Measurement of the antiproton-proton total cross section at s =546 and 1800 GeV

We report a measurement of the proton-antiproton total cross section, VT, at c.m.s. energies fi = 546 and .I800 GeV. Using the luminosity’independent method, we find Q=61.26&0.93 mb at ,/k546 GeV and 80.03f2.24 mb at fi = 1800 GeV. In this energy range, the ratio v,l/UT increases from 0.2lOkO.002 to 0.246~0.004. PACS numbers: 13.85.Lg, 12.40.Gg, 12.4O.P~ We have measured the total proton-antiproton cross section at the Fermilab Tevatron Collider at c.m.8. energies fi=546 and 1800 GeV using the luminosity independent method [l, 21. This method is based on the simultaneous measurement of the elastic scattering differential cross section at low four-momentum transfer-squared (t) and the total inelastic rate. The total cross section is the sum of the elastic and inelastic rates divided by +k machine luminosity L : aT = ; . (&I + &,) (1) The optical theorem relates the total cross section to the imaginary part of the forward elastic scattering rate, ,T+ = 16x(hc)s 1 1+ pz . L d%c/d%o where p is the ratio of the real to imaginary part of the forward elastic scattering amplitude . Dividing (2) by (1) yields ~~ = W~c)* d%c/dtlt=o 1+P2 . RI+& (3) At present, only this method provides a precise measurement of the Tevatron luminosity and of the total cross section. I. EXPERIMENTAL METHOD The data for the total cross section measurement were collected in short dedicated runs during the 1988-1989 data taking period of CDF. At each energy, the machine optics was specially tuned to enable detection of low-t elastic scattering events. The elastic scattering and inelastic rates were measured simultaneously (the inelastic trigger was conveniently prescaled). The elastic &&Wing measurement is reported in the preceding paper [3]. The apparatus II& ti measure the inelastic rate is shown in Fig. 1. The region of polar angles 3.5” 6’ > 177.44”), corresponding to 3.8 < ]u( < 5.5. Each FTB/FTF telescope consisted of four drift chambers separated by 25 cm along the z-axis[5]. Each chamber contained a front section, which measured the (horizontal) x-coordinate in four parallel drift cells (4 cm wide by 36 cm long) on each side of the beam-pipe, and an identical back section with sense wires rotated by 90” for measuring the (vertical) y-coordinate. In addition, in every drift cell, the coordinate perpendicular to the drift direction was measured with a delay line placed close to the sense wire, providing in most cases unambiguous reconstruction of space points. The drift time measurement provided single-hit accuracy of 700 pm and two-track resolution of 4.0 mm. The single-hit accuracy of the delay line was 2.0 cm and the twotrack resolution about 12 q The S4 and Sg telescopes extended the polar angle coverage down to 6 N 0.14” and 6 N 179.86” (191 =6.7), respectively. Each telescope contained two drift chambers separated by 1 m along the a-axis. Each chamber had two sections, one above and one below the beam line. These sections were inserted in a beam pipe with variable aperture. When stable beam conditions were reached, the two sections were pushed