“One more centimetre,” said the chief technician, while operating the hydraulic jack system on 14 August. The 5-m-diameter, 5-m-long cylindrical detector gently slid into the parking position, 56 metres below the ground in the ALICE cavern at LHC Point 2, where it will stand for some time. This operation culminates the many-years-long upgrade of ALICE’s Time Projection Chamber (TPC), the large tracking device of the LHC’s heavy-ion specialist.
The ALICE TPC is a big, gas-filled cylinder with a hole in the centre – to accommodate the silicon tracker as well as the beam pipe – where the charge produced by ionising radiation is projected onto detectors arranged in the two endplates. These detectors used to be multi-wire proportional chambers, 72 in total, which have now been replaced by detectors based on Gas Electron Multipliers (GEM), a micro-pattern structure developed at CERN. These new devices, together with new readout electronics that feature a continuous readout mode, will allow ALICE to record the information of all tracks produced in lead–lead collisions at rates of 50 kHz, producing data at a staggering rate of 3.5 TB/s. The average load on the chambers under these conditions is expected to be as high as 10 nA/cm², and the GEM detectors are able to cope with this. But will these new devices perform as nicely as their predecessors?
In order to answer this question, several years of intensive R&D were necessary, since the large number of positive ions produced at the detectors would lead to excessive track distortions. This, combined with the necessity of keeping excellent energy-loss (dE/dx) resolution for particle identification, and the imperative robustness against discharges, posed an exciting challenge that led to a novel configuration of GEM-based detectors.
As the fabrication of over 800 GEM foils was taking place at the CERN PCB workshop, the new chambers and electronics were being constructed and thoroughly tested around the world – quite a logistic exercise. The ALICE team proceeded with the final steps of the upgrade process during the ongoing second long shutdown of CERN’s accelerator complex (LS2). First, the TPC was extracted from the underground cavern and brought, inside its blue frame, to a large clean room at the surface. Cranes, jacks and a huge truck were used for careful transportation. The chamber replacement, electronics installation and tests with a laser system, cosmic rays and X-rays took over a year. In July 2020, the TPC was declared ready for being re-installed in the cavern. Cranes, truck and jacks once again.
ALICE achieved a major milestone with the completion of the TPC upgrade, after many years of intense R&D, construction and assembly. At the end of 2020, all the services will be connected and the full, upgraded TPC will be operated and commissioned together with all other detectors in the experiment. The real excitement will be when the first post-LS2 collisions from the LHC are delivered.The TPC being lowered down the shaft to the experimental cavern (Images: CERN)
The 12th International School of Trigger and Data Acquisition (ISOTDAQ) will introduce those with an education in physics, engineering or computing (ranging from undergrads to postdocs) to the arts and crafts of triggering and acquiring data for physics experiments. The school will be held from 10th - 19th February 2021, at INFN & DFA “E. Majorana” in Catania, Italy.
The school will provide an up-to-date overview of the basic instruments and methodologies used in high-energy physics, spanning from small experiments in the lab to the gigantic LHC experiments, presenting the main building blocks, as well as the different solutions and architectures at different levels of complexity.
The main topics of the school include the basics of Data Acquisition (DAQ) programming concepts (e.g. threaded programming, data storage, networking, I/O programming, FPGA programming), hardware bus systems (VMEbus, PCIe, MicroTCA), basic Trigger Logic and Hardware (NIM) as well as intelligent trigger systems based on Associative Memories and GPUs. PC based readout and trigger design will also be covered with reviews of modern TDAQ systems from LHC and fixed target experiments.
The school consists of 50% lectures (given mainly by physicists and engineers working daily on complex TDAQ systems) and 50% of practical exercises where students will be able to work in small groups on a wide variety of electronics components of TDAQ systems. The main aim of the school is to provide students with a wide but introductory level of the TDAQ domain. It will also be of interest to students from other research domains such as astrophysics or nuclear physics.
Please find more information (including application instructions) at our website: https://indico.cern.ch/e/isotdaq2021.
Application deadline is November 1st, 2020.
The CMS collaboration announced the winner of its 2019 PhD Thesis Award in June. The award honours the best PhD of the year based on impact, originality and clarity. The jury faced the difficult task of choosing a single winner from among the 25 nominated PhD theses in a two-round process.
This year, Marcel Riegler from RWTH Aachen University in Germany made it to the top with a thesis exploring the so-called “ttH” production, the process in which a Higgs boson is created in high-energy particle collisions in combination with two top quarks.
Marcel contributed to the first observation of ttH production in 2018 by developing methods employing neural networks and deep-learning technology. This observation was a landmark event for CMS and ATLAS, since the interaction is extremely rare and its study could confirm or disprove predictions of the Standard Model. The first studies on the interaction were unveiled earlier this year.
“A PhD is a unique opportunity to contribute to fundamental research, which, in my experience, was a rewarding and memorable time I look back on with joy,” remarked Riegler. “CERN, CMS and the values they embody are a blueprint for peaceful and fruitful collaboration between people irrespective of ethnic origin, religion and nationality, and I enjoy working in this community.”
Read more about this story on the CMS website.
Chris Parkes of the University of Manchester in the UK has been appointed as the new spokesperson of the LHCb experiment collaboration. Parkes, who was previously the deputy spokesperson of the collaboration, will represent more than 1400 people from 85 institutions in 19 countries for a period of three years, beginning 1 July 2020.
Parkes takes over the LHCb leadership from Giovanni Passaleva of the National Institute for Nuclear Physics in Florence, Italy, who has served as LHCb spokesperson since 1 July 2017.
“It’s an exciting time to take the reins of LHCb,” say Parkes. “We are preparing many exciting physics results from analyses of the full data taken during the first decade of LHC operations. We’re currently constructing and installing our new detector apparatus, the LHCb Upgrade I. It will allow us to collect larger data sets and relies on a new paradigm of real-time analysis, free of the restrictions that come with a traditional hardware trigger. The construction activities have been heavily disrupted by the COVID-19 pandemic, but we are working together across the international collaboration to complete the experiment. For the further future, we are planning an Upgrade II of the detector that will allow the full exploitation of the High-Luminosity LHC. LHCb is a growing global community that celebrates our diversity and spirit of open collaboration. It will be a pleasure and honour to lead the collaboration in the next stage of its journey.”
“It has been a great pleasure serving the collaboration these last three years,” says Passaleva. “During this term Chris and I have led a major renewal and improvement of the experiment for the upcoming LHC Run 3. And we had the fortune to witness historical discoveries! It was really great to work with Chris and I have no doubt he will lead LHCb to new heights.”
Parkes is a professor at the University of Manchester, UK. He has been deputy spokesperson of LHCb for the past three years and has been a member of the collaboration for more than twenty years. Parkes was one of the instigators of both the LHCb Upgrade I and II, and led the UK’s construction activities for the LHCb Upgrade I. He has worked extensively on physics studies involving the charm quark and on the LHCb Vertex Locator (VELO) detector, serving as the detector’s Project Leader during the first LHC physics period (2010–2012). Prior to LHCb, he worked on W-boson physics with the DELPHI experiment at the previous CERN collider, LEP.
On 11 June, LHCb announced the winners of the 2020 PhD Thesis and Early Career Scientist Awards.
The LHCb Thesis Awards recognize excellent PhD theses and additional work that have made an exceptional contribution to LHCb. In parallel, the Early Career Scientist prizes are awarded to recognize outstanding achievements of early career scientists to the benefit of LHCb.
This year’s winners of the Thesis prize are Philippe D'Argent (Heidelberg University) and Laurent Dufour (Nikhef/Groningen University. Carlos Abellan Beteta (Zurich), Claudia Bertella (CERN), Daniel Campora (Nikhef), Nadim Conti (INFN, Milan), Edgar Lemos Cid (Santiago de Compostela), Olli Lupton (Warwick), Mark Smith (Imperial College), Dorothea vom Bruch (LPNHE, Paris) were awarded the Early Career prize.
“The number of brilliant winners of the Early Career Scientist prize and the extraordinary level of the PhD theses evaluated, show how crucial the contribution of younger colleagues to the experiment activities truly is”, point out Francesca Dordei and Stephanie Hansmann-Menzemer, Chairs of the Prize Committees. “It was really hard for the Committees to select only a few names among the many early career scientists and PhD students that not only contribute but often lead cutting edge developments in LHCb physics, detector and software developments”. Almost 350 PhD students study in the collaboration on diverse areas of LHCb physics, ranging from physics analysis to advanced detector and software developments.
Plastic scintillators are one of the most used active materials in high-energy physics. Their properties make it possible to track and distinguish between particle topologies. Among other things, scintillators are used in the detectors of neutrino oscillation experiments, where they reconstruct the final state of the neutrino interaction. Measurements of oscillation phenomena are carried out through comparison of observations of neutrinos in near detectors (close to the target) and far detectors (up to several hundred kilometres away).
CERN is strongly involved in the T2K experiment, the current world-leading neutrino oscillation experiment, in Japan, which recently released promising results. A future upgrade of the experiment’s near detector will pave the way for more precise results. The novel detector will comprise a two-tonne polystyrene-based plastic scintillator detector segmented into 1 x 1 x 1 cm3 cubes, leading to a total of around two million sensitive elements: the smaller the cubes, the more precise the results. This technology could be adopted for other projects, such as the DUNE near detector. However, more precise measurements would require finer granularity, making the detector assembly harder.
This is where the CERN EP-Neutrino group – led by Albert De Roeck – steps in, developing a new plastic scintillator production technique that involves additive manufacturing. The R&D is carried out in collaboration with the Institute for Scintillation Materials (ISMA) of the National Academy of Science of Ukraine, which has strong expertise in the development of scintillator materials, and the Haute École d’Ingénierie et Gestion du Canton de Vaud (HEIG-VD), which is expert in additive manufacturing. The final goal is to 3D-print a “super-cube”, that is, a single massive block of scintillator containing many optically independent cubes. 3D-printing would solve the issue of assembling the individual cubes, which could thus be produced in any size, including smaller than 1 cm3, and relatively quickly (volumes bigger than 20 x 20 x 20 cm3 can be produced in about a day).
So far, the collaboration has been fruitful. A preliminary test gave the first proof of concept: the scintillation light yield of a polystyrene-based scintillator 3D-printed with fused deposition modelling (see fig. 2) has been found to be comparable to that of a traditional scintillator. But the road towards a ready-to-use super-cube is still long. Further optimisation of the scintillator parameters and tuning of the 3D-printer configuration, followed by a full characterisation of the 3D-printed scintillator, will need to be achieved before the light reflector material for optically isolating the cubes can be developed.
This new technique could also open up new possibilities for the field of particle detection. A successful 3D-printed plastic scintillator detector could pave the way for a broader use of this technology in detector building, which could shake up the field of high-energy physics, as well as that of medicine, where particle detectors are used, for instance, in cancer therapy. Moreover, the greatly cost-effective 3D-printer could be replicated quite easily and used in a vast number of settings. Umut Kose, from the EP-neutrino group and Neutrino Platform at CERN, explains: “Our dream goes beyond the super-cube. We like to think that, in a few years, 3D-printing will allow high-school students to make their own radiation detection systems. The outreach potential of this technology is mind-blowing”.
Davide Sgalaberna, now at ETH Zurich, cannot hide his enthusiasm for this adventure: “This is the first time that 3D-printing could be used for real particle detectors. We are transforming our personal will into a project, and we are hopeful that this could lead to a breakthrough. That is thrilling”. A thrill shared by Davide’s colleagues, who are more than ready to resume work on the 3D-printed detector once the easing of lockdown allows everyone to return to CERN.
Read the full story in the EP newsletter