News and Events
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.