CERNJuly/August 2021 cerncourier.com COURIERReporting on international high-energy physics WELCOME CERN Courier – digital edition Welcome to the digital edition of the July/August 2021 issue of CERN Courier. Since the early 1980s, successive generations of silicon trackers have driven numerous discoveries (p39). The LHC detectors represent the state of the art in particle-tracking applications, delivering high-granularity data at speed under the most extreme operating conditions imaginable. Containing some 12.5 Gpixels, the recently installed upgraded inner tracker for the ALICE detector, pictured on this issue’s cover, is the largest pixel detector ever built and the first at the LHC to use monolithic active pixel sensors (p29). Next year, LHCb will also be equipped with an entirely new pixel tracker, the VELO, while ATLAS and CMS are developing advanced pixel trackers to be installed for future high-luminosity LHC operations (p36). Silicon-pixel detectors developed for particle physics have also had a major impact on medical imaging, in particular via the CERN-led Medipix and Timepix collaborations (p23). Sticking with societal impact, this issue’s Viewpoint argues for an exascale computing facility based on the organisation of CERN (p49). Elsewhere in our summer issue: collider neutrinos on the horizon (p7); particle accelerators meet gravitational waves (p18); reducing greenhouse gases in detectors (p20); exploring the Hubble tension (p51); reviews (p55); careers (p59); PIXEL and much more. To sign up to the new-issue alert, please visit: PERFECT http://comms.iop.org/k/iop/cerncourier Exploring the Hubble tension To subscribe to the magazine, please visit: A CERN for climate change https://cerncourier.com/p/about-cern-courier Medical technologies EDITOR: MATTHEW CHALMERS, CERN DIGITAL EDITION CREATED BY IOP PUBLISHING CCJulAug21_Cover_v3.indd 1 11/06/2021 09:38 CERNCOURIER www. V OLUME 6 1 N UMBER 4 J ULY /A UGUST 2 0 2 1 CERNCOURIER.COM IN THIS ISSUE V OLUME 61 N UMBER 4 J ULY /A UGUST 2 02 1 FASER CollaborationFASER D Dominguez/KTTGROUP-PHO-TECH-2018-002-3 F Camallonga New frontier Collider neutrinos on the Clinical dimensions CERN’s growing impact on Expanding views Cosmologist horizon at FASERν and SND@LHC. 7 medical technologies. 23 Licia Verde on the Hubble tension. 51 NEWS PEOPLE ANALYSIS ENERGY FRONTIERS FIELD NOTES CAREERS OBITUARIES Collider neutrinos Four top quarks seen at Accelerators meet From CERN to the Gerd-Jürgen Beyer • X boson feels the once • Gauge–boson gravitational waves environment • Vladimir Kukulin squeeze • Matter– polarisation • Hadron • Greening gaseous How skills developed in • Herbert Lengeler antimatter flips • Neutron formation • Charmed- detectors • Astroparticle high-energy physics can • Luc Pape • Jean Sacton. lifetime-puzzle • Latvia baryon lifetime. 15 theory in rude health. 18 be transferred to careers 65 joins CERN • Observatory in the environment nets PeV gamma rays. 7 industry. 59 FEATURES TSMC High-density wiring MEDTECH ALICE ATLAS, CMS AND LHCb HISTORY CERN’s impact on ALICE tracks State-of-the-art Tracking the rise Our new high-density wiring is a medical technology new territory tracking for high of pixel detectors Accelerators and their A look at the largest pixel luminosities Silicon pixel detectors modular option for the Bluefors side- detectors catalyse detector ever built and The tracking systems have blossomed into loading XLDsl dilution refrigerator innovative technology the first at the LHC to of ATLAS, CMS and LHCb beautiful creations that system that enables a large scale-up for medical applications. use monolithic active are undergoing complete have driven numerous of the experimental wiring, especially 23 pixel sensors. 29 overhauls. 36 discoveries. 39 for high-frequency signals. It is easy to install and to maintain. OPINION DEPARTMENTS VIEWPOINT INTERVIEW REVIEWS FROM THE EDITOR 5 ‘A CERN for Exploring the A relational take on NEWS DIGEST 13 climate change’ Hubble tension quantum mechanics APPOINTMENTS 60 Tim Palmer and Bjorn Licia Verde discusses Helgoland Particle & AWARDS • ALICE-PHO-ITS-2021-001-32 Stevens argue for an the current tension in Detectors: Fundamentals RECRUITMENT 61 exascale computing the measurement of the and Application • Le On the cover: The outer facility based on the Hubble constant. 51 Neutrino de Majorana. 55 barrel of ALICE’s new inner BACKGROUND 70 CERN model. 49 tracking system installed in March. 29 CERN COURIER JULY/AUGUST 2021 3 CCJulAug21_Contents_v3.indd 3 11/06/2021 09:53 20201112 Physics World Bluefors ad - 213 x 282 mm plus bleed 3 mm - High-density wiring2.indd 1 19.01.2021 10:20:02 CERNCOURIER www. V OLUME 6 1 N UMBER 4 J ULY /A UGUST 2 0 2 1 CERNCOURIER.COM FROM THE EDITOR SHR Marvels of engineering and collaboration he story of silicon pixel detectors is like that of an Nikhef ULTRA PRECISE HIGH VOLTAGE art form, describes our in-depth take on their history T (p39): with well-defined beginnings half a century ago, the technology has morphed into a vast array of spectacular SOURCE MEASURE UNIT creations. One, packing 10 million pixels into your pocket, is the smartphone camera; another is the newly installed, upgraded inner tracker for the ALICE detector adorning the DESIGNED FOR UNIVERSAL LABORATORY USE Matthew cover of this issue. Containing some 12.5 Gpixels, it is the Chalmers largest pixel detector ever built and the first at the LHC to use Editor monolithic active pixel sensors, or MAPS (p29). As well as disrupting photography, the silicon pixel detector – i n p a r a l l e l w it h it s c l o s e s i bl i n g t h e s i l i c o n-m i c r o s t r i p d e t e c t or, which will be explored in a future issue – revolutionised scientific imaging in the 1980s and 1990s. Charge-coupled devices (CCDs) tend to be the preferred option for astronomical applications, On point A LHCb VELO pixel module being assembled at Nikhef. most recently the 3.2 Gpixel optical camera for the Vera Rubin Observatory, while MAPS tend to be used for ultrafast imaging Beyond tracking such as studies of protein dynamics at X-ray free-electron lasers. Silicon-pixel detectors developed for particle physics have ALSO AVAILABLE It t o o k a fe w y e a r s t o m o v e a w a y f r o m g a s e o u s d r i f t c h a m b e r s for also had a major impact on medical imaging, for example AS NIM-DEVICE: t he h ig hest prec ision t r ac k i ng, but pa r t ic le physic ist s adopted via the CERN-led Medipix and Timepix collaborations (p23). silicon detectors for these applications in the early 1980s and Medipix chips recently enabled the first 3D colour X-rays never looked back. Successive generations of trackers based and, via CERN spin-out ADVACAM, are soon to be sent to the SK NHR on CCDs, MAPS and hybrid-pixel architectures have driven lunar surface to assess radiation levels ahead of NASA’s first A ER nu m e r o u s d i s c o v e r i e s. W it h t h e c o n s u m e r e l e c t r o n i c s i n d u s t r y c r e w e d fl i g ht t o t h e M o o n i n 50 y e a r s. A s pi n- o ut f r o mthePaul S? IC N H continuing to push chips to new levels of sophistication there S c h e r r e r I n s t it ut e c a l l e d DE C T R IS, m e a n w h i l e, h a s pio n e e r e d O ! I are also no sig ns t hat adv ances are slow ing dow n. the development of hybrid-pixel X-ray detectors for use in T S The LHC detectors represent the state-of-the-art in particle- light sources, medicine and industry. E t r a c k i n g a p pl i c a t i o n s, d e l i v e r i n g h i g h-g r a nu l a r it y d a t a a t s p e e d Sticking with the societal-impact theme, this issue’s U Q Silicon-pixel under the most extreme operating conditions imaginable. The Viewpoint by two leading climate scientists (p49) argues for a detectors chips themselves are only one part of the story. They need to “CERN for climate change” – an exascale computing facility developed be integrated into modules with minimal material budget and based on the organisation of CERN that would allow better for particle installed with great precision in confined spaces, cooled, cabled quant ificat ion of climate models. Elsewhere in our summer W-IE-NE-R + ISEG PERFECT FOR physics have and read-out (p36). From R&D to construction, this complex issue: learn about the fascinating potential for particle accel- SUPPORT OFFICE AT CERN task, like that for the other LHC-experiment upgrades, is shared e r a t or s t o d e t e c t g r a v it a t i o n a l w a v e s ( p18), t h e d e t e c t i o n o f t h e also had a Dr.