Wuppertal summer school: Interdisciplinary perspectives on particle physics
On 23–30 July 2018, physicists joined forces with researchers from the humanities to address historical, philosophical and sociological aspects of particle physics in Wuppertal, Germany. The event, the third in a series of spring and summer schools, was organised by the research unit The Epistemology of the Large Hadron Collider (ELHC), and was funded by the German Research Foundation and the Austrian Science Fund, with additional support by the University of Wuppertal. ELHC is an international collaboration between physicists, philosophers, historians and sociologists that aims for a comprehensive understanding of the goals and methods of LHC research. The unit has been active for approximately two years and follows the lead of three earlier projects at Wuppertal conducted between 2009 and 2015.
Discussions focussed on the theme “Particle physics at the crossroads”: with no evidence of physics beyond the Standard Model from the LHC, where is particle physics headed? While these challenges are first and foremost being addressed by physicists, scholars from the humanities and social sciences can help identify the surrounding issues, such as the potential influences from social organisation. The talks at this year’s summer school were all exemplars of how work in the humanities and social sciences has a bearing on current issues in high-energy physics.
Kent Staley, a philosopher from St. Louis University in the US, analysed the statistical reasoning involved in LHC research, arguing that pragmatic considerations can explain why the practice of high-energy physics relies more on frequentist statistical methods than on Bayesian ones. As an example, he contemplated what the repercussions of erroneous claims to the discovery of a Higgs boson would have been for the community, and argued that frequentist methods are better suited to avoid such claims.
Friedrich Steinle, a historian of science from the Technical University Berlin, provided case studies of Newton and Faraday that demonstrated the fundamental role of concepts in physics, both in opening new vistas and providing long-term boundaries. For instance, Steinle argued that Newton’s embedding of a vis motrix (“moving force”) into a rich conceptual structure contributed to the success of Newtonian mechanics, and conjectured that a similarly deep conceptual change could open up new avenues in particle physics.
Rafaela Hillerbrand, a philosopher from Karlsruhe Institute of Technology, turned to another tool in LHC research – computer simulations. She proposed a classification of simulations depending on whether they provide information on abstract, laboratory or real-world systems, and discussed whether they should be seen as a theoretical or an experimental activity. This latter issue is hotly debated among philosophers, and LHC experiments, which rely on complex simulations, have attracted their attention.
Philosopher Chris Smeenk from Western University in Canada discussed a central topic in the philosophy of science: how can we ever claim even the approximate truth of a theory when the history of science shows that there were often alternative theories that had also been well confirmed empirically? Smeenk explored the extent to which this problem can be tamed by parameterising the space of alternative theories and using constraints to rule out some classes of theories. Giving an example, he explained that perturbative expansions around Minkowski space–time can be parameterised in such a way that possible alternatives to general relativity are fixed by the value ranges of these parameters.
Catherine Westfall, a science historian from Michigan State University, drew on the history of Fermilab during the 1960s and 1970s to highlight decision-making in the community. Even though in hindsight some of Fermilab’s research strategies (such as its initial focus on smaller and inexpensive experiments) seem wrong-headed, she explained, the expectation of finding new phenomena at higher energies eventually paid off, for instance with the discovery of the bottom quark.
Anne Dippel from Jena University in Germany offered an anthropologist’s perspective on the practice of particle physics. She emphasised that fierce competition, which is conducive to knowledge production at institutes such as CERN, manifests itself in many playful and even humorous elements in the daily work of researchers, such as the animal shelter for computer mice on the CERN campus. She also highlighted the creative potential of unforeseen incidents such as the incident at the LHC in September 2008 that temporarily forced the machine to close down.
Martina Merz, a scholar in science and technology studies at AAU Klagenfurt/Vienna, argued for the indispensability of images, such as event displays and plots of confidence limits, in reducing the complexity of the underlying data and establishing the existence of elementary particles such as the Higgs boson.
This programme was complemented by three inside views from physics. John Ellis from King’s College London and CERN offered his view on future theoretical developments; former CERN Director-General Rolf-Dieter Heuer provided insights into the factors driving particle-physics research; and ATLAS member Christian Zeitnitz from Wuppertal University, as well as Margarete Mühlleitner from the Karlsruhe Institute of Technology, gave introductory lectures on experiment and theory, respectively.
At the end of the school, the discussions returned to the central theme of “particle physics at the crossroads”, and found that the metaphor of a jungle, in which not even paths are clearly laid out, might be apt to characterise the current situation. One may feel reminded here of the situation in the 1960s where a “zoo” of particles was discovered without any hint, at least at first, of what theoretical structures underpinned them. However, the current situation is rather different because it is precisely such hopes for discovering particles beyond the current theory that have been dashed by the LHC so far.
The participants agreed that bringing together philosophy, history, sociology and particle physics was fruitful and less hampered by controversy than one might have expected. As the so-called science wars of the 1990s showed, it requires an open mind on all sides to facilitate a fruitful discussion between the natural sciences, the social sciences and the humanities. The future of particle physics may be uncertain, but collaborative efforts such as the Wuppertal summer school will certainly contribute to a better assessment of the aims and relevance of this branch of fundamental physics research.
Florian Boge RWTH Aachen University/IZWT Wuppertal and Adrian Wüthrich Technical University Berlin.
DIS2018: The future of deep-inelastic scattering
The most recent edition of the International Workshop on Deep Inelastic Scattering and Related Subjects (DIS2018) was held in Kobe, Japan, on 16–20 April 2018. The event continued in the style of a workshop, with almost 250 talks presenting new results on all things hadron physics: spin and 3D structure, structure functions and parton densities, and quantum chromodynamics (QCD) studies for high-sensitivity electroweak, Higgs and beyond-Standard Model measurements, to name a few.
The vast range of physics covered in DIS workshops cannot be easily integrated into a single theoretical framework, and there are slightly different views on hadronic interactions depending on the type and energy of the underlying collisions. One view, which applies to high-energy collisions, is a combination of fast-moving partons with little transverse momentum and a large amount of radiation in the initial and final states. Another is the parton and spin dynamics in hadrons and nuclei viewed “in 3D”, where the transverse momentum and collective motions of partons play an important role in describing hadron behaviour.
Traditionally, these two views are discussed separately at DIS meetings, but the situation is gradually changing owing to projects for new lepton–hadron colliders. The proposed Electron Ion Collider (EIC) at the Brookhaven National Laboratory or Jefferson Lab in the US, at centre-of-mass energies of about 100 GeV (CERN Courier October 2018 p31), would offer not only a detailed tomographic view of the space and spin structure of quarks and gluons inside nucleons and nuclei, but also, thanks to its very high luminosity, high-precision probes of partons that carry a high-momentum fraction of the parent hadron.
Meanwhile, the proposed Large Hadron electron Collider (LHeC) at CERN, bringing proton beams from the LHC into collision with electrons accelerated up to 60 GeV through a dedicated energy-recovery linac, would provide, in addition to precise measurements in the Higgs sector, more information on hadron structure through electron–proton and electron–ion collisions in regions of very low Bjorken-x and very high Q2. LHeC would also allow researchers to see, through the behaviour of total and diffractive cross sections in the high-energy limit, if there is any saturation in the parton evolution inside nucleons and nuclei. Further down the line, the Future Circular Collider hadron–electron (FCC-he) project at CERN, as well the proposed very-high-energy electron–proton (VHEeP) collider with a 3 TeV electron beam accelerated by a proton-driven wakefield, also at CERN, could probe hadron structure in the high-energy limit too. These projects are intimately related, and call for a unified discussion of hadron physics across collision energies.
Given these developments, the 2018 DIS workshop comprised experimental and theory talks covering results from various energy regimes, as well as review talks on related subjects such as neutrino–nuclei scattering, parton fragmentation and exotic hadrons, to seek possible connections between traditional DIS studies and new ones. In addition, this year’s event featured a special discussion session on future strategies for DIS studies and related subjects, following presentations by experimentalists from EIC, LHeC, VHEeP and FCC-he, and theorists working on QCD and heavy-ion physics. The responses of the participants were positive, noting the importance and complementarity of the projects. The outcome of the discussion has been summarised in a document that was submitted to the update of the European Strategy for Particle Physics.
The event also featured the award ceremony for the 2018 Guido Altarelli Award (CERN Courier July/August 2018 p36), which recognised the work of early-career scientists Jun Gao, on precision QCD theory, and Or Hen, on the “EMC effect” and the valence down- and up-quark ratio.
The next DIS workshop will take place in Turin, Italy, from 8 to 12 April 2019.
Yuji Yamazaki Kobe University and chair of the DIS2018 organising committee.
RUPAC2018: Russian accelerator science in focus
The 26th Russian Particle Accelerator Conference, RUPAC2018, was convened on 1–5 October 2018 in Protvino, Russia, at the Institute for High Energy Physics of the National Research Centre “Kurchatov Institute” (NRC KI–IHEP). This year the traditional biennial conference, which started in 1968, gathered some 170 participants from accelerator centres in Russia, Germany, Italy, Sweden, Romania, Canada and China to discuss the latest developments and results in accelerator science and engineering. The conference was organised bу the Budker Institute of Nuclear Physics (BINP), the Joint Institute for Nuclear Research (JINR), and the NRC KI–IHEP under the auspices of the Russian Academy of Sciences.
The 54 oral talks and 135 poster contributions featured both national and international accelerator facilities, but attention was directed at Russia’s domestic machines. BINP in Novosibirsk presented status reports on the VEPP-2000 and VEPP-4M electron–positron colliders, the operation of which has improved noticeably after the commissioning of a new positron injection chain. Talks from NRC KI–IHEP in Protvino reviewed the U70 proton synchrotron, which is now operated for 50–60 GeV fixed-target experimental physics, proton radiography studies and applied radiobiology research using carbon–nuclei beams.
The bulk of reports from JINR in Dubna were devoted to progress in the Nuclotron-based Ion Collider Facility (NICA) project at the nuclotron facility. Significant progress was also reported for the heavy-ion cyclotrons of the JINR’s Flerov Laboratory of Nuclear Reactions (FLNR). The status of, and plans for, the other operational domestic machines – the high-intensity proton linear accelerator at INR (Troitsk), the synchrotron radiation (SR) source KSSR-2 at NRC KI (Moscow) and the 1 GeV synchrocyclotron SC-1000 at NRC KI–PNPI (Gatchina) – were also presented. Due attention was also given to two new SR projects: the Siberian Circular Photon Source (SKIF) and the fourth-generation Specialized Synchrotron Radiation Source-4.
It was fitting that the conference was held in a year of a few round-figure anniversaries for the Russian accelerator community: 75 years of the Kurchatov Institute (Moscow); 60 years of BINP (Novosibirsk) and 100 years of its founder and first director Gersh Budker; 55 years of IHEP (Protvino); and 50 years since the first national particle accelerator conference, the forerunner of the RUPAC series, was convened. The next meeting will be held in the autumn of 2020.
Sergey Ivanov chair of the RUPAC2018 organising committee.
LHCb workshop: Community talks heavy-flavour physics and more
On 17–19 October 2018, physicists from the LHCb collaboration and the theory community gathered at CERN to discuss the implications of LHCb’s results and prospects for future studies. This was the eighth in a series of workshops that has become an annual tradition, attracting more than 200 physicists from all over the world, plus more participants connected remotely by video link.
LHCb is at the forefront of heavy-flavour physics research – as well as being active in heavy-ion and forward-electroweak physics – and the workshop was a welcome opportunity to discuss the latest developments, including some that were shown for the first time, and to consider what will be possible with LHCb’s planned upgrades. The workshop was capped by a theory keynote talk by Antonio Pich from Valencia, which addressed current tensions between the Standard Model (SM) and recent results in flavour physics.
The physics content of the workshop was divided into four streams. The first was on mixing and CP violation in beauty and charm hadrons, looking at non-leptonic decays. A major focus was on extracting the γ parameter of the Cabibbo–Kobayashi–Maskawa quark-mixing matrix and the B0 and Bs0 mixing angles, with experimental updates presented. Measurements of Bs0 mixing play an especially important role in constraining physics beyond the SM, and improved inputs from lattice quantum chromodynamics (QCD) calculations are crucial to this endeavour. Part of the session was dedicated to the decays of B mesons to multibody final states; the large CP asymmetries seen in these decays remain puzzling, and the community is eagerly waiting for experimental updates. The description of the final-state interactions in these decays is important but theoretically challenging. Many new, promising theoretical approaches, such as the use of triangle diagrams to describe the interactions, were discussed.
In the second stream, semileptonic decays, rare decays and tests of lepton flavour universality were covered. Discussions triggered by the tantalising hints of lepton-flavour-universality violation seen in tree-level and loop-
suppressed decays – RK and RK*, R(D) and R(D*), and the kinematic and angular
distributions of b → s μ+μ– decays – were the highlight of this stream. After reviewing LHCb’s experimental results, theory talks presented overviews of the status of SM calculations based on approaches such as non-perturbative lattice QCD simulations or QCD sum rules. Further new ideas were presented to improve SM predictions and address theory uncertainties, particularly those affecting predictions for B → D*ℓν decays. Finally, the implications of the present anomalies were discussed from a model-building point of view, with special emphasis on models including leptoquarks, which could explain several of the current anomalies at once.
The third stream of the workshop covered the active experimental programme spanning electroweak physics, exotica, heavy flavour, heavy ions and central exclusive production. In the related theory talks, the unique potential of LHCb’s forward acceptance to pin down the proton parton distribution functions in the unconstrained QCD regimes of low and high longitudinal momentum fraction (x) was discussed, as were a variety of models with the distinctive signature of displaced heavy neutral lepton decays that could explain neutrino oscillations and non-zero neutrino masses. Presentations also focused on the full multitude of charmonia (cc– states) accessible to LHCb beyond the J/ψ, from the ηc to exotic X, Y and Z states. Future measurements of these states in a variety of collision systems will shed light on the low-x QCD regime, on nuclear structure and on the as-yet-unresolved puzzle of quarkonium production itself. Finally, progress on CODEX-b, a proposed additional detector to search for long-lived particles at LHCb, was presented: the background flux in the cavern has been measured, and simulation studies of potential backgrounds were shown.
The fourth physics stream was devoted to QCD spectroscopy. LHCb reported discoveries of several new baryons with heavy flavour, and theory talks discussed the impressive success of a semi-empirical approach to predict their masses. There were also new results from LHCb on exotic hadrons – those that defy interpretation as conventional mesons or baryons – and predictions from theory for related future discoveries. Several different quark models as well as lattice QCD agree in predicting a stable tetraquark with two bottom quarks and two light antiquarks. Experimental prospects for its discovery with the upgraded LHCb detector were discussed, and a new experimental method using Bc+ mesons not originating at a primary vertex as a signature was proposed for identifying this and other hadrons with two bottom quarks.
Fresh results using data from LHC Run 2 were served up in all four streams, but there was a strong appetite for more. Key questions remain on the nature of the lepton flavour anomalies and on whether they will persist or fade as more data are added (CERN Courier April 2018 p23). Crucial questions also remain about the origin of the large local CP violation seen in multibody decays, the nature of exotic hadrons, and more. By the next workshop we will hopefully have some answers – and perhaps a few more questions. Preparations for the Run 3 physics programme will also be in full swing, ready for the big boost in statistics that will come from a complete overhaul of the detector and its readout system during the next two years (see p34). LHCb is also planning further upgrades, and the prospects for what we might learn with much more data – a factor 30 more than today – will surely be a hot topic.
Mat Charles on behalf of the LHCb collaboration and theory contributors.
CERN–South Africa: South Africa marks 10 years of CERN collaboration
An event commemorating the 10th anniversary of the CERN–South Africa programme took place at iThemba Laboratory for Accelerator-Based Sciences (iThemba LABS) in Cape Town from 19 to 21 November 2018, highlighting the importance of South African involvement in CERN and opportunities to further strengthen the partnership. The event was packed out, with the French and Swiss ambassadors to South Africa, the vice-chancellors of the universities of Cape Town and the Witwatersrand, internationally renowned physicists from CERN and South Africa, and many young students from South Africa and from other parts of Africa attending. The event also included impressive exhibitions and presentations from local industry.
In terms of the number of participating scientists and engineers, South Africa is CERN’s most important partner on the African continent. Researchers from several universities participate in the ALICE and ATLAS experiments as well as in ISOLDE, and are also visitors to CERN’s theoretical physics department. The South African particle-physics community continues to grow and is expected to benefit from important synergies with the Square Kilometre Array (SKA) radio-telescope project, which South Africa will host jointly with Australia and which will require a massive computing infrastructure similar to the worldwide LHC computing grid. In fact, the SKA organisation signed an agreement with CERN in 2017 to address the challenges of such “exascale” computing and data storage (CERN Courier September 2017 p9).
The LHC has brought many opportunities for South Africa’s science community, including contributions to major breakthroughs such as the discovery of the Higgs boson in 2012. In return, the CERN–South Africa partnership has helped to strengthen nuclear and particle physics efforts in South Africa. It has also accelerated technology development, enhancing both technological and social innovation and providing advanced scientific training for the next generation of South African scientists and engineers. It is expected and hoped that this valuable crossover of skills will continue long into the future.
Emmanuel Tsesmelis CERN.
ISOLDE workshop: Users highlight successful campaigns
On 5–7 December 2018, the annual ISOLDE Workshop and Users meeting took place at CERN, attracting 153 participants. The programme consisted of 41 presentations, of which 22 were invited talks and 19 were oral contributions selected from 74 submitted abstracts.
ISOLDE, CERN’s long-running nuclear research facility, directs a high-intensity proton beam from the Proton Synchrotron Booster (PSB) at a target station to produce a range of isotopes. Different devices are used to extract, ionise and separate the isotopes according to their mass, forming low-energy beams that are delivered to various experiments. These radioactive ion beams (RIBs) can also be re-accelerated using the REX/HIE-ISOLDE linear accelerators (linacs). An energy upgrade of the HIE-ISOLDE superconducting linac was completed this year, enabling RIBs with an energy up to about 10 MeV per nucleon.
A focus of the 2018 ISOLDE workshop concerned plans for upgrades and consolidation works during the second long shutdown of CERN’s accelerator complex (LS2), including replacing 10-year-old equipment and adding more beam-monitoring systems. Five sessions were devoted to overviews from ISOLDE users on the outcome of physics campaigns at the different experimental set-ups, two sessions discussed progress at other RIB facilities in the world, and one session focused on applications in life sciences with an emphasis on the CERN MEDICIS programme.
The meeting began with an overview of successful experimental campaigns at the HIE-ISOLDE RIB accelerator, with operational set-ups achieved at all three beam lines. A total of 17 different RIBs were accelerated during July–November 2018. Beams of isotopes with an atomic mass from 7 to 228, with the radium-228 beam being the heaviest ever accelerated beam at ISOLDE, were delivered. The HIE-ISOLDE campaign began with seven experiments at the first beam line, with the MINIBALL detector array and its ancillary detectors. In October two experiments used the new ISOLDE solenoid spectrometer at the second beam line for the first time, with an inner detector lent from Argonne National Laboratory. For these, the full accelerator capacity was used for the first time. At the third beam line, used for “traveling experiments”, three experiments used the scattering chamber – a large vacuum chamber that can hold several combinations of particle detectors brought by the users; one experiment used an optical time projection chamber to look for very rare proton decays from the halo nucleus beryllium-11.
The last experiment was performed in the scattering chamber, after protons stopped circulating in CERN’s accelerator complex, by extracting long-lived beryllium-7 from an ISOLDE target that had been irradiated earlier. The first HIE-ISOLDE physics paper, accepted for publication in Physical Review Letters, was also highlighted. It provides the first direct proof that the very neutron-rich tin-132 nucleus, considered to be doubly magic, does indeed merit this special status.
Other sessions were dedicated to the rich low-energy experimental physics programme at ISOLDE. Overview talks were presented on recent achievements in high-precision mass studies, with indium-100 as a highlight; on collinear laser spectroscopy studies, with a long series of antimony isotopes and isomers; on decay-spectroscopy experiments; and on the solid-state physics programmes. Participants also heard about recent studies with antiprotons at the Antiproton Decelerator at CERN and about the extremely exotic isotopes produced at the Radioactive Isotope Beam Factory (RIBF) facility at RIKEN in Japan. The study of exotic isotopes using the VAMOS spectrometer at the French GANIL laboratory was discussed, as were new beam-production facilities at the Selective Production of Exotic Species (SPES) facility at Legnaro National Laboratory in Italy and the new neutron detector array NEULAND at the Facility for Antiprotons and Ions Research (FAIR) at GSI in Germany.
The meeting ended with the handing over of four prizes, sponsored by CAEN, for the best talks and posters presented by young researchers (see image). The 2018 ISOLDE users meeting was a great success, highlighting the important research being done at this unique facility.
Gerda Neyens ISOLDE physics group leader.
CERN-Austria: Silver celebration for student programme
Young researchers from throughout the world came together at CERN on 30 November to celebrate the 25th anniversary of the CERN–Austrian doctoral student programme. Founded in 1993, following an agreement between CERN and the Austrian Ministry for Science and Research, the programme supports students from Austrian universities to pursue their PhD research at CERN in technology-related fields.
So far the programme has trained nearly 200 students in the stimulating environment offered by CERN. The bulk of these were in the fields of accelerator and detector research, with information technology and electronics also featuring large. Statistics from the programme show that, in the medium term, one third of all programme participants return to Austria, while much of the rest remain at CERN or work in other European countries.
Working in a cross-disciplinary and multicultural research environment such as CERN, participants learn how to collaborate in international networks, are exposed to leading-edge technologies and hone their language skills. The Austrian Ambassador, Elisabeth Tichy-Fisslberger, who participated in the celebration, underlined that the programme has also helped strengthen broader links between CERN and Austria, allowing significant technology transfer and networking with Austrian universities and high-tech industries.
The CERN–Austrian PhD programme serves as a model of efficient collaboration between CERN and its member states, and has inspired similar initiatives from other countries.
Michael Benedikt CERN.