Low mass lepton pair production in hadron collisions

The hadroproduction of lepton pairs with mass $Q$ and transverse momentum $Q_T$ can be described in perturbative QCD by the same partonic subprocesses as prompt photon production. We demonstrate that, like prompt photon production, lepton pair production is dominated by quark-gluon scattering in the region $Q_T>Q/2$. This leads to sensitivity to the gluon density in kinematical regimes that are accessible both at collider and fixed target experiments while eliminating the theoretical and experimental uncertainties present in prompt photon production.Comment: Talk given by M. Klasen at the International Conference on the Structure and Interactions of the Photon, PHOTON 99, Freiburg i. Brsg., Germany, May 23-27, 1999. To be published in the proceedings. 6 pages, 6 postscript figure

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

J/\Psi production in two-photon collisions at next-to-leading order

In this paper, we report on the calculation of the cross section of J/\Psi plus jet inclusive production in direct two-photon collisions at next-to-leading order within the factorization formalism of nonrelativistic quantum chromodynamics (NRQCD). Theoretical predictions for the future e^+e^- linear collider TESLA are also presented.Comment: 5 pages, 2 figures, talk given at the 7th DESY Workshop on Elementary Particle Theory: Loops and Legs in Quantum Field Theory, Zinnowitz, Germany, 25-30 April, 2004: added references for section

Large Transverse Momentum Jet Production and DIS Distributions of the Proton

We have calculated the single jet inclusive cross section as measured at Fermilab in next-to-leading order QCD using recent parton distributions of the CTEQ collaboration. We studied the scheme dependence of the jet cross section by employing the \overline{\mbox{MS}} and DIS factorization schemes consistently. For $E_T > 200$ GeV, we find that the cross section in the DIS scheme is larger than in the \overline{\mbox{MS}} scheme yielding a satisfactory description of the CDF data over the whole $E_T$ range in the DIS scheme.Comment: 7 pages, latex, 2 figures include

Electroproduction Cross Section of Large_Et Hadrons at NLO and Virtual Photon Structure Function

We calculate Higher Order corrections to the resolved component of the electroproduction cross section of large-Et hadrons. The parton distributions in the virtual photon are studied in detail and a NLO parametrization of the latter is proposed. The contribution of the resolved component to the forward production of large-Et hadrons is calculated and its connection with the BFKL cross section is discussed.Comment: Latex, 32 pages with 6 figure

Reward system and temporal pole contributions to affective evaluation during a first person shooter video game

<p>Abstract</p> <p>Background</p> <p>Violent content in video games evokes many concerns but there is little research concerning its rewarding aspects. It was demonstrated that playing a video game leads to striatal dopamine release. It is unclear, however, which aspects of the game cause this reward system activation and if violent content contributes to it. We combined functional Magnetic Resonance Imaging (fMRI) with individual affect measures to address the neuronal correlates of violence in a video game.</p> <p>Results</p> <p>Thirteen male German volunteers played a first-person shooter game (<it>Tactical Ops: Assault on Terror</it>) during fMRI measurement. We defined success as eliminating opponents, and failure as being eliminated themselves. Affect was measured directly before and after game play using the Positive and Negative Affect Schedule (PANAS). Failure and success events evoked increased activity in visual cortex but only failure decreased activity in orbitofrontal cortex and caudate nucleus. A negative correlation between negative affect and responses to failure was evident in the right temporal pole (rTP).</p> <p>Conclusions</p> <p>The deactivation of the caudate nucleus during failure is in accordance with its role in reward-prediction error: it occurred whenever subject missed an expected reward (being eliminated rather than eliminating the opponent). We found no indication that violence events were directly rewarding for the players. We addressed subjective evaluations of affect change due to gameplay to study the reward system. Subjects reporting greater negative affect after playing the game had less rTP activity associated with failure. The rTP may therefore be involved in evaluating the failure events in a social context, to regulate the players' mood.</p

An NLO calculation of the electroproduction of large-E_\bot hadrons

We present a Next-to-Leading Order calculation of the cross section for the leptoproduction of large-$E_{\bot}$ hadrons and we compare our predictions with H1 data on the forward production of $\pi^0$. We find large higher order corrections and an important sensitivity to the renormalization and factorization scales. These large corrections are shown to arise in part from BFKL-like diagrams at the lowest order.Comment: 24 pages, plain LaTeX2e, 10 figure