From photons to dikaon -- theoretical insights into $K^+K^-$ production in nuclear collisions

TL;DR

This paper develops a unified theoretical framework for di-kaon production in ultraperipheral heavy-ion collisions by combining photoproduction and two-photon fusion channels. It uses the EPA with vector-meson dominance and Glauber formalisms to model photon-induced $\phi$ production and its decay to $K^+K^-$, including Drell-Söding interference between resonant and nonresonant continua, and extends the same formalism to $\gamma\gamma \to K^+K^-$ with resonances up to about $W_{\gamma\gamma} \sim 4$ GeV and hand-bag contributions. The authors compute nuclear cross sections for $Pb+Pb$ collisions at $\sqrt{s_{NN}}=5.02$ TeV and compare to Belle, ALEPH, TPC/Two-Gamma, STAR, ALICE, LHCb, and CMS data, finding that the $\phi$ peak and higher resonances shape the invariant-mass distributions and highlighting the need for a broader resonance spectrum and angular-distribution analyses to fully describe the measurements. The work provides a coherent bridge between elementary $\gamma\gamma$ dynamics and exclusive production in UPCs, offering a practical framework for interpreting current and future data.

Abstract

The production of charged kaon pairs in ultraperipheral heavy-ion collisions can proceed via photoproduction (gamma-Pomeron interaction) or via photon-photon fusion. An important contribution to this process arises from the decays of scalar, tensor and vector mesons. This study provides a consistent description of K+K- production at both the elementary level (gamma gamma -> meson -> K+K-) and the nuclear level (Pb Pb -> Pb Pb K+K-). The gamma gamma fusion cross section is compared with experimental results from Belle, TPC/Two-Gamma and ARGUS. A comparison with existing midrapidity measurements is presented, together with theoretical predictions for ultraperipheral Pb-Pb collisions at sqrt(sNN) = 5.02 TeV.

Figures (2)

• Figure 1: Differential cross section for the $\gamma\gamma \to K^{+}K^{-}$ process as a function of the two-photon center-of-mass energy $W_{\gamma\gamma}$ for $|\cos\theta| < 0.6$. Theoretical curves correspond to individual resonance contributions from $f_{2}(1525)$, $a_{2}(1750)$, $f_{2}(2010)$, and $f_{2}(2300)$, together with the nonresonant continuum and the contribution from the hand-bag mechanism. The solid red line represents the coherent sum of all components. Experimental data points from the Belle BelleBelle2, ALEPH ALEPH2003, and TPC/Two-Gamma experiments are shown for comparison.
• Figure 2: Differential cross section as a function of di-kaon invariant mass for UPC of $Pb-Pb$ at the energy of $\sqrt{s_{NN}}=5.02$ TeV.