The total photon deuteron hadronic cross section in the energy range 0.265–4.215 GeV

The total cross section for photoproduction of hadrons on the deutron, σ_T^d, has been measured for photon energies in the range 0.265–40215 GeV. From this, using results for the photon total cross section, obtained previously with the same apparatus, the neutron total cross section has been determined in the resonance region. The resonant structure is found to be quite different from that for the proton. Thereafter the neutron cross section falls off steadily with energy, and the values obtained are consistently lower than those for the proton. Forward scattering amplitudes have been evaluated for the deuteron.     

A measurement of the photonuclear interactions of 180 GeV muons in iron

The energy spectrum and the cross section of photonuclear interactions of 180 GeV muons in iron were measured at the CERN SPS using prototype modules of the ATLAS hadron calorimeter. The differential cross section for a muon fractional energy loss was measured in the range 0.1<v<1. The integrated cross section is cm²g^-1 in agreement with the theoretical prediction of cm²g^-1. The best adjustment of the data to the theory is achieved for the value of of the photon-nucleon cross section for photons with energies in the range from 18 to 180 GeV. Received: 22 January 2003 / Published online: 5 May 2003     

A-dependence of the charm production cross section in 300 GeV/c proton interactions

The A-dependence of the charm production cross section is determined by measuring the yield of prompt single muons in a beam-dump experiment, using a 300 GeV/c proton beam on Al, Fe, and U targets. Assuming that the production cross section varies as A^α, we obtain α(μ⁺) = 0.79±0.12 and α(μ⁻) = 0.76±0.13 in the kinematical region x_F≳0.1 of the charm.     

The energy dependence of nuclear reaction cross sections

The reaction cross section σ_R^pA(E) for proton-nucleus collisions varies with energy as the total cross section σ_t^pN(E) does for proton-nucleon scattering in the energy regime 100 MeV ? E ?400 GeV. We propose several empirical relations, and test them by a χ² analysis of various data. Within the framework of Glauber theory, the parameters in the relations can be linked to the cross section for a single inelastic collision.     

Measurement of elastic J/ψ photoproduction at HERA

The reaction γ p → J/ψ p has been studied in ep interactions using the ZEUS detector at HERA. The cross section for elastic J/ψ photoproduction has been measured as a function of the photon-proton centre of mass energy W in the range 40 < W < 140 GeV at a median photon virtuality Q ² of 5 × 10^?5 GeV². The photoproduction cross section, σ_{γp→ J/ψp}, is observed to rise steeply with W. A fit to the data presented in this paper to determine the parameter δ in the form σ_{γp→ J/ψp} α W ^δ yields the value δ = 0.92±0.14±0.10. The differential cross section dσ/d ¦t¦is presented over the range ¦t¦< 1.0 GeV² where t is the square of the four-momentum exchanged at the proton vertex. dσ/d ¦t¦falls exponentially with a slope parameter of $4.6pm 0.4_{-0.6}^{+0.4} {? GeV}^{-2}$. The measured decay angular distributions are consistent with s-channel helicity conservation.     

Inclusive production of D-mesons in e+e− annihilation at 7 GeV

Inclusive momentum and energy spectra of neutral and charged D-mesons produced in e⁺e^? annihilation at energies near 7 GeV are presented. The slope of the energy spectrum is similar to the charged pion spectrum at the same energy. The inclusive cross section σ(e⁺e^?→ D or $\text{D}$ + anything) at 7 GeV is 4.8±1.3 nb.     

Absolute photofission cross section of 209Bi in the energy range from 40 to 65 MeV

The absolute photofission cross section of ²⁰⁹Bi has been measured with monoenergetic γ-radiation between 40 and 65 MeV photon energy. Cross-section data have been obtained with an accuracy between 9 and 20%. The experimental result is compared with the excitation function calculated on the basis of the statistical model. In order to reproduce the measured data on σ_γf, the (γ, n) cross section must decrease with increasing photon energy faster than the experimental total (γ, n) cross section. This behaviour can possibly be explained by the assumption that after photon absorption a compound nucleus is formed only for a small, and with photon energy decreasing, fraction of all decays.     

Diffractive proteon fragmentation in 16, 32, and 110 GeV/cK − p interactions and the diffractive production of heavy quarks(s\bar s,c\bar c)

The inclusive proton diffraction dissociation cross sections in 16, 32, and 110 GeV/cK ^? p interactions are determined from the spike nearx=1 in the inclusive negative particle spectra and are compared to those obtained inK?p interactions using other selection methods at various energies. The same procedure is applied to events containing aV ⁰ in order to obtain the cross section for diffractive \(s\bar s\) production. While the total cross section for proton diffraction is found to be approximately constant in the energy range studied here, proton diffraction yielding an \(s\bar s - pair\) is found to increase significantly. In particular it is almost constant at 85 μb forΛ ⁰ and Σ production but for \(NK\bar K\) it rises from zero at 16 GeV.c to about 200 μb at 110 GeV/c. From the result for \(s\bar s\) diffractive production an estimate for the \(c\bar c\) diffractive production cross section of approximately 1–10 μb at 110 GeV/c is obtained.     

微扰QCD对Drell-Yan过程能量损失效应的修正

利用Glauber模型以及DGLAP方程下的核内核子的部分子分布函数, 在次领头阶QCD下计算了Drell-Yan过程中的能量损失效应, 计算表明QCD修正并不能改善理论结果与试验结果的符合, 尤其是p-W与p-Be以x₁为变量的微分截面比. 原因是所用的核内核子部分子的分布函数是以领头阶近似为基础并通过演化方程得到的. 于是利用在次领头阶微扰QCD下得到的核遮蔽效应核内核子的部分子分布函数重新计算了次领头阶QCD修正对Drell-Yan过程能量损失的贡献. 计算结果表明康普顿散射过程与湮没过程中应该有更多的能量损失.     

Experimental investigation of ρ<Superscript>0</Superscript> photoproduction on the pion in the H1 experiment

Experimental results on quasielastic photoproduction of the ρ⁰ meson in association with a neutron, obtained at the HERA collider, are presented. The total and differential cross sections of the γp → ρ⁰ nπ⁺ reaction at the positron–proton center-of-mass energy of √s =319 GeV are measured. The data collected with the H1 detector in 2006 and 2007 correspond to an integrated luminosity of 1.16 pb^?1. The kinematic region of the photon–proton cms energy of 20 < W _γp <100 GeV, photon virtuality of Q ² < 2 GeV², and the ρ⁰ transverse momentum below 1 GeV/c is analyzed. Secondary neutrons with energies x _L > 0.35 (in proton-energy units) and emission angles below 0.75 mrad are selected. The model of double peripheral exchange, in which the ρ⁰ is elastically produced via the photon interaction with the virtual pion from the proton–neutron vertex, is employed for interpreting the results. The cross section for the ρ⁰ elastic photoproduction on the pion, γπ⁺→ ρ⁰π⁺, is extracted in the one-pion-exchange approximation. The magnitude of the cross section suggests that the γp → ρ⁰ nπ⁺ reaction is significantly affected by absorption.     

Detection of the production and decays of neutral charmed mesons in proton-nucleus interactions at 70 GeV with the SVD-2 facility

The results of processing the data of the SERP-E-184 experiment that studied mechanisms of the production of charmed particles in proton-nucleus interactions at 70 GeV and their decays are reported. The data were obtained in irradiating the SVD-2 active target consisting of carbon, silicon, and lead plates with a proton beam of energy 70 GeV. A signal from the two-body decay of neutral charmed mesons D ⁰ and Ď ⁰ is separated. The signal-to-background ratio is (51 ± 17)/(38 ± 13). A detailed simulation of relevant processes on the basis of the FRITIOF and GEANT codes made it possible to find meson-detection efficiencies and to evaluate the charm-production cross section at this energy: σ(c ĉ) = 7.1 ± 2.4(stat.) ± 1.4(syst.) μb/nucleon.     

Measurement of elastic ω photoproduction at HERA ZEUS Collaboration

The reaction γp →ωp(ω → π⁺π^?π⁰ and π⁰ → γ γ) has been studied in ep interactions using the ZEUS detector at photon-proton centre-of-mass energies between 70 and 90GeV and ∣t∣ < 0.6GeV², where t is the squared four momentum transferred at the proton vertex. The elastic ω photoproduction cross section has been measured to be σ_{γp → ωp} = 1.21 ±0.12 ±0.23 μb. The differential cross section dσ_γp→ωp/d¦t¦ has an exponential shape e^?b∣t∣ with a slope b =10.0 ± 1.2 ± 1.3 GeV^?2. The angular distributions of the decay pions are consistent with s-channel helicity conservation. When compared to low energy data, the features of ω photoproduction as measured at HERA energies are in agreement with those of a soft diffractive process. Previous measurements of the ρ⁰ and ? photoproduction cross sections at HERA show a similar behaviour.     

Experimental study of the photoemission of protons off12C using tagged photons in the energy range 200–385 MeV

Data are presented for proton emission off¹²C using tagged photons in the energy range 200–385 MeV. The protons are detected in a magnetic spectrometer. In addition, charged or neutral particles can be measured with a scintillation counter setup. Contributions to the proton energy spectra from primary pion production and quasideuteron reactions are separated using the coincidence data. The total¹²C(γ, p)X cross section is derived as a function of the photon energy. The data are compared to the predictions of an intranuclear cascade calculation. Final state interactions have to be taken into account to describe the data.     

Positron production by muon neutrinos BEBC filled with a neon-hydrogen mixture

For e⁺ energy > 0.3 GeV and 10 GeV < visible energy < 100 GeV we find that: (i) $\text{? = (v}{}_{\mathrm{\mu }}\text{+}\text{Ne}\text{→ μ}{}^{\mathrm{?}}\text{e}{}^{\mathrm{+}}\text{)/(v}{}_{\mathrm{\mu }}\text{+}\text{Ne}\text{→ μ}{}^{\mathrm{?}}\text{) = (0.41 ± 0.15)\%}$; (ii) 1.2 ± 0.5 neutral strange particles are produced per μ^?e⁺ event; (iii) the lifetime of possible positron-parent particles is < 3 × 10^?10 s (90% C.L.); (iv) the cross section for direct e⁺ production via the neutral current is < 0.2 times that via the charged current (90% C.L.); (v) the cross section for producing heavy leptons, L⁺, decaying into e⁺ … is < 0.7 × 10^?3 times that for μ^?production, implying M(L⁺) > 10 GeV.     

Is there an excess of electron neutrinos in the atmospheric flux?

Summary The background produced by isolated neutrons in Cherenkov detectors studying the atmospheric neutrinos is discussed. The neutrons are generated in nuclear showers initiated by muons in the rock surrounding the detectors. It is shown that, taking into account the detection of π⁰ events from reactions of nA→π⁰X, which look likev _e detection, results in an observedI(v _μ)/I(v _e) ratio close to the expected one for the energy range 0.2–5 GeV.     

Inclusive photoproduction of neutral pions in the photon hemisphere at HERA

The inclusive cross section for the photoproduction of neutral pions has been measured as a function of the transverse momentum, rapidity, and Feynman x of the mesons at an average photon–proton centre-of-mass energy of 208 GeV and for photon virtualities below GeV. The measurement extends the range covered by previous charged particle measurements at HERA by two units of rapidity in the photon direction down to a value of in the centre-of-mass frame. The transverse momentum distribution is well described over the whole measured range by a power law ansatz, while an exponential fit falls below the data at transverse momentum values above 1.5 GeV/c. Good agreement with the predictions of the Monte Carlo models PYTHIA and PHOJET is found. In the context of the PYTHIA model the data are inconsistent with large intrinsic transverse momentum values in the photon. Received: 14 June 2000 / Published online: 27 November 2000     

A total energy trigger at large angles used in a calorimetric study of 150 GeV and 300 GeV pion and proton interactions on hydrogen

Hard hadronic scattering was studied by selecting 150 GeV and 300 GeV π^?p and pp events with large energy in a 240 cell calorimeter covering 452 to 1352 in the c.m.s. polar angle and the full 2π azimuth. A downstream calorimeter measured the remaining energy flow at smaller angles. For large energy deposited in the segmented calorimeter the proton induced cross section drops below the pion induced cross section, as expected in a constituent scattering picture. However, neither a simple energy scaling of the cross section nor a dominant jet structure of the events is observed. No evidence was found for recently proposed higher-twist mechanisms leading to events     

Observation of the two photon cascade 3.7 → 3.1 + γγ via an intermediate state Pc

The two photon cascade decay of the 3.7 GeV resonance into the 3.1 GeV resonance has been observed in two nearly independent experiments. The clustering of the photon energies around 160 MeV and 420 MeV observed in the channel 3.7 → (3.1 → μ⁺μ^?) + γγ indicates the existence of at least one intermediate state with even charge conjugation at a mass around 3.52 GeV or 3.26 GeV.     

Elastic electroproduction of \rho mesons at HERA

The elastic electroproduction of mesons is studied at HERA with the H1 detector for a photon virtuality in the range and for a hadronic centre of mass energy in the range GeV. The shape of the () mass distribution in the resonance region is measured as a function of . The full set of spin density matrix elements is determined, and evidence is found for a helicity flip amplitude at the level of of the non-flip amplitudes. Measurements are presented of the dependence of the cross section on , W and t (the four-momentum transfer squared to the proton). They suggest that, especially at large , the cross section develops a stronger W dependence than that expected from the behaviour of elastic and total hadron–hadron cross sections. Received: 22 February 1999 / Published online: 25 February 2000     

Small-angle photon scattering on complex nuclei

Photons of 3 GeV and 5 GeV were scattered on 7 different elements, ranging from Be to Au, and detected with a pair spectrometer. The angular distributions show diffractive patterns consistent with known nuclear sizes. Forward cross sections are 20–30% lower than expected from an A² dependence. This shadowing effect is qualitatively explained by photon interactions via intermediate hadronic states.