Suppression factors in diffractive photoproduction of dijets

After new publications of H1 data for the diffractive photoproduction of dijets, which overlap with the earlier published H1 data and the recently published data of the ZEUS collaboration, have appeared, we have recalculated the cross sections for this process in next-to-leading order (NLO) of perturbative QCD to see whether they can be interpreted consistently. The results of these calculations are compared to the data of both collaborations. We find that the NLO cross sections disagree with the data, showing that factorization breaking occurs at that order. If direct and resolved contributions are both suppressed by the same amount, the global suppression factor depends on the transverse-energy cut. However, by suppressing only the resolved contribution, also reasonably good agreement with all the data is found with a suppression factor independent of the transverse-energy cut.Comment: 28 pages, 11 figures, 3 table

Dijet photoproduction of massless charm jets at next-to-leading order of QCD

We compute the charm dijet photoproduction cross section at next-to-leading order of QCD in the zero-mass variable flavour number scheme, i.e. with active charm quarks in the proton and photon. The results are compared to recent measurements from the ZEUS experiment at HERA. The predictions for various distributions agree well with the data, in particular for large momentum fractions of the the partons in the photon, where direct photon processes dominate. At low momentum fractions, the predictions are quite sensitive to the charm content in the photon. The experimental data are shown to favour parameterizations with a substantial charm quark density such as the one proposed by Cornet et al.Comment: 18 pages, 11 figure

Factorization Breaking in Dijet Photoproduction with a Leading Neutron

The production of dijets with a leading neutron in ep-interactions at HERA is calculated in leading order and next-to-leading order of perturbative QCD using a pion-exchange model. Differential cross sections for deep-inelastic scattering (DIS) and photoproduction are presented as a function of several kinematic variables. By comparing the theoretical predictions for DIS dijets to recent H1 data, the pion flux factor together with the parton distribution functions of the pion is determined. The dijet cross sections in photoproduction show factorization breaking if compared to the H1 photoproduction data. The suppression factor is S = 0.48 (0.64) for resolved (global) suppression.Comment: 16 pages, 5 figure

Exotic Rickettsiae in Ixodes ricinus: fact or artifact?

Several pathogenic Rickettsia species can be transmitted via Ixodes ricinus ticks to humans and animals. Surveys of I. ricinus for the presence of Rickettsiae using part of its 16S rRNA gene yield a plethora of new and different Rickettsia sequences. Interpreting these data is sometimes difficult and presenting these findings as new or potentially pathogenic Rickettsiae should be done with caution: a recent report suggested presence of a known human pathogen, R. australis, in questing I. ricinus ticks in Europe. A refined analysis of these results revealed that R. helvetica was most likely to be misinterpreted as R. australis. Evidence in the literature is accumulating that rickettsial DNA sequences found in tick lysates can also be derived from other sources than viable, pathogenic Rickettsiae. For example, from endosymbionts, environmental contamination or even horizontal gene transfer

Phalangeal fractures of the hand:An analysis of gender and age-related incidence and aetiology

The incidence and aetiology of 6,857 phalangeal fractures of the hand have been reviewed in a series of 235,427 patients, looking for an age-specific vulnerability to fracture. We found sports to be the main cause of fracture in the 10-29 years age groups and accidental falls to be the leading cause in those aged 70 years or older. We made a new observation that the highest incidence occurs in the male 40-69 age group and machinery was the dominant cause of fracture in this group. Recognition of the frequency of industrial trauma is needed, and public expenditure should be invested in its prevention and treatment.</p

On the mechanisms of heavy-quarkonium hadroproduction

We discuss the various mechanisms potentially at work in hadroproduction of heavy quarkonia in the light of computations of higher-order QCD corrections both in the Colour-Singlet (CS) and Colour-Octet (CO) channels and the inclusion of the contribution arising from the s-channel cut in the CS channel. We also discuss new observables meant to better discriminate between these different mechanisms.Comment: Invited review talk at 3rd International Conference On Hard And Electromagnetic Probes Of High-Energy Nuclear Collisions (HP2008), 8-14 June 2008, Illa da Toxa, Galicia, Spain. 11 pages, 21 figures, LaTeX, uses svjour.cls and svepj.clo (included

Jet photoproduction and the structure of the photon

Various jet observables in photoproduction are studied and compared to data from HERA. The feasibility of using a dijet sample for constraining the parton distributions in the photon is then studied. For the current data the experimental and theoretical uncertainties are comparable to the variation due to changing the photon parton distribution set.Comment: 20 pages including 11 figures. Latex using revtex and psfig macros. Several references added. Submitted to Phys. Rev.

Sfermion Pair Production in Polarized and Unpolarized γγ\gamma\gamma Collisions

We calculate total and differential cross sections for the production of sfermion pairs in photon-photon collisions, including contributions from resolved photons and arbitrary photon polarization. Sfermion production in photon collisions depends only on the sfermion mass and charge. It is thus independent of the details of the SUSY breaking mechanism, but highly sensitive to the sfermion charge. We compare the total cross sections for bremsstrahlung, beamstrahlung, and laser backscattering photons to those in $e^+e^-$ annihilation. We find that the total cross section at a polarized photon collider is larger than the $e^+e^-$ annihilation cross section up to the kinematic limit of the photon collider.Comment: 19 pages, Latex, 18 (e)ps-figure