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Observation of the γγtoττ process in Pb+Pb collisions and constraints on the τ-lepton anomalous magnetic moment with the ATLAS detector
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Observation of the γγtoττ process in Pb+Pb collisions and constraints on the τ-lepton anomalous magnetic moment with the ATLAS detector
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This Letter reports the observation of $\tau$-lepton pair production in ultraperipheral lead-lead collisions, $\text{Pb+Pb} \to \text{Pb}(\gamma\gamma \to \tau\tau)\text{Pb}$, and constraints on the $\tau$-lepton anomalous magnetic moment, $a_\tau$. The dataset corresponds to an integrated luminosity of 1.44 nb$^{-1}$ of LHC Pb+Pb collisions at $\sqrt{s_{_\text{NN}}} = 5.02$ TeV recorded by the ATLAS experiment in 2018. Selected events contain one muon from a $\tau$-lepton decay, an electron or charged-particle track(s) from the other $\tau$-lepton decay, little additional central-detector activity, and no forward neutrons. The $\gamma\gamma \to \tau\tau$ process is observed in Pb+Pb collisions with a significance exceeding 5 standard deviations, and a signal strength of $\mu_{\tau\tau} = 1.03^{+0.06}_{-0.05}$ assuming the Standard Model value for $a_\tau$. To measure $a_\tau$, a template fit to the muon transverse-momentum distribution from $\tau$-lepton candidates is performed, using a dimuon ($\gamma\gamma \to \mu\mu$) control sample to constrain systematic uncertainties. The observed 95% confidence-level interval for $a_\tau$ is $-0.057 < a_\tau < 0.024$.
Forward citations
Cited by 13 Pith papers
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Muon-induced di-tau production as a probe of new physics
Proposal to use muon trident process with HEMERA detector on 10^18 TeV muons to extend B-factory and (g-2)μ bounds on leptophilic scalar couplings by over an order of magnitude.
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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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Light new physics and the $\tau$ lepton dipole moments: prospects at Belle II
Light new particles generate asymmetries in e+e- to tau+tau- that allow model-dependent constraints on tau dipole moments, including non-zero effects without electron polarization via imaginary parts.
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Light new physics and the $\tau$ lepton dipole moments
This work provides a comprehensive analysis of light new physics contributions to tau lepton dipole moments, detailing interpretations of asymmetry measurements for spin-0 and spin-1 bosons, their decoupling to the EF...
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Measurement of the $\gamma\gamma \to \tau \tau$ cross section and constraints on the anomalous magnetic moment of the $\tau$ lepton in ultraperipheral PbPb collisions at $\sqrt{s_\mathrm{NN}}$ = 5.02 TeV
CMS measures gamma-gamma -> tau+tau- in PbPb UPCs and constrains the tau anomalous magnetic moment to -0.039 < a_tau < 0.032 (95% CL), with a fiducial cross-section of 555+60-14 microbarns.
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Femtoscopy-driven searches for saturated gluonic matter in inclusive photonuclear processes
Femtoscopy is presented as a method to isolate gluon saturation and nuclear shadowing effects via space-time structure in photonuclear collisions.
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Probing the imaginary parts and their $q^2$ dependences for the tau $g-2$ and EDM
Explores q² dependence and imaginary parts of tau g-2 and EDM in SMEFT and 2HDM, proposing methods to measure them at Belle II and STCF to improve a_τ bounds by over an order of magnitude.
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Four-fermion operators, $Z$-boson exchange, and $\tau$ lepton dipole moments
Z-boson exchange contributes ~3e-6 to the relevant asymmetries while four-fermion operators can reach ~1e-5 times Wilson coefficients, with loop insertions offering an additional path to a_tau without beam polarization.
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Polarized tau decay and CP violation in ultraperipheral heavy-ion collisions
Proposes that the relative polarization of tau+ and tau- decay products in UPCs, aligned to the magnetic field, provides a sensitive probe for CP violation.
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Spin effects in the tau-lepton pair induced by anomalous magnetic and electric dipole moments
Anomalous dipole moments of the tau lepton produce measurable effects on tau polarization and spin correlations in gamma-gamma and quark-antiquark induced pair production.
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Probing electromagnetic moments of the tau lepton in PbPb collisions at the FCC-hh
Obtains 95% CL exclusion and 3σ/5σ sensitivity limits on a_τ and d_τ from PbPb collisions at FCC-hh with comparisons to other future colliders.
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Ultra-peripheral Collisions
Ultra-peripheral collisions of heavy ions are reviewed as the energy frontier for photon physics; the paper consolidates a decade of LHC/RHIC results and proposes no new measurement.
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