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THE SPANISH INVOLVEMENT IN LEP

J. Salicio

Abstract

In this article the involvement of the Spanish High-Energy Physics (HEP) groups in LEP is overviewed, covering the period from 1981 to 1992. We refer to the effort made by the initially small community in order to actively participate in the construction of the LEP detectors and in the analysis of the experimental data.

1. Introduction implementation of a Steering Plan(**) for its development. As a The success of the UAl and UAZ experiments at the CERN consequence, several new groups were created: the Autonomous SPS collider, which lead to the discovery of the intermediate Universities of Barcelona and Madrid, the University Com— bosons [1] Z0 and W1“, renewed the interest for the already plutense of Madrid, and the Universities of Santiago and approved high performance e+e— European collider machine: the Zaragoza. Large Electron Positron (LEP) collider; most of the HEP commu— nity was willing to participate in its experimental programme. Contacts had started in the early 80s to establish collabo— 2. The LEP collider rations and to take responsibilities in the design and construction The LEP is the largest machine built to date. Its construction of the different parts of the possible experiments. was approved by the CERN Council in its December 1981 Although at that time Spain was not a member of CERN, the session, and it took nearly eight years until the first interactions experimental HEP community (mainly concentrated in the groups were observed in the four experiments: ALEPH, DELPHI, L3 from CIEMAT(*) Madrid. and the universities of Valencia and and OPAL [2]. The total cost of the machine was ~ 1000 MCHF. Santander) was following with maximum interest the develop— The following data give an idea of the size of the project. The ment of LEP with a view to possible participation in its ex- LEP tunnel, 27 km in circumference, is filled with ~ 3300 six— periments. metres long magnetic dipoles. ~ 800 quadrupoles with lengths of The group from CIEMAT, one of the pioneers of the experi- 1.6 and 2 m, ~ 500 sextupoles, ~ 600 orbit correctors and 128 mental HEP community of Spain, was lead by profes- accelerating and storage RF cavities. The entire LEP complex sor J.A. Rubio, who made preliminary contacts with the various requires of the order of 75 MW of electric power. Ultra—high groups of physicists who intended to form collaborations. The vacuum (~ 10’10 Torr) must be maintained in the vacuum cham- CIEMAT, as well as the groups from Valencia and Santander, bers, around the 27 km LEP ring, to avoid beam—gas collisions was already participating in specific experiments of the CERN which would adversely affect the beam lifetime. programme and also in the programmes of other laboratories in Many European companies participated in the construction Europe and the USA. and equipment of the machine and related services. Among these, In 1981, the CIEMAT joined the MARK—J collaboration we would like to mention the contribution of a few Spanish in DESY, whose spokesman was the Nobel laureate, profes- companies [3] such as Entrecanales y Tavora in civil engineering, sor S.C.C. Ting. This was the beginning of a long and fruitful ANISA in air conditioning and ducts, and INESPAL in the collaboration lasting till nowadays. production of sealing and alignment elements for the ultra—high The accession of Spain to CERN in 1983 marked the begin- vacuum chambers of LEP. ning of a new epoque for HEP in Spain and triggered the

3. Participation of Spain in the LEP experiments The Spanish contribution to the LEP experimental pro- (*) The “Centio de Investigaciones Energeticas. MedioAmbientales y gramme was, and is being, carried out by the groups of CIEMAT, Tecnologicas" was previously known as JEN, Junta de Energia Nuclear. the Autonomous University of Barcelona, the University Com— was approved by the Spanish (**) The “Plan Movilizador de Altas Energias". plutense of Madrid, and the Universities of Santander and Parliament in 1984. In 1988 it was replaced by the “Programa Nacional de The CIEMAT was one of the first groups involved in 69 Fisica de Altas Energias" in the framework of the recently promulgated “Ley Valencia. de la Ciencia". the L3 experiment, while the universities Complutense of Madrid,

Santander and Valencia decided to join DELPHI. The new group from the Autonomous University of Barcelona joined the ALEPH collaboration. All these groups took responsibilities in the design and construction of specific parts of the detectors and in their maintenance, as well as in the analysis of the data. The LEP detectors are complex devices incorporating new technologies (sometimes specially developed), and requiring an important effort, both in human and in material resources. The cost of the detectors varied between 100 and 200 MCHF. More than 1200 physicists from countries all over the world participated in the various phases of the construction and assembly of the detectors, the DAQ systems, the monitoring, the safety systems, etc., all requiring a high level of coordination in a complex and sometimes difficult environment. The Spanish participation concentrated on many of the activities referred to above, its achievements being remarkable given the lack of experience of most of the groups.

3.1 L3 — CIEMAT With the commitment of CIEMAT to build an important part of the L3 muon spectrometer [4], the Spanish industrial participation in HEP experiments began to be relevant. The aim of the CIEMAT leader was to establish a strong collaboration with industry in order to increase the presence of Spanish industry in The L3 muon spectrometer HEP technologies. . The muon spectrometer (fig. 1) had been designed to measure high-energy muons to an accuracy Ap/p = 2% at 50 GeV, thus providing a 1.4% dimuon mass resolution at 100 GeV. It consists of 16 basic units (octant modules) arranged in two Ferris wheels; on each wheel, 8 of these units surround a stainless steel cylinder (support tube) whose axis matches the direction of the beams of electrons and positrons circulating around the LEP machine. Each octant module (fig. 2) is a high precision aluminium structure (array stand) holding three parallel layers of precision wire drift chambers: there are two chambers (MOL, MOR) in the outer layer, two chambers (MML, MMR) in the middle layer and one chamber (MI) in the inner level. The active material of the precision drift chambers is a gas mixture, 35% ethane and 65% argon, which becomes ionized when a charged particle crosses by, the free electrons being collected by sense wires situated parallel to the beam line. An electric field is maintained to have a well—defined drift path for the electrons. The volume of the inner and the outer precision chambers is closed on the sides by precision aluminium structures (end frames and side panels), and on the top and bottom by drift chambers with sense wires perpendicular to the beam line (Z chambers [5]). All the chambers are submerged in a 5 kG magnetic field that bends the charged particles in a plane perpendicular to the beam line. A muon of 50 GeV deviates from a straight line by a sagitta, 70 S = 3.5 mm, which is very precisely measured in the region between the support tube and the magnet coil by the three layers An octant module of the L3 muon spectrometer J. Salicio

of precision muon chambers. To get Ap/p = 2%, we must measure simulate the final attachment to the Ferris wheel, the octants were As/s to 2%, i.e. As ~ 70 pm. placed on four support feet, which were positioned on a plane to This requires a long-term chamber alignment to S 30 um. The 50 um. Critical distances between reference surfaces were array stands have been designed to avoid tensor force transmis- measured to 5 um by means of special tools calibrated with a sion, thus the octant behaviour is fully predictable under all laser interferometer. Angles were measured with electronic conditions of stress, load and temperature. bubble levels, which have an intrinsic resolution of better than The HEP group of the CIEMAT took responsibility for the 1 urad. Temperature changes were and are constantly monitored design and construction of a large part of the muon spectrometer: through probes installed in eight different points of an octant. The 17 array stands (16 for the muon spectrometer and 1 for a test readout is made with VME ADC modules, designed and made at station) including the special pieces (~ 300 small precision pieces the CIEMAT. per octant module) to keep the precision chambers in a well- Personnel from the CIEMAT contributed to the design of the defined position within each other to accuracies of a few micro- cooling system and control of the racks holding the electronics of metres, production of the end frames and side panels for the MI, the L3 experiment. MOL and MOR chambers as well as 102 Z drift chambers (96 for In addition to the specific software responsibilities associated the spectrometer and 6 for the test station). with the hardware equipment, such as monitoring of the u At the design stage, SENER, a Spanish engineering company, spectrometer, gas control, u-trigger system, etc., the CIEMAT in collaboration with the Draper Lab., an American company, and also made an important effort in the development of the off-line the physicists of the L3 collaboration, had a major role in coming software base of L3. They had a major role in the design of the up with the ideas to reach the required mechanical performance L3 database structure, its management, handling of the informa— of the precision chambers and array stands. tion, and in the design of tools to automatically and periodically Although the CIEMAT worshops had the capacity to produce update the database replicas that are kept at each collaborating many of the components, such as the Z chambers, parts of the end institute. frames and special pieces for the array stands, other parts had The criteria and programmes to select the u-data sample, the been produced by Spanish industry. This was the case for the u-reconstruction programmes, the design of several MC gene- array stands fabricated by ENSA (Equipos Nucleares SA, a high- rators simulating processes of interest for LEP, etc., are other technology company specialized in the production of nuclear contributions of the CIEMAT physicists. equipment), in collaboration with ALUGASA (Aluminios de Within the context of the L3 experiment although not directly Galicia SA), under the supervision of the CIEMAT engineers and related with the CIEMAT, one should mention the participation physicists. The required accuracies, a few micrometres over of another Spanish company, ABENGOA, in the assembly of the distances of a few metres should be emphasized. L3 magnet, the magnet cooling system and the support tube. MASA (Mecanizaciones Aeronauticas SA), a company ABENGOA was charged with the cooling engineering and the specialized in precision machining, produced, in collaboration welding of the 168 aluminium coils each of 12 m diameter with the CIEMAT, most of the end frames for the precision (1100 t weight). The homologation and tests for the aluminium chambers. Many other companies, such as ENDASA, PHEMSA, welding were done in ABENGOA’s workshops in Sevilla, as INDUNOR, NOVALTI, to quote several, supplied materials for were the designs of the magnet cooling system. The assembly in the construction of Z chambers in the CIEMAT workshops. situ was performed by the ABENGOA—SDEM group. Figure 3 The CIEMAT took the major responsibility for the overall shows the installation of the support tube inside the L3 magnet. assembly of the octant modules at CERN, the transport of the modules to the experimental area and the assembly of the whole muon spectrometer in situ. For this purpose, a team of 5 physi- 3.2 DELPHI — Universities Complutense of Madrid, cists, 2 engineers and 5 specialized technicians was permanently Santander and Valencia detached at CERN until completing the installation of the muon Two important hardware contributions to the DELPHI experi— spectrometer in the experimental hall, and testing its perfor- ment [6] were made by a joint effort of the groups from the mance. A picture of a fully equipped octant module in the process Universities of Valencia and Santander: the design and construc- of being transported is shown in fig. 2. tion of the TOF (time-of-ﬂight) detector and participation in the The assembly of the octant modules is a very complex design and construction of the FEMC (forward electromagnetic operation involving not only the mechanical attachment of the calorimeter). different elements but also the very precise alignment of these The TOF is a classic detector [7] made of 172 scintillating elements and the careful and constant monitoring of critical plastic strips, each 3.5 m long and 20 X 2 cm2, surrounding the parameters, in order to achieve the required performance. interaction point with an original design of the light guides which During the assembly phase, the CIEMAT team did, allows the photomultipliers (PM) to be placed in a region where 71 for each octant, detailed dimension and reference checks. To the magnetic field is not important. J Salicio

The L3 support tube to be placed inside the L3 detector Partial view of the DELPHI detector prior to the insertion of the superconducting magnet. The inner cylinder shows the guides where the TOF counters were inserted.

The design of the detector and the associated electronics was (c) The Fastbus slave detector cards for data acquisition and done in its entirety in Valencia. trigger (the TSU and TDU cards). NE110 and EMI9902 were choosen as basic components, The TSU is a multipurpose card containing eight TDC after careful studies of the results obtained with cosmic muons channels of 8 bits and 500 ps least count. The detector was traversing different prototypes of counters. One of the problems organized in sectors (each sector made of 4 detectors matching in the design was that the whole counter had to be mounted inside the yoke structure of 24 sectors), doubled for the Z coordinate the yoke and not much space was available. The solution found positive and negative (there are 24 sectors for each barrel at each for this problem was to bend and attach the light guides on top of side of the interaction point). A TSU card is associated with each the scintillators and to choose small window PMs one and a half double sector. Two Fastbus crates are needed to hold all the TSU inches in diameter. cards of the TOF detector. Another important function of the The light guides, the assembly, the mechanics for mounting TSU is to provide a trigger signal to localize any particle crossing all the scintillators in the iron yoke of DELPHI, as well as the PM a sector. For this, the OR of each of the four PM signals on each mechanics, were all done in Spain, with the participation of side of the sector are the inputs of a mean—timer that provides a Spanish industry. Here, we would like to mention the role of coincidence with the proper timing. Talleres Herga SA in the production of the mechanics for the The TDU is a Fastbus card responsible for the local trigger TOF; of PLASTISA and PLEXISA, as suppliers of the light decision matrix for cosmic muons and also for the trigger signal guides, and FIBROCOSA, in optical fibers for the TOF cali- sent to the muon subtrigger unit, where other detectors enter. This bration. Figure 4 shows the mechanical support of the TOF module also performs the timing of all the gates and strobes detector during installation. needed for the correct handling of signals. All the electronics associated with the TOF detector were The output from the PMs is split in two, and one of the designed in Valencia, i.e: signals is connected to ADC (analog—to-digital) standard Fastbus (a) The PM voltage divider, optimized for fast pulses (the high modules available on the market. voltage supply used was a standard in DELPHI). The forward electromagnetic calorimeter (FEMC) was 72 (b) The amplifiers and splitters, handling the signals coming originally designed to have very good efficiency, energy reso- from the PMs through 40 m of cable. lution and granularity for the measurement of high-energy .l. Sallcio

photons and electrons emitted in the forward cone, which is the region not covered by the barrel detectors (those with cylindrical symmetry). In the case of DELPHI, the FEMC subtends the angular region ranging from 10—38 degrees. The collaboration responsible for the construction of the detector was composed of Italian (Padova, Trieste and Milano) and Spanish (Valencia and Santander) groups. The group from Valencia had been a participant in this detector since the very first design and prototype studies in 1984. After these early studies, the detector selected was based on lead glass bars. This ensured the best parameters. As the detector was to operate inside the DELPHI solenoid (where the magnetic field is 1.2 Tesla), it was decided that the readout solution ought to be based on a new variety of photomultipliers with only one dynode: the phototriodes. The special design of the phototriodes makes them capable of operating satisfactorily inside high magnetic fields [8]. The FEMC is therefore structured in two parts: one in the “forward” and the other in the “backward” side (seen by the electrons). On each side there are ~ 60 steel modules containing ~ 80 lead glass bars with a size of 5 X 5 cm2 and a depth of 40 cm (equivalent to 22 radiation lengths). This makes a very large electromagnetic calorimeter composed of a total of almost 10 000 detectors (lead glass blocks and Photograph of the DELPHI FEMC. phototriodes), each of which is equipped with electronics inside the module (voltage divider, preamplifier and calibration cir- cuits), as well as the readout electronics for all the channels. Figure 5 shows one part of the FEMC mounted on one of the DELPHI end caps. contribute to the unique task offered by LEP of providing a large Using the purchased materials needed for the FEMC (lead statistical sample of Z boson decays. glass blocks and phototriodes) a total of 2000 blocks were The groups from the Universities of Santander and Com- completely assembled in Valencia, with the cooperation of the plutense of Madrid concentrated mainly on the software develop- Santander group. The Santander group was responsible for the ment for the DELPHI experiment. mechanical construction of the steel plates, made by the company The HEP group of the University of Santander took a major ENSA, which housed the blocks in groups of 80. Before the role in the design, development, maintenance and optimization of assembly, a careful quality check was performed on each compo— a program for the DELPHI detector simulation, where the nent, using a test station mounted in the laboratory for this pur— geometry and physical processes were simplified such that the pose: the gain and the noise of each phototriode was measured CPU time is reduced by more than two orders of magnitude and only the good candidates were selected. A xenon lamp with without losing accuracy. the aid of a light distribution system was used to calibrate the The coordination of the on-line software associated to the detectors. A similar system has now been implemented on the TOF and the development of algorithms to perform the analysis actual detector. of data from the FEMC are other servicing responsibilities of this The Valencia group was also responsible for designing part of group. the trigger electronics. This was also developed in Fastbus The University Complutense of Madrid contributed mainly protocol. The purpose of the Fastbus card (called MMU) was to on the software side, due to the expertise they have in this field. elaborate the multiplicity of the cluster produced by an electro— Hence, the Monte Carlo production in DELPHI is one of their magnetic shower in the mosaic of the FEMC. responsibilities. The implementation of many of the simulation The contributions of the Valencia group to the DELPHI data handling and analysis programs for VM/CMS was carried detector are numerous and important. Here we have reviewed the out by them. technical details related to the detectors that have been designed In conclusion, the participation of these Spanish groups in and built under the responsibility of Valencia physicists and DELPHI is sizeable and is recognized by the collaborators as 73 technicians. These detectors are now operating satisfactorily, and important and successful. J. Salicio

3.3 ALEPH — Autonomous University of Barcelona The integration into the electronics, and the data acquisition The group from the Autonomous University of Barcelona of the whole ALEPH system was also the responsibility of the contributed to two aspects of the ALEPH [9] experiment: the group from the Autonomous University of Barcelona. Bhabha Calorimeter (BCAL), also known as the small angle The FALCON system [11] is a solution for the computing luminosity monitor, and the Facility for ALEPH Computing and power needed to reconstruct, as quickly as possible, the data Networking (FALCON). taken by the ALEPH detector. Based on the fact that events are The main goal of the BCAL [10] is to provide on-line independent of each other, a system composed of many proces- monitoring of the relative LEP luminosity in the ALEPH sors running in parallel, each working on a given event at a time, detector, in order to be available to the persons on shift and to could satisfactorily perform the event processing at the rate LEP machine control. It consists of four calorimeter modules demanded by data taking. placed in groups of two at both sides of the interaction point The system was developed in the framework of a research along the beam pipe. Each of the four modules is a sampling agreement signed by Digital Equipment Corporation (DEC) in calorimeter made of ten tungsten converter sheets interspersed Spain and the HEP group at the Autonomous University of with ten sampling layers made of plastic scintillator and one Barcelona. The final configuration of FALCON, which is now plane of 40 vertical silicon strips. Each module is a rectangular being used successfully in ALEPH, is shown in fig. 7. It consists box of dimensions 3 x 5 X 14 cm situated at 7.8 m from the of 10 diskless, screenless and keyboardless DEC VAX stations interaction point and at 6.5 cm from the beam. The ten scintillator connected as a local area VAX cluster, with u VAXes acting as plastics per module are grouped in pairs and read through 5 file servers. Two additional workstations connected to the cluster, photomultiplier tubes of the type Hamamatsu R—l635—02. The with local disks and with colour monitors, are used for monitor- plane of silicon strips is located at shower maximum. Its function ing purposes. is to measure the impact point of the original electron in the front face of the calorimeter. This is inferred from the shower centroid. The front-end electronics for the silicon strips is built around the Amplex chips which were originally developed at CERN. Five of i_ _i Parallel processors such chips process the signals from each silicon strip plane. £‘ 6 x VS 4000/60 Figure 6 shows two calorimeter modules with their electronics. i J 4 x VS 3100/76 The design and construction of the mechanics and electronics (~ 20 CERN units) of these modules were done entirely at Barcelona. KONEY, a laboratory from Barcelona, did the design and production of the multilayer printed boards that constitute the front—end readout of the silicon strips. File servers CEFlN Ethernet i- . ::¥%glOO/76 Flaw + POT (reprocessing) IDSS|2x4OOMB+2x1GB il

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74 Photograph of the ALEPH BCAL. Squeteh of the ALEPH FALCON system. .1. Salicio

The data coming from the different ALEPH subdetectors go e+ e“ —> Z0 —> hadrons through the on—line system of computers and are written on four large magnetic disks. These magnetic disks are shared with 30 f, 30 1 ﬂ FALCON, which selects the events and distributes them to the different processors. The output of the processors is put together 20 and sent through a remote link to the CERN IBM and to the l '1' 20 .4 \

[nb] ALEPH analysis computer cluster. One specially important [nb]

o feature of FALCON is that it runs entirely automatically, without 0' operator intervention. 1 0 o" e._ 10 , {if it. The optimization of the system parameters of the cluster for this application and the development of the application software to perform the event reconstruction in parallel, was the responsibility of the Barcelona group. Outside the contribution of the Barcelona HEP group, the company ENSA, produced the mechanical structure of the hadron 307 so /, calorimeter end caps/magnet yoke for the ALEPH detector. The OPAL . l end caps, weighing ~ 450 t each, are made out of six similar modules. The modules have 16 slabs of iron, 5 cm thick, one slab 20 207 I \ 10 cm thick at the end, and 6 additional slabs in the narrower end

[a [nb]

6 close to the beam line, which protrude into the inner part of the o ALEPH detector. 107

4. The LEP physics outcome The important contribution of the Spanish HEP groups to the 9:0 95 design and construction of the different parts of the detectors and \IE (GeV) to the development of the basic software, shows the fast improve- ment of their technological capabilities. The hadronic cross section of the LEP experiments as a function of the centre-of- Their participation in other activities such as data handling, mass energy (vs). The data shown, collected in 1991. are preliminary. analysis and interpretation, has also been significant. Many of the published results were achieved by physicists from these groups, through their contribution to the development of experimental analysis techniques to compare the data to the predictions of The SM predictions for the various fermion-gauge boson cou- theories and models [12]. Hence, the role of the members of these plings, accessible to the LEP data, agree with the experimental groups is widely recognized by the collaborations and the entire measurements. The precision measurement of the Z0 parameters scientific community. stated the existence of only three fermion families, each com- The measurement of the leptonic and hadronic line shape of posed of a doublet (a lepton and its neutrino) and a corresponding the Z0 (fig. 8), results on the BB mixing, measurement of the r doublet of quarks. lifetime, branching ratios, polarization, search for new particles, Although a member of one of the quark doublets (the t quark) to name but a few of the subjects, are examples of a participation has not yet been found, limits on its mass were given through the that has only but started(*). measurement of the line shape and the asymmetries of the Z0 As a consequence of these analyses, based on a huge amount decays. A value, m[ = 148 GeV, with 20% uncertainty [13] was of data(**), many fundamental questions found an answer. The obtained. gauge sector of the Standard Model (SM), responsible for the The central issue for the LEP experiments is, probably, the underlying interactions based on the SU(3) ® SU(2) ® U(l) search for the Higgs particle(s) responsible within the SM for the symmetry, has been tested, establishing the validity of the SM. mass of all the elementary fermions. Lower limits to its (their) mass(es) were given by the four LEP experiments [14]. Searches for new particles (supersymmetric particles, heavy leptons, leptoquarks, etc.), predicted by various models looking to (*) About 10 PhD. theses have been finished in the last few years and IS are in the ultimate theory, were also performed. process by these physicists working at LEP. (**) The data collected by the four experiments at LEP from 1989 to the fall of The expected operation of LEP at higher energies (~ 200 GeV) 75 1991 amount to a total of ~ 2 millions of Z0 events. will allow the precision measurement of the W mass, the absolute I. Salicio

e+e“ cross section and the value of the strength of three boson [7] A. Ferreretal.,Ana1es de Fisica BS3 (1987) 29 I; couplings, the search for particles including the Higgs in a new P. Allen etal.,Nuc1. Instr. and Meth. A277 (1989) 347; energy range. etc. J.M. Benlloch et al., Nucl. Instr. and Meth. A290 (1990) There is an exceptionally broad and extremely interesting 327 and A292 (1990) 319. physics programme at LEP, which will probably extend over the [8] P. Checchia et al., Nucl. Instr. and Meth. A248 (1986) 317; next six years. . P. Checchia et al., Nucl. Instr. and Meth. A275 (1989) 49. The participation of the initially small Spanish Community“) [9] D. Decamp et al., ALEPH — A detector for electron—positron in the LEP programme, will hopefully maintain the high technical annihilations at LEP, Nucl. Instr. and Meth. A294 (1990) and scientific level reached after a decade of successful efforts 127—178. and after a decade of progress. [10] E. Fernandez et al., A very forward luminosity monitor for the ALEPH detector at LEP; Nucl. Instr. and Meth. A297 (1990) 153—162. [1 l] M. Delfino et al., The ALEPH event reconstruction facility: parallel processing using workstations, UAB—LFAE Acknowledgements 89—01 (1989). This article has been prepared with information and material [12] F. Dydak, Summary on particle physics, proc. of the provided by M. Aguilar-Benitez and professors A. Ferrer, XXVI‘h Rencontre de Moriond: ‘91 Electroweak E. Fernandez and A. Ruiz. I thank all of them for their help. Interactions and Unified Theories, Editions Frontieres, I wish to thank J.A. Rubio for his comments and advice in the (1991); preparation of this article. The LEP collaborations, Electroweak parameters of the Z0 1 am grateful to Rita Kirkby for her effort in correcting the resonance and the standard model, CERN/PPE 91—232 English version of this article. (1991); Z Physics at LEP I, report CERN 89—08 (1989). [13] D. Schaile, Tests of the standard model at LEP, proc. of Les Rencontres de Physique de la Vallée D’Aoste, Results and Perspectives in Particle Physics, La Thuile, Aosta Valley (1992). [14] G. Herten, Search for new phenomena at LEP, proc. of Les References Rencontres de Physique de la Vallée D’Aoste, Results and [1] G. Arnison et al., Phys. Lett. B122 (1983) 103, and B126 Perspectives in Particle Physics, La Thuile, Aosta Valley (1983) 398; (1992). P. Bagnaia et al., Phys. Lett. B129 (1983) 130; R. Ansari et al., Phys. Lett. B186 (1987) 440. [2] B. Adeva et al., Phys. Lett. B231 (1989) 509; D. Decamp et al., Phys. Lett. B231 (1989) 519; P. Aarnio et al., Phys. Lett. B231 (1989) 539; Address: M.Z. Akrawy et al., Phys. Lett. B231 (1989) 530. J. Salicio [3] N. Siege]. Spanish Industry and CERN, this issue. CERN [4] L3 collaboration, Letter of Intent (January 1982); CH—l2l 1 Geneva (Switzerland) L3 collaboration, Technical Proposal (May 1983); B. Adeva et al., The construction of the L3 experiment, Nucl. Instr. and Meth. A289 (1990) 35-102. [5] M. Cerrada et al., Results of the calibration of multicell drift chamber prototypes for the L3—LEP muon spectrometer, Nucl. Inst. and Meth. A263 (1988) 343—350. [6] P. Aarnio et al., The‘ DELPHI detector at LEP, Nucl. Instr. and Meth. A303 (1991) 233—276. Received on May 1992.

(*) In 1983. the Spanish HEP community consisted of ~ 30 experimental 76 physicists (~ 15 tenured) distributed in 3 groups Now. in 1992. there are =: ~ 120 physicists (~ 35 tenured) distributed in 8 groups.