K.R. Schubert

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.

Rapidity correlations in inclusive two-particle production at storage ring energies

Abstract Inclusive two-particle production in the reaction pp → γ + ch + (anything) has been measured at the CERN ISR for four energies ( ✓s = 23,30.5,45, and 53 GeV ) at two production angles of the charged particles (ch) and the eight production angles of the γ-rays. The rapidity correlation of the two particles is weak and of short range. The peak correlation is σ inel ( d 2 σ γ ch d σ γ d σ ch ) − 1 = 0.62 ± 0.08 , the correlation range 〈yγ − ych〉 = 1.17 ± 0.05, independently of s. The φ correlation extends over a wide gap in rapidity; its strength is increasing with increasing transverse momentum.

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.

TRANSVERSE MOMENTUM DISTRIBUTION OF PHOTONS PRODUCED IN PROTON--PROTON COLLISIONS AT THE INTERSECTING STORAGE RINGS.

Abstract The energy spectrum of γ-rays produced in proton-proton collisions at the CERN Intersecting Storage Rings (ISR) has been measured at 90°. The spectrum is an exponential function of the transverse momentum. Its slope is found to be energy independent from 6.7 GeV to 53 GeV center of mass energy. It is shown that the same result holds for neutral pions.

The phase of ηoo and the invariances CPT and T

Abstract The decay amplitude ϵ o = 2 3 η +− + 1 3η oo is decomposed into a CPT-conserving, T-violating part ϵ, and a T-conserving, CPT-violating part δ. Using the measurement of the phase of ηoo together with other results on Ko decays we obtain: Reϵ = (1.68 ± 0.30) × 10−3, IM ϵ = (1.45 ± 0.30) × 10−3. Re δ = (0.07 ±) × 10 −3 , Im δ = (−0.30 ± 0.45) × 10 −3 .

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.

Observation of high mass μ+μ− pairs at the ISR

Abstract Observation of 16 μ + μ − pairs of invariant mass greater than 2.7 GeV/ c 2 in the reaction pp → μ + μ − + anything at s = 52 GeV at the CERN Intersecting Storage Rings (ISR) is reported. These events can be interpreted as originating from J(3.1) decay into μ + μ − . Their p T distribution suggests a hadronic production. The cross section for J production is given and compared to the cross section for single lepton production. We conclude that J(3.1) production cannot fully account for single lepton production.

Experimental evidence for double-pomeron exchange at ISR energies

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.

Observation of the interference between KLo and KSo in the πoπo decay mode

Data obtained with a copper regenerator on the interference between the decays KLo → 2πo and KSo → 2π o are presented. The analysis leads to the results: φoo = 510 ± 30o, |ηoo| = (1.23 ± 0.24) (|ƒ − ƒko) × 10−3 where (ƒ−ƒ)ko is the regeneration amplitude for copper at 2 GeV/c in fm2. Present experimental data suggest (ƒ−ƒ)ko = 2.7 ± 0.3.

Decay Angular Distributions in Diffractive One Pion Production at ISR Energy

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.