We have searched for the production of a selectron and a squark in
e
+
p collisions at a center-of-mass energy of 300 GeV using the ZEUS detector at HERA. The selectron and squark are sought in the ...direct decay into the lightest neutralino in the framework of supersymmetric extensions to the Standard Model which conserve
R-parity. No evidence for the production of supersymmetric particles has been found in a data sample corresponding to 46.6 pb
−1 of integrated luminosity. We express upper limits on the product of the cross section times the decay branching ratios as excluded regions in the parameter space of the Minimal Supersymmetric Standard Model.
The production of φ mesons in the reaction
e
+
p →
e
+
φp (
φ →
K
+
K
−), for
7 <
Q
2 < 25
GeV
2
and virtual photon-proton centre of mass energies (
W) in the range 42–134 GeV, has been studied with ...the ZEUS detector at HERA. When compared to lower energy data at similar
Q
2, the results show that the
γ
∗p → φp
cross section rises strongly with
W. This behaviour is similar to that previously found for the
γ
∗p → ϱ
0p
cross section. This strong dependence cannot be explained by production through soft pomeron exchange. It is, however, consistent with perturbative QCD expectations, where it reflects the rise of the gluon momentum density in the proton at small
x. The ratio of
σ(φ)
σ(ϱ
0)
, which has previously been determined by ZEUS to be 0.065 ± 0.013 (stat.) in photoproduction at a mean
W of 70 GeV, is measured to be 0.18 ± 0.05 (stat.) ± 0.03 (syst.) at a mean
Q
2 of 12.3 GeV
2 and mean
W of ≈ 100 GeV and is thus approaching at large
Q
2 the value of
2
9
predicted from the quark charges of the vector mesons and a flavour independent production mechanism.
Spinal cord segmentation in the dog Salazar, I; Troconiz, P F; Ruiz Pesini, P ...
Trabajos del Instituto Cajal,
1984, Letnik:
75, Številka:
1-4
Journal Article
PDF
