Technical University of Dortmund

About: Technical University of Dortmund is a education organization based out in Dortmund, Nordrhein-Westfalen, Germany. It is known for research contribution in the topics: Large Hadron Collider & Neutrino. The organization has 13028 authors who have published 27666 publications receiving 615557 citations. The organization is also known as: Dortmund University & University of Dortmund.

When Recurrent Neural Networks meet the Neighborhood for Session-Based Recommendation

Abstract: Deep learning methods have led to substantial progress in various application fields of AI, and in recent years a number of proposals were made to improve recommender systems with artificial neural networks. For the problem of making session-based recommendations, i.e., for recommending the next item in an anonymous session, Hidasi et al.~recently investigated the application of recurrent neural networks with Gated Recurrent Units (GRU4REC). Assessing the true effectiveness of such novel approaches based only on what is reported in the literature is however difficult when no standard evaluation protocols are applied and when the strength of the baselines used in the performance comparison is not clear. In this work we show based on a comprehensive empirical evaluation that a heuristics-based nearest neighbor (kNN) scheme for sessions outperforms GRU4REC in the large majority of the tested configurations and datasets. Neighborhood sampling and efficient in-memory data structures ensure the scalability of the kNN method. The best results in the end were often achieved when we combine the kNN approach with GRU4REC, which shows that RNNs can leverage sequential signals in the data that cannot be detected by the co-occurrence-based kNN method.

Angular analysis of the B 0 → K *0 μ + μ − decay using 3 fb −1 of integrated luminosity

Abstract: An angular analysis of the B0 → K*0(→ K+π−)μ+μ− decay is presented. The dataset corresponds to an integrated luminosity of 3.0 fb−1 of pp collision data collected at the LHCb experiment. The complete angular information from the decay is used to determine CP-averaged observables and CP asymmetries, taking account of possible contamination from decays with the K+π− system in an S-wave configuration. The angular observables and their correlations are reported in bins of q2, the invariant mass squared of the dimuon system. The observables are determined both from an unbinned maximum likelihood fit and by using the principal moments of the angular distribution. In addition, by fitting for q2-dependent decay amplitudes in the region 1.1 < q2 < 6.0 GeV2/c4, the zero-crossing points of several angular observables are computed. A global fit is performed to the complete set of CP-averaged observables obtained from the maximum likelihood fit. This fit indicates differences with predictions based on the Standard Model at the level of 3.4 standard deviations. These differences could be explained by contributions from physics beyond the Standard Model, or by an unexpectedly large hadronic effect that is not accounted for in the Standard Model predictions.[Figure not available: see fulltext.]

First Evidence for the Decay B-s(0) -> mu(+) mu(-)

Abstract: A search for the rare decays Bs->mu+mu- and B0->mu+mu- is performed using data collected in 2011 and 2012 with the LHCb experiment at the Large Hadron Collider. The data samples comprise 1.1 fb^-1 of proton-proton collisions at sqrt{s} = 8 TeV and 1.0 fb^-1 at sqrt{s}=7 TeV. We observe an excess of Bs -> mu+ mu- candidates with respect to the background expectation. The probability that the background could produce such an excess or larger is 5.3 x 10^-4 corresponding to a signal significance of 3.5 standard deviations. A maximum-likelihood fit gives a branching fraction of BR(Bs -> mu+ mu-) = (3.2^{+1.5}_{-1.2}) x 10^-9, where the statistical uncertainty is 95% of the total uncertainty. This result is in agreement with the Standard Model expectation. The observed number of B0 -> mu+ mu- candidates is consistent with the background expectation, giving an upper limit of BR(B0 -> mu+ mu-) < 9.4 x 10^-10 at 95% confidence level.

Photonic parton distributions

Abstract: The quark and gluon distributions of the photon are determined in leading and higher order by imposing a vector-meson dominance (VMD) valencelike structure at a low resolution scale adopted from the pion. This leaves only one free parameter, not sufficiently constrained by VMD, to be fixed by experiment. Our predictions are in agreement with presently available data for ${F}_{2}^{\ensuremath{\gamma}}(x,{Q}^{2})$. Simple parametrizations of the resulting parton distributions are presented in the range ${10}^{\ensuremath{-}5}\ensuremath{\lesssim}xl1$, $0.3\ensuremath{\lesssim}{Q}^{2}\ensuremath{\lesssim}{10}^{6}$ ${\mathrm{GeV}}^{2}$ as obtained from the leading- and higher-order evolution equations.

Magic discovery of very high energy emission from the fsrq pks 1222+21

Abstract: Very high energy (VHE) gamma-ray emission from the flat spectrum radio quasar (FSRQ) PKS 1222+ 21 (4C 21.35, z = 0.432) was detected with the MAGIC Cherenkov telescopes during a short observation (similar to 0.5 hr) performed on 2010 June 17. The MAGIC detection coincides with high-energy MeV/ GeV gamma-ray activity measured by the Large Area Telescope (LAT) on board the Fermi satellite. The VHE spectrum measured by MAGIC extends from about 70 GeV up to at least 400 GeV and can be well described by a power-law dN/dE proportional to E-Gamma with a photon index Gamma = 3.75 +/- 0.27(stat) +/- 0.2(syst). The averaged integral flux above 100 GeV is (4.6 +/- 0.5) x 10(-10) cm(-2) s(-1) (similar to 1 Crab Nebula flux). The VHE flux measured by MAGIC varies significantly within the 30 minute exposure implying a flux doubling time of about 10 minutes. The VHE and MeV/GeV spectra, corrected for the absorption by the extragalactic background light (EBL), can be described by a single power law with photon index 2.72 +/- 0.34 between 3 GeV and 400 GeV, and is consistent with emission belonging to a single component in the jet. The absence of a spectral cutoff constrains the gamma-ray emission region to lie outside the broad-line region, which would otherwise absorb the VHE gamma-rays. Together with the detected fast variability, this challenges present emission models from jets in FSRQs. Moreover, the combined Fermi/LAT and MAGIC spectral data yield constraints on the density of the EBL in the UV-optical to near-infrared range that are compatible with recent models.