The ZEUS detector has been used to study dissociation of virtual photons in events with a leading proton, \(\gamma^{*} p \to X p\), in e + p collisions at HERA. The data cover photon virtualities in ...two ranges, 0.03 < Q2 < 0.60 GeV2 and 2 < Q2 < 100 GeV2, with MX > 1.5 GeV, where MX is the mass of the hadronic final state, X. Events were required to have a leading proton, detected in the ZEUS leading proton spectrometer, carrying at least 90% of the incoming proton energy. The cross section is presented as a function of t, the squared four-momentum transfer at the proton vertex, \(\Phi\), the azimuthal angle between the positron scattering plane and the proton scattering plane, and Q2. The data are presented in terms of the diffractive structure function, \(F_2^{\smasht{D(3)}}\). A next-to-leading-order QCD fit to the higher-Q2 data set and to previously published diffractive charm production data is presented.
At COSY pp-bremsstrahlung was measured at a beam momentum of 797 MeV/c using an external proton beam. Data were taken with a wide angle spectrometer covering a solid angle of approximately 1 sr. The ...complete data set is presented in a series of c.m. angular distributions as well as a single Dalitz plot. The absence of final state interaction effects is understood as being due to a general insensitivity of the pp
γ reaction to the spin-singlet component of the NN interaction. Coplanar angular distributions (in the laboratory system) are well reproduced by recent model calculations; also good agreement is found with the original TRIUMF data K. Michaelian et al., Phys. Rev. D 41 (1990) 286 when omitting the rescaling factor of 2/3.
Several available codes for hadronic event generation and shower simulation are discussed and their predictions are compared to experimental data in order to obtain a satisfactory description of ...hadronic processes in Monte Carlo studies of detector systems for medium energy experiments. The most reasonable description is found for the intra-nuclear-cascade (INC) model of Bertini which employs microscopic description of the INC, taking into account elastic and inelastic pion–nucleon and nucleon–nucleon scattering. The isobar model of Sternheimer and Lindenbaum is used to simulate the inelastic elementary collisions inside the nucleus via formation and decay of the
Δ
33-resonance which, however, limits the model at higher energies.
To overcome this limitation, the INC model has been extended by using the resonance model of the HADRIN code, considering all resonances in elementary collisions contributing more than 2% to the total cross-section up to kinetic energies of 5
GeV. In addition, angular distributions based on phase shift analysis are used for elastic nucleon–nucleon as well as elastic and charge exchange pion–nucleon scattering. Also kaons and antinucleons can be treated as projectiles. Good agreement with experimental data is found predominantly for lower projectile energies, i.e. in the regime of the Bertini code.
The original as well as the extended Bertini model have been implemented as shower codes into the high energy detector simulation package GEANT-3.14, allowing now its use also in full Monte Carlo studies of detector systems at intermediate energies. The GEANT-3.14 here have been used mainly for its powerful geometry and analysing packages due to the complex EDDA detector system.
The production of neutrons carrying at least 20% of the proton beam energy (
x
L
>
0.2
) in
e
+
p collisions has been studied with the ZEUS detector at HERA for a wide range of
Q
2, the photon ...virtuality, from photoproduction to deep inelastic scattering. The neutron-tagged cross section,
ep→
e′
Xn, is measured relative to the inclusive cross section,
ep→
e′
X, thereby reducing the systematic uncertainties. For
x
L> 0.3, the rate of neutrons in photoproduction is about half of that measured in hadroproduction, which constitutes a clear breaking of factorisation. There is about a 20% rise in the neutron rate between photoproduction and deep inelastic scattering, which may be attributed to absorptive rescattering in the
γp system. For 0.64<
x
L<0.82, the rate of neutrons is almost independent of the Bjorken scaling variable
x and
Q
2. However, at lower and higher
x
L values, there is a clear but weak dependence on these variables, thus demonstrating the breaking of limiting fragmentation. The neutron-tagged structure function,
F
LN(3)
2(
x,
Q
2,
x
L), rises at low values of
x in a way similar to that of the inclusive
F
2(
x,
Q
2) of the proton. The total
γπ cross section and the structure function of the pion,
F
π
2(
x
π
,
Q
2) where
x
π
=
x/(1−
x
L), have been determined using a one-pion-exchange model, up to uncertainties in the normalisation due to the poorly understood pion flux. At fixed
Q
2,
F
π
2 has approximately the same
x dependence as
F
2 of the proton.
A search for single-top production, ep→etX, has been made with the ZEUS detector at HERA using an integrated luminosity of 130.1pb−1. Events from both the leptonic and hadronic decay channels of the ...W boson resulting from the decay of the top quark were sought. For the leptonic mode, the search was made for events with isolated high-energy leptons and significant missing transverse momentum. For the hadronic decay mode, three-jet events in which two of the jets had an invariant mass consistent with that of the W were selected. No evidence for top production was found. The results are used to constrain single-top production via flavour-changing neutral current (FCNC) transitions. The ZEUS limit excludes a substantial region in the FCNC tuγ coupling not ruled out by other experiments.
— A purely physical model is presented describing the depth‐ and size‐dependence of the production of cosmogenic nuclides in meteoroids with radii up to 85 cm and in planetary surfaces by galactic ...cosmic ray protons. The model is based on Monte Carlo calculations of the intra‐ and internuclear cascades, by which depth‐ and size‐dependent spectra of primary and secondary protons and of secondary neutrons are derived, and on experimental and theoretical thin‐target cross sections of the underlying nuclear reactions. Model calculations are presented for production rates of 53Mn, 26Al, 22Ne, and 21Ne in H‐ and L‐chondrites and of 53Mn and 26Al in lunar surface material and compared with experimental data. From the analysis of 53Mn and 26Al in the Apollo 15 lunar drill core and in the L‐chondrite Knyahinya GCR p‐spectra and integral particle fluxes at 1 A.U. and in the meteoroid orbits averaged over the last 10 Ma are derived. An analysis of experimental depth profiles in four H‐ and L‐chondrites demonstrates, that the new model is well capable of describing depth‐ and size‐dependences of production rates of cosmogenic nuclides. Moreover, it is possible to determine exposure ages for these meteorites on the basis of the theoretical 21Ne production rates. The model calculations further explain the depth‐ and size‐dependence of 22Ne/21Ne‐ratios and the dependences on these ratios of 21Ne, 26Al and 53Mn production rates. The future requirements for model calculations of cosmogenic nuclide production rates in extraterrestrial matter are outlined.
The beauty production cross section for deep inelastic scattering events with at least one hard jet in the Breit frame together with a muon has been measured, for photon virtualities Q2>2 GeV2, with ...the ZEUS detector at HERA using integrated luminosity of 72 pb−1. The total visible cross section is σbb¯(ep→e jet μX)=40.9±5.7(stat.)−4.4+6.0(syst.) pb. The next-to-leading order QCD prediction lies about 2.5 standard deviations below the data. The differential cross sections are in general consistent with the NLO QCD predictions; however at low values of Q2, Bjorken x, and muon transverse momentum, and high values of jet transverse energy and muon pseudorapidity, the prediction is about two standard deviations below the data.
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