Simultaneous measurement of 2 and 3 spins in proton proton elastic scattering at 6 GeVc

The elastic cross section for proton proton scattering at 6 $\text{GeV}\text{c}$ was measured using a 70% polarized beam and a 75% polarized target at the Argonne ZGS. In the range $\text{P}{}_{\mathrm{\perp }}{}^2\text{= 0.5 → 2.0(}\text{GeV}\text{c}\text{)}{}^2$ we obtained small error measurements for the ↑↑, ↓↓ and ↑↓ initial spin states perpendicular to the scattering plane. At P_⊥² = 0.5 we also measured the recoil spin and found that the 5 different cross sections were very unequal.     

The effect of the parton transverse motion in large-p⊥ reaction

The parton transverse motion within the incident hadrons cannot be neglected when calculating large-p_⊥ reaction cross sections in the framework of hard scattering models. We give a general discussion of this effect for a large class of models. The results depend strongly on the parametrization of the hard scattering cross section at small momentum transfer in the parton-parton center of mass. With reasonable assumptions, we find that the parton transverse motion enhances the hard scattering model predictions for Edσ/dp by a factor of two and reduces

$\text{E}\text{d}\text{N}\text{d}\text{p}\text{=}\text{∫}\text{d}\text{p′}\text{E′}\text{EE′}\text{d}{}^{\mathrm{(2)}}\text{σ}\text{d}\text{p}\text{d}\text{p′}\text{E′}\text{E′}\text{d}\text{σ}\text{d}\text{p′}$

by a comparable factor, in the range p_⊥ ? 2?3 GeV/c. We study the correlations between the large-p_⊥ trigger and the background low-p_⊥ secondaries and give an estimate of the encountered azimuthal asymmetry around the beam momentum with a simple model.     

Large transverse momenta from statistical bootstrap with spin

We show that statistical bootstrap models (SBM) with their prediction of exponentially decreasing p distributions (equivalently: constant maximal temperature τ₀ ≈ m_π) are not ruled out by the large p_⊥ observed above ≈ 100 GeV lab energy in hadron collisions. Usual SBM sum over all spin angular momenta of the decaying fireball; if a particular spin is fixed, SBM leads to large p_⊥. We discuss in this paper (after having justified a classical approach) several mechanisms yielding high-mass, high-spin fireballs, select arbitrarily one of these (single fireball excitation) and calculate in SBM with fixed spin the decay structure. The cross section $\text{d}\text{σ}\text{d}\text{M}$ is taken to be an empirical function, fitted to existing p_⊥ data at one energy and then calculable at other energies. We can easily reproduce the p_⊥ distribution. Further results concern multiplicities rising with p_⊥, anisotropy of the single-particle inclusive distribution and various correlations. Unexpectedly, but a posteriori rather naturally a jet-like structure is found in the spin-orthogonal plane.     

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.     

Measurement of π−p → π0n at large momentum transfer

New results on a high statistics measurement of pion-nucleon charge exchange scattering at 40 GeV/c, extending in momentum transfer up to ?t = 1.8 (GeV/c)², are reported and compared with an optical impact parameter model, together with previous data for the reaction π^?p → ηn at the same energy. The imaginary part of the pole trajectory b₀(s) is determined from the slope of the tangent to the maxima of $\text{(?t)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{d}\text{σ}\text{d}\text{t}$. The linear increase of Im b₀(s) with log s, which has been observed at low energies, continues up to 40 GeV/c.     

K−p and pp elastic scattering at 10.1 GeV/c

The differential cross sections for K^?p and $\text{p}$p elastic scattering have been measured over the range of four-momentum transfer squared 0.18<?t<3.3 (GeV/c)². The K^?p data decrease smoothly as a function of ?t, whereas, the $\text{p}\text{p}$ data shows a break at ?t = 0.6 (GeV/c)² followed by a fast drop to ?t ? 1.6 (GeV/c)² where the differential cross section levels off and stays constant out to ?t = 3 (GeV/c)².     

Hadron production at transverse momenta from 0.5 up to 2.2 GeV/c in proton-proton collisions at 70 GeV

The cross sections for π^±, K^±, p, and $\text{p}$ production in pp collisions have been measured at transverse momenta from 0.48 up to 2.21 GeV/c at 70 GeV. The data are compared with results obtained at lower and higher proton energies and also with the quantum chromodynamics parton model (QPM) calculations. Common behaviour of the cross sections of the form $\text{g(p}{}_{\mathrm{\perp }}\text{)?(x}{}_{\mathrm{\perp }}\text{)}$ in the energy range above 200 GeV does not take place at lower energies. Qualitatively QPM fits the data and the best agreement is for π⁺/π^? and K⁺/π⁺ ratios.     

Elastic proton scattering from 4He at 0.58 and 0.72 GeV

The energy spectra of α-particles recoiling from a ⁴He gas target bombarded by 0.58 and 0.72 GeV protons have been measured to obtain the differential cross sections for elastic scattering $\text{d}{}_{\mathrm{\sigma }}\text{d}{}_{\mathrm{t}}$, in the region of four-momentum transfer squared, ?t=0.13 ? 0.55 (GeV/c)². The experiment was designed especially to observe the region between the first and second diffraction maxima.     

Mueller-Regge analysis in the central region

Mueller-Regge analysis of inclusive spectra in the central region for fixed p⊥ is carried out from 12 GeV/c to ISR energies. An analysis of the difference between π⁺ and π^? single- particle spectra reveals that both Mueller-Regge energy dependence and factorization are in accord with experiments only in a limited region of moderate value of $\text{p?}$, i.e. $\text{p? ? 0.7}\text{GeV/c}$. This suggests that double Regge exchange is a good approximation only for 0;t∥ and ∥u∥ ? 4 GeV². The K/π ratio calculated on the basis of an additive quark-counting picture is also consistent with experiments inside this region. The P? central vertex determined from ISR data turns out to be much smaller than one would obtain from low energy (12–24 GeV/c) data. The P-M-P exchange contribution to ππ correlations in rapidity thus estimated can explain only a part of observed correlations, which indicates that there should be a large positive contribution from some other effects, such as long range effects and/or Q exchange. The transverse momentum dependence of the P? central vertex also determined from ISR data predicts that the P-?-P exchange contribution to normalized ππ correlations increases as $\text{p}{}_1\text{?}$ and $\text{p}{}_{\mathrm{2?}}$ increase.     

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.     

Backward polarization as a direct experimental measure of peripherality

Striking regularities are observed in πN backward elastic scattering for p_lab ? 1 GeV. The rich structure of the polarization and differential cross section vary rapidly in both angle and energy. For a fixed energy however, the observables approximately satisfy the derivative relation $\text{P(θ)}\text{d}\text{σ}\text{d}\text{θ}\text{∝}\text{?}\text{t6θ}\text{(}\text{d}\text{σ}\text{d}\text{θ}\text{)}$. This empirical relation is shown to be the consequence of the peripheral nature of the interaction at high energies and the dominance of successive partial waves with increasing energy W = √s at lower energies: l = 2,3,4 … for W = 1.68, 1.95, 2.18 … GeV, respectively. $\text{“l-}\text{dominance}\text{”}$ suggests a pattern where N,Δ and Δ,Δ states appear in nearly degenerate pairs with the same l and parity but with $\text{J = l +}\text{1}\text{2}\text{and}\text{J = l ?}\text{1}\text{2}$. The observed regularities are consistent with measurements in the inelastic channel π^?p → ΛK⁰ and could provide a useful tool for an extension of phase-shift analyses to higher energies where no prominent peaks in the total cross section constrain the solution. At the highest energy (p_lab = 6 GeV/c) a possible deviation from the derivative rule implies the onset of a non-peripheral contribution not present at lower energies.     

Measurement of the spin parameters A and Ann in pp elastic scattering in the 1–3 GeV/c region

We have measured the asymmetry parameter A and the spin correlation parameter A_nn in pp elastic scattering, using the Argonne ZGS polarized proton beam and a polarized proton target. Angular distributions of A and A_nn for |t| ? 0.2 (GeV/c)²wereobtainedateightmomentabetween 1.10 and 2if2.75 GeV/c. We find significant structure in both the energy and t-dependence of A_nn at these energies. At p_lab ≈ 1.34 GeV/cA_nn reaches a very large value of about 0.8–0.9 near θ_cm = 90°.     

A study of the reaction pp → π− π+ at 10 GeV/c

The reaction $\text{p}\text{p}\text{→ π}{}^{\mathrm{?}}\text{π}{}^{\mathrm{+}}$ has been studied at 10.1 GeV/c in the ?t interval from 0.15 to 1.5 (GeV/c)². A line-reversal comparison with backward elastic scattering π⁺p → pπ⁺ shows good agreement for ?t > 0.3 (GeV/c)².     

Depolarization in proton inclusive inelastic scattering and in the (d,p) reaction on medium-weight nuclei

The energy-averaged depolarization parameter K_y^y′ has been measured for the inelastic scattering of 18 MeV protons from ⁵⁴Fe, ⁶³Cu and ⁹²Mo at 45°, 90° and 135°, and for 14.35 MeV protons from ⁶³Cu at 45° and 135°. In all cases K_y^y′ varies from approximately unity for scattering with low energy loss to approximately zero for inelastic scattering to high excitation energies. The change from one of these values to the other occurs over a region ≈ 6 MeV wide centered at about 5 MeV excitation. A simple two-component model fits both the K_y^y′ and inelastic crosssection data. K_y^y′ has also been measured for the ⁵⁴Fe($\text{d}$, $\text{p}$)Fe reaction with 16 MeV deuterons incident. Here K_y^y′ changes from approximately the maximum possible value, $\text{2}\text{3}$, to about zero in a 6 MeV region centered at roughly 13 MeV excitation. The ($\text{d}$,$\text{p}$) data can be fitted by an extension of the model used for the proton scattering data.     

Production and decay of quark-gluon strings: inclusive distributions of hadrons in p⊥ and x

The dependence of inclusive cross sections of the production of hadrons $\text{p}\text{p}\text{→ hX}$ on p_⊥ (and also on x and √s) is calculated at high energy in the region of small p_⊥ ? 1–2 GeV. The model of production and decay of quark-gluon strings is used under the simplest assumptions about the k_⊥ dependence of the quark distributions in nucleons ～ exp(?γ₁k²_⊥) and about the form of the string fragmentation function $\text{G}\text{?}{}^{\mathrm{<mtext>h</mtext>}}\text{～}\text{exp}\text{[?γ}{}^{\mathrm{<mtext>h</mtext>}}\text{(}\text{p}{}_{\mathrm{\perp }}\text{? z}\text{k}{}_{\mathrm{\perp }}\text{)}{}^2\text{]}$ where γ₁ and γ^h are some constants. The theory reproduces all existing experimental data and yields the “seagull effect” for the dependence of 〈p_⊥〉 on x. Predictions are given for the p_⊥ dependence of the spectra of π^± mesons produced at high energies at SPS and other future colliders.     

The reaction pp→pπ−π+p at 25 and 40 GeV/c

The reaction $\text{p}\text{p}\text{→}\text{p}\text{π}{}^{\mathrm{?}}\text{π}{}^{\mathrm{+}}\text{p}$ has been studied at 25 and 40 GeV/c at the Serpukhov proton synchroton using the CERN-IHEP spectrometer. The differential cross section has been determined as a function of four-momentum transfer to the proton (0.05–0.30 (GeV/c)²) and $\text{p}\text{ππ}$ mass (up to 2.2 and 2.6 GeV/c²). At both energies there is a broad low-mass maximum with an enhancement at 1.6–1.8 GeV/c². The cross section in a given mass band falls rapidly with |t|, with an exponential slope that decreases with increasing mass. In both the background and the 1.7 GeV/c² peak there is a strong $\text{Δ}{}^{\mathrm{??}}\text{π}{}^{\mathrm{+}}$ component. Possible spin-parity (J^P) contributions to it are discussed. Throughout the range 1.5–2.2 GeV there is at least one state of $\text{J ?}\text{3}\text{2}$ and there is interference between states of opposite P, |ΔJ| ? 1. At the peak there is a $\text{J ?}\text{5}\text{2}$ component. There are striking parallels between this reaction and the boson reactions π^?p→π^?π^?π⁺p and K^? → K^?π^?π⁺p.     

The charge exchange pp → nn at 5.0 and 7.76 GeV/c near the forward direction

The differential cross section for the charge exchange $\text{p}\text{p}\text{→}\text{n}\text{n}$ has been measured with high statistics at 7.76 GeV/c and at 5.0 GeV/c. The 7.76 GeV/c data show a very narrow [Δt ? 0.01 (GeV/c)²] forward peak superposed on a slow exponential fall-off.     

Inclusive single-particle distributions in π±p reactions at 8 and 16 GeV/c

Invariant single-particle cross sections for pion and proton production in π^±p interactions at 8 and 16 GeV/c are presented in terms of integrated distributions as functions of x, reduced rapidity ζ and p_⊥², and also in terms of double differential cross sections E d²σ/(dx dp_⊥²) and dζ dp_⊥²). A comparison of π^± and π^? induced reactions is made and the energy dependence is discussed. It is shown that the single-particle structure function cannot be factorized in its dependece on transverse and longitudinal momentum. For the beam-unlike pion, there is an indication for factorizability in terms of rapidity and transverse momentum in a small central region.     

Determination of the one-pion exchange potential from pn and pp charge exchange scattering

The πNN vertex function is determined from $\text{d}\text{σ}\text{d}\text{t}$ for pn → np and $\text{p}\text{p →}\text{n}\text{n}$ at 8 GeV/c in the interval 0 < ? t < 0.1 GeV². A “regularor mass” of 3.5m_π=488 MeV is found, corresponding to an “extension” of 0.40 fm of the πNN vertex. The resulting OPE potential is discussed.     

Target asymmetry for neutral π meson photoproduction on polarized protons at 4 GeV in the forward direction

The asymmetry $\text{A =}\text{(σ}{}^{\mathrm{+}}\text{?σ}{}^{\mathrm{?}}\text{)}\text{(σ}{}^{\mathrm{+}}\text{+σ}{}^{\mathrm{?}}\text{)}$ of the reaction γp↑↓ → π⁰p was measured at the Deutsches Elektronen Synchrotron DESY, Hamburg at a mean photon energy of 4.0 GeV in the four-momentum transfer range 0.2 (GeV/c)² ? ?t ? 1.1 (GeV/c)² in steps of approximately 0.08 (GeV/c)². The π⁰-meson and the proton were detected in coincidence. The asymmetry is compatible with zero in the t-range 0.2 (GeV/c)² ? ?t ? 0.4 (GeV/c)² and negative in the t-range ? 0.5 (GeV/c)².