W. Bartl

Measurements of Elastic Proton Proton Scattering at Large Momentum Transfer at the CERN Intersecting Storage Rings

Abstract Final results of our measurements of elastic proton-proton scattering at the CERN Intersecting Storage Rings (ISR) for c.m. energies √ s from 23 to 63 GeV and momentum transfers | t | from 0.8 to 10 GeV 2 are presented. Absolute differential cross sections have been obtained using the split-field magnet detector facility (SFM) at the five standard energies for integrated luminosities ranging from 0.3 to 4.9 (pb) −1 . The rising total cross section is found to define a scale for diffractive phenomena near the forward peak, including the position of the diffraction minimum near t = −1.4 GeV 2 . The cross section at the minimum is strongly energy dependent, approximately as the ratio of the real to imaginary part of the scattering amplitude in the forward direction. The phase of the scattering amplitude is found to change sign near the minimum. The component of diffraction scattering beyond the second maximum has a much weaker t -dependence than expected in simple eikonal or constituent pictures connecting this region to the forward peak. A further break in slope is observed near t = −6 GeV 2 . There is no evidence for another minimum for t values up to 10 GeV 2 .

Experimental results on large angle elastic pp scattering at the CERN ISR

Abstract New experimental results are presented on proton-proton elastic scattering at centre-of-mass energies s =23 GeV and s =62 GeV . The data are obtained using the Split Field Magnet detector at the CERN Intersecting Storage Rings. The absolute differential cross-sections show an energy-dependent behaviour. The position of the diffraction minimum changes from t=(−1.44±0.02)GeV2 at 23 GeV to (−1.26±0.03)GeV2 at 62 GeV. The cross-section at the second maximum is increasing with s . The connection of these observations with the hypothesis of “geometrical scaling” is discussed.

Experimental Results on Diffractive One Pion Production at the CERN ISR

New experimental results are reported on diffractive dissociation of protons into (nπ+) in proton-proton collisions at a centre-of-mass energy of s = 45 GeV. The data were obtained using the Split-Field-Magnet detector at the CERN Intersecting Storage Rings. We have searched for resonance contributions and found peaks at mass values of 1.5 GeV, 1.65 GeV, and 2.1 GeV. A dip in dσdt is observed at low t and low mass; it is most pronounced for events with neutrons emitted at 90° in the Gottfried-Jackson frame. The correlation between mass and slope depends strongly on θJ. The cross section of the channel pp → pnπ+ is 400 ± 110 μb at s = 45 GeV, giving an energy dependence of s−0.30±0.07 for isospin exchange zero in this channel.

Large t elastic proton-proton scattering at √s = 53 GeV

New experimental results are presented on proton-proton elastic scattering in the range of momentum transfer 0.8GeV2 < −t < 9 GeV2 at a centre-of-mass energy of √s = 53 GeV. The data are obtained sing the Split-Field- Magnet Detector at the CERN Intersecting Storage Rings. The cross section has well-known minimum at −t = (1.34±0.02) GeV2 but no further minimum or change of slope is observed between 2 and 6.5 GeV2.

Evidence for a change of slope in large

Abstract New experimental results are presented on proton-proton elastic scattering in the range of momentum transfer 4 GeV 2 t 2 at the centre-of-mass energy of √ s = 53 GeV. The data have been obtained using the Split-Field Magnet detector at the CERN Intersecting Storage Rings. We observe another change of slope of the differential cross section near − t =6.5 GeV 2 .

-t

Abstract Studying the reaction pp → ppπ+π− at s = 23 GeV and 45 GeV at the CERN ISR we have found an experimental definition of a new class of diffractive events which we attribute to double-Pomeron exchange. The correlation of the quasi-elastically scattered protons, the energy dependence of the cross section, and the angular momentum of the (π+π−) state are analysed and found to be in agreement with theoretical expectations for double-Pomeron exchange.

elastic proton-proton scattering at

The polarization parameter in pp elastic scattering at 150 GeV/c, and in the momentum transfer interval 0.4 ⩽ −t ⩽ 3.0 GeV2, has been measured in an MWPC and scintillation counter experiment at the CERN SPS using a polarized proton target. The polarization is decreasing steadily from zero to ≈ − 10% in the range 0.4 < −t < 1.3 GeV2; for higher |t| the data suggests a change of sign. Results are also given for the differential cross section, which exhibits a small dip at −t = (1.46 ± 0.01) GeV.

\sqrt s

New experimental results are reported on decay angular distributions in diffractive dissociation of protons into (nπ+) in proton-proton collisions at a centre-of-mass energy of s = 45 GeV. There is a strong evidence for two distinct components of diffraction dissociation which have different decay angular distributions in the Gottfried-Jackson frame; the resonant and the non-resonant component with (nπ+) invariant mass in the interval 1.6 < m < 1.7 GeV are separated by their different t dependence. We find strong violation of s-channel and t-channel helicity consevation for both the resonant and the non-resonant component.

= 53 GeV

Abstract We report on a study of the charge-exchange reaction pp → nΔ ++ (1232) at the CERN intersecting storage rings (ISR) in the energy range √ s = 23 to 53 GeV. From our analysis of the energy dependence of the total cross-section, of the differential cross-section d σ /d t and of the decay angular distributions we find evidence that pion exchange is dominant up to √ s = 23 GeV and that ( ϱ +A 2 ) exchange dominates the reaction for √ s ⩾ 30 GeV, as described by simple Regge-pole models.

Experimental evidence for double-pomeron exchange at ISR energies

Abstract Proton elastic scattering off a polarized proton target has been measured at 150 GeV/ c , in the |; t |-range 0.2–3.0 GeV 2 . The results on polarization and differential cross section are presented.