B. Naroska

OBSERVATION OF A DIFFRACTION MINIMUM IN THE PROTON-PROTON ELASTIC SCATTERING AT THE ISR

Abstract We have investigated the pp elastic scattering at the CERN Intersecting Storage Rings (ISR). We report results for centre-of-mass scattering angles between 30 and 100 mrad and for centre-of-mass energies of 23.5,30.7, 44.9 and 53 GeV. The elastic differential cross-section shows a diffraction-like shape with a sharp minimum at about t = −1.4 GeV 2 .

Diffractive production of the charmed baryon Λ+c at the CERN ISR☆

Abstract In a sample of diffractive events of high multiplicity a sharp five standard deviation signal is observed at M = 2255 MeV/c2 in the K−pπ+ mass distribution and, although with less statistical strength, at the same mass in the Λ0π+π+π− channel. These signals are identified as being due to the decay of the charmed baryon Λ+c which is produced with a cross section times branching ratio σcB in the range 0.7−1.8 μb for the K−π+p decay and 0.3−0.7 μb for the Λ-π+π+ π− system.

Measurements of the proton-proton total cross section and small angle elastic scattering at ISR energies

Measurements of the total cross section have been performed at the ISR with c.m. energies between 23.5 GeV and 62.5 GeV. Two independent experimental methods have been applied, a measurement of total interaction rate and of small angle elastic scattering. Both experiments give consistent results showing that the total cross section increases by (11.8±1.5) % over the ISR energy range. This experiment has also measured the slope of the forward diffraction peak in elastic scattering at small momentum transfer. The elastic cross section shows the same relative rise as the total cross section, and the ratio λ of elastic to total cross section approaches a constant value of λ=0.178±0.003.

Experimental observation of a copious yield of electrons with small transverse momenta in pp collisions at high energies

Abstract Inclusive electron and positron emission have been observed for θcm = 30° and s = 2800 GeV2 at the CERN Intersecting Storage Rings (ISR). Over the transverse momentum interval 0.2 GeV/c

Production of nucleon resonances by single diffraction dissociation at the CERN ISR

The single diffraction dissociation process pp → (pπ+π−)p has been studied at the CERN ISR at √s = 45 GeV and 0.1 < −t < 0.6 GeV2. The reaction is dominated by nucleon resonance production: pp → pN (1520) and pp → pN(1688) with cross-sections (0.25 ± 0.08) mb and (0.56 ± 0.19) mb respectively.

Λ0 polarization in proton-proton interactions at √s = 53 and 62 GeV

Abstract Λ 0 s produced in the inclusive reaction pp → Λ° + X with √s = 53 and 62 GeV at the CERN Intersecting Storage Rings are observed to be polarized along the normal to the production plane. In the ranges of longitudinal and transverse momenta, 15–24 and 0.6-1.4 GeV/ c , respectively, the mean polarization is found to be −(0.357±0.055).

Evidence for double Pomeron exchange at the CERN ISR

Abstract We have observed events at the CERN Intersecting Storage Rings (ISR) which are consistent with the double Pomeron exchange process p + p → p + X + p, where X represents a system of particles in the central region of the rapidity distribution separated by at least two units from the outgoing protons in the forward directions. The observed low charge multiplicity of the central cluster X indicates that this process is dominated by the formation of a low-mass system in the central region. In particular, we find that the differential cross-section for the process p + p → p + h + + h - + p, where h represents a charged particle, shows no correlation between t A and t B and has an exponential slope of 9.9 ± 1.8 GeV −2 independent of energy. The cross-section for this process is found to be approximately 20 μb over the ISR energy range.

Further evidence for production of electrons with small transverse momenta in pp collisions

A new measurement of prompt lepton production at small transverse momenta in pp collisions at the ISR, for s = 53 GeV, is presented. The cπ ratio, which is about 10−4 for pT > 1 GeV/c, rises rapidly as pT goes to smaller values, confirming our original results. The data are consistent with equality between the numbers of e+ and e− produced in each transverse momentum interval.

Diffraction dissociation in the reaction p+p→Λ°+K++p at the CERN ISR

The exclusive reaction pp→Λ°K+p has been studied at 0.1<−tpp<0.6 GeV2 and energies √s=45 GeV and 53 GeV at the CERN ISR. Diffractive excitation p→Λ°K+ occurs predominantly in the mass range M(Λ°K+)≈2.1 GeV and peaks at 1.7 GeV. The cross section for pp→Λ°K+p is 10±3μb for M(Λ°K+)<2.5 GeV, and the tpp dependence is exp (bt) with b=7.0±0.5 GeV−2.

Observation of diffraction excitation in pp → (pπ+π−)+X at the CERN-ISR and tests of limiting fragmentation

Abstract In a single-arm magnetic spectrometer experiment at the CERN Intersecting Storage Rings (ISR), a prominent diffractive enhancement is observed for inclusive production of (pπ+π−) systems near x ∼ 1 at √s = 53 and 35 GeV. In testing limiting fragmentation and scaling for this system, inclusive pπ+π− diffractive excitation into a fixed invariant mass range is found to possess a cross-section independent of s to within (3 ± 5)%. The main component in the (pπ+π−) system is Δ(1236)π, with a charge structure compatible with the break-up of an isotopic spin 1 2 system.