Nuclear Theory·nucl-th

Monday·September 12, 2022

9 papers—4 primary·5 cross-listed

05
The LPM effect in sequential bremsstrahlung: incorporation of "instantaneous'' interactions for QCD
Peter Arnold🇺🇸 · Tyler Gorda🇩🇪 · Shahin Iqbal🇵🇰
The splitting processes of bremsstrahlung and pair production in a medium are coherent over large distances in the very high energy limit, which leads to a suppression known as the Landau-Pomeranchuk-Migdal (LPM) effect. We continue study of the case when the coherence lengths (formation lengths) of two consecutive splitting processes overlap, avoiding soft-emission approximations. Previous work made a ``nearly-complete'' calculation of the effect of overlapping formation times on gluonic splittings such as $g \to g g \to g g g$ (with simplifying assumptions such as an infinite QCD medium and the large- $N_{c}$ limit). In this paper, we extend those previous rate calculations from nearly-complete to complete by including processes involving the exchange of longitudinally-polarized gluons. In the context of Lightcone Pertubation Theory, used earlier for the ``nearly-complete'' calculation, such exchanges are instantaneous in lightcone time and have their own diagrammatic representation.
↳ hep-phnucl-thJHEP(2022)·12 citations
06
Fixed-target charmonium production and pion parton distributions
Wen-Chen Chang🇹🇼 · Jen-Chieh Peng🇺🇸 · Stephane Platchkov🇫🇷 · Takahiro Sawada🇯🇵
We investigate how charmonium hadroproduction at fixed-target energies can be used to constrain the gluon distribution in pions. Using nonrelativistic QCD (NRQCD) formulation, the $J / ψ$ and $ψ (2 S)$ cross sections as a function of longitudinal momentum fraction $x_{F}$ from pions and protons colliding with light targets, as well as the $ψ (2 S)$ to $J / ψ$ cross section ratios, are included in the analysis. The color-octet long-distance matrix elements are found to have a pronounced dependence on the pion parton distribution functions (PDFs). This study shows that the $x_{F}$ differential cross sections of pion-induced charmonium production impose strong constraints on the pion's quark and gluon PDFs. In particular, the pion PDFs with larger gluon densities provide a significantly better description of the data. It is also found that the production of the $ψ (2 S)$ state is associated with a larger quark-antiquark contribution, compared with $J / ψ$ .
↳ hep-phhep-exnucl-exnucl-thPRD(2023)·11 citations
07
Moments and power corrections of longitudinal and transverse proton structure functions from lattice QCD
M. Batelaan🇦🇺 · K. U. Can🇦🇺 · A. Hannaford-Gunn🇦🇺 · R. Horsley🇬🇧 · Y. Nakamura🇯🇵 · H. Perlt🇩🇪 · P. E. L. Rakow🇬🇧 · G. Schierholz🇩🇪 · H. Stüben🇩🇪 · R. D. Young🇦🇺 · J. M. Zanotti🇦🇺
We present a simultaneous extraction of the moments of $F_{2}$ and $F_{L}$ structure functions of the proton for a range of photon virtuality, $Q^{2}$ . This is achieved by computing the forward Compton amplitude on the lattice utilizing the second-order Feynman-Hellmann theorem. Our calculations are performed on configurations with two different lattice spacings and volumes, all at the $S U (3)$ symmetric point. We find the moments of $F_{2}$ and $F_{L}$ in good agreement with experiment. Power corrections turn out to be significant. This is the first time the $Q^{2}$ dependence of the lowest moment of $F_{2}$ has been quantified.
↳ hep-lathep-phnucl-thPRD(2023)·14 citations
08
The $X (3872)$ 's excitation and its connection with production at hadron colliders
M.C. Gordillo🇪🇸 · F. De Soto🇪🇸 · J. Segovia🇪🇸
The LHCb collaboration has found that the production rate of $X (3872)$ in proton-proton collisions decreases as final state particle multiplicity increases. Moreover, the ALICE experiment at CERN has observed that the number of deuterons produced increases with multiplicity, a behavior that is qualitatively different from that of the $X (3872)$ . These experimental findings may point to a compact structure for the $X (3872)$ or, at least, that its hadronization could proceed through a charm-anticharm core. We have recently used a diffusion Monte Carlo method to solve the many-body Schrödinger equation that describes the $X (3872)$ as a $c c ˉ q q ˉ$ tetraquark system with quantum numbers $I^{G} (J^{P C}) = 0^{+} (1^{++})$ and $1^{-} (1^{++})$ . According to our structural analysis, the quark--(anti-)quark correlations resemble light-meson--heavy-meson molecules of type $ω J / ψ$ and $ρ J / ψ$ , rather than the most extended $D D ˉ^{*}$ interpretation. It was argued that this fact may be the key to make compatible the molecular features of the $X (3872)$ with its production observables. The same formalism allows us to compute the first color excited $c c ˉ q q ˉ$ tetraquark state with either $I^{G} (J^{P C}) = 0^{+} (1^{++})$ or $1^{-} (1^{++})$ . A bound-state is found in each channel, their masses are around 4.0 GeV which is an energy region where many new exotic candidates have been collected by the Particle Data Group. Concerning their structural properties, these states cluster in a compact diquark-antidiquark arrangement which matches perfectly with a so-called Born-Oppenheimer tetraquark configuration. The promptly production rates of these states in proton-proton, proton-nucleus and nucleus-nucleus collisions should fall off equal to or even faster than those of the $X (3872)$ .
↳ hep-phhep-exhep-latnucl-ex+1PRD(2022)·10 citations
09
Heavy-flavor meson and baryon production in high-energy nucleus-nucleus collisions
Andrea Beraudo🇮🇹 · Arturo De Pace🇮🇹 · Daniel Pablos Alfonso🇮🇹 · Francesco Prino🇮🇹 · Marco Monteno🇮🇹 · Marzia Nardi🇮🇹
We present a new model for the description of heavy-flavor hadronization in relativistic heavy-ion collisions. We explore its effect on the charmed hadron yields and kinematic distributions once the latter is applied at the end of transport calculations used to simulate the propagation of heavy quarks in the deconfined fireball produced in the collision. The model is based on the formation of color-singlet clusters through the recombination of charm quarks with light antiquarks or diquarks from the same fluid cell. This local mechanism of color neutralization leads to a strong space-momentum correlation, which provides a substantial enhancement of charmed baryon production and of the collective flow of all charmed hadrons.
↳ hep-phnucl-exnucl-thEPJ Web Conf.(2023)·0 citations

Affiliations

first authorsco-authorsvia INSPIRE

The LPM effect in sequential bremsstrahlung: incorporation of "instantaneous'' interactions for QCD

Fixed-target charmonium production and pion parton distributions

Moments and power corrections of longitudinal and transverse proton structure functions from lattice QCD

The X(3872)'s excitation and its connection with production at hadron colliders

Heavy-flavor meson and baryon production in high-energy nucleus-nucleus collisions

Affiliations

The $X (3872)$ 's excitation and its connection with production at hadron colliders