Interview with Razmik Mirzoyan and Stefan Wagner on their successful measurements of GRBs with MAGIC and H.E.S.S.
On 14 January 2019, Swift has reported the detection of a long GRB 190114C (GCN #23688). The MAGIC telescopes started observations of this GRB about 50 s after the Swift-BAT alert, reaching more than 20 sigma of significance in 2 hours. At the CTA Science Symposium on 6-9 May 2019, also H.E.S.S. announced the detection of GRB 180720B in its afterglow phase at the level of 5 sigma in about 2 hours of observations. Three papers on these relevant findings where later published in Nature. We would like to congratulate on this major breakthrough and interviewed the two spokespersons of the experiments, Razmik Mirzoyan and Stefan Wagner.
Artist view of a GRB. Credits: DESY, Science Communication Lab
MAGIC observed bright early emission from GRB 190114C in January 2019, H.E.S.S. the faint afterglow emission of GRB 180720B in July 2018. What do you think led to the breakthrough in these observations?
Mirzoyan:
MAGIC detection of the GRB 190114C has been published in ATel #12390 and the GCN Circular #23701 in the night of 14/15th January 2019. MAGIC detected the most intense ever gamma-ray signal from any celestial source since the invent of ground-based very high energy gamma-ray astronomy; in the first 30s the intensity of emission was 130 times that from Crab Nebula, the standard candle in VHE astronomy. This is a very happy occasion to celebrate the 30 years birthday of the ground-based gamma-ray astronomy.
In late 1990’s many technological novelties were suggested, developed and implemented in the design of MAGIC, it was planned as a real High-Tech telescope and our senior colleague Eckart Lorenz has a major contribution in these. The main goal was in the first time to measure Active Galactic Nuclei, GRB, pulsars and galactic sources in the not yet explored energy range below 200 GeV, down to few tens of GeV. For this purpose we optimised most parameters of the telescope. One of the main goals was to promptly react to GRB alerts from satellite missions. With a lot of technological efforts we were finally able to re-position the telescope to an arbitrary position in the sky within 25 s.
Although MAGIC was designed to observe GRBs, our multiple tries year-over-year remained unsuccessful. Despite that, we “polished” the GRB observation strategy of MAGIC over years and in the end we could operate these in a fully automatic observation mode; the incoming alert, after short evaluation by the software, triggers a sequence of actions for possibly fast observing the alerted position; no human interaction is involved in these. We were very well prepared for the next-best GRB alert arrival. And this is what has happened in the evening of January 14th 2019, when the telescopes fully automatically moved to the position alerted by the Swift satellite and started observations.
Initially the crew on the shift was astonished because despite the large zenith angle of ~60° and the presence of the partial Moon they could observe very fast increasing in intensity signal from the unknown position. Late in the evening of January 14th I got a call from the shift crew in La Palma and got informed about what was going on; the collected data for the first 20 minutes showed more than 20 sigma significance in the online analysis. I asked the crew to observe the GRB as long as it is possible during that night. The rest of the night I spent communicating with my colleagues scattered worldwide, checking again and again the authenticity of the signal. Few hours after the onset of the burst, in the hope that possibly large number of instruments could join observations of the GRB 190114C, I sent an ATel and a GCN circular. Very early on the following morning I flew to Tucson, AZ, for attending the inauguration of the Schwarzschild-Couder telescope. Big was my surprise when arriving at the conference location I was overwhelmed by curious questions and numerous congratulations from my colleagues, including also the leading colleagues from Veritas, H.E.S.S., and CTA.
Wagner:
We commenced our specific GRB program very early after the H.E.S.S. array started observations and have followed up several dozen triggers over the past 15 years. While many features of the GRB programme were continuously improved in order to enable a fast reaction to automatic triggers, the very first GRB ever to be detected with our telescopes last year was actually discovered in the deep afterglow phase, more than 10 hours after the initial event. At the time of the prompt burst, the source was below the horizon for the H.E.S.S. telescopes. The burst originated at a rather high redshift (by VHE standards) and hence suffers from significant photon-photon pair-absorption on the extragalactic background light. The discovery was possible thanks to the enormous light collection power of the 28m CT5 telescope of the H.E.S.S. array.
What can we learn about GRBs from these new measurements? Did they lead to a common picture concerning the modelling of gamma-ray bursts?
Wagner:
The most important message of the first detection is that GRBs clearly emit very high energy emission deep in the afterglow phase. At least in the specific case of GRB180720B the energy flux in the VHE band is comparable to the energy flux in the X-ray band even 10 hours after the burst – similar to the match between the X-ray band and the HE band probed with Fermi 100s after the burst when the flux was still 5000 times brighter.
SED development of GRB 190114C in time measured by Swift XRT/BAT, Fermi GBM/LAT and by MAGIC. The MAGIC measurement is split into 5 consecutive periods of time. For the first 2 time bins also the data from the mentioned satellites are shown.
Mirzoyan:
The first measurements show that the afterglow of GRBs is accompanied by the second peak in its spectral energy distribution (SED) at (sub-)TeVs, resembling much the blazars. And this second Synchrotron-Self-Compton (SSC) is pretty energetic, it has a power comparable to that of synchrotron emission at lower energies. This means that until the recent past researchers were missing a substantial part of energy from the GRBs and that these are more powerful than thought before. The presence of the 2nd peak will help us to constrain and pinpoint many physical parameters of GRB jets and of the surrounding medium. We made a significant step towards improving our understanding of GRBs.
Wagner:
Not all GRBs are alike and it is not credible to claim a unique common picture based on two different observations of two different bursts. The interpretation of the GRB180720B data is not straightforward. Both, a standard synchrotron and a standard synchrotron-self-Compton are difficult to reconcile with the data.
And is it relevant to have seen both the prompt and also the after glow emission with respect to the models?
Mirzoyan:
Only a wide field of view (FoV) instrument can observe a GRB in its prompt phase. The narrow FoV instruments like Imaging Air Cherenkov Telescopes (IACTs) also in future would rely on satellite mission alerts on GRBs. MAGIC observation of GRB 190114C started at 58 seconds after the onset of the GRB, so although this should be the in the afterglow phase, a small contribution from the prompt phase cannot be excluded. Our modelling indicates that about half of the radiative output of the GRB 190114C is emitted in the prompt emission phase and the other half in the afterglow phase. The afterglow contains a wealth of information on the interaction of the relativistic jet launched by GRB with the ambient medium. Of course it would be fantastic to observe a GRB in its prompt phase with a ground-based instrument, which covers, for example, an area in excess of 25000 m² (HAWC, LHAASO); the initial rate of gammas would be so high that one needs to carefully design the DAQ system, for preventing its saturation. Observation of the prompt phase with its structured signal at TeVs could provide additional important clues like, for example, to processes when and how a jet is launched and expands, for unravelling the sequence of the complex processes happening at the initial phase of the bursts.
Wagner:
It is extremely important to cover GRBs during the prompt and the afterglow phases. We would have profited a lot from observations of the prompt phase of GRB180720B or longer-lasting observations of GRB 190114C. The two bursts are different and the two data sets do not lead to an unambiguous common scenario. We will need to observe many more bursts in more detail to fully understand the mechanism giving rise to the VHE emission.
Was it a coincidence that both experiments achieved this result at about the same time, or did the technology develop in such a way that such measurements are now feasible and we will be able to measure GRBs more frequently in the future?
Mirzoyan:
The question that in the past year we frequently asked ourselves is why it took so long, say 15 years, to measure a gamma-ray signal from a GRB at TeV? The first answer is that these happen not so frequently at relatively low red-shifts. It is well-known that the strong EBL (extragalactic background light) absorption limits the reach of IACTs at high energies; for example, we estimated that the 1 TeV emission from the GRB 190114C, residing at the red-shift of 0.42, is attenuated by 300 times. The second answer is that the probability is higher that these will happen at large zenith angles (i.e. at energies much higher than the threshold of a given ground-based instrument); one needs to correspondingly plan the reaction of instruments to alerts. The third reason is that one needs to observe a GRB at any, even at barely acceptable ambient lighting conditions, once it is relevant; this further enhances the chance probability. And the last but not least answer is that one needed to show in the first time that in fact, it is do possible to measure a (sub)-TeV signal from a GRB and this is just what MAGIC did. The good thing is that the GRBs will become regular observational targets at (sub)-TeVs and soon the successful measurements will provide wealth of data allowing us to find clues to many puzzling questions about these monstrous explosions.
The giant CT5 telescope of the H.E.S.S. array. With its 28m lage main mirror it is by far the largest Cherenkov telecope in the world. Its light gathering power was instrumental for the discovery of the first GRB ever discovered in the VHE band – GRB 180720B. Credit: HESS/Vikas Chander
Wagner:
GRB180720B was an extraordinarily bright burst. Our GRB alert scheme would have identified such an exceptional burst many years earlier and we would have aimed for follow-up observations in case the position of the burst in the sky and weather conditions would have allowed observations. The discovery would have been possible earlier, but such bright bursts are rare. Given the delay of 10 hours after the event before the position in the sky became observable, the CT5 telescope, which started operations about 5 years before GRB180720B, was essential. The technology continuously advances, and the rare GRBs have always been a much sought-after target in the entire community such that any improvement raises the likelihood of successful observations. We are hence optimistic that we will be able to measure GRBs more frequently in the future. As with any rare and unpredictable event, however, one needs to be prepared, alert, – and lucky.
At what point were you aware that you had actually detected GRBs and what are the verifications you needed to do from detection to publication?
Mirzoyan:
We got convinced that in fact MAGIC has measured a monstrous strong signal >20 sigma from GRB 190114C within the first two hours after the alert from the Swift satellite mission, in the late evening of 14th January 2019. In the next morning, while sitting in the plane aiming to Tucson, I was surprised to see ten (10) analyses results, performed by the collaboration members from Spain to Germany, from Italy to Japan. The reported signal strength were in the range 40-60 sigma (this value depends on the used cuts). From that moment on we started carefully evaluating the systematic errors related to our detection. So essentially we looked into diverse technical issues for carefully evaluating the systematic errors. There were no problems related either to signal strength, statistical errors or remaining background (the latter was really negligible). We spent a lot of time for coordinating exchange of data with about two dozen space-born and ground-based instruments, which observed the GRB 190114C, for developing our model of the GRB afterglow emission.
Wagner:
We knew from the start that GRB180720B is an exceptional burst. The information in the initial trigger information clearly identified it as an unusual bright GRB even before the position became visible for H.E.S.S. and this information was folded in when the observational strategy was set. Nonetheless it was a rather faint signal which did not allow an unambiguous detection during the observations. Any H.E.S.S. result is cross-checked using different analyses and flaring events – which cannot be re-observed – require careful control of the trial factors in the analysis. Given the X-ray brightness of the prompt burst it was clear that even an upper limit would provide important constraints and we used a dedicated unblinding procedure for off-line analysis in the weeks following the event. The verification of the analysis and final publication goes much beyond the mere detection and involved spectral and temporal analysis.
Future CTA Telescopes – This image illustrates all three classes of the 99 telescopes planned for the southern hemisphere as viewed from the centre of the array. While not an accurate representation of the final array layout (the smallest telescopes will be spread just beyond the centre), this rendering illustrates the enormous scale of the CTA telescopes and the array, itself. Credit: Gabriel Pérez Diaz, IAC / Marc-André Besel, CTAO
What do you expect from future experiments like CTA?
Wagner:
GRBs have been one of the key motivations when designing CTA and it is reassuring to see these discoveries now. Some of us started to worry about not having detected GRBs despite the more than decade-long searches with H.E.S.S. and MAGIC. In our discovery paper we address CTA perspectives and estimate that we should detect one GRB with CTA every 4 months on average and be able to observe the afterglow for about 10 bursts every year.
Mirzoyan:
I expect that already the current generation of telescopes will measure a solid sample of GRB emissions in the afterglow phase. The future will become only better with operation of the large number of well-designed and optimised CTA telescopes. One may anticipate that due to the higher sensitivity the CTA telescopes can find fainter GRB emissions and possibly in rather late phases of their emission. The very low threshold of the telescopes will probably not play a decisive role because the GRBs will mostly happen under large observational angles, well above the threshold. Of course it is very much desirable to have a threshold as low as few tens of GeV; this could help to observe the population of GRBs from beyond the red-shift of 1. I anticipate that within the next 10 years we will gain a very solid knowledge on the GRB afterglow and maybe with a piece of good luck in a few cases, also on the prompt phase.
A very-high-energy component deep in the γ-ray burst afterglow; The H.E.S.S. collaboration; Nature, 2019;
DOI: 10.1038/s41586-019-1743-9
Teraelectronvolt emission from the γ-ray burst GRB 190114C; The MAGIC collaboration; Nature, 2019;
DOI: 10.1038/s41586-019-1750-x
Observation of inverse Compton emission from a long γ-ray burst; The MAGIC Collaboration; Nature, 2019;
DOI : 10.1038/s41586-019-1754-6
Razmik Mirzoyan
Stefan Wagner
Dr. Razmik Mirzoyan is an astro-physicist, since 1992 working at the Max-Planck-Institute for Physics in Munich, Germany. He is currently the spokesperson of the MAGIC collaboration and the EU spokesperson of the TAIGA collaboration. His main interests are in astrophysics, astro-particle physics, cosmic and gamma rays, cosmology and in photon sensors. He defended his PhD thesis in FIAN in 1984. Since then he is working in the ground-based very high energy gamma-ray astronomy with imaging air Cherenkov telescopes (IACT). He is one of the founders of the HEGRA IACT array (1991-2002) as well as the co-founder of the MAGIC IACTs (2003- till now). He has made strong contributions in fast photo sensors as the classical PMTs, SiPMs, Hybrid Photo-Diodes, significantly improving and boosting their performance. He is co-authoring 15 patents in EU and in a number of foreign countries. He is a honorary professor of Irkutsk State University and a foreign member of the National Academy of Sciences of Republic of Armenia.
Prof. Stefan Wagner is a professor for astrophysics at Heidelberg University and Co-sokesperson of its IMPRS graduate school on astronomy and Cosmic Physics. Having worked mostly of active galactic nuclei he is very much engaged in multi-wavelength studies of non-thermal sources and time-domain astronomy. He co-founded the H.E.S.S. experiment, has coordinated its multi-wavelength working group for many years and is the current director of the H.E.S.S. facility and spokesperson of the collaboration. He has been responsible for CTA governance and hosted the international CTA project office during its design phase.
The APPEC General Assembly (GA) came together in Lisbon at the Laboratory of Instrumentation and Experimental Particle Physics (LIP). The meeting started on the evening of 2 December with an excellent dinner, which was already used for first informal discussions. On the next day the APPEC Chair Teresa Montaruli and the local organizer and representative of Portugal, Mario Pimenta welcomed the GA and Pimenta opened the session with an overview on Astroparticle Physics in Portugal. Subsequently, the resumption of Poland participation to APPEC with CAMK representing it was approved by the General Assembly. Prof. Leszek Roszkowski will be the selected representative of Poland in the GA. He informed the Assembly of the excellent European Community financed AstroCENT (https://astrocent.camk.edu.pl), which has the scope of developing dedicated projects in astroparticle physics with the scope to develop innovation at the border between this field, computing, sensor and electronic development and medical applications.
Then the list of discussion points was worked through. It covered
an status report on the European Particle Physics Strategy Update and proposed recommendations,
the proposal towards a more sustainable APPEC,
the organisation of the next Town Meeting,
the proposal of a technology forum of APPEC open to ECFA and NuPECC,
and the progress of the Scientific Advisory Committee.
Regarding the last point we would like to highlight the final report of the Neutrinoless Double Beta Decay sub-committee, see also here.
The time for the meeting was by then almost over and the remaining was used for a report from the Joint Secretary (JS). Unfortunately we had to let one of our JS colleagues go and we would like to take this opportunity to thank Francesca Moglia for her time at APPEC and wish her all the best for her future.
A new instrument mounted atop a telescope in Arizona has aimed its robotic array of 5,000 fiber-optic “eyes” at the night sky to capture the first images showing its unique view of galaxy light.
DESI’s 5000 spectroscopic “eyes” can cover an area of sky about 38 times larger than that of the full moon, as seen in this overlay of DESI’s focal plane on the night sky (top). Each one of these robotically controlled eyes can fix a fiber-optic cable on a single object to gather its light. The gathered light collected from a small region in the Triangulum galaxy (bottom) by a single fiber-optic cable (red dot) is split into a spectrum (bottom) that reveals the fingerprints of the elements present in the galaxy and aid in gauging the distance to the galaxy. The test spectrum shown here was collected by DESI on Oct. 22. (Credit: DESI Collaboration; Legacy Surveys; NASA/JPL-Caltech/UCLA)
It was the first test of the Dark Energy Spectroscopic Instrument, known as DESI, with its nearly complete complement of components. The long-awaited instrument is designed to explore the mystery of dark energy, which makes up about 68 percent of the universe and is speeding up its expansion.
DESI’s components are designed to automatically point at preselected sets of galaxies, gather their light, and then split that light into narrow bands of color to precisely map their distance from Earth and gauge how much the universe expanded as this light traveled to Earth. In ideal conditions DESI can cycle through a new set of 5,000 galaxies every 20 minutes.
The latest milestone, achieved Oct. 22, marks the opening of DESI’s final testing toward the formal start of observations in early 2020. Installation of DESI began in February 2018 at the Nicholas U. Mayall Telescope at Kitt Peak National Observatory near Tucson, Arizona. Over the past 18 months, a bevy of DESI components were shipped to the site from institutions around the globe and installed on the telescope.
A view of DESI’s fully installed focal plane, which features 5,000 automated robotic positioners, each carrying a fiber-optic cable to gather galaxies’ light. (Credit: DESI Collaboration)
DESI’s focal plane, which carries 5,000 robotic positioners that swivel in a choreographed “dance” to individually focus on galaxies, is at the top of the telescope. These little robots – which each hold a light-gathering fiber-optic cable that is about the average width of a human hair – serve as DESI’s eyes. It takes about 10 seconds for the positioners to swivel to a new sequence of targeted galaxies. With its unprecedented surveying speed, DESI will map over 20 times more objects than any predecessor experiment. The focal plane is fed by corrector optics which provide a 3-degree-diameter field of view. The optical fibers mounted to the positioners extend 50 meters down the telescope to feed 10 broad-band spectrographs, each containing three detectors. The spectrographs cover a spectral range of 360 nanometers (nm) to 980 nm with a resolution of 2,000 to 5,000, enabling DESI to probe redshifts up to 1.7 for emission line galaxies and 3.5 for the lyman-α spectra from quasars.
“This is a very exciting moment,” said Nathalie Palanque-Delabrouille, a DESI spokesperson and an astrophysics researcher at France’s Atomic Energy Commission (CEA) who has participated in the selection process to determine which galaxies and other objects DESI will observe. “The instrument is all there. It has been very exciting to be a part of this from the start,” she said. “This is a very significant advance compared to previous experiments. By looking at objects very far away from us, we can actually map the history of the universe and see what the universe is composed of by looking at very different objects from different eras.”
All this was only possible with substantial contributions to DESI from European partners: The University College London oversaw the optical system of large lenses in the corrector, Durham University the fiber optic system that brings light from the focal plane to the spectrographs. The Aix-Marseille University worked closely with the spectrograph vendor Winlight (in Pertuis, France) to assemble and test the spectrographs, CEA/Saclay provided the system of 30 cryostats for the ultra low-noise sensors inside each spectrograph, the Laboratoire de Physique Nucléaire et de Hautes Énergies in Paris developed and installed the calibration system for the spectrographs. A Barcelona-Madrid consortium including IFAE (Institut de Fisica d’Altes Energies), ICE (Institut de Ciències de l’Espai), CIEMAT (Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas) and IFT (Instituto de Física Teórica) developed the ten high-sensitivity guiders that reside on the focal plane – these guide the Mayall telescope on our targets. The École Polytechnique Fédérale de Lausanne worked with US partners and the Swiss vendor Maxon (in Sachsein, Switzerland) to develop the robotic system in DESI.
Interview with Anatael Cabrera on the development of an opaque scintillator.
In this issue we would like to give Anatael Cabrera the opportunity to present his new development of a liquid scintillation detector — “LiquidO”. In contrast to established scintillators, which are transparent, LiquidO consists of an opaque scintillator and a dense array of fibres. Anatael Cabrera will tell us more about it:
Can you briefly explain the idea behind LiquidO? What is the difference between this detector and the established scintillators?
LiquidO is essentially an evolution of the popular scintillator detectors pioneered by the Reines (et al.) in the 50’s for the neutrino discovery. Their approach used transparency so that the light emitted upon
neutrino interactions is detected by photo-sensors located up to some meters apart. Their detection principle shaped much of the neutrino detection technology since. Instead, LiquidO breaks with the need for transparency to, ironically maybe, allow for unprecedented sub-atomic particle imaging based on scintillation light for the first time. Counter-intuitively, light diffusion is used to sharpen otherwise blurred patterns, as optical photons are stochastically confined locally to each particle energy deposition. The level of detail is at first glance spectacular. For example, one could recognise the annihilation of anti-matter, such as a positron (e+), even with negligible kinetic energy as illustrated in figure 1.
Figure 1: The back-to-back pattern is due to the two γ-rays (511keV) obtained upon the annihilation of a positron (e+), whose imaging could be exploited to tag low energy anti-neutrino CC interactions and medical practical applications in the PET scanner instrumentation. Each point represents a fibre, pitched 1cm apart. The colour code is proportional to the number of photons hit per fibre, while in today’s technology, the photon detection efficiency is ≤5.0% (~1/20x less). All other event-displays are done using detected photons. However, today, the light level is subjected to possible optimisations, particularly envisaged for energy deposition <1MeV.
This imaging allows, in turn, event-wise particle identification for the first time in liquid scintillator medium up to the MeV in energy. This game-changing capability may help us impact much of today’s neutrino detection paradigm. For example, we might reduce our dependence on passive shielding, including deep overburden in underground laboratories to yield major background rejection. Besides, the light opaque medium offers a relaxed optical scenario enabling us to consider both new scintillation technology — first explorations are ongoing — and the ability to accommodate large doping levels, boosted by up to one order of magnitude relative to today’s state of the art. Altogether, LiquidO seems to offer a novel detection framework inheriting many feature from the well known scintillation detection legacy while capable, should performance allows, to seed some degree of revolution in some physics channels.
You also illustrated your idea in a poster at the JENAS 2019, the Joint ECFA-NuPECC-APPEC Seminar. Could all the three disciplines benefit from the new technology?
I think so. Let me suggest two examples below.
First, LiquidO was born in neutrino physics; a subject historically bridging across particle, nuclear and astro-particle physics domains like very few. A concrete example is laid by our most recent studies, where the potential of LiquidO for GeV neutrino physics have been explored. This was first presented in November 2019 in the context of the DUNE experiment. A LiquidO detector there could play a competitive role in particle physics via the first explorations of leptonic CP-violation. Neutrinos, in turn, are unique probes to challenging nuclear physics where LiquidO may offer new handles — under active study — aimed for the better control of systematics and background recognition. Our preliminary studies suggest that LiquidO may yield comparable topology to the exquisite liquid-argon TPC detectors. We have identified even some unique additional but complementary features, as illustrated in FIG II. In such a large detector located far from reactors, even the first explorations on 40K geo-neutrinos may be considered for the first time, see here, thus providing unique insight to our understanding of our planet, that might draw other general lessons in the context of astro-physical planet formation and dynamics.
Second, there appears an increasing number of cases where LiquidO might offer a rich detection framework beyond neutrino and rare decay. Since, I am far less of an expert, I’d just quote a few examples. Some colleagues are interested in calorimetry and search for rare particles in HEP colliders, thus exploiting LiquidO’s calorimetric-tracking ability and its high duty-cycle. This might benefit LHC or future FCC/ILC programmes. Even, possible societal/industrial applications, such as medical and reactor nuclear industry, are under active consideration. Our teams are exploring LiquidO as possible technology for a full-body PET scanners and remote reactor monitoring — a topic of high interest to the IAEA in the context of non-proliferation.
Which experiments may benefit from the LiquidO technology?
Figure 2: An electron neutrino CC interaction is illustrated, where the detected light is coloured coded. The leading lepton (e±) undergoes an electromagnetic shower. A halo of low energy depositions, including e+ annihilation, surround the shower. An outgoing track (π±) decays into a μ± when stopped. An energetic neutron (n) is also ejected from the interaction point. The n is recognised from the proton-recoil ionisation and its energy can be measured via time-of-flight.
Well, the more we study LiquidO, the more it appears this question may have more answers than we originally suspected. Although LiquidO was forged in reactor neutrino brainstorming, it appears surprisingly versatile beyond. Personally, I think that its ability to handle low MeV is most precious, even boosting its ability to handle higher energies with rich details, as shown in figure 2. Besides, the neutrino MeV range is rich in challenges, including many neutrino sources, such as the sun, the Earth, supernovae, reactors and decay at rest beam neutrinos. Today, much of our effort is devoted to address your question, where several publications are envisaged or even under preparation. We keep careful track of the physics to design and target the critical ongoing detector R&D — always limited by our very humble resources, specially manpower.
Figure 3: The most explored p→π0 + e+ proton decay channel is illustrated. The decay kinematical back-to-back pattern is expected, where the π0 decay into two γ’s is particularly clear thanks to the low density and long radiation length of LiquidO. The e+ electromagnetic shower can also be observed. The full pattern provides a strong event-wise rejection to possible background cases with high efficienc
As of today, our main studies, so far, had brought us to consider two main potential experimental topics — leptonic unitarity and high mass ββ decay searches. These subjects are renown for their possible discovery potential beyond our successful Standard Model of Particle Physics. While still early, the first feasibility publications are materialising shortly with very promising results. A remarkable research potential beyond today’s reach seems attainable. The observation of leptonic unitarity violation would imply the direct manifestation of new physics via the existence of non-standard neutrino states and/or non-standard interactions — either way, a breakthrough. Likewise, the positive observation of the neutrinoless double beta decay might reveal the deepest nature of the neutrino itself for the first time, including direct and unique sensitivity to its absolute mass scale. The first project was first presented in the EPS-HEP conference (July 2019), where we highlighted the potential to improve the precision on θ13 by almost one order of magnitude. We have developed a full strategy employing reactor neutrinos with a 10 kton LiquidO detector located at Chooz (France), thus the historical Chooz remains one of the best reactor sites in Europe. This hypothetical project, called for now “Super Chooz”, offers an additional uniquely “open sky” research programme, including proton decay as well as supernovae and solar neutrinos detection. LiquidO may excel in the proton decay discovery potential, as illustrated in figure 3. Whereas unprecedented explorations of the sun, and even supernovae, neutrinos may be possible via interactions on doped indium (Raghavan 1976), leading to a robust coincide signature for detection. Although indium based detection has never seen light in an experiment, much of the past groundbreaking R&D demonstrated that large doping levels (order 10%) are feasible. The second project was however first hinted in the NOW-2018 conference (September 2018) and a publication is in preparation. These ambitious experimental goals have so far encounter no evident scientific showstopper. However, we are looking forward to further pushing our detector performance quantification for consolidation in feasibility. While more challenges will surely be ahead, today I can tell that the background control for the ββ programme is one of the most extreme requirements so far.
Have you already gained some experience with the new detector or is it all based on simulations?
First prototype of the LiquidO detector.
Indeed, the experimental validation was, for me, a critical necessary condition to disclose LiquidO, conceived around 2013 but otherwise kept secret till the materialisation of its robust proof-of-principle. Until then, “it looked too good to be true”. Ironically, since LiquidO inherits from the well known scintillation detection, the addition of light scattering may have appeared as a trivial extrapolation. And while it may well be true, the new powerful imaging goes so far beyond today’s performance — and intuition — that dedicated experimental demonstration was highly desirable to ensure performance beyond surprises. This was achieved between mid-2018 and early-2019 using a “tiny” 0.25 litre prototype. The data was easily obtained with our new opaque scintillator (see Novel Opaque Scintillator for Neutrino Detection), but much thinking, extra support laboratory measurements and simulations aided the final corroboration, thus succeeding our first unambiguous experimental proof-of-principle. Since then, we have found no evidence whatsoever of any inconsistency to our scattering dominated model. Hence, LiquidO was decided to be officially released in June 2019 along with our first publication (see LiquidO: Novel Opaque Neutrino Detection Technology and Neutrino Physics with an Opaque Detector).
What are the next steps you have planned?
In 2020, we expect the culmination of our small prototype based R&D and much of the ongoing physics prospect explorations. This should lead to several beautiful publications. Beyond that, we believe neutrino based data is needed to sizeably proceed and yield final consolidating demonstration. Hence, we aim for a few tons full scale demonstrator LiquidO detector to yield accurate performance quantification for physics feasibility. While scaling always entails somewhat a step into the unknown, the experimental programme proposed enables demonstration via leading measurements in the context of neutrino detection and ββ-decay background sensitivity hosted in two European underground laboratories. This programme, proposed in Europe, is led by four principal investigators, including spokespersons from 3 experiments and the extra support by the recently formed LiquidO proto-collaboration and cooperators. We are ready to proceed, as soon as the funding comes along.
Anatael Cabrera is a neutrino physicist since 2001 when he started his DPhil degree at the University of Oxford (UK) within the MINOS experiment. He is currently CNRS/IN2P3 scientific staff at the Linear Accelerator Laboratory (Orsay, France). Since 2014, he is director of the underground LNCA laboratory (Chooz, France). He is currently spokesperson in the Double Chooz and also supports the JUNO experiment, where he led the co-coordination of the JUNO electronics/trigger system. In 2015, he conceived, proposed and co-coordinates since the Dual Calorimetry system aimed for extra high precision calorimetry control and its dedicated physics programme. Around 2013, he conceived the LiquidO detection technique. Today, LiquidO stands as an international scientific project supported by a proto-collaboration. He is co-spokesperson of LiquidO along with Prof. F. Suekane (RCNS/Tohoku University, Japan).
The APPEC General Assembly and the Scientific Advisory Committee (SAC) appointed a sub-committee to discuss the searches for the neutrinoless double beta decay and the future of the European programme. This sub-committee should advise APPEC on the European (and international) programme in double beta decay physics. It should report to the APPEC SAC, providing an assessment of the current and future scientific opportunities in double beta decay over the next 10 year period. In October this year, the sub-committee published their report on arXiv: https://arxiv.org/abs/1910.04688. This document, which was approved by the APPEC SAC was then discussed during the APPEC Community Meeting on Neutrinoless Double Beta Decay held in London on Oct. 31, 2019. About 50 people attended it and discussed the contents of the document and the necessary future steps for neutrinoless double beta (0nubb) decay especially in Europe. All presentations are collected in https://indico.cern.ch/event/832454/timetable/#20191031.
The meeting was opened by the APPEC Chair, Teresa Montaruli, who highlighted the importance to receive comments from the APPEC Community on the document and endorse it and the recommendations contained in it. The Chair of the SAC, Laura Baudis, remembered the APPEC Roadmap recommendation on neutrinoless double beta decay: APPEC strongly supports the present range of direct-neutrino mass measurements and searches for neutrinoless double-beta decay. Guided by the results of experiments currently in operation and in consultation of its global partners, APPEC intends to converge on a roadmap for the next generation of experiments into neutrino mass and nature by 2020. Laura Baudis explained the full process of forming the panel who edited the document and the mandate of the panel defined by the SAC to execute APPEC recommendation of the panel.
“Given the importance of neutrinoless double beta decay searches, the leading role Europe is playing and the prospects for the future, we provide below the key recommendations in order of relevance.
Recommendation 1. The search for neutrinoless double beta decay searches is a top priority in particle and astroparticle physics.
Recommendation 2. A sustained and enhanced support of the European experimental programme is required to maintain the leadership in the field and exploit the broad range of expertise and infrastructure,and fostering existing and future international collaborations.
Recommendation 3. A multi-isotope program at the highest level of sensitivity should supported in Europe in order to mitigate the risks and to extend the physics reach of a possible discovery.
Recommendation 4. A programme of R&D should be devised on the path towards the meV scale for the effective Majorana mass parameter.
Recommendation 5. The European underground laboratories should provide the required space and infrastructures for next generation double beta decay experiments and coordinate efforts in screening and prototyping.
Recommendation 6. The theoretical assessment of the particle physics implications of a positive observation and of the broader physics reach of these experiments should be continued. A dedicated theoretical and experimental effort, in collaboration with the nuclear physics community, is needed to achieve a more accurate determination of the NMEs.“
The KM3NeT Collaboration launches the drawing contest “Draw me a neutrino”:
Participants from France, Georgia, Greece, Italy, Morocco, South Africa, and Spain are invited to submit, before March 15h 2020, their best interpretation of a neutrino. The drawings can be realised using any technique or support (digital drawings are welcome) and will be judged based on their originality, the creativity demonstrated by the author and the harmony with the properties and origin of the neutrinos.
Three different groups will enter the competition:
The budding scientists will imagine how is an electron neutrino like;
Teenagers that have already been in contact with physics are in charge of drawing a muon neutrino;
Adults are invited to tackle the tau neutrino.
In addition to the national contests organised in the countries previously mentioned, an international competition will be organised. Selected drawings will be part of the Art & Science across Italy exhibition at the National Archeological Museum in Napoli, Italy in May 2020. Besides receiving a selection of KM3NeT goodies, the winners will also have the opportunity to give their names to one of the sensors deployed in the Mediterranean Sea that will participate to the next discoveries made with KM3NeT.
Through this contest, the KM3NeT Collaboration is seeking to familiarize the broad public to the science carried out with this new European facility that is currently under construction more than 2000 metres deep in the Mediterranean Sea. While the completion of the detector, whose sites will be located off-shore Toulon in France and Capo Passero in Italy, is expected for 2025, the Collaboration is already searching for the best illustration of the neutrinos it will detect!
More information about the contest, the rules, and the neutrino itself can be found on: http://wos.ba.infn.it
The 4th Workshop of Big Data Science in Astroparticle Physics – Deep Learning & Open Data – will take place from 17 -19 February 2020 in Aachen, Germany. The workshop covers the following topics:
Hands-on tutorials
Deep Learning
Open Data-Software-Analysis
Actual developments
For those who never worked with deep network there is the possibility to participate in a beginners tutorial on Deep Learning.
This workshop is supported by Helmholtz Alliance for Astroparticle Physics HAP and Arbeitskreis Physik, moderne Informationstechnologie und Künstliche Intelligenz der Deutschen Physikalischen Gesellschaft e. V. AKPIK.
In November 2019 about 300 scientists and guests from all over the world celebrated the 20th anniversary of the Pierre Auger Observatory with a ceremony and a scientific symposium at the site of the Observatory in Argentina. The Pierre Auger Observatory has been built to study ultra-high energy cosmic rays, particles of the highest energies ever observed.
The participants of the celebration lined up in front of the main building of the observatory for a group picture (photo: Miguel Martin).
Ultra-High Energy Cosmic-Rays
Cosmic-rays are charged particles constantly bombarding the Earth and are one of the cosmic messengers that help us understand our Universe. At the highest energies, they are not much deflected by the Galactic and extragalactic magnetic fields, opening up the possibility of a new window in astronomy, the observation of the near-by Universe with charged-particles. The goal of the Pierre Auger Observatory is to study the nature and origin of those ultra-high energy cosmic rays, whose energy exceeds more than 100,000 times the energy that can be achieved in man-made accelerators.
The Pierre Auger Observatory
The Pierre Auger Observatory was conceived by Jim Cronin, Alan Watson and other scientists in 1991 to address the mysteries of the origin and nature of the highest-energy cosmic rays. It was clear to them that only a very large detector would reach the exposure to collect enough events to answer the questions raised by a century of earlier experiments. The Observatory design employs a „hybrid“ detector system consisting of a 3000 km2 array of 1660 particle detectors overlooked by 27 optical telescopes. These complementary detector techniques record both the particles and the faint fluorescence light resulting from the gigantic particle cascade initiated in the atmosphere by these mysterious cosmic rays. Soon after the foundation in 1999, construction of the Observatory started and was completed in 2008.
20th Anniversary
f.l.t.r.: Roberto Rivarola (Member of Board of Directors of CONICET), Fernando Ferroni (Chair of Finance Board), Ingo Allekotte (Bariloche, Project Manager Pierre Auger Observatory), Jorge Vergara Martínez (Mayor of Malargüe), Paula Nahirñak (Sub-secretary of State in Secretariat for Science and Technology), Osvaldo Calzetta (President CNEA), Ralph Engel (KIT, Spokesperson Pierre Auger Observatory), Alberto Etchegoyen (CNEA, Site Spokesperson), Julio Cobos (National Senator for the Province of Mendoza), Laura Montero (Vice-governor of the Province of Mendoza), Ernesto Maqueda (CNEA), Alan Watson (former Spokesperson Pierre Auger Observatory) (photo: Miguel Martin)
Scientists of the 90 participating institutes and groups, as well as representatives of all 17 member states of the international collaboration met in Malargüe, Argentina in mid-November to celebrate the 20th anniversary of the experiment as well as the scientific results achieved so far. A scientific symposium opened the festivities and highlighted the state of research. On the second day, the participants visited the detectors of the Observatory in the Argentine Pampa. Many of the scientists and guests participated also in the parade for the anniversary of the city of Malargüe. The meeting continued with a ceremonial act at the campus of the Observatory. Venerable members of the collaboration as well as representatives of funding agencies and local politicians addressed the audience and congratulated the collaboration not only on the scientific successes, but also on the social relevance and impact of the project in the province of Mendoza. One highlight of the ceremony was the conferral of the status “Honorable Senator” to the Pierre Auger Observatory by the Senate of Argentina. After unveiling a sculpture by Juan Pezzani symbolizing the role of the Pierre Auger Observatory in Argentina, the meeting concluded with a dinner banquet with typical Argentine barbecue and wine.
A Bright Future
Spurred by the science results obtained so far, the Observatory is currently undergoing an upgrade („AugerPrime“), mostly aimed at improving the sensitivity of the observatory to the particle type and mass of ultra-high energy cosmic rays. This is done by installing new electronics, and additional and complementary detectors, allowing for a better separation of the type of the incoming particle on an event-by-event basis. The added observables are critical to select the subset of particle cascades that were produced most likely by lighter primary cosmic rays, which in turn may hold the key to identifying and studying the cosmic accelerators outside our own galaxy. More generally, the data collected with AugerPrime will also be used to explore fundamental particle physics at energies beyond those accessible at terrestrial accelerators, and perhaps yield the observation of new physics phenomena.
— CANCELLED/POSTPONED, please check the website of the event for further information —
The second EPS (European Physical Society) Conference on Gravitation is held at King’s College (London, UK) from April 7th to April 9th, 2020. The aim of the conference is to discuss experimental aspects of Gravity, including General Relativity tests, measurements of the G constant, Geodesy, and Gravitational Waves.
The conference is organized in days focused around key topics introduced by invited speakers and followed by contributed talks. There will also be a poster session, together with four Young Scientist Awards to the best poster contributions by skilled young researchers .
Early registration ends 1st March, 2020 and abstract submission ends 2nd February, 2020.
— CANCELLED/POSTPONED, please check the website of the event for further information —
The first Pollica Summer Workshop on Dark Matter aims to bring together the world’s leading experts, both from theory and experiment, working on a broad range of ideas, existing and proposed experiments. This workshop, which will take place in the beautiful setting of the medieval town of Pollica in the Cilento region in Italy is an opportunity to galvanize theoretical efforts in a period where new experiments come online and the particle physics community must think broadly about new frontiers ahead. This is an exciting time to connect fundamental physics to the upcoming experimental landscape. The workshop is scheduled for the dates of 15-26 June 2020 and will be hosted in the 14th century Castello Dei Principi Capano.
The deadline for applications is January 31st 2020.
The APPEC General Assembly and the Scientific Advisory Committee (SAC) appointed a sub-committee to discuss the searches for the neutrinoless double beta decay and the future of the European programme. This sub-committee should advise APPEC on the European (and international) programme in double beta decay physics. It should report to the APPEC SAC, providing an assessment of the current and future scientific opportunities in double beta decay over the next 10 year period. In October this year, the sub-committee published their report on arXiv: 
Participants from France, Georgia, Greece, Italy, Morocco, South Africa, and Spain are invited to submit, before March 15h 2020, their best interpretation of a neutrino. The drawings can be realised using any technique or support (digital drawings are welcome) and will be judged based on their originality, the creativity demonstrated by the author and the harmony with the properties and origin of the neutrinos.
The 4th Workshop of Big Data Science in Astroparticle Physics – Deep Learning & Open Data – will take place from 17 -19 February 2020 in Aachen, Germany. The workshop covers the following topics:
