Light-by-light scattering in ultraperipheral Pb-Pb collisions at energies available at the CERN Large Hadron Collider

Abstract

We calculate cross sections for diphoton production in (semi)exclusive PbPb collisions, relevant for the LHC. The calculation is based on equivalent photon approximation in the impact parameter space. The cross sections for elementary γγ → γγ subprocess are calculated including two different mechanisms. We take into account box diagrams with leptons and quarks in the loops. In addition, we consider a vector-meson dominance (VDM-Regge) contribution with virtual intermediate hadronic (vector-like) excitations of the photons. We get much higher cross sections in PbPb collisions than in earlier calculation from the literature. This opens a possibility to study the γγ → γγ (quasi)elastic scattering at the LHC. We present many interesting differential distributions which could be measured by the ALICE, CMS or ATLAS Collaborations at the LHC. We study whether a separation or identification of different components (boxes, VDM-Regge) is possible. We find that the cross section for elastic γγ scattering could be measured in the heavy-ion collisions for subprocess energies smaller than W γγ ≈ 15 − 20 GeV.

Searching for Axionlike Particles with Ultraperipheral Heavy-Ion Collisions

“…2. We have computed the rate for LBL in the equivalent photon approximation using the one-loop matrix element for massless fermions [28] and find reasonably good agreement with detailed calculations in [26,29,30]. Such a background is irreducible but follows a continuum (except for small effects at around the bb threshold), as can be seen in Fig.…”

$\gamma\gamma \to \gamma \gamma$ scattering in ultrarelativistic UPC

“…4 in Ref. [1]) which causes that some regions in the two-dimensional space are almost not populated. The second half of the (y γ 1 , y γ 2 ) space can be obtained from the symmetry around the y γ 1 = y γ 2 diagonal.…”

“…Then we have to generalize Eq. (3.1) by adding extra integration over additional parameter related to angular distribution for the subprocess [1]. The two first panels of Fig.…”

“…More details can be found e.g. in [1,9]. In our recent papers we tried to answer the question whether the reaction can be measured with the help of LHC detectors.…”

“…It was realized only recently that ultraperipheral collisions (UPC) of heavy-ions can be also a good place where photon-photon elastic scattering could be tested experimentally. Our theoretical predictions [1] became a motivation for experimental groups to perform corresponding experimental studies. Recently the ATLAS Collaboration observed 13 events for light-by-light scattering in Pb-Pb UPC [2].…”