Differential measurements of γγ → ττ and constraints on τ-lepton electromagnetic moments in Pb+Pb collisions at √(s_NN)=5.02 TeV with ATLAS

@article{collaboration2026differential,
  title = {{Differential measurements of γγ → ττ and constraints on τ-lepton electromagnetic moments in Pb+Pb collisions at $$ \sqrts_\mathrmNN=5.02 $$ TeV with ATLAS}},
  author = {The ATLAS collaboration and G. Aad and E. Aakvaag and B. Abbott and S. Abdelhameed and K. Abeling and N. J. Abicht and S. H. Abidi and M. Aboelela and A. Aboulhorma and H. Abramowicz and B. S. Acharya and A. Ackermann and J. Ackerschott and C. Adam Bourdarios and L. Adamczyk and S. V. Addepalli and M. J. Addison and J. Adelman and A. Adiguzel and T. Adye and A. A. Affolder and Y. Afik and M. N. Agaras and A. Aggarwal and C. Agheorghiesei and A. Ahmad and F. Ahmadov and S. Ahuja and X. Ai and G. Aielli and A. Aikot and M. Ait Tamlihat and T. P. A. Åkesson and D. Akiyama and N. N. Akolkar and S. Aktas and G. L. Alberghi and J. Albert and U. Alberti and P. Albicocco and S. Alderweireldt and Z. L. Alegria and M. Aleksa and I. N. Aleksandrov and C. Alexa and T. Alexopoulos and F. Alfonsi and M. Algren and M. Alhroob and B. Ali and H. M. J. Ali and S. Ali and S. W. Alibocus and M. Aliev and G. Alimonti and C. Allaire and B. M. M. Allbrooke and D. R. Allen and J. S. Allen},
  journal = {Journal of High Energy Physics},
  year = {2026},
  month = oct,
  doi = {10.1007/jhep10(2026)053},
  url = {https://link.springer.com/article/10.1007/JHEP10(2026)053},
  note = {CC BY 4.0},
}

TY  - JOUR
TI  - Differential measurements of γγ → ττ and constraints on τ-lepton electromagnetic moments in Pb+Pb collisions at √(s_NN)=5.02 TeV with ATLAS
AU  - The ATLAS collaboration
AU  - G. Aad
AU  - E. Aakvaag
AU  - B. Abbott
AU  - S. Abdelhameed
AU  - K. Abeling
AU  - N. J. Abicht
AU  - S. H. Abidi
AU  - M. Aboelela
AU  - A. Aboulhorma
AU  - H. Abramowicz
AU  - B. S. Acharya
AU  - A. Ackermann
AU  - J. Ackerschott
AU  - C. Adam Bourdarios
AU  - L. Adamczyk
AU  - S. V. Addepalli
AU  - M. J. Addison
AU  - J. Adelman
AU  - A. Adiguzel
AU  - T. Adye
AU  - A. A. Affolder
AU  - Y. Afik
AU  - M. N. Agaras
AU  - A. Aggarwal
AU  - C. Agheorghiesei
AU  - A. Ahmad
AU  - F. Ahmadov
AU  - S. Ahuja
AU  - X. Ai
AU  - G. Aielli
AU  - A. Aikot
AU  - M. Ait Tamlihat
AU  - T. P. A. Åkesson
AU  - D. Akiyama
AU  - N. N. Akolkar
AU  - S. Aktas
AU  - G. L. Alberghi
AU  - J. Albert
AU  - U. Alberti
AU  - P. Albicocco
AU  - S. Alderweireldt
AU  - Z. L. Alegria
AU  - M. Aleksa
AU  - I. N. Aleksandrov
AU  - C. Alexa
AU  - T. Alexopoulos
AU  - F. Alfonsi
AU  - M. Algren
AU  - M. Alhroob
AU  - B. Ali
AU  - H. M. J. Ali
AU  - S. Ali
AU  - S. W. Alibocus
AU  - M. Aliev
AU  - G. Alimonti
AU  - C. Allaire
AU  - B. M. M. Allbrooke
AU  - D. R. Allen
AU  - J. S. Allen
PY  - 2026
DA  - 2026/10/05
JO  - Journal of High Energy Physics
DO  - 10.1007/jhep10(2026)053
UR  - https://link.springer.com/article/10.1007/JHEP10(2026)053
AB  - A bstract : This paper presents the first differential fiducial measurements of γγ → ττ using 1.93 nb − 1 of Pb+Pb data at √(s_NN)=5.02 s NN = 5.02 TeV recorded by the ATLAS detector. Events in which one of the τ -leptons decays into a muon and two neutrinos τ → ν_τ ν̅_μμ τ → ν τ ν ¯ μ μ are selected and are categorized into three regions by the presence of an electron or either one or three charged-particle track(s) from the second τ -lepton decay. The measurement is performed in events where both Pb ions remain intact and no neutrons are emitted. Differential cross-sections are measured for seven variables in three fiducial regions at particle level. The measurements are compared to theory predictions with different photon flux models and spin correlation effects. For the fiducial region with one muon and one electron in the final state, comparisons to next-to-leading-order electroweak predictions are also made. The transverse momentum ( p T ) of the decay muon, the p T of the visible decay particles of the other τ -lepton, the total p T , invariant mass, and pseudorapidity of the visible particles from the di- τ system, and the rapidity and acoplanarity of the visible decay particles from either τ -lepton are measured. A maximum-likelihood fit to the muon transverse-momentum distributions in the three regions before unfolding is performed to extract the τ -lepton anomalous magnetic moment a τ and electric dipole moment d τ , the latter for the first time in heavy ion collisions. The observed 95% confidence level intervals are − 0 . 057 < a τ < 0 . 035 and |d τ | < 2 . 7 × 10 − 16 e cm.
SN  - 1029-8479
ER  -