The exclusive deep inelastic electroproduction of ψ(2S) and J/ψ(1S) at an ep centre-of-mass energy of 317 GeV has been studied with the ZEUS detector at HERA in the kinematic range 2<Q2<80 GeV2, ...30<W<210 GeV and |t|<1 GeV2, where Q2 is the photon virtuality, W is the photon–proton centre-of-mass energy and t is the squared four-momentum transfer at the proton vertex. The data for 2<Q2<5 GeV2 were taken in the HERA I running period and correspond to an integrated luminosity of 114 pb−1. The data for 5<Q2<80 GeV2 are from both HERA I and HERA II periods and correspond to an integrated luminosity of 468 pb−1. The decay modes analysed were μ+μ− and J/ψ(1S)π+π− for the ψ(2S) and μ+μ− for the J/ψ(1S). The cross-section ratio σψ(2S)/σJ/ψ(1S) has been measured as a function of Q2,W and t. The results are compared to predictions of QCD-inspired models of exclusive vector-meson production.
The photoproduction of isolated photons, both inclusive and together with a jet, has been measured with the ZEUS detector at HERA using an integrated luminosity of 374 pb−1. Differential cross ...sections are presented in the isolated-photon transverse-energy and pseudorapidity ranges 6<ETγ<15 GeV and −0.7<ηγ<0.9, and for jet transverse-energy and pseudorapidity ranges 4<ETjet<35 GeV and −1.5<ηjet<1.8, for exchanged-photon virtualities Q2<1 GeV2. Differential cross sections are also presented for inclusive isolated-photon production as functions of the transverse energy and pseudorapidity of the photon. Higher-order theoretical calculations are compared to the results.
A search for a narrow baryonic state in the pKS0 and p‾KS0 system has been performed in ep collisions at HERA with the ZEUS detector using an integrated luminosity of 358pb−1 taken in 2003–2007. The ...search was performed with deep inelastic scattering events at an ep centre-of-mass energy of 318GeV for exchanged photon virtuality, Q2, between 20 and 100GeV2. Contrary to evidence presented for such a state around 1.52 GeV in a previous ZEUS analysis using a sample of 121 pb−1 taken in 1996–2000, no resonance peak was found in the p(p‾)KS0 invariant-mass distribution in the range 1.45–1.7 GeV. Upper limits on the production cross section are set.
A combination is presented of all inclusive deep inelastic cross sections previously published by the H1 and ZEUS collaborations at HERA for neutral and charged current
e
±
p
scattering for zero beam ...polarisation. The data were taken at proton beam energies of 920, 820, 575 and 460 GeV and an electron beam energy of 27.5 GeV. The data correspond to an integrated luminosity of about 1 fb
-
1
and span six orders of magnitude in negative four-momentum-transfer squared,
Q
2
, and Bjorken
x
. The correlations of the systematic uncertainties were evaluated and taken into account for the combination. The combined cross sections were input to QCD analyses at leading order, next-to-leading order and at next-to-next-to-leading order, providing a new set of parton distribution functions, called HERAPDF2.0. In addition to the experimental uncertainties, model and parameterisation uncertainties were assessed for these parton distribution functions. Variants of HERAPDF2.0 with an alternative gluon parameterisation, HERAPDF2.0AG, and using fixed-flavour-number schemes, HERAPDF2.0FF, are presented. The analysis was extended by including HERA data on charm and jet production, resulting in the variant HERAPDF2.0Jets. The inclusion of jet-production cross sections made a simultaneous determination of these parton distributions and the strong coupling constant possible, resulting in
α
s
(
M
Z
2
)
=
0.1183
±
0.0009
(
exp
)
±
0.0005
(
model
/
parameterisation
)
±
0.0012
(
hadronisation
)
-
0.0030
+
0.0037
(
scale
)
. An extraction of
x
F
3
γ
Z
and results on electroweak unification and scaling violations are also presented.
The production of the excited charm mesons D1(2420) and D2⁎(2460) in ep collisions has been measured with the ZEUS detector at HERA using an integrated luminosity of 373 pb−1. The masses of the ...neutral and charged states, the widths of the neutral states, and the helicity parameter of D1(2420)0 were determined and compared with other measurements and with theoretical expectations. The measured helicity parameter of the D10 allows for some mixing of S- and D-waves in its decay to D⁎±π∓. The result is also consistent with a pure D-wave decay. Ratios of branching fractions of the two decay modes of the D2⁎(2460)0 and D2⁎(2460)± states were measured and compared with previous measurements. The fractions of charm quarks hadronising into D1 and D2⁎ were measured and are consistent with those obtained in e+e− annihilations.
The production of Z0 bosons in the reaction ep→eZ0p(⁎), where p(⁎) stands for a proton or a low-mass nucleon resonance, has been studied in ep collisions at HERA using the ZEUS detector. The analysis ...is based on a data sample collected between 1996 and 2007, amounting to 496 pb−1 of integrated luminosity. The Z0 was measured in the hadronic decay mode. The elasticity of the events was ensured by a cut on ηmax<3.0, where ηmax is the maximum pseudorapidity of energy deposits in the calorimeter defined with respect to the proton beam direction. A signal was observed at the Z0 mass. The cross section of the reaction ep→eZ0p(⁎) was measured to be σ(ep→eZ0p(⁎))=0.13±0.06(stat.)±0.01(syst.) pb, in agreement with the Standard Model prediction of 0.16 pb. This is the first measurement of Z0 production in ep collisions.
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