A search for stop production in R-parity-violating supersymmetry has been performed in e+p interactions with the ZEUS detector at HERA, using an integrated luminosity of 65 pb-1. At HERA, the ...R-parity-violating coupling λ’ allows resonant squark production, \(e^+d\to\tilde{q}\). Since the lowest-mass squark state in most supersymmetry models is the light stop, \(\tilde{t}\), this search concentrated on production of \(\tilde{t}\), followed either by a direct R-parity-violating decay, or by the gauge decay to \(b\tilde{\chi}^+_{1}\). No evidence for stop production was found and limits were set on λ’131 as a function of the stop mass in the framework of the minimal supersymmetric standard model. The results have also been interpreted in terms of constraints on the parameters of the minimal supergravity model.
Beauty production in deep inelastic scattering with events in which a muon and a jet are observed in the final state has been measured with the ZEUS detector at HERA using an integrated luminosity of ...114 pb
−1
. The fraction of events with beauty quarks in the data was determined using the distribution of the transverse momentum of the muon relative to the jet. The cross section for beauty production was measured in the kinematic range of photon virtuality,
Q
2
>2 GeV
2
, and inelasticity, 0.05<
y
<0.7, with the requirement of a muon and a jet. Total and differential cross sections are presented and compared to QCD predictions. The beauty contribution to the structure function
F
2
was extracted and is compared to theoretical predictions.
The photon–proton total cross section has been measured in the process
e
+
p→
e
+
γp→
e
+
X with the ZEUS detector at HERA. Events were collected with photon virtuality
Q
2<0.02 GeV
2 and average
γp ...center-of-mass energy
W
γp
=209 GeV in a dedicated run, designed to control systematic effects, with an integrated luminosity of 49 nb
−1. The measured total cross section is
σ
tot
γp
=174±1 (stat.)±13 (syst.) μb. The energy dependence of the cross section is compatible with parameterizations of high-energy
pp and
p
p
̄
data.
The production and semi-leptonic decay of heavy quarks have been studied in the photoproduction process \(e^+p \rightarrow e^+ + \mbox{dijet} + e^- + X\) with the ZEUS detector at HERA using an ...integrated luminosity of 38.5 pb\(^{-1}}\). Events with photon-proton centre-of-mass energies, \(W_{\gamma p}\), between 134 and 269 GeV and a photon virtuality, \(Q^2\), less than 1 GeV\(^2\) were selected requiring at least two jets of transverse energy \(E_T^{\rm jet1(2)} >7(6)\) GeV and an electron in the final state. The electrons were identified by employing the ionisation energy loss measurement. The contribution of beauty quarks was determined using the transverse momentum of the electron relative to the axis of the closest jet, \(p_T^{\rm rel}\). The data, after background subtraction, were fit with a Monte Carlo simulation including beauty and charm decays. The measured beauty cross section was extrapolated to the parton level with the b quark restricted to the region of transverse momentum \(p_T^{b} > p_T^{\rm min} =\) 5 GeV and pseudorapidity \(|\eta^{b}| <\) 2. The extrapolated cross section is \(1.6 \pm 0.4 (stat.)^{+0.3}_{-0.5} (syst.) ^{+0.2}_{-0.4} (ext.) \mbox{nb}\). The result is compared to a perturbative QCD calculation performed to next-to-leading order.
The production of D super(c)- and D super(0)-mesons has been measured with the ZEUS detector at HERA using an integrated luminosity of 133.6 pb super(-1). The measurements cover the kinematic range ...5<Q super(2)<1000 GeV super(2), 0.02<y<0.7, 1.5<p sub(T) super(D )<15 GeV and
Inclusive K_{S};{0}K_{S};{0} production in ep collisions at the DESY ep collider HERA was studied with the ZEUS detector using an integrated luminosity of 0.5 fb;{-1}. Enhancements in the mass ...spectrum were observed and are attributed to the production of f_{2}(1270)/a_{2};{0}(1320), f_{2};{'}(1525) and f_{0}(1710). Masses and widths were obtained using a fit which takes into account theoretical predictions based on SU(3) symmetry arguments, and are consistent with the Particle Data Group values. The f_{0}(1710) state, which has a mass consistent with a glueball candidate, was observed with a statistical significance of 5 standard deviations. However, if this state is the same as that seen in gammagamma-->K_{S};{0}K_{S};{0}, it is unlikely to be a pure glueball state.
Measurements of the neutral current cross sections for deep inelastic scattering in e−p collisions at HERA with a longitudinally polarised electron beam are presented. The single-differential ...cross-sections dσ/dQ2, dσ/dx and dσ/dy and the double-differential cross sections in Q2 and x are measured in the kinematic region y<0.9 and Q2>185 GeV2 for both positively and negatively polarised electron beams and for each polarisation state separately. The measurements are based on an integrated luminosity of 169.9 pb−1 taken with the ZEUS detector in 2005 and 2006 at a centre-of-mass energy of 318 GeV. The structure functions \(x\tilde{F_{3}}\) and xF3γZ are determined by combining the e−p results presented in this paper with previously measured e+p neutral current data. The asymmetry parameter A− is used to demonstrate the parity violating effects of electroweak interactions at large spacelike photon virtuality. The measurements agree well with the predictions of the Standard Model.
A new method is employed to measure the neutral current cross section up to Bjorken-x values of one with the ZEUS detector at HERA using an integrated luminosity of 65.1 pb-1 for e+p collisions and ...16.7 pb-1 for e-p collisions at \(\sqrt{s}=318\,\mathrm{GeV}\) and 38.6 pb-1 for e+p collisions at \(\sqrt{s}=300\,\mathrm{GeV}\). Cross sections have been extracted for Q2≥648 GeV2 and are compared to predictions using different parton density functions. For the highest x bins, the data have a tendency to lie above the expectations using recent parton density function parametrizations.
GaAs detectors for hard X-ray astronomy Dubecký, F.; Krempaský, M.; Pelfer, P.G. ...
Nuclear physics. Section B, Proceedings supplement,
03/1997, Letnik:
54, Številka:
3
Journal Article
Recenzirano
Particle detectors fabricated from bulk semi-insulating (SI) GaAs of 4 different suppliers are investigated. I-V, C-V characteristics, material transport parameters as well as inhomogeneities are ...studied and correlated with detector performances. It was observed that the charge collection efficiency and the energy resolution of detectors tested by 5.48 MeV α-particles and 122 keV X-rays is strongly affected by physical properties of the base material. It is concluded that detectors fabricated from the graded bulk SI GaAs material are suitable for application in hard X-ray astronomy.
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