Mon·Mar 17, 2025Monday·March 17, 2025

1. 01*

   Exclusive photon-fusion production of even-spin resonances and exotic QED atoms in high-energy hadron collisions

   David d'Enterria🇨🇭 · Karen Kang🇺🇸

   The cross sections for the single exclusive production of (pseudo)scalar and (pseudo)tensor hadrons, as well as of even-spin QED bound states formed by pairs of opposite-charge leptons or hadrons, are estimated for photon-fusion processes in ultraperipheral collisions (UPCs) of proton-proton, proton-nucleus, and nucleus-nucleus at the RHIC, LHC and FCC colliders, as well as in proton-air interactions at the highest energies reached by cosmic-rays impinging on Earth. The UPC cross sections are computed in the equivalent photon approximation with realistic photon fluxes from the charged form factors of proton, lead, gold, and nitrogen ions. The production of four types of even-spin systems are considered: quarkonium (spin-0,2,4 meson bound states, from the lightest ${\pi }^0$ meson up to toponium), exotic hadrons (including candidate multiquark states), leptonium (positronium, dimuonium, and ditauonium), as well as mesonium (pionium, kaonium, D-onium, and B-onium) and baryonium (notably, protonium) QED atoms. The expected yields at the different colliders are presented for about 50 such even-spin composite resonances, for which the ALICE and LHCb experiments have potential reconstruction capabilities at the LHC. The impact of the diphoton decays of such even-spin states is also discussed as resonant backgrounds in the measurement of light-by-light scattering ($\gamma \gamma \to \gamma \gamma$) over $m_{\gamma \gamma }=0.1$--15 GeV in PbPb UPCs at the LHC.

   ↳ hep-phhep-exnucl-exnucl-thPRD(2025)·16 citations
2. 02*

   Gravitational form factors in the perturbative limit

   Qin-Tao Song🇨🇳 · O. V. Teryaev🇷🇺 · Shinsuke Yoshida🇨🇳

   Generalized distribution amplitudes (GDAs) have attracted significant attention in recent years due to their connection with the energy-momentum tensor (EMT) form factors (FFs). The GDAs can be experimentally accessed through the study of amplitudes in ${\gamma }^{\ast }\gamma \to M_1{M}_2$ and ${\gamma }^{\ast }\to M_1{M}_2\gamma$, where $M_1{M}_2$ is a pseudoscalar meson pair such as $\pi \eta$ and $\eta {\eta }^{\prime }$. In this work, we calculate these amplitudes in the perturbative limit and express the extracted $M_1{M}_2$ GDAs in terms of meson distribution amplitudes that have been constrained by the previous experiments. Our explicit calculation verifies the existence of a new EMT FF that violates the conservation law of EMT when the hadronic matrix element of the EMT operator is considered separately for each quark flavor. In addition, our result shows that the $M_1{M}_2$ GDAs are identical in ${\gamma }^{\ast }\gamma \to M_1{M}_2$ and ${\gamma }^{\ast }\to M_1{M}_2\gamma$, which confirms the universality of GDAs in the perturbative limit. In the future, the GDAs and the EMT FFs studied in this paper can be probed at Belle II. Our study enhances the accessibility to the $P$-wave GDAs in ${\gamma }^{\ast }\gamma \to M_1{M}_2$ and ${\gamma }^{\ast }\to M_1{M}_2\gamma$, and provides a promising approach for searching for exotic hybrid mesons in future experiments.

   ↳ hep-phhep-lathep-thnucl-ex+1PLB(2025)·9 citations
3. 03*

   Identified Hadron Production at Hadron Colliders in Next-to-Next-to-Leading-Order QCD

   Michał Czakon🇩🇪 · Terry Generet🇬🇧 · Alexander Mitov🇬🇧 · Rene Poncelet🇵🇱

   In this work we calculate for the first time the next-to-next-to leading order (NNLO) QCD corrections to identified hadron production at hadron colliders. The inclusion of the NNLO correction has an important impact on all observables considered in this work. Higher order corrections reduce scale uncertainty and in almost all cases are moderate. Overall, good perturbative convergence is observed across kinematics and observables. The uncertainty due to missing higher orders is relatively small and, in many cases, smaller than the experimental uncertainty. The largest source of theoretical uncertainty at present is from the knowledge of the non-perturbative parton-to-hadron fragmentation functions (FF), which dwarfs the scale uncertainty in most kinematic ranges. The inclusion of NNLO corrections demonstrates the precision studies potential of this class of observables. To fully realize this potential, however, a new generation of improved fragmentation functions may be needed. The results of the present work will enable global fits of FF with NNLO precision.

   ↳ hep-phhep-exnucl-exnucl-thPRL(2025)·17 citations
4. 04*

   Testing the QCD formation time with reconstructed parton splittings

   Jasmine Brewer🇬🇧 · Wilke van der Schee🇨🇭 · Urs Wiedemann🇨🇭

   In high-energy elementary collisions the space-time ordering of parton branching processes is not accessible experimentally. In contrast, in heavy-ion collisions, parton showers interact with a spatially extended dense medium. This sets a reference length scale with respect to which the space-time ordering may be analysed. Here, we explore the possibility of identifying experimental signatures of the QCD formation time, ${\tau }_f$, on the level of a single parton splitting. Since heavy flavour offers an additional handle on tracing the propagation of individual quarks through the medium, we focus on the $g\to c\bar{c}$ splitting. Combining adapted versions of the Cambridge-Aachen and FlavourCone jet finding algorithms with grooming techniques, we show how the kinematics of such splittings can be reconstructed with high fidelity using either final state partons or hadrons, and how the formation time distribution of parton splittings can be constructed therefrom. Medium modification leads to a characteristic modification of this ${\tau }_f$ distribution. This effect can be used to construct experimentally-accessible ratios of ${\tau }_f$ distributions, in which the sensitivity of the medium modification to the QCD formation time becomes measurable.

   ↳ hep-phnucl-exnucl-th5 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.