Z0 decaying leptons as a probe of electromagnetic field and quantum radiation reaction
Yifeng Sun
Shanghai Jiao Tong University
8th International Workshop on Nuclear Dynamics in Heavy-ion Reactions
Taiyuan Shanxi, Aug. 21-25, 2026
Collaborators: Linghai Li, Xin-Nian Wang, Vincenzo Greco
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Outline
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Introduction: electromagnetic (e.m.) field effects, strong field quantum electrodynamics (SFQED) and radiation reaction
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Z0 leptonic invariant mass as a probe of e.m. field and quantum radiation reaction
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Summary
Introduction E.m. fields & quantum radiation reaction Summary
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Outline
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Introduction: electromagnetic (e.m.) field effects, strong field quantum electrodynamics (SFQED) and radiation reaction
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Z0 leptonic invariant mass as a probe of e.m. field and quantum radiation reaction
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Summary
Introduction E.m. fields & quantum radiation reaction Summary
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Electromagnetic (e.m.) field effects
Electromagnetic fields have long given rise to important and intriguing phenomena in physics
D. Lai, RMP 73, 629 (2001)
R. Durrer and A. Neronov, AAR 21, 62 (2013)
A. Gonoskov et al., RMP 94, 045001 (2022)
10-12 10-8 10-4 100 T 104 108 1012 1016
Stellar, Galaxy & Galaxy-cluster Near-Earth Space Laboratory Systems Compact Stars Heavy-Ion Collisions
Stellar evolution
Cosmic ray acceleration
AGN feedback
Large-scale structure formation
Solar wind deflection
Cosmic ray cutoff
Charged particle trapping
Magnetic reconnection
Zeeman effect
Magnetic resonance
Magnetoresistance
Meissner effect
Quantum Hall effect
Quantum oscillations
Abrikosov vortices
Phase transitions
Magnetic deformation of atoms
Photon splitting
Magnetic pair conversion
Vacuum birefringence
Chiral magnetic transport
Phase transition
Quarkonium mixing
Spin polarization and alignment
SFQED：
Introduction E.m. fields & quantum radiation reaction Summary
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SFQED
A. Gonoskov et al., RMP 94, 045001 (2022)
The cube of relativistic, quantum, and strong-field physics
High-intensity laser facilities relevant to SFQED
Introduction E.m. fields & quantum radiation reaction Summary
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Radiation Reaction (RR)
Synchrotron radiation power spectrum
T.N. Wistisen et al., NC 795 (2018)
Introduction E.m. fields & quantum radiation reaction Summary
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Radiation Reaction (RR)
Experimental verification of a quantum, strong-field description of radiation reaction is fundamentally important
Radiation reaction: recoil force experienced by an accelerated charge due to radiation emission
Lorentz-Abraham-Dirac (LAD) model
P. A. M. Dirac, PRSA 167 (929), 148 (1938)
Landau-Lifshitz (LL) model
L. D. Landau, and E. M. Lifshitz, The Classical Theory of Field (1941)
Self-accelerating (runaway) solution
Introduction E.m. fields & quantum radiation reaction Summary
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Current Experimental Status
A high significance ( > 5σ) observation of strong-field radiation reaction (RR) is found;
Strong evidence favouring the quantum model over the classical model
E.E. Los et al., NC 17, 1157 (2026)
Quantum nonlinearity invariant parameter:
Introduction E.m. fields & quantum radiation reaction Summary
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Outline
01
Introduction: electromagnetic (e.m.) field effects, strong field quantum electrodynamics (SFQED) and radiation reaction
02
Z0 leptonic invariant mass as a probe of e.m. field and quantum radiation reaction
03
Summary
Introduction E.m. fields & quantum radiation reaction Summary
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Hadron Directed Flow as A Probe of E.M. Field
STAR Collaboration, PRX 14, 011028 (2024)
Electromagnetic Field:
Using hadrons as probes is complicated by their interactions with the QGP and hadronic matter, as well as by the hadronization mechanism
ALICE Collaboration, PRL 125 (2020), 022301
Introduction E.m. fields & quantum radiation reaction Summary
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More Ideal Probe
Leptons from Z0 decay as an ideal probe
High Precision
Sun, Greco and Wang, PLB 827, 136962 (2022)
Introduction E.m. fields & quantum radiation reaction Summary
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Experimental Preliminary Data
Qualitatively reproduces the sign and centrality-dependent trends of both the mean and the width in the dimuon channel;
CMS Collaboration, QM2025
Sun, Greco and Wang, PLB 827, 136962 (2022)
Remaining work:
Introduction E.m. fields & quantum radiation reaction Summary
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Kinematic Cuts Impact
Introduction E.m. fields & quantum radiation reaction Summary
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RR Impact
Near-instantaneous energy loss: The classical LL model predicts an almost complete depletion of the dimuon energy
L. D. Landau, and E. M. Lifshitz, The Classical Theory of Field (1941)
ALICE Collaboration, JHEP 09 (2020) 076
Larmor formula of radiation:
LHC Z0 decaying muon kinematics
Muon: dE/dt=-8.44×105 GeV/(fm/c)
Lorentz force: 7.3 GeV/(fm/c)
Introduction E.m. fields & quantum radiation reaction Summary
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Quantum Correction on RR
V. B. Berestetsky, E. M. Lifshitz and L. P. Pitaevsky, “Quantum Electrodynamics,” §90
Quantum corrections
Gaunt factor:
CMS Collaboration, QM2025
Substantially improved agreement: including radiation reaction brings the predicted dimuon mean value much closer to the preliminary measurement.
Introduction E.m. fields & quantum radiation reaction Summary
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Joint Measurement
V. B. Berestetsky, E. M. Lifshitz and L. P. Pitaevsky, “Quantum Electrodynamics,” §90
A unique test of quantum radiation: for , the explicit lepton-mass dependence vanishes, making a combined comparison of the dimuon and dielectron channels especially powerful.
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Dielectron Channel
Exclusion of classical radiation reaction: the dielectron channel measurement could decisively discriminate between classical and quantum descriptions.
E.M. field: 10-2 lasts 1 fm/c
Introduction E.m. fields & quantum radiation reaction Summary
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Summary
Thank you!
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