First differential cross-sections for γγ→ττ in Pb+Pb collisions yield 95% CL intervals -0.057 < a_τ < 0.035 and |d_τ| < 2.7×10^{-16} e cm.
Two-Photon Interactions with Nuclear Breakup in Relativistic Heavy Ion Collisions
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abstract
Highly charged relativistic heavy ions have high cross-sections for two-photon interactions. The photon flux is high enough that two-photon interactions may be accompanied by additional photonuclear interactions. Except for the shared impact parameter, these interactions are independent. Additional interactions like mutual Coulomb excitation are of experimental interest, since the neutrons from the nuclear dissociation provide a simple, relatively unbiased trigger. We calculate the cross sections, rapidity, mass and transverse momentum ($p_T)$ distributions for exclusive $\gamma\gamma$ production of mesons and lepton pairs, and for $\gamma\gamma$ reactions accompanied by mutual Coulomb dissociation. The cross-sections for $\gamma\gamma$ interactions accompanied by multiple neutron emission ($XnXn$) and single neutron emission ($1n1n$) are about 1/10 and 1/100 of that for the unaccompanied $\gamma\gamma$ interactions. We discuss the accuracy with which these cross-sections may be calculated. The typical $p_T$ of $\gamma\gamma$ final states is several times smaller than for comparable coherent photonuclear interactions, so $p_T$ may be an effective tool for separating the two classes of interactions.
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Hadrons from ion electromagnetic dissociation break exclusivity conditions in ultraperipheral collisions, resolving tensions in exclusive muon-pair and coherent J/ψ measurements at the LHC.
ALICE reports new rapidity-differential cross sections for coherent J/ψ and ψ(2S) photoproduction and exclusive dimuons in forward rapidity UPC Pb-Pb collisions at 5.36 TeV, showing nuclear shadowing ratios of approximately 0.76 and 0.71.
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Differential measurements of $\gamma\gamma\to\tau\tau$ and constraints on $\tau$-lepton electromagnetic moments in Pb+Pb collisions at $\sqrt{s_{_\text{NN}}} = 5.02$ TeV with ATLAS
First differential cross-sections for γγ→ττ in Pb+Pb collisions yield 95% CL intervals -0.057 < a_τ < 0.035 and |d_τ| < 2.7×10^{-16} e cm.
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A First Account of the Impact of Ion Electromagnetic Dissociation on Event Exclusivity in Ultraperipheral LHC Collisions
Hadrons from ion electromagnetic dissociation break exclusivity conditions in ultraperipheral collisions, resolving tensions in exclusive muon-pair and coherent J/ψ measurements at the LHC.
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Exclusive dimuon production and coherent charmonium photoproduction at forward rapidity in ultra-peripheral Pb$-$Pb collisions at $\mathbf{\sqrt{s_{\rm NN}}=5.36}$ TeV
ALICE reports new rapidity-differential cross sections for coherent J/ψ and ψ(2S) photoproduction and exclusive dimuons in forward rapidity UPC Pb-Pb collisions at 5.36 TeV, showing nuclear shadowing ratios of approximately 0.76 and 0.71.