G. Chiefari

Measurement of the proton-antiproton total and elastic cross sections at the CERN SPS collider

Abstract The proton-antiproton total cross section was measured at the CM energy √s = 546 GeV . The result is σ tot = 61.9± 1.5 mb . The ratio of the elastic to the total cross section is σ e l / σ tot = 0.215±0.005. A comparison to the lower energy data shows that the increase of the total cross section with energy is very close to a log 2 s behaviour.

Low momentum transfer elastic scattering at the CERN proton-antiproton collider

Proton-antiproton elastic scattering was measured at the CM energy √s = 546 GeV in the four-momentum transfer range 0.03<−t<0.32GeV2 For −<0.15GeV2 the data are well described by a simple exponential form exp(bt) with slope parameter b=15.2±0.2GeV−2. This value is significantly larger than the one measured in the region 0.21<−t<0.50 GeV2.

Elastic scattering at the CERN SPS collider up to a four-momentum transfer of 1.55 GeV2

Abstract Proton-antiproton elastic scattering was measured at the center-of-mass energy s =546 GeV in the four-momentum transfer range 0.45⩽−⩽1.55GeV 2 . The shape of the t -distribution is quite different from that observed in proton-proton scattering at the ISR. Rather than a dip-bump structure, a kink is present at − ≈0.9GeV 2 followed by a shoulder. The cross section at the second maximum is more than one order of magnitude higher than at the ISR.

The cross section of diffraction dissociation at the cern SPS collider

Single diffraction dissociation was measured in the reaction p¯p→p¯X at the centre-of-mass energy √s = 546 GeV. The mass M of the system X was deduced from the pseudorapidity distribution of the observed charged tracks. The cross section of single diffraction dissociation for M2/s⩽0.05isσsd=9.4 ± 0.7 mb. Comparison to the ISR data shows that σsd increases with energy less fast than the total and the elastic cross sections.

Measurement of the proton-antiproton elastic and total cross section at a centre-of-mass energy of 540 GeV

Abstract First results on the measurement of the elastic and total cross section at the CERN pp Collider are presented. Combining the measurement of elastic scattering at low momentum transfer with the rate of inelastic interactions, a value of the total cross section of 66 mb with a 10% statistical error was obtained.

Single diffraction dissociation at the CERN SPS collider

Abstract The reaction p p → p X was studied at a centre-of-mass energy s = 540 GeV by measuring the momentum spectrum of the antiproton. Data are presented in the four-momentum transfer range 05 t 2 . The shape of the mass distribution of the system X shows a diffractive component as already observed at lower energies. The differential cross section scales approximately with energy when compared to the ISR data.

Large-t elastic scattering at the CERN SPS collider at s = 630 GeV

Abstract Proton-antiproton elastic scattering was measured at the centre-of-mass energy s = 630 GeV in the four-momentum transfer range 0.7 ⩽ − t ⩽ 2.2 GeV2. The new data confirm our previous results at s = 546 GeV on the presence of a break in the t-distribution at −t ≃ 0.9 GeV2 which is followed by a shoulder, and extend the momentum transfer range to larger values. The t-dependence of the differential cross section beyond the break is discussed.

Pseudorapidity distribution of charged particles in diffraction dissociation events at the CERN SPS collider

Abstract The reaction p p → p X was studied as a function of the mass M of the system X at the centre-of-mass energy s = 546 GeV in the kinematical region where diffraction dissociation dominates. The pseudorapidity distribution of charged tracks, produced in the fragmentation of the system X, is well described within the limits of cylindrical phase space. The fragments of the X-system behave very similarly to the products of non-diffractive inelastic collisions at s = M .

The “Roman pot” spectrometer and the vertex detector of experiment UA4 at the CERN SPS collider

We describe the apparatus used in experiment UA4 to study proton-antiproton elastic and inelastic interactions at the CERN SPS Collider. Elastically scattered particles, travelling at very small angles, are observed by detectors placed inside movable sections (“Roman pots”) of the SPS vacuum chamber. The deflection in the field of the machine quadrupoles allow the measurement of the particle momentum. Inelastic interactions are observed by a left-right symmetric system of trigger counter hodoscopes and drift-chamber telescopes. The apparatus reconstructs the interaction vertex and measures the pseudorapidity η of charged particles in the range 2.5 < ‖η‖ < 5.6.

First results on low momentum transfer elastic scattering at the CERN proton-antiproton collider

Abstract Proton-antiproton elastic scattering at a centre-of-mass energy of 540 GeV was measured in the four-momentum transfer range 0.05 t s .19 GeV 2 . The t -distribution can be fitted by the exponential exp( b ) with b =17.2±1.0 GeV −2 . This result indicates a rapid decrease of the width of the diffraction peak between ISR and Collider energies.