November 2020 Issue

Details: Category: Бюллетень "Глобальная нейтринная сеть"; Published: 04 December 2020

News from ANTARES

As reported in the August edition of GNN Monthly, one of the ANTARES lines (continuously working since 2007, and the Junction Box to which the line is connected since 2001) failed to communicate with the shore station, so that ANTARES had to continue data taking with only 10 active lines. Since ANTARES will likely be dismantled during 2021, no attempt was planned to repair the fault. However, in November the collaboration could benefit from a sea campaign of the Victor submarine and performed a maintenance operation. Indeed they have been able to reconnect the line to the detector, so ANTARES is again data taking with all 11 lines!

APC and Université Paris are organizing an online workshop “Cosmic Rays and Neutrinos in the Multi-Messenger Era” at December 7-11 (see https://indico.in2p3.fr/event/20789/overview). The workshop aims to bring together the communities working on high-energy cosmic rays and neutrinos, covering experimental, theoretical and phenomenological aspects. In addition to detailed presentations of theoretical models dealing with the production of cosmic rays and astrophysical neutrinos, the workshop will include reviews of the latest experimental results as well as prospects for the next decade. Each session will end with a general discussion of the presented results. Additionally there will be two poster sessions for PhD students and young researchers.

News from Baikal-GVD

Since ICRC 2019, the Baikal Collaboration hasn’t posted papers on arXiv because analyses of the first data taken with Baikal-GVD were still ongoing. Now a talk of Dmitry Zaborov from INR Moscow with the title High-energy neutrino astronomy and the Baikal-GVD neutrino telescope has been posted at https://arxiv.org/pdf/2011.09209.pdf. The paper reviews the scientific case for Baikal-GVD, the construction plan, and first results from the initial configuration (meanwhile about 2000 optical modules at 56 strings). Results include the zenith angle distribution for the first sample of upward moving muons from neutrino interactions, as well as a smaller sample of energetic cascade events, where one of them comes from below horizon and has an energy deposit of 91±10 TeV. This appears to be a very clear neutrino candidate, with a high chance to be of astrophysical origin (see the reports in previous GNN Monthly editions).

Preparation of the Baikal deployment campaign from February to April is well underway. All optical modules for the two news clusters have been assembled, and half of them already arrived in the town Baikalsk. The electronic modules (section-, string- and cluster-controllers) have also been fully assembled and are under long-term test in Moscow.

The autumn collaboration meeting (online) is ongoing from November 30 to December 4.

News from IceCube

First 2021 winterover at the Pole! After more than a week delay due to bad weather and repeatedly cancelled flights, the first of the two winterovers made it to the South Pole. Martin Wolf arrived at November 24, and there is hope that Josh Veitch-Michaelis will follow it this week.

Meanwhile, in early November, the 32nd annual Holiday Fantasy in Lights event in Madison has opened. The picture below shows the IceCube Laboratory, this time not at the Pole but in the Madison Olin park.

News from KM3NeT:

A second junction box (JB) has been successfully connected to the KM3NeT/ORCA seafloor network. It was deployed to within a metre of its nominal position at a depth of 2450 m.

The junction box provides the power to the strings (“Detection Units” or “DUs” in KM3NeT language) and distributes/collects the optical fibres used for the data transmission. The shore cable (“main electro-optic cable” or “MEOC”) provides the input power on a single conductor at 3300 VAC which is transformed in the JB to 400 VAC to power the DUs. The power return is via the sea. The JB provides eight wet-mateable output connectors to which the DUs or Earth and Sea Sciences instrumentation (ESS) are connected via so called interlink cables. Four DUs are daisy-chained to a single connector, so a single JB can connect up to 32 DUs. The JB was in fact ready since spring 2020 but due to COVID restrictions its connection was delayed until now.

The campaign took place at Oct 16-24. The operation was quite complex involving the coordination of three ships: i) The huge cable-layer ship Raymond Croze (click Raymond Croze - Orange Marine) from the Orange Marine Company which managed the deployment of the junction box and the jointing of the main electro optical cables on the input and output of the junction box. ii) The Castor boat from Foselev Marine Company which managed the output main electro optical cable which, in a future operation, will be connected to a dedicated ESS junction box. iii) The Onyx boat, also from Foselev Marine, which took care of the precision acoustic positioning of the junction box during its installation on the sea floor.

The CPPM team with the assembled and tested Junction Box

The three vessels in operation

The Junction box being lifted over the railing

During the sea operation one end of the output MEOC was transferred from the Castor to the Raymond Croze for jointing (first time the ANTARES/OCRA team has done that) and then the Castor lowered the output cable in synchronisation with the lowering of the JB. All in all, three joints were made; each joint requiring the splicing of up to 36 optical fibres and taking about 24 hours including encapsulation and X-ray control of the joint. The operation included also a weather standby of 36 hours.

Deploying the junction box

The connection of the new junction box doubles the capacity of the ORCA seafloor network to connect DUs. In order to complete the ORCA sea floor network, two more JBs will be needed; these will be connected to the MEOC currently being used by the ANTARES telescope, once it is decommissioned and the extremity of the MEOC rerouted to the KM3NeT/ORCA site.

The present configuration of the KM3NeT/ORCA site: N1 is the first junction box. The present six ORCA DUs (top left) are linked to this JB. Cable 1 (“MEOC-1”) connects N1 to shore. N2 is the new junction box. Cable 2 will be the relocated ANTARES shore cable. MII, BJS, NSVT are earth and sea science instrumentation.
Mission accomplished! Happy CPPM members, from left to right: Michel Billault, Paschal Coyle, Patrick Lamare, Michel Ageron, Damien Dornic.

A short drone video of the deployment part of the sea operation can be viewed here.

A great idea and wonderful results! The KM3NeT Collaboration has made a call for a drawing competition “Draw me a neutrino”. Now, the winners of the competition have been announced. More than 500 drawings were submitted from 16 different countries (from KM3NeT member or observer states Australia, Ecuador, France, Georgia, Greece, Italy, Morocco, Netherlands, Russia and Spain but also from Belgium, Bulgaria, Canada, India, Switzerland and UK).

The drawings, realized using various techniques and supports, have been judged based on their originality, the creativity of the realization, and the harmony with the properties and origin of the neutrino.

Three different age categories had been defined:

Budding scientists imagined what an electron neutrino is like;
Teenagers, that have already been in contact with physics, were charged with drawing a muon neutrino;
Adults were invited to tackle the tau neutrino.

The results were announced during an online ceremony attended by more than 150 people. The two winners in each category, as well as the drawings selected for the various contests, are now part of an online exhibition in the Virtual Neutrino Art Centre (hub.link/ZZwzhf7).

Through this contest, the KM3NeT Collaboration was seeking to familiarize a broad public with the science to be carried out by KM3NeT. 60% of the participants learnt about neutrinos for the first time, and 86% of them discovered the existence of the KM3NeT project.

More information about the contest, the rules, and the winners can be found on: http://wos.ba.infn.it Here just two of them, taken from Results – Draw me a neutrino (infn.it).

2nd place , International contest, category “muon neutrino”: “The birth of my Cosmic Muon-Neutrino”, by Maria N. Pavlopoulou, Greece (spray art)

1st place, World contest, category “tau neutrino”: “Once in a life time”, by Vs. sai Karthik, India

Publications

1 The IceCube collaboration has submitted a paper Search for sub–TeV neutrino emission from transient sources with three years of IceCube data to the Journal of Cosmology and Astroparticle Physics (see https://arxiv.org/abs/2011.05096). Transient sources emit neutrinos primarily within a relatively short window of time. This is the first transient result from IceCube to use all neutrino flavors in the 1-100 GeV energy range.

The analysis uses the GRECO event selection (GRECO stands for “GeV Reconstructed Events with Containment for Oscillation”). This selection was originally developed for the (published) tau neutrino appearance analysis. The next figure shows the effective area as a function of energy.

All sky (4π) average neutrino effective area for the GRECO event selection. The effective area of the previous low-energy transient analysis from IceCube, which was made only for νµ , is indicated by the purple dashed line.

The analysis has used neutrino data collected with DeepCore, the densely instrumented inner region of IceCube, between April 2012 and May 2015 and searched for any low-energy neutrinos that were coincident in time and direction in a way that indicated a neutrino emission from a transient astrophysical phenomenon. Note that at such low energies the directional accuracy is only in the 10°-40° range, so time coincidence is the dominant factor of background rejection (time bandwidth chosen for GRBs is 100 seconds)

Top candidates for transient sources are Gamma-Ray Bursts. Some scenarios predict that GRBs emit neutrinos of low energies (~10-100 GeV) without the usual gamma ray counterpart. This could happen, for example, if relativistic GRB jets are “choked off” by a dense envelope of matter before they become visible via their bright gamma-ray appearance; even if gamma rays cannot make it out, neutrinos (especially low-energy neutrinos) can get through and reach Earth.

Over the three years no signature of transient neutrino emission has been found, resulting in an upper limit on the volumetric rate (i.e. transients in a volume of space per year) of 700-2300 Gpc−3 yr−1 for sources having a sub-photospheric energy spectrum with a mean energy of 100 GeV and a bolometric energy of 1052 erg.

New upper bounds on the volumetric rate of transient neutrino point sources as a function of their bolometric neutrino energy that were determined from this analysis. This is compared to models for high- and low-luminosity gamma-ray bursts (Murase et al. 2013; Liang et al. 2007). The light blue bands cover the declination dependencies of the upper bounds. The figure shows results based on sources with a mean energy of 20 GeV.

The figure demonstrates that the limit is still a factor 3-5 away from most optimistic model predictions for GRBs. However, further improvements in analysis methods, use of data from more than three years and in particular the planned compactification of DeepCore (“IceCube Upgrade”) will clearly allow testing the High Luminosity prediction (red star in the figure). Moreover – while this analysis was optimized for a specific class of GRBs – it is also sensitive to many other transient neutrino emitters that may exist in the sub-TeV region but have not yet been predicted by theorists.

Presently the analysis method is being adapted to a real-time analysis. It would complement the existing high-energy, real-time alert systems installed at the South Pole. The present alert system notifies observatories around the world whenever IceCube sees a high-energy (TeV-PeV) neutrino-candidate event that meets certain criteria; adapting this analysis would extend the alerts’ energy range down to 10 GeV, opening up a new, unexplored energy regime for real-time follow-up.

2 GNN readers will remember the paper Measurement of the multi-TeV neutrino interaction cross-section with IceCube using Earth absorption, posted at https://arxiv.org/abs/1711.08119 and published on November 22, 2017 in Nature). There, about 11,000 energetic upward-going neutrino-induced muons have been analysed to study the attenuation of the parent-neutrinos when transiting long paths through the Earth and to estimate their cross section. Soon later, Mauricio Bustamante and Amy Connolly used published HESE events with energies > 18 TeV to derive differential cross sections (rather than an integrated one, like in the Nature publication), see 1711.11043.pdf (arxiv.org) and the figure below.

Neutrino-nucleon charged-current cross section, averaged for neutrinos and anti-neutrinos, from different predictions (lines), compared to measurements from this work (stars). The low-energy global average (dashed light-gray line) has a linear dependence on Eν below ∼10 TeV. The prediction of a model of large extra dimensions (dashed dark-gray line, from Alvarez-Muniz, Halzen, Han, Hooper, Phys. Rev. Lett. 88, 021301) is included for illustration and was here corrected to match modern standard predictions of the cross section below 1 PeV. (Figure taken from the Bustamante and Connolly paper)

In a new paper Measurement of the high-energy all flavor neutrino-nucleon cross section with IceCube (https://arxiv.org/abs/2011.03560) submitted to Phys. Rev.D) the neutrino cross section between 60 TeV and 10 PeV is determined by using the high-energy starting events (HESE) sample from IceCube with 7.5 years of data.

The result is binned in neutrino energy and obtained using both Bayesian and frequentist statistics. As in the 2017 analysis, the cross section turns out to be compatible with predictions from the Standard Model. Flavor information is explicitly included through updated topology classifiers. This is the first such measurement to use the three topologies as observables.

Neutrino-nucleon cross section as a function of energy. The black and blue lines show two predictions based on the formalism of the Standard Model. The gray shaded region indicates the result of the previous IceCube measurement based on up-going muon tracks (published 2017 in Nature).

Most of the large error is due to limited statistics. This, of course, will fundamentally improve with IceCube-Gen2.

3 A paper Measurement of Astrophysical Tau Neutrinos in IceCube’s High-Energy Starting Events has been posted at https://arxiv.org/2011.03561. The same 7.5 years of HESE events as in the previous paper have been used to search for signatures of double-bang events where the first bang emerges from a tau-neutrino charged current interaction and the second from decay of the tau lepton generated in that interaction. Two candidate events have been found, with probabilities of ∼ 98% and ∼ 76% of being produced by astrophysical tau neutrinos. The two events have already been shown on numerous conferences. In this paper, remaining uncertainties have been fixed. Here areOn the next column again the two central figures of the paper.

The well known double cascade event (98% probability to stem from a tau neutrino interaction). The two vertices are indicated by brown circles (17 m away), the arrow indicates the direction. The event view is surrounded by five waveforms which indicate a double-pulse form.

Measured flavor composition of IceCube HESE events with ternary topology identifier and an extended multi-dimensional analysis of the double cascades (black star and lines). Contours show the 1σ and 2σ confidence intervals. The shaded regions show previously published results which had no direct sensitivity to the tau neutrino component. Flavor compositions expected from various astrophysical neutrino production mechanisms are marked, and the entire accessible range of flavor compositions assuming standard 3- flavor mixing is shown.

The resultant astrophysical neutrino flavor measurement is consistent with expectations, disfavoring a vanishing astrophysical tau neutrino flux scenario with 2.8σ significance and being consistent with a ratio ν_e : ν_µ : ν_τ = 1 : 1 : 1.

4 Another paper on the 7.5 years HESE sample: The IceCube high-energy starting event sample: Description and flux characterization with 7.5 years of data. This is an extensive 57-page work, posted at https://arxiv.org/abs/2011.03545. It revisits the analysis of the HESE sample with an additional 4.5 years of data, newer glacial ice models, and improved systematics treatment. The paper describes the sample in detail, reports on the latest astrophysical neutrino flux measurements, and presents a source search for astrophysical neutrinos. Also it gives the compatibility of these observations with specific isotropic flux models proposed in the literature as well as generic power-law-like scenarios. Assuming ν_e : ν_µ : ν_τ = 1 : 1 : 1. and an equal flux of neutrinos and antineutrinos, the astrophysical neutrino spectrum is found to be compatible with an unbroken power law, with a preferred spectral index of 2.87±0.20 for the 68.3 % confidence interval.

Here are some illustrative figures from the paper.

Impact of systematic uncertainties on the single power-law parameters (astrophysical spectral index, left and normalization, right). The impact (horizontal axis) is defined as the change in the parameter of interest relative to its uncertainty when modifying one systematic nuisance parameter. Orange bars indicate the effect of increasing the value of the nuisance parameter from its maximum a posteriori value by 1σ as defined by the nuisance parameter’s 68.3 % highest posterior density region, while purple bars indicate the corresponding reduction of the parameter. The prompt normalization (Φprompt) and DOM efficiency (εDOM) have the largest effect on the astrophysical parameters. All other systematics pull the astrophysical parameters by significantly less than 0.5σ (see the paper for more than the self-explaining notations).

The well-known fit of three components to the cosine of the measured zenith angle distribution: astrophysical and atmospheric neutrinos plus a background contribution of atmospheric muons.

The same, but now with the attempt to fit the distribution without astrophysical neutrinos. This requires a huge contribution of “prompt” atmospheric neutrinos from charm decays, but still is not able to describe the angular distribution (form of the charm distribution fixed, normalization fitted).

Distribution of the deposited energy, also fitted under the assumption of a zero flux from astrophysical neutrinos and fixed form of the prompt neutrino spectrum. Most of the distribution, with the exclusion of the three most energetic events (Ernie, Bert and Bigbird), can be covered by prompt atmospheric neutrinos. This demonstrates the importance of the angular distribution shown above for the conclusion about the existence of a cosmic neutrinos flux.

The last figure shows contour plots for the fitted parameters, assuming a single-power law for the astrophysical flux.

Contour plots for the fitted parameters, assuming a single-power law for the astrophysical flux. Shown are probability plots for bottom: prompt flux versus power index and normalization of astrophysical flux (right the projection to the prompt flux), middle: normalization of astrophysical flux versus its power index, and projection to the astrophysical flux, top: projection to the power index of the astrophysical flux. The innermost contours show the two-dimensional 68.3 % highest posteriori density (HPD) region, and the outermost contours the 95.4 % HPD region. The grayscale of the histogram within the contours shows the probability density in an arbitrary scale. See the paper for more information.

Similar figures are given for double-power law spectra (with the parameters flux hard/soft and power index hard/soft) and for comparing different source models with each other.