Measurements of elastic scattering in alpha-alpha and alpha-proton collisions at the CERN intersecting storage rings

We measured the elastic scattering of $\text{αα}\text{at}\text{s}\text{= 126}\text{GeV}$ and of αp at $\text{s}\text{= 89}\text{GeV}$. For αα, the differential cross section dσ/dt has a diffractive pattern minima at |t| = 0.10 and 0.38 GeV². At small |t| = 0.05?0.07 GeV², this cross section behaves like exp[(100 ± 10) t]. Extrapolating a fit to the data to the optical point, we obtained for the total cross section α_tot(αα) = 250 ± 50 mb and an integrated elastic cross section σ_e1(αα) = 45 ± mb. Another method of estimating σ_tot(αα), based on measuring the interaction rate, yielded 295 ± 40 mb. For αp, dσ/dt has aminimum at |t| = 0.20 GeV², and for 0.05 < |t| < 0.18 GeV² behaves like exp[(41 ± 2) t]. Extrapolating this slope to |t| = 0, we found σ_tot(αp) = 130 ± 20 and σ_e1(αp) = 20 ± 4mb. Results on pp elastic scattering at $\text{s}\text{= 63}\text{GeV}$ agree with previous ISR experiments.     

Measurement of elastic scattering in antiproton-proton collisions at 52.8 GeV centre-of-mass energy

We measured the differential cross section for p?p and pp elastic scattering in the momentum-transfer range 0.01 <|t| < 1.0 GeV² at the CERN Intersecting Storage Rings with center-of-mass energy $\text{s}\text{= 52.8}\text{GeV}$. Fitting the differential cross section with an exponential [Aexp (bt)], we found $\text{b}\text{p}\text{p = 13.92 ± 0.59}\text{GeV}{}^{\mathrm{?2}}$ for |t| < 0.05 GeV², whilst for |t| > 0.09 GeV², $\text{b}\text{p}\text{p = 10.68 ± 0.26}\text{GeV}{}^{\mathrm{?2}}$. Using the optical theorem, we obtained for the total cross section $\text{σ}{}_{\mathrm{<mtext>tot</mtext>}}\text{(}\text{p}\text{p)= 44.86 ± 0.78}\text{mb}$ and, by integrating the differential cross section, we obtained for the total elastic cross section $\text{σ}{}_{\mathrm{<mtext>el</mtext>}}\text{(}\text{p}\text{p) = 7.89 ± 0.28}\text{mb}$. Calculations of σ_tot combining elastic-rate and total-rate measurements are also given. All of these measurements were also performed for pp scattering at the same energy, and the results for both reactions are compared.     

pp interactions at 303 GeVc: Analysis of diffraction excitation in the reaction pp → pX

The properties of the diffractively excited system observed at low missing mass in the inclusive pp → pX reaction at $\text{303}\text{GeV}\text{c}$ are presented. For diffraction excitation with |x| > 0.9, the cross section, σ_D=(5.6±0.8) mb, the mean charged multiplicity depends on the mass of the diffractive system approximately at 〈n_c〉 ≈ 0.6M_x + 2, and the slope of the momentum transfer distribution with |t| < 0.5 GeV² is 7.5±0.8 GeV^?2.     

Study of K−p→K1(890)n at 13 GeV

The results of a wire chamber spectrometer experiment studying $\text{K}$¹ (890) production in the reaction K^?p→ K^?π⁺n at 13 GeV are presented. Strong forward structure is observed for |t|< m²_π in the s-channel density matrix elements and differential cross section. These features are similar to those observed in π^?p→?⁰n data and are characteristics of π exchange. In contrast in the intermediate, |t| ～ 0.2 GeV², and large momentum transfer regions $\text{K}$¹ (890) production is demonstrated by the natural parity ??A₂ exchange contribution.     

Regge cuts and large-|t| pp scattering

It is shown that recent measurements of the large-|t| pp elastic-scattering differential cross section at FNAL and CERN-ISR agree with earlier predictions based on the dominance of a pomeron pole(P) with αp(t) = 1.067 + 0.10 t, and a P ? P cut, out to the largest measured |t| values (12 GeV²). Some of the problems raised by this success are discussed.     

Measurement of the polarization parameter in pp elastic scattering at 150 GeV/c

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.     

Scaling violation favouring high multiplicity events at 540 GeV CMS energy

New data are presented on the charged multiplicity distribution for non single-diffractive events produced in pp? interactions at a CM energy $\text{s}\text{= 540}\text{GeV}$. The distribution in the full pseudorapidity range is compared with data from the ISR. Using the scaling variable $\text{z =}\text{n}\text{〈n〉}$ a change of shape is observed. The effect is manifested as an increase from 2% to 6% in the proportion of high multiplicity (z > 2) events. For the central pseudorapidity range, |η| ? 1.5, scaling is approximately valid up to $\text{s}\text{= 540}\text{GeV}$.     

Measurement of the polarization parameter in π−p elastic scattering at 40 GeV/c

We report our first measurements of the polarization in the elastic scattering of negative pions from polarized protons at an incident pion momentum of 40 GeV/c. The momentum-transfer region covered was 0.08 < |t| < 1.3 (GeV/c)². The angular distribution of the polarization exhibits a first minimum of ～ ? 5% and the well-known zero around t ≈ ? 0.6 (GeV/c)². The energy variation of the first minimum (at around t = ? 0.2) may be expressed in a simple form, $\text{P}{}_{\mathrm{<mtext>avr</mtext>}}\text{= ?(0.48±0.06) s}{}^{\mathrm{?0.52\pm 0.05}}$.     

New evaluation of muon (g − 2) hadronic anomaly

The hadronic part a_H of the muon g-factor anomaly $\text{a ≡}\text{(g ? 2)}\text{2}$ is evaluated from latest data on σ(e⁺e^? → hadrons). For a p-wave ππ scattering length of a₁ = 0.04±0.005 we calculate a_H = (66±10) × 10^?9, compared to a(experiment) ? a(QED) = (60±29) × 10^?9. Half of the uncertainty on a_H is associated with the energy interval $\text{0.92 <}\text{s}\text{< 2}\text{GeV}$.     

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

New experimental results are presented on proton-proton elastic scattering at centre-of-mass energies $\text{s}\text{=23}\text{GeV}$ and $\text{s}\text{=62}\text{GeV}$. 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 $\text{s}$. The connection of these observations with the hypothesis of “geometrical scaling” is discussed.     

Elastic pp scattering in the cern sps energy region

The pronounced dip-bump structure with a sharp minimum at |t| = 1.5 (GeV/c)², recently observed in elastic $\text{p}$p scattering at P_L = 50 GeV/c at the CERN SPS, is explained by the quark multiple scattering model with a realistic wavefunction for the proton and the antiproton. It is predicted that a second dip will appear around |t| = 7 (GeV/c)² at P_L = 50 GeV/ c and at higher energies.     

A comparison between pp and pp diffractive peaks at and beyond ISR energies

Although a substantial difference between pp differential cross section at ISR energies and $\text{p}\text{p}$ differential cross section at SPS energy has been reported, we demonstrate that both differential cross sections, at least up to |t| ～ 1.2 GeV², can be satisfactory accounted for within the usual eikonal model in which the diffractive component is crossing even. Thus at a given ultra high energy, there is no suggestive evidence for a difference between pp and $\text{p}\text{p}$ diffractive peaks.     

K−p elastic scattering at 14.3 GeV/c

Results are presented of a bubble chamber experiment on K^?p elastic scattering at 14.3 GeV/c, in four-momentum transfer range 0.04 < |t| < 2.74 GeV² using an initial set of 40 000 events. The total elastic cross section is (2.96 ± 0.10) mb. The results are compared with K⁺p elastic scattering data at 13.8 GeV/c, and the effective Regge trajectory is calculated using K^?p data from 5 to 100 GeV/c.     

Off-shell NN annihilation studied in π+p interactions at 8 and 16 GeV/c

Interactions in which the baryon is emitted forwards in the c.m.s. are studied in 8 and 16 GeV/cπ⁺p collisions. These interactions are interpreted as representing baryon exchange. The properties of such off-shell $\text{N}$N annihilation events are studied. It is found that the multiplicity distribution of the multi-pion system as a function of the effective mass for events with |u_pp| < 1 GeV² is the same as for real $\text{N}\text{N}$ annihilations.     

Calculation of the γγ → ϱ0ϱ0 cross section at high energies

The processes with the cross sections not decreasing with energy become important at high energies. The simplest processes of this kind are γγ → V_i⁰V_j⁰ where V⁰ = ?⁰, ω, ?, ….. We calculate their cross sections in the high-energy small angle region s ? |t| ? μ². The cross section γγ → ?⁰?⁰ at high energies (s ? 10 GeV²) exceeds those of γγ → ππ, ?⁺?^? considerably. At $\text{s ? 10}{}^4\text{GeV}{}^2$ (this is the characteristic energy for the VLEPP and SLC colliders) and $\text{|t| ? 2}\text{GeV}{}^2$, the ratio $\text{(}\text{d}\text{σ/}\text{d}\text{t)(γγ → ?}{}^0\text{?}{}^0\text{)/(}\text{d}\text{σ/}\text{d}\text{t)(γγ → μ}{}^{\mathrm{+}}\text{μ}{}^{\mathrm{?}}\text{) ? 70}$.     

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.     

Differential cross sections of elastic pp scattering in the energy range 8–70 GeV

In this paper we present tables of absolute differential cross sections of elastic pp scattering together with the values of the slope parameter B and the real-part parameter α, where $\text{B=}\text{d}\text{d}\text{t}\text{In}\text{dσ}\text{d}\text{t}\text{α=}\text{Re A(0)}\text{Im A(0)}$ and A(0) is the amplitude of elastic pp scattering at t = 0. The cross-section data have been obtained at the Serpukhov accelerator from 8 to 70 GeV in the |t|-range 0.0007 ? 0.12 (GeV/c)².     

Single diffraction dissociation at the CERN SPS collider

The reaction $\text{p}\text{p}\text{→}\text{p}\text{X}$ was studied at a centre-of-mass energy $\text{s}\text{= 540}\text{GeV}$ by measuring the momentum spectrum of the antiproton. Data are presented in the four-momentum transfer range 05 < ?t < 1.2GeV². 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.