Differential dijet cross sections are measured in photoproduction in the region of photon virtualities Q2<1 GeV2 with the H1 detector at the HERA ep collider using an integrated luminosity of 66.6 ...pb−1. Jets are defined with the inclusive k⊥ algorithm and a minimum transverse momentum of the leading jet of 25 GeV is required. Dijet cross sections are measured in direct and resolved photon enhanced regions separately. Longitudinal proton momentum fractions up to 0.7 are reached. The data compare well with predictions from Monte Carlo event generators based on leading order QCD and parton showers and with next-to-leading order QCD calculations corrected for hadronisation effects.
Results are presented on the photoproduction of isolated prompt photons, inclusively and associated with jets, in the \(\gamma p\) center of mass energy range 142 < W < 266 GeV. The cross sections ...are measured for the transverse momentum range of the photons \(5 < E_T^{\gamma} < 10\) GeV and for associated jets with ETjet > 4.5 GeV. They are measured differentially as a function of \(E_T^{\gamma}, E_T^{\mathrm{jet}}\), the pseudorapidities \(\eta^{\gamma}\) and \(\eta^{\mathrm{jet}}\) and estimators of the momentum fractions \(x_{\gamma}\) and xp of the incident photon and proton carried by the constituents participating in the hard process. In order to further investigate the underlying dynamics, the angular correlation between the prompt photon and the jet in the transverse plane is studied. Predictions by perturbative QCD calculations in next to leading order are about \(30\%\) below the inclusive prompt photon data after corrections for hadronisation and multiple interactions, but are in reasonable agreement with the results for prompt photons associated with jets. Comparisons with the predictions of the event generators PYTHIA and HERWIG are also presented.
The work is devoted to a comparative study of the fatty acid composition of white and black sesame oils, as well as the development of a relatively effective method for isolating the natural ...antioxidant sesamol. The purpose of this work was to determine the comparative indicators of the content of fatty and free organic acids in the studied oils by gas and high-performance liquid chromatography, confirm their suitability and further use. The optimal conditions for obtaining high-quality unrefined oil from sesame seeds for the food and pharmaceutical industries were determined by the method of cold pressing (pressing chamber temperature was 100℃, oil outlet temperature was ≤ 40℃). Under these conditions, the oil yield was 30% and 27%, respectively. It was shown that finished sesame seed oils contain a highly effective natural antioxidant sesamol (oxyhydroquinone methyl ester) – 0.140 mg/kg, due to which they can be stored at room conditions for more than 3 years. The extracts of squeezes of sesame oils contain valuable free organic acids: oxalic – 0.017 mg/mL, malic – 0.02 mg/mL, fumaric – 0.001 mg/mL. Based on the research, the fatty acid composition of oils was determined and a relatively effective method for the complex processing of sesame raw materials was developed to obtain a highly effective natural antioxidant sesamol.
The cross section for anti-deuteron photoproduction is measured at HERA at a mean centre-of-mass energy of \(W_{\gamma p} = 200\) GeV in the range 0.2 < pT/M < 0.7 and |y| < 0.4, where M, pT and y ...are the mass, transverse momentum and rapidity of the anti-deuteron in the HERA laboratory frame, respectively. The numbers of anti-deuterons per event are found to be similar in photoproduction to those in central proton-proton collisions at the CERN ISR but much lower than those in central Au-Au collisions at RHIC. The coalescence parameter B2, which characterizes the likelihood of anti-deuteron production, is measured in photoproduction to be \(0.010 \pm 0.002 \pm 0.001\), which is much higher than in Au-Au collisions at a similar nucleon-nucleon centre-of-mass energy. No significant production of particles heavier than deuterons is observed and upper limits are set on the photoproduction cross sections for such particles.
A search for single top quark production is performed in \(e^{\pm}p\) collisions at HERA. The search exploits data corresponding to an integrated luminosity of 118.3 pb-1. A model for the anomalous ...production of top quarks in a flavour changing neutral current process involving a \(tu\gamma\) coupling is investigated. Decays of top quarks into a b quark and a W boson are considered in the leptonic and the hadronic decay channels of the W. Both a cut-based analysis and a multivariate likelihood analysis are performed to discriminate anomalous top quark production from Standard Model background processes. In the leptonic channel, 5 events are found while 1.31 \(\pm\) 0.22 events are expected from the Standard Model background. In the hadronic channel, no excess above the expectation for Standard Model processes is found. These observations lead to a cross section \(\sigma (ep \rightarrow e t X) = 0.29 ^{ + 0.15}_{-0.14} \ {\rm pb}\) at \(\sqrt{s} = 319 \ {\rm GeV}\). Alternatively, assuming that the observed events are due to a statistical fluctuation, upper limits of 0.55 pb on the anomalous top production cross section and of 0.27 on the \(tu\gamma\) coupling \(\kappa_{tu\gamma}\) are established at the 95% confidence level.
The diffractive photoproduction of ρ mesons, ep→eρY, with large momentum transfer squared at the proton vertex, |t|, is studied with the H1 detector at HERA using an integrated luminosity of ...20.1 pb−1. The photon–proton centre of mass energy spans the range 75<W<95 GeV, the photon virtuality is restricted to Q2<0.01 GeV2 and the mass MY of the proton remnant is below 5 GeV. The t dependence of the cross section is measured for the range 1.5<|t|<10.0 GeV2 and is well described by a power law, dσ/d|t|∝|t|−n. The spin density matrix elements, which provide information on the helicity structure of the interaction, are extracted using measurements of angular distributions of the ρ decay products. The data indicate a violation of s-channel helicity conservation, with contributions from both single and double helicity-flip being observed. The results are compared to the predictions of perturbative QCD models.
A search for the lepton flavour violating processes ep→μX and ep→τX is performed with the H1 experiment at HERA. Final states with a muon or tau and a hadronic jet are searched for in a data sample ...corresponding to an integrated luminosity of 66.5 pb-1 for e+p collisions and 13.7 pb-1 for e-p collisions at a centre-of-mass energy of 319 GeV. No evidence for lepton flavour violation is found. Limits are derived on the mass and the couplings of leptoquarks inducing lepton flavour violation in an extension of the Buchmüller–Rückl–Wyler effective model. Leptoquarks produced in ep collisions with a coupling strength of λ=0.3 and decaying with the same coupling strength to a muon–quark pair or a tau–quark pair are excluded at 95% confidence level up to masses of 459 GeV and 379 GeV, respectively.
A direct search has been made for magnetic monopoles produced in e + p collisions at a centre of mass energy of 300 GeV at HERA. The beam pipe surrounding the interaction region in 1995-1997 was ...investigated using a SQUID magnetometer to look for stopped magnetic monopoles. During this time an integrated luminosity of 62 pb-1 was delivered. No magnetic monopoles were observed and charge and mass dependent upper limits on the e + p production cross section are set.
A model-independent search for deviations from the Standard Model prediction is performed in
e
+
p
and
e
−
p
collisions at HERA using H1 data corresponding to an integrated luminosity of
117
pb
−
1
.... For the first time all event topologies involving isolated electrons, photons, muons, neutrinos and jets with high transverse momenta are investigated in a single analysis. Events are assigned to exclusive classes according to their final state. A statistical algorithm is developed to search for deviations from the Standard Model in the distributions of the scalar sum of transverse momenta or invariant mass of final state particles and to quantify their significance. A good agreement with the Standard Model prediction is observed in most of the event classes. The most significant deviation is found for a topology containing an isolated muon, missing transverse momentum and a jet, consistent with a previously reported observation.
A measurement of charm and beauty dijet photoproduction cross sections at the ep collider HERA is presented. Events are selected with two or more jets of transverse momentum ptjet1(2)>11(8) GeV in ...the central range of pseudo-rapidity -0.9<ηjet1(2)<1.3. The fractions of events containing charm and beauty quarks are determined using a method based on the impact parameter, in the transverse plane, of tracks to the primary vertex, as measured by the H1 central vertex detector. Differential dijet cross sections for charm and beauty, and their relative contributions to the flavour inclusive dijet photoproduction cross section, are measured as a function of the transverse momentum of the leading jet, the average pseudo-rapidity of the two jets and the observable xγobs. Taking into account the theoretical uncertainties, the charm cross sections are consistent with a QCD calculation in next-to-leading order, while the predicted cross sections for beauty production are somewhat lower than the measurement.
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