A long-term workshop on experimental Astroparticle Physics will be held from 02 to 27 November 2020 at Institut Pascal in Orsay. This workshop is a continuation of the Paris-Saclay AstroParticle Symposium of 2019 on theoretical Astroparticle Physics.
The aim is to gather specialists of the field on the topics of High-Energy Astroparticle Physics including high-energy cosmic rays, gammas, neutrinos and gravitational waves with special emphasis on multi-wave length and multi-messenger studies. The workshop includes working sessions every day (only one informal discussion per day, and on Friday, a ‘conference’ format day with speakers). They intend to invite confirmed researchers accompanied by their students and/or postdocs to make working conditions as enticing as possible. The aim is to initiate/continue/finalise research projects in an inspiring environment.
Scientists from the international XENON collaboration announced on June 17th that data from their XENON1T, the world’s most sensitive dark matter experiment, show a surprising excess of events. The scientists do not claim to have found dark matter. Instead, they say to have observed an unexpected rate of events, the source of which is not yet fully understood. The signature of the excess is similar to what might result from a tiny residual amount of tritium, but could also be a sign of something more exciting – such as the existence of a new particle known as the solar axion or the indication of previously unknown properties of neutrinos.
“Our result could be the onset of new physics” says Prof. Manfred Lindner (MPIK), Co-Spokesperson of the XENON Collaboration and APPEC-SAC member. “We emphasize very carefully conventional explanations of the observed excess, but about 90 theoretical publications within one month show that it could point to exciting new physics”.
The central part (the TPC) of the XENON1T detector. Credits: XENON Collaboration
XENON1T was operated deep underground at the INFN Laboratori Nazionali del Gran Sasso in Italy, from 2016 to 2018. It was primarily designed to detect dark matter, which makes up 85% of the matter in the universe. So far, scientists have only observed indirect evidence of dark matter, and a definitive, direct detection is yet to be made. So-called WIMPs (Weakly Interacting Massive Particles) are among the theoretically preferred candidates, and XENON1T has thus far set the best limit on their interaction probability over a wide range of WIMP masses. In addition to WIMP dark matter, XENON1T was also sensitive to different types of new particles and interactions that could explain other open questions in physics. Last year, using the same detector, these scientists published in Nature the observation of the rarest nuclear decay ever directly measured.
“While our detector was mainly designed to detect dark matter particles, its low energy threshold coupled to an extremely low background allows us to search for other rare interactions and particles beyond the standard model of particle physics,” says Prof. Laura Baudis (UZH), member of the APPEC SAC, and one of the leading members of the project.
The XENON1T detector was filled with 3.2 tonnes of ultra-pure liquefied xenon, 2.0 t of which served as a target for particle interactions. When a particle crosses the target, it can generate tiny signals of light and free electrons from a xenon atom. Most of these interactions occur from particles that are known to exist. Scientists therefore carefully estimated the number of background events in XENON1T. When data of XENON1T were compared to known backgrounds, a surprising excess of 53 events over the expected 232 events was observed. This raises the exciting question: where is this excess coming from?
One explanation could be a new, previously unconsidered source of background, caused by the presence of tiny amounts of tritium in the XENON1T detector. Tritium, a radioactive isotope of hydrogen, spontaneously decays by emitting an electron with an energy similar to what was observed. Only a few tritium atoms for every 1025 xenon atoms would be needed to explain the excess. Currently, there are no independent measurements that can confirm or disprove the presence of tritium at that level in the detector, so a definitive answer to this explanation is not yet possible.
View into the water tank, lined with reflecting foil, and the XENON1T detector. Sensitive sensors identify light signals induced in the water by cosmic radiation. Credits: XENON Collaboration
More excitingly, another explanation could be the existence of a new particle. In fact, the excess observed has an energy spectrum similar to that expected from axions produced in the Sun. Axions are hypothetical particles that were proposed to preserve a time-reversal symmetry of the nuclear force, and the Sun may be a strong source of them. While these solar axions are not dark matter candidates, their detection would mark the first observation of a well-motivated but never observed class of new particles.
“This would have a large impact on our understanding of fundamental physics, and of astrophysical phenomena. Moreover, axions produced in the early universe could also be the source of dark matter,” says Baudis.
Alternatively, the excess could also be due to neutrinos, trillions of which pass through your body, unhindered, every second. One explanation could be that the magnetic moment of neutrinos is larger than its value in the Standard Model of elementary particles. This would be a strong hint to some other new physics needed to explain it.
Of the three explanations considered by the XENON collaboration, the observed excess is most consistent with a solar axion signal. In statistical terms, the solar axion hypothesis has a significance of 3.5 sigma, meaning that there is about a 2 / 10,000 chance that the observed excess is due to a random fluctuation rather than a signal. While this significance is fairly high, it is not large enough to conclude that axions exist. The significance of both the tritium and neutrino magnetic moment hypotheses corresponds to 3.2 sigma, meaning that they are also consistent with the data.
“We are very excited about this new result from our tonne-scale liquid xenon detector with an incredibly low background that hasn’t been reached by any other experiment in the field” says Baudis.
XENON1T is now upgrading to its next phase – XENONnT – with an active xenon mass three times larger and a background that is expected to be lower than that of XENON1T. With better data from XENONnT, the XENON collaboration is confident it will soon find out whether this excess is a mere statistical fluke, a background contaminant, or something far more exciting: a new particle or interaction that goes beyond known physics.
“XENON1T was primarily built to search for WIMPs”, says Lindner. “This are top candidates for the Dark Matter in the Universe, but the record exposure and the very low threshold allows us to look for other exciting new physics. Maybe we stepped on some other exciting new physics which we can further explore with XENONnT which was already assembled and should become operational in the next months”.
The XENON collaboration comprises 163 scientists from 28 institutions across 11 countries. The European participation in XENON is very strong, with the following groups being involved: INFN Gran Sasso, Bologna, Napoli and Torino, and L’Aquila University in Italy, MPIK Heidelberg, the Universities of Freiburg, Mainz, Münster and KIT Karlsruhe in Germany, the University of Zurich in Switzerland, Subatech, LAL, LPNHE in France, Nikhef in the Netherlands, Stockholm University in Sweden and the University of Coimbra in Portugal.
Together with the other international collaborators, these groups are responsible for many of the crucial systems in XENON: the TPC and the photosensors and their readout, the data acquisition and light calibration systems, the xenon storage and distillation systems for radon and krypton, the material screening and radon emanation measurements, along with other background mitigation techniques, the neutron and muon veto systems.
APPEC congratulates the CERN Council for its decision to update the European Strategy for Particle Physics setting up a vision for the future of particle physics, a process that was inclusive of the full Particle and Astroparticle Physics communities. The general considerations of the 2020 update acknowledge the importance of the rich and complementary physics programs of neighbouring fields, and in particular acknowledge:
the groundbreaking discovery of gravitational waves which occurred since last strategy update in 2013 and has contributed burgeoning multi-messenger observations of the universe;
that dark matter and flavor puzzles are outstanding mysteries. They require synergy with cosmological and astronomical observations and experiments looking for direct interactions of dark matter or axions and in the neutrino sector, with neutrinoless double beta decay experiments also having potential to reveal violation of the global lepton number;
that neutrinos are a fascinating portal towards Physics beyond the Standard Model, which can be addressed by accelerator, reactor, atmospheric neutrino, as well as cosmic neutrino and cosmic ray experiments;
the importance of synergy on theory, which concretized in the creation of the EuCAPT Astroparticle theory centre, with its first hub located at CERN;
that the Recognised Experiment program needs to be expanded for some cases into specific agreements on technical and scientific cooperation in fields, such as gravitational waves and dark matter, which can strongly advance the field of Particle and Astroparticle Physics, as well as innovation;
the coordinated activities in Astroparticle Physics by APPEC.
We look forward for the years to come and work together on the realization of these many synergies between Particle Physics and Astroparticle Physics to address the hiding secrets of fundamental physics laws in the tiny nooks of space and time.
The 9th edition of the Very Large Volume Neutrino Telescope Workshop (VLVνT-2021) will be held from 20th to 23th April 2021, in Valencia, Spain. The workshop provides an ideal forum to discuss the latest developments in neutrino astronomy together with progress on the technological and instrumentation aspects of current and future large scale detectors in water and ice. It brings together the main collaborations working on neutrino telescopes (ANTARES, IceCube, KM3NeT, GVD) and is sponsored by the Global Neutrino Network (GNN).
In April 2020 the previous observer Poland became an official member of APPEC. In the General Assembly they are represented by Leszek Roszkowski from CAMK, who is director of AstroCeNT – the Particle Astrophysics Science and Technology Centre. Leszek Roszkowski also chairs the APPEC SAC sub-committee preparing a strategy report on direct detection of dark matter.
The quest for B-mode polarization of the Cosmic Microwave Background (CMB) is one of the major challenges of observational cosmology. A positive detection would signify the presence of primordial gravitational waves, theoretically expected from the inflation era. This is one of the most difficult measurements to make because the expected signal is very small and requires highly sensitive instruments with little systematic bias and with wide frequency coverage in order to separate the primordial signal from the foreground.
The QUBIC collaboration meeting of November 2019 at APC. Credits: QUBIC
QUBIC (QU Bolometric Interferometer for Cosmology: http://qubic.in2p3.fr) is an instrument based on a new concept called bolometric interferometry. The objective of QUBIC is to search for the B-mode polarization constructed from the Q and U modes (the two Stokes parameters describing the shape of the polarization ellipse of the microwave radiation). QUBIC combines the advantages of very sensitive and wide band cryogenic bolometers with the precise control of systematic instrumental effects possible with an interferometer, giving also the added capability of spectroscopic imaging. The original idea dates back to the early 2000s and, since then, European physicists have played a leading role in the development and exploitation of this innovative technology. After some initial projects, the QUBIC collaboration was created in 2008. New technical developments in European laboratories have enabled the creation of advanced detectors.
¼ focal plane of QUBIC composed of 256 TES cooled at 300mK and detection chain. Credits: QUBIC
The technological demonstrator (TD), identical to the nominal instrument but with fewer detectors and interferometry channels, smaller mirrors and without dichroic filter, was integrated at APC, Paris, in 2018 and underwent a test phase throughout 2019. It is intended to be installed at the QUBIC site at an altitude of 4800 m in the province of Salta in Argentina. Built by French, Italian, Irish, British and Argentinian laboratories, the technological demonstrator of QUBIC passed, in January, a review requested by the IN2P3-CNRS with the participation of the INFN. The review highlighted the innovation of the technical demonstrator as the first ever bolometric interferometry telescope and its potential for cosmology.
QUBIC synthesized beam, as measured (left) and expected (right). Credits: QUBIC
In the synthesis of the scientific presentations of the review group, which included international experts, the following evaluation was given on the general context of QUBIC:
“The interferometric nature of the synthesized beam results in a change of its multiply peaked pattern as a function of EM wavelength. Consequently, QUBIC would have sensitivity to space patterns on the sky as well as to their EM spectrum. QUBIC is therefore designed as a spectro-imager capable of measuring up to 5 sub-bands in each of our physical bands providing extra EM spectrum resolution with respect to traditional imagers. This unique feature could be a game-changer in the current context of a strong limitation to primordial B-mode observations from foregrounds (dust, synchrotron) whose spectral behaviour is not known and could significantly depart from a power-law (which is usually assumed in any component-separation so far).
QUBIC site at 5000m altitude at Alto Chorillos, near San Antonio de los Cobres, Salta province, Argentina. The Tuzgle volcano is visible. Credits: QUBIC
The target QUBIC installation site will be on the La Puna plateau in Argentina at 4800 m altitude. This site is an excellent compromise between the atmospheric conditions (humidity, stability) similar to that of the neighbouring Atacama and little degraded compared to a site in Antarctica and secondly a possible accessibility almost all year long, incomparable to that of an Antarctic site.”
In the general remarks of the conclusions, the progress made over the past two years is considered impressive. The demonstrator is assessed as convincing and successful, since the concept’s polarization and spectroscopy capabilities have been found to be excellent and in particular, the spectroscopic feature is of utmost utility for foreground characterization and analysis.
QUBIC instrument in the APC intégration hall (Paris). Credits: QUBIC
Several instruments installed on various sites are already measuring the CMB in search of the B-mode signal. The strength of this signal is summarized by the ratio “r” between the amplitudes of the tensor and scalar modes of perturbation of the metric of the primordial Universe. As the PI, Jean-Christophe Hamilton, explains, QUBIC’s sensitivity and statistics, once operational, will be lower than some of the running experiments. Nevertheless, QUBIC’s novel approach to systematic effects and to the foreground subtraction could be decisive for the discovery or confirmation of the extremely weak expected signal. QUBIC’s new technology aims to be integrated into next generation large detectors through a multi-year deployment and sensitivity enhancement program.
Regarding the current phase of QUBIC, Aniello Mennella, system scientist, says that the next steps envisaged are the finalization of the tests at APC, the shipping of the TD to Argentina and the commissioning on the sky (which will suffer delays due to the health crisis unfortunately). Following the upgrade to the complete instrument which will improve the sensitivity, there will be an observing campaign of 2 years leading to an estimate of sigma(r) = 0.01, corresponding to the sensitivity of Stage III instruments in the terminology of the CMB community.
In the longer term, potential future developments of QUBIC are already envisaged in order to reach Stage IV sensitivity (sigma (r) = 0.001) within a few years. These include:
Upgrading the current cryostat for a gain in sensitivity (~ x5) and in spectral capacity using multimode optics.
Producing similar cryostats which multiply the sensitivity by a comparable amount.
Installation of a similar bolometric interferometer at the focus of the 12m LLAMA antenna, opening access to polarization physics at small angular scales (masses and number of neutrinos, Dark Energy, physics of galaxy clusters).
It should be reminded here that the coordination of European laboratories for the development of the burgeoning field of experiments for Stages III and IV has appeared necessary since some years. APPEC has contributed to global coordination of this field through the Florence CMB Workshop series that started in 2015 and that helped incubate multiple European initiatives for contributing to CMB Stage IV. Information and links are available from the last meeting https://indico.in2p3.fr/event/19414/overview
For several weeks now our everyday life has been quite disrupted by the novel corona virus. We all have to master difficult situations in this unusual time, facing conditions we never experienced before. Although everybody has to deal with a different situation some things are common for almost all of us and our institutions.
“These last weeks will leave a deep sign in my life forever, as possibly the life of many, who will remember the time of COVID. In first place, this time is making me understand better what it means to still have your house to refugee and think how important is our role to understand and help who do not even have it.”Teresa Montaruli
Most institutions have set up a COVID-19 task force to inform and update their employees and to find the right balance between keeping the business running and at the same time protecting the health of the employees in the best possible way.
Despite some people working in the lab most of us have to work from home. There, many have to combine taking care of their kids and doing their daily office work, which is more and more challenging the longer this situation holds.
To keep everybody motivated and to keep contact with colleagues many institutes organize not only scientific virtual meetings but also social events like common coffee breaks, lunches or even concerts.
Traditionally, personal contacts at collaboration meetings, exchanges with scientists – whether within our own working group or during visits to other institutes – and national and international exchanges at conferences make up a large part of our scientific life. But many conferences were cancelled or postponed, like the APPEC Town Meeting which was planned for this autumn is now postponed to 2021.
“I am now working from home for almost 3 months. It is amazing to see how much is still possible using video meetings, chats and the good old phone and email. On the other hand I miss the informal talks with colleagues, and unexpected chats while visiting labs and meetings. This informal opportunities are needed for make progress in delicate and complex topics. But we will learn week by week how to optimize in working from home.”Job de Kleuver
Many meetings and events had to move to a virtual place, which has both, advantages and disadvantages. One advantage of moving many activities to the virtual world is that more people can join. Here are some examples for online conferences, colloquia and seminars:
But having all kind of meetings, like Collaboration meetings, group meeting etc. online is sometimes also very exhausting and it is hard to stay concentrated after hours of a zoom meeting.
“On the positive side of this CoVID crisis, family is now more easily reconciled with my work since at least being a single mom of two kids I do not need to travel. This is despite I need to scholarize them at home while I work. The times I was forced to travel, were problematic to me from the organisation point of view and from the responsibility one. I would be very happy if we understand how effective are video meetings even for audiences of 100 people, if well guided. Another aspect is mobility that our research work requires. It detaches you from families. We should be more tolerant in not considering it as a must in the career of physicists.”Teresa Montaruli
Many of us do not only have to deal with online conferences but with online teaching duties. Some might be well prepared but for some this might be a new field and a lot of additional preparatory work was necessary to provide lectures at an equal level as usual.
“Overalls, this period of telematic contacts found me well prepared. I have migrated my courses completely online and now I am registering them and I will continue to do this also in the future when we will be back in classrooms. I think most physicists must have been able to do this step egregiously well.” Teresa Montaruli
But in addition to this current challenges some scientist are worried about their future. Especially those with temporary contracts or those just finishing their studies or PhDs, are now in a difficult situation. Not only they have to worry about the next month but also worry if this will have negative influence on their future career.
“I hope we find ways to safeguard the young scientists from career damage. Maybe this is a good moment to discuss what really matters: the quality and prospects of talented young scientists or just the numbers of their output in this early stage of their careers.” Job de Kleuver
This is accompanied by the overall funding situation for the following years. Science and experiments will be delayed and also funding opportunities might get worse in the future.
Despite these worries it is great to see that science still keeps going and even new experiments get deployed (XENONnT (German), Baikal-GVD). This is also reflected in the following topics.
Online Outreach Activities
Normally many science institutes have offers for students and pupils and also the general public to get insights in their labs or allow access to their experiments. Often also school labs are an important outreach tool. All these kind of things now have to be transferred to online activities. Sometimes this can be very successful but some experience is just not possible in this way and we are looking forward to the time when we can offer hands-on-experience for our students and pupils.
Until then you can checkout these links to online accessible outreach activities for students:
Besides the attempt to advance everyday physics in the home office and at online conferences, many scientists and institutes also want to participate directly in the fight against COVID-19. And many have found ways and possibilities to do so! They use their 3d printers to produce protective equipment for hospitals, many provide their computing power for virologic investigations into the structure of the coronavirus (Folding@Home, Rosetta@Home), and physicists are performing simulations on the spread of the pandemic. But it is important to keep in mind that we can only provide resources to support those who are experts in the respective field. In the following list you can find links to all kind of activities, perhaps this will motivate even more institutes to get engaged.
https://science-responds.org/ – This website was built to facilitate interaction between COVID-19 researchers and the broader science community (Particle Physics origin)
https://globalyoungacademy.net/covid19/ Covid19 – Initiatives of the GYA, Young Academies and Partners – repository for global and national young academies as well as partner institutions to link their work on Covid19, any statements, or information dissemination activities, initiatives to support scientists, to coordinate and facilitate institutions or governments
Activities from individual institutes or countries:
This list of different activities shows that we defy the difficult situation and accept it as a challenge. And even if the situation seems to relax a bit at the moment, we will have to live with this, for us still unusual, situation for a longer time.
“The Covid-19 crisis is serious and we will remember this for long, but I am convinced that things will go better again, maybe later than we had hoped. Let’s try to keep the spirit and continue as good as it can be with the exciting Astroparticle Physics science and the construction and design of new infrastructures. Let’s be prepared with excellent well-thought plans at the moment that governments will think about new investments to stimulate their economies. And let science in general, and Astroparticle Physics more specificially, demonstrate that Europe is strong when we join the efforts and work together. But for now, take care of your families and stay healthy!”Job de Kleuver
The list of links and information provided here is by far not complete. If you like to add something please contact us.
Interview with Federico Sanchez about the recent results of T2K collaboration
Recently the T2K experiment published in Nature their results on the constraint of leptonic CP violation. Although there is no one-to-one link between the matter antimatter asymmetry and the value of delta from the T2K measurement, these results are a major step forward in the study of difference between matter and antimatter. Federico Sanchez explains how T2K measures CP violation and what they can conclude.
Congratulations for your results and their publication. Can you explain why a different behaviour of matter and antimatter is so important?
Inside the Super-K detector. Credit: Kamioka Observatory, Institute for Cosmic Ray Research, University of Tokyo
The different behavior of particle and antiparticles, or matter and antimatter, is by its own a breakthrough result. The different behavior of particle and antiparticles is a possibility contemplated in the Standard Model describing the fundamental particles. CP violation with leptons is described by a fundamental parameter, the phase angle δCP which is the parameter measured at the T2K experiment. There is no specific prediction of the value of this angle in our theoretical models. Its determination is important to advance in the understanding of the standard model. CP violation is related to flavor-changing mechanisms in the standard model, its measurement may help to understand more deeply the flavor dynamics. Flavor is what physicists identify with the differences between the three lepton families (electron, muon, and tau) or the three quark families. CP violation is a known phenomenon in processes involving quarks since the 1960’s. It has taken the particle physics community almost 60 years to start seen similar behavior in leptons. I believe this is the most relevant implication of the T2K result.
Besides the relevance to particle physics, CP violation might have implications in the understanding of our matter-dominated Universe. The existence of CP violation mechanism is one of the three conditions proposed by Andrei Sakharov to explain the baryon(or matter) asymmetry of the Universe. Baryon number violation and interactions out of thermal equilibrium are the other two. CP violation is then a necessary condition although not a sufficient one. The CP violation amount and its origin are relevant to model this asymmetry. I would like to stress that we are still far from understanding this mechanism, the baryon number violation has not been proved experimentally so far, and it is not obvious that the CP violation in neutrinos and quarks are the mechanisms required to explain the baryon asymmetry in the universe. Although some theoretical models connect both phenomena, there is a long way to go. Hopefully, the new results can help in this challenging enterprise.
Can you explain the measurement principles of T2K?
The observed electron neutrino (left) and electron antineutrino (right) candidate events with predictions for maximal neutrino enhancement (red, long dash) and maximum antineutrino enhancement (blue, short dash). Credit: the T2K experiment
T2K collaboration studies the so-called neutrino oscillations. The neutrino oscillation is a quantum mechanical interference caused by the fact that every neutrino of the type electron, muon, or tau is a combination of three neutrino masses. The neutrino type electron, muon, or tau is determined by the associated heavy lepton (electron, muon, or tau) in the interaction. The neutrino has three paths to travel from the production to the interaction points. Each one associated with one neutrino mass. The neutrinos travel as a superposition of these three states, each one with a different mass and speed, producing the interference patterns. Experimentally, this quantum mechanical interference is measured by looking at the appearance of types of neutrinos at the interaction point different from the ones that were produced. Particularly in T2K, we look for the transformation of muon neutrinos into electron neutrinos. The CP phase induces differences in the oscillation for the neutrinos and its antiparticles, the antineutrinos. In T2K, we have measured the oscillation parameters for neutrinos and antineutrinos and from the difference, we can infer the value of the CP violation phase. The T2K experiment can produce both neutrinos and antineutrinos simply by focusing or defocusing positively charged pions and negatively charged pions. The positive pions produce neutrinos during its disintegration and negative pions produce antineutrinos.
Your experiment is sensitive to the δCP Phase, which parameter space can you exclude and what does this mean?
The arrow indicates the value most compatible with the data. The gray region is disfavored at 99.7% (3σ) confidence level. Nearly half of the possible values are excluded. Credit: the T2K experiment
The result from T2K excludes half of the possible values of δCP, particularly the positive values of the phase angle are excluded with a confidence level of 99.7%. If we take possible values of δCP from -180 degrees to 180 degrees we excluded values from -1.7 degrees to 164.6 degrees. This is the first time we have measured experimentally this fundamental parameter in the Standard Model.The other important read of the T2K results is that the most probable value of the δCP is close to -90 degrees implying the maximal violation of the CP symmetry in neutrinos. The fact that it can be maximal open possible ways to understand the mechanism that differentiates neutrino mass states from flavor states.
What are the consequences of the constrain of T2K on the δCP in the neutrino sector on the matter-anti-matter asymmetry?
When confirmed, the result might have several implications. First of all, it is a new source of CP violation beyond the traditional one in the quark sector. This additional source plus the special properties of neutrinos might explain through a relevant theory the origin of the matter-dominated Universe through theoretical models. Another relevant implication is related to the value of δCP. If the result is confirmed to be maximal as suggested by T2K, this might have theoretical implications since it might be a reflection of hidden symmetries in a model.
What are your ideas to further improve the measurements?
In particle physics, 99.7% is not sufficient to claim a discovery. We need values of the confidence level of 99.9999%. To reach this precision we need more data, the 115 events collected by T2K are not enough. To achieve larger statistics there are few venues we are taking. The first one implies running longer time, the second to increase the flux of neutrinos, and third to increase the mass of the far detector. The first step is just time and money, we will keep running a few years more hopefully doubling or tripling the number of neutrinos we detect. The second step can be done by increasing the total number of protons we can accumulate in the accelerator per unit of time. Protons produce the pions that subsequently produce neutrinos by decay. There is already an approved project that will almost double the number of protons during the next years. The third one requires new detectors. Recently, the upgrade of the T2K far detector, SuperKamiokande, was approved by the Japanese authorities. The new project, HyperKamiokande, will increase the detector mass and the number of detected neutrinos per unit of proton in the accelerator by almost a factor of ten. With this increase, we can accumulate ten times more neutrinos for the same number of protons than we do today. Unfortunately, this will not be sufficient. In parallel, we need to understand some of the uncertainties of the experiment. These uncertainties are related to better control of the neutrino flux predictions and the modeling of neutrinos interacting with nuclei. Both are at the moment the most relevant non-statistical uncertainties in the measurement and they will become dominant when we increase the number of detected neutrinos. To address these issues, we need supporting experiments to help to understand the production of pions by proton interactions and to improve the understanding of neutrino interactions. We also need to develop more precise theoretical models describing the interaction of neutrinos with nuclei so we can interpret these experiments correctly, and in parallel, we need to prove experimentally they are correct.
We would like to add a short comment by Silvia Pascoli in which she discusses the results of the T2K experiment in a theoretical context. We asked her about the connection between T2K results and the baryon asymmetry of the Universe.
A simple assumption, justified by cosmological inflation, is that the Universe at the very beginning contained the same amounts of matter and antimatter. In the 60’ A. Sakharov identified the conditions which are required for some process in the Early Universe to generate a small asymmetry between matter and antimatter: the violation of the C and CP symmetry, lepton (or baryon) number violation, which is testable in neutrino less double beta decay, and the out of equilibrium condition.
Leptogenesis, using leptonic CP violation, is among the favourite explanations of the baryon asymmetry as it takes place in models which have been proposed to explain the observed neutrino masses. Under certain conditions, specifically in see-saw type I neutrino mass models, it has been shown that the leptonic CP violating delta phase searched for in long baseline neutrino oscillation experiments can be the source of the observed matter-antimatter asymmetry. This is a highly non-trivial statement as in many other models the baryon asymmetry that can be generated is too small.
Observing leptonic CP violation and the violation of lepton number would provide circumstantial evidence (although not a proof) towards leptogenesis as the origin of the matter-antimatter asymmetry of the Universe.
We asked her to further comment on the connection to neutrinoless double beta decay.
First of all, as I discussed above, lepton number violation is one of the three key criteria for leptogenesis to explain the baryon asymmetry of the Universe. Neutrino less double beta decay is the most sensitive test we have of this global symmetry of the Standard Model. Moreover, the results of T2K and NOvA and other neutrino oscillation experiments on the ordering of neutrino masses play a key role in the predictions for the lifetime of the decay process. So, mass ordering information is very important to plan the future program in this field and to interpret the results from future experiments.
Federico Sanchez graduated at the Univ. of Sevilla and got his PhD at the Universitat Autònoma de Barcelona working at an experiment at CERN. He worked as a researcher at DESY and at the Max Planck Institute fur Kernphysik in Heidelberg where he acted as co-physics coordinator of the HERA-B experiment. He has worked at several particle physics experiments such as ALEPH and LHCB at CERN or HERA-B at DESY.
In 2002, he joined the K2K experiment in Japan and since then he was working on neutrino physics as the leader of the group at IFAE. He participates in the T2K experiment in Japan from almost the very beginning. In 2016, he was one of the researchers awarded the Breakthrough prize on fundamental physics which was given to the K2K and T2K collaborations for the experimental establishment of neutrino oscillations. Between 2007 and 2011, he was a member of the Nemo and SuperNemo collaborations and contributed to the preliminary ideas of the NEXT experiment.
In August 2018, he moved as a professor at the Université of Genève to take the responsibility of the group dedicated to neutrino physics at the T2K and HK experiments. In April 2019, Federico was elected International Co-Spokesperson of the T2K collaboration.
In the U.S., the Snowmass 2021 process will take place over the next year. Organized by the Division of Particles and Fields (DPF) of the American Physical Society (APS), this process is intended to define the most important questions for the particle physics community and to identify the most promising ways to address these questions in a global context. Snowmass provides an opportunity for the entire HEP community to come together to identify and document a vision for the future of particle physics in the US and its international partners. Given the increasing importance of interdisciplinary work, a strong participation of related fields such as astrophysics, cosmology, gravity, nuclear physics, accelerator physics, AMO and materials science is expected.
Between autumn 2020 and summer 2021 there will be a series of preparatory meetings and workshops organized by Snowmass conveners from ten frontiers (energy, neutrino, rare processes & precision, cosmic, theory, accelerator, instrumentation, computation, underground facilities, and community involvement).
The Frontier Conveners are nominated by the community and selected by the DPF Executive Committee plus members of the chair lines of Division of Astrophysics (DAP), Division of Physics of Beams (DPB), Division of Nuclear Physics (DNP) and Division of Gravitational Physics (DGRAV). Their first task is to identify topical group conveners. This process was developed in order to provide a diverse and representative leadership including junior and senior researchers, theorists and experimentalists, and balance regarding gender, geographical distribution, and background.
Besides there is the Steering group, which consists of the DPF Chair line and one representative each of the related units DAP, DPB, DNP, and DGRAV. This Steering group oversees the process and meets regularly with the Frontier Conveners. An inclusive Advisory Group is consulted on major decisions, and consists of the Steering Group plus the rest of the DPF Executive Committee (members at large, secretary/treasurer, and councillor), an editor, a communication liaison, and a set of International Advisors.
One of these International Advisers is Berrie Giebels as representative for APPEC.
Berrie Giebels, APPEC representative in the Snowmass 2021
Berrie Giebels defended his dissertation in 1998 and was a research associate at SLAC for 3 years. Since 2001 he is physicist at CNRS in the field of high energy astroparticle physics (Fermi, HESS, CTA). Since 2016 he is IN2P3/CNRS deputy director in charge of the astroparticle physics & cosmology perimeter including the large research infrastructures (EGO-Virgo, CTA, LSST, KM3NeT, Auger,..).
„The Snowmass Process, while essentially aimed at developing a vision for the future of particle physics in the U.S., is also a very inclusive process – thematically, integrating other fields of research such as astroparticle physics, and geographically, through the inclusion of the international community in its advisory group. Participating to this process as a European scientist is a unique opportunity to reach beyond our currently closed borders and reaffirm that research in physics relies on worldwide cooperation and collective goals. The APPEC roadmap objectives and priorities should provide valuable insights to shape the Snowmass 2021 vision, which will in return have an influence on the next European Astroparticle physics strategy update.“ – Berrie Giebels
To optimally engage all participants in the process, the Division of Particles and Fields invites the international community to submit written documents. Given the increasing importance of interdisciplinary work in related fields such as astrophysics, cosmology, gravity, nuclear physics, accelerator physics, AMO, and materials science, members of the Divisions of Astrophysics, Gravitational Physics, Nuclear Physics, Physics of Beams and members of other units with a connection to particle physics are strongly encouraged by the DPF Chair, Young-Kee Kim to participate in this process:
Letters of Interest (submission period: April 1, 2020 – August 31, 2020)
Letters of interest allow Snowmass conveners to see what proposals to expect and to encourage the community to begin studying them. They will help conveners to prepare the Snowmass Planning Meeting that will take place on November 4 – 6, 2020 at Fermilab. Letters should give brief descriptions of the proposal and cite the relevant papers to study. Instructions for submitting letters are available at https://snowmass21.org/loi. Authors of the letters are encouraged to submit a full writeup for their work as a contributed paper.
Contributed Papers (submission period: April 1, 2020 – July 31, 2021) Contributed papers will be part of the Snowmass proceedings. They may include white papers on specific scientific areas, technical articles presenting new results on relevant physics topics, and reasoned expressions of physics priorities, including those related to community involvement. These papers and discussions throughout the Snowmass process will help shape the long-term strategy of particle physics in the U.S. Contributed papers will remain part of the permanent record of Snowmass 2021. Instructions for submitting contributed papers are available at https://snowmass21.org/submissions/.
The Snowmass homepage (https://snowmass21.org) provides you further information on the current status of Snowmass 2021.
From February 17 to April 10, two new clusters of optical modules were installed, the sixth and the seventh, at Baikal-GVD Deep Underwater Neutrino Telescope. The effective volume of the facility, corresponding to the detection of hadronic showers produced by neutrinos, reached 0.35 km3.
Credits: B. A. Shaybonov
The Baikal-GVD Neutrino Telescope is designed for detecting and studying high-energy neutrino fluxes from astrophysical sources. Scientists plan to explore the astrophysical processes with huge energy releases occurred at the time when the Universe was hundreds of millions or billions of years younger.
According to the project, the volume of the facility in Lake Baikal should be about one cubic kilometer. The installing of the two new clusters in 2020 was an important step towards this goal. The effective volume of the facility, corresponding to the detection of neutrino produced showers, reached ~ 0.35 cubic kilometer. The estimates, based on existing algorithms (which are constantly improving), suggest that the current setup should be able to detect 3-4 neutrino interactions per year with the neutrino energy exceeding 100 TeV.
The Baikal Neutrino Telescope, being still under construction, is a unique scientific facility, one of four pillars of the Global Neutrino Network (GNN), along with IceCube at the South Pole, KM3NeT and ANTARES in the Mediterranean Sea. They explore all together the Universe considering neutrinos as messengers.
The installation site of the Baikal Neutrino Telescope is 3.5 km away from the shore. The facility is assembled at the depth of 750-1300 m in the Southern Hollow of Lake Baikal from about one-meter-thick ice surface, what greatly simplifies the installation.
Credits: B. A. Shaybonov
This year, the expedition met hard times because of anomalous weather conditions. During the ice formation period, a strong wind broke the ice cover of the lake. Huge ice blocks and ridges grew all across the lake, which significantly impeded the mounting. Nothing like that was observed in the whole 40-year-long history of the Baikal expeditions. It was not clear whether the team would be able to cut the ice through all these ice ridges to lay the cables to the new facility.
Thanks to a great experience of the team, the appropriate solution was found and the two new clusters were installed. In addition to them, an experimental technological string with five calibration laser light sources and underwater fibre-optic cables for data exchange was mounted. At present, all devices are successfully taking data.
Credits: B. A. Shaybonov
In total, 60 researchers, engineers, technicians, workers, including volunteers, participated in the expedition. The 2020 expedition program has been fully completed.
This year, the International Scientific Baikal-GVD Collaboration comprises the Institute for Nuclear Research of RAS (Moscow), the Joint Institute for Nuclear Research (Dubna), Irkutsk State University, Nizhny Novgorod State Technical University, St. Petersburg State Marine Technical University, the Institute of Experimental and Applied Physics of Czech Technical University in Prague, the Faculty of Mathematics, Physics and Informatics of Comenius University in Bratislava (Slovakia), the Institute of Nuclear Physics of the Polish Academy of Sciences (Krakow, Poland), EvoLogics GmbH (Berlin, Germany).
The expedition was organized by the Institute for Nuclear Research of the Russian Academy of Sciences (Moscow) and the Joint Institute for Nuclear Research (Dubna).
G.V. Domogatsky, spokesman of the Baikal-GVD Collaboration
The 9th edition of the Very Large Volume Neutrino Telescope Workshop (VLVνT-2021) will be held from 20th to 23th April 2021, in Valencia, Spain. The workshop provides an ideal forum to discuss the latest developments in neutrino astronomy together with progress on the technological and instrumentation aspects of current and future large scale detectors in water and ice. It brings together the main collaborations working on neutrino telescopes (ANTARES, IceCube, KM3NeT, GVD) and is sponsored by the Global Neutrino Network (GNN).
