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Weighing up the LHC’s future

As the LHC’s 2017 run drew to a close late last year, CERN hosted a workshop addressing future physics opportunities at the flagship collider. The first workshop on the physics of High-Luminosity LHC (HL-LHC) and perspectives at High-Energy LHC (HE-LHC) took place from 30 October to 1 November, attracting around 500 participants. HL-LHC is an approved extension of the LHC programme that aims to achieve a total integrated luminosity of 3 ab–1 by the second half of the 2030s (for reference, the LHC has amassed around 0.1 ab–1 so far). HE-LHC, by contrast, is one of CERN’s possible options for the future beyond the LHC; its target collision energy of 27 TeV, twice the LHC energy, would be made possible using the 16 T dipole magnets under development in the context of the Future Circular Collider study.

The workshop was the first of a series of meetings scheduled throughout 2018 to review and further refine our understanding of the physics potential of the HL-LHC, and to begin a systematic study of physics at the HE-LHC.

Close to 2000 physics papers have been published by the LHC experiments. In addition to the discovery of the Higgs boson and the first studies of its properties, these papers document progress in hundreds of different directions, ranging from searches for new particles and interactions to the measurement of a multitude of cross-sections with unprecedented precision, from the improved determination of the top-quark and W-boson masses to the opening of new directions in the exploration of flavour phenomena, from the discovery of hadrons made of exotic quark configurations to the observation of new collective phenomena in both proton and nuclear collisions. That these results were extracted from datasets representing only a few percent of the data sample promised by the HL-LHC, shows how vast and incisive its ultimate achievements may be.

There is nevertheless a recurrent concern expressed by many physicists that the lack of direct evidence for new physics at the LHC is already diminishing the expected returns from the HL-LHC. The conflict with the expectation that new physics should have already appeared at the LHC forces us to reconsider that prejudice, and strongly underscores the mysterious origin of the Higgs boson and the need to study it in the greatest detail. This orients the HL-LHC goals towards increasing the sensitivity to elusive exotic phenomena, and increasing the precision of Standard Model measurements and of their interpretation, in particular for the Higgs. These directions pose severe challenges to experimentalists and theorists, pushing us to develop original approaches for the best exploitation of the HL-LHC statistics and to use experience to reduce future systematic uncertainties in theory and experiment. The full HL-LHC dataset will be needed to challenge the Higgs mechanism. With it, we will be able to attain percent-level precision for the most prominent of the Higgs interactions, test the couplings to the second fermion generation, and find evidence for the self-interaction of the Higgs.

A priority of the workshop series is to study the added value provided by the HE-LHC. And, since minor deviations from the Standard Model could be hiding anywhere, no stone should be left unturned. We have already seen the emergence of new proposals and techniques, which have extended beyond expectations the new-physics reach. Examples include the use of boosted jet topologies to enhance sensitivity to weakly interacting light particles decaying hadronically, or the use of quantum interference effects to constrain the Higgs-decay width. New proposals are also emerging to detect exotic long-lived particles, with the possible help of additional detector elements. The workshop environment should stimulate the youngest researchers to develop ideas and leave their own signature on future analyses.

Indications of lepton-flavour-universality violation (see “Implications of LHCb results brought into focus”) are being closely monitored and will be further scrutinised during the workshop. Were these hints to be confirmed with more data, it would open a hunt for their microscopic origin and provide concrete ground in which to examine the power of the HL-LHC and the potential of a future HE-LHC to test the proposed models. The workshop series will explore the synergy and complementarity of the flavour studies carried out with the precise measurement of b-hadron decays and with the direct search for these new interactions.

The LHC running into the mid-2030s also provides new opportunities for the study of hadronic matter at high densities. The established existence of a quark-gluon plasma phase should be probed under a broader set of experimental conditions, using ions lighter than lead, and thoroughly addressing the novel indications that unexpected collective effects appear in proton collisions. Surprises such as this show that the field of high-density hadronic matter is rapidly evolving, and the workshop will outline the ambitious future programme needed to answer all open questions.

The discussion of the prospects of HL-LHC physics builds on the experience gained so far by the LHC experiments, in particular the dedicated work done for the preparation of future detector upgrades to cope with the harsher high-luminosity environment of HL-LHC, addressing problems of increased event rates and complexity. The workshop will try to go beyond the existing performance studies, exploring the opportunities offered by the superior detector and data-acquisition systems.

On the theory side, the computing techniques discovered in the last few years are being pushed to new heights, promising continued progress in the modelling of LHC interactions. This goes hand in hand with the improved precision of the measurements, and the workshop will examine new ideas for the direct validation of theoretical calculations, to improve the extraction of Standard Model parameters and to gain higher sensitivity to deviations from the Standard Model.

The strong attendance at the kick-off workshop attests the great interest present in the community in the post-LHC era. The outcomes will be documented in a report to be submitted to the 2019 review of the European Strategy for Particle Physics. The projections for the ultimate outcome of the HL-LHC will provide an essential reference for the assessment of the other future initiatives to be evaluated during the strategy review.

indico.cern.ch/event/647676

All change

Ninety years after the famous photograph of the 1927 Solvay conference (top) was taken, depicting 28 male scientists and a single woman (Marie Skłodowska Curie), the University of Trento and the Italian Physical Society created a more modern picture: a new photo showing 28 female physicists and one man (former CMS spokesperson Guido Tonelli). The aim was to give more visibility to women in physics, one of the topics of the conference of the Italian Physical Society in Trento after which the photo was taken on 14 September. At the 1927 Solvay conference, devoted to electrons and photons, 17 of the 29 attendees photographed were or became Nobel Prize winners – including Curie, who alone among them, had won Nobel Prizes in two separate scientific disciplines.

Maria Krawczyk 1946–2017

Maria Krawczyk passed away suddenly on 24 May 2017. It was a shock not only for her family but also for many of the physicists and her friends in the faculty of physics at the University of Warsaw and abroad. She was a very well-known and respected scientist within the physics community for her passion and involvement in research, teaching and outreach.

Maria graduated from the University of Warsaw, and her scientific career was intertwined with the university, first as an assistant, then adjunct university professor and full professor. In 1975 she defended her PhD thesis under the supervision of Grzegorz Białkowski based on studies of the charge exchange reaction πp → π0n. During a postdoc at the Max Planck Institute in Munich in 1977/78 her scientific interest shifted towards the parton model and quantum chromodynamics (QCD). She worked on the hadronic properties of photons within QCD, where her speculations on direct photon pair production in hard collisions were then verified by experiments. Later she worked on the resummation of higher order QCD corrections.

In 1990 Maria became interested in electroweak interactions, in particular the Brout–Englert–Higgs mechanism of spontaneous electroweak symmetry breaking and the Higgs sector. The Higgs particle became her main research direction, including the two-Higgs-doublet models, searches for light Higgs particles in existing and planned accelerators, the CP properties of the scalar sector, the role of the Higgs in astrophysics and cosmology, and the structure of the vacuum. She was an enthusiast for studying photon collisions at a future linear collider, and took an active role in workshops devoted to the physics potential of future experiments. During a stay at CERN in 2002 she initiated discussions and studies of CP violation in non-standard Higgs models, becoming an organiser of the workshop on CP studies and non-standard Higgs physics – which culminated in the delivery of a CERN Yellow Report. With the advent of the LHC, she concentrated mainly on LHC physics.

During her career, Maria collaborated with many distinguished physicists around the world and coordinated a number of scientific grants financed by Polish and European agencies – right up to her last project, HARMONIA. She served in a number of advisory committees and was involved in several international workshops and conferences. Maria served on the TESLA collaboration board, represented Poland in outreach within the European linear collider steering group, and in 2004 was invited to join the programme committee of the Rencontres de Moriond series of conferences on QCD.

Maria enjoyed contact with students. She was concerned not only with their scientific development but also their living conditions, and helped in sending them to physics schools and conferences, finding grant opportunities and editing grant applications. She was very active in daily matters at the faculty and university, and engaged heavily in outreach activities, giving radio and TV interviews, lecturing at scientific festivals and organising LHC exhibitions.

Maria was a very kind and helpful person. Her advice, including in private matters, and friendliness will be greatly missed. She was also a beloved wife, a mother of two children and grandmother of four grandchildren.

Lev Lipatov 1940–2017

On 4 September our friend and colleague Lev Nikolaevich Lipatov of the Russian Academy of Sciences (RAS) passed away unexpectedly while attending a physics meeting in Dubna. Lev grew up in Leningrad (now St. Petersburg) and entered the physics faculty at the Leningrad State University in 1957. In 1963 he joined the group of Vladimir Gribov at the Ioffe Physical-Technical Institute of RAS, defending his dissertation in 1968. He remained in Gribov’s group when it moved to the Leningrad Nuclear Physics Institute in Gatchina in 1970 and obtained a permanent position. He became a professor of physics in 1990 and, since 1997, was the director of the theory division. In 1998 he also became a member of St. Petersburg State University, where he lectured, and in 2011 he was elected as a full member of the RAS.

Lev was a leading figure worldwide in the high-energy behaviour of quantum field theory. Supported by Gribov, he began to analyse the high-energy behaviour of QED processes and became involved in the investigation of the “double logarithms”. His main focus was first on the Regge limit (at the time, Regge theory had just started to become popular for analysing high-energy scattering processes), but the discovery of Bjorken scaling transferred his focus to the kinematic limit of deep inelastic scattering. It was after a seminar given by Gribov when Lev spotted a gap in the theoretical argument – leading to the famous “GL” paper, which later became a theoretical cornerstone of the DGLAP evolution equations. These are now an important pillar in the analysis of high-energy scattering processes at the LHC.

After the rise of non-abelian gauge theories in the early 1970s, it was again the Regge limit that attracted Lev’s interest: together with his collaborators in 1975 he derived an integral equation which, after applying it to QCD, became known as the “BFKL” equation. It took several years before this equation received international attention, but today the BFKL papers are among the publications with the highest numbers of citations in high-energy physics.

Lev’s scientific work extends much further, however. He found a new approach for investigating large orders in perturbation theory, generalized the concept of partonic evolution equations beyond the leading-twist approximation and spent several years computing the NLO corrections to the BFKL equation. He discovered that the BFKL Hamiltonian (after generalizing to many-gluon states) is equivalent to an integrable Heisenberg spin model, thus demonstrating that the concept of integrability plays an important role in high-energy physics, and developed a new formulation in terms of a gauge-invariant “effective action”. In gravity he discovered the reggeization of the graviton and within the conjectured AdS/CFT duality he pointed out the need for correcting the BDS formula using remainder functions, and worked on the duality of the BFKL pomeron with the graviton. Although Lev’s work was purely theoretical, he never neglected experimental data: his last papers studied the application of the QCD BFKL equation to HERA data, thus gaining a deeper understanding of his “favourite child”, the BFKL pomeron.

Lev was well known in the high-energy physics community and was invited to give talks at countless international meetings and conferences. He set up numerous collaborations, paid several visits to CERN and, since the early 1990s, made regular visits to DESY. Lev received many national and international prizes and awards, including the research award of the Alexander von Humboldt Foundation in 1993, the Pomeranchuk Prize in 2001, the Marie Curie Excellence Chair of the European Community, hosted by Hamburg University in 2006–2009, and the European Physical Society High Energy and Particle Physics Prize in 2015. As well as his research in Russia, he set up collaborations in Germany, France, England, Spain, Israel and Chile.

Those who had the privilege to know Lev up close experienced a very friendly person whose interest and understanding in physics was extraordinary. In any situation he was ready and more than happy to discuss physics, and was enthusiastic about new ideas. Behind this, Lev was a loving husband to his wife Elvira and a caring father of his daughters Irina and Katja, and their families. Last but not least, he was very attached to his home city of Leningrad and to his home country of Russia.

Together with his numerous collaborators and friends, we deeply regret that Lev is no longer with us.

International committee backs 250 GeV ILC

Illustration of the proposed International Linear Collider.

On 7 November, during its triennial seminar in Ottawa, Canada, the International Committee for Future Accelerators (ICFA) issued a statement of support for the International Linear Collider (ILC) as a Higgs-boson factory operating at a centre-of-mass energy of 250 GeV. That is half the energy set out five years ago in the ILC’s technical design report (TDR), shortening the length of the previous design (31 km) by around a third and slashing its cost by up to 40%.

The statement follows physics studies by the Japanese Association of High Energy Physicists (JAHEP) and Linear Collider Collaboration (LCC) outlining the physics case for a 250 GeV Higgs factory. Following the 2012 discovery of the Higgs boson, the first elementary scalar particle, it is imperative that physicists undertake precision studies of its properties and couplings to further scrutinise the Standard Model. The ILC would produce copious quantities of Higgs bosons in association with Z bosons in a clean electron–positron collision environment, making it complementary to the LHC and its high-luminosity upgrade.

One loss to the ILC physics program would be top-quark physics, which requires a centre-of-mass energy of around 350 GeV. However, ICFA underscored the extendibility of the ILC to higher energies via improving the acceleration technology and/or extending the tunnel length – a unique advantage of linear colliders – and noted the large discovery potential accessible beyond 250 GeV. The committee also reinforced the ILC as an international project led by a Japanese initiative.

Thanks to experience gained from advanced X-ray sources, in particular the European XFEL in Hamburg (CERN Courier July/August 2017 p25), the superconducting radiofrequency (SRF) acceleration technology of the ILC is now well established. Achieving a 40% cost reduction relative to the TDR price tag of $7.8 billion also requires new “nitrogen-infusion” SRF technology recently discovered at Fermilab.

“We have demonstrated that with nitrogen doping a factor-three improvement in the cavity quality-factor is realisable in large scale machines such as LCLS-II, which can bring substantial cost reduction for the ILC and all future SRF machines,” explains Fermilab’s Anna Grassellino, who is leading the SRF R&D. “With nitrogen doping at low temperature, we are now paving the way for simultaneous improvement of efficiency and accelerating gradients of SRF cavities. Fermilab, KEK, Cornell, JLAB and DESY are all working towards higher gradients with higher quality factors that can be realised within the ILC timeline.”

With the ILC having been on the table for more than two decades, the linear-collider community is keen that the machine’s future is decided soon. Results from LHC Run 2 are a key factor in shaping the physics case for the next collider, and important discussions about the post-LHC accelerator landscape will also take place during the update of the European Strategy for Particle Physics in the next two years.

“The Linear Collider Board strongly supports the JAHEP proposal to construct a 250GeV ILC in Japan and encourages the Japanese government to give the proposal serious consideration for a timely decision,” says LCC director Lyn Evans.

The case of the disappearing neutrinos

Neutrinos are popularly thought to penetrate everything owing to their extremely weak interactions with matter. A recent analysis by the IceCube neutrino observatory at the South Pole proves this is not the case, confirming predictions that the neutrino–nucleon interaction cross section rises with energy to the point where even an object as tiny as the Earth can stop high-energy neutrinos in their tracks.

By studying a sample of 10,784 neutrino events, the IceCube team found that neutrinos with energies between 6.3 and 980 TeV were absorbed in the Earth. From this, they concluded that the neutrino–nucleon cross-section was 1.30+0.21–0.19 (stat) +0.39–0.43 (syst) times the Standard Model (SM) cross-section in that energy range. IceCube did not observe a large increase in the cross-section as is predicted in some models of physics beyond the SM, including those with leptoquarks or extra dimensions.

The analysis used the 1km 3 volume of IceCube to collect a sample of upward-going muons produced by neutrino interactions in the rock and ice below and around the detector, selecting 10,784 muons with an energy above 1 TeV. Since the zenith angles of these neutrinos are known to about one degree, the absorber thickness can be precisely determined. The data were compared to a simulation containing atmospheric and astrophysical neutrinos, including simulated neutrino interactions in the Earth such as neutral-current interactions. Consequently, IceCube extended previous accelerator measurements upward in energy by several orders of magnitude, with the result in good agreement with the SM prediction (see figure, above).

Neutrinos are key to probing the deep structure of matter and the high-energy universe, yet until recently their interactions had only been measured at laboratory energies up to about 350 GeV. The high-energy neutrinos detected by IceCube, partially of astrophysical origin, provide an opportunity to measure their interactions at higher energies.

In an additional analysis of six years of IceCube data, Amy Connolly and Mauricio Bustamante of Ohio State University employ an alternative approach which uses 58 IceCube-contained events (in which the neutrino interaction took place within the detector) to measure the neutrino cross-section. Although these events mostly have well-measured energies, their neutrino zenith angles are less well known and they are also much less numerous, limiting the statistical precision.

Nevertheless, the team was able to measure the neutrino cross-section in four energy bins from 18 TeV to 2 PeV with factor-of-ten uncertainties, showing for the first time that the energy dependence of the cross section above 18 TeV agrees with the predicted softer-than-linear dependence and reaffirming the absence of new physics at TeV energy scales.

Future analyses from the IceCube Collaboration will use more data to measure the cross-sections in narrower bins of neutrino energy and to reach higher energies, making the measurements considerably more sensitive to beyond-SM physics. Planned larger detectors such as IceCube-Gen2 and the full KM3NeT can push these measurements further upwards in energy, while even larger detectors would be able to search for the coherent radio Cherenkov pulses produced when neutrinos with energies above 1017 eV interact in ice.

Proposals for future experiments such as ARA and ARIANNA envision the use of relatively-inexpensive detector arrays to instrument volumes above 100 km3, enough to measure “GZK” neutrinos produced when cosmic-rays interact with the cosmic-microwave background radiation. At these energies, the Earth is almost opaque and detectors should be able to extend cross-section measurements above 1019 eV, thereby probing beyond LHC energies.

These analyses join previous results on neutrino oscillations and exotic particle searches in showing that IceCube can also contribute to nuclear and particle physics, going beyond its original mission of studying astrophysical neutrinos.

Copper reveals nickel’s doubly magic nature

Teams at CERN’s ISOLDE facility and at RIKEN in Japan have found evidence that an exotic isotope of the metallic element nickel (78Ni) is doubly magic, opening a new vista on an important region of the nuclear-stability chart.

Like electrons in an atom, protons and neutrons in a nucleus have a penchant for configurations that offer extra stability, called magic numbers. Nuclei that have magic numbers of both protons and neutrons are of particular interest for understanding how nucleons bind together. Examples are 16O, containing eight protons and eight neutrons, and 40Ca (20 protons and 20 neutrons), both of which are stable nuclides.

One of the main efforts in modern nuclear physics is to create systems at the extremes of nuclear stability to test whether these magic numbers, and the nuclear shell model from which they derive, are still valid. Two usual suspects are 132Sn (with a half-life of 40 s) and 78Ni (0.12 s). Sn (tin) is the element with the highest number of stable isotopes (10), attesting to the magic nature of its 50 protons.

The next magic number is 82, corresponding to the number of neutrons in 132Sn. Nickel has a magic number of 28 protons but the recipe for adding the magic 50 neutrons to make 78Ni has proven challenging for today’s radioactive beam factories. CERN’s ISOLDE facility has now got very close, taking researchers to the precipice via nickel’s nuclear neighbour 79Cu containing 50 neutrons and 29 protons.

Andree Welker of TU Dresden and collaborators used ISOLDE’s precision mass spectrometer ISOLTRAP to determine the masses and thus binding energies of the neutron-rich copper isotope 79Cu, revealing that this next-door neighbour of 78Ni also exhibits a binding-energy enhancement. To probe the enhancement, Ruben de Groote of KU Leuven and collaborators used another setup at ISOLDE called CRIS to measure the electromagnetic moments of the odd-N neighbour 78Cu, providing detailed information about the underlying wave functions. Both the ISOLTRAP masses and the CRIS moments were compared with large-scale shell-model calculations involving the many relevant orbitals. Both are in excellent agreement with the ISOLDE results, suggesting that the predictions for the neighbouring 78Ni can be taken with great confidence.

An independent study of 79Cu carried out by Louis Olivier at the IN2P3–CNRS in France and colleagues based on a totally different technique has reached the same conclusion. Using in-beam gamma-ray spectroscopy of 79Cu at the Radioactive Isotope Beam Factory at RIKEN in Japan, the team produced 79Cu via proton “knockout” reactions in a 270 MeV beam of 80Zn. No significant knockout was observed in the relevant energy region, showing that the 79Cu nucleus can be described in terms of a valence proton outside a 78Ni core and affirming nickel’s doubly magic character.

Novartis acquires CERN spin-off

Global healthcare company Novartis has announced plans to acquire Advanced Accelerator Applications (AAA), a spin-off radiopharmaceutical firm established by former CERN physicist Stefano Buono in 2002. With an expected price of $3.9B, said the firm in a statement, the acquisition will strengthen Novartis’ oncology portfolio by introducing a new therapy platform for tackling neuroendocrine tumours. Trademarked Lutathera, and based on the isotope lutetium-177, the technology was approved in Europe in September 2017 for the treatment of certain neuroendocrine tumours and is under review in the US.

With its roots in nuclear-physics expertise acquired at CERN, AAA started its commercial activity with the production of radiotracers for medical imaging. The successful model made it possible for AAA to invest in nuclear research to produce innovative radiopharmaceuticals. “We believe that the combination of our expertise in radiopharmaceuticals and theragnostic strategy together with the global oncology experience and infrastructure of Novartis, provide the best prospects for our patients, physicians and employees, as well as the broader nuclear medicine community,” said Buono, who is CEO of AAA.

Fermilab joins CERN openlab on data reduction

In November, Fermilab became a research member of CERN openlab – a public-private partnership between CERN and major ICT companies established in 2001 to meet the demands of particle-physics research. Fermilab researchers will now collaborate with members of the LHC’s CMS experiment and the CERN IT department to improve technologies related to physics data reduction, which is vital for gaining insights from the vast amounts of data produced by high-energy physics experiments.

The work will take place within an existing CERN openlab project with Intel on big-data analytics. The goal is to use industry-standard big-data tools to create a new tool for filtering many petabytes of heterogeneous collision data to create manageable, but still rich, datasets of a few terabytes for analysis. Using current systems, this kind of targeted data reduction can often take weeks, but the Intel-CERN project aims to reduce it to a matter of hours.

The team plans to first create a prototype capable of processing 1 PB of data with about 1000 computer cores. Based on current projections, this is about one twentieth of the scale of the final system that would be needed to handle the data produced when the High-Luminosity LHC comes online in 2026. “This kind of work, investigating big-data analytics techniques is vital for high-energy physics — both in terms of physics data and data from industrial control systems on the LHC,” says Maria Girone, CERN openlab CTO

SESAME sees first light

At 10.50 a.m. on 22 November 2017, the third-generation light source SESAME in Jordan produced its first X-ray photons, signalling the start of the regional laboratory’s experimental program. Researchers sent a beam of monochromatic light through the XAFS/XRF (X-ray absorption fine structure/X-ray fluorescence) spectroscopy beamline, the first to come on stream at SESAME and targeted at research ranging from solid state physics to environmental science and archaeology.

Obtaining first light is an important step in the commissioning of a new synchrotron light source, and the milestone comes 10 months after SESAME circulated its first electrons (CERN Courier March 2017 p8). Nevertheless, it is just one step on the way to full operation. The SESAME synchrotron is currently operating with a beam current of just over 80 milliamps while the design value is 400 milliamps. Over the coming weeks and months as experiments get underway, the current will be gradually increased.

SESAME’s initial research program will be carried out at two beamlines, the XAFS/XRF beamline and an infrared spectro-microscopy beamline that is scheduled to join the XAFS/XRF beamline this year. A third beamline devoted to materials science will come on stream in 2018. “After years of preparation, it’s great to see light on target,” said XAFS/XRF beamline scientist Messaoud Harfouche. “We have a fantastic experimental programme ahead of us, starting with an experiment to investigate heavy metals contaminating soils in the region.”

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