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Register a new userTrue muonium production in ultraperipheral $PbPb$ collisions
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In this paper we investigate the production of a true muonium state, which is an atom consisting of a $mu^+ mu^-$ bound state, by $gamma gamma$ interactions in ultraperipheral $PbPb$ collisions considering an accurate treatment of the absorptive corrections and for the nuclear form factor. The rapidity distributions and cross sections are estimated considering the RHIC, LHC and FCC energies. Our results indicate that the experimental analysis can be useful to observe, for the first time, the true muonium state.
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In this paper we perform a systematic study of the exclusive dilepton production by $gamma gamma$ interactions in $PbPb$ collisions at the LHC Run 2 energies considering different levels of precision for the treatment of the absorptive corrections and for the nuclear form factor. The rapidity and invariant mass distributions are estimated taking into account the experimental cutoffs and a comparison with the recent ALICE and ATLAS data for the $e^+ e^-$ and $mu^+ mu^-$ production is presented.
In this letter we propose the search of dark photons in the decay of pions produced by $gamma gamma$ interactions in ultraperipheral $PbPb$ collisions. The cross section is estimated considering an accurate treatment for the absorptive corrections and for the nuclear form factor. Predictions for the event rates are presented considering the expected luminosities for the LHC, High -- Luminosity LHC and High -- Energy LHC as well as for the Future Circular Collider. Our results indicate that a future experimental analysis of the pion production in ultraperipheral heavy ion collisions can be useful to probe the dark photon production and constrain its properties.
We study the potential of the LHCb experiment to discover, for the first time, the $mu^+mu^-$ true muonium bound state. We propose a search for the vector $1^3S_1$ state, $mathcal{T!M}$, which kinetically mixes with the photon and dominantly decays to $e^+e^-$. We demonstrate that a search for $eta to gamma mathcal{T!M}$, $mathcal{T!M}to e^+e^-$ in a displaced vertex can exceed a significance of 5 standard deviations assuming statistical uncertainties. We present two possible searches: an inclusive search for the $e^+e^-$ vertex, and an exclusive search which requires an additional photon and a reconstruction of the $eta$ mass.
Heavy quarkonium production in ultraperipheral nuclear collisions is described within the QCD dipole formalism. Realistic quarkonium wave functions in the rest frame are calculated solving the Schrodinger equation with a subsequent Lorentz boost to high energy. We rely on several selected $Qbar Q$ potentials, which provide the best description of quarkonium spectra and decay widths, as well as data on diffractive electroproduction of quarkonia on protons. Nuclear effects are calculated with the phenomenological dipole cross sections fitted to DIS data. Higher twist effect related to the lowest $Qbar Q$ Fock component of the photon, as well as the leading twist effects, related to higher components containing gluons, are included. The results for coherent and incoherent photoproduction of charmonia and bottomonia on nuclei are in a good accord with available data from the recent UPC measurements at the LHC. They can also be verified in future experiments at the planned electron-ion colliders.
Recent data on the nuclear modification of W and Z boson production measured by the ATLAS collaboration in PbPb collisions at $sqrt{s_{rm nn}}=5.02$ TeV show an enhancement in peripheral collisions, seemingly contradicting predictions of the Glauber model. The data were previously explained by arguing that the nucleon-nucleon cross section may be shadowed in nucleus-nucleus collisions, and hence suppressed compared to the proton-proton cross section at the same collision energy. This interpretation has quite significant consequences for the understanding of heavy-ion data, in particular in the context of the Glauber model. Instead, we provide an alternative explanation of the data by assuming that there is a mild bias present in the centrality determination of the measurement; on the size of the related systematic uncertainty. Using this assumption, we show that the data is in agreement with theoretical calculations using nuclear parton distribution functions. Finally, we speculate that the centrality dependence of the W$^-$/W$^{+}$ ratio may point to the relevance of a larger skin thickness of the Pb nucleus, which, if present, would result in a few percent larger PbPb cross section than currently accounted for in the Glauber model and may hence be the root of the centrality bias.
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