Events with no hadronic energy flow in a large interval of pseudo-rapidity in the proton direction are observed in photon-proton interactions at an average centre of mass energy 〈√s
γp〉 of 200 GeV ...These events are interpreted as photon diffractive dissociation. Evidence for hard scattering in photon diffractive dissociation is demonstrated using inclusive single particle spectra, thrust as a function of transverse energy, and the observation of jet production. The data can be described by a Monte Carlo calculation including hard photon-pomeron scattering.
The photoproduction of \(D^{*\pm}\) mesons has been measured with the ZEUS detector at HERA at three different ep centre-of-mass energies, \(\sqrt{s}\), of 318, 251 and 225 GeV. For each data set, ...\(D^*\) mesons were required to have transverse momentum, \(p_T^{D^*}\), and pseudorapidity, \(\eta^{D^*}\), in the ranges \(1.9 < p_T^{D^*} < 20\) GeV and \(|\eta^{D^*}|<1.6\). The events were required to have a virtuality of the incoming photon, \(Q^2\), of less than 1 GeV\(^2\). The dependence on \(\sqrt{s}\) was studied by normalising to the high-statistics measurement at \(\sqrt{s} =318\) GeV. This led to the cancellation of a number of systematic effects both in data and theory. Predictions from next-to-leading-order QCD describe the \(\sqrt{s}\) dependence of the data well.
Progress with Schottky diode and p i n diode GaAs detectors for minimum ionizing particles is reported here. The radiation hardness and potential speed of simple diodes is shown to be more than ...competitive with silicon detectors. A discussion is given of the present understanding of the charge transport mechanism in the detectors as it influences their charge collection efficiency. Early results from micro-strip detectors are also described, (which are relevant for high radiation regions of LHC detectors near the beam pipe and in the forward region).
The production of beauty and charm quarks in ep interactions has been studied with the ZEUS detector at HERA for exchanged four-momentum squared 5 < Q^2 < 1000 GeV^2 using an integrated luminosity of ...354 pb^{-1}. The beauty and charm content in events with at least one jet have been extracted using the invariant mass of charged tracks associated with secondary vertices and the decay-length significance of these vertices. Differential cross sections as a function of Q^2, Bjorken x, jet transverse energy and pseudorapidity were measured and compared with next-to-leading-order QCD calculations. The beauty and charm contributions to the proton structure functions were extracted from the double-differential cross section as a function of x and Q^2. The running beauty-quark mass, m_b at the scale m_b, was determined from a QCD fit at next-to-leading order to HERA data for the first time and found to be 4.07 \pm 0.14 (fit} ^{+0.01}_{-0.07} (mod.) ^{+0.05}_{-0.00} (param.) ^{+0.08}_{-0.05} (theo) GeV.
The reduced cross sections for \(e^{+}p\) deep inelastic scattering have been measured with the ZEUS detector at HERA at three different centre-of-mass energies, \(318\), \(251\) and \(225\) GeV. The ...cross sections, measured double differentially in Bjorken \(x\) and the virtuality, \(Q^2\), were obtained in the region \(0.13\ \leq\ y\ \leq\ 0.75\), where \(y\) denotes the inelasticity and \(5\ \leq\ Q^2\ \leq\ 110\) GeV\(^2\). The proton structure functions \(F_2\) and \(F_L\) were extracted from the measured cross sections.
The HERAPDF2.0 ensemble of parton distribution functions (PDFs) was introduced in 2015. The final stage is presented, a next-to-next-to-leading-order (NNLO) analysis of the HERA data on inclusive ...deep inelastic \(ep\) scattering together with jet data as published by the H1 and ZEUS collaborations. A perturbative QCD fit, simultaneously of \(\alpha_s(M_Z^2)\) and and the PDFs, was performed with the result \(\alpha_s(M_Z^2) = 0.1156 \pm 0.0011~{\rm (exp)}~ ^{+0.0001}_{-0.0002}~ {\rm (model}\) \({\rm +~parameterisation)}~ \pm 0.0029~{\rm (scale)}\). The PDF sets of HERAPDF2.0Jets NNLO were determined with separate fits using two fixed values of \(\alpha_s(M_Z^2)\), \(\alpha_s(M_Z^2)=0.1155\) and \(0.118\), since the latter value was already chosen for the published HERAPDF2.0 NNLO analysis based on HERA inclusive DIS data only. The different sets of PDFs are presented, evaluated and compared. The consistency of the PDFs determined with and without the jet data demonstrates the consistency of HERA inclusive and jet-production cross-section data. The inclusion of the jet data reduced the uncertainty on the gluon PDF. Predictions based on the PDFs of HERAPDF2.0Jets NNLO give an excellent description of the jet-production data used as input.
Collective behaviour of final-state hadrons, and multiparton interactions are
studied in high-multiplicity $ep$ scattering at a centre-of-mass energy
$\sqrt{s}=318$ GeV with the ZEUS detector at ...HERA. Two- and four-particle
azimuthal correlations, as well as multiplicity, transverse momentum, and
pseudorapidity distributions for charged-particle multiplicities $N_{\textrm
ch} \geq 20$ are measured. The dependence of two-particle correlations on the
virtuality of the exchanged photon shows a clear transition from
photoproduction to neutral current deep inelastic scattering. For the
multiplicities studied, neither the measurements in photoproduction processes
nor those in neutral current deep inelastic scattering indicate significant
collective behaviour of the kind observed in high-multiplicity hadronic
collisions at RHIC and the LHC. Comparisons of PYTHIA predictions with the
measurements in photoproduction strongly indicate the presence of multiparton
interactions from hadronic fluctuations of the exchanged photon.
The dependence of dijet production on the virtuality of the exchanged photon, Q2, has been studied by measuring dijet cross sections in the range \(0 \lesssim Q^2 < 2000 {\;\rm GeV}^2\) with the ZEUS ...detector at HERA using an integrated luminosity of 38.6 pb-1. Dijet cross sections were measured for jets with transverse energy \(E_T^{\rm jet} > 7.5\) and 6.5 GeV and pseudorapidities in the photon-proton centre-of-mass frame in the range \(-3 < \eta^{\rm jet} < 0\). The variable \(x^{\rm obs}_{\gamma}\), a measure of the photon momentum entering the hard process, was used to enhance the sensitivity of the measurement to the photon structure. The Q2 dependence of the ratio of low- to high- \(\smashb x^{\rm obs}_{\gamma} \) events was measured. Next-to-leading-order QCD predictions were found to generally underestimate the low- \(\smasht x^{\rm obs}_{\gamma} \) contribution relative to that at high \(\smasht x^{\rm obs}_{\gamma} \). Monte Carlo models based on leading-logarithmic parton-showers, using a partonic structure for the photon which falls smoothly with increasing Q2, provide a qualitative description of the data.
Gallium arsenide microstrip detectors for charged particles
Nuclear instruments and methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment/Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
09/1992
Journal Article
Di-jet event rates have been measured for deep-inelastic scattering in the kinematic domain \(5 \lesssim Q^2 \lesssim 100\) GeV\(^2\) and \(10^{-4} \lesssim x_{Bj} \lesssim 10^{-2}\), and for jet ...transverse momenta squared \(p_t^{*2}\gtrsim Q^2\). The analysis is based on data collected with the H1 detector at HERA in 1994 corresponding to an integrated luminosity of about 2 pb\(^{-1}\). Jets are defined using a cone algorithm in the photon-proton centre of mass system requiring jet transverse momenta of at least 5 GeV. The di-jet event rates are shown as a function of \(Q^2\) and \(x_{Bj}\). Leading order models of point-like interacting photons fail to describe the data. Models which add resolved interacting photons or which implement the colour dipole model give a good description of the di-jet event rate. This is also the case for next-to-leading order calculations including contributions from direct and resolved photons.
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