- Email: [email protected]
The CLEO III drift chamber
Nuclear Instruments and Methods in Physics Research A 478 (2002) 142–146
The CLEO III drift chamber$ D. Petersona,*, K. Berkelmana, R. Briereb, G. Chenb, D. Cronin-Hennessyc, S. Csornad, M. Dicksona, S. von Dombrowskia, K.M. Ecklunda, A. Lyonc, Sz. Markad, T.O. Meyera, J.R. Pattersona, A. Sadoffe, P. Thiesa, E.H. Thorndikec, D. Urnera a
Wilson Laboratory of Nuclear Studies, Cornell University, Ithaca, NY 14853, USA b Carnegie Mellon University, Pittsburgh, PA 15213, USA c University of Rochester, Rochester, NY 14627, USA d Vanderbilt University, Nashville, TN 37235, USA e Ithaca College, Ithaca, NY 14850, USA
Abstract The CLEO group at the Cornell Electron Storage Ring has constructed and commissioned a new central drift chamber. With 9796 cells arranged in 47 layers ranging in radius from 13.2 to 79 cm; the new drift chamber has a smaller outer radius and fewer wires than the drift chamber it replaces, but allows the CLEO tracking system to have improved momentum resolution. Reduced scattering material in the chamber gas and in the inner skin separating the drift chamber from the silicon vertex detector provides a reduction of the multiple scattering component of the momentum resolution and an extension of the usable measurement length into the silicon. Momentum resolution is further improved through quality control in wire positioning and symmetry of the electric fields in the drift cells which have provided a reduction in the spatial resolution to 88 mm (averaged over the full drift range). r 2002 Elsevier Science B.V. All rights reserved.
The CLEO III detector has been commissioned at the Cornell Electron Storage Ring (CESR). As part of the staged upgrade [1–4] of CLEO [5] and CESR, it includes a new drift chamber [6,7] as well as a ring imaging Cherenkov particle identification system (RICH) [8,9] and silicon vertex detector [10–14] installed inside the existing CLEO CsI electromagnetic calorimeter, 1:5 T magnet and muon detectors. The CLEO III detector is optimized for studying properties of B-meson $ This work was supported by the U.S. National Science Foundation and by the U.S. Department of Energy. *Corresponding author. E-mail address: [email protected] (D. Peterson).
decays in resonant U(4S) production. The new detector elements extend the capabilities to study rare decays, e.g. Bo -Kþ p ; and provide compatibility with the improved interaction optics in CESR. The drift chamber radial extent is constrained to be in the range of 12.5–82 cm by the CESR upgrade interaction region optics and the inner radius of the RICH. However, physics goals require that the CLEO III tracking system momentum resolution match that of the CLEO II tracking system (outer radius: 95 cm). This criterion is met throughout the relevant momentum range, 100 MeV–2:6 GeV; by reducing scattering material in the chamber and extending the
0168-9002/02/$ - see front matter r 2002 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 9 0 0 2 ( 0 1 ) 0 1 7 3 7 - 5
D. Peterson et al. / Nuclear Instruments and Methods in Physics Research A 478 (2002) 142–146
momentum measurement volume to include the outermost layer of a silicon device mounted inside the drift chamber [3]. The drift chamber is required to have an average spatial resolution of p150 mm, while using a chamber of gas with the radiation length X330 m and to have an inner wall with thickness limited to 0.15% radiation length. In each case, the CLEO III drift chamber improves upon these specifications. The drift chamber endplate, shown in Fig. 1, is made up of two sections. The small radius section provides the space required for the focusing magnets while allowing measurement of charged particles within jcos yjp0:93: It is assembled from a set of 8 aluminum rings interconnected with nonmagnetic steel bands via radial screws and dowel pins. This construction method allows wire locat-
143
ing holes to be accurately drilled on simple flat rings. Interconnection of the rings is sufficiently precise to provide a consistent cell geometry and is calibrated to be within 15 mm: Coherent transverse motion of the small radius sections due to wire load and an external load of interaction region elements caused motions less than 50 mm that have been calibrated with high momentum tracks. The outer section is machined from 16:5 cm thick aluminum plate. Although the surface is terraced to allow flat surfaces for drilling and wireholding devices, the general shape is conic with a thickness of 1:55 cm and sagitta 7:6 cm: Stiffness added by the integral outer support ring and the constraint of angular deflection at the inner radius limits the measured deflection under the wire load to 0:6 mm (each endplate) at the inner radius of
Fig. 1. CLEO III drift chamber in staging area during final gas sealing.
144
D. Peterson et al. / Nuclear Instruments and Methods in Physics Research A 478 (2002) 142–146
the outer section. The deflection measured at the inner radius of the small radius section is 1:5 mm relative to the outer radius of the chamber. This design allows a substantial reduction in scattering material shadowing the endcap CsI calorimeter while providing the stiffness required to support the thin inner skin. Wire mounting holes drilled into the endplate sections have been demonstrated to be within 75 mm (hard limit) of design; variations will not affect individual wire drift times. Individual hole locations were measured to an accuracy of 25 mm; allowing corrections to be made during the track fitting. However, the spatial resolution reported below is obtained without these corrections. The inner skin, which provides the gas seal and RF shielding, is made from 2:0 mm expanded acrylic with 20 mm aluminum skins. This composite construction has a total thickness of only 0.12% radiation length. It also satisfies a limit of radial distortion. Radial distortion must be limited to 250 mm because the grounded outer surface of the inner skin is located only 10 mm from the innermost sense wires to make optimal use of the limited radial space. Beryllium and carbon fiber prototypes failed the radial distortion limit. While meeting the radiation thickness requirements of CLEO III, the inner skin is fragile; it provides no mechanical restraint of the endplate and has a strain limit of 0:8 mm: Installation was delayed until further endplate motions due to aluminum wire creep were negligible. The CLEO III drift chamber is operated with He–C3 H8 (60–40) which was chosen on the basis of test chamber aging and performance studies [4,15] and operation in the CLEO II drift chamber beginning in 1995 [6]. Drift cells are ‘‘square’’, having approximately concentric isochrones and a 7 mm half-cell size (maximum drift distance). Field layers alternate with sense layers (contain alternating sense and field wires) providing 3 field wires per sense wire. Layers are arranged in superlayers with half cell staggering. While the 16 sense layers in the small radius section are all axial, the 31 sense layers in the outer section are all stereo with sequential superlayers (of 4 layers each) alternating in stereo angle sign.
Radial asymmetries in the drift cell electric field are a source of left–right asymmetries of the time-to-distance drift function in the presence of the 1:5 T magnetic field. Details in the cell geometry minimize the left–right asymmetries and eliminate the longitudinal dependencies of the left–right asymmetries thereby simplifying the calibration of the drift function. One design feature might be expected to cause a longitudinal dependence of electric field asymmetry: to maximize active volume, common field layers are used at super layer boundaries (except in the single axial–stereo boundary) even though the superlayers contain differing number of cells per layer. The common field layer has the number of wires corresponding to the larger radius super layer; the outer layer of each super-layer has a cage shaped field, at the boundary, with wires having a varying phase relative to the sense wires. Measurements from the previous CLEO drift chamber and simulations indicate that this phase is unimportant; the drift time variation is smaller than the resolution at all drift distances. However, similar studies indicate that radial spacing of layers is significant. Grouping the stereo layers together, with common field layers at the boundaries, allows the elimination of longitudinal dependent variations of the drift function only if the wire layer spacings are held longitudinally constant. Stereo angles vary from dðrfÞ=dz ¼ 0:02 to 0.03. Details of the geometry provide an unslanted cell shape at all longitudinal positions and maintain stereo sag variations between layers to within 80 mm: Independent of longitudinal position, the use of common field layers at boundaries and, to a lesser extent, the trapezoidal shape of cells in a cylindrical chamber, can cause a radial electric field asymmetry which, if uncompensated, would result in left–right asymmetries of the drift function of up to 1 mm: Compensating this asymmetry by varying potentials on the field wires would result in complications in grounding RF noise. Rather, the asymmetry is compensated by corrections to the wire layer relative radii by up to 0:4 mm allowing most field wires to be grounded to the endplate. Field potentials are applied only at the extreme radii. The grounded inner skin is
D. Peterson et al. / Nuclear Instruments and Methods in Physics Research A 478 (2002) 142–146
separated from the first sense layer by only 10 mm: The resulting field distortion is compensated by a 300 V potential applied to the separating field wire layer. A segmented cathode forms the outer field cage of the outermost layer creating a longitudinal dependent asymmetry because the anode is stereo while the cathode is cylindrical. In this case, the potential is applied to the cathode strips. The potential varies from 250 to 300 V depending on the anode–cathode spacing. Field wires are 110 mm Al with 0:75 mm Au plating. Production wire has passed tests for strength, gold thickness, and creep rate. Sense wires are 20 mm Au plated W (3% Re). Wires are held by individual crimp pins and insulating feedthroughs. The feed-throughs are made from injection molded Vectra1, a low shrinkage plastic which allows control of the inner and outer diameters to 6 mm and limitation of the offset of the inner diameter axis to 25 mm: The crimp pins are made of two concentrically drawn and formed tubes. Breakdown of the high voltage feedthroughs is reduced by using crimp pins that extend beyond the endplate, limiting the electric field. Aluminum wire breakage is eliminated by using an aluminum alloy core in field wire crimp pins that is softer than the wire so that the pin material flows around the wire when crimped rather than distorting the wire. Sense wires were installed with tension varying from 10g at the innermost (short) layers to 28g at the outer layers; field wire tensions were installed with tension varying from 87g to 215g: During stringing, aluminum field wires experienced creep to the extent that the asymptotic zero-tension-length increased by 15% of the applied strain. Tensions at the innermost layers have increased to 21g (sense) and 100g (field) while gravitational sag differences (sense-field) are less than 30 mm in all the layers. At the same time, the endplate deflection, measured at the smallest radius endplate component, decreased by 0:3 mm: Readout is through an endplate mounted preamplifier, a remotely mounted intermediate stage (TQTFsee below), and a LeCroy 1877s multi-hit Time to Digital Converter (TDC). The pre1
‘‘Vectra’’ is a brand of Hoecht Celanese.
145
amplifier operates at a transimpedence gain of 6 kO and outputs a bipolar signal with an 8 ns rise time. The TQT discriminates the input time signal and converts integrated charge information into another time signal. Discriminators may be individually set for each channel and operate at about 0:7 mA: Retriggering is inhibited for 500 ns to eliminate retriggering on single tracks. Charge of all input signals is continually integrated in a capacitor circuit and reset with a 40 ms time constant. Given an input event trigger signal, the charge is converted to a time signal. Since this is a square cell chamber, and because the multiplicity of events from an eþ e storage ring in this energy range does not require it, the multi-hit capability of the TDCs is not used to record multiple tracks in the same event. Rather, it is used to record the time and the noise history of the cell, in the form of time signals for the previous 30 ms; and the integrated charge signal. In the case of multiple time hits, the hit closest to the event time is selected off-line and the charge signal is identified as corrupted. Spatial resolution and hit efficiency are measured with 5:28 GeV Bhabha scattering tracks. The efficiency averages 98% in the stereo section and 92% in the axial section; the loss in the axial section is due to external connections to the endplate mounted electronics. Spatial resolution is parameterized as two Gaussian distributions, with the fraction in the narrower component fixed at 80%. (This standardization provides a consistent means of comparing effects of calibration improvements independent of effects that contribute to the tails of the distribution.) We currently observe the narrow component having 88 mm resolution when averaged over the full cell in all the layers. This narrow component has a minimum of 65 mm at 3:5 mm drift distance. The minimum indicates that there would be little improvement from implementing the individual hole measurements. The full distribution has 110 mm resolution when averaged over the full cell in all the layers. Momentum resolution for Bhabha scattering tracks is 55 MeV using only drift chamber anode information. The segmented outer cathode provides a longitudinal position measurement at the outer radius.
146
D. Peterson et al. / Nuclear Instruments and Methods in Physics Research A 478 (2002) 142–146
It is 95% efficient in the 78% of solid angle that it covers. The resolution for 5:28 GeV electrons is 1:2 mm; an improvement over the longitudinal position resolution available from the stereo wire information, 1:5 mm: Specific ionization is measured in all the layers. Corrections are made for drift distance and charge saturation near a normal polar incidence. The resolution for 5:28 GeV electrons is 5.0% while K=p separation extends to 700 MeV: The CLEO III detector, including the new drift chamber, has been installed and been taking physics data since July 2000, at 10:56 GeV center of mass energy, at a rate of 1 fb1 per month. The drift chamber performs beyond the design specifications and is an excellent tool for studying properties of B-meson decays.
References [1] The CESR/CLEO Upgrade Project, CESR and CLEO Staff, Cornell Laboratory of Nuclear Studies, CLNS 93/ 1265, 1993, preprint. [2] R.S. Galik, Nucl. Phys. B (Proc. Suppl.) 50B (1996) 280. [3] D. Peterson, Nucl. Instr. and Meth. A 360 (1995) 263. [4] D. Peterson, Nucl. Phys. B (Proc. Suppl.) 54B (1997) 31. [5] Y. Kubota, et al., Nucl. Instr. and Meth. A 320 (1992) 66. [6] D. Peterson, Nucl. Instr. and Meth. A 409 (1998) 204. [7] S. Csorna, et al., Nucl. Instr. and Meth. A 419 (1998) 306. [8] M. Artuso, et al., Nucl. Instr. and Meth. A 441 (2000) 374. [9] G. Viehhauser, Nucl. Instr. and Meth. A 419 (1998) 557. [10] P.I. Hopman, et al., Nucl. Instr. and Meth. A 383 (1996) 98. [11] I. Shipsey, et al., Nucl. Instr. and Meth. A 386 (1997) 37. [12] P. Skubic, et al., Nucl. Instr. and Meth. A 418 (1998) 40. [13] J. Fast, et al., in: Nucl. Instr. and Meth. A 435 (1999) 9. [14] E. von Toerne, et al., in: Vertex2000 Conference Proceedings, Nucl. Instr. and Meth. A 473 (2001) 17. [15] K.K. Gan, et al., Nucl. Instr. and Meth. A 374 (1996) 27.
The CLEO III drift chamber$ D. Petersona,*, K. Berkelmana, R. Briereb, G. Chenb, D. Cronin-Hennessyc, S. Csornad, M. Dicksona, S. von Dombrowskia, K.M. Ecklunda, A. Lyonc, Sz. Markad, T.O. Meyera, J.R. Pattersona, A. Sadoffe, P. Thiesa, E.H. Thorndikec, D. Urnera a
Wilson Laboratory of Nuclear Studies, Cornell University, Ithaca, NY 14853, USA b Carnegie Mellon University, Pittsburgh, PA 15213, USA c University of Rochester, Rochester, NY 14627, USA d Vanderbilt University, Nashville, TN 37235, USA e Ithaca College, Ithaca, NY 14850, USA
Abstract The CLEO group at the Cornell Electron Storage Ring has constructed and commissioned a new central drift chamber. With 9796 cells arranged in 47 layers ranging in radius from 13.2 to 79 cm; the new drift chamber has a smaller outer radius and fewer wires than the drift chamber it replaces, but allows the CLEO tracking system to have improved momentum resolution. Reduced scattering material in the chamber gas and in the inner skin separating the drift chamber from the silicon vertex detector provides a reduction of the multiple scattering component of the momentum resolution and an extension of the usable measurement length into the silicon. Momentum resolution is further improved through quality control in wire positioning and symmetry of the electric fields in the drift cells which have provided a reduction in the spatial resolution to 88 mm (averaged over the full drift range). r 2002 Elsevier Science B.V. All rights reserved.
The CLEO III detector has been commissioned at the Cornell Electron Storage Ring (CESR). As part of the staged upgrade [1–4] of CLEO [5] and CESR, it includes a new drift chamber [6,7] as well as a ring imaging Cherenkov particle identification system (RICH) [8,9] and silicon vertex detector [10–14] installed inside the existing CLEO CsI electromagnetic calorimeter, 1:5 T magnet and muon detectors. The CLEO III detector is optimized for studying properties of B-meson $ This work was supported by the U.S. National Science Foundation and by the U.S. Department of Energy. *Corresponding author. E-mail address: [email protected] (D. Peterson).
decays in resonant U(4S) production. The new detector elements extend the capabilities to study rare decays, e.g. Bo -Kþ p ; and provide compatibility with the improved interaction optics in CESR. The drift chamber radial extent is constrained to be in the range of 12.5–82 cm by the CESR upgrade interaction region optics and the inner radius of the RICH. However, physics goals require that the CLEO III tracking system momentum resolution match that of the CLEO II tracking system (outer radius: 95 cm). This criterion is met throughout the relevant momentum range, 100 MeV–2:6 GeV; by reducing scattering material in the chamber and extending the
0168-9002/02/$ - see front matter r 2002 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 9 0 0 2 ( 0 1 ) 0 1 7 3 7 - 5
D. Peterson et al. / Nuclear Instruments and Methods in Physics Research A 478 (2002) 142–146
momentum measurement volume to include the outermost layer of a silicon device mounted inside the drift chamber [3]. The drift chamber is required to have an average spatial resolution of p150 mm, while using a chamber of gas with the radiation length X330 m and to have an inner wall with thickness limited to 0.15% radiation length. In each case, the CLEO III drift chamber improves upon these specifications. The drift chamber endplate, shown in Fig. 1, is made up of two sections. The small radius section provides the space required for the focusing magnets while allowing measurement of charged particles within jcos yjp0:93: It is assembled from a set of 8 aluminum rings interconnected with nonmagnetic steel bands via radial screws and dowel pins. This construction method allows wire locat-
143
ing holes to be accurately drilled on simple flat rings. Interconnection of the rings is sufficiently precise to provide a consistent cell geometry and is calibrated to be within 15 mm: Coherent transverse motion of the small radius sections due to wire load and an external load of interaction region elements caused motions less than 50 mm that have been calibrated with high momentum tracks. The outer section is machined from 16:5 cm thick aluminum plate. Although the surface is terraced to allow flat surfaces for drilling and wireholding devices, the general shape is conic with a thickness of 1:55 cm and sagitta 7:6 cm: Stiffness added by the integral outer support ring and the constraint of angular deflection at the inner radius limits the measured deflection under the wire load to 0:6 mm (each endplate) at the inner radius of
Fig. 1. CLEO III drift chamber in staging area during final gas sealing.
144
D. Peterson et al. / Nuclear Instruments and Methods in Physics Research A 478 (2002) 142–146
the outer section. The deflection measured at the inner radius of the small radius section is 1:5 mm relative to the outer radius of the chamber. This design allows a substantial reduction in scattering material shadowing the endcap CsI calorimeter while providing the stiffness required to support the thin inner skin. Wire mounting holes drilled into the endplate sections have been demonstrated to be within 75 mm (hard limit) of design; variations will not affect individual wire drift times. Individual hole locations were measured to an accuracy of 25 mm; allowing corrections to be made during the track fitting. However, the spatial resolution reported below is obtained without these corrections. The inner skin, which provides the gas seal and RF shielding, is made from 2:0 mm expanded acrylic with 20 mm aluminum skins. This composite construction has a total thickness of only 0.12% radiation length. It also satisfies a limit of radial distortion. Radial distortion must be limited to 250 mm because the grounded outer surface of the inner skin is located only 10 mm from the innermost sense wires to make optimal use of the limited radial space. Beryllium and carbon fiber prototypes failed the radial distortion limit. While meeting the radiation thickness requirements of CLEO III, the inner skin is fragile; it provides no mechanical restraint of the endplate and has a strain limit of 0:8 mm: Installation was delayed until further endplate motions due to aluminum wire creep were negligible. The CLEO III drift chamber is operated with He–C3 H8 (60–40) which was chosen on the basis of test chamber aging and performance studies [4,15] and operation in the CLEO II drift chamber beginning in 1995 [6]. Drift cells are ‘‘square’’, having approximately concentric isochrones and a 7 mm half-cell size (maximum drift distance). Field layers alternate with sense layers (contain alternating sense and field wires) providing 3 field wires per sense wire. Layers are arranged in superlayers with half cell staggering. While the 16 sense layers in the small radius section are all axial, the 31 sense layers in the outer section are all stereo with sequential superlayers (of 4 layers each) alternating in stereo angle sign.
Radial asymmetries in the drift cell electric field are a source of left–right asymmetries of the time-to-distance drift function in the presence of the 1:5 T magnetic field. Details in the cell geometry minimize the left–right asymmetries and eliminate the longitudinal dependencies of the left–right asymmetries thereby simplifying the calibration of the drift function. One design feature might be expected to cause a longitudinal dependence of electric field asymmetry: to maximize active volume, common field layers are used at super layer boundaries (except in the single axial–stereo boundary) even though the superlayers contain differing number of cells per layer. The common field layer has the number of wires corresponding to the larger radius super layer; the outer layer of each super-layer has a cage shaped field, at the boundary, with wires having a varying phase relative to the sense wires. Measurements from the previous CLEO drift chamber and simulations indicate that this phase is unimportant; the drift time variation is smaller than the resolution at all drift distances. However, similar studies indicate that radial spacing of layers is significant. Grouping the stereo layers together, with common field layers at the boundaries, allows the elimination of longitudinal dependent variations of the drift function only if the wire layer spacings are held longitudinally constant. Stereo angles vary from dðrfÞ=dz ¼ 0:02 to 0.03. Details of the geometry provide an unslanted cell shape at all longitudinal positions and maintain stereo sag variations between layers to within 80 mm: Independent of longitudinal position, the use of common field layers at boundaries and, to a lesser extent, the trapezoidal shape of cells in a cylindrical chamber, can cause a radial electric field asymmetry which, if uncompensated, would result in left–right asymmetries of the drift function of up to 1 mm: Compensating this asymmetry by varying potentials on the field wires would result in complications in grounding RF noise. Rather, the asymmetry is compensated by corrections to the wire layer relative radii by up to 0:4 mm allowing most field wires to be grounded to the endplate. Field potentials are applied only at the extreme radii. The grounded inner skin is
D. Peterson et al. / Nuclear Instruments and Methods in Physics Research A 478 (2002) 142–146
separated from the first sense layer by only 10 mm: The resulting field distortion is compensated by a 300 V potential applied to the separating field wire layer. A segmented cathode forms the outer field cage of the outermost layer creating a longitudinal dependent asymmetry because the anode is stereo while the cathode is cylindrical. In this case, the potential is applied to the cathode strips. The potential varies from 250 to 300 V depending on the anode–cathode spacing. Field wires are 110 mm Al with 0:75 mm Au plating. Production wire has passed tests for strength, gold thickness, and creep rate. Sense wires are 20 mm Au plated W (3% Re). Wires are held by individual crimp pins and insulating feedthroughs. The feed-throughs are made from injection molded Vectra1, a low shrinkage plastic which allows control of the inner and outer diameters to 6 mm and limitation of the offset of the inner diameter axis to 25 mm: The crimp pins are made of two concentrically drawn and formed tubes. Breakdown of the high voltage feedthroughs is reduced by using crimp pins that extend beyond the endplate, limiting the electric field. Aluminum wire breakage is eliminated by using an aluminum alloy core in field wire crimp pins that is softer than the wire so that the pin material flows around the wire when crimped rather than distorting the wire. Sense wires were installed with tension varying from 10g at the innermost (short) layers to 28g at the outer layers; field wire tensions were installed with tension varying from 87g to 215g: During stringing, aluminum field wires experienced creep to the extent that the asymptotic zero-tension-length increased by 15% of the applied strain. Tensions at the innermost layers have increased to 21g (sense) and 100g (field) while gravitational sag differences (sense-field) are less than 30 mm in all the layers. At the same time, the endplate deflection, measured at the smallest radius endplate component, decreased by 0:3 mm: Readout is through an endplate mounted preamplifier, a remotely mounted intermediate stage (TQTFsee below), and a LeCroy 1877s multi-hit Time to Digital Converter (TDC). The pre1
‘‘Vectra’’ is a brand of Hoecht Celanese.
145
amplifier operates at a transimpedence gain of 6 kO and outputs a bipolar signal with an 8 ns rise time. The TQT discriminates the input time signal and converts integrated charge information into another time signal. Discriminators may be individually set for each channel and operate at about 0:7 mA: Retriggering is inhibited for 500 ns to eliminate retriggering on single tracks. Charge of all input signals is continually integrated in a capacitor circuit and reset with a 40 ms time constant. Given an input event trigger signal, the charge is converted to a time signal. Since this is a square cell chamber, and because the multiplicity of events from an eþ e storage ring in this energy range does not require it, the multi-hit capability of the TDCs is not used to record multiple tracks in the same event. Rather, it is used to record the time and the noise history of the cell, in the form of time signals for the previous 30 ms; and the integrated charge signal. In the case of multiple time hits, the hit closest to the event time is selected off-line and the charge signal is identified as corrupted. Spatial resolution and hit efficiency are measured with 5:28 GeV Bhabha scattering tracks. The efficiency averages 98% in the stereo section and 92% in the axial section; the loss in the axial section is due to external connections to the endplate mounted electronics. Spatial resolution is parameterized as two Gaussian distributions, with the fraction in the narrower component fixed at 80%. (This standardization provides a consistent means of comparing effects of calibration improvements independent of effects that contribute to the tails of the distribution.) We currently observe the narrow component having 88 mm resolution when averaged over the full cell in all the layers. This narrow component has a minimum of 65 mm at 3:5 mm drift distance. The minimum indicates that there would be little improvement from implementing the individual hole measurements. The full distribution has 110 mm resolution when averaged over the full cell in all the layers. Momentum resolution for Bhabha scattering tracks is 55 MeV using only drift chamber anode information. The segmented outer cathode provides a longitudinal position measurement at the outer radius.
146
D. Peterson et al. / Nuclear Instruments and Methods in Physics Research A 478 (2002) 142–146
It is 95% efficient in the 78% of solid angle that it covers. The resolution for 5:28 GeV electrons is 1:2 mm; an improvement over the longitudinal position resolution available from the stereo wire information, 1:5 mm: Specific ionization is measured in all the layers. Corrections are made for drift distance and charge saturation near a normal polar incidence. The resolution for 5:28 GeV electrons is 5.0% while K=p separation extends to 700 MeV: The CLEO III detector, including the new drift chamber, has been installed and been taking physics data since July 2000, at 10:56 GeV center of mass energy, at a rate of 1 fb1 per month. The drift chamber performs beyond the design specifications and is an excellent tool for studying properties of B-meson decays.
References [1] The CESR/CLEO Upgrade Project, CESR and CLEO Staff, Cornell Laboratory of Nuclear Studies, CLNS 93/ 1265, 1993, preprint. [2] R.S. Galik, Nucl. Phys. B (Proc. Suppl.) 50B (1996) 280. [3] D. Peterson, Nucl. Instr. and Meth. A 360 (1995) 263. [4] D. Peterson, Nucl. Phys. B (Proc. Suppl.) 54B (1997) 31. [5] Y. Kubota, et al., Nucl. Instr. and Meth. A 320 (1992) 66. [6] D. Peterson, Nucl. Instr. and Meth. A 409 (1998) 204. [7] S. Csorna, et al., Nucl. Instr. and Meth. A 419 (1998) 306. [8] M. Artuso, et al., Nucl. Instr. and Meth. A 441 (2000) 374. [9] G. Viehhauser, Nucl. Instr. and Meth. A 419 (1998) 557. [10] P.I. Hopman, et al., Nucl. Instr. and Meth. A 383 (1996) 98. [11] I. Shipsey, et al., Nucl. Instr. and Meth. A 386 (1997) 37. [12] P. Skubic, et al., Nucl. Instr. and Meth. A 418 (1998) 40. [13] J. Fast, et al., in: Nucl. Instr. and Meth. A 435 (1999) 9. [14] E. von Toerne, et al., in: Vertex2000 Conference Proceedings, Nucl. Instr. and Meth. A 473 (2001) 17. [15] K.K. Gan, et al., Nucl. Instr. and Meth. A 374 (1996) 27.