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The Design and Performance of the ZEUS Micro Vertex Detector

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The Design and Performance of the ZEUS Micro Vertex Detector The design and performance of the ZEUS Micro Vertex Detector A. Polini University and INFN Bologna, Bologna, Italy1 I. Brock, S. Goers, A. Kappes, U. F. Katz, E. Hilger, J. Rautenberg, A. Weber Physikalisch.es Institut der Universitdt Bonn, Bonn, Germany2 2007 A. Mastroberardino, E. Tassi Caia&ria Dnireraitp, PApsica Department and DVPW, Coaenza, dtatp ^ Aug V. Adler, L. A. T. Bauerdick, L Bloch, T. Haas *, U. Klein, U. Koetz, G. Kramberger, 21 E. Lobodzinska, R. Mankel, J. Ng, D. Notz, M. C. Petrucci, B. Sarrow, G. Watt, C. Youngman, W. Zeuner Deutsches Elektronen-Synchrotron DESY, Hamburg, Germany C. Coldewey, R. Heller Deutsches Elektronen-Synchrotron DESY, Zeuthen, Germany E. Gallo University and. INFN, Florence, Italy1 T. Carli, V. Chiochia, D. Dannheim, E. Fretwurst, A. Garfagnini, R. Klanner, B. Koppitz, J. Martens, M. Milite [physics.ins-det] Hamburg University, Institute of Exp. Physics, Hamburg, Germ.a.ny 3 Katsuo Tokushuku Institute of Particle and Nuclear Studies, KEK, Tsukuba, Japan.4 I. Redondo Dnireraidad Antonoma de Madrid, Madrid, .Spain ^ H. Boterenbrood, E. KofTeman, P. Kooijman, E. Maddox, H. Tiecke, M. Vazquez, J. Velthuis, L. Wiggers, NIKHEF and University of Amsterdam., Amsterdam, Netherlands 6 R.C.E. Devenish, M. Dawson, J. Ferrando, G. Grzelak, K. Korcsak-Gorzo, T. Matsushita, K. Oliver, P. Shield, R. Walczak arXiv:0708.3011vl Department o/ f Apaics, Dnireraitp o/ Oa^ord, Oa^ord, United kingdom ' DESYOT-131 A. Bertolin, E. Borsato, R. Carlin, F. Dal Corso, A. Longhin, M. Turcato Dipartimento di Fisica dell' University and INFN, Padova, Italy*1 T. Fusayasu, R. Hori, T. Kohno, S. Shimizu Department of Physics, University of Tokyo, Tokyo, Japan 4 H. E. Larsen, R. Sacchi, A. Staiano University di Torino and INFN, Torino, Italy 1 6 M. Arneodo, M. Ruspa University del Piemonte Orientale, Novara, and INFN, Torino, Italy 1 J. Butterworth, C. Gwenlan, J. Fraser, D. Hayes, M. Hayes, J. Lane, G. Nixon, M. Postranecky, M. Sutton, M. Warren Physics and Astronomy Department, University College London, London, United Kingdom 7 Abstract In order to extend the tracking acceptance, to improve the primary and secondary vertex reconstruction and thus enhancing the tagging capabilities for short lived particles, the ZEUS experiment at the HERA Collider at DESY installed a silicon strip vertex detector. The barrel part of the detector is a 63 cm long cylinder with silicon sensors arranged around an elliptical beampipe. The forward part consists of four circular shaped disks. In total just over 200k channels are read out using 2.9 m2 3of silicon. In this report a detailed overview of the design and construction of the detector is given and the performance of the completed system is reviewed. Key words: ZEUS, Silicon, Microstrip, Tracking, Vertexing PACS: 29.40.Gx, 29.40.Wk, 07.05.Fb, 07.05.Hd 1. Introduction * Corresponding author. Deutsches Elektronensyn- In the HERA storage ring 27.5 GeV positrons or chrotron, Notkestrasse 85, D-22607 Hamburg, Germany, electrons collide with 920 GeV protons. The ZEUS Tel.: +49-40-89983281; email: [email protected] experiment [1,2] is one of two large multi-purpose 1 supported by the Italian National Institute for Nuclear Physics (INFN) collider detectors installed at HERA. From 1992 to 2 supported by the German Federal Ministry for Educa­ 2000 HERA delivered ca. 200 pb -1 of luminosity tion and Research (BMBF), under contract number No 05 and the ZEUS experiment recorded ca. 180 million HZ6PDA collision events. Following the successful comple ­ 3 supported by the German Federal Ministry for Educa­ tion and Research (BMBF), under contract number No 05 tion of that program in 2000 the accelerator and HZ4GUA the experiments underwent an extensive upgrade 4 supported by the Japanese Ministry of Education, Cul­ during 9 months in 2000/2001 with the goal to ture, Sports, Science and Technology achieve a five-fold increase in integrated luminos ­ 5 supported by the Spanish Ministry of Education and ity by 2006. Science through funds provided by CICYT 6 supported by the Netherlands Foundation for Research As part of the upgrade of the ZEUS experiment, on Matter (FOM) the tracking capabilities were enhanced by the in ­ 7 supported by the Science and Technology Facilities stallation of a Microvertex Detector (MVD) in ­ Council, UK 2 side the existing Central Tracking Detector (CTD). cables and cooling is arranged from the rear. The goal was to provide the experiment with the The ZEUS MVD was built in a collaboration of capability of tagging heavy quarks by identifying several institutes within the context of the ZEUS displaced vertices. In addition the aim was to im­ collaboration during 1997 through 2000. It was in ­ prove the efficiency, acceptance and resolution of stalled inside ZEUS in the spring of 2001. In the the tracking system. During the design phase the fall of 2001 the detector recorded first events. From following requirements were specified in order to then until the end of HERA operation in June 2007 achieve that goal: the detector has been successfully operated over a - Polar angular coverage between 10° — 170°; period of almost 6 years. During that time a lu­ - Three spatial measurements per track, in two minosity of approximately 430 pb -1 was collected projections; and more than 600 million electron-proton scatter­ - 20 qm intrinsic hit position resolution for normal ing events were recorded using the detector. incident tracks; In the following sections we give a comprehensive - Impact parameter resolution of about 100 qm for description of the different detector subsystems tracks with polar angle of 90°, increasing grad­ and we discuss how the requirements set forth were ually to 1 mm at 20°, for tracks with momenta met taking the constraints into account. We also greater than 2 GeV; adress the conclusions that we have drawn. The - Noise occupancy < 10-3; following detector subsystems will be described in - Hit efficiency > 97%; detail: - Alignment accuracy better than 20 qm; - Silicon Sensors, - Two-track separation better than 200 |xm. - Readout Electronics, A number of constraints also had to be taken into - Mechanical Construction, account. These were - Data Acquisition System, - The space available for the Microvertex Detec­ - Slow Control, tor is limited by the inner bore of the central - Radiation Protection, tracking detector (diameter 324mm); - Data Quality Monitoring, - The longitudinal size of the HERA beam spot - Alignment and Tracking. extends over about 40 cm ; At the end we show some representative physics - The readout electronics and therefore also cool­ results obtained with the detector and we end with ing and cabling have to be located very close to a conclusion. the sensors to cope with the 96 ns bunch cross­ ing time of HERA; - The detector and the frontend electronics need to operate inside a 1.4 T axial magnetic field. 2. Silicon Sensor Design The geometrical layout of the MVD consists of a barrel (BMVD) and a forward (FMVD) section. The design of the silicon sensors of the ZEUS Here we note that the ZEUS coordinate system is MVD as well as the prototype and acceptance tests right-handed with the Z-axis along the incoming have been described in detail in [3]. Here we just proton beam direction, the X-axis in the horizontal summarize the main features of the sensors and plane pointing to the inside of the HERA ring and give some additional information on the ideas be ­ the Y-axis pointing upwards. The barrel section, hind the design chosen. centered at the interaction point, is about 63 cm Three different sensor geometries have been de­ long. The silicon sensors are arranged in three con ­ signed: square sensors for the barrel part (BMVD), centric cylindric layers. The innermost layer is in ­ and two wedge shaped sensors for the forward complete in the polar angle range of 60° around the part (FMVD) of the detector. Table 1 gives the positive X-axis. The forward section is composed relevant geometrical parameters. of four vertical planes extending the angular cov ­ Apart from their geometry, the three sensor erage down to 7 ° from the beam line. Access for types are identical. They are single-sided strip de- 3 type shape dimensions p+ strip length # of readout strips active area BMVD h=64.2mm 62.2mm 512 38.6cm^ w=64.2mm FMVD1 h=73.5mm 5.6 - 73.3mm 480 32.6cm^ wl=64.3mm w2=30.7mm ‘ FMVD2 h=48.5mm 5.6 - 47.4mm 480 23.9 cm3 wl=64.1mm w2=42.0mm Table 1 Geometrical parameters of the BMVD and FMVD sensors. tectors on high ohmic n-type silicon. The readout be understood. After exploring different options pitch is 120 pm with 5 intermediate strips for ca­ the HELIX 128-v3 chip [5] was selected for the pacitive charge division. The p+-readout strips are frontend readout; AC-coupled through a Si02-Si3N4 double layer to Single-sided readout was chosen because of the Al-strips, which are connected via wire bonds ei­ ease of mechanical mounting, the larger number of ther to a Polyimide foil with Cu strips (Upilex [4]) vendors of sensors, costs and, last but not least, or a glass fan-out. The p+-readout strips and the because of a tight time schedule. The compromise p+-intermediate strips are connected individually of an additional 0.33 % of a radiation length per via 1.5 Mil poly-silicon resistors to the biasing two dimensional coordinate, which increases sec­ ring. Three p+-guard rings surround the biasing ondary interactions and multiple scattering, was ring. The innermost guard ring is connected re- considered an acceptable compromise; sistively to ground and collects the current from The readout pitch of 120 pm and need of serial defects outside of the sensor ’s sensitive volume.
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