Proton-proton Cross Section Research Articles

Extending the frontiers: Reconciling accelerator and cosmic rayp−pcross sections

We simultaneously fit a QCD-inspired parameterization of all accelerator data on forward proton-proton and antiproton-proton scattering amplitudes, together with cosmic ray data (using Glauber theory), to predict proton-air and proton-proton cross sections at energies near \sqrt s \approx 30 TeV. The p-air cosmic ray measurements provide a strong constraint on the inclusive particle production cross section, as well as greatly reducing the errors on the fit parameters---in turn, greatly reducing the errors in the high energy proton-proton and proton-air cross section predictions.

Predicting Proton-Air Cross Sections ats∼30TeVUsing Accelerator and Cosmic Ray Data

We use the high-energy predictions of a QCD-inspired parametrization of all accelerator data on forward proton-proton and antiproton-proton scattering amplitudes, along with Glauber theory, to predict proton-air cross sections at energies near $\sqrt{s}\ensuremath{\approx}30\mathrm{TeV}$. The parametrization of the proton-proton cross section incorporates analyticity and unitarity and demands that the asymptotic proton is a black disk of soft partons. By comparing with the $p$-air cosmic ray measurements, our analysis results in a constraint on the inclusive particle production cross section.

Exclusive Measurements of Virtual Bremsstrahlung in Proton-Proton Scattering at 190 MeV

Exclusive differential cross sections of virtual bremsstrahlung ih proton-proton scattering below the pion-production threshold have been measured for the first time. The total cross section integrated over photon invariant masses of 15 to 80 MeV/c(2) and integrated over the acceptance of the detector is 3.2 +/- 0.1 +/- 0.5 pb. The data are compared to a low-energy calculation and a fully relativistic microscopic model, which predict a virtual bremsstrahlung cross section of 3.4 and 5.9 pb, respectively. Over the entire experimentally covered phase space, the low-energy calculation gives a better description of the data than the microscopic model. [S0031-9007(99)08793-1].

Proton-nucleus cross section at high energies

Cross sections for proton inelastic collisions with different nuclei are described within the Glauber and multiple scattering approximations. A significant difference between the approximate `Glauber' formula and exact calculation with a geometrical scaling assumption for very high-energy cross section is shown. Experimental values of proton-proton cross sections obtained using extensive air shower data are based on the relationship of proton-proton and respective proton-air absorption cross sections. According to obtained results values reported by the Akeno and Fly's Eye experimental groups are about 10% overestimated. The proper energy dependence of absorption cross section for collisions with air nuclei is of a great importance for studies of high-energy cosmic rays using the Monte Carlo technique.

Proton-proton cross section ats∼30TeV

There are both theoretical and experimental uncertainties in using data from cosmic-ray air showers to estimate hadronic cross sections above accelerator energies. We outline these problems and compare the physics used to extract \sigma_{pp}^{tot} from air shower data to the widely used parameterization of the proton-proton cross section of Donnachie and Landshoff and other contemporary models. We conclude that the published cosmic-ray cross section values do not strongly constrain \sigma_{pp}^{tot} fits from lower energy accelerator data.

Screening effects on the elastic nucleon-nucleon cross section in relativistic nuclear matter

We investigate the screening effects on the nucleon-nucleon elastic cross section inside nuclear matter at zero and finite temperature. The N - N interaction is described phenomenologically via meson exchanges (σ, π and ω) in the framework of a relativistic lagrangian model. The expressions for the in-medium meson propagators, which take into account the effects of matter polarization and renormalized vacuum polarization, are used in the calculation of the various meson contributions to the total cross section in the one-boson exchange approximation. The final expressions allow a satisfactory fit of the Coulomb substracted proton-proton cross section data in vacuum. At finite density or temperature the cross section is reduced as compared to the vacuum values and compatible with the existing experimental constraints. At high density the p- p differential cross section gets increasingly forward and backward peaked. The σ-ω mixing plays a key role in the understanding of the results.

Bremsstrahlung in intermediate-energy nucleon reactions within an effective one-boson exchange model

Within a covariant effective one-boson exchange model for the T matrix of NN interactions we present detailed calculations of bremsstrahlung cross sections for proton-proton and proton-neutron reactions at beam energies in the 1 GeV region. Besides pure bremsstrahlung processes we consider photons from Λ decays and contributions from the η → γγ process. At beam energies above 700 MeV the Λ decay channel dominates the spectra at large photon energies, where the interference between non-resonance processes and the Λ decay channel becomes also important. Low energy photons stem from pure bremsstrahlung processes. The available experimental data at 730 MeV beam energy is well described. We extrapolate the model down to 280 MeV, where more detailed experimental data exist, and find agreement with angular distributions.

Chou-Yang-Glauber model for the pp and $$p\bar p$$ scatteringscattering

Scattering cross-sections of proton-proton an proton-antiproton are investigated with recourse to the Chou-Yang-Glauber model which is modified by adding an extra term so as to fit the data of differential cross-sections. The experimental data are reproduced very well in the energy region from a few GeV up to 1.8 TeV in the centre-of-mass system. The elastic and the total cross-sections and the ϱ parameters are calculated for the multi-TeV region by extrapolating the parameters above 1.8 TeV. The results coincide with that obtained by the dispersion theoretic parameterization. The total cross-section agrees with that of the cosmic-ray experiment. It is inferred that the asymptotic form of the differential cross-section is given by a simple formula.

A hydrodynamic model for nuclear stopping

Abstract A three-fluid one-dimensional hydrodynamic model for relativistic heavy-ion collisions is presented. The three fluids are left- and right-moving nucleonic matter and a third fluid representing the energy produced by the collisions of the nucleonic particles. For the collision of nucleons with the energy fluid, the cross section per proton mass of fluid is taken equal to the proton-proton cross section. The energy exchange per collision is assumed to be about 1.4 GeV. Complete stopping at the CERN energy of 200 GeV/N occurs in this model. The results are fairly insensitive to the nucleon-energy-fluid cross section.

Non-perturbative scales in soft hadronic collisions at high energy

We investigate the role of non-perturbative quark-gluon dynamics in soft high energy processes. In order to reproduce differential and total cross sections for elastic proton-proton and proton-antiproton scattering at high energy and small momentum transfer it turns out that we need two scales, the gluonic correlation length and a confinement scale. We find a small gluonic correlation length, a ∼- 0.2 fm, in accordance with recent lattice QCD results.

Medium effects on spin observables of proton knockout reactions.

Medium modifications of the properties of bound nucleons and mesons are investigated by means of intermediate energy quasifree proton knockout reactions with polarized incident protons, by comparison of quantities which are insensitive against wave distortions. The sensitivity of the spin observables of the quasifree proton-proton cross section to modifications of the nucleon and meson properties is studied using the Bonn one-boson exchange model of the nucleon-nucleon interaction. A method proposed to extract the pp analyzing power in medium from the (p, 2p) asymmetries indicates a reduction of this quantity compared to its free space value. This reduction is linked to modifications of masses and coupling constants of the nucleons and mesons in the nucleus. The implications of these modifications for another spin observable to be measured in the future are discussed.

HADRON ’93: Experiments

In this summary, we briefly recall what may be considered as the main new experimental results that have been presented at HADRON ’93: on proton-proton and photon-proton cross-sections, on the first HERA results on structure functions, on the spin-dependent structure functions of the nucleons, on top, beauty and charm quark spectroscopy and on light-quark baryon and meson spectroscopy.

Microscopic calculation of in-medium proton-proton cross sections.

We derive in-medium proton-proton cross sections in a microscopic model based upon the Bonn nucleon-nucleon potential and the Dirac-Brueckner approach for nuclear matter. We demonstrate the difference between proton-proton and neutron-proton cross sections and point out the need to distinguish carefully between the two cases. We also find substantial differences between our in-medium cross sections and phenomenological parametrizations that are commonly used in heavy-ion reactions.

Effective fire tube and geometric scaling in proton-proton and proton-antiproton collisions.

A simple phenomenological model for the proton-proton process used earlier is developed. The model combines a fireball formation process via the string fragmentation mechanism for the spacetime development of a nonperturbative fire tube of an excited vacuum, with subsequent final-hadron production through fireball decays. The effective string tension is proportional to the fire-tube transversal area determined by the overlap area of the two colliding protons. The overlap area is a function of the impact parameter and the proton-proton total cross section. Excellent agreement with experimental data is obtained for a wide energy range covering from {radical}{ital s} {similar to}20 GeV to 1 TeV.

Energy dependence of proton-proton differential cross section

Energy dependence of proton-proton differential cross section

Novel transmission detector used for total cross section measurements

A new apparatus for total cross section measurements was developed and tested at Saturne II, Sacalay. The transmission ratios are determined using a ring-counter system coded in the Gray code, involving an exclusive four-fold coincidence between 4 counters among 8. Beam rate effects are suppressed by an electronic device which permits reaching an accuracy of better than 10 −4 in any transmission ratio. The apparatus was first used at SIN for the measurements of the total polarized proton-proton cross section difference Δσ L and of the spin correlation parameter A 00 kk in pp → pp and pp → dπ + reactions, and then at Saturne II for Δσ γ and Δσ L measurements in p-p scattering.

Consequence of isospin conservation in nucleon-nucleon scattering

Isospin conservation in nucleon-nucleon scattering leads to an extension of the optical theorem to backward angles. The total neutron-proton and proton-proton cross sections are related to the imaginary parts of the neutron-proton amplitudes at backward angles. We suggest to incorporate the above relations in the phase shift analysis, especially above 600 MeV lab energy were dibaryons are suspected to exist.NUCLEAR REACTIONS Nucleon-nucleon scattering, isospin conservation.

Proton-proton cross sections from 1 to 100 TeV

Recent direct measurements of the energy spectrum of protons in primary cosmic rays by the Japanese-American cooperative emulsion-chamber experiment remove the most important uncertainty in deriving proton-proton total cross sections from cosmic-ray data. The data are reanalyzed and it is shown that ${\ensuremath{\sigma}}_{\mathrm{pp}}$ is approximately equal to ${\ensuremath{\sigma}}_{\overline{p}p}$ at 50 TeV. The $\mathrm{pp}$ cross section is shown to be free to a large extent of systematic uncertainties.

Proton-helium elastic scattering from 45 to 400 GeV

The elastic proton-helium differential cross section has been determined for incident laboratory energies from 45 to 400 GeV in the range $0.003\ensuremath{\le}|t|\ensuremath{\le}0.52$ (${\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^{2}$ by means of the internal-gas-jet-target technique. The differential cross section drops 4-5 orders of magnitude to the first dip at $|t|\ensuremath{\simeq}0.22$ (${\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^{2}$. The shrinkage in the slope of the differential cross section is found to be twice as fast as that in the proton-proton case. The slope parameter at $|t|\ensuremath{\simeq}0$ is described by the formula $b=24+1.13\mathrm{ln}s$, where $b$ is in (${\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^{\ensuremath{-}2}$ and $s$ is in ${\mathrm{GeV}}^{2}$. The elastic proton-helium cross section is normalized to the known elastic proton-proton cross section using data taken with a helium and hydrogen mixture as a target. The proton-helium total cross section is determined from the optical theorem. The total cross section rises by 4% between 100 and 400 GeV. Results are presented on the real part of the elastic-scattering amplitude and on the total elastic cross section. The experimental differential cross sections are compared to Glauber-model predictions.

Proton-Proton Total Cross Sections and the Neglect of Masses in Data Fitting in the Regge Region

It is shown by taking the example of pp total cross .sections that the use of the approximation s ~ 2qs-t while fitting data in the Regge region can be misleading. Several standard fits to O"tot(pp) data are based on the assumption of weak p-f-w-A2 exchange degeneracy (EXD). However, these fits involve the use of the approximation mentioned. We find, quite surprisingly, that it is impossible to fit the O"tot(pp) data in the range 6 ~ Plab ~ 2092 GeVjc using the precise factor 2qs~ in conjunction with weak p-f-w-A2 EXD. OUf investigation shows that O"tot(pp) data alone seem to indicate either a breaking of weak p-f-w-A 2 EXD or the presence of low-lying contributions, or both, provided one does not ignore the masses of the interacting particles in data fitting in the Regge region (Plab ;:;: 5 GeVjc). Caution is therefore urged in the use of such approximations in phenomenological calculations.