Speaker
Description
We discuss possible future studies of photon-photon (light-by-light)
scattering using planned FoCal and ALICE 3 detectors.
We include different mechanisms of $\gamma\gamma\to\gamma\gamma$
scattering such as double-hadronic photon fluctuations,
$t/u$-channel neutral pion exchange or resonance excitations
($\gamma \gamma \to R$) and deexcitation ($R \to \gamma \gamma$).
The broad range of (pseudo)rapidities and lower cuts on transverse
momenta open a necessity to consider not only dominant box
contributions but also other subleading contributions.
Here we include low mass resonant $R = \pi^0$, $\eta$, $\eta'$
contributions.
The resonance contributions give intermediate photon transverse
momenta.
However, these contributions can be eliminated by imposing windows
on di-photon invariant mass.
We study and quantify individual box contributions (leptonic, quarkish).
The electron/positron boxes dominate at low $M_{\gamma \gamma}~<$~1~GeV
di-photon invariant masses.
The PbPb$\to$PbPb$\gamma \gamma$ cross section is calculated
within equivalent photon approximation in the impact parameter space.
Several differential distributions are presented and discussed.
We consider four different kinematic regions. We predict cross
section in the (mb-b) range for typical ALICE 3 cuts, a few orders
of magnitude larger than for the current ATLAS or CMS experiments.
We also consider the two-$\pi^0$ background which can, in principle,
be eliminated at the new kinematical range of the ALICE 3 measurements
by imposing dedicated cuts on di-photon transverse momentum
and$\slash$or so-called vector asymmetry.
