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Astronomy potential of ARCA

22 November 2024 – In a paper with the title ‘Astronomy potential of KM3NeT/ARCA’ we present improvements that indeed enhance the astronomy potential of the ARCA detector.

An important scientific objective for constructing the ARCA detector is the detection of high-energy cosmic neutrinos from point-like sources. Scattering off the quarks inside a nucleon, neutrinos induce hadrons that generate a shower of particles. In so-called charge current interactions also a charged lepton is produced: a muon, electron or tau. These leptons have different signatures in the detector. Muons traverse the detector with a straight track of light, while electrons and taus generate outburst of light in the detector. $W^{\pm}$

With the ARCA detector, we can use both detection signatures for investigating the Southern Sky, where many neutrino sources are expected along the Galactic Plane. For this we further improved the neutrino event selection method and the event reconstruction software of both track-like and shower-like events.

Simulations show that the improvements enhanced the sensitivity and discovery potential of ARCA for neutrino sources by 5-15%.

The paper is published in EPJ-C:

Eur. Phys. J. C 84, 885 (2024)

DOI: 10.1140/epjc/s10052-024-13137-2)

In the image (click on the image for a better resolution):

The ARCA point-like source sensitivity (black curves) as a function of sin(δ) (δ is the declination angle) with γ = 2.0 (γ is spectral index, which matches the energy spectrum of cosmic rays undergoing Fermi acceleration) . For comparison, the results of 15 years of observation with the ANTARES telescope (green curve) and 7 and 10 years of of observation with the IceCube telescope (red curves) are also shown.

First searches for Dark Matter

20 November 2024 – In a new paper with the title ‘First searches for Dark Matter with the KM3NeT Neutrino Telescopes’ we present limits for neutrino production by Dark Matter annihilation in the Sun and the Galactic Centre. For the analysis we used the data of early configurations of the ARCA and ORCA detectors of KM3NeT.

We tested for different dark matter masses, spanning from a few GeV/c^2 up to 100 TeV/c^2, but did not find a dark matter signal in the data of ARCA from the direction of the Galactic Centre. Instead, we set a limit on the self-annihilation cross section of dark matter into five different Standard Model particles, for the different dark matter masses tested.

In the data of ORCA we did not find a dark matter signal from the Sun. In this case, we could set a limit on the cross section of the scattering process between dark matter and nucleons.

The paper is submitted to JCAP. A pre-print is stored at the arXiv: https://arxiv.org/abs/2411.10092

In the image:
90% CF upper limits on the thermally-averaged Weakly Interacting Massive Particles (WIMPs, candidate Dark Matter particles) annihilation cross section as a function of the WIMP mass for the τ⁺τ^–annihilation channel. The limit was obtained using data sets from the ARCA8, ARCA19 and ARCA21 configurations. For comparison, results obtained by other experiments are also shown.

KM3NeT gathered online for its fall collaboration meeting

13 November 2024 – Last week , the KM3NeT Collaboration has met online for its fall meeting.

During the meeting, we reviewed the current status of data taking for both ARCA and ORCA detectors, discussed the advancements in their construction, the progresses in MC simulation and detector calibration, and outlined the plans for the ongoing data analyses.

It was also the occasion to celebrate our two last sea campaigns and thus the expanded configurations of the detectors, ARCA 33 and ORCA24. The deployment of new instrumentation on the ORCA site will allow for a precise monitoring of the detector position and water properties.

During the meeting Antoine Kouchner started his mandate as chairperson of the Institute Board, taking over from Uli Katz: with many thanks to Uli for all the work done in the past years, and good luck to Antoine for his new duty.

Also during the meeting, the process to elect the new Management Team of the Collaboration was started.

Finally, KM3NeT gave a heartfelt greeting to its new members. Juan Antonio Aguilar Sánchez of the Université Libre de Bruxelles, Belgium, and Elisa Bernardini of Padova University, Italy, joined as Observers, while the team led by Arthur Ukleja from the University of Krakow, Poland, was endorsed as Full Member.

A warm welcome to everyone!

It was great to see the advancements in the physics analyses as well as the simulation and calibration works, to discuss recent scientific advancements and to see the Collaboration continue to grow.

The next Collaboration Meeting is scheduled for January, in Belgium, at Louvain-la-Neuve.

Quantum decoherence with ORCA6

30 October 2024 – Search for quantum decoherence in neutrino oscillations with six detection units of KM3NeT/ORCA

(KM3NeT paper, submitted to JCAP, arXiv: 2410.01388)

In a new paper we search for quantum decoherence in neutrino oscillations by looking for deviations of the standard neutrino oscillation pattern. We report upper limits on the decoherence parameters using data from ORCA6.

Usually, neutrino oscillations are studied in the framework of quantum mechanics assuming that the neutrino system is isolated. In this paper we study neutrino oscillations in the framework of open quantum systems, where the neutrino is coupled to a larger environment.

Several theories of quantum gravity postulate fluctuations in spacetime as a stochastic environment. A neutrino that propagates in such an environment will experience changes to its quantum phase. This will lead to a loss of coherence of the neutrino mass eigenstates during propagation. The phenomenon is referred to as decoherence in neutrino oscillations.

The search for decoherence in neutrino oscillations provides a rare opportunity to investigate quantum gravitational effects which are usually beyond the reach of current experiments.

The ORCA detector of KM3NeT is particularly designed to detect neutrinos generated in collision of cosmic ray particles with the Earth’s atmosphere. The atmospheric neutrinos are good probes to study oscillations and hence to search for quantum decoherence effects.

We used the neutrino data collected by the ORCA6 detector – an early detector configuration with six detection units – in the period January 2020 to November 2021. In the analysis we focused on atmospheric neutrinos with energies of a few GeV to 100 GeV. We measured the parameters Γ₂₁and Γ₃₁, that describe decoherence, assuming a power-law dependency on the neutrino energy Γ_ij ∝ (E/E₀)ⁿand explored two cases: with n = -2 and with n = -1.

Results

No significant deviation with respect to the standard oscillation hypothesis is observed. Therefore, 90% CL upper limits for the two cases are estimated as

The decoherence sensitivity of ORCA depends on the neutrino mass ordering. Therefore, we report upper limits for both normal and inverted ordering.

The results are comparable to bounds reported for IceCube/DeepCore and display the same dependency on the mass ordering.

In the figure below the 90% confidence level contours for Γ₂₁ and Γ₃₁ are shown for a decoherence model fitting both normal (NO) and inverted (IO) neutrino mass orderings.

Neutrino oscillations with ORCA6

29 October 2024 – Measurement of neutrino oscillation parameters with the first six detection units of KM3NeT/ORCA

(KM3NeT paper, accepted by JHEP, arXiv: 2408.07015)

In a new paper we show the potential of the ORCA detector: the measurements of neutrino oscillation parameters – with only 5% of ORCA’s final volume and during limited observation time – align with those from other experiments and are already becoming competitive.

Since the discovery of neutrino oscillations, the three-flavour neutrino model with non-zero neutrino masses has become well-established. The oscillation parameters are being measured with improving precision by several experiments world-wide. However, several questions persist. Among them the question what the value of the neutrino mixing angle θ₂₃ is and the question whether the ordering of the three neutrino masses is “normal” (NO) with m₁<m₂≪m₃ or “inverted” (IO) with m₃≪m₁<m₂. KM3NeT has joined the effort to answering these questions using its ORCA detector.

Neutrinos created in collisions of cosmic ray particles with the Earth’s atmosphere are good probes to study the neutrino oscillations. The ORCA detector in the Mediterranean Sea is particularly designed to detect atmospheric neutrinos. Therefore, it is an optimal detector for the measurement of neutrino oscillation parameters.

However, the ORCA detector is still under construction. The paper reports on the measurements with ORCA6 – an initial detector configuration that comprises six out of the foreseen 115 detection units. We extracted a high-purity neutrino sample, corresponding to an exposure of 433 kton-years. The sample of 5828 neutrino candidates was analysed following a binned log-likelihood method in the reconstructed neutrino energy and the cosine of the zenith angle.

Results

The atmospheric oscillation parameters measured with ORCA6 for both normal (NO) and inverted (IO) neutrino mass ordering are:

The inverted neutrino mass ordering hypothesis is disfavoured with a p-value of 0.25.

The 90% confidence level contours for the fitted oscillation parameters are shown in the left figure below with a solid line assuming normal ordering (NO) and a dashed line assuming inverted ordering (IO).

In the figure at the right you find a comparison of the contour – assuming NO – with the corresponding contours measured by other experiments. The ORCA contour aligns with those other measurements and, moreover, it shows that ORCA is becoming competitive.

Welcome ARCA33 and ORCA24!

28 October 2024 – The latest sea campaigns at both the KM3NeT’s ARCA and ORCA sites have led to major progress in expanding detector installations and improving calibration systems.

The number of detection units in operation in the deep sea has been increased to 57: 33 in ARCA and 24 in ORCA.

Despite bad weather at the ARCA site, the so-called Phase-1 part of the apparatus was completed, while construction of Phase-2 was started with the installation of two new junction boxes, three detection units (exploiting a new data acquisition architecture), and calibration components. The operations also included important maintenance tasks, such as recovering and replacing acoustic beacons. All optical modules of the deployed strings are fully operational. KM3NeT/ARCA now comprises 33 detection units.

At the ORCA site, a 60-hour calm weather window allowed the team to deploy the Calibration Unit (Calibration Base+Instrumentation Unit) and to install an additional detection unit. After these successful installations, node 1 of ORCA is complete and fully functional, an important milestone in the construction of ORCA. The total number of functional detection units at ORCA has now reached 24.

These recent efforts at both sites underscore KM3NeT’s expanding capability in detecting and studying neutrinos from the sea’s depths. The whole Collaboration extends its gratitude to the offshore and onshore teams whose hard work made these successful operations possible.

A furled detection unit ready for the deployment at the ORCA site

ORCA offshore team on the Castor 02 ship

Components for ARCA on the deck of the Optimus Prime ship: in the foreground is one junction box, behind it there are a couple of spools with the submarine interlink cables and then some detection units

ARCA onshore shift crew at the site of Portopalo

ATLAS comet visible from the harbour of Portopalo di Capo Passero

Sonar scan of the ORCA site taken by the ROV at the end of the operation. The anchors of the detections Units (DUs), the junction box (JB1), the Calibration Base (CB), the Instrumentation Unit (IU) and the Module Instrumentation Interface (MII) are all visible.

Search for neutrinos from GRB 221009A

13 August 2024 – Gamma-ray bursts are promising candidate sources of high-energy astrophysical neutrinos. The recent GRB 221009A event, identified as the brightest gamma-ray burst ever detected, provides a unique opportunity to investigate hadronic emissions involving neutrinos.

KM3NeT participated in the worldwide follow-up effort triggered by the GRB 221009A event, searching for neutrino events.

In a paper with the title ‘Search for neutrino emission from GRB 221009A using the KM3NeT ARCA and ORCA detectors’ we summarise subsequent searches in the energy range from MeV up to a few PeVs.

We did not find neutrino events, but set upper limits on the neutrino emission associated with GRB 221009A.

The paper is published in:

JCAP08(2024)006

DOI: 10.1088/1475-7516/2024/08/006

In the image:

90% CL upper limits on the neutrino flux from GRB 221009A for ARCA (blue) and ORCA (red). For comparison the results of IceCube are also shown (green) as well as the gamma-ray observations of Fermi-GBM, Fermi-LAT, and LHAASO (gray dashed lines).

Neutrino 2024 Poster Winner: Isabel Goos

03 July 2024 – In June, KM3NeT scientist participated to the XXXI International Conference on Neutrino Physics and Astrophysics (Neutrino 2024), held in Milan, Italy, and organized by the University of Milano – Bicocca, the University of Milan and the Istituto Nazionale di Fisica Nucleare (INFN).

As one of the largest conferences in astroparticle physics, neutrino physics and cosmology, it was the occasion to share latest findings, innovative concepts and future outlooks among experts of the field.

Isabel Goos at Neutrino 2024 (credits Neutrino2024)

During the conference, Isabel Goos, KM3NeT’s researcher at the University of Paris Cité, was awarded one of the four prizes for the best-poster award. In her poster, titled “KM3NeT’s sensitivity to the next core-collapse supernova”, she discusses how individual multi-PMT optical modules of KM3NeT can be used as standalone detectors for the detection of low-energy neutrinos from Core Collapsed Super Novae. It has been selected among 460 accepted posters, of which 319 eligible for this acknowledgement.

KM3NeT joins in congratulating Isabel on her great achievement!

In total, KM3NeT presented 17 posters, covering topics including neutrino astronomy, neutrino oscillations, dark matter & exotics, cosmic-ray studies and technologies for neutrino physics.

In addition, four members of the KM3NeT Collaboration had a plenary talk: João Coelho, who discussed the latests results from KM3NeT; Maurizio Spurio, debating open problems in neutrino astrophysics; Naoko Kurahashi Neilson, contributing on the present and future of high-energy neutrino astronomy, and Jürgen Brunner presenting future detectors for atmospheric neutrinos.

Neutrino 2026 will be held at the University of California – Irvine. Looking forward to sharing our advancements also on that occasion!

The KM3NeT Collaboration reunited in Texel for its spring meeting

23 June 2024 – KM3NeT has met, in Texel (The Netherlands) and online, for its spring Collaboration meeting, hosted by NIOZ, the Royal Netherlands Institute for Sea Research.

The meeting brought together collaborators in order to review the status of the ongoing analyses, Monte Carlo simulations and calibration efforts, for both the ARCA and ORCA detectors, and prepare exciting contributions to the Neutrino 2024 Conference.

During the week, the progress of detector construction was discussed, celebrating the achievement of assembling the 1,500th DOM. Additionally, plans for upcoming sea campaigns were refined.

Furthermore, Antoine Kouchner has been elected chair of the KM3NeT Institute Board, taking over from Uli Katz. The full Collaboration joins in thanking Uli for his outstanding work and wishes the best of luck to Antoine for the incoming endeavors!

The meeting was also the opportunity to welcome the new members of the Collaboration. Both the Max Planck Institute for Radio Astronomy (Bonn, Germany) and the Khalifa University (United Arab Emirates) have been endorsed as Full Members, with Yuri Y. Kovalev and Satyendra Thoudam as PIs respectively. Kristina Giesel from ECAP Erlangen (Germany) joined as a new Associated Member. Welcome to all of you!

It was wonderful to engage in fruitful discussions about recent scientific developments and to see the Collaboration continue to grow.

Thanks a lot to NIOZ for the hospitality and to the whole local team for the organization!

The next meeting is scheduled for late autumn in online mode.

ORCA enlarged with four new detection units

15 June 2024 – A new marine operation took place in the last week for enlarging the ORCA deep-sea neutrino telescope.

Taking advantage of a spot of good weather of 48 hours, four new detection units were added to the apparatus.

For each of such units, the following steps were required: installation on the bottom of the sea, connection to the apparatus, functionality check, unfurling from the launcher vehicle, final test to check the functionality post-unfurling and recovery of the launcher vehicle. During the operation one acoustic beacon, which was in need of refurbishment, was recovered from the bottom of the sea.

The campaign was performed with two ships and a deep-sea ROV. A team onshore performed all needed tests on the newly installed detection units.

After the new installations, ORCA now comprises 23 detection units; only one more detection unit is needed for completing all connections on the first of the submarine nodes of the apparatus.

Many thanks to all teams involved for this important step forward!

The deck of Castor-2 of Foselev Marine loaded with the new detection units awaiting deployment, at dawn, while starting up the campaign.

A detection unit splashing to start its journey to the bottom of the sea.

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KM3NeT - News Archive

In a new paper we search for quantum decoherence in neutrino oscillations by looking for deviations of the standard neutrino oscillation pattern. We report upper limits on the decoherence parameters using data from ORCA6.

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