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# Detection of a particle shower at the Glashow resonance with IceCube

### Subjects

A Publisher Correction to this article was published on 31 March 2021

## Abstract

The Glashow resonance describes the resonant formation of a W boson during the interaction of a high-energy electron antineutrino with an electron1, peaking at an antineutrino energy of 6.3 petaelectronvolts (PeV) in the rest frame of the electron. Whereas this energy scale is out of reach for currently operating and future planned particle accelerators, natural astrophysical phenomena are expected to produce antineutrinos with energies beyond the PeV scale. Here we report the detection by the IceCube neutrino observatory of a cascade of high-energy particles (a particle shower) consistent with being created at the Glashow resonance. A shower with an energy of 6.05 ± 0.72 PeV (determined from Cherenkov radiation in the Antarctic Ice Sheet) was measured. Features consistent with the production of secondary muons in the particle shower indicate the hadronic decay of a resonant W boson, confirm that the source is astrophysical and provide improved directional localization. The evidence of the Glashow resonance suggests the presence of electron antineutrinos in the astrophysical flux, while also providing further validation of the standard model of particle physics. Its unique signature indicates a method of distinguishing neutrinos from antineutrinos, thus providing a way to identify astronomical accelerators that produce neutrinos via hadronuclear or photohadronic interactions, with or without strong magnetic fields. As such, knowledge of both the flavour (that is, electron, muon or tau neutrinos) and charge (neutrino or antineutrino) will facilitate the advancement of neutrino astronomy.

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## Data availability

The full event data, including the location of each DOM, the time and charge of all pulses associated with this event, and relevant calibration details are available at https://doi.org/10.21234/gr2021. Additionally, the 90% contour of the hybrid cascade+track reconstruction shown in Fig. 2 and the measured flux shown in Fig. 4 can be found at the same URL.

## Code availability

Much of the analysis code is IceCube proprietary and exists as part of the IceCube simulation and production framework. IceCube open-source code can be found at https://github.com/icecube. Additional information is available from analysis@icecube.wisc.edu upon request.

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## Acknowledgements

We thank T. Pierog, D. Heck and C. Baus for discussions on realistic hadronic shower simulations in ice. We gratefully acknowledge support from the following agencies and institutions: USA—the US National Science Foundation-Office of Polar Programs, the US National Science Foundation Physics Division, the Wisconsin Alumni Research Foundation, the Center for High Throughput Computing (CHTC) at the University of Wisconsin-Madison, the Open Science Grid (OSG), the Extreme Science and Engineering Discovery Environment (XSEDE), the Frontera computing project at the Texas Advanced Computing Center, the US Department of Energy-National Energy Research Scientific Computing Center, the Particle Astrophysics Research Computing Center at the University of Maryland, the Institute for Cyber-Enabled Research at Michigan State University, and the Astroparticle Physics Computational Facility at Marquette University; Belgium—the Funds for Scientific Research (FRS-FNRS and FWO), the FWO Odysseus and Big Science programmes, and the Belgian Federal Science Policy Office (Belspo); Germany—the Bundesministerium für Bildung und Forschung (BMBF), the Deutsche Forschungsgemeinschaft (DFG), the Helmholtz Alliance for Astroparticle Physics (HAP), the Initiative and Networking Fund of the Helmholtz Association, the Deutsches Elektronen Synchrotron (DESY), and the High Performance Computing Cluster of RWTH Aachen; Sweden—the Swedish Research Council, the Swedish Polar Research Secretariat, the Swedish National Infrastructure for Computing (SNIC), and the Knut and Alice Wallenberg Foundation; Australia—the Australian Research Council; Canada—the Natural Sciences and Engineering Research Council of Canada, Calcul Québec, Compute Ontario, the Canada Foundation for Innovation, WestGrid, and Compute Canada; Denmark—the Villum Fonden, the Danish National Research Foundation (DNRF), the Carlsberg Foundation; New Zealand—the Marsden Fund; Japan—the Japan Society for Promotion of Science (JSPS) and the Institute for Global Prominent Research (IGPR) of Chiba University; Korea—the National Research Foundation of Korea (NRF); Switzerland—the Swiss National Science Foundation (SNSF); the UK—the Department of Physics, University of Oxford.

## Author information

### Contributions

The IceCube neutrino observatory was constructed and is maintained by the IceCube Collaboration. A large number of authors contributed to the data processing, detector calibration and MC simulations used in this work. The IceCube collaboration acknowledges the substantial contributions to this manuscript from L.L., T.Y. and C. Haack. The final manuscript was reviewed and approved by all authors.

### Corresponding author

Correspondence to F. Halzen.

## Ethics declarations

### Competing interests

The authors declare no competing interests.

Peer review information Nature thanks Sergio Navas and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

## Extended data figures and tables

### Extended Data Fig. 1 The BDT distribution for events with a reconstructed energy above 4 PeV.

The plotted events are required to be consistent with a cascade hypothesis based on the goodness of fit. The PEPE event selection requires a BDT score greater than 0.5. Good data–MC agreements were observed across the background and the signal region. See Methods for details.

### Extended Data Fig. 2 Effect of ice anisotropy on the reconstructed direction.

Shown are reconstructed directions assuming three different ice anisotropy models41 (A, B and C). While the cascade-based reconstructions (red) exhibit some shifts, the hybrid cascade+track reconstructions (blue) appear less susceptible to ice model differences.

### Extended Data Fig. 3 The number of strings that observed early pulses for a given muon energy.

The colour scale shows the probability of observing the number of strings with early pulses, Ns, as function of the simulated muon energy.

### Extended Data Fig. 4 First-photon arrival times on four strings.

Left, first-photon arrival times ($${t}_{{\rm{DOM}}}^{{\rm{first}}}$$) on photosensors deployed on four strings (‘Str.’, shown in different colours) nearest to the reconstructed vertex plotted against their depth relative to the centre of IceCube (z). Observed times are shown as circles, with the size of each circle corresponding to the total charge on that DOM. Predicted arrival times assuming a cascade without escaping muons are shown as lines with shaded regions corresponding to the quartiles obtained from repeated resimulations. Three DOMs on string 67 stand out and have first-photon arrival times that are inconsistent with predictions. Right, with the addition of a highly relativistic muon, much better consistency is obtained between observed and predicted first-photon arrival times on the three DOMs with early pulses.

### Extended Data Fig. 5 The test statistic distribution under the null hypothesis.

Cumulative distribution of Γ under the null hypothesis, as generated under the sampling scheme described in the text. The test statistic for the data event is shown in black.

## Rights and permissions

Reprints and Permissions

The IceCube Collaboration., Aartsen, M.G., Abbasi, R. et al. Detection of a particle shower at the Glashow resonance with IceCube. Nature 591, 220–224 (2021). https://doi.org/10.1038/s41586-021-03256-1

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• ### Ten years of IceCube

• Ankita Anirban

Nature Reviews Physics (2021)