Physics monitor

Georges Charpak (left), the inventor of the multiwire proportional chamber, in discussion with Vice-Director of Novosibirsk's Institute for Nuclear Physics Benyamin Sidorov at this year's Vienna Wire Chamber Conference.

pharmaceutical production, or for nuclear waste transmutation.

A highlight of the Dallas meeting was Gus Voss' 'farewell' speech following his recent retirement from the DESY Laboratory in Hamburg, extracts from which will be published in a forthcoming issue.

(Information compiled by Daniel Dekkers, Helmut Haseroth, Albert Hofmann, Kurt Hubner, Eberhard Keil, Stuart Turner and Ted Wilson)

DETECTORS Vienna - beyond the wire

n 1986, at the fourth Vienna Wire I Chamber Conference, Georges the impression of a biased selection. positrons in cosmic rays attracted a Charpak, the inventor of the multiwire The fact that silicon detectors, lot of attention. proportional chamber, had confi­ electronics and track reconstruction The next day covered wire cham­ dently announced "Les funerailles strategies were, with the exception of bers in general. V. Polychronakos des chambres a fils". Was this the the invited talks, restricted to poster presented applications of cathode writing on the wall for the conference presentations led to the same conclu­ strip chambers in muon spectro­ series as well as this type of detector sion. As a result the organizing meters for experiments at CERN's technology? committee saw that it will have to LHC proton-proton detector. Cer­ The demand for detector innova­ revise its brief for the next confer­ tainly the challenges of LHC for tion, coupled with imaginative think­ ence. detector development dominated ing on the part of the organizers, The conference opened with philo­ many presentations. Both ATLAS have kept the Vienna venue at the sophical thoughts by Nobel Prizewin­ and CMS demonstrated different forefront of the physics calendar. An ner Georges Charpak. The first day approaches to mastering the difficul­ additional boost to the success of the at Vienna is traditionally devoted to ties of covering large areas with series was certainly the Nobel Prize applications of gaseous detectors precise detectors capable of resolv­ awarded to Georges Charpak in outside high energy physics. L. ing consecutive bunches. Proposed 1992. Shektman gave an overview of wire techniques included thin gap cham­ While the major topic naturally is chambers for medical imaging. bers, straw drift tubes, pressurized still wire chambers, alternative tech­ Further applications in medicine and drift tubes, resistive plate cham­ nologies are also covered. However in other fields like biology and space bers in fields like calorimetry or ring science were described by subse­ Next year will see the commission­ imaging Cherenkovs, a sample of quent speakers. The exciting idea of ing of Frascati's DAFNE phi factory, only a few prominent detectors were flying a spectrometer on a balloon to and several presentations were presented, giving some participants study the fraction of electrons and made by the DAFNE FINUDA and

CERN Courier, September 1995 29 Physics monitor

KLOE collaborations. Remarkable is presentations on Cherenkov detec­ General aspects of tracking at high KLOE's large volume drift chamber, tors covered large working systems intensities, including trigger and with results from a 3 m3 prototype. like the DELPHI RICH, new develop­ software, were covered by D. Saxon. Although silicon detectors are ments, for example for the HERA-B He pointed out that, especially for strictly not within the scope of the RICH, and new concepts like the triggers, we are on a fast learning conference, it is traditional to have an optical discriminator shown by Y. curve from ZEUS to HERA-B and to invited talk on this subject. This year Giomataris. The principle of the LHC. The appealing features of G. Lutz gave an excellent overview optical discriminator is that only light neural networks for pattern recogni­ on standard detectors and new from particles traversing the detector tion, for the determination of masses, detector structures. He reported on under specific geometrical angles for energy and track parameters as the development of monolithic and emitting light under specific well as for their implementation for detectors with integrated electronics Cherenkov angles is guided to the triggers were shown by H. Kolanoski. to avoid connection capacitances, photon detector. The geometrical The outstanding features of cesium implying the development of transis­ angle can be a function of the impact iodide as a secondary electron tors built into detector technology. parameter of the particle, thus emitter were exploited by several A new and promising material, allowing to B mesons to be tagged, groups. Cesium iodide gaseous diamond films, was featured in two for example. detectors are used in detectors for talks (by H. Pernegger and W. A long session was devoted to UV light and fast RICH detectors to Oulinski). Irradiation studies with microstrip gas counters (MSGC) and detect thermal neutrons and for these materials show an increase in similar devices. A. Oed, one of the imaging in various fields. the signal response at low doses, inventors, described the properties of Requests for copies of transparen­ possibly due to the passivation of MSGCs and spoke on new develop­ cies of individual talks reflected the charge traps and no degradation ments. LHC experiments, where main interests of participants. It was after irradiation with photons (10 designs soon have to be fixed, are no surprise that talks on MSGCs and Mrad), protons (5 x 1013 cm2) and making considerable efforts to MGCs were the most popular. These pions (1014 cm2). The second talk understand and model the physics of were closely followed by diamond looked at the production of microstrip MSGCs, an essential part of ongoing detectors. detectors on diamond films and detector systems. Industry again took an active role in showed initial results from beam A major concern is still time stability the conference, but the idea to limit tests. for high rate operation. The results the industrial exhibition to the first Progress was also reported on the on stability using different substrate half of the week was widely appreci­ development of precision noble liquid materials, strip materials and gas ated. In general contacts with indus­ calorimeters. The large effort to build mixtures show some common ten­ try have progressed to a new level, the liquid argon calorimeter for dency but not all the effects could be especially when viewing the chal­ ATLAS to measure not only energy explained. Controversial discussions lenge of LHC. This challenge will but also shower position with excel­ followed some of the presentations. It require close links between the lent timing was shown by D. was further stressed that a careful physics community and industry to Fournier. Results from the NA48 choice of materials in contact with the provide a cornerstone for future (CP-violation experiment) collabora­ gas (boxes, glue,...) and the monitor­ systems. tion at CERN and from a group ing of the gas purity using a gas The Wire Chamber Conference was represented by V. Radeka showed chromatograph is essential. Some followed by a one-day workshop on that liquid krypton has also been groups favour a slightly different the application of gaseous and other mastered. Prototypes of the NA48 geometry - the so-called micro-gap radiation detectors in medicine and calorimeter achieved an energy chamber (MGC). Several MGC biology, organized by W. Bartl. As resolution of 3.5 % and a timing prototypes have been built to study well as standard applications in resolution below 300 ps. the properties. A MGC coupled to a radiography and positron emission Detectors based on Cherenkov light UV photocathode was used to build a tomography, wire chambers are also are continuously being improved and photon detector with single electron used to study rapidly-changing X-ray employed in new applications. The response. images. This opens new opportuni-

30 CERN Courier, September 1995 Superlatives for Superconducting Magnets

DIPOLES • QUADRUPOLES . CRYOSTATS • REMOTE HANDLING • DISMANTLING

NOELL GmbH is developing logy and break new ground in NOELL is also involved in superconducting twin aperture the field of electromechanical the developement of components prototype dipoles in cooperation engineering. All the materials used for nuclear fusion e.g. for JET, with CERN for the Large Hadron have to withstand the stresses Wendelstein VII X, TJ II and TFTR. Collider (LHC). These magnets are arising from mechanical forces Please contact us for further designed for a nominal current of produced by the high magnetic information. 12,400 A and a magnetic field of field and from being cooled to 8.4 Tesla. They are at the forefront -271.3°C (1.8K), and guarantee NOELL GMBH of superconducting magnet techno­ safe operation at this temperature Dept. V29 97064 Wurzburg near absolute zero. Germany Two superconducting dipoles Phone: 09 31/ 9 03-13 18 have already been delivered and Fax: 09 31/9 03-10 16 tested. The third dipole is now in fabrication and will be delivered soon. A press for the curing, colla­ ring and welding of LHC dipoles is currently being commissioned. The 1 8 m long press produces a total force of 270 MN.

A Member of the Preussag Group ^^Sfr Physics monitor

ties for physicians and biologists. will continue for the next meeting (the A special effort by the organizing 8th), to be held in 1998. Looking hard at the committee ensured a wide attend­ ance of scientists from the states of By Manfred Krammer and Meinhard electroweak force the former Soviet Union and from the Regler countries of the eastern parts of hile recent experiments have Central Europe, for which Vienna is W beautifully confirmed many of now the entry point to the European the predictions of the electroweak Union. unification of electromagnetism and This year the conference again the weak nuclear force, some direct broke the record for the number of consequences of the electroweak participants, reaching 300, in spite of symmetry involve special properties the fact that the International Advi­ of the three force carriers - the sory Committee had had to reject electrically charged W and neutral Z many submitted papers, not so much carrying the weak force and the because of their quality, but more photon of electromagnetism. These because of limited progress since the special properties have yet to be Although wire chambers are no longer the previous conference. measured accurately. major subject of the Vienna Wire Chamber Such 'rejected' contributions never­ Conference, the central physics objectives, In the electroweak picture these theless could be presented as such as high performance particle tracking, force carriers (vector bosons) can posters in a special open area, now a remain the same. This shows the opto­ interact with each other. These distinctive characteristic of the electronics readout system for a tracker based on scintillating fibres for the Chorus neutrino properties are 'non-abelian' - they are Vienna Conference. In the end, only experiment at CERN. Comprising more than a dependent on the order in which they a few applications had to be with­ million fibres with a total length of about 2,500 are applied. [Most operations can be drawn. kilometres, it is claimed to be the largest fibre- applied in any order, for example The organizers were also reassured based tracker built so far. For calibration, the fibre ribbons are interleaved with 'flappers' - simple arithmetic: 6x(3+2) = by the large number of young scien­ spacers containing a few fibres - which are (6x3)+(6x2). These are 'abelian'. An tists attending. Hopefully this trend grouped and coupled to a LED pulser. example of a non-abelian operator is the logarithm: log(x+y) does not equal log(x) + log(y).] Summarizing the current theoretical and experimental understanding of these self-interactions, and discuss­ ing the prospects of measuring them in future experiments, was the purpose of the "International Sympo­ sium on Vector Boson Self-Interac­ tions" held earlier this year at UCLA, the first meeting entirely devoted to this topic. Progress in measuring the self- couplings of vector bosons has been fueled recently by the CDF and DO Collaborations at Fermilab's proton- antiproton collider. Using data from vector boson pair production, these studies are extracting information on light from LED pulser the WW-photon, WWZ and ZZ- photon interactions, as well as the

32 CERN Courier, September 1995