News and Events
Swiss LHC computing Tier-2 moves to HPC
The ATLAS computing group of LHEP has pioneered the integration of High Performance Computing (HPC) systems with the ATLAS distributed computing frameworks, starting as far back in 2004. The work resulted in the first successful integration of a Cray supercomputer at CSCS, which ran in production for ATLAS for several months [Hostettler M, Enabling the ATLAS Experiment at the LHC for High Performance Computing, Masterarbeit an der philosophisch-naturwissenschaftlichen Fakultaet der Universitaet Bern 2015].
This venture catalysed the interest of the Swiss CMS and LHCb colleagues and also of some European and worldwide centres, which have since adopted the innovative solution devised at LHEP. It also triggered a Swiss-wide HPC integration effort, involving all the CHIPP partners and CSCS: the LHConCray project ran for about two years in 2016-17, with the aim of integrating the flagship Cray supercomputer at CSCS (Piz Daint) with the three LHC experiment frameworks. Its success, lead by the LHEP ATLAS effort, resulted in the bold decision by the CHIPP computing board to fully migrate the Swiss Tier-2 centre hosted at CSCS from a dedicated linux cluster to Piz Daint. The transition has been completed on 1st April 2019.
This is the first time a supercomputer is used as part of the Worldwide LHC Computing Grid (WLCG) to handle data processing for all LHC experiments workflows as Tier-2 centre. The WLCG tier-2 hosted at CSCS on behalf of CHIPP has been previously operated for over ten years on a dedicated linux cluster, specifically engineered for the LHC experiment workloads.
Sciacca F G, Weber M, Production experience and performance for ATLAS data processing on a Cray XC-50 at CSCS, in 23rd International Conference on Computing in High Energy and Nuclear Physics, CHEP 2018, Sofia, Bulgaria, 9 - 13 Jul 2018, http://cds.cern.ch/record/2649473
Elementary particles reveal the landscape of Switzerland
Muon radiography is a method to inspect internal structure of large objects by means of cosmic muons. This method has been applied to glaciological studies of the Bernese Alps from a team of LHEP physicists in collaboration with a research group of the Institute of Geology of the University of Bern. A large area (600 x 300 m^2) of the Eiger glacier was indeed "roentgraphed". The results published in Nature Scientific Reports (link: https://www.nature.com/articles/s41598-019-43527-6) revealed strong lateral glacial erosion of active glacier, which have never been studied by other methods. This work provides new understanding of the landscape of Switzerland.
More information: University of Bern press release
First demonstration of antimatter wave interferometry
Wave-particle duality of single positrons in a double-slit like experiment has been demonstrated by the QUPLAS collaboration. It is the first antimatter equivalent of the single electron interference experiment proposed by A. Einstein and R. Feynman and realized in 1976 by Merli, Missiroli, Pozzi and in 1980 by Tonomura. A team of particle physicists from the University of Bern provided important contributions to the experiment.
More information: University of Bern press release
Bern students visit Fermilab
A group of bachelor students of this semester course of particle physics of the University of Bern visited Fermilab. They had the unique chance to meet scientists involved in state of the art experiments and to have dedicated lectures on the various activities of the American laboratory. In particular, they visited the MicroBooNE and SBND experiments where researchers of AEC/LHEP Bern are involved. They also met the Fermilab Director Nigel Lokyer and the two co-spokespersons of the MicroBooNE experiment Bonnie Fleming and Sam Zeller (see photograph).
DUNE RRB and PIP-II groundbreaking
With a ceremony held on March 15th 2019, the Fermi National Accelerator Laboratory officially broke ground on a major new particle accelerator project that will power cutting-edge physics experiments for many decades to come.
The new 200 meter-long linear accelerator, part of the laboratory’s Proton Improvement Plan II (PIP-II), will be the first accelerator project built in the United States with significant contributions from international partners. When complete, the new machine will become the heart of the laboratory’s accelerator complex, vastly improving what is already the world’s most powerful particle beam for neutrino experiments and providing for the long-term future of Fermilab’s research program.
The new PIP-II accelerator will make use of the latest superconducting technology. Its flexible design will enable it to work as a new first stage for Fermilab’s chain of accelerators, powering both the laboratory’s flagship project — the international Deep Underground Neutrino Experiment (DUNE), hosted by Fermilab — and its extensive suite of on-site particle physics experiments, including searches for new particles and new forces in our universe.
An AEC-LHEP group is intensively involved in the LBNF/DUNE activities centered in particular of the innovative ArgonCube concept for the Near Detector complex of the experimental setup.
New experiment at the LHC, FASER, approved
On March 5th 2019, CERN approved the FASER experiment, which will search for new particles (e.g. dark photon) at the LHC. In contrast to the conventional experiments (ATLAS, CMS) that search for strongly interacting heavy particles, FASER will look for light and weakly interacting particles that may be created in the proton-proton collision at the LHC. The detector will be located at 480 m downstream of the ATLAS detector.
LHEP is a part of the FASER Collaboration (represented by A. Ariga) and is contributing to the beam characterization and background measurements. During 2018, we performed an in-situ measurement in the LHC tunnel using emulsion detectors. The results helped to confirm the feasibility of the experiment.
National Future Day
On this year's National Future Day (Zukunftstag) several kids visited the laboratories of LHEP. They experienced the "typical everday life" of mechanics and physicists by manufacturing their own toy-cars, making liquid nitrogen ice-cream, and launching water-bottle rockets.
Novel neutron interferometry concept published and funded
A proposed new method to measure the electric charge of the neutron has been published recently [F.M. Piegsa, Phys. Rev. C 98 (2018) 045503]. The concept is based on a so-called Talbot-Lau interferometer which represents a unique high-sensitivty instrument to detect the smallest beam deflections. These deflections can either be caused by ultra-small angle scattering, gravitational interaction, or electromagnetic interaction of the neutron. Ultimately, such an interferometer can be employed to perform a future high-precision measurement of the neutron electric charge at the upcoming European Spallation Source in Sweden. The Swiss National Science Foundation will fund the realization of this novel effort of the Fundamental Neutron Physics Group of LHEP for the next three years.
Neutron beam time at PSI completed
The Fundamental Neutron Physics Group of LHEP has just completed another successful beam time at the BOA beam line at the Paul Scherrer Institute (PSI). During the four-week-long beam time we tested several crucial components and methods of the new Beam EDM proposal. Among them was the use of high-voltage electrodes to measure the relativistic vxE-effect and the pulsed neutron beam measurement mode. This will give us further important information on how to further upgrade our high-precision neutron Ramsey spectrometer.
First particle tracks in ProtoDUNE
The largest liquid-argon neutrino detector in the world has just recorded its first particle tracks, signaling the start of a new chapter in the story of the international Deep Underground Neutrino Experiment (DUNE). DUNE’s scientific mission is dedicated to unlocking the mysteries of neutrinos, the most abundant (and most mysterious) matter particles in the universe. The enormous ProtoDUNE detector – the size of a three-story house and the shape of a gigantic cube – is a prototype (1:20 in size) built at CERN for a part of the DUNE detectors which will be located in South Dakota (USA) to record neutrinos produced at Fermilab (near Chicago) 1300 km away. The ProtoDUNE detector took two years to build and eight weeks to fill with 800 tons of liquid argon. The detector records traces of particles in that argon, from both cosmic rays and a beam created at CERN’s accelerator complex. Now that the first tracks have been seen, the detector will be operated over the next several months to test the technology in depth. The LHEP at the University of Bern is leading the design of the detector used to measure the neutrinos at Fermilab at the start of their path to the DUNE site in South Dakota. An animation of how the DUNE and ProtoDUNE detectors work, along with other videos about DUNE, is available here: https://www.fnal.gov/pub/science/lbnf-dune/photos-videos.html. See also the CERN press release: https://press.cern/press-releases/2018/09/first-particle-tracks-seen-prototype-international-neutrino-experiment.
Prototype of the Resistive Shell LAr TPC
We have been able to realize and operate a first prototype of the so-called Resistive Shell LAr TPC. The TPC has a 7x7 cm2 footprint and 15 cm in length, and features a field cage built out of a thin (~50 um) resistive Kapton-based film, replacing the set of field-shaping rings normally used for such devices. One can create a resistive shell with a continuous linear potential distribution along the drift direction. The cathode plane is made of the same material, as well. The film is perforated to provide adequate liquid purification inside the active volume; this has been done only for the first test: we believe that we will not need any perforation for the ArgonCube design, where the film will be deposited directly onto the module walls. A tension of up to -15 kV is applied to the TPC cathode to generate a 1kV/cm drift field inside the drift volume. The total current through the resistive shell for -15 kV is 10 uA. No liquid boiling was observed during operation.
The anode readout plane has semi-classical projective readout, with 32 wires printed on each side of thin Kapton foil. The side facing the drift volume acts as collection plane, while the other side picks up the induction signal (opposite to the classical wire grid implementation). Therefore, the device can be referred to as a full-Kapton LAr TPC. The active area of the readout is 6x6 cm2 with a “wire" pitch of 1.875 mm. The readout electronics used in the test setup is based on the LARASIC7 cold charge preamplifier ASIC designed at BNL, and to the readout scheme of the former ArgonTube detector. During the first tests, trigger and t0 were given by a coincidence signal of two SiPM-based scintillating counters, placed directly in the liquid above and below the "field cage".
Two event displays of cosmic-muons for -3kV (200 V/cm) can be seen in pictures, together with the TPC itself. Needless to say, we will have to work further to assess all features of this detector, but we are confident that this technique could be a valid solution for future large-scale applications, notably in DUNE.
EU RISE grant for neutrino research
The group working on the Fermilab neutrino program has been awarded an EU RISE grant for the INTENSE project. The project is carried out with several European institutions in collaboration with US and Japanese groups. The goal of INTENSE is to promote and reinforce the collaboration among European, American and Japanese research institutions involved in some of the most important research projects in fundamental physics. In the last few years, INTENSE researchers have made outstanding contributions to the design of cutting-edge physics experiments capable of opening new windows in the field of particle physics. They are now involved in the construction, commissioning and data analysis of these projects, and the next generation of projects which require substantial technological advancements which also have applications outside of particle physics.
Three major observations cannot find an explanation in the Standard Model of particle physics. These include the baryon asymmetry of the Universe, the lack of a viable dark matter candidate and finally neutrino oscillations. The concept of flavour, i.e. the existence of three replicas of each family of elementary fermions with the same quantum numbers but different masses is a cornerstone in the physics of elementary particles, and it is realized in the SM by introducing three copies of the same gauge representations of the fermion fields.
The funds will be mainly used to foster mobility and networking between the groups involved in the SBN program at Fermilab (MicroBooNE and SBND for the Bern group).
A boon for physicists: new MicroBooNE results at Neutrino 2018
The MicroBooNE collaboration has produced their first collection of science results and presented them at the Neutrino 2018 conference in Heidelberg (D), attended by 800 physicists. MicroBooNE started operations in the fall of 2015. The detector, about the size of a school bus, is filled with 170 tons of liquid argon and has recorded interactions of hundreds of thousands of neutrinos, produced by an accelerator complex at Fermilab near Chicago (USA). It features a time projection chamber (TPC) that record the particle tracks created by the neutrino colliding an argon nucleus, similar to a 3D digital camera recording images of fireworks.Scientists at LHEP and AEC of the University of Bern are experts in the technology of liquid argon TPC and are playing a leading role in the experiment, including the physics measurements. Important systems to calibrate the detector with a UV-laser and to record signals from cosmic rays that also hit the detector were designed and built in Bern and are operated now in the experiment in the USA.
MicroBooNE is the first low-energy neutrino experiment to make detailed observations of the subatomic processes that happen when a muon neutrino hits and interacts with an argon nucleus, leading to showers of secondary particles including protons, pions, muons and more. The new results reported at the Neutrino 2018 conference include first measurements of the multiplicity – or number of particles – generated in these collisions, along with absolute yields per incident neutrino of collisions producing a neutral pion or a more inclusive final state.
The measurements are of great importance for the groundbreaking measurements to be performed in the search for a fourth neutrino type and in preparation for the Deep Underground Neutrino Experiment (DUNE) in which the University of Bern will also play a central role, together with other Swiss Universities. DUNE will be operational in the 2020ies and explore the role of neutrinos in the evolution of the universe.
OPERA collaboration presents its final result
On May 22nd 2018, the OPERA collaboration presented its final result on the muon neutrino to tau neutrino oscillation experiment. LHEP has been one of the leading groups in the OPERA experiment. Our journey started at the end of the last century. We took data in the CNGS (CERN to Gran Sasso) neutrino beam in 2008 - 2012, and the first tau neutrino event was reported in 2010. Followed by four more tau neutrino events, we announced the discovery of tau neutrino appearance in 2015. The result of OPERA gave a significant contribution to the 2015 Nobel Physics Prize for the discovery of neutrino oscillations. In this final result published in Physical Review Letters, the OPERA collaboration applied a new analysis strategy proposed by LHEP. A total of 10 tau neutrino events, twice more statistics than the previous result, allowed us to provide better constraints of the oscillation parameters in appearance mode. All data of these 10 events are now publicly available on the CERN open data portal. Beyond the contribution to neutrino physics, the particle detection and microscope technologies of OPERA are being applied to a wider field of research, such as the muon radiography of the Swiss glaciers (Geoscience) and intravital microscopy to study immune cells (Immunology).
PixLAr beam test completed
The collaboration between LHEP/AEC and Fermilab (USA) led to another new result: a novel pixelated charge readout system, an essential part of ARGONCUBE project, was successfully tested within the PixLAr experiment at beam test facility at Fermilab. Several millions of particle tracks were detected and reconstructed in a small-scale liquid argon detector. The PixLAr experiment is an evolution of the LArIAT experiment, improved, apart of pixel charge readout, with the novel photon detector designed at LHEP - ArCLight. Both systems have demonstrated excellent performance. A detailed data analysis is ongoing.
A study in Tau: DsTau-Project
The DsTau project is a newly launched project, aiming to study tau neutrino production in proton interactions. This study is prerequisite for future tau neutrino experiments, e.g. the SHiP experiment. Recently, the international DsTau collaboration (consisting of members from five countries) has submitted a proposal to the CERN SPS and PS Experiments Committee (SPSC). In January 2018, SPSC recommended a pilot run this year and a subsequent DsTau physics run in 2021 after the long shutdown of the CERN accelerator complex. DsTau is led by Dr. Akitaka Ariga from AEC/LHEP at the University of Bern. For more information, please visit the DsTau project web site: http://dstau.lhep.unibe.ch
ARGONCUBE module becomes reality
In January 2018, the assembly of the very first ARGONCUBE module (so called Mod-0) started at LHEP. The first one of four modules will serve as a test bed for several novelties of the ARGONCUBE concept - modular scalable large-mass Liquid Argon Time Projection Chamber of the future. The module will incorporate a small argon purity monitor and a light readout system. First wet tests at cryogenic temperatures are expected in May 2018.
Results on ArCLight sensor published
The ArCLight photon counting device combines advantages of two well-known photon detectors: vacuum photomultiplier tubes (PMT) and silicon photo-multipliers (SiPM). Large sensitive area of the one, merged with robustness and compactness of the other. This results in a very compact, flat, almost fully-dielectric photon readout device, perfectly suited for use in high electric field environment, such as in Liquid Argon TPCs. First results on characterization of the device have been published: http://www.mdpi.com/2410-390X/2/1/3/
Axion Dark Matter Search
The nEDM collaboration has published new results on a laboratory-based search for axion dark matter in the journal Physical Review X. It provides valuable constraints for the properties that these hypothetical particles can have — and thus a guide to where to look next. LHEP is a member of the international collaboration which performs its high-precision experiment at the ultracold neutron source at the Paul Scherrer Insititute.
Particle Physics at "Nacht der Forschung"
As every three years, the night was lit up by science and dance, mixed in an interactive experience. For one night the visitors of the University of Bern could explore the wonders of research of the infinitely small. From seeing particle detectors in action to discussions with theorists as well as playing with interactive simulations, "treating cancer" patients with hadron therapy, collide protons by kicking them, exploring detectors in virtual reality, or enjoying an ice cream made with liquid nitrogen. Anyone visiting and presenting had a lot of fun learning and sharing. We cordially thank everybody that came to this year's "Nacht der Forschung".
Link to the official video of "Nacht der Forschung".
Successful neutron beam time at PSI
The members of the Fundamental Neutron Physics Group of LHEP have just completed their first beam time of four weeks at the neutron spallation source SINQ at the Paul Scherrer Institute. First experiments were performed using a high-precision neutron Ramsey prototype apparatus. The setup is ultimately intended for a novel neutron electric dipole moment search using a neutron beam. This first results will provide valuable input for the future development of the setup. Another beam time is scheduled for January/February 2018 - this time at the European research facility Institute Laue-Langevin in Grenoble (France).
First SBND neutrino data with Cosmic Ray Tagger from Bern
On the morning of June 22, a first subdetector of the Short-Baseline Near Detector (SBND) began taking data at Fermilab (USA, Chicago). The subdetector called Cosmic Ray Tagger (CRT) is designed and constructed at LHEP. The CRT is composed of many finely grained modules capable of measuring a particle interaction instance with the accuracy of a nanosecond in time, and a centimeter in space. With the newly operational Cosmic Ray Tagger in its current configuration (beam telescope), SBND is currently characterizing the flux of particles called muons. These muons are produced by neutrinos from the Booster Neutrino Beamline and they carry information about parameters of the parent neutrino beam at SBND pit. Data taken during this characterization stage will be a great asset on the way to simulation and analysis for the whole SBND detector later on.
Muon radiography of Alpine glaciers
The interdisciplinary project "Eiger-mu GT (Eiger muon glacier tomography)" has published a new paper recently. It was highlighted by Geophysical Research Letters, one of the most prestigious journals in geophysics. The paper reports the results from the first feasibility test of muon radiography at Alpine glaciers. The researchers installed small detectors, made of emulsion films, at several locations inside the Jungfrau railway. After analyzing the films with the high-resolution microscopes in LHEP, they succeeded in resolving the interface between glacial ice and granite rocks in the very uppermost part of the Aletsch glacier, the largest glacier in the Central Swiss Alps. The project is a collaboration between the Laboratory for High-Energy Physics (LHEP) and the Institute of Geological Sciences (GEO), University of Bern, supported by Swiss National Science Foundation.
Bern cyclotron laboratory is promoting science in particle accelerator applications
Saverio Braccini and Paola Scampoli from AEC-LHEP edited a special issue of Modern Physics Letters A (MPLA) dedicated to cyclotrons and their applications (http://www.worldscientific.com/toc/mpla/32/17). The idea originated from the 12th workshop of the European Cyclotron Network (CYCLEUR 2016) held in Bern on 23-24 June 2016 together with the 2nd Bern Cyclotron Symposium. Experts form the main cyclotron facilities in Europe came together to discuss about current cutting-edge results and future prospects on a broad spectrum of scientific topics. In the last years, an increasing number of medical cyclotrons allowed for routine production of isotopes for diagnosis and therapy as well as for beams for cancer hadron-therapy. At the same time, research was conducted to foster advances in several directions by means of dedicated infrastructures. The book collects specific contributions giving a picture of the rich scientific research programs based on cyclotrons.
Ultracold Neutron Workshop in Bern
For three days Bern became the capital of ultracold neutron physics. More than 40 international scientists from Belgium, France, Germany, Poland, the United Kingdom, the United States, and Switzerland participated in a three days workshop at the University of Bern. The workshop, which was hosted by LHEP and the Albert Einstein Center, focused on the low-energy high-precision Neutron Electric Dipole Moment (nEDM) experiment carried out at the Paul Scherrer Institute (Switzerland).
The search for a nEDM is currently considered to be one of the flagship experiments in fundamental physics at low energy and presents a route for finding new physics beyond the standard model of particle physics. A permanent nEDM violates discretes symmetries, e.g. parity and time-reversal symmetry. Such new sources of symmetry violation can be directly related to the observed matter-antimatter asymmetry of our universe.
ERC Starting Grant
Florian Piegsa from LHEP has been awarded with a prestigious ERC Starting Grant (ERC). Over the next five years, the grant will allow him to further establish his reseach projects at the University of Bern and to push forward a new experimental appraoch to search for a neutron electric dipole moment. The corresponding experiments will be carried out in Bern, at the Paul Scherrer Institute (PSI) and international neutron research facilities. These activities will foster the already existing strong links and collaborations between PSI and the University of Bern.
The new LHEP-wepage is online since April 2017.
New research group in LHEP
Florian Piegsa, previously working in the Institute for Particle Physics at ETH Zurich, has joined LHEP on a SNSF-professorship position in October 2016. His new research group is investigating the fundamental properties of the neutron in precision low-energy particle physics experiments. The research activities of the group are summarized here.
T2K presents first results on CP violation
The question why the Universe is matter dominated, instead of being made of equal parts matter and antimatter, is still unsolved as of today. One of the conditions required to develop the observed dominance of matter over antimatter is the violation of the Charge-Parity (CP) symmetry. This says that the laws of physics should be the same if viewed upside-down in a mirror (P), with all matter exchanged by antimatter (C). If CP violation occurs in neutrino physics, it will manifest itself as a difference in the oscillation probabilities of neutrinos and antineutrinos. The international T2K Collaboration recently observed that the electron antineutrino appearance rate is lower than expected from the electron neutrino appearance rate, assuming that CP symmetry is conserved. The image shows an anti-electron neutrino.
The new result was announced at the 38th International Conference on High Energy Physics in Chicago. With nearly twice as much antineutrino data than before, T2K continues to see the trends observed in 2015: a preference for maximal disappearance of muon neutrinos and a discrepancy between the electron neutrino and electron antineutrino appearance rates. When analyzed in a three-neutrino framework, and combined with measurements of electron antineutrino disappearance from reactor experiments, the T2K data favor maximal CP violation (δCP=–0.5π). The CP conserving values (δCP=0 and δCP=π) are outside of the 90% confidence level interval. This result is based on a total data set of 1.51x10e21 protons on target, which is 19% of the planned exposure.
In the T2K experiment, a muon neutrino beam is produced at Japan's east coast and sento to the gigantic Super-Kamiokande underground detector, 295 kilometers away. The T2K Bern group is deeply involved in the near detecor (ND280) data analysis with the aims of constraining and improving the neutrino cross section parameters used as inputs to the T2K oscillation analyses. It also measures neutrino cross sections, which are essential for current and future neutrino oscillation experiments.
European cyclotron experts meet in Bern
The 12th workshop of the European Cyclotron Network (CYCLEUR 2016) was held in Bern on 23-24 June 2016, organized by the Albert Einstein Center for Fundamental Physics (AEC) and supported by the swissHADRON foundation. It reassembled cyclotron experts from about 40 cyclotron laboratories in Europe, Canada, Korea and Tunisia. It was followed by the 2nd Bern Cyclotron Symposium, where specific topics were presented by invited speakers. With about 25 talks, this event gave an updated overview on scientific activities at cyclotron laboratories as well as in industry.
The main highlights are reported in the following. Accelerator physics developments for radioisotope production and proton therapy are focused on compact and effective solutions for medical applications. Novel beam monitoring detectors are instrumental for optimal production of non-standard radioisotopes for medicine. In this domain, increasing interest is shown on theranostics, which means the use of isotopes of the same element for diagnostics and therapy. In particular, scandium and gallium are proposed for PET and scandium and astatine for metabolic therapy. A recent field of application is the use of radioactive nanoparticles. Radiation protection plays a crucial role and traces of specific radioisotopes can be used to detect the artificial production of radioactivity as in the case of nuclear explosions.
The participants had the opportunity to visit the Bern cyclotron laboratory, where industrial GMP PET radioisotope production is performed together with multi-disciplinary research activities.
The science opportunities of DARWIN
The DARWIN collaboration has recently published a detailed article on the multi-ton dark matter observatory DARWIN, its science channels, its background and on the R&D towards its realization. DARWIN's main goal is to explore all experimentally accessible parameter space in the search for weakly interacting massive particles (WIMPs), a prime dark matter candidate. The study, signed by 119 authors and with key contributions from the Bern DARWIN group can be found here: arXiv:1606.07001.
With a design target mass of 40 tons of liquid xenon, DARWIN will be able to search for
- WIMP dark matter in the spin-independent, spin-dependent and inelastic channels,
- axions and axion-like particles via the axio-electric effect,
- low energy solar neutrinos (pp-neutrinos, 7Be neutrinos),
- coherent neutrino-nucleus scattering,
- neutrinos from supernova explosions,
- neutrinoless double-beta decay of 136Xe,
- and other rare nuclear processes.
The Figure from the publication shows the sensitivity of DARWIN to the effective Majorana neutrino mass via a search for the neutrinoless double-beta decay of 136Xe. Two different exposures (30 t x y and 150 t x y) at two different background levels are shown. The 'ultimate' case assumes that background from the detector materials can be removed completely, thus the remaining backgrounds are from 222Rn in the Xe target, 8B solar neutrinos and the two-neutrino double beta decay.
LHC and ATLAS back into operation
On March 25, 2016, the most powerful collider in the world, the Large Hadron Collider (LHC) at CERN, has resumed operation after its annual winter break, with a center of mass energy of 13 TeV. The Laboratory of High Energy Physics and the Albert Einstein Center at Bern (LHEP/AEC) play a key role in ATLAS, one of the four large experiments. The accelerator complex and the experiments have been turned on and tested over the last weeks and detectors have now started the data taking. The Figure below shows one of the the first collision events with stable beams, recorded on April 23, 2016. The LHC operators will increase the intensity of the beams gradually until the maximal rate of collisions is reached.
During the winter break the detectors were further improved. The ATLAS experiment went through an optimization of the track recording detectors (silicon pixel detector), which are located closest to the collision points right in the center of ATLAS. The Bern ATLAS group has important responsibilities for this detector system. In fact, it leads the largest upgrade performed during the shutdown, which concerned the installation of new detector readout components to double the readout speed in order to overcome bandwidth saturation. New optical readout components were specifically developed and built in Bern, together with new software which was integrated in the final readout system. The picture below shows test of the optical plugin in the laboratory in Bern.
Science with a medical PET cyclotron
Beyond routine radioisotope production for medical purposes, compact medical cyclotrons can be at the heart of multidisciplinary research facilities. The cyclotron laboratory in Bern is a prime example, as described by the AEC-LHEP scientists Saverio Braccini and Paola Scampoli in a recent article published in the April issue of the CERN Courier.
Medical PET cyclotrons are usually employed by hospitals and radiopharmaceutical industries for the routine production of radioisotopes. To match the patient's examination schedule, they run during the night or early in the morning, while their beams are not used during daytime and could in principle be used for other projects. This represents an opportunity to exploit the science potential of these accelerators well beyond Positron Emission Tomography (PET) applications. To perform multidisciplinary research, beams of variable shape and intensity must be available together with the possibility of accessing the beam area. For this purpose, the Bern facility is equipped with a transport line leading the beam to an experimental area, which is always accessible for scientific activities.
Thanks to this solution, the AEC-LHEP medical application group is conducting scientific activities in several research fields, such as as nuclear and detector physics, material science, radiation hardness, and radiation protection. The Bern facility daily serves the local University Hospital (Inselspital) and other Swiss healthcare centers with FDG, the most common PET radiotracer, and actively searches for alternative medical radioisotopes. In particular, scandium-43 has been proposed as novel radioisotope, having nearly ideal nuclear decay properties for PET.
Eiger-µ GT launched
The new interdisciplinary project "Eiger-µ GT (Eiger muon glacier tomography)" has been launched recently. It is a collaboration between the Laboratory for High-Energy Physics (LHEP) and the Institute of Geological Sciences (GEO), University of Bern, aiming to "see" inside glaciers of the Swiss Alps using cosmic-ray muons. Thesse are are most abundant charged particles in cosmic rays and can penetrate several kilometers of rock. The project will rely on this high penetration power to investigate the thickness of the glacier in way similar to medical X-ray radiographies in hospitals.
The first target is the Eiger glacier, which straddles at the western flank of the famous Eiger mountain. Several small detectors, made of higly sensitive emulsion films with a micrometer resolution, were installed at several locations inside the Jungfrau railway tunnel in December 2015. The detectors will sit in the tunnel until the end of March 2016, when they will be recovered and read out using the scanning microscopes at LHEP Bern. The reconstruction of the arrival direction of the muons, using their tracks in the emulsion films, will allow the reconstruction of the material between the detector and the mountain surface, which is important to answer several geological questions.
XENON1T gears up to search for dark matter
After several years of design, R&D and construction work, the new XENON1T experiment is now close to completion. The instrument, which uses about 3.5 tons of cryogenic liquid xenon as detector material to search for galactic dark matter, was recently inaugurated at the Italian Gran Sasso laboratory, where it is protected from cosmic rays by 1400 m of rock. The astroparticle physics group of AEC/LHEP Bern is a key member in this project. It is responsible for core components such as the design, construction and assembly of the central time projection chamber and its electronic readout. The video summarizes more than 2 years of construction effort by more than 120 scientists from 21 insitutions in about 5 minutes.
Beam currents in the pA-range obtained at the Bern medical cyclotron
Medical cyclotrons for the production of radioisotopes are designed to operate with beam currents of the order of 100 microampere (µA). These particle accelerators have a large potential for multi-disciplinary research provided that access to the beam area is possible and currents orders of magnitude lower are achievable. To obtain stable proton beams down to the pA range, the AEC-LHEP medical applications group developed a method based on ion source, radio-frequency and magnetic field tuning. The results were published recently in Measurement Science and Technology.
The 18 MeV cyclotron at the Bern University Hospital (Inselspital) is used every night for the production of radioisotopes for Positron Emission Tomography (PET) while, during the day, the proton beam is available for scientific activities. Researchers can access the irradiation area by means of a second bunker, where a transport line provides beams of variable shape and intensity, a peculiar feature for a hospital-based facility. While currents above 10 µA are standard for this kind of accelerator, its operation at lower intensities is challenging, especially if high stability is required for specific experimental activities. By operating the ion source at the minimum of 1 mA and by tuning the radio-frequency peak voltage together with the magnetic field produced by the main coil, stable beams down to 1.5 pA were obtained. A further decrease of intensity can be obtained by means of collimators. The importance of this method relies on the fact that it opens the way to the exploitation of radioisotope production medical cyclotrons in fields such as novel detector physics, material science, dosimetry and radiation biophysics.
The Nobel Prize in Physics for Neutrino Research
The Nobel Prize in Physics for the year 2015 has been jointly awarded to Takaaki Kajita and Arthur B. McDonald for the discovery of neutrino oscillations. In 1998, Kajita and collaborators discovered with the Super Kamiokande detector that the flux of atmospheric muon neutrinos observed on Earth depends on the energy and travel distance of neutrinos, as expected if neutrinos do oscillate. Later on, McDonald together with his colleagues of the SNO collaboration, reported the evidence for flavour conversion of solar neutrinos.
The two experimental results were sensational. However, this was not end of the story, since independent measurements with "artificially created neutrinos" (e.g. from accelerators) were needed to firmly assess these ground-breaking results. In this spirit, the OPERA experiment, originally proposed in 1997 by Ereditato - now director of LHEP Bern -, Niwa and Strolin, was designed and built to measure for the first time the same oscillation channel of atmospheric neutrinos in Super Kamiokande, but in appearance mode, namely detecting the event-by-event appearance of tau neutrinos emerging via oscillations from an initially pure muon neutrino beam.
OPERA successfully reported the first tau neutrino event in 2010 and finally reached a five-sigma statistical significance (required to claim the discovery of tau appearance) in spring 2015. The article was recently published in Physics Review Letters. In addition, the T2K collaboration, in which LHEP researchers are involved as well, started data taking in 2009 and reported the appearance of electron neutrinos in a muon neutrino beam in 2013.
Both OPERA and T2K provided the the "final" strong support to the oscillation hypothesis, as recognized by the Nobel Committee:
"Super-Kamiokande’s oscillation results were later confirmed by the detectors MACRO and Soudan, the long-baseline accelerator experiments K2K, MINOS and T2K and more recently also by the large neutrino telescopes ANTARES and IceCube. Appearance of tau-neutrinos in a muon-neutrino beam has been demonstrated on an event-by-event basis by the OPERA experiment in Gran Sasso, with a neutrino beam from CERN."
All LHEP researchers congratulate Takaaki Kajita and Arthur B. McDonald for receiving this years Nobel Prize in Physics.
MicroBooNE sees first events
The MicroBooNE experiment at Fermilab consists of a 170 ton liquid argon time projection chamber (TPC), installed along the short baseline Booster neutrino meanline. The experiment will measure low energy neutrino cross sections and investigate the low energy excess events observed by other experiment, which might be explained by sterile neutrinos. The TPC technology allows for the precise measurement of the tracks of charged particles, a crucial feature for particle identification and energy measurements. After months of commissioning work in the initial phase of the experiment, MicroBoone recently observed its first cosmic ray and UV-laser generated events. This is reported in the press release issue by Fermilab.
The Bern MicroBoone group is responsible for the UV-laser calibration of the detector, for which one event is shown above. The laser track is the one ending with the "red blob" at the TPC cathode. This calibration is crucial as space-charges modify the local electric fields in the TPC, and the straight laser tracks are used to correct for this effect. The MicroBoone experiment will start "hunting" for sterile neutrinos in the near future.
ARGONCUBE is gaining momentum
The ARGONCUBE project is the follow-up of the successful ARGONTUBE R&D program at LHEP Bern, which demonstrated for the first time that charges can be drifted over the world-record length of 5 m in liqid argon. The new concept of the ARGONCUBE liquid argon time projection chamber (TPC) for future neutrino experiments, based on many identical "cubic" modules immersed into a big liquid argon volume, was suggested by the researchers from LHEP Bern. It has attracted the interest of various groups from Portugal, Switzerland, Turkey, UK and USA, who came to Bern on August 27th, 2015 for the first meeting of the Collaboration. A Letter of Intent has been sumbitted to the CERN SPSC, which encouraged the Collaboration to conduct the first phase of the research at LHEP Bern.