Pp Total Cross Section Research Articles

EAS-TOP: The proton-air inelastic cross-section at [formula omitted

The proton-air inelastic cross section measurement at s ≈ 2 TeV from the EAS-TOP Extensive Air Shower experiment is reported. The technique exploits cosmic ray proton primaries, in the energy region E 0 = ( 1.5 ÷ 2.5 ) ⋅ 10 15 eV , studying the absorption length of their cascades when detected at maximum development. Primary energies are selected through the EAS muon number ( N e ), and proton originated cascades at maximum development by means of the shower size ( N e ). The shower and detector fluctuations are obtained with simulations performed using the CORSIKA code and the QGSJET II and SIBYLL interaction models. The simulations provide the conversion factor ( k = λ o b s / λ i n t ), from the observed absorption length ( λ o b s e x p ) to the interaction length ( λ p − air ). The obtained value of the p-air inelastic cross section at s ≈ 2 TeV is σ p − air i n e l = 338 ± 21 ( s t a t ) ± 19 ( s y s t ) − 28 ( s y s t ) mb . The relevant issue of systematic uncertainties have been studied. The connections with the pp ( p ¯ p ) total cross section measurements are discussed.

Absolute Total np and pp Cross-Section Determinations

Absolute total cross sections for np and pp scattering below 1000 MeV are determined based on partial-wave analyses (PWAs) of nucleon-nucleon scattering data. These cross sections are compared with most recent ENDF/B and JENDL data files, and the Nijmegen PWA. Systematic deviations from the ENDF/B and JENDL evaluations are found to exist in the low-energy region.

FORWARD PHYSICS AT THE LHC: ELASTIC SCATTERING

The following effects in the nearly forward ("soft") region of the LHC are proposed to be investigated: • At small |t| the fine structure of the cone (Pomeron) should be scrutinized: (a) a break of the cone near t ≈ -0.1 GeV 2, due to the two-pion threshold, and required by t-channel unitarity, and (b) possible small-period oscillations between t = 0 and the dip region. • In measuring the elastic pp scattering and total pp cross-section at the LHC, the experimentalists are urged to treat the total cross-section σt, the ratio ρ of real to imaginary part of the forward scattering amplitude, the forward slope B and the luminosity [Formula: see text] as free parameters, and to publish model-independent results on dN/dt. • Of extreme interest are the details of the expected diffraction minimum in the differential cross-section. Its position, expected in the interval 0.4 < -t < 1 GeV 2 at the level of about 10-2 mb · GeV -2–10-1 mb · GeV -2, cannot be predicted unambiguously, and its depth, i.e. the ratio of dσ/dt at the minimum to that at the subsequent maximum (about -t = 5 GeV 2, which is about 5) is of great importance. • The expected slow-down with increasing |t| of the shrinkage of the second cone (beyond the dip-bump), together with the transition from an exponential to a power decrease in -t, will be indicative of the transition from "soft" to "hard" physics. Explicit models are proposed to help in quantifying this transition. • In a number of papers a limiting behavior, or saturation of the black disk limit (BDL), was predicted. This controversial phenomenon shows that the BDL may not be the ultimate limit, instead a transition from shadow to antishadow scattering may by typical of the LHC energy scale.

The TOTEM Experiment at the CERN Large Hadron Collider

The TOTEM Experiment will measure the total pp cross-section with theluminosity-independent method and study elastic and diffractive scattering at the LHC. To achieve optimum forwardcoverage for charged particles emitted by the pp collisions in the interaction point IP5, two tracking telescopes, T1 and T2, will be installed on each sidein the pseudorapidity region 3.1 ⩽ |η| ⩽ 6.5, and Roman Pot stations will be placed at distances of ±147 m and ±220 m from IP5. Being an independent experiment but technically integrated into CMS, TOTEM will first operate in standalone mode to pursue its own physics programme and at a later stage together with CMS for a common physics programme.This article gives a description of the TOTEM apparatus and its performance.

The pp→K+ Σ +n cross-section from missing-mass spectra

We utilize existing inclusive data on K+-meson momentum spectra of the reaction pp→K + X at T p = 2.3-2.85GeV to deduce total cross-sections for pp→K + Σ + n. The method used to extract those cross-sections is explained and discussed in detail. Our result for T p = 2.85GeV is consistent with the data point from a direct measurement at the same beam energy. The cross-section obtained for T p = 2.3GeV is with 13.7±2.3μb considerably smaller than the value found in a recent experiment by the COSY-11 Collaboration at a somewhat lower beam energy, indicating that the pp→K + Σ + n reaction cross-section could exhibit a rather unusual energy dependence.

Investigation of the reaction pp → pK0π+Λ in search of the pentaquark

The reaction pp → pK0π+Λ has been studied with the ANKE spectrometer at COSY-Jülich at a beam momentum of 3.65 GeV/c in order to search for a possible signal of the pentaquark Θ+(1540), decaying into the pK0 system. By detecting four charged particles in the final state (π+, π− and two protons), the K0 and the Λ have been reconstructed to tag strangeness production. It has been found that the π+Λ missing-mass spectrum displays no significant signal expected from the Θ+(1540) excitation. The total cross section for the reaction pp → pK0π+Λ has been deduced, as well as an upper limit for the Θ+ production cross section. The intermediate Δ++K0Λ state seems to provide a significant contribution to the reaction.

ELASTIC SCATTERING AND THE PROTON FORM FACTOR

We use the QCD pomeron model proposed by Landshoff and Nachtmann to compute the differential and the total cross-sections for pp scattering in order to discuss a QCD-based approach to the proton form factor. This model is quite dependent on the experimental electromagnetic form factor, and it is not totally clear why this form factor gives good results even at moderate transferred momentum. We exchange the electromagnetic form factor by the asymptotic QCD proton form factor determined by Brodsky and Lepage (BL) plus a prescription for its low energy behavior dictated by the existence of a dynamically generated gluon mass. We fit the data with this QCD inspired form factor and a value for the dynamical gluon mass consistent with the ones determined in the literature. Our results also provide a determination of the proton wave function at the origin, which appears in the BL form factor.

Uncertainties in Air Showers from Small- x pQCD Mini-Jets

To investigate uncertainties in air shower simulations caused by the small-x regime, a model including leading-twist hard pQCD plus soft processes was built, which are separated by an energy dependent transverse momentum cut-off. We provide a fit of the cut-off to the total pp cross section for different PDFs using the eikonal formalism and show that for modern PDF sets there is only a small uncertainty in the mini-jet cross section, and hence in the finalstate multiplicity and the number of produced muons.

On the scale variation of the total cross section for Higgs production at the LHC and at the Tevatron

We present a detailed study of the total pp cross section for scalar Higgs production to next-to-next-to-leading order in αs at LHC energies, and of the pp̄ cross section at the Tevatron, combining an implementation of the solutions of the parton evolution equations at the three-loop order with the corresponding hard scatterings, evaluated at the same perturbative order. Our solutions of the DGLAP equations are implemented directly in x-space and allow for the study of the dependence of the results on the factorization (μF) and renormalization scales (μR) typical of a given process, together with the stability of the perturbative expansion. The input sets for the parton evolutions are those given by Martin, Roberts, Stirling and Thorne and by Alekhin. Results for K-factors are also presented. The NNLO corrections can be quite sizeable at typical collider energies. The stability region of the perturbative expansion is found when μR>mH∼μF.

The Elusive p-air cross section

For the \(\bar pp\) and pp systems, we have used all of the extensive data of the Particle Data Group [K. Hagiwara et al. (Particle Data Group), Phys. Rev. D 66, 010001 (2002)]. We then subject these data to a screening process, the “Sieve” algorithm [M. M. Block, physics/0506010], in order to eliminate “ outliers” that can skew a χ2 fit. With the “Sieve” algorithm, a robust fit using a Lorentzian distribution is first made to all of the data to sieve out abnormally high Δχ 2 i , the individual ith point’s contribution to the total χ2. The χ2 fits are then made to the sieved data. We demonstrate that we cleanly discriminate between asymptotic ln s and ln2 s behavior of total hadronic cross sections when we require that these amplitudes also describe, on average, low energy data dominated by resonances. We simultaneously fit real analytic amplitudes to the “sieved” high energy measurements of \(\bar pp\) and pp total cross sections and ρ-values for \(\sqrt s \) ≥ GeV, while requiring that their asymptotic fits smoothly join the the σ pp and σpp total cross sections at \(\sqrt s \) = 4.0 GeV—again both in magnitude and slope. Our results strongly favor a high energy ln2 s fit, basically excluding a ln s fit. Finally, we make a screened Glauber fit for the p-air cross section, using as input our precisely-determined pp cross sections at cosmic ray energies.

Kaon pair production close to threshold

The total cross section of the reaction pp→ppK+K− has been measured at excess energies Q=10 MeV and 28 MeV with the magnetic spectrometer COSY-11. The new data show a significant enhancement of the total cross section compared to pure phase space expectations or calculations within a one boson exchange model. In addition, we present invariant mass spectra of two particle subsystems. While the K+K− system is rather constant for different invariant masses, there is an enhancement in the pK− system towards lower masses which could at least be partially connected to the influence of the Λ(1405) resonance.

Searching for Extremely High-Energy Behavior from Accelerator-Energy Regions

We use rich information on πp total cross sections below N(∼10 GeV) in addition to high-energy data in order to discriminate whether these cross sections increase like log v or log 2 v at high energies. A finite-energy sum rule (FESR) which is derived in the spirit of the P sum rule as well as the n=1 moment FESR have been required to constrain the high-energy parameters. We then searched for the best fit of σ (+) tot above 70 GeV in terms of high-energy parameters constrained by these two FESR. We have shown from this analysis that the log 2 v behavior are preferred to the log v behavior. We also propose to search for pp, pp total cross sections at extremely high-energy from accelerator-energy regions using the similar technique.

The TOTEM experiment

TOTEM will measure the total pp cross-section at LHC by using a luminosity independent method based on simultaneous evaluation of the total elastic and inelastic rates. For an extended coverage of the inelastic and diffractive events, two forward tracking telescope are employed. The elastically or diffractively scattered protons are measured by a set of special detectors, which can be moved close to the circulating protons beams. The paper describes the physics reach of the experiment and the detectors which are being considered.

Nucleon-nucleon, γp and γγ scattering using factorization: the Aspen model and analytic amplitude analysis

Using the Aspen, model, a QCD-inspired eikonal model, we fit high energy nucleon-nucleon total cross sections, nuclear slopes and ϱ-values, including cosmic ray p-air data. This model which is crossing symmetric, insures unitarity and analyticity, as well as satisfying the Froissrt bound. Assuming that the ratio of σelastic/σtotal is independent of process, the Aspen model predicts factorization. Utilizing the model parameters found for nucleon-nucleon scattering, we predict the total cross sections and nuclear slope parameters for γp reactions, as well as total cross sections for γγ scattering, by invoking the naive quark model and vector dominance. In particular, by making a χ2 fit to the nuclear slope parameters for the ‘elastic’ reactions γ + p → ϱ+p, γ+p → φ+p, γ+p → ω+p, we find the proportionality constant κ = 0.661±0.008, in excellent agreement with the value of κ = 23 predicted by the naive vector quark model (2 quarks in the vector meson-like photon and 3 quarks in the nucleon). We next test the (lack of) sensitivity of the factorization theorems to the assumed distributions of the impact parameter b, for nucleon-nucleon, γp and γγ scattering, that are used in the eikonal. Finally, making an independent analysis utilizing real analytical amplitudes and assuming factorization, we make a simultaneous fit to the total cross sections for pp, pp, γp and γγ cross sections, as well as the ϱ-values for pp and pp. In this global fit we separately fit to the results of L3 and OPAL obtained using either the PHOJET or PYTHIA Monte Carlo program—the published values use the average of the two. It should be noted that these two Monte Carlos give different normalizations as well as different energy behaviors. The overall fit is good using PHOJET and poor using PYTHIA, lending strong support for the factorization hypothesis, as well as the naive quark model and vector dominance.

Rho(0) meson production in the pp-->pppi(+)pi(-) reaction at 3.67 GeV/c.

Total and differential cross sections for the exclusive reaction pp-->pp rho observed via the pi(+)pi(-) decay channel have been measured at p(beam)=3.67 GeV/c. The observed total meson production cross section is determined to be (23.4+/-0.8+/-8) mu b and is significantly lower than typical cross sections used in model calculations for heavy-ion collisions. The differential cross sections measured indicate a strong anisotropy (approximately cos(theta(CM)(rho)) in the rho(0) meson production.

Total cross-section from particle accelerators, colliders, and cosmic ray phenomena: Some new global fits

The total cross-sections in high energy hadronic collisions constitute a crucial physical observable in the areas of both particle physics and cosmic ray physics phenomena. In fact, this acts as the linking bridge between these two fields of persistent studies—both experimental and theoretical. In the present work we aim at providing some global and excellent fits to the latest available data on PP total cross-sections from the viewpoint of two phenomenological models. The fits would then be compared and discussed.

S-wave η′-proton FSI; phenomenological analysis of near-threshold production of π0, η, and η′ mesons in proton-proton collisions

We describe a novel technique for comparing total cross sections for the reactions pp→ ppπ 0, pp→ ppη, and pp→ ppη′ close to threshold. The initial and final state proton-proton interactions are factored out of the total cross section, and the dependence of this reduced cross section on the volume of phase space is discussed. Different models of the proton-proton interaction are compared. We argue that the scattering length of the S-wave η′-proton interaction is of the order of 0.1 fm.

Leptoquark contribution to Higgs boson production at the CERN LHC

In this report we study how a light-scalar leptoquark could affect the Higgs boson production cross-section at the LHC collider. We construct the most general renormalizable and gauge invariant effective Lagrangian involving the standard model particles and a scalar, isoscalar leptoquark, \eta. The total cross-section for pp -> H+X is then calculated for different values of the unknown parameters \lambda_eta, m_eta and m_H.(Here \lambda_eta is the coupling associated with the Higgs-leptoquark interaction.) We find that if \lambda_eta is moderately large and m_eta is around a few hundred GeV, then the cross-section is significantly larger than the standard model value.

K − meson production in the proton–proton reaction at 3.67 GeV/ c

The total cross section of the reaction pp→ ppK + K − has been determined for proton–proton reactions with p beam =3.67 GeV/c . This represents the first cross section measurement of the pp→ ppK − K + channel near threshold, and is equivalent to the inclusive pp→ ppK − X cross section at this beam momentum. The cross section determined at this beam momentum is about a factor 20 lower than that for inclusive pp→ ppK + X meson production at the same CM energy above the corresponding threshold. This large difference in the K + and K − meson inclusive production cross sections in proton-proton reactions is in strong contrast to cross sections measured in sub-threshold heavy ion collisions, which are similar in magnitude at the same energy per nucleon below the respective thresholds.

New measurements of the [formula omitted] annihilation cross section at very low energy

The pp total annihilation cross section has been measured at four values of the p ̄ incident momentum, between 70 MeV/c and 38 MeV/c, with the Obelix apparatus at LEAR. The new measurements are in agreement with the trend of previous measurements of the pp total annihilation cross section at low energy, performed by the Obelix experiment [A. Bertin et al., Phys. Lett. B 369 (1996) 77; A. Benedettini et al., Nucl. Phys. B (Proc. Suppl.) 56A (1997) 58], as well as with a fit of the latter data based on a low energy expansion of the scattering amplitude [J. Carbonell, K.V. Protasov, A. Zenoni, Phys. Lett. B 397 (1997) 345]. The departure of the annihilation cross section from a smooth behaviour, suggested by a previous measurement of the cross section around 44 MeV/c [A. Bertin et al., Phys. Lett. B 369 (1996) 77], is not confirmed by the new data.