The ALEPH collaboration, in view of the importance of effective vertex detection for the Higgs boson search at LEP 2, decided to upgrade the previous vertex detector. Main changes were an increased length (±20 cm), a higher granularity for rφ view (50 µm), a new preamplifier (MX7 rad hard chip), a polymide (upilex) fan-out on z side to carry the signals from the strips to the front-end electronics outside the fiducial region reducing consequently the passive material in the central region by a factor of two. The detector, the running experience and its performance will be described

Barber, G.

Billault, M.

Bizzell, J.P.

Black, S.

Blanc, P.E.

Bonissent, A.

Bosi, F.

Bosisio, L.

Bozzi, C.

Bujosa, G.

Burns, M.

Calvet, D.

Cameron, W.

Carr, J.

Coyle, P.

Creanza, D.

Dann, J.

de Palma, M.

Dell'Orso, R.

Destelle, J.J.

Diaconu, C.

Dietl, H.

Dornan, P.

Elmer, P.

Focardi, E.

Frank, M.

Gentry, D.

Halley, A.

Karst, P.

Kim, H.Y.

Konstantinidis, N.

Maggi, G.

Maley, P.D.

Moneta, L.

Moser, H.G.

Moutoussi, A.

Nash, J.

O'Shea, V.

Parrini, G.

Payre, P.

Price, D.

Profeti, A.

Putz, J.

Raine, C.

Raso, G.

Rizzo, G.

Rothberg, J.

Rousseau, D.

Scarlini, E.

Selvaggi, G.

Settles, R.

Seywerd, H.

Sguazzoni, G.

Silvestris, L.

Stacey, A.

Tempesta, P.

Thompson, J.C.

Thulasidas, M.

Toudup, L.W.

Verdini, P.G.

Wachnik, M.

Wagner, A.

Walsh, J.

Waltermann, G.

Wasserbaech, S.

Williams, M.I.

Wright, A.E.

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The new ALEPH Silicon Vertex DetectorD. Creanza, M. De Palma, G. Maggi, G. Selvaggi, L. Silvestris, G. Raso, P.Tempesta, M. Burns, P. Coyle, M. Frank, et al.To cite this version:D. Creanza, M. De Palma, G. Maggi, G. Selvaggi, L. Silvestris, et al.. The new ALEPH SiliconVertex Detector. The 7th Pisa Meeting on Advanced Detectors, May 1997, La Biodola, IsolaD’Elba, Italy. 409, pp.157-160, 1998. <in2p3-00012092>HAL Id: in2p3-00012092http://hal.in2p3.fr/in2p3-00012092Submitted on 22 Mar 1999HAL is a multi-disciplinary open accessarchive for the deposit and dissemination of sci-entific research documents, whether they are pub-lished or not. The documents may come fromteaching and research institutions in France orabroad, or from public or private research centers.L’archive ouverte pluridisciplinaire HAL, estdestine´e au de´poˆt et a` la diffusion de documentsscientifiques de niveau recherche, publie´s ou non,e´manant des e´tablissements d’enseignement et derecherche franc¸ais ou e´trangers, des laboratoirespublics ou prive´s.*Corresponding author.Nuclear Instruments and Methods in Physics Research A 409 (1998) 157—160The new ALEPH Silicon Vertex DetectorD. Creanza!, M. de Palma!, G. Maggi!, G. Selvaggi!, L. Silvestris!, G. Raso!,P. Tempesta!, M. Burns", P. Coyle", M. Frank", L. Moneta", G. Rizzo", M. Wachnik",A. Wagner", E. Focardi#,*, G. Parrini#, E. Scarlini#, A. Halley$, V. O’Shea$, C. Raine$,G. Barber%, W. Cameron%, P. Dornan%, D. Gentry%, N. Konstantinidis%, A. Moutoussi%,J. Nash%, D. Price%, A. Stacey%, L.W. Toudup%, M.I. Williams&, M. Billault', A. Bonissent',G. Bujosa', D. Calvet', J. Carr', C. Diaconu', P.E. Blanc', J.J. Destelle', P. Karst',P. Payre', D. Rousseau', M. Thulasidas', H. Dietl), H.G. Moser), R. Settles), H. Seywerd),G. Waltermann), F. Bosi*, C. Bozzi*, R. Dell’Orso*, A. Profeti*, G. Sguazzoni*, P.G. Verdini*,J.P. Bizzell+, P.D. Maley+, J.C. Thompson+, A.E. Wright+, S. Black,, J. Dann,, H.Y. Kim,,L. Bosisio-, J. Putz., J. Rothberg., S. Wasserbaech., P. Elmer/, J. Walsh/! Dip. di Fisica, INFN Sezione di Bari, 70126 Bari, Italy" European Laboratory for Particle Physics (CERN), CH 1211 Geneva 23, Switzerland# Dip. di Fisica dell+Universita% e INFN Sezione di Firenze, 50125 Firenze, Italy$ Dept. of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ, UK% Dept. of Physics, Imperial College, London SW7 2BZ, UK& Dept. of Physics, University of Lancaster, Lancaster LA1 4YB, UK' Centre de Physique des Particules, Faculte& des Sciences de Luminy, IN2P3-CNRS, 13288 Marseille, France) Max-Planck-Institut fu( r Physik, Werner-Heisenberg-Institut, 80805 Mu( nchen, Germany* Dip. di Fisica dell+Universita% , INFN Sezione di Pisa e Scuola Normale Superiore, 56010 Pisa, Italy+ Particle Physics Dept., Rutherford Appleton Laboratory, Chilton, Didcot, Oxon OX11 OQX, UK, Institute for Particle Physics, University of California at Santa Cruz, Santa Cruz, CA 95064, USA- Dip. di Fisica dell+Universita% e INFN Sezione di Trieste, 34127 Trieste, Italy. Experimental Elementary Particle Physics, University of Washington, WA 98195 Seattle, USA/ Dept. of Physics, University of Wisconsin, Madison, WI 53706, USAAbstractThe ALEPH collaboration, in view of the importance of effective vertex detection for the Higgs boson search at LEP 2,decided to upgrade the previous vertex detector. Main changes were an increased length ($20 cm), a higher granularityfor r/ view (50lm), a new preamplifier (MX7 rad hard chip), a polymide (upilex) fan-out on z side to carry the signalsfrom the strips to the front-end electronics outside the fiducial region reducing consequently the passive material in thecentral region by a factor of two. The detector, the running experience and its performance will be described. ( 1998Elsevier Science B.V. All rights reserved.0168-9002/98/$19.00 ( 1998 Elsevier Science B.V. All rights reservedPII S 0 1 6 8 - 9 0 0 2 ( 9 7 ) 0 1 2 5 5 - 2 II. TRACKING (SOLID STATE)Fig. 1. VDET face.1. IntroductionThe extensive study of the heavy flavour physicscurrently under way in the present generation ofcolliders made the Silicon Vertex Detectors the keytool to identify particles with heavy quarks (b,c).Tracks with the impact parameters in the 100 lmrange are identified with high accuracy when extrapo-lated to the interaction point. Secondary vertices fewmm apart from the interaction point are clearly dis-tinguished. For an accurate track reconstruction inspace it was decided to use double-sided siliconstrip detectors arranged in a cylindrical two-layerdetector with a coverage of Dcos hD(0.85 for tracksto pass through at least the inner layer. The de-tector (VDET I) worked as expected during theLEP1 phase from 1991 until 1995.The Higgs boson search at LEP2 increased theimportance of effective vertex detection. The Alephcollaboration consequently decided to upgrade thepreviously installed VDET. Main features of thenew vertex detector are1. increased length ($20 cm), 6 detectors/face areused;2. a polymide (upilex) fan-out is used on the z-side tocarry the signals from the strips to the front-endelectronics outside the active region; in this waythe passive material is reduced by a factor of two;3. the preamplifier chip used now is MX7 radi-ation hard;4. the strip read-out pitch is 50lm for r—/ viewand 100lm for the z view.For an overall description of VDET I and a com-parison between VDET I and VDET II, see Ref. [2].2. Detector descriptionVDET II consists of 48 modules glued in 24 faces(Fig. 1) mounted in two concentric layers. The in-ner layer with 9 faces is located at an average radiusof 6.3 cm while the outer layer with 15 faces is ata radius of 11 cm. Fig. 2 shows an overall view ofthe detector. Each module has three double-sidedsilicon strip detectors with dimensions 6.4]5.3 cm2each, the thickness is 300 lm. The design of thesilicon detectors is similar to the one used forVDET I [1] with strip pitch of 25 lm on the junc-tion side (r—/ view) and 50 lm on the ohmic side (zview). Implanted p` strips between the n` strips onthe ohmic side are used to block the electron accu-mulation layer present at the Si—SiO2interface.Guard rings surrounding the active region is usedto bias the strips; on the junction side the punch-trough mechanism is used to provide the bias withthe p` strips ending a few microns from the guardring implant. On the ohmic side n` strips are bi-ased taking advantage of the electron accumulationlayer: the end of p` blocking strips is used to definea channel between the n` strips and the guard ring;the value of the bias resistor, determined by thelength and the width of this low resistivity layer(&30k) per square), is Rs~gr"12—20M). Thedetectors are operated at a voltage slightly abovethe depletion value. One end of each module is158 D. Creanza et al. /Nucl. Instr. and Meth. in Phys. Res. A 409 (1998) 157—160Table 1Properties of the ALEPH Silicon DetectorsDetector dimensions 52.6mm ] 65.4mmWafer thickness 300lmBulk resistivity 6—30k) cmDepletion voltage 20—62VJunction side, r/-side Ohmic side, z-sideActive area 51.0mm]63.92mm 49.68mm]63.90mmp-strips (diodes) 2041 —p-blocking strips — 1280n-strips — 1279(p/n) pitch 25lm 50lmStrip length 63.92mm 49.68mmStrip width 12lm 12lmReadout pitch 50lm 100lmBond pad size 300lm ] 50 lm 300lm ] 50 lmFig. 2. VDET overall view.equipped with two electronic hybrids, one for thez view and the other for the r—/ view. Each hybridhas eight radiation hard MX7 chip and associateddecoupling capacitors with protection diodes. EachMX7 chip shifts out the signals from 128 stripchannels and the 1024 channels of each view areoutput sequentially (every 2ls) onto a single analogdata line. Electronic chips are cooled with a gravityfed water distribution system and air flow is used toreduce temperature gradients along the detector.The total power dissipation is about 200W. In ther—/ view 1021 strips are read-out while in thez view 960 strips are read-out with a total of 95088for the complete detector. Table 1 summarizes thebasic properties of the detectors.3. PerformanceThe complete detector was installed inAleph during the spring 1996; 16000 hadronicZ0 decays were collected at the start of the run inJuly’96. These data have been used to study theperformance of the detector; the signal/noise mea-sured after the installation was similar to that ob-tained in the laboratory (Fig. 3). The face distortionproblem found during the previous run in Novem-D. Creanza et al. /Nucl. Instr. and Meth. in Phys. Res. A 409 (1998) 157—160 159II. TRACKING (SOLID STATE)Fig. 3. Comparison of signal to noise ratio from laboratorymeasurements with that from Z0 run data (June ’96). Points areplotted for all 48 VDET II modules: triangles for z view andcircles for the r—/ view.Fig. 4. VDET resolution measured from tracks with three hitsin the overlaps.Table 2Summary of VDET II performancez side r—/ sidePhysical strip pitch 50lm 25lmNumber of physical strips per wafer 1279 2041Readout strip pitch 100lm 50lmNumber of readout strips per wafer 640 1021Number of readout strips per module 960 1021Signal/noise (90°) 18 31Resolution (90°) 15lm 10lmber ’95 [2], was solved by reinforcing the kevlarsupport that holds the two modules in a face witha similar carbon fibre omega beam support gluedon top of the kevlar one. The distortions as mea-sured by a laser position monitoring system [3] arenow below 5 lm. Z0 data have been used to alignthe detector. An alignment precision better than theintrinsic resolution of the detector itself was reach-ed by using the measurements of the wafer relativepositions within a face done after fabrication andconstraining tracks, in events without secondaryvertices, to come from the same primary vertex. Theresolution is measured from tracks passing throughthe overlap regions where two hits are used topredict the position of the third hit. The resolutionas a function of cos h is shown in Fig. 4. The aver-age efficiency to find a cluster on one side whena cluster is found on the other side is 95% for r—/view and 93% for z view. The performance ofVDET II is summarized in Table 2.4. ConclusionA new Silicon Vertex Detector has been installedin ALEPH for LEP2 operations. The discoverypotential for the Higgs search has been increasedby extending the angular coverage and by reducingthe material in the tracking volume. In the r—/ viewthe granularity has been increased by using 50 lmread-out strip pitch. The device is performing asexpected with a mechanical stability better than5lm. The spatial resolution obtained is 10lm onthe r—/ side and 15 lm on the z side.References[1] B. Mours et al., Nucl. Instr. and Meth. A 379 (1996) 101.[2] E. Focardi, Nucl. Instr. and Meth. A 386 (1997) 18.[3] A. Wagner, The laser calibration system for VDET II,ALEPH 97—006 MINIV 97-001, 1997.160 D. Creanza et al. /Nucl. Instr. and Meth. in Phys. Res. A 409 (1998) 157—160

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