September/October 2020 Issue

Details: Category: Бюллетень "Глобальная нейтринная сеть"; Published: 07 September 2020

News from Baikal-GVD

The Baikal collaboration is preparing to deploy up to 2 clusters with a total of 288 optical modules on each cluster in the upcoming field season. While the production is somewhat behind schedule due to Covid-19, Оptical Modules and Control Modules for somewhat more than one cluster have been assembled. Presently, the Control Modules are in long-term testing.

An improved understanding of upward going muons from interactions of atmospheric neutrinos has been achieved over the summer time. The figure below shows the zenith angle distribution of 57 neutrino candidates, based on data from 323 cluster × days taken during low-light background periods. This agrees well with MC expectations (54.3 events from atmospheric neutrinos and < 1 misreconstructed down-going muon).

Note that the events close to horizon (cosine of zenith angle = 0) do not pass the analysis. This is a lever-arm effect, since the diameter of a cluster is small compared to its length. More horizontal events are triggered but hard to separate from background. This situation is expected to improve by merging data from several clusters for event reconstruction and background rejection.

The Dubna group has set up a popular scientific webpage “Baikal GVD: Neutrino Hunters” at https://dlnp.jinr.ru/en/baikal-gvd/okhotniki-za-nejtrino. The webpage includes a series of educational videos, covering the construction of GVD, the physics behind the experiment, and interviews with people involved (the interviews in Russian). To quote the authors: “This series illustrates all the serious and funny, the magnificent and ordinary, the simple and complicated—everything that the people face striving to reveal the next mystery of the Universe.”

Most of the photos have been taken by Bair Shaibonov (Dubna) – like the following, taken with a telephoto lens and opening a spectacular view on the mountains 60 km away on the opposite shore of the Lake.

News from KM3NeT

The upgrade of the Capo Passero shore station has been completed to a large part. With the shore station operating, the one string (aka Detection Unit, DU) which is in the water since 2015 could now be powered on again, with 17 out of 18 DOMs properly functioning. The Collaboration is planning to deploy new Junction Boxes and up to 18 DUs in 2021.

Almost all DOMs for ARCA Phase 1 have been assembled (instrumentation for about 22 out of 24 DU's). The assembly of the five next DUs is currently proceeding in parallel. One of them is already wound on the launcher module, i.e. fully ready for deployment – see the picture. Currently, the team is also on schedule for completing the five DUs on time (provided no bad COVID-19 surprises!).

The communication of the DU to shore, via bottom cables and Junction Box, is done by the so-called base module shown on the next picture.

Last but not least, a fully tested prototype version of the new Junction Box is ready since July (see GNN Monthly of July 2020) and will be deployed in April 2021. Later this prototype will be replaced by the final version of the Junction Box.

The junction box will be carried by a frame made of titanium, see the figure. This frame is also ready for deployment. It houses an interlink cable, equipped with wet-mateable connectors, and the base container. The base container incorporates dedicated optical components and an acoustic receiver used for positioning of the detector elements.

So much on KM3NeT-ARCA…

KM3NeT-ORCA Phase-1 has been in continous operation since 8 months with an average data taking efficiency approaching 99%. Additional DUs are expected to be deployed in 2021.

During the last week of September and the first week of October the second KM3NeT Remote Collaboration Meeting has been organized. During this meeting, the new Management has been elected. Its term begins in February 2021: Paschal Coyle is the next Spokes-person, Rosa Coniglione his Deputy, Aart Heijboer the Physics Coordinator and Miles Lindsey Clark the Technical Coordinator (see the picture, from left to right).

Congratulations and good luck for you four!

News from IceCube

Pole Operations:

This year it is a rocky road to get the new Winterovers to the Pole: COVID-19 is the big enemy, as everywhere! Nobody from IceCube except the two Winterovers will go to the Pole this season. At the time of this writing the two – Martin Wolf and Josh Veitch-Michaelis – are down in Christchurch doing their teambuilding. Both WOs are non-US nationals, which created some Covid related travel problems, on top of the multiple quarantines: they started their journeys more than a month ago from Munich (Martin) and London (Josh), went to San Francisco and quarantined there twice. Now they are in quarantine #3 in Christchurch, New Zealand. They should arrive at Pole by early November. One of the current WOs will stay through the end of January to complete the training which had to be done via Zoom and was cut short by the September travels.

In this context: at early November a call for next year's WO crew will be posted. To the younger readers of GNN Monthly: Feel free to apply!

Maintenance and Operation of IceCube are minimally impacted: the operating system upgrade for the Pole computing system is deferred by one year, as well as a major overhaul in the online processing and filtering. Also plans for surface scintillator deployment have to be shifted to the following season.

The drill hose for the 7-string upgrade was delivered by the same Italian company that made it for the present IceCube. It is now in Port Hueneme at the Californian coast (From this harbour, the ships to the Antarctic McMurdo station are leaving the USA). The drill hose will likely go in January 2021 to McMurdo.

(thanks to Kael Hanson for providing this information)

Collaboration Meeting:

The IceCube Collaboration had its Fall Collaboration Meeting as virtual meeting, September 14-25.
Meanwhile at the Pole: the Sun is rising and rising (photo sent by WO Yuya Makino)

IceCube Augmented Reality:

Thanks to a new augmented reality (AR) app, anyone in the world now can see what is happening deep in the ice. IceCubeAR shows you real IceCube events projected onto the environment around you through your phone screen. Users of the app will get alerts about neutrino candidate events in close to real time. See for more information (including a “how to use”) the IceCube News at https://icecube.wisc.edu/news/view/776.

The project was headed by IceCube collaborator Lu Lu, postdoc at Chiba University, with co-developers Colin Baus, Vsevolod Yugov, and Thomas Hauth. Search 'ICEcuBEAR' in Google playstore or Apple appstore to get the app.

Top: Lu

Side: a screen shot of the AR

P-ONE

After a first pathfinder mission STRAW (STRings for Absorption length in Water) in 2018, the P-ONE group has deployed a successor called STRAW-b. Their goal is to investigate the optical properties of the Canadian Cascadia Basin site and qualify it for P-ONE (see also GNN Monthly from May 2020 and https://www.nature.com/articles/s41550-020-1182-4) STRAW-b is closer to a full prototype of a P-ONE line, with mostly spherical modules and a longer mooring line (430 meters).

STRAW-b carries ten modules: a Wavelength Shifting Optical Module from University of Mainz (the first in-situ operation of a WOM), three spheres with boards to measure ambient parameters, two LiDARs for the measurement of the scattering length in water, two PMT-based and one CCD-based spectrometer for the study of the emission spectrum of bioluminescence and a sphere with scintillation plates which trigger on muons crossing the plates. On October 1st, STRAW-b was deployed by an ONC crew (ONC stands for Ocean Network Canada), since due to COVID-19 the developers of STRAW-b could not travel to Canada. The line was connected via a remotely operated underwater vehicle. Nine of the ten modules are fully functioning. Commissioning of the STRAW-b line and first analyses are on-going. The line is continuously taking data since the deployment time, and no issues have been observed so far.

(information provided by Elisa Resconi and Lutz Koepke).

The Mainz WOM during deployment

STRAW-b: PMT spectrometer rates with different filters

Publications

IceCube, HAWC and AMON: The IceCube and HAWC Collaborations, together with an AMON team, have posted (still in August but too late for the August GNN edition) a paper Multi-messenger Gamma-Ray and Neutrino Coincidence Alerts using HAWC and IceCube sub-threshold Data. (https://arxiv.org/pdf/2008.10616.pdf).

AMON stands for Astrophysical Multimessenger Observatory Network. HAWC and IceCube, through AMON, have developed a multimessenger joint search for extragalactic astrophysical sources. AMON is running continuously, receiving sub-threshold data (i.e. data that is not suited on its own to do astrophysical searches) from HAWC and IceCube, and combining them in real-time. The paper describes the analysis algorithm, as well as results from archival data collected between June 2015 and August 2018 (total live-time ~3.0 years). Two coincident events with a false alarm rate of less than one coincidence per year are found, consistent with the background expectations. The real-time implementation of the analysis in the AMON system began on November 20th, 2019, and issues alerts to the community through the Gamma-ray Coordinates Network with a false alarm threshold of < 4 coincidences per year; see the figure.

ANTARES: The ANTARES Collaboration has posted a paper Monte Carlo simulations for the ANTARES underwater neutrino telescope. See https://arxiv.org/pdf/2010.06621.pdf.

The paper leads the reader through the main steps of the MC simulation procedure for ANTARES. The peculiarities of the marine environment and the variations of the contribution to the optical background require special care to follow up and reproduce the time evolution of the data taking conditions. Thanks to a procedure that extracts ongoing information directly from the real data (the run-by-run simulation), the MC samples produced so far have been a reliable tool for all ANTARES physics analyses. Though the details of the simulation are strictly connected to the installation site of the detector, to its properties, and to the geometry of the OMs, the general scheme is valid for any other underwater detector, in particular for KM3NeT.

Review papers from GNN authors: Over the last months, a few review papers written by GNN authors have been posted. They provide didactical introductions in our field, as well as nice summaries of the status.

1. Andrea Palladino, Maurizio Spurio, Francesco Vissan, “Neutrino telescopes and high-energy cosmic neutrinos,” https://arxiv.org/pdf/2009.01919.pdf

2. Gisela Anton, “Neutrino Telescopes,” https://arxiv.org/pdf/2010.06012.pdf. Chapter of "Probing particle physics with neutrino telescopes", ed. Carlos de los Heros, World Scientific; написано в 2018 г.

3. Carlos de los Heros: Status, Challenges and Directions in Indirect Dark Matter Searches, Symmetry Magazine 12 (2020) 1648, https://www.mdpi.com/2073-8994/12/10/1648

Blazars or not Blazars, that’s the question

In a paper Directional association of TeV to PeV astrophysical neutrinos with active galaxies hosting compact radio jets https://arxiv.org/pdf/2009.08914.pdf A. Plavin, Y. Kovalev, Yu. Kovalev, and S.Troitsky (Moscow, Irkutsk and Bonn) underpin their recent result (https://arxiv.org/pdf/2001.00930.pdf) that IceCube neutrinos above 200 TeV are produced within several parsecs in the central regions of radio-bright active galactic nuclei. Citing from their abstract: “To independently test this result and to extend the analysis to a wider energy range, we use now public data for all energies from seven years of IceCube observations. The IceCube point-source likelihood map is analyzed against positions of AGNs from a large complete sample selected by their compact radio flux density. The latter analysis delivers 3.0σ significance, with the combined post-trial significance of both studies being 4.1σ. The correlation is driven by a large number of AGNs. Together with fainter but physically similar sources not included in the sample, these radio-bright quasars may explain the entire IceCube astrophysical neutrino flux as derived from muon-track analyses. The neutrinos can be produced in interactions of relativistic protons with X-ray self-Compton photons in parsec-scale AGN jets.”

Similarly, T. Hovatta et al. (Finland, Greece, Chile, USA) have posted a paper Association of IceCube neutrinos with radio sources observed at Owens Valley and Metsähovi Radio Observatories, see https://arxiv.org/pdf/2009.10523.pdf. In their abstract they write: “We find radio source associations within our samples with 16 high-energy neutrino events detected by IceCube. Nearly half of the associated sources are not detected in the γ-ray energies, but their radio variability properties and Doppler boosting factors are similar to the γ-ray detected objects in our sample so that they could still be potential neutrino emitters. We find that the number of strongly flaring objects in our samples is unlikely to occur due to a random coincidence (at 2σ level), and in the case of OVRO samples, the sample of associated sources is on average at an active state compared to random samples. Based on our results we conclude that although it is clear that not all neutrino events are associated with strong radio flaring blazars, when we see large amplitude radio flares in a blazar at the same time as a neutrino event, it is unlikely to happen by random coincidence.”

The hypothesis that gamma-ray emission may not the best way to correlate blazars with neutrino flares is also suggested by the paper Neutrino emission during the γ-suppressed state of blazars by Emma Kun, Imre Bartos, Julia Becker Tjus, Peter Biermann, Francis Halzen and György Mező, posted at https://arxiv.org/pdf/2009.09792.pdf. Here their abstract: “Despite the uncovered association of a high-energy neutrino with the apparent flaring state of blazar TXS 0506+056 in 2017, the mechanisms leading to astrophysical particle acceleration and neutrino production are still uncertain. Recent studies found that blazars in a γ-flaring state are too sparse for neutrino production, making the multi-messenger observation of TXS 0506+056 difficult to explain. Here we show that the Fermi-LAT γ flux of another blazar, PKS 1502+106 was at a local minimum when IceCube recorded a coincident high-energy neutrino IC-190730A. This suggests the presence of a large target photon and proton density that helps produce neutrinos while temporarily suppressing observable γ emission. Using data from the OVRO 40-meter Telescope, we find that radio emission from PKS 1502+106 at the time of the coincident neutrino IC-190730A was in a high state, in contrast to other time periods when radio and γ fluxes are correlated. This points to an active outflow that is γ-suppressed at the time of neutrino production. We find similar local γ suppression in other blazars, including the MAGIC flux of TXS 0506+056 and the Fermi-LAT flux of PKS B1424-418 at the time of coincident IceCube neutrino detections, further supporting the above model. Using temporary γ-suppression, neutrino-blazar coincidence searches could be substantially more sensitive than previously assumed, enabling the identification of the origin of IceCube’s diffuse neutrino flux possibly with already existing data.”