out that recently obtained results imply that, at least in the covariant gauge, DχSB in QCD is located close to the critical point and is thus a delicate effect. In addition, requiring a precise determination of QCD’s three-point functions, DχSB is established, in particular in view of earlier studies, by an intricate interplay of the self-consistently determined magnitude and momentum dependence of various tensorial components of the gluon–gluon and the quark–gluon interactions.

Elliptic billiard with harmonic potential: Classical description.

The classical dynamics of the isotropic two-dimensional harmonic oscillator confined by an elliptic hard wall is discussed. The interplay between the harmonic potential with circular symmetry and the boundary with elliptical symmetry does not spoil the separability in elliptic coordinates; however, it generates nontrivial energy and momentum dependencies in the billiard. We analyze the equimomentum surfaces in the parameter space and classify the kinds of motion the particle can have in the billiard. The winding numbers and periods of the rotational and librational trajectories are analytically calculated and numerically verified. A remarkable finding is the possibility of having degenerate rotational trajectories with the same energy but different second constant of motion and different caustics and periods. The conditions to get these degenerate trajectories are analyzed. Similarly, we show that obtaining two different rotational trajectories with the same period and second constant of motion but different energy is possible.

Prevailing Charge Order in Overdoped La_{2-x}Sr_{x}CuO_{4} beyond the Superconducting Dome.

The extremely overdoped cuprates are generally considered to be Fermi liquid metals without exotic orders, whereas the underdoped cuprates harbor intertwined states. Contrary to this conventional wisdom, using Cu L_{3}-edge and O K-edge resonant x-ray scattering, we reveal a charge order (CO) correlation in overdoped La_{2-x}Sr_{x}CuO_{4} (0.35≤x≤0.6) beyond the superconducting dome. This CO has a periodicity of ∼6 lattice units with correlation lengths of ∼20 lattice units. It shows similar in-plane momentum and polarization dependence and dispersive excitations as the CO of underdoped cuprates, but its maximum intensity differs along the c direction and persists up to 300K. This CO correlation cannot be explained by the Fermi surface instability and its origin remains to be understood. Our results suggest that CO is prevailing in the overdoped metallic regime and requires a reassessment of the picture of overdoped cuprates as weakly correlated Fermi liquids.

Rescattering effects in nucleon-to-meson form factors and application to tau-lepton-induced proton decay

Nucleon decays put extremely stringent bounds on baryon-number-violating interactions. However, in case the corresponding operators involve only τ leptons, the direct two-body decays, e.g., p→π0τ+, are kinematically not allowed and nucleon decay can only proceed via an off-shell τ, leading to p→π0ℓ+νℓν¯τ. To calculate such processes, the momentum dependence of the form factors for nucleon-to-meson transitions, which describe the hadronization of the underlying process at the quark level, is needed. In this work, we point out new isospin and Fierz relations among such proton–kaon matrix elements and calculate the momentum dependence of the nucleon-to-meson form factors from the universal final-state interactions in terms of pion–nucleon or kaon–nucleon scattering phase shifts. We use these results to derive novel limits on the Wilson coefficients of the baryon-number-violating dimension-6 operators involving a τ lepton, which were previously unconstrained.

Momentum-independent magnetic excitation continuum in the honeycomb iridate H3LiIr2O6

Understanding the interplay between the inherent disorder and the correlated fluctuating-spin ground state is a key element in the search for quantum spin liquids. H3LiIr2O6 is considered to be a spin liquid that is proximate to the Kitaev-limit quantum spin liquid. Its ground state shows no magnetic order or spin freezing as expected for the spin liquid state. However, hydrogen zero-point motion and stacking faults are known to be present. The resulting bond disorder has been invoked to explain the existence of unexpected low-energy spin excitations, although data interpretation remains challenging. Here, we use resonant X-ray spectroscopies to map the collective excitations in H3LiIr2O6 and characterize its magnetic state. In the low-temperature correlated state, we reveal a broad bandwidth of magnetic excitations. The central energy and the high-energy tail of the continuum are consistent with expectations for dominant ferromagnetic Kitaev interactions between dynamically fluctuating spins. Furthermore, the absence of a momentum dependence to these excitations are consistent with disorder-induced broken translational invariance. Our low-energy data and the energy and width of the crystal field excitations support an interpretation of H3LiIr2O6 as a disordered topological spin liquid in close proximity to bond-disordered versions of the Kitaev quantum spin liquid.

Pines’ demon observed as a 3D acoustic plasmon in Sr2RuO4

The characteristic excitation of a metal is its plasmon, which is a quantized collective oscillation of its electron density. In 1956, David Pines predicted that a distinct type of plasmon, dubbed a ‘demon’, could exist in three-dimensional (3D) metals containing more than one species of charge carrier1. Consisting of out-of-phase movement of electrons in different bands, demons are acoustic, electrically neutral and do not couple to light, so have never been detected in an equilibrium, 3D metal. Nevertheless, demons are believed to be critical for diverse phenomena including phase transitions in mixed-valence semimetals2, optical properties of metal nanoparticles3, soundarons in Weyl semimetals4 and high-temperature superconductivity in, for example, metal hydrides3,5–7. Here, we present evidence for a demon in Sr2RuO4 from momentum-resolved electron energy-loss spectroscopy. Formed of electrons in the β and γ bands, the demon is gapless with critical momentum qc = 0.08 reciprocal lattice units and room-temperature velocity v = (1.065 ± 0.12) × 105 m s−1 that undergoes a 31% renormalization upon cooling to 30 K because of coupling to the particle–hole continuum. The momentum dependence of the intensity of the demon confirms its neutral character. Our study confirms a 67-year old prediction and indicates that demons may be a pervasive feature of multiband metals.

New resonances in wave–particle interactions

One of the most characteristic features of relativistic particle dynamics at cyclotron resonances is the stepwise dependence of energy and momentum on time [V. A. Buts and A. G. Zagorodny, Phys. Plasmas 28(2), 022311 (2021)]. The reason for these steps is the phase synchronization of charged particles and waves. To describe other features, we introduce new dependent variables in this paper. These variables allow us to find a convenient representation of the relativistic resonance that fits the numerical results and thus establish new expressions for the stationary phase, as well as analytically describe effects that were previously visible only in numerical experiment. In particular, the temporal width of the steps, the dynamics of particles on the steps, and, most importantly, the moments of random jumps of particles from one step to another are determined. Analysis of the obtained results opens the possibility to find the conditions for the unlimited acceleration of electrons by transverse electromagnetic waves in a vacuum without an external magnetic field.

Spin-fluctuation glue disfavors high-critical temperature of superconductivity?

Antiferromagnetic fluctuations are believed to be a promising glue to drive high-temperature superconductivity especially in cuprates. Here, we perform a close inspection of the superconducting mechanism from spin fluctuations in the Eliashberg framework by employing a typical one-band model on a square lattice. While spin fluctuations can eventually drive superconductivity as is well established, we find that the superconducting tendency is suppressed substantially by a seemingly negligible contribution from a small momentum transfer far away from . This suppression comes from phase frustration of the pairing gap and is expected to be a general feature due to the repulsive pairing interaction of spin fluctuations. Furthermore, we find that the momentum dependence of the pairing gap largely deviates from the functional form of , although this form is well established in cuprate superconductors. We argue that an instantaneous magnetic interaction plays the important role to understand high-critical temperature of superconductivity as well as the momentum dependence of the pairing gap.

Hydrodynamic model of heavy-ion collisions with low momentum components

Relativistic heavy-ion collisions suggest that low-momentum regions of the observed particle spectra are thermal and hydrodynamic, while medium-high momentum regions are non-thermal and perturbative. In this study, I construct a hydrodynamic model of heavy-ion collisions by cutting off the medium-high momentum contributions and investigate the phenomenological consequences. Numerical simulations indicate that the temperature of the quark matter can be higher at earlier times owing to the modification of the equation of state. It is also suggested that direct photon elliptic flow can be sensitive to the momentum dependence of thermalization.