122500188
Evidence for a narrow anti-charmed baryon state
A narrow resonance in D*(-)p and D*(+)(p) over bar invariant mass combinations is observed in inelastic electron-proton collisions at centre-of-mass energies of 300 GeV and 320 GeV at HERA. The resonance has a mass of 3099 +/- 3(stat.) +/- 5(syst.) MeV and a measured Gaussian width of 12 +/- 3(stat.) MeV, compatible with the experimental resolution. The resonance is interpreted as an anti-charmed baryon with a minimal constituent quark composition of uudd (c) over bar, together with the charge conjugate. (C) 2004 Elsevier B.V. All rights reserved.
53073574
The ATLAS High Level Trigger Steering
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.
209834301
Search for supersymmetry in events with photons, bottom quarks, and missing transverse momentum in proton–proton collisions at a centre-of-mass energy of 7 TeV with the ATLAS detector
A search has been performed for the experimental signature of an isolated photon with high transverse momentum, at least one jet identified as originating from a bottom quark, and high missing transverse momentum. Such a final state may originate from supersymmetric models with gauge-mediated supersymmetry breaking in events in which one of a pair of higgsino-like neutralinos decays into a photon and a gravitino while the other decays into a Higgs boson and a gravitino. The search is performed using the full dataset of 7 TeV proton–proton collisions recorded with the ATLAS detector at the LHC in 2011, corresponding to an integrated luminosity of 4.7 fb−1. A total of 7 candidate events are observed while 7.5±2.2 events are expected from the Standard Model background. The results of the search are interpreted in the context of general gauge mediation to exclude certain regions of a benchmark plane for higgsino-like neutralino production.
104358197
Measurement of $\cos_{2beta}$ in $B^0 \to D^{(*)}$ 0 h0 decays with a time-dependent Dalitz plot analysis of $D^0 \to K^0_{s} \pi^{+} \pi^{-}$
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.
125358056
Evidence for the $B^0 \to \rho^0 \rho^0$ decay and implications for the CKM angle $\alpha$
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.
118500591
Measurement of moments of the hadronic-mass and energy spectrum in inclusive semileptonic anti-B ---> X(c) l- anti-nu decays
119288966
Multiple Coulomb scattering in thin silicon
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.
125611661
Measurement of diffractive Φ meson photoproduction at HERA with the H1 fast track trigger
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.) −0.03(syst.) + t · (0.16 ± 0.09(stat.) −0.02(syst.))GeV−2. 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.) −0.03(syst.) + t · (0.16 ± 0.09(stat.) −0.02(syst.))GeV−2. 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.
53645813
High-voltage pixel detectors in commercial CMOS technologies for ATLAS, CLIC and Mu3e experiments☆
Abstract High-voltage particle detectors in commercial CMOS technologies are a detector family that allows implementation of low-cost, thin and radiation-tolerant detectors with a high time resolution. In the R/D phase of the development, a radiation tolerance of 10 15 n eq / cm 2, nearly 100% detection efficiency and a spatial resolution of about 3 μm were demonstrated. Since 2011 the HV detectors have first applications: the technology is presently the main option for the pixel detector of the planned Mu3e experiment at PSI (Switzerland). Several prototype sensors have been designed in a standard 180 nm HV CMOS process and successfully tested. Thanks to its high radiation tolerance, the HV detectors are also seen at CERN as a promising alternative to the standard options for ATLAS upgrade and CLIC. In order to test the concept, within ATLAS upgrade R/D, we are currently exploring an active pixel detector demonstrator HV2FEI4; also implemented in the 180 nm HV process.