Around the Laboratories

A superconducting radiofrequency accelera­ tion cavity for CERN's LEP2 electron-positron collider leaves the preparation area en route to installation in the ring. (Photo CERN HI28.9.85)

cholesterol cleansing therapies, parasitology, unique biological cell culture substrates, bacteria and virus filtration, etc. The Brookhaven Tandem is a good example of an accelerator designed for physics research for which addi­ tional parallel applications have been developed, to the mutual benefit of both the applications and the original research mission. Success in such endeavours demands recognition of the substantial differences between scientific and industrial requirements, and a considerable investment in time and effort to develop and install the specialized facilities.

Peter Thieberger machine's first circulating beam. The increase the luminosity by squeezing 30,000 Z decays recorded by each in more bunches. In 1993, the 'pret­ experiment in 1989 confirmed that zel' scheme (October 1992, page CERN matter comes in just three distinct 17), so called because of the shape families of quarks and leptons. traced out by the circulating beams, End of LEP's Z era The values of the Z mass and width was running with eight bunches per quoted in 1990 were 91.161 ± 0.031 beam, and helped LEP to further chapter of history at CERN's GeV and 2.534 ± 0.027 GeV. By the tighten the precision of the Z fix. A LEP electron-positron collider beginning of 1995, these had been As new skills were mastered, the closed in October when the four big fine-tuned to the extraordinary 27-kilometre circumference machine experiments, Aleph, Delphi, L3 and accuracy of 91.1884 ± 0.0022 GeV became a remarkable precision Opal, logged their final data at the Z and 2.4963 ± 0.0032 GeV, and when instrument. 1992 saw the LEP beam energy, just over six years after data from this year's run is included, energy measurement become LEP's first Z was detected. The LEP will be even better. These results, sensitive to the moon (January 1993, Z era has been one of great success, combined with precision data from page 4). Later, LEP was found to both in terms of physics results and neutrino experiments and from react to heavy rainfall. These phe­ the advances which have been made Fermilab's Tevatron proton- nomena cause slight movements in with the machine itself. LEP now antiproton collider, have put the the surrounding rock and are ampli­ takes a step towards becoming Standard Model of quarks and fied by the machine. LEP2, when the energy is wound up leptons through its most gruelling test In 1995, LEP machine physicists from around 45 GeV to about 70 GeV yet. opted for the bunch train approach per beam (September, page 6). Right from the start, collaboration (September, page 14) to further By the end of LEP's 1995 run, each between LEP experiments and the increase the luminosity. The basic of the four LEP experiments had accelerator team has been close, idea was to split each bunch of seen almost five million Zs. Now the with frequent scheduling meetings particles into a string of smaller spotlight at LEP shifts to producing determining how the machine is run. 'bunchlets' - the bunch train - which pairs of W particles, the electrically For the first few years, LEP ran on a holds more particles than the bunch it charged counterparts of the Z. diet of four bunches of electrons and replaces. In this way, LEP2 will be LEP's first Zs were recorded in four of positrons, but by the end of able to supply the increased event August 1989, one month after the 1992, a way had been found to rates needed for W physics.

4 CERN Courier, November 1995 Around the Laboratories

The beamline from CERN's 1 GeV Booster synchrotron which feeds the ISOLDE on-line isotope separator. Catering for a special community, ISOLDE is assured of a bright future, and continues to be a major feature of CERN's diversified research programme. (Photo CERN 40.2.1992)

Diverse portfolio

ERN has always taken a pride Cin the diversity of its research programme. While the high energy frontier, with its heavy demands for resources, has always provided the main research push, CERN's unique interconnected chain of accelerators naturally provides a broad stage for science. With each machine taking particle beams one step higher in energy to feed the next in the chain, some particles can always be creamed off at each stage for re­ search at an intermediate energy. Currently, CERN's star attraction is the LEP electron-positron collider. Tuned around the Z resonance since its 1989 commissioning, this machine is soon to be boosted in energy to cover new research aims (Septem­ ber, page 6). Alongside LEP is the research tool naturally produces way from the neutrino sources. impressive programme with heavy anguish. Under such circumstances, Candidates for such distant detec­ ion beams and other fixed-target the new possibilities which will be tors are the ICARUS liquid argon studies at the SPS proton synchro­ opened up have to be kept firmly in time projection chamber in the 700 tron, with two major experimental mind. kilometre-distant Italian Gran Sasso areas to the West and the North of This summer, a special meeting at underground facility (April 1993, page the site, at the LEAR low energy the alpine resort of Cogne looked into 15), or the even more distant antiproton ring, at the PS proton the crystal ball, to see what research NESTOR underwater project in the synchrotron, and at the ISOLDE commitments CERN could keep and Mediterranean Sea off Greece isotope separator using beams from which could be discarded during the (November 1993, page 39). Any such the 1 GeV Booster. (For a broad run-up to LHC. distant detector could benefit from a summary of this programme, see the At the SPS proton synchrotron, the 'short baseline' counterpart mounted March 1994 issue, page 1). Chorus and Nomad neutrino beam on-site at CERN, close to the neu­ However the heavy implications of studies (November 1991, page 7) trino source. having to commit additional re­ have yet to produce initial results and Neutrinos apart, the research sources for construction of the LHC will continue to take data at least until programme in the SPS West Experi­ proton collider mean that other 1997. What happens on the neutrino mental Area is now mature and sectors of the research programme front after 1997 depends on what reaching a natural conclusion. will have to be squeezed. Ten years Chorus and Nomad will discover. A However fruitful studies of heavy ago, when CERN had to tighten its continuing search for neutrino oscilla­ quark spectroscopy based on the belt in preparation for LEP construc­ tions after the Chorus and Nomad Omega detector merit continued tion, the Intersecting Storage Rings era would use new neutrino beams effort. (ISR) and BEBC bubble chamber based on LHC infrastructure. With With neutrinos a traditional feature were phased out prematurely in order these beams, increased sensitivity of the SPS West Experimental Area, to liberate resources. would come from a larger detector, the North Experimental Area's Such decisions are not easy, or and possibly from a long baseline' counterpart muon beam has resulted even popular. Closure of a productive experiment, with a detector a long in important discoveries in the field of

CERN Courier, November 1995 5 Around the Laboratories

The FERMI (digital Front-End and Readout Microsystem) project is developing a novel approach to the construction of readout systems for LHC calorimetric detectors. This is a microphotograph of a 11 x 17 mm FERMI Channel Chip containing one million transis­ tors and including the look-up table and pipeline memory for three channels.

nucleon structure. The current muon experiment, the SMC Spin Muon Collaboration, is looking for a succes­ sor. This and ongoing spectroscopy requirements could be accommo­ dated in a single spectrometer, provided a strong and committed community can assemble the neces­ sary resources. Another flagship SPS experiment is the NA48 study of CP violation (March 1992, page 7). The apparatus will be ready soon, and data taking would take several years. CERN's heavy ion programme received a major boost last year with the arrival of the first beams of lead ions (December 1994, page 15). First physics results are eagerly awaited, and already effects seen by earlier runs using sulphur beams suggest follow-up studies. The plan is to review CERN's heavy ion pro­ on 'trapped' antiparticles.. Microelectronics for gramme sometime next year in the Also at lower energies, the PS light of initial results from the lead proton synchrotron now carries out LHC detector elements beam studies. valuable studies on neutron Away from the SPS, at the LEAR spallation for investigations on he electronics required to in­ low energy antiproton ring some possible new routes to the exploita­ T strument the detectors to be major studies are nearing the end of tion of nuclear energy (April, page 7). used at CERN's future LHC proton- their initial objectives - notably the A particular highlight of CERN's proton collider represents one of the CP LEAR experiment providing a research programme the ISOLDE biggest challenges so far. With valuable new window on CP viola­ isotope separator. After having been proton bunches only 25 nanoseconds tion, and the Obelix spectroscopy moved from its original home at the apart, the experiments will have study. However other experiments, now-closed synchrocyclotron, a minimal time to digest some very notably the Crystal Barrel, could revamped ISOLDE reappeared in complex interactions, with hundreds benefit from continued running. 1992 using beams from the 1 GeV of secondary particles in each bunch Reluctantly, CERN's Research Board Booster. Catering for a special crossing (April, page 4). considers that the resources needed community, ISOLDE is assured of a Capturing this data from LHC's big for continued LEAR running are not bright future. A new pilot experiment high-performance detectors is a real commensurate with the gains, and on neutron-rich nuclei will greatly venture for the designers, given the recommend that LEAR should be enrich the ISOLDE programme and new level of precision, granularity closed next year. point to new directions for future and data rate required by these However with CERN's pioneer research. experiments. In addition, the harsh tradition of antiproton physics, it While CERN's research programme radiation environment and a certain would be a pity if antimatter beams over in the coming years will inevita­ degree of inaccessibility create new evaporated completely. Studies are bly be slimmer than at present, it will demands for reliability and autono­ underway to seek a cost-effective still be a valuable complement to mous running. way of continuing to supply a modest LHC. An LHC experiment, with its tens of level of antiprotons for experiments millions of electronics channels, will

6 CERN Courier, November 1995 Around the Laboratories

Reconstructed waveform from the liquid argon 'Spanish Fan' endcap calorimeter prototype for the ATLAS experiment, showing the excellent imaging properties of the FERMI acquisition chain.

be impossible to assemble in the reduction, for a number of channels classical way with the electronics in to be integrated on a single silicon crates and racks accessible outside substrate. The current FERMI proto­ the detector volume. To operate fast type microsystem contains almost enough, a substantial part of the 4x106 transistors on a 5x5 cm electronics must be placed directly substrate, comparable to a Digital on the detector elements and the Equipment Alpha CPU chip. data considerably compacted before FERMI is based on early digitization being transferred to external data of compressed analog information acquisition and storage systems. from the detector, absolute data This generates in turn further de­ correction through look-up tables, mands on the electronics in terms of and digital signal processing for the 200 400 600 800 1000 1200 1400 power consumption, fault tolerance feature extraction, both for trigger Time [ns] and local signal processing power. and readout. Modern data processing Some LHC detectors, notably techniques and high level integration calorimeters, demand a huge dy­ allow, for the first time, absolute (40 or 80 MS/s). To reduce the data namic range of 16-17 bits (105) with calibration to be achieved in parallel volume and, for the trigger functions, a resolution of up to 11 bits in order for each channel at the detector to identify the time origin of the that uncertainties introduced by level, and in real time. signal, extensive Digital Signal electronic quantization will not affect In 1991, when the FERMI project Processing (DSP) techniques are the measurements. was started, adequate analog to applied. Test beam results show that As part of CERN's Detector Re­ digital converters (ADCs) did not this provides an almost continuous search and Development programme exist. With the LHC requirements in imaging of the input waveform, such (April, page 3), the RD16/FERMI view, an R&D programme aimed at that the input signal is completely (digital Front-End and Readout producing, as a first step, a 10-bit 70 reconstructed and the relevant Microsystem) project is developing a megasample(MS)/s converter with parameters are retrieved, even under novel approach to the construction of minimal power consumption. Two severe distortions generated by readout systems for LHC calorimetric approaches were pursued, a "Two- heavy pile-up conditions, as encoun­ detectors, integrating directly on the Step" and a "Parallel Successive tered when operating at very high detector most of the acquisition and Approximation" converter. The latter, event rates. processing functions using a fully patented, is now operational and For all DSP operations the digital digital approach. It involves a col­ must be considered as one of the data is linearized and corrected by laboration of nine research institutes best A/D converters available today. look-up tables, guaranteeing that the in France, Italy, Sweden and Switzer­ Key parameters at 40 MS/s (the LHC information used for the real-time land, together with three high-tech­ bunch crossing rate) are: Resolution trigger decisions is identical to the nology industrial firms. 10 bits; Differential non-linearity ±0.7 data later used during the analysis. FERMI's aims are achieved using LSB (least significant bit)/ 0.18 LSB The filter retrieving the final energy microsystems, with a higher level of RMS; Power consumption 150 mW information has an intrinsic resolution integration combining, in a modular (plus that of the reference voltage of 0.07%. architecture, a number of functional ladder). The complexity arising from moving blocks in the form of high-speed Recent improvements in semicon­ such massive processing power onto applications-specific integrated ductor technologies allow even better the detector itself led FERMI to adopt circuits (ASICs). Recent develop­ performances and an ambitious modern fault tolerance techniques, ments in the domain of multi-chip- programme aiming at a 12-bit 100 such as those currently applied in modules allow all the functional MS/s converter has been initiated as spaceborne applications, in order to blocks required for the acquisition a joint project between FERMI and maintain, and even improve, reliabil­ and processing of very high dynamic ETH-Zurich, Switzerland. ity. Only error detection and recov­ range data, including the extraction Information from the detector is ery, functional redundancy (spare of trigger information and local data continuously sampled at high speed capacity) and some level of program-

CERN Courier, November 1995 7 Around the Laboratories

mable reconfigurability in situ - Spectrometer (AMS) - the first large together with radiation-hard ASIC SPACE experiment equipped with a magnet technologies - can guarantee system ever placed in orbit - to study cosmic survival under extreme operating Major particle physics particles and nuclei. conditions. experiment Special contributions have come The requirements of large-scale from Bologna, ITEP (Moscow), ETH reliability and high performance also Zurich, Geneva and Perugia. apply to the assembly and packaging ASA and the US Department of Sam Ting, who shared the Nobel aspects. Wire bonding, as used in NEnergy (DOE) have signed an Prize in 1976 with Burton Richter for standard IC packages, exhibits agreement to fly a major particle their independent 1974 discoveries of limited reliability in terms of both physics experiment on the Space the J/psi particle, currently leads the mechanical properties and signal Shuttle in 1998 and later on the large L3 experiment at CERN's LEP integrity for these high-end applica­ international Space Station. Samuel electron-positron collider. He de­ tions. As a consequence, flip-chip C.C. Ting of MIT will lead the experi­ scribed plans for the AMS experi­ connection techniques have been ment's scientific team. ment in his summary talk at this adopted for final assembly of FERMI The DOE-sponsored experiment year's major international Lepton- microsystems. will look for antimatter originating Photon Symposium in Beijing. Thanks to its inherent modularity from outside our galaxy and give The 3-tonne AMS magnetic and interconnection possibilities, hints of the mysterious 'dark matter' - spectrometer will include a solid-state FERMI is being developed for vari­ as yet undiscovered material that (silicon) tracker measuring to within ous applications, mainly in the could make up most of the universe. 10 microns, supplemented by domain of calorimetry and signal It extends the repertory of space- Cherenkov counters and with strip/ imaging for CMS and ATLAS at LHC, borne detection techniques to ex­ scintillator assemblies for triggering. as well as for the HERA-B (DESY, plore the Universe beyond the stifling The detector design ensures that it Hamburg) and ICARUS (Gran Sasso, blanket of the Earth's atmosphere. is as light as possible compatible with Italy) experiments. A collaboration of some 37 universi­ its aim of making repeated measure­ VME modules, consisting of the ties and laboratories in Europe, the ments, while providing a high level of FERMI analog ASIC together with a US, Russia, China and Taiwan will spare capacity (called 'redundancy' simplified digital part, and with a use the Alpha Magnetic by physicists) ensuring that the dynamic range exceeding 15 bits, have been used in beam tests with detector prototypes from both ATLAS and CMS, with extremely encourag­ ing pulse resolution results. FERMI is an excellent example of the innovative technology required to face the challenge of the ultra-high interaction rates of 21st-century physics.

Artist's impression of the International Space Station, showing the position of the AMS (Alpha Magnetic Spectrometer) for extraterres­ trial particle physics studies.

8 CERN Courier, November 1995