BABAR  &  L. de Brunhoff Drift Chamber System BABAR Drift Chamber Project Co-System Managers D.B.MacFarlane, McGill University A.J.S.Smith, Princeton University

BABAR  &  L. de Brunhoff Drift Chamber System Drift Chamber Structure l Flat aluminum rear (24 mm) and forward (24+12 mm) endplates –Forward endplate with thin outer section to minimize material –Preamplifier and digitizer electronics on rear endplate only l Load-bearing inner and outer walls to reduce deflections –Inner wall of 1 mm-beryllium (40% load) –Segmented outer wall of 2x1.5 mm CF skins on Nomex core (60% load)

BABAR  &  L. de Brunhoff Drift Chamber System Drift System Layout l 40-layer small-cell chamber –Cells are 12x18 mm 2 in size –7104 drift cells with hexagonal field wire pattern –80 and 120  m gold-plated aluminum field wires l Layers organized into superlayers with same orientation –Wire directions for 4 consecutive layers: axial-u-v-stereo –Required for fast reduction of input to Level 1 trigger via segment finding –Transition field shaping voltages to maintain reasonably uniform performance

BABAR  &  L. de Brunhoff Drift Chamber System Drift Cell Characteristics l Nominal 80:20 helium-isobutane gas mixture –Low-mass gases able to achieve sub-100  m position resolutions –Low multiple scattering required by soft B decay products –dE/dx performance comparable to argon-based mixtures l Small Lorentz angle should lead to good cell efficiency –Modest entrance-angle dependence to STR l Performance confirmed by measurements with full-length prototype

BABAR  &  L. de Brunhoff Drift Chamber System Drift Chamber Performance Expected mass resolution for B 0     about 22 MeV/c 2 –Nearly uniform over center-of-mass polar angle distribution

BABAR  &  L. de Brunhoff Drift Chamber System Drift Chamber Collaboration Canada: University of British Columbia Carleton University McGill University University of Montreal TRIUMF National Laboratory University of Victoria United States: University of Colorado Colorado State University Lawrence Berkeley Laboratory University of Maryland Massachusetts Institute of Technology Princeton University UC Santa Cruz Stanford Linear Accelerator Center Italy: INFN Padova INFN Pisa INFN Rome France: Laboratoire d'Annecy-le-Vieux de Physique des Particules About 50 physicists and 25 engineers & technicians

BABAR  &  L. de Brunhoff Drift Chamber System Project Budget l Canadian contributions from Natural Sciences & Engineering Research Council and the TRIUMF National Laboratory l US contributions are funded through Department of Energy l Italian contributions are supported by INFN and include only materials & supplies, with staff engineering & technical support l French contributions are supported by IN2P3 and include only materials & supplies, with staff engineering & technical support l Additional $3M for Drift Chamber electronics budget not included here NSERC & TRIUMF 760K DOE1650K INFN 453K IN2P3 87K Total2950K Baseline, no contingency

BABAR  &  L. de Brunhoff Drift Chamber System Institutional Responsibilities l IPP/TRIUMF: Assembly and stringing, design & fabrication of assembly fixtures, stringing tooling, QC & tension testing, clean room, slow controls, aging tests l INFN-Pisa, Padova, Rome: Automation for stringing, outer CF cylinder, HV & LV power supplies & controls, collaboration on inner cylinder l IN2P3-Annecy: Gas system, monitors & controls, dE/dx studies l Colorado: Service boards, tension measurement l Colorado State: Feedthrough design & procurement, aging tests, wire replacement techniques l Maryland: Environmental controls l Princeton: Collaboration on endplate design, procurement & QC of endplates, fabrication of assembly fixtures, wire procurement & testing, tension magnet l SLAC: Integration, mechanical design center, electronics and support structures, prototype construction, inner cylinder design and procurement

BABAR  &  L. de Brunhoff Drift Chamber System Drift Chamber Status & Schedule l Endplates machined & drilled by Brenner Tool & Die; delivered to TRIUMF January 31 l Beryllium inner cylinder from Electrofusion; delivered May 9 l Outer cylinder completed & test fitted June 20 l Assembly & alignment fixtures available at TRIUMF; chamber structure completed & aligned May 23 l Automated stringing tooling assembled & operational after extensive development by August 6 l Wire orders complete, feedthroughs in production & nearly complete l Main stringing period August-December 1997 at TRIUMF; delivery to SLAC in March 1998 Project is on schedule for July 1998 installation into BABAR & on budget