November 2021 Issue

Details: Category: Бюллетень "Глобальная нейтринная сеть"; Published: 16 December 2021

News from the experiments

KM3NeT

1) Sea campaign completed - 10 detection units in operation at ORCA!

At November 22, a successful sea operation at the ORCA site was completed. The campaign had started at Nov. 18. After a stand-by of 24 hours, due to uncertain weather conditions, the Castor and the Janus vessel left the French coast and headed to the KM3NeT/ORCA site. Onboard the Castor were seven new detection units (DUs) and one autonomous acoustic beacon. The Janus was instead equipped with a Remotely Operated Vehicle (ROV), which was maneuvered from the ship to perform the deep-sea action: inspection of the submarine structures and connections of the new detection units to the already installed submarine network.

The two ships in action at the ORCA site: Castor (in the foreground) and Janus (in the background).

The plan was to deploy as many DUs as the weather allows. At the end, four new DU have been deployed, the last two on Nov. 22. As the sea condition rapidly degraded during the day, it was decided to terminate the campaign. The remaining detection units on deck will be saved for next time.

The final outcome of the campaign is: ORCA enlarged from 6 to 10 detection units!

The team onboard the Castor showing the ’10’ sign in front of a recovered launcher vehicle.

See also the KM3NeT blog on the sea operation: https://www.km3net.org/category/blog/

Congratulation to the heroic teams who have made such great effort onboard the two ships and in the shore station. And now: on to resume data taking with an enlarged ORCA-10!

2) KM3NeT/ANTARES collaboration meeting

Last week the collaboration met for its Fall meeting – the 5th to be organized online. Many new data analyses were presented, and more than 120 participants connected to the sessions.

The KM3NeT collaboration welcomed three new institutes in the Collaboration:
– University of Sharjah, Abu Dhabi, UAE (having had already an observer status before);
– Lebedev Physical Institute, Russia;
– UC Louvain, Belgium.
The new institutes will work on various topics ranging from neutrino astronomy to neutrino physics and also contribute to the detector construction.

Finally, the collaboration celebrated 6 months of ARCA data taking with 6 detection units. For that occasion, some of the artists in the KM3NeT collaboration prepared a 6–hand piano piece. Go to Online but happy collaboration meeting! - KM3NeT and enjoy!

Baikal-GVD

No news. DOM production is running normally. If you can read Russian or just like nice photos, you may go to Нейтринный телескоп Baikal-GVD: как изучают Вселенную на Байкале (verbludvogne.ru). (Neutrino telescope Baikal-GVD: how to investigate the universe at Lake Baikal). “Verblud v ogne” is the name of the Irkutsk city journal. One of the photos shows the old wooden house, the former home of the shore station (center), together with the new shore station (right).

IceCube

On October 24, the first USAP Basler airplane arrived at the South Pole. It came from the British Rothera station on Adelaide Island (close to the Antarctic Peninsula) and refueled at the Pole on its way to McMurdo. It also took the first two of the 39 winter-overs back to McMurdo.

Two winterovers boarding the Basler. These modified DC-3 aircrafts have been in service since WW2, though significantly upgraded since then. As you can see from the decal, this plane has been operating for 50 years!

The present IceCube winterovers Martin and Josh got their COVID vaccine (not existing yet last November) on October 28. The new winterovers Moreno and Celas arrived on November 4 and 5.

Martin and Josh vaccinated

Good news for the IceCube Upgrade project: a) A second shipment south was sent from Madison last week. b) A logistics review concluded with panel recognizing the experience and strength of the team. c) The Madison team is working with NSF on a logistics support plan. The project office is optimistic that they can agree on three more field seasons beginning November 2022 which would put the installation of all 7 strings beginning December 2024. d) And, last but not least, the production of the d-egg optical modules in Japan is complete!

Good news for IceCube-Gen2: The Astro2020 decadal report on the US came out. It is broadly positive to IceCube-Gen2. See Decadal Survey on Astronomy and Astrophysics 2020 (Astro2020) | National Academies.

Some citations:

The panel sees a compelling opportunity to dramatically open the discovery space of astronomy
through a bold, broad multi-messenger program, with three components:

∙ Neutrino program: A large-scale (MREFC) investment by the National Science Foundation (NSF) in IceCube-Gen2, to resolve the bright, hard-spectrum, TeV–PeV diffuse background discovered by IceCube into discrete sources and to make first detections at higher energies.

∙ Gravitational-wave program and gamma-ray program: see the full text of the decadal survey.

Also, with a positive reference to technologies for PeV-ZeV energies:

To develop discovery-class observatories for astrophysical neutrinos over a wide energy range, the panel endorses continued growth in this field under U.S. leadership. The centerpiece would be IceCube-Gen2; compared to IceCube—one of the largest, most successful, and most visible NSF investments—it would have greatly increased sensitivity while having a comparable RY cost. IceCube- Gen2 is designed to resolve IceCube’s observed TeV–PeV diffuse background into sources and to open new frontiers at higher energies, up to the EeV–ZeV range. In addition, as discussed in Section L.4.4, the panel also endorses technology development that may facilitate even larger future experiments at those higher energies.

And, for aficionados of bold projections to the future, the report has the following figure … ?

Publications

The IceCube Collaboration has submitted a paper Search for Quantum Gravity Using Astrophysical Neutrino Flavour with IceCube (posted at 2111.04654.pdf (arxiv.org)).

GNN readers may remember the paper Neutrino Interferometry for High-Precision Tests of Lorentz Symmetry with IceCube, Nature Phys. 14, 961–966 (2018), 1709.03434.pdf (arxiv.org). There, high-energy atmospheric neutrinos in IceCube have been used to search for anomalous neutrino oscillations as signals of Lorentz invariance violation, see the next figure. Violation of Lorentz Symmetry would be induced by a new space-time structure at the quantum gravity scale. These effects would develop stronger over large distances (vertical neutrinos) than for short distances (horizontal neutrinos). No effects beyond the standard oscillation assumption have been observed and limits on the LIV operators in the Hamiltonian derived.

Instead of atmospheric neutrinos, the present analysis uses a neutrino sample dominated by cosmic neutrinos which are affected along their way by quantum gravity effects (see next figure).

Here, high-energy astrophysical neutrinos (shown by a long arrow) from 60 TeV to 2 PeV are assumed to be emitted from distant high-energy sources. The neutrino propagation may be affected by space-time defects which can be viewed as an aether-like media in vacuum. In general, these defects have directions depicted by red arrows but are assumed to be isotropic in this analysis.

The effective Hamilton operator including Quantum Gravity effects is assumed to have the form

The first term in this Hamiltonian describes the neutrino mass term (assuming the normal mass ordering), the other terms are possible new physics operators with different energy dependence. All terms are 3×3 complex matrices (according to 3 neutrino flavors). The solution of this Hamiltonian describes the evolution of neutrino flavors. Since the energy of IceCube’s cosmic neutrinos is much higher than that of accelerator neutrinos, superior limits can be achieved for the E² and E³ terms.

The present analysis puts limits to the E³ terms. It starts from the astrophysical neutrino flavor triangle, derived in the paper Measurement of Astrophysical Tau Neutrinos in IceCube’s High-Energy Starting Events, (2020), https://arxiv.org/pdf/2011.03561.pdf Which has been presented in GNN Monthly a year ago.

The figure below is taken from the Quantum Gravity paper discussed here and reproduces the 68% and 95% C.L. contours from the 2020 tau neutrino analysis as blue solid and dashed lines.

The pink region represents expected flavor ratios from the standard astrophysical neutrino production, i.e. all parameters \(\mathring{a}^{(3)} ... \mathring{c}^{(6)}\) vanishing. The three empty circles denote the standard physics compositions on Earth for flavor ratios of 1:0:0, 2:1:0 and 1:0:0 in the source, respectively. If the \(\mathring{c}^{(6)}\) parameters are raised smoothly from 0 to 1, the flavor ratios move along the colored lines, ending for c⁽⁶⁾ = 1 in the circles with the dot in their center (see the explanation in the legend). From the shown contours, record limits on the various c⁽⁶⁾ parameters for new physics have been derived – see the paper for their values and for a comparison to previous limits.

The IceCube collaboration has now posted on the archive the Nature paper on the observation of a neutrino event with the energy just on the Glashow resonance (Nature 591 (2021) 220), so it now is available to everybody: 2110.15051.pdf (arxiv.org). Since the Nature paper has been presented already in GNN Monthly, I just reproduce the most essential figure from the paper. It shows in the top part the posterior probability density of the visible energy for this event and at the bottom the expected Monte Carlo event distributions in visible energy of hadrons from W− decay (GR h., blue), the electron from W− decay (GR e., orange), charged-current interactions (CC; red) and neutral-current interactions (NC; green) for a live-time of 4.6 years and assuming the ratio anti-ν : ν = 1 : 1, a flavor ratio of 1 : 1 : 1 at Earth, an astrophysical spectrum as measured by IceCube, and cross-sections according to Cooper-Sarkar, Mertsch and Sarkar.

The measured energy of the event is 6.05 ± 0.72PeV and the p-value against backgrounds of the order of 0.01. The number of expected Glashow events for a spectral index of -2.5 and a normalization of 2,3 × 10⁻¹⁸ GeV⁻¹ cm⁻² s⁻¹ sr⁻¹ is 1,55.

The next three IceCube papers all appeared on the archive on November 22:

Search for GeV-scale Dark Matter Annihilation in the Sun with IceCube DeepCore (2111.09970.pdf (arxiv.org)). The Sun provides an excellent target for studying spin-dependent dark matter-proton scattering due to its abundant hydrogen content. Dark matter particles can elastically interact with Solar nuclei, be captured and thermalized. The captured dark matter can annihilate into Standard Model particles including an observable flux of neutrinos. The paper presents the results of a search for low-energy (< 500 GeV) neutrinos correlated with the direction of the Sun using 7 years of IceCube data. It utilizes, for the first time, new optimized cuts to extend IceCube’s sensitivity to dark matter mass down to 5 GeV. No excess of neutrinos from the Sun is observed, excluding the capture by spin-dependent dark matter-proton scattering with cross-section down to a few times 10^-41 cm² (assuming there is equilibrium with annihilation into neutrinos/anti-neutrinos for dark matter masses between 5 GeV and 100 GeV). For dark matter annihilation directly into ν-anti-ν, these are the strongest constraints at GeV energies:

The paper A search for neutrino emission from cores of Active Galactic Nuclei is posted at 2111.10169.pdf (arxiv.org).

The sources of almost all high-energy astrophysical neutrinos observed with IceCube are still unknown. Only the gamma-ray blazar TXS 0506+056 could be associated with neutrino emission, while several studies suggest that the neutrinos from all gamma-ray blazars can only account for a small fraction of the total astrophysical flux. The present work probes the production of high-energy neutrinos in the cores of Active Galactic Nuclei, induced by accelerated cosmic rays in the accretion disk region. The likelihood analysis is based on eight years of IceCube data and searches for a cumulative neutrino signal from three (overlapping) AGN samples, created for this work. See the paper for the justification to study just these samples and the next figure showing the overlapping.

The neutrino emission is assumed to be proportional to the accretion disk luminosity estimated from the soft X-ray flux. Next to the observed soft X-ray flux, the objects for the three samples have been selected based on their radio emission and infrared color properties. For the largest sample in this search (IR-selected AGN), an excess of high-energy neutrino events with respect to an isotropic background of atmospheric and astrophysical neutrinos is found, corresponding to a post-trial significance of 2.60 σ (for the other two samples it is only 1.6 and 1.0 σ). Assuming a power-law spectrum, the best-fit spectral index for the IR selected AGN sample is 2.03 (+0.14, -0.11), consistent with expectations from particle acceleration in astrophysical sources, see next figure.

The figure suggests that at 100 TeV, 27% to 100% of IceCube’s astrophysical neutrinos arise from particle acceleration in the core of AGN.

The paper Improved Characterization of the Astrophysical Muon-Neutrino Flux with 9.5 Years of IceCube Data is posted at 2111.10299.pdf (arxiv.org).

The measurement uses a high-purity selection of 650k neutrino-induced muon tracks from the Northern celestial hemisphere, corresponding to 9.5 years of experimental data. With respect to previous publications, the measurement is improved by the increased size of the event sample and the extended model testing beyond simple power-law hypotheses. Updated treatment of systematic uncertainties and atmospheric background fluxes have been implemented based on recent models. The best-fit single power-law parameterization for the astro-physical energy spectrum results in a flux at 100 TeV of

1,44± 0,25 × 10^-18 GeV^-1 cm^-2 s^-1 sr^-1and a spectral index of 2.37±0.09, constrained in the energy range from 15 TeV to 5 PeV. The spectral index is a bit larger (but compatible with) the spectral index presented five years ago (2.13±0.13).

In addition to the single power law, the data have been fitted to several other models, including a single power law with a spectral cutoff at high energies, a log-parabola model, several source-class specific flux predictions from the literature and a model-independent spectral unfolding, see the next figure.

The data is well consistent with a single power law hypothesis. Interestingly, spectra with softening above one PeV are statistically more favorable at a two-sigma level.

The KM3NeT Collaboration has submitted a paper Nanobeacon: A time calibration device for the KM3NeT neutrino telescope to the Journal Microsystems & Nanoengineering, posted at https://arxiv.org/pdf/2111.00223.pdf.

KM3NeT requires relative time synchronization between photomultipliers of the order of 1 ns which is needed to guarantee the required angular resolution of the detector. Due to a large number of optical modules, cost reduction of the different KM3NeT systems is a priority. To this end, an inexpensive Nanobeacon has been designed and developed. At present, more than 600 Nanobeacons have been already produced. The paper describes the main features of the Nanobeacon design, production and operation, together with the main properties of the light pulse generated, angular profile, pulse form (see below) and wavelength emission profile.