Abstract
Possibility of PbPb→PbPbγγ measurement at smaller (< 5 GeV) diphoton invariant mass will be presented. Analysis focuses only on ultraperipheral heavy-ion collisions. This estimate shows that the γγ → γγ collisions can be measured at the LHC by ALICE and LHCb experiments for diphoton invariant mass > 2 GeV. Predictions for the γγ → η, γγ → η′ resonance scattering shows that these resonances can be measured with rather good statistics. A possible observation of peaks related to intermediate η, η′(958), ηc(1S), ηc(2S), χc0(1P) mesons will be presented too. Attempts of reduction of background which comes from dipion production will be considered.
Highlights
Light-by-light scattering was realized experimentally only recently [1, 2] in ultraperipheral ultrarelativistic heavy ion collisions
For ions of charges Z1, Z2, the cross section is enhanced by Z12Z22 factor compared to proton-proton collisions, at least at low diphoton invariant masses equal to diphoton collision energies, where the initial photons are quasi real with extremely low virtualities
Our theoretical calculations 103 ± 0.034 nb are in the good agreement with the experimental fiducial cross section: σ = 122 ± 46 ±29 nb
Summary
Light-by-light scattering was realized experimentally only recently [1, 2] in ultraperipheral ultrarelativistic heavy ion collisions. For ions of charges Z1, Z2, the cross section is enhanced by Z12Z22 factor compared to proton-proton collisions, at least at low diphoton invariant masses equal to diphoton collision energies, where the initial photons are quasi real with extremely low virtualities. ATLAS measured a fiducial cross section of σ = 70±24 (stat.) ±17 (syst.) nb and our theoretical calculations (including experimental acceptance) gave 49 ± 10 nb [3]. ATLAS comparison of its experimental results to the predictions from Ref.[3] show a reasonable agreement. Our theoretical calculations 103 ± 0.034 nb are in the good agreement with the experimental fiducial cross section: σ = 122 ± 46 (stat.) ±29 (syst.) nb. This note will answer to a question whether we can go to lower γγ scattering energies at the LHC. At lower energies (Wγγ < 4 GeV) meson resonances may play some role in addition to the Standard Model box diagrams [4] or double photon fluctuations into light vector mesons [3] or two-gluon exchanges [5]
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