Search

The reaction γ p → K + K − p has been investigated with tagged photons in the energy range of 20 E γ

An analysis is presented of the channel γp→K + K − π + π − p. Evidence is found for a K + Kπ enhancement of mass ≈1.9 GeV and width ≈0.4 GeV. The spin-parity of the enhancement is consistent with being 1 − .

Measurements of ω and η production in the reaction γp→π+π−π+π−π0p are presented, showihg that the ωπ+π− channel is made up of an enhancement at ∼1.7 GeV of width ∼0.5 GeV, which is consistent with being a 1− state, together with a distribution at higher masses containing higher angular momentum terms. The ηπ+π− final state is produced with a similar cross section and also shows a low-mass enhancement.

The differential cross sections for the elastic scattering of ..pi../sup +/, ..pi../sup -/, K/sup +/, K/sup -/, p, and p-bar on protons have been measured in the t interval -0.04 to -0.75 GeV/sup 2/ at five momenta: 50, 70, 100, 140, and 175 GeV/c. The t distributions have been parametrized by the quadratic exponential form dsigma/dt = A exp( B abs. value(t) + C abs. value(t)/sup 2/ and the energy dependence has been described in terms of a single-pole Regge model. The pp and K/sup +/p diffraction peaks are found to shrink with ..cap alpha..' approx. 0.20 and approx. 0.15 GeV/sup -2/, respectively. The p-barp diffraction peak is antishrinking while ..pi../sup +/- and K/sup -/p are relatively energy-independent. Total elastic cross sections are calculated by integrating the differential cross sections. The rapid decline in sigma/sub el/ observed at low energies has stopped and all six reactions approach relatively constant values of sigma/sub el/. The ratio of sigma/sub el//sigma/sub tot/ approaches a constant value for all six reactions by 100 GeV, consistent with the predictions of the geometric-scaling hypothesis. This ratio is approx. 0.18 for pp and p-barp, and approx. 0.12--0.14 for ..pi../sup +/- and K/sup +/-. A crossover is observedmore » between K/sup +/p and K/sup -/p scattering at abs. value t approx =0.19 GeV/sup 2/, and between pp and p-barp at abs. value t approx=0.11 GeV/sup 2/. Inversion of the cross sections into impact-parameter space shows that protons are quite transparent to mesons even in head-on collisions. The probability for a meson to pass through a proton head-on without interaction inelastically is approx. 20%, while it is only approx. 6% for an incident proton or antiproton. Finally, the results are compared with various quark-model predictions.« less

Results on charged particle yields in proton-proton collisions at 14.2, 19.2 and 24.0 GeV/c for secondary momenta above 4 GeV/c and lab angles between 10 and 150 mrad are reported. Cross sections for inclusive reactions involving the production of π± K±, p and p are presented. The general features of the dependence of the data on transverse and longitudinal momentum, missing mass, and four-momentum transfer are described and the approach to limiting distributions in the 10 to 30 GeV energy range is discussed.

An analysis is presented of the channel γp→π+π−π0π0p. Evidence is found for an ωπ0 enhancement of mass ≈1.25 GeV and width ≈0.3 GeV. The enhancement is a mixed spin-parity state with 1− dominant.

A dipion enhancement of mass 1.59 GeV and width 0.23 GeV is observed in the channel γp→π + π − p. The spin-parity of the enhancement is consistent with being 1 − .

Measurements of the reaction γ p → p π + π − π + π − are presented, in which π + π − π + π − systems with masses up to 3 GeV are produced from fragmentation of the incident photon. The reaction is dominated by production of the large peak of the ϱ′(1600) meson and, at higher masses ≳2 GeV, y production of jet-like 4 π systems. The ϱ′(1600) meson is produced by a predominantly s -channel helicity conserving mechanism. At higher masses there are also indications of ϱπ peaks, of masses 1.3 GeV (the A 2 meson) and 1.75 GeV, produced with a recoiling π meson by a mechanism consistent with the Deck effect.

Results are presented on inclusive photoproduction in hydrogen of Σ0, Σ1385±, Ξ−0, and their antiparticles for incident energies between 20 and 70 GeV. Hyperons and antihyperons are mainly measured in the kinematical range of central and forward production (xF > −0.3). We find the cross-section ratios σ(Σ 1385 + ) σ(Σ 1385 − ) = 1.4 ± 0.1 , σ( Σ 1385 + ) σ( Σ 1385 − ) = 1.3 ± 0.2 and an antiparticle/particle ratio of about 0.3 for the three sigma states. The results suggest an important role of the valence quarks of both the beam projectile and target in the production process in qualitative agreement with current ideas of quark fusion models. The inclusive production of Σ1385± is also observed in a small subsample of the events containing Λ Λ pairs. The xF distribution of Λ ( Λ ) in Λ Λ events as well as those in Λ p ( p Λ ) is the same as those in single Λ( Λ ) inclusive events. Weak signals in the K− pπ+ and Λπ+ π+ π− mass spectra are observed around a mass of 2.26 GeV.

The production and decay of a D0 have been observed in a nuclear emulsion exposed to a photon beam from the CERN super proton synchroton in conjunction with the Omega spectrometer. All the decay products have been detected and measured in the emulsion and in the spectrometer. The mass of the charmed particle is 1866 ± 8 MeV/c2 and its decay time is (2.26 ± 0.05) × 10−14 s.

We report on diffractive production of 6 π systems with a continuum of masses from 2 to 5 GeV/c 2 in the reaction γ p→ π + π − π + π − π + π - p. The event structure is compared in detail with Monte Carlo studies of p T limited phase space, and with the jets observed in hadronic systems produced by electron-positron annihilation. Strong similarities are found. For this jet-like structure of the 6 π system the axis is consistent with being along the incident photon direction.

Proton-proton elastic scattering has been measured at the CERN Intersecting Storage Rings in the four-momentum transfer range 0.001 ⩽… t …⩽ 0.015 GeV 2 at centre-of-mass energies of 23 and 31 GeV. The detection of Coulomb scattering and of its interference with nuclear scattering leads to the determination of the real part of the nuclear amplitude and of the total proton-proton cross section by the optical theorem.

Electron-proton elastic scattering cross sections have been measured at the Stanford Linear Accelerator Center at four-momentum transfers squared (q2) of 1.0, 1.5, 2.0, 2.5and 3.75 (GeV/c)2. The angular distributions at q2 = 2.5 and 3.75 (GeV/c)2are sufficient to provide values of the ratio GE/GMindependent of the results from other laboratories. Our results are compatible with scaling, GE(q2) = GM(q2)/μ, within the experimental errors.

Angular distributions of proton-proton elastic scattering have been measured for incident beam momenta of 10.0, 12.0, 14.2 and 24.0 GeV/ c over a range of lab scattering angles from 12 to 152 mrad. This is equivalent to a range of four-momentum transfer squared from about 0.1 to 6.7 GeV 2 at the highest momentum. Nucleon resonance production in the two-body reaction p + p → p + X has been studied at 24.0 GeV/ c incident momentum from 13.5 to 112 mrad by measuring the proton momentum spectra from the elastic peak down to a momentum corresponding to a missing mass of about 2.6 GeV. The new data are compared with previous results and theoretical models.

The momentum spectra of protons scattered inelastically in proton-proton collisions were obtained in an external beam at NIMROD, using incident-proton momenta of 2.85, 4.55, 6.06 and 7.88 GeV/c, and various scattering angles in the range 22 to 144 mrad. The isobars of mass 1236, 1518 and 1688 MeV are clearly seen. There is evidence also in the spectra at small angles for the production of the 1410 MeV isobar at a mass of (1410±15) MeV and width (125±20) MeV. It is shown that the observed peak cannot be explained by the Deck effect. The differential cross-sections for the production of these isobars are presented in terms of the usual variabless andt, and are compared with absorption and Regge-pole model predictions. Fits to the data with various empirical functions of these variables are also investigated. The behaviour of the total cross-section for the 1236 MeV isobar is found to exhibit energy-dependence consistent with one-pion exchange, whereas the 1410 MeV and 1688 MeV isobar total cross-sections are found to be energy-independent. Also the total cross-section for the 1518 MeV isobar is found to exhibit energy-dependence in this energy range.

The experiment was made at the Rutherford Laboratory on the Proton Linear Accelerator using the polarized proton source. Five high-pressure helium gas polarization analysers were grouped round a liquid-hydrogen target. The results are as follows: 23.5° −0.061 ±0.031 39.0° −0.011 0.034 54.7° −0.009 0.025 71.3° +0.088 0.027 87.1° +0.166 0.022 c.m. These values have been used in phase-shift analyses which show that solutions of type No. 2 can now be excluded. The solutions of type No. 1 give a lower, more precise value of the 3P0 phase-shift.

Proton-proton elastic scattering has been measured over the angular range 7 to 16 mrad at centre-of-mass energies of 31, 45 and 53 GeV using the CERN Intersecting Storage Rings. The results indicate that the diffraction peak has continued to shrink with increasing energy, but not as fast as suggested by the results at lower energies.

Measurements are reported of the A and R parameters in proton-proton scattering at five angles at a proton energy of 47.8 MeV and three angles at 27.6 MeV using the Proton Linear Accelerator of the Rutherford Laboratory. The values have been used in phase shift analyses with the result that the phase shifts are as well defined near 27 MeV as near 50 MeV. The behaviour of the 3 P 0 phase shift which previously had the largest uncertainty is now defined as precisely as at higher energies.

Nucleon resonance production in the two-body reaction p + p → p + N ∗ has been studied at 24 GeV/ c incident momentum for angles from 12 to 117 mrad by measuring proton momentum spectra from the elastic peak down to a momentum corresponding to a missing mass of about 2.6 GeV.

Momentum spectra of protons scattered inelastically in proton-proton collisions were obtained in an external beam at Nimrod using incident proton momenta of 2.85, 4.55, 6.06, and 7.88 GeV/c and various scattering angles in the range 22 to 144 mrad. There is evidence for the production of the 1410 MeV isobar at small angles. The well-known isobars of mass values 1236, 1518, and 1688 MeV are also seen. The differential cross sections are presented for the production of these isobars. They are analyzed in terms of the usual variables $s$ and $t$. Fits to the observed momentum spectra indicate for the ${N}^{*}(1410)$ a mass of 1410 \ifmmode\pm\else\textpm\fi{} 15 MeV and a width of 125 \ifmmode\pm\else\textpm\fi{} 20 MeV.

The general design features of the threshold, differential, and DISC types of gas Cherenkov counters are discussed in the context of their application as particle detectors at high energies.

A new type of Cerenkov counter is described for the detection of multiparticle events emitted from a small-size production target. The detector focuses the Cerenkov light produced by a particle of a given velocity β 0 to a spot image. The counter produces an output of the angular coordinates and, for particles having γ values within a given range, provides a determination of the velocity of each detected particle. The general principles of the design of this type of detector are presented, together with the computed results for a particular example.

Measurements of proton-deuteron scattering have been performed using an incident 24.0 GeV/ c proton beam. Momentum-loss spectra of forward-scattered protons were measured by a single-arm spectrometer over a range of proton angles from 13 to 107 mr. The contributions to the proton spectra of single and double scattering can be separated experimentally, thus allowing estimates of proton-neutron elastic cross sections to be deduced from the data over a range of four-momentum transfer squared, |t| 5.8 GeV 2 . Elastic p - d scattering, in which the proton and deuteron were detected in coincidence, has also been measured over a range of | t | from 0.6 to 1.8 GeV 2 .

The angular distribution of proton-proton elastic scattering has been measured for incident beam momenta of 10.0, 12.0, 14.2 and 24.0 GeV/c over a range of laboratory scattering angles from 12 to about 140 mrad. The results are compared with the fourth power of the electromagnetic form of the proton.

Measurements of inclusive hadron processes of the type a+p..-->..b+xxx have been made at energies of 50 to 175 GeV for Feynman x in the range 0.75 to 0.95 and -t's up to 0.65 GeV/sup 2/. The invariant cross sections are satisfactorily parametrized by a simple form derived from Regge theory. (AIP)

A facility which tags the arrival and measures the momentum of photons has been constructed, tested and used in photoproduction experiments with the Omega spectrometer at CERN. The photons are produced by electron bremsstrahlung and are tagged by detecting the scattered electrons. By also measuring the parameters of the incident electron the photon's direction and position at the hydrogen target are reconstructed to ± 70 μ rad and ±2 mm,respectively. The accuracy of the photon momentum determination varies from ±0.25 GeV/ c at 25 GeV/ c to ±0.09 GeV/ c at 70 GeV/ c . Using a beam of ∼2×10 7 electrons per burst, at a momentum of 80 GeV/ c , obtained from 4×10 12 protons at an energy of 240 GeV, the facility tags ∼10 6 photons in the momentum range 25–70 GeV/ c .

Results are presented on inclusive φ photoproduction for incident energies between 25 and 70 GeV. Distributions in Feynman x, pT and decay angles are presented and interpreted in terms of quark fusion models. We demonstrate a similarity with the corresponding pion-induced reaction and obtain information on the hadronic nature of the photon.

Inelastic differential cross sections have been measured for p, p, and p+-p at 140- and 175- GeV/c incident momentum over a mod t range from 0.05 to 0.6 GeV/sup 2/ and covering a missing-mass region from 2.4 to 9 GeV/sup 2/. For M/sub x//sup 2/ greater than 4 GeV/sup 2/, the invariant quantity M/sub x//sup 2/d/sup 2/sigma/dtdM/sub x//sup 2/ was found to be independent of M/sub x//sup 2/ at fixed t and could be adeuately described by a simple triple-Pomeron form. The values obtained for the triple-Pomeron couplings are identical within statistics for all channels. (AIP)

Exclusive and inclusive p p photoproduction (with ⩾ 2 accompanying charged particles) have been measured in the photon energy range 44–70 GeV. The exclusive process shows no prominent features; the inclusive process shows evidence for S(1936) production as a resonant-like structure with mass 1930 ± 2 MeV and width 12 ± 7 MeV.

We present results on photoproduction of ϱ 0 and ω in the reactions γ p→ π + π − p and γ p→ π + π − π 0 p by tagged photons in the energy ranges 20 to 70 GeV and 20 to 45 GeV, respectively. The production of the ϱ 0 shows dominantly the characteristics of a diffractive process with respect to the E γ and t dependence of the cross section and the spin density matrix. The ϱ 0 photoproduction yields on average over the photon energy range a total cross section of σ ( γ p→ ϱ 0 p) = 9.4±0.1 μ b with an additional systematic error of ±1 μ b, and average slope parameters of the t distribution d σ /d t ≈exp(− b | t | + ct 2 ), of b =9.1±0.1 GeV −2 and c = 3.1 ±±0.2 GeV −4 . The shape of the ϱ 0 peak in the π + π − invariant spectra shows a skewing similar to that observed at lower energies. The photoproduction of ω is also consistent with a diffractive process and has a cross section of σ ( γ p→ ω p) = 1.2± 0.1 μ b with an additional systematic error of ±0.2 μ b. The average slope parameters of the t distribution are b =8.3 ± 1.3 GeV −2 and c = 3.4±2.6 GeV −4 .

Impact-parameter representations of elastic differential cross sections for the processes ..pi../sup plus-or-minus/p, K/sup plus-or-minus/p, pp, and p-barp at incident energies from 50 GeV to 175 GeV and in the -t range 0.03--0.75 GeV/sup 2/ are presented. The meson-baryon interactions are found to be 20% more transparent than the baryon-baryon interaction, and to have an interaction radius which is 6% smaller. The increase in the p-p total cross section as a function of energy is shown to come primarily from an increase in the p-p interaction radius, while in the K/sup +/p case an increase is seen in both the central opacity and the interaction radius. (AIP)

We report preliminary values of electron-proton elastic scattering measurements at the Stanford Linear Accelerator Center (SLAC) carried out at squared four-momentum transfers q^2 from 0.7 to 25.0 (GeV/c)^2. In the newly accessible region of q^2 above 10 (GeV/c)^2, the principal feature is the continued decrease of the magnetic form factor approximately as 1/q^4.

Electron-proton elastic-scattering cross sections have been measured at the Stanford Linear Accelerator Center for four-momentum transfers squared q^2 from 1.0 to 25.0 (GeV/c)^2. The electric (GEp) and magnetic (GMp) form factors of the proton were not separated, since angular distributions were not measured at each q^2. However, values for GMp were derived assuming various relations between GEp and GMp. Several theoretical models for the behavior of the proton magnetic form factor at high values of q^2 are compared with the data.