Probing a low-mass $Z^{\prime}$ gauge boson at IceCube and prospects for IceCube-Gen2

TL;DR

This work tests a light $Z'$ boson from the $L_ - L_ au$ gauge symmetry as a modifier of astrophysical neutrino propagation and IceCube observations. It develops a transport framework that includes $Z'$-mediated absorption and regeneration, two source redshift distributions (star formation rate and BL Lac objects), and two neutrino-mass schemes, solving for the Earth-bound flux and predicting IceCube event rates via deep inelastic scattering and Glashow resonance with CT14 PDFs. A likelihood analysis of 12 years of HESE data shows a mild best-fit around $m_{Z'} \approx 6$ MeV for some configurations, but model comparison via AIC/AICc does not decisively favor the $Z'$ over the Standard Model. The study then projects IceCube-Gen2 capabilities, finding it can probe new regions of the $(g',m_{Z'})$ parameter space not excluded by Borexino or NA64, especially for the SFR redshift model, thereby offering a powerful test of muon\(-g-2\) motivated scenarios with light gauge bosons. Overall, the results demonstrate that high-energy astrophysical neutrinos provide complementary constraints on light $Z'$ models and can illuminate beyond-Standard-Model neutrino interactions with the cosmic neutrino background.

Abstract

In this work, we investigate the impact of the $L_μ- L_τ$ model, which predicts a new massive gauge boson, $Z'$, on astrophysical neutrino events at the IceCube Observatory. This new gauge boson couples with leptons from the second and third families, and would break the power law of the astrophysical neutrino flux due to the interaction of this flux with the cosmic neutrino background. We derive the sensitivity of the IceCube to this model considering the HESE data from 12 years of observation by assuming different assumptions for the redshift distributions of astrophysical neutrino sources, mass ordering, and sum of neutrino masses. Our results indicate that the current IceCube data is able to probe small coupling and masses of the order of some few MeV, with the covered parameter space being larger if a distribution of neutrino sources is described by the star formation rate model. In addition, we demonstrate that the IceCube-Gen2 will cover a large region of the parameter space and will allow us to improve our understanding of the $L_μ- L_τ$ model.

Figures (6)

• Figure 1: Neutrino flux as a function of neutrino energy, considering a $Z'$ boson with $m_{Z'} = 10$ MeV and spectral index $\gamma = 3.0$. Left: Comparison between SFR and BLL redshift distributions for neutrino sources, assuming Normal Ordering and upper mass limit. Middle: Comparison between Normal Ordering (NO) and Inverted Ordering (IO), assuming SFR as the neutrino source and upper mass limit. Right: Comparison between upper limit and lower limit for mass sum, assuming SFR as the neutrino source and Normal Ordering.
• Figure 2: Number of events in the HESE at IceCube Observatory as a function of deposited energy (left) and azimuthal angle (right) per 12 years. Each color of the histogram specify different contributions to the events, accordingly to the best fit parameters: astrophysical neutrinos (yellow), atmospheric neutrinos (red) and atmospheric muons (purple). In the blue dashed line, we present our results for the best fit obtained considering a $Z'$ boson with mass of 6 MeV, Inverted Ordering, BLL for the redshift distribution and superior limit for the mass sum.
• Figure 3: Results for the sensitivity of HESE data at IceCube Observatory for the astrophysical neutrino flux to the presence of the $Z'$ gauge boson predicted by the $L_\mu - L_\tau$ model, derived considering a normal ordering of neutrino masses. Predictions, at the $2\sigma$ level, obtained considering the redshift distribution of BLL (left panels) and SFR (right panels), and the superior (upper panels) and inferior (lower panels) limits for sum of neutrino masses. For comparison, the existing constraints from other processes and experiments are also presented. The green bands represent the parameter space in which the presence of a $Z'$ solves the muon magnetic moment anomaly at the $1\sigma$ and $2\sigma$ levels.
• Figure 4: Results for the sensitivity of HESE data at IceCube Observatory for the astrophysical neutrino flux to the presence of the $Z'$ gauge boson predicted by the $L_\mu - L_\tau$ model, derived considering an inverted ordering of neutrino masses. Predictions, at the $2\sigma$ level, obtained considering the redshift distribution of BLL (left panels) and SFR (right panels), and the superior (upper panels) and inferior (lower panels) limits for sum of neutrino masses. For comparison, the existing constraints from other processes and experiments are also presented. The green bands represent the parameter space in which the presence of a $Z'$ solves the muon magnetic moment anomaly at the $1\sigma$ and $2\sigma$ levels.
• Figure 5: Results for the sensitivity of HESE data expected at IceCube-Gen2 Observatory for the astrophysical neutrino flux to the presence of the $Z'$ gauge boson predicted by the $L_\mu - L_\tau$ model, derived considering a normal ordering of neutrino masses. Predictions, at the $2\sigma$ level, obtained considering the redshift distribution of BLL (left panels) and SFR (right panels), and the superior (upper panels) and inferior (lower panels) limits for sum of neutrino masses. For comparison, the existing constraints from other processes and experiments are also presented. The green bands represent the parameter space in which the presence of a $Z'$ solves the muon magnetic moment anomaly at the $1\sigma$ and $2\sigma$ levels.