Search for resonances decaying into top-quark pairs using fully hadronic decays in pp collisions with ATLAS at $ \sqrt{s}=7 $ TeV
A bstractA search for resonances produced in 7 TeV proton-proton collisions and decaying into top-quark pairs is described. In this Letter events where the top-quark decay produces two massive jets with large transverse momenta recorded with the ATLAS detector at the Large Hadron Collider are considered. Two techniques that rely on jet substructure are used to separate top-quark jets from those arising from light quarks and gluons. In addition, each massive jet is required to have evidence of an associated bottom-quark decay. The data are consistent with the Standard Model, and limits can be set on the production cross section times branching fraction of a Z′ boson and a Kaluza-Klein gluon resonance. These limits exclude, at the 95% credibility level, Z′ bosons with masses 0.70-1.00 TeV as well as 1.28-1.32 TeV and Kaluza-Klein gluons with masses 0.70-1.62 TeV.

title: Search for quark contact interactions in dijet angular distributions in pp collisions at s=7 TeV measured with the ATLAS detector
abstract: Dijet angular distributions from the first LHC pp collisions at center-of-mass energy sqrt(s) = 7 TeV have been measured with the ATLAS detector. The dataset used for this analysis represents an integrated luminosity of 3.1 pb-1. Dijet $\chi$ distributions and centrality ratios have been measured up to dijet masses of 2.8 TeV, and found to be in good agreement with Standard Model predictions. Analysis of the $\chi$ distributions excludes quark contact interactions with a compositeness scale $\Lambda$ below 3.4 TeV, at 95% confidence level, significantly exceeding previous limits.

title: Evidence for the $B^0 \to \rho^0 \rho^0$ decay and implications for the CKM angle $\alpha$
abstract: We search for the decays B0->rho0rho0, B0->rho0f0, and B0->f0f0 in a sample of about 348 million Upsilon(4S)->BBbar decays collected with the BABAR detector at the PEP-II asymmetric-energy e+e- collider at SLAC. We find evidence for B0->rho0rho0 with 3.0 sigma significance and measure the branching fraction B = (1.16 +0.37-0.36 +-0.27) 10^{-6} and longitudinal polarization fraction f_L = 0.86 +0.11-0.13 +-0.05. As a consequence, the uncertainty on the CKM unitarity angle alpha due to penguin contributions in B->rhorho decays is estimated to be 18 degrees at 1 sigma level. We also set upper limits on the B0->rho0f0 and B0->f0f0 decay rates. All results are preliminary.

title: Measurement of moments of the hadronic-mass and energy spectrum in inclusive semileptonic anti-B ---> X(c) l- anti-nu decays

title: The ATLAS High Level Trigger Steering
abstract: The High Level Trigger (HLT) of the ATLAS experiment at the Large Hadron Collider receives events which pass the LVL1 trigger at ~75 kHz and has to reduce the rate to ~200 Hz while retaining the most interesting physics. It is a software trigger and performs the reduction in two stages: the LVL2 trigger and the Event Filter (EF). At the heart of the HLT is the Steering software. To minimise processing time and data transfers it implements the novel event selection strategies of seeded, step-wise reconstruction and early rejection. The HLT is seeded by regions of interest identified at LVL1. These and the static configuration determine which algorithms are run to reconstruct event data and test the validity of trigger signatures. The decision to reject the event or continue is based on the valid signatures, taking into account pre-scale and pass-through. After the EF, event classification tags are assigned for streaming purposes. Several powerful new features for commissioning and operation have been added: comprehensive monitoring is now built in to the framework; for validation and debugging, reconstructed data can be written out; the steering is integrated with the new configuration (presented separately), and topological and global triggers have been added. This paper will present details of the final design and its implementation, the principles behind it, and the requirements and constraints it is subject to. The experience gained from technical runs with realistic trigger menus will be described.

title: Measurement of $\cos_{2beta}$ in $B^0 \to D^{(*)}$ 0 h0 decays with a time-dependent Dalitz plot analysis of $D^0 \to K^0_{s} \pi^{+} \pi^{-}$
abstract: We report a preliminary measurement of $\cos2\beta$ in $B^0\to D^{(*)0}h^0$ decays with a time-dependent Dalitz plot analysis of $D^0\to K_S\pi^+\pi^-$, where $h^0$ is a light neutral meson such as $\pi^0$, $\eta$, $\eta'$ or $\omega$. The strong phase variation on the Dalitz plot allows the access to the angle $\beta$ with only a two-fold ambiguity ($\beta+\pi$). Using $311\times 10^{6}$ $B\bar{B}$ pairs collected at the Babar detector, we obtain $\cos2\beta = 0.54 \pm 0.54 \pm 0.08 \pm 0.18$, $\sin2\beta = 0.45 \pm 0.36 \pm 0.05 \pm 0.07$, and $|\lambda| = 0.975^{+0.093}_{-0.085} \pm 0.012 \pm 0.002 $, where the first errors are statistical, the second are experimental systematic uncertainties, and the third are the signal Dalitz model uncertainties. This measurement favors the solution of $\beta= 22^\circ$ over $68^\circ$ at an 87% confidence level.

title: Multiple Coulomb scattering in thin silicon
abstract: We present a measurement of multiple Coulomb scattering of 1 to 6 GeV/c electrons in thin (50–140 μm) silicon targets. The data were obtained with the EUDET telescope Aconite at DESY and are compared to parametrisations as used in the Geant4 software package. We find good agreement between data and simulation in the scattering distribution width but large deviations in the shape of the distribution. In order to achieve a better description of the shape, a new scattering model based on a Student's t distribution is developed and compared to the data.

title: Partial Wave Analysis using Graphics Cards
abstract: Partial wave analysis is a key technique in hadron spectroscopy. The use of unbinned likelihood fits on large statistics data samples and ever more complex physics models makes this analysis technique computationally very expensive. Parallel computing techniques, in particular the use of graphics processing units, are a powerful means to speed up analyses; in the contexts of the BES III, Compass and GlueX experiments, parallel analysis frameworks have been created. They provide both fits that are faster by more than two orders of magnitude than legacy code and environments to quickly program and run an analysis. This in turn allows the physicists to focus on the many difficult open problems pertaining to partial wave analysis.

title: Partial wave analysis at BES III harnessing the power of GPUs
abstract: Partial wave analysis (PWA) is a core tool for determining resonance properties in hadron spectroscopy. The unbinned likelihood fits employed are however computationally very expensive especially in view of the very large data samples being collected at the Beijing Spectrometer (BES) III experiment and expected from future experiments such as Glue‐X and PANDA. Using the power of massively parallel floating point calculations on graphics processing units (GPUs), we have managed to speed up PWA by more than two orders of magnitude compared to legacy implementations. The resulting software framework allows for the fast creation and running of PWA code. Modern hardware and software thus solve the PWA speed problems—many questions concerning fit methods and especially the reliability of fit results however remain open.

title: Measurement of diffractive Φ meson photoproduction at HERA with the H1 fast track trigger
abstract: A new measurement of diffractive φ meson photoproduction is performed with the H1 experiment at the electron-proton collider HERA. In the kinematic range 30 < Wγp < 90 GeV and 0.2 < |t| < 1.5 GeV, cross sections are determined double differentially in Wγp and t. From these data, the pomeron trajectory in elastic φ meson photoproduction is determined to be α(t) = 1.15 ± 0.05(stat. A combined fit with data from fixed target experiments and the ZEUS collaboration yields the most precise trajectory measurement using φ mesons to date, α(t) = 1.122 ± 0.008 + t · (0.150 ± 0.017) GeV. The spin density matrix elements, which provide information on the helicity structure of the interaction, are extracted using measurements of angular distributions of the φ meson decay products and are found to be in agreement with expectations from s-channel helicity conservation. The presented cross section measurement was made possible by the Fast Track Trigger (FTT). This new trigger based on signals from selected wire layers of the H1 central drift chamber provides information to the first three trigger levels of the H1 experiment. The first level performs a coarse two-dimensional track reconstruction within 2 μs, whilst the second trigger level reconstructs the event vertex along the beam line, performs a precise three-dimensional track fit and determines invariant masses of track pairs in 20 μs. The third trigger level reconstructs final states from up to 48 tracks and allows for particle identification using information from the calorimeter and the muon system within 100 μs. Zusammenfassung Mit dem H1-Experiment am Elektron-Proton-Beschleuniger HERA wird eine neue Messung diffraktiver φ-Meson-Photoproduktion durchgeführt. Im kinematischen Bereich 30 < Wγp < 90 GeV und 0.2 < |t| < 1.5 GeV werden Wirkungsquerschnitte doppeltdifferenziell in Wγp und t gemessen. Aus diesen Daten bestimmt sich die PomeronTrajektorie in elastischer φ-Meson-Photoproduktion zu α(t) = 1.15 ± 0.05(stat. Eine gemeinsame Anpassung mit Daten von Experimenten mit ruhendem Target und der ZEUS-Kollaboration liefert die bisher genaueste Messung der Trajektorie mit Hilfe von φ-Mesonen: α(t) = 1.122 ± 0.008 + t · (0.150 ± 0.017) GeV. Aus der Messung der Winkelverteilung der φ-Meson-Zerfallsprodukte werden drei Elemente der Spindichtematrix bestimmt. Diese sind verträglich mit s-Kanal-Helizitätserhaltung. Die vorliegende Messung wurde durch den schnellen Spurtrigger (Fast Track Trigger, FTT) ermöglicht. Dieser neue Trigger leitet aus Signalen von ausgewählten Drahtlagen der zentralen Spurkammer von H1 Informationen für die ersten drei Triggerstufen des H1 Experimentes ab. Auf der ersten Stufe wird innert 2 μs eine grobe, zweidimensionale Spurrekonstruktion durchgeführt. In 20 μs rekonstruiert die zweite Stufe den EreignisVertex entlang der Strahllinie, führt eine präzise, dreidimensionale Spuranpassung durch und bestimmt die invariante Masse von Spurpaaren. Auf der dritten Stufe werden innert 100 μs aus bis zu 48 Spuren Endzustände rekonstruiert und mit Hilfe von Informationen aus dem Kalorimeter und dem Myon-System Teilchen identifiziert.